J.A. Woollam Newsletter - Issue 23

Issue #23

J.A. Woollam Annual Newsletter 311 South 7th Street Lincoln, NE 68508 USA

+1.402.477.7501 info@jawoollam.com www.jawoollam.com

Contents 04

About Our Company

06

The Wave Front: Cutting-Edge Applications Using Spectroscopic Ellipsometry

08

New Instrument: alpha 2.0

10

In Situ Spectroscopic Ellipsometry: Applications to Atomic Layer Deposition

16

Featured Researcher: Parag Banerjee

20

CompleteEASE: More Complete. More User-friendly.

22

Tom Tiwald's Artistic Legacy Through the Lens of Infrared-SE

29

Educational + Software Support

31

Employee Spotlights

32

J.A. Woollam Scholarship Recipients

33

Featured International Rep: Quantum Design Europe

34

Worldwide Sales & Support

35

Schedule of Events

GREETINGS from John Woollam Our company continues to grow. We are halfway through a two-year project to more than double our present floor space. More space allows for continued growth for manufacturing, inventory, R&D, and general work space.

Our employee numbers increase as our worldwide markets grow across all instrument categories. In Lincoln we are now 70 employees.

Growth means we will better serve you, our customers and friends.

We are eager to shorten lead times for instrument deliveries, improve instrument performance, and strengthen customer support.

Every year, we highlight a researcher in our newsletter. This year we feature Professor Parag Banerjee and his University of Central Florida research group. It’s evident that Parag does a great job getting students excited about research and advanced studies. Graduate school is a time of non-stop learning and is a noble and rewarding experience. Exciting new discoveries are made that inspire both faculty and students: It can be great fun for everyone involved. It is a time when life-long friendships and mutual respect are developed between students and faculty. These aspects are clearly shown in Parag’s article.

The article about Dr. Tom Tiwald brings back fond memories of working with Tom and others at the University of Nebraska starting in the early 1980s. We’ve been friends ever since. I love the photos of Tom and Tom Zillig celebrating the birth of the company’s first commercial instrument. It was built for Dr. Sam Alterovitz of NASA Lewis Research Center. The actual engineering on this instrument was done by graduate students at the time, many of whom (Tom Tiwald, Craig Herzinger, and Duane Meyer) still work at our company.

I am now in my 80s, yet still at the company much of the time because these employees are my long-time “family” friends. I greatly enjoy being with them and sharing the excitement of what we do.

Enjoyable interactions with colleagues are part of our company culture that includes you, our friends and customers!

With kind regards,

About our Company J.A. Woollam was founded in 1987 by Dr. John A. Woollam. Starting as a spin-off from the University of Nebraska, the company has expanded to serve universities, industrial laboratories, and manufacturing worldwide. Today, over seventy employees are dedicated to the continued development and manufacturing of high-quality instruments with exemplary customer support. With continuous innovation for over 35 years, we have secured over 200 patents, produced nine core instrument types, designed 48 accessories, and developed multiple software platforms for applications in a variety of industries and research areas.

Instruments

Software

Accessories

Our core technology has continuously evolved over the last 35 years leading to hardware with world-class accuracy and reliability. We continue to refine our line of ellipsometers with the latest technological advancements.

Our software includes a full data analysis suite that’s intuitive and easy to use. We regularly update the software with features to improve the user experience while also developing technical solutions for new complex materials.

Ellipsometry experiments can be combined with sample stages to vary the relative pressure, temperature and liquid ambient within the sample environment.

We have integrated a large variety of accessories to create the experimental conditions you need.

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we innovate, so you can discover.

We strive to provide our customers with: +Accurate and reliable instrumentation +Powerful and easy-to-use software +Responsive application and hardware support +Customization to fit your research

Options

Research + Development

Support

We offer the ability to customize our ellipsometers to match your budget and research requirements. Typical options include wavelength range, mapping area, and beam size. We will help you determine which options are most relevant to your application.

Our dedication to innovation has led to over 200 patents in the field of ellipsometry. We are committed to providing market-leading, state-of-the-art software and instrumentation.

Our commitment to customer support sets us apart. We offer a variety of learning opportunities each year all over the world, both online and on-site. We stand behind our products and ensure that you can get the most out of them.

J.A. Woollam Newsletter | 5

the wave front: Written by: Ron Synowicki and Jeremy Van Derslice

Perovskites

Lithography + Computer Chips

In the 2000s, research and development in thin-film solar led to higher efficiency solar panels at a lower cost, primarily driven by the performance of CdTe and CIGS panels. Between 2009 and 2012, the price of crystalline silicon panels dropped by almost 3x, eliminating the cost-benefit advantage of thin-film solar, leading to a collapse of the thin-film solar market and reduced research in this area. Lower-cost silicon panels have been great news for consumers, but the general excitement in research and development of solar diminished as funding slowed. Fast forward a few years, and thin-film research for solar has again gained momentum, but now driven by perovskites.

Electronic devices are continuously updated with noticeable performance improvements in every new generation of computer, laptop, smartphone, and gaming system. The technology driving these improvements includes faster processor chips, memory chips with larger capacity, and higher-resolution cameras and displays. In each case the circuitry in these chips and displays is smaller than the previous generation, allowing billions of transistors to occupy a small area of silicon and to be used for smaller, higher-resolution pixels for ultra-high-definition cameras and displays.

Perovskite is the general term referring to organic-inorganic hybrid materials that have an octahedral crystal structure (shown above) with the formula ABX3 where A is an organic cation; B is generally lead, cadmium, or tin; and X is iodine, chlorine, or bromine. The hybrid material acts as a highly efficient absorber for use in solar cells and can be produced at a significantly lower cost than bulk crystalline silicon.

Research into perovskites has substantially increased over the last decade. Scientists have investigated different material hybrids, searching for the best combination of efficiency and stability.

Researchers caution that our understanding of perovskites for solar cells is still in the early stages of development with many challenges ahead. One often-discussed challenge involves the lifespan of perovskites. In the early days, degradation caused by air and moisture was so rapid that some of the perovskite cells lasted only seconds in the open atmosphere. Since then, lifespans have grown to weeks, then months, and now years, but there’s still a long road ahead to achieve the 25-year lifespans of crystalline silicon. While challenges remain, researchers are optimistic about the outlook for perovskite solar cells.

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How is this accomplished? Optical lithography is a method of patterning circuitry or pixels directly onto a semiconductor or glass surface (a lithograph). The circuit pattern is first laid out on a glass plate called a photomask. The photomask contains areas that transmit light and others that reflect or absorb light.

Ultraviolet light shines through the mask, and the circuit pattern focuses on the surface. The circuit pattern must be captured by the surface, which is accomplished by a layer called a photoresist.

A photoresist acts like photographic film but is actually a thin film applied to the surface. Areas of the photoresist exposed to light from the mask become harder to etch (i.e., resist etching) than areas not exposed. To see the circuit pattern, the resist must be etched using wet chemicals, somewhat similar to photographic film processing.

Ellipsometry is used to determine the thickness and absorption properties of photoresist films for semiconductors, phase-shift layers on photomasks, and the thickness and optical properties of the red, green, and blue subpixel films in displays. Ellipsometry helps make sure these properties are uniform over the entire surface of the wafer or glass panel, which is always challenging since they keep increasing in size!

Cutting-Edge Applications Using Spectroscopic Ellipsometry

Optical Coatings + Lenses Have you ever wondered why camera lenses often have a purple or green color? How are colored sunglasses made? Your optometrist recommends anti-glare coatings for your eyeglasses. How’s it done?

With optical coatings! These coatings are vacuum deposited with their thickness and optical properties monitored with spectroscopic ellipsometry.

Historically, a single layer of magnesium fluoride (MgF2) was the first antireflective optical coating, which is still used today. MgF2 is often the purple color you see on camera and binocular lenses.

Transmission through the lens is improved, since the MgF2 coating has a refractive index between air and the glass lens, which serves to reduce reflections at the air-glass interface. Coatings can be made better by adding a second layer, causing even lower reflectance over a wider spectral range.

With enough interfaces, it’s possible to make mirrors with reflectance values extremely close to 100%! This is accomplished using many layers with different refractive indices. Reflections occur at each interface in the stack, so reflections from many interfaces combine to create extremely high reflectance. However, the stack must be carefully designed for maximum reflectance at a particular wavelength or band of wavelengths. These multilayer film stacks can be complicated to design, and the layer stacks are even more difficult to produce, which is where ellipsometry can help to monitor the coating process in real time.

The optical properties can vary with deposition conditions, so ellipsometry is used to determine if the film thickness is correct and if the optical properties such as refractive index and absorption are correct. These values are used to further refine the stack design and performance. Additionally, by combining this with lithography and displays, the world of AR/VR becomes possible!

Displays Pure electrical insulators are highly transparent, but highly conductive metals are opaque. So what material can be used that is both transparent and conductive? We must find such a material to make our displays and touchscreens work.

Indium tin oxide (ITO) is both transparent and conductive.

ITO optical properties vary a lot with deposition conditions and annealing, so monitoring the quality of the ITO and its thickness is important. Ellipsometry is used for monitoring ITO film thickness and transparency at visible wavelengths while also being sensitive to absorptions in the ultraviolet, but it is very important for monitoring absorption in the infrared, which corresponds to the film’s electrical conductivity.

Improvements in display speed are critical for fast action in movies and sports. Imagine a baseball, golf ball, or hockey puck leaving a comet tail behind on the screen because the display cannot refresh fast enough. Display pixel speed has been significantly enhanced using crystallized silicon films on the rear panel of the display. Ellipsometry is used to monitor the thickness and crystallinity of these deposited polysilicon films.

LCD displays used to be small, monochrome in color, and used in calculators, digital watches, etc. Modern displays are full color, extremely fast, and very large. The coated films must be uniform over the entire panel size, and film uniformity has been a limiting factor in the size of displays for decades. With each new generation of larger displays, the film uniformity must be maintained. An ellipsometer can fly over the large panels as they move on a production line to monitor film quality.

J.A. Woollam Newsletter | 7

New instrument: alpha 2.0

Written by: Jeremy Van Derslice, Applications Engineer

W

e are excited to introduce our alpha 2.0. The alpha 2.0 is the second generation of the alpha-SE, which was first developed in 2003 and was created to provide researchers with an ellipsometer that was budget-friendly, reliable, robust, and accurate for routine measurements of film thickness and refractive index.

Over the years, enhancements were added to the alpha-SE; we added multiple angles of incidence, adjusted the optical layout for improved data quality, and added some accessories. However, the underlying technology largely remained consistent. The alpha-SE was a step-scan, rotating-compensator instrument, which means a stepper motor moves the compensator to a position and holds it there while data is collected, then it moves to the next position, and so on. The step-scan approach met our goals of being robust, reliable, and accurate, but it needed to be faster. In addition, the alpha-SE used a third-party spectrometer as part of the polarization state detector. Although the detector wasn’t purpose-built for our ellipsometer, it performed well and still does an excellent job.

After a long run, we thought it was time to enhance the underlying technology. The result of these updates is our alpha 2.0, which features our patented dual-rotation technology and thus joins our iSE and theta-SE ellipsometers. These instruments are all part of our budget-friendly offerings, each designed for a specific market: the alpha 2.0 for research customers, the iSE for in-situ applications, and the theta-SE for customers with uniformity 8 | J.A. Woollam Newsletter

mapping needs. The dual-rotation technology uses a rotating compensator before the sample and a rotating analyzer after the sample. With dual rotation, the instrument captures polarization information from multiple optical orientations, which always provides high-accuracy measurements. The alpha 2.0 also provides 12 elements of the Mueller matrix in a single optical cycle, meaning Mueller matrix measurements can be obtained quickly without “stitching” multiple measurements together.

The new design of the alpha 2.0 also contains many of the features that made alpha-SE a great instrument, starting with the price. We made sure to provide customers with a budgetfriendly ellipsometer that’s reliable, robust, and accurate. One of the main differentiators between the alpha-SE and alpha 2.0 is the spectrometer. We incorporated our custom-made spectrometer, which is built on 35+ years of experience in spectrometer design for ellipsometry. The alpha 2.0 uses a QTH light source in combination with CCD detection to provide information over the visible spectral range with 190 wavelengths between 400 and 1000 nm. The thickness and refractive index can be determined for a variety of sample types, from simple transparent films to semi-absorbing films and anisotropic materials.

Many of the mechanical aspects of the instrument remain the same. For those familiar with the alpha-SE, you will notice the

Specifications Spectral Range

400 nm to 1000 nm, 190 wavelengths

Angle of Incidence

Manual adjustment 65°, 70°, 75°, or 90° (straight-through)

System Overview

Dual-Rotation optical design CCD detection Automated sample alignment

Data Acquisition Rate

5-10 seconds for full spectrum [typical]

Software

CompleteEASE for data acquisition, data analysis, and optical simulations

Beam Diameter Focused: < 1 mm

Power Requirements 100/240 VAC, 47-63 Hz, < 1 Amp

Sample Size

Up to 200 mm diameter and 16 mm thick

Light Source

Quartz Tungsten Halogen (QTH)

alpha 2.0, for the most part, looks the same. This is largely because we are continuing with the manually adjusted, multi-angle system design. We find the multiple-angle capability to be a beneficial feature because it enables sensitivity to material parameters for multi-layer stacks and complex materials, including absorbers and anisotropic materials. The additional sensitivity is, in part, derived from the change in path length that occurs at each angle as light travels through the film, as defined by Snell’s law.

The multi-angle concept provides a benefit for the more complex samples.

Sample alignment features remain similar. With the alpha 2.0, the sample can simply be placed on the stage, and the signal will be maximized prior to measurement with no user-required adjustments. Our goal in the design translated to a straightforward, fast, and reliable measurement process. Like its predecessor, the alpha 2.0 is a benchtop instrument with a small footprint, measuring 476 mm (width), 324 mm (depth), and 311 mm (height).

It is lightweight and requires less than 1 amp at 100/240 VAC, so it should be easy to place on a lab table.

Please contact our applications group or your local representative if you have questions about the alpha 2.0, and we’d be pleased to discuss with you in greater detail.

J.A. Woollam Newsletter | 9

In Situ Spectroscopic Ellipsometry Applications to Atomic Layer Deposition By: Jeremy Van Derslice1, James Hilfiker1, Joshua W. Pinder2, and Matthew R. Linford2; 1J.A. Woollam Co., Inc., Lincoln, NE USA; 2Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT USA (Article originally published in VT&C Magazine, Part 2, November 2022)

introduction In situ spectroscopic ellipsometry has become a vital tool for monitoring and studying ALD film growth (and even etch) in real time. The combination of ALD and spectroscopic ellipsometry (SE) is particularly popular because in situ SE measurements are both direct and nondestructive. By ‘direct’ we mean that the measurement probes the sample of interest and not some other surface. (An example of an indirect film thickness measurement is deposition on the quartz surface in a quartz crystal monitor within a deposition chamber. These measurements are generally quite good, but they may not always represent what is happening on the surface in question.) SE is ‘nondestructive’ because the light it uses to probe the surface rarely influences or modifies the surface. Furthermore, SE does not require a thin film to be scratched or cut as for atomic force microscopy, profilometry, or scanning electron microscopy step height or profile measurements.

SE is particularly well suited for determining the thicknesses of very thin films because it measures the change in the polarization of the light that reflects from a surface, which includes the phase shift caused by a thin film. This phase information provides sensitivity to very thin films, i.e., those less than 10 nm thick. Thus, SE is ideally suited to ALD because ALD is commonly used to deposit ultra-thin films. This sensitivity is not available from reflection or transmission intensity-based measurements. A final advantage of in situ SE in ALD is the excellent match between the measurement times (data acquisition rates) of modern SE systems and the deposition rates of ALD processes. A full SE spectrum with a thousand wavelengths can be collected in a fraction of a second, giving insight into the chemistry at the surface of an ALD process. These advantages of in situ SE also apply to most other thin film deposition methods.

This article covers various aspects of in situ SE as applied to ALD. We first provide a brief history and overview of ALD. We then discuss the incorporation of SE instruments onto ALD chambers. We end with an overview of in situ SE data analysis, including a brief discussion of modeling concepts for substrates, oxides, and metal films.

A Brief History and Introduction to ALD These brief comments on the history of ALD come from Kääriäinen’s excellent book on the subject [6]. The first ALD experiments were performed in the 1960s by Aleskovski in Russia.[ref 6 – p. 10]. Suntola and coworkers from Finland then worked in this area in the 1970s. [ref 6 – p.11]. Suntola called his method ‘atomic layer epitaxy (ALE).’ However, as ALD evolved, it became clear that many of the films it produces are amorphous, so ‘atomic layer deposition (ALD)’ appeared to be a better name for it. Since the 1970s, there has been increasing interest in ALD. However, when ALD first appeared, it was arguably a niche technique.

Nevertheless, ALD has become extremely important in modern 10 | J.A. Woollam Newsletter

technology, and especially for semiconductor manufacturing, because (i) semiconductor device features have decreased to match the thicknesses of the films that are easily produced

by ALD, (ii) semiconductor manufacturing relies on the deposition of the type of ultrathin, conformal films that can be produced by ALD (to coat three-dimensional features), and (iii) there are now many vetted ALD reactions that can be used to deposit many different types of materials, often under conditions that are not extreme – at moderate temperatures and low vacuums, but not extremely low vacuums.

ellipsometry has been used for process optimization where the cycle and purge times are monitored and minimized to improve the deposition rate and save time. Indeed, SE can map out an ALD process, providing important details [9,10]. For example, Figure 2 shows layer-by-layer growth during a plasma-enhanced

Figure 1. (A) A hydroxyl-terminated surface. (B) The surface in A or C after reaction with TMA. (C) The surface in B after reaction with water.

After the introduction of each reagent (TMA or water), there is a purge step in which the unreacted reagent is removed.

In its classical embodiment, ALD is performed in two half cycles/ reactions with two different gas phase reagents/precursors. In the first half cycle, one of the gas phase reagents is introduced and allowed to react with the surface. Any unreacted reagent is then removed/purged from the system. The second gas phase reagent is then introduced and allowed to react with the surface. Any unreacted second reagent is then removed, and the process is repeated to build up a thin film in a layer-by-layer fashion. This process is illustrated in Figure 1 for the ALD deposition of alumina from trimethylaluminum (TMA) and water. This deposition often starts with a hydroxylterminated surface (see Figure 1A). This surface is then exposed to TMA, which reacts with the surface hydroxyl groups (see Figure 1B). The surface is then exposed to water (see Figure 1C). In each step, aluminum (from TMA) or oxygen (from water) is deposited on the surface. If this process is continued, alumina films of varying thicknesses can be grown.

In general, ALD reactions are quick – the half reactants used in ALD are often reactive (at least with each other). In addition, ALD half-reactions are designed to be self-limiting. Accordingly, each half-reaction produces up to a monolayer of material on a surface. Accordingly, ALD is not usually the best method for producing very thick films – films that are microns thick.

However, it excels at producing films that are a few nanometers to tens of nanometers thick, which is the perfect range for modern semiconductor manufacturing. Obviously, ALD relies on the fact that the functional groups created in each half-reaction react with the reagent introduced in the next step. Also, more complex ALD approaches have been developed than that shown in Figure 1, e.g., with plasma activation, with more than two reagents, etc., and the reader is directed to an excellent blog from Eindhoven University of Technology, which provides a thorough database for both ALD and ALE processes [7].

Temperature is a critical parameter in ALD [6]. If the temperature is too low, the reactions will be too slow or a reagent may condense on the surface. However, if it is too high, the reagents may not spend enough time on the surface to react, or they may decompose.

Between these extremes is the ‘growth window.’ In situ SE has been used for recipe development, including rapidly determining the growth window for a given set of precursors [8]. In addition,

ALD (PE-ALD) of an Al2O3 film. The film thicknesses were determined from SE data collected every 50 ms to easily resolve the deposition process. In Figure 2, the abrupt increases in film thickness and subsequent slanted plateau correspond to the introduction and surface reaction of the aluminum precursor, and the drop to the next slanted plateau, including these plateaus, corresponds to the introduction and reaction of the oxygen plasma.

Figure 2. Plasma enhanced (PE)-ALD of Al2O3 measured with 50 ms time resolution. [Data courtesy of V. Vandalon & H. Knoops (Eindhoven University of Technology)]

Incorporation of in situ SE into ALD systems Ellipsometry requires a precise angle of incidence for accurate measurements. For ex situ SE, this angle is easily controlled by precision goniometers that adjust the source and receiver positions of the instrument with respect to the sample normal. Ex situ measurements often allow complete control over sample alignment (tip-tilt-z), which ensures consistent sample positioning. Unfortunately, this level of precise control is rare for in situ SE. First, the sample resides within a vacuum chamber, while the SE instrument is mounted outside of the chamber.

Second, the SE measurement beam reaches the sample after traveling through optical viewports (see Figure 3). These viewports are transparent windows mounted on the chamber, typically with a 2¾ inch conflat flange, at an angle of incidence of 60 – 75 degrees from the sample normal. The SE receiver is mounted to a port to collect the reflected light at an equal but opposite angle. Physically attaching an ellipsometer to a deposition chamber generally restricts any future modifications to the angle of incidence and limits independent sample alignment. Thus, in situ SE measurements are often acquired at a single angle of incidence with a modified sample alignment procedure. Here, the SE is aligned to the sample J.A. Woollam Newsletter | 11

ii. Window strain can alter the polarization state of light traveling through the window, even at normal incidence. SE is a measure of the polarization change caused by the sample, so polarization changes from window strain are problematic. Window strain may occur in the production process. However, even windows that are strain-free (as produced) can have strain induced from the mounting process. Window strain caused by mounting can be mitigated by applying uniform torque while tightening the bolts (in a star pattern) when attaching the window. Any changes in polarization caused by window strain need to be determined during a calibration procedure.

Figure 3. ALD chamber with an in situ ellipsometer (source and receiver) attached to it.

rather than the sample being aligned to the SE. That is, the SE source and receiver are each mounted to viewports via adapter plates. The plates allow tip-tilt adjustment to control the measurement beam direction (source) or the internal alignment (receiver/detector). Because the sample is often fixed within the chamber, alignment starts by adjusting the source. The source is tilted to position the measurement beam on the sample at a position that reflects the light to the receiver window. The receiver unit is then aligned to ensure the measurement beam is inline with the receiver optics. Additionally, the receiver can often be translated to ensure the beam is fully captured. A well-aligned in situ SE is one where the signal at the detector has been maximized. However, this alignment procedure does not ensure an exact angle of incidence.

Thus, it is important to pre-determine the angle of incidence during a “calibration” step, often by measuring a well-known sample such as an SiO2-coated Si wafer. If the sample load process is reproducible, the SE does not have to be repositioned, and the “calibrated” angle remains true. Fortunately, ALD chambers traditionally use fixedposition sample stages that are not designed to rotate as in some other deposition techniques, and, therefore, the sample load position is quite reproducible. As previously stated, for in situ ALD, the SE measurement beam is generated at the source, passes through a window, reflects from the sample, passes through a second window, and is detected at the receiver. There are a few considerations regarding these windows: (i) window transmissibility, (ii) window strain, and (iii) unintentional coatings. We now discuss these issues. i. Obviously, SE requires the windows to be transparent over the measurement range of the ellipsometer. These requirements depend on the wavelength range of the instrument used to monitor the process, which, from an ellipsometry perspective, is most commonly from deep ultraviolet to near infrared wavelengths. High-quality fused silica is a commonly used window material because it is highly transmissible at these wavelengths and it is relatively inexpensive.

Low-cost glass windows may be adequate if ultraviolet wavelengths are not measured. For mid-infrared wavelengths, in situ SE would require windows transparent at these wavelengths, typically from zinc selenide or potassium bromide.

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iii. The windows in an ALD chamber may be unintentionally coated during the deposition process. That is, in ALD, films are deposited on all surfaces the gases encounter, which can include the windows. Fortunately, isotropic thin films coated on windows do not alter the polarization of light. In fact, the polarization change in SE is determined from a ratio of the intensities of orthogonal directions, so an SE measurement remains reasonably accurate even as the intensity of the light is reduced by window contamination, at least until the beam is absorbed so much that light no longer reaches the receiver. Basically, absorbing films attenuate the signal intensity and lead to noise in the measurement at the wavelengths where the absorption occurs. Commercial vendors of ALD tools have developed strategies to mitigate this issue by: (a) Using port valves to block precursors from reaching the window, where the valves are opened between cycles for the ellipsometric measurement, (b) Purging the port tubes to prevent the reagents from reaching the windows, or (c) Using a sacrificial window that is low-cost and can be easily replaced when coated.

Each practice has advantages and disadvantages, but they are all effective in enabling real-time monitoring of thin films produced by ALD. After the ellipsometer is mounted on the chamber, aligned, and calibrated, we are ready to collect SE measurements.

In situ SE of substrates, and oxide and metal/conducting thin films Before starting an ALD process, it is common to collect SE data from the underlying substrate, where silicon is a common substrate material. That is, SE is a model-based technique, so it is beneficial to build a model that describes the substrate prior to deposition. Any misfit or inadequacy in the model at this point could lead to inaccuracies in the analysis of the deposited films.

A well-aligned and calibrated SE typically has no issues meeting this requirement. Figure 4 shows in situ SE data from a silicon substrate prior to ALD processing. To demonstrate the importance of understanding/modeling the substrate prior to ALD, we show a model calculation for an ideal silicon substrate with 1.5 nm of native oxide (blue dashed curves). However, these results deviate

significantly from our measurement, especially in delta – the phase information (delta) is highly sensitive to ultra-thin coatings on a surface. To properly fit our measured data, our model increases the native oxide thickness to 3.36 nm (to account for a dirty substrate) and adjusts the substrate silicon temperature to 220 °C (the optical constants of silicon are temperature dependent). The results of this model (black dashed curves) provide an accurate starting point for our fitting/modeling.

Figure 6. Using these values, we can determine the thickness of the film versus time as is also shown in Figure 6. The final thickness of the Al2O3 thin film is 146 nm, so we see that this deposition was quite slow (it had not been optimized) – it had a linear growth rate of ~0.9 Å per cycle. Of course, this approach assumes that the optical constants of the film are not changing with film thickness. We cannot usually make this assumption when we are dealing with thin metal films.

Figure 5. In situ SE data from an Al2O3 deposition.

Figure 4. Experimental psi (red line) (a) and delta spectra (green line) (b) for a silicon substrate prior to any ALD deposition compared to an ideal substrate model (dashed blue line) and best-fit model (dashed black line) that includes the substrate temperature and a thicker native oxide to account for a “dirty” substrate.

Figure 5 shows five psi values at different wavelengths from an ALD deposition of alumina monitored by in situ SE. As described in a previous month’s article [1], the SE data oscillate with time during ALD due to the interference between light reflecting from the top surface of the film and light traveling through the film. That is, the oscillations in Figure 5 indicate that the thin film thickness is changing with time. While SE is very sensitive to film thickness, even to ultrathin films, the sensitivity to the film’s refractive index increases as the film thickness increases [5]. Thus, it is common when studying new materials to consider/use the thin film’s optical constants at the end of deposition – when it is thickest. For the deposition shown in Figure 5, we consider the data designated by the red arrow. At this point, the Al2O3 film is quite thick, and we have the best sensitivity to its refractive index. In addition, the film is transparent at all wavelengths, so we use a Cauchy dispersion relation to describe the refractive index [11], shown in the inset of

The data shown in Figures 5 and 6 were collected at a relatively low data acquisition rate because the end goals of this study were only to determine the film refractive index and growth rate. However, as shown in Figure 2, fast in situ SE measurements may also be applied to study the underlying deposition chemistry. Here, when the optical properties of the film are known, the film thickness can be accurately determined even during the first few cycles.

This allows one to use fewer cycles to determine the growth rate and enables determination of any nucleation delay and other reaction kinetics. Recipes are thus developed to define important parameters relevant to deposition of high-quality films including optimal times for each half-cycle and purge step. Recipes for many different metal oxides are available [7], which produce predictable, high-quality films. Metal oxides are typically transparent at visible and near infrared wavelengths and are therefore rather easy to characterize by SE.

Figure 6. Thickness versus time for a growing Al2O3 film determined from the data in Figure 5, which shows a growth rate of around 0.9 Å per cycle. The inset shows the index of refraction for this film.

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The need for new ultrathin films has also led to the ALD of metals/metallic materials such as platinum and titanium nitride [12]. These conductive materials are more complex optically than the oxide materials that were just mentioned and require special treatment for successful in situ SE. The most common approach to determine both the film thicknesses and optical properties of such absorbing materials is to use “interference enhancement,” which was discussed in a previous article [13]. Interference enhancement requires the substrate to be terminated with a thick dielectric film. For example, silicon substrates terminated with 300 nm to 1000 nm of thermally grown SiO2 are commonly used for interference enhanced SE. Figure 7 is a cartoon of a sample that can take advantage of interference enhancement, which consists of a thin platinum film on a thick oxide layer on a silicon substrate. The thick oxide layer produces an “enhanced” reflection (an interference pattern) for any light that travels through the absorbing film, which, in this case, is a thin platinum layer deposited by ALD. As discussed in [13], the large interference oscillations (peaks and valleys) from the thick oxide in our data will be suppressed by a growing thin metal film – see Figure 8, where the information in these signals provides adequate information to determine both the platinum film thickness and its optical constants.

Figure 7. Representation of a thin Pt ALD film on a thick SiO2 layer on a silicon substrate. Such thick oxide substrates are used in interference enhancement SE, which provides additional information in SE measurements such that both film thicknesses and optical constants can be simultaneously determined.

A wealth of information about conductive materials can be gained from in situ SE measurements during ALD. For example, ellipsometry has shown that growth of many conductive materials begins with the formation of islands [14]. These islands restrict the free flow of electrons, and therefore ultra thin metal layers have little-to-no conductivity in the early stages of growth. As growth proceeds and the islands coalesce into continuous films, the conductivity of the deposited material increases. In many cases, it takes 20-30 nm of deposited material before the conductive film properties stabilize. An example of this effect is shown in Figure 9, where the extinction coefficient, k, is graphed for different film thicknesses during ALD growth of a metallic material. Conductive materials exhibit large absorption at longer wavelengths due to free carrier absorption.

Thus, larger near infrared (NIR) absorption indicates more conductive thin films.

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Figure 8. Red line: SE psi spectrum from a thick oxide substrate used for interference enhancement, which shows an oscillation pattern. Gray line: Spectrum of the same thick oxide substrate as represented by the red line but with a thin Pt film on it showing a suppression of the signal from the substrate.

We see from Figure 9 that the NIR absorption is non-existent for the thinnest layers, indicating that growth is likely confined to islands, which inhibits the “flow” of free-carriers. In other words, the thin layers are not conductive. As the layer thickness increases, we see the NIR absorption also increase, which suggests the film is becoming more continuous and thus, more conductive. The NIR absorption doesn’t stabilize until the film is about 15 nm thick.

Figure 9. The extinction coefficient of a thin film of a conductive material as a function of its thickness.

Conclusions In situ SE is a powerful tool for monitoring ALD thin film growth, where it can provide film growth rates, film optical constants, and even more detailed information about growing thin films. The mounting of an SE instrument on an ALD chamber requires special considerations, including regarding the windows of the chamber. Good modeling of in situ SE data should begin with an appropriate model of the substrate.

Oxide films that are transparent over wide wavelength ranges are simpler to analyze by in situ SE than metal films, which often require interference enhancement ellipsometry.

References For references, use the QR code to the right to access the online version of the article originally published in VT&C Magazine; Part 2, November 2022, pages 27-32.

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J.A. Woollam Newsletter | 15

FEA TURED RESEARCHER:

Parag BanerJee

Understanding and Controlling the Atomistic Mechanisms of Atomic Layer Deposition (ALD)

16 || J.A. J.A. Woollam Woollam Newsletter Newsletter 16

Interview by: James Hilfiker, Applications Engineer

Right photo: My parents, elder brother, and I at the Taj Mahal in 1984

Where are you from?

Where did you get your education?

I am originally from India. I was born in a picturesque city called Chandigarh in the foothills of the Himalayan mountains.

I obtained my undergraduate degree in metallurgical engineering from the Indian Institute of Technology Roorkee, a master’s in Materials Science and Engineering from Washington State University, and a Ph.D. in Materials Science and Engineering from the University of Maryland.

Growing up, were you always interested in science? How did you end up in your niche area of study?

My father was a physicist in a national laboratory. He led the development of the first indigenously built electron microscope in the late 1960s. Growing up, I remember my father spreading engineering graph papers with circuit diagrams on our dinner table and working late into the night. When I could, I would visit him in his lab and be mesmerized by the instruments. There were all kinds of microscopes, vacuum deposition chambers, and plasma etchers. I was fascinated by the interplay of vacuum systems and their ability to ‘cook’ new materials. I suppose you can say I was always interested in science because I knew no better!

What was your favorite college course and professor?

I have two! I think my favorite undergraduate professor was Professor Patwardhan. He taught a class on steel metallurgy that I took during my junior year. This topic can be quite boring to a young person because a lot of the concepts are just qualitative and require a lot of rote learning – you add element ‘A’ to steel, you get property ‘B’. So, it’s just a rundown of what elements affect steel properties. However, Professor Patwardhan added so much more context to the course. I felt that for the first time I was truly learning to be an engineer.

And the best part? He had no books assigned! He taught from his own experience and memory, some colored chalks, and a dusty chalk board.

My second favorite professor is from my graduate school at Maryland: Professor Greg Jackson. Professor Jackson taught us molecular thermodynamics – an incredibly difficult course.

But his lecture style and the attention to detail in his notes were simply awesome. At the end of the lectures, I always thought I understood even the most complex concepts with clarity.

Who has influenced you the most? Any role models or mentors that you have stories about?

My dad, Pradeep Banerjee (circa 1988), on a lab visit to the U.S.

My advisor Dr. Gary Rubloff has been instrumental in defining my career path. I was still working in industry when I decided to move back to school for my Ph.D. While searching for J.A. Woollam Newsletter | 17

Below: ALD in Seattle, WA with part of the research group (2023)

Above: AVS 67 in Pittsburgh, PA (2022)

potential research groups and universities to join, I ended up talking to Gary on the phone. That conversation happened in my company's parking lot and lasted 90 minutes until I lost charge on my phone! I knew then that I had to join Gary’s group at Maryland.

The rest is history.

What was the best constructive criticism or advice you received?

Perfect is the enemy of good. Too often in research we are seeking perfection in our approach and understanding. It has taken me a lot to realize that most research is far from perfect. Research is messy.

You take two steps forward and then one step back. Research is incremental too. The “aha moments” are few and far between. So many times you have to be satisfied with good and move on. The beauty of research is that it has a long arc, and it will always allow you to come back and refine things you have looked at many years ago. You just have to be patient.

Did any of your research topics in school involve ellipsometr y?

Only for measuring film thickness.

When did you first learn ellipsometr y and for what application?

When I was a process engineer (2000 – 2006) at Micron Technology Inc., we used ellipsometry as an in-line metrology tool.

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Above: STEMS UCF Conference (2023)

What does your current research involve?

Why is this research important? How do you use ellipsometr y?

My current research involves understanding and controlling the atomistic mechanisms of atomic layer deposition (ALD).

Our group uses ellipsometry as one of the “in situ” tools to study how various process parameters affect complex surface reactions in ALD, which in turn affect deposition rates.

What excites you about the future of your field?

The semiconductor industry in the U.S. is going through a “take 2.0” of sorts. After a slipping competitive advantage in the past, there is now palpable excitement!

What has been the most rewarding part of your career?

Teaching students and watching them mature as researchers has been incredibly rewarding.

Do you have any recent publications?

I have a few recent papers – the first one is “Surface oxidation of hydrophobic ZnSe for enhanced growth of atomic layer deposited aluminum oxide” where we show we can effectively convert a surface from hydrophobic to hydrophilic, and this directly affects the incubation to growth during ALD.

“The beauty of research is that it has a long arc, and it will always allow you to come back and refine things you have looked at many years ago. You just have to be patient. "

This study could not have been conducted without in situ spectroscopic ellipsometry. Another nice paper we have recently published is “In situ spectroscopic ellipsometry and rigorous coupled wave analysis for real time profile evolution of atomic layer deposited films inside SiO2 nanotrenches.”

In this paper, we collaborated with Onto Innovation, used in situ ellipsometry data generated on the M-2000, and analyzed it using rigorous coupled wave analysis (RCWA) to generate film profiles inside 3D nanostructures. Both papers highlight the importance of in situ ellipsometry during film growth as a means to rapidly learn about a deposition process.

What conferences do you attend?

Which was your favorite? Why? I regularly attend the topical ALD/ALE (run by AVS) and AVS International. I love them both as they allow me to interact with my near and extended research community.

Above: at UCF Lab with a J.A. Woollam ellipsometer (2023)

What do you enjoy doing in your free time?

While living on the West Coast, I used to hike a lot into the mountains. Since moving to Florida, I have given up on that and have now picked up gardening; I am fascinated by the science and engineering of growing food. I have new-found respect for farmers everywhere! I am also an avid tennis player.

Above: Ph.D. advisor Gary Rubloff with Banerjee group at ALD in San Diego, CA (2013)

Above: at Machu Picchu with elder daughter (2019) J.A. Woollam Newsletter | 19

CompleteEASE:

More Complete. More user-friendly.

Written by: Joel Mohrmann

F

ew today remember what the acronym “EASE” in “CompleteEASE” even stands for. If you’ve ever wondered why our premier ellipsometry software is called CompleteEASE, allow me to explain: CompleteEASE is short for Complete Easy-to-use Acquisition/Analysis Software for Spectroscopic Ellipsometry. That’s a mouthful, and yes, it’s a bit of a pun, but it’s also a succinct way to describe what our goals for this software platform have been and continue to be. We want CompleteEASE to provide the best methods to acquire spectroscopic ellipsometry data and then be able to use state-of-the-art techniques to analyze that data to obtain useful results. We want CompleteEASE to be the “one-stop shop” for ellipsometry data that is accessible, intuitive, and straightforward.

To that end, we’re always working to improve CompleteEASE’s user experience and add to its many data acquisition and analysis features to provide the best and most complete results whatever your application may be.

The release of CompleteEASE 6 in 2017 was a major upgrade for its functionality and usability. Since then, we have built on this foundation to simplify many CompleteEASE features and expand its functionality. This article will highlight some of the incremental improvements we have made throughout last year in order to enhance CompleteEASE for all users.

Network Licenses To use CompleteEASE 6, you will need a license for each computer you use. Each ellipsometer is shipped with five licenses of CompleteEASE, meaning it can be used on up to five different computers. However, this can sometimes be restrictive. What if you have more than five users who need to use CompleteEASE, but some only use it periodically and

20 | J.A. Woollam Newsletter

don’t need a full license dedicated to their computer alone? To bring more flexibility to the use of CompleteEASE and address situations like these, we have developed a new licensing method.

CompleteEASE can now be licensed using so-called “floating” licenses, installed on a network or server computer. This way, anyone that you designate who has access to your network can use CompleteEASE. CompleteEASE can now be configured to operate like many other software platforms where licenses are not fixed to a particular computer but rather can be used by any computer as needed, providing greater usability and increased accessibility.

Memory Optimization Years ago, when CompleteEASE was first in development, it had to be designed for computers with, as we would look back on today, limited available memory and other limited capabilities.

However, with the advancement of modern computing in terms of speed and memory, we are no longer bound by those same old constraints. Thus, we have made a concerted effort to redesign aspects of CompleteEASE so that it doesn’t remain unnecessarily limited by these old restrictions. For example, CompleteEASE now allows you to append an unlimited number of data sets or select

an unlimited number of points on a thickness-uniformity map.

CompleteEASE will also allow you to plot an unlimited number of curves on a graph. The number of B-Spline nodes that can be applied to a model is unlimited. You can measure at an unlimited number of angles of incidence. An unlimited number of layers can be added to the layer stack in a model. You can even now have an unlimited number of sublevels below project folders in the file dialog. CompleteEASE’s memory management algorithms have been enhanced to enable all of this, so as long as your computer has the RAM to handle it, the sky’s now the limit for what CompleteEASE can accomplish.

Helpful Modeling Tips While using CompleteEASE, we want your experience to be as easy as possible. However, while analyzing data, there are some common mistakes and pitfalls that users can experience when they aren’t as knowledgeable about what to watch out for. That’s why we’ve implemented some “safety checks” to help users know when they might encounter one of these pitfalls. For example, we’ve implemented a warning to let you know when the resulting optical constants for a layer, such as a Cauchy, become unphysical. If the B-Spline is limited to a range where it does not have enough nodes to enforce Kramers-Kronig consistency; CompleteEASE will now let you know.

Tabulated optical constants can be a useful tool for analyzing data or pre-seeding a model, but sometimes the optical constants aren’t tabulated in a region that is covered by your measured data.

Therefore, CompleteEASE will warn you if the spectral range of your experimental data exceeds the ranges of the tabulated material files being used in your model. Coupled parameters and derived parameters in a model refer to other fit parameters, but sometimes multiple parameters in a model can have the same name, creating ambiguity. Therefore, CompleteEASE will now indicate when a coupled or derived parameter has referred to a parameter name that is used more than once, allowing you to specify which parameter you wish to use. These are just some of the ways in which we have made CompleteEASE more helpful and user-friendly.

Flexible Graphing Once ellipsometry data has been measured and analyzed, many people want to make good-quality graphs of their data and results for use in academic papers, reports, presentations, scientific articles, etc. CompleteEASE now contains more features and increased flexibility when constructing high-quality graphs of data and results. Inside CompleteEASE’s Graph Scratchpad, there is now an option to change the order of curves in the legend. There are also more line styles for graph curves, and the style of the line can be shown in the graph’s legend box for easy identification. This

allows a “black and white” mode for CompleteEASE graphs, useful for publications that cannot be printed in color. Additionally, custom equations can now be edited directly after they are created, and the procedure for adding trendlines has been simplified so that the relevant range of interest is more easily identified.

Once a graph is made just the way you want it, you will have to export it outside of CompleteEASE to be used where needed. In the past, this was always done via the clipboard, but now you can save graph images as .png files directly from CompleteEASE. You can also save images of the model structure in this same way. In the past, images of graphs and model layer stacks had a white, rectangular background when they were copied and pasted elsewhere, but in the latest version of CompleteEASE, graph and model-layer-stack images can now be exported with transparent backgrounds so that they can be used in any setting on any background. From greater flexibility in constructing graph components to new line styles to transparent backgrounds, these features give you the tools to make the high-quality graphics of ellipsometric data and model analysis results you desire.

…And Much More This only begins to scratch the surface of the many ways in which we have improved CompleteEASE. We haven’t mentioned that graph scratchpad files (with the “.scratch” extension) can now be opened directly in CompleteEASE by double-clicking on them in the file system. The way to export measured experimental data to a text-file format has been completely redesigned to be more user-friendly and less confusing. You can now open Gen-Osc material files made in WVASE directly into CompleteEASE. You can now build complex semiconductor models using the full PSemi capability popularized in WVASE. Numerous enhancements have been made to CompleteEASE’s Environment Cell attachment, which controls the partial pressure of various solvents surrounding a sample. And as of a couple of years ago, CompleteEASE even has a new reference manual, complete with better explanations of major features, updated tutorials and examples, and more reference information about data analysis and modeling. The new manual is included with each new installation of CompleteEASE simply by pressing the F1 key.

So, are you ready to get your hands on an improved and updated CompleteEASE? CompleteEASE is designed to easily install over the top of any old versions you may have, while preserving all of your configurations and settings as well as data, model, material, and recipe files. If you would like a copy of the most recent version of CompleteEASE, contact your local J.A. Woollam representative or, if in the United States, email sales@jawoollam.com. We would be happy to provide you with an updated copy and help you use any of these new features or other specialized advancements offered by CompleteEASE.

J.A. Woollam Newsletter | 21

SPOTLIGHT STORY / TOM TIWALD

Tom Tiwald's Artistic Legacy through the lens of Infrared-SE "Much of what we do is not trivial or simple, and a number of complex steps and judgments are required to accomplish certain tasks. I like helping customers do that. That has been the most satisfying part of my job."

Can you tell me a little about your educational background?

Educationally, I tried many different things for 20 years, eventually settling into the field of ellipsometry, which I have done for almost 30 years.

After high school in Omaha, I spent one semester as an English major at the University of Nebraska–Lincoln. I quit school because I was bored, and spent one year “semiretired.” I hitchhiked around the West Coast for a couple of months, worked as a bike mechanic in Omaha, and worked as a house painter.

On my way home from a three-week canoe trip to the Boundary Waters in northern Minnesota, I stopped in Minneapolis for one night, where I saw a performance by an improv theater group called “Dudley Riggs’ Brave New Workshop.” It was (and still is) the most extraordinary theater experience I ever had. I was hooked. I enrolled at the University of Nebraska Omaha theater program as an actor, and after one semester I received an offer to attend the Drama Studio in London. I spent one year there, studying acting and enjoying the pubs as a 19-year-old. I earned the equivalent of an associate degree in theater.

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I came home to Omaha to pursue a career in acting. Of course, it was hard to get any work outside of community theater – the unemployment rate for actors is more than 90%! At that time I met Jeanette, who would become my wife (45 years and counting!), so I delayed plans to move to New York or Los Angeles to begin my career in earnest.

To earn some money, I was working as a janitor at the local children’s theater. A friend of mine, a musician, had enrolled at a private electronics tech school. He encouraged me to do the same. He told me that I could earn a better salary as an electronic technician and set my own schedule while I continued to pursue work as an actor. I enrolled, and after 18 months I earned another associate degree, this time in electronics.

This was the late 1970s, and most consumer electronic products had discrete components – vacuum tubes, transistors, resistors, capacitors, inductors – all soldered onto circuit boards. Only a few products had integrated circuits. Most consumer devices were analog, although a few had rudimentary digital integrated circuits. I discovered that I really enjoyed learning about electronics, and what I enjoyed most was the theory about how the various components worked. Photovoltaics were a popular topic in the news, with plenty of government-funded research. I was really interested in that at the time.

With my acting career going nowhere, I enrolled at the University of Nebraska–Lincoln as an Electrical Engineering major. When I was finishing my undergraduate degree, my advisor encouraged me to pursue a master’s degree. My master’s degree was in electronic materials, specifically deposited and electrically characterized sputtered SiC films.

However, my actual start in material characterization began when I went to work for Motorola in Austin, Texas. There, I worked in a surface analytical lab conducting secondary ion mass spectroscopy (SIMS). Mostly, I measured trace contaminating elements like sodium in MOS devices. I also performed a little bit of Auger, SEM, and TEM. In late 1993, my wife Jeanette got an offer to work as a teacher leader for the Reading Recovery program in the public schools in Lincoln, Nebraska. The offer was too good to pass up. So, I had to figure out what to do. What is a semiconductor engineer going to do in Lincoln, Nebraska?

I thought maybe I could go back to UNL and get my Ph.D. So, I visited Lincoln and John Woollam invited me to look around his labs.

That’s when I first saw an infrared ellipsometer. It was a prototype, and there were only three or four such instruments in the world at that time. I thought, “I know

what to do with that!” I knew IR spectroscopy was used to study material properties, which I had been doing at Motorola, and really, since I started my master’s program. So, I returned to Lincoln as a Ph.D. student for John Woollam in 1994 with a focus on infrared ellipsometry of semiconductor devices (since I knew something about semiconductors from my work at Motorola).

Jeanette and I moved the family back to Lincoln, and she started her job with the public schools. I began my Ph.D. work and helped with caring for three kids. After my Ph.D., I was hired by J.A. Woollam. Infrared ellipsometry became my primary responsibility at the company, although I do a wide variety of projects just like everyone in the applications group.

What materials can be studied using infrared spectroscopic ellipsometry?

Almost any material substrate or film can be studied. The key is that the surface is “optically smooth,” or “mirrorlike”, which means when light hits it, the light reflects specularly (low scattering). Of course, in the infrared, a “mirror-like” finish is different than for the visible wavelength range because the wavelengths are ten times longer. Surfaces that behave as rough and scattering in the visible may behave as a smooth surface in the J.A. Woollam Newsletter | 23

IR because the wavelengths are longer. Most materials have some infrared vibrational modes where the atoms or groups of atoms vibrate at one or more frequencies (or modes) when illuminated with infrared light. That can be used to identify materials. If you observe certain modes in the data, you could say, “that’s water” or “SiO2” or “sapphire,” etc. You can sometimes identify contaminants in the material because they will have their own unique signature in the infrared spectrum.

What are some of the applications of infrared Ellipsometry?

Ellipsometry is primarily used to study the thickness and optical properties of films or substrates. There are quite a few applications for infrared ellipsometry. One application is infrared detectors (MCT and other types). Another application is optical coatings and lens substrates for infrared cameras and sensors. Many infrared cameras and sensors operate in the 2-6 µm and 8-12 µm wavelength ranges. The IR-VASE easily covers both those ranges and much more – it is specified to cover 1.7 to 30 µm, and it can measure up to 40 µm if the sample is sufficiently reflective. People who design infrared cameras must know the optical behavior of the lenses, mirrors, and films in those cameras over that wavelength range.

Also, there are many applications related to materials science.

Chemists are interested in what happens to a material when it is processed in a certain way, i.e., when you heat it or cool it, subject it to certain gases, or immerse it in certain liquids. That change in chemistry is often reflected in changes to the magnitudes, broadenings, and spectral positions of the infrared vibrational modes. Physicists use IR ellipsometry to study crystalline materials, semiconductors, and metals. They are interested in phonon vibrational modes and free-charge-carrier contributions as they vary with temperature, strain, composition, etc. Infrared ellipsometry combined with magnetic fields can determine carrier concentration and species, mobility, and effective mass of semiconductors.

approximately the median wavelength of the IR ellipsometer. A film thickness of 50 nm is a small fraction of the measurement wavelengths, so there is little sensitivity to the film properties.

This limitation becomes an advantage for very thick films, which would be too thick to measure with conventional ellipsometry wavelengths.

There are other practical limitations. For instance, the surface must be sufficiently smooth – the smoother, the better. The rougher the surface is, the more difficult it is to extract useful information from the data. Of course, the roughness limit is larger than for conventional ellipsometry. However, if the surface is too rough, even infrared light will scatter away from the detector, and you won’t be able to collect any data.

The IR instrument also has difficulty measuring samples smaller than 10 mm x 10 mm because the incident light beam is about 5 mm in diameter. It is difficult to obtain a smaller collimated beam that has sufficient intensity yet covers a broad spectral range (1.7 to 30 µm). IR lasers have sufficient intensity to obtain a relatively small beam but have limited spectral range. Because of this (and for other reasons involving the detector), if a sample is too small, it isn't easy to measure without time averaging for a very long time.

Are there challenges or limitations with using IR Ellipsometry?

Was there a person who inspired you to go into this particular field? How did you get started at J.A. Woollam?

Certainly there are some limitations. One arises from the longer wavelengths that are used to probe the sample. At those wavelengths IR ellipsometry is not very sensitive to films less than 10 nm thick. Even for films that are between 10 and 50 nm thick, IR ellipsometry provides limited information. That’s because 50 nm is 200 times smaller than a wavelength of 10 µm, which is

I have a very long relationship with John Woollam. I was in one of the first classes he taught when I was an undergraduate in 1980.

Then I got to really know him in the mid-1980s as I was finishing my master’s degree. He was running a very active group at that time, working on projects that involved ellipsometry as well as several other materials science projects. (If you spend time with

24 | J.A. Woollam Newsletter

John, you will find that he’s as interested in materials science as he is in ellipsometry.) I got involved with his group when I was finishing my master’s degree because my master’s advisor ran out of money, so I had to find other sources of funding. John actually funded the last 5 or 6 months of my master’s degree. I started doing odd jobs for him.

At that time he had rented a room in Nebraska Hall at the University—a single room where he was assembling his first ellipsometer. He had a good friend at NASA who wanted an ellipsometer just like the one John had at the University of Nebraska. This was his first sale, and John formed the company to build and sell that system. I helped with a little bit of that work. In fact, I happened to be there when the person who was assembling the instrument—Tom Zillig—first turned on the light; that's called "first light." I happened to be studying at the University late. It was about midnight when he came running into my office saying, “I have first light! Come on, we’re going to celebrate!” He had planned for this, so he had brought along two cigars and had made a poster that said “baby ellipsometer” with the date and time. He attached the poster over John’s office door. We had a late-night janitor take a photograph of us (yes, Tom had brought a camera too!) with the cigars in our mouths standing in front of the poster.

I remember helping John a little bit with the ellipsometer, so I was involved with the company even then. The ellipsometer consisted of a big aluminum plate, maybe 6 feet long, with the following bolted to the top: the light source, polarizer, goniometer, detector, and so on. Someone suggested that the aluminum plate should be painted to make it look nicer.

So, I helped John take it to an auto body shop for painting. At that point I don’t think he even knew exactly how to build an instrument for sale, but he went ahead and did it anyway. I think this is precisely the mindset of a successful entrepreneur: you may not always know exactly what you are doing, but you have to make decisions anyway, constantly pushing forward.

John was very energetic; he did all of this while still teaching and running a research group.

After I graduated with my master’s degree, John wanted me to start on a Ph.D. But by then, I had two kids, so I needed to make some money. I went to work at Motorola in Austin, Texas, working in their semiconductor products sector. I worked in this surface analysis lab where I was doing mass spectroscopy and some other techniques. I was there six years, from 1988-1994.

Above: Tom Tiwald and Tom Zillig celebrating the assembly of the very first J.A. Woollam ellipsometer - John sold this system to NASA (photo taken following "first light").

What was it like collaborating with other employees and industry leaders over the years? ­

In science and engineering everything is a collaborative effort. At Motorola, I was part of teams that typically consisted of five to ten engineers, but there might be 50 or 60 engineers working on large projects. Everything was a collaboration, and I was just doing a part of it. That level of collaboration certainly continues here at J.A. Woollam.

I work in an applications engineering group where we help customers with their technical problems and teach them about ellipsometry and data analysis. To do that, all the members of the applications group are constantly collaborating on various projects, including demonstrating new applications and so on. We also spend a great deal of time collaborating with the design and software engineers, as well as the production and servicing technicians. It is a two-way street: we learn J.A. Woollam Newsletter | 25

from them, but we also bring the customers’ viewpoints and concerns to the engineers. Also, we in the applications group perform thousands of measurements each year on an extensive variety of samples and substrate types, shapes, and sizes – as a group we may perform more measurements than any other lab in the world! We use the hardware and software in ways the hardware and software design engineers often haven’t thought about, so we often uncover problems that they haven’t considered.

entire careers, and that was very much my approach when I was in school. I realize now that the more fluent you are in mathematics, the better you understand what opportunities a technology may offer, and also its limitations. To me, the fun parts of science and engineering are understanding the abstract concepts behind the methods and technologies and realizing that you can take two entirely different things that both fit into the same abstract concept.

What are you most proud of? And, what advice would you tell the younger version of yourself?

If you could go back and take any class or pursue any other area, what would that be?

I’m most proud of all the short courses I’ve developed and taught over the years. Every day I spend time helping customers resolve their problems and understand the measurement and analysis software.

Much of what we do is not trivial or simple, and several complex steps and judgments are required to accomplish specific tasks. I like helping customers do that. That has been the most satisfying part of my job.

I wouldn’t mind learning a musical instrument. I love the cello and the saxophone. I like the piano too, which seems to be the most versatile instrument. What other class would I take? As a matter of fact, I'm thinking about taking some of these mathematical classes mainly for the pleasure of learning. Recently, I watched a YouTube video of a lecture on perturbation theory, and it was terrific. When I first learned about perturbation theory in my quantum mechanics class, it was just something to get through. However, this guy on YouTube was using this theory to solve problems that were unsolvable any other way! That was very interesting to me.

I regret not taking full advantage of the courses available as a student.

For instance, when I was a young pup working towards a master’s degree, I didn’t take matrix theory, complex variables, vector algebra – classes like that. I thought, “I don’t need that stuff; I’m not going to bother to take those.” My advisor gave me choices, and I chose other things. And you know what I use every day? I use matrix theory, vector algebra, and complex variables. I mean, I have used them EVERY day for the past 20-25 years. So, that is what I regret: I did not take advantage of those opportunities when I had the chance. I’ve always felt a little bit behind the curve.

What advice would you give today’s college student or the next generation who’d like to pursue your field?

The main thing is just to be aggressively curious about everything.

Particularly as a young engineer, don’t shut yourself off. Be curious about every class and every project and really understand how it works.

Don’t just slide through it.

Obviously, you have to know the fundamentals of classical electromagnetics, polarization, and optics. For ellipsometric analysis you have to develop an optical model. The typical model is based on the Fresnel reflection and transmission coefficients and matrix methods. So, you need some background in that. Fitting is usually accomplished via regression analysis, so you also need some knowledge about that. Also, some statistical background will help you determine if your parameters are correlated and if there is any impact from noise and systematic error.

The best engineers I’ve known…let me put it this way: the best engineers pay attention to the mathematics and theory and know how important those are. Many engineers think, “I’ve got a feel for it, and that’s all I need to do my job.” Many engineers operate that way their 26 | J.A. Woollam Newsletter

My other passion, I suppose would be the outdoors, hiking and camping. The place I’ve gone back to over and over is a mountain range called Snowy Range. It’s about 30 miles west of Laramie, Wyoming, and only about 7.5 hours from Lincoln.

I still love it. There are several high mountain lakes and peaks that are relatively close to the road, so you don’t have to spend three hours hiking to get to the interesting parts, which was great for my kids. I didn’t have to drag them on a long trail to see the interesting things. Recently, I’ve spent some time exploring the canyons of the desert Southwest.

Do you have any stories to share?

I’m sure my colleagues have some funny stories to share about me!

However, I must say this about John Woollam: to this day he has a tremendous amount of energy. John can be a force of nature. Over the last 30-40 years, he has been a college professor. He has been very active in a number of areas of materials science, and for years he ran a large research group. And on top of that, he runs J.A. Woollam. It is amazing that he could juggle all those things. He also would be brimming with ideas. As a graduate student, I might meet him in a hallway at the university and he’d say, “Tom, come walk with me.” And in that little five-minute walk, my life would change. He would say, “You know, I think I want you to do this now, and tomorrow I’m going to call my friend ‘so and so’ at some university or company, and he will contact

you and help you make this happen.” With that mindset, John wanted things to happen now, not six months from now. So, basically my life would change during that five-minute walk. He did this more than once. Years later, I mentioned it to him again. He said, “Oh, I kind of regret doing that; I think I did that a little too much.” I don’t know if that’s true. Whether it’s true or not, I think that is typical John, just bursting with ideas. You know, energy just flows out of him like a glow, just constantly thinking and changing things. And this attracted energetic people around him. I have fond memories of those times.

This leads me to a piece of advice that I’d give someone entering into a master’s or Ph.D. program: talk to the other members of the group, the grad students and post-docs too. Are they enjoying their research? Do they feel that their work is supported? As a group, are they keeping up with the literature? There is a lot of synergy in a motivated research group. You want to be doing interesting work with interesting people, because that’s what makes graduate education fun.

Above: Niobrara River trip (2002)

Do you have plans for retirement?

Six months ago, I had lots of plans. They don’t seem to be happening very rapidly. My current plan is to move to Albuquerque, New Mexico, sometime in the next, let's say, year, just to put a number on it. I have family there, and there are mountains and deserts and doesn’t snow much, and I don’t have to take care of a lawn.

Is there a message you'd like to leave your colleagues?

Don’t get in a rut.

Stay interested. Do and try new things.

That’s what makes work at J.A. Woollam interesting. It’s a great company because those who hire new people choose well, and people tend to mesh really well. This place has a great vibe with a great culture.

Above: Tom and Jeanette (2002)

Above: Colorado hiking (2008)

J.A. Woollam Newsletter | 27

powerful Efficient high-speed compact multi-angle budget-friendly Introducing alpha 2.0

Spectroscopic ellipsometry for thickness and refractive index at a low cost.

Power meets efficiency with the alpha 2.0.

28 | J.A. Woollam Newsletter

Educational + Software

for more information about upcoming training opportunities or upgrading your software, scan the QR code to the right.

SUPPORT

Our commitment to continual customer support is what sets us apart. We offer a variety of learning opportunities each year that take place all over the world–both online and on-location. We stand behind our products and continuously offer guidance and assistance, so you can be confident about getting the most out of your experience with our products and move forward with your research and custom projects.

short courses Short courses include extensive training through examples and interaction with other students and instructors. We offer these opportunities multiple times per year at various locations across the globe. Our course syllabus follows a three-day format with two sessions per day:

Session 1: Introduction to Ellipsometry Session 2: Transparent Materials Session 3: B-Spline for Absorbing Materials Session 4: General Oscillator Modeling Session 5: Complexities & Non-idealities Session 6: Analyzing Mapping & In-situ Data Contact your local representative or sales@jawoollam.com for more information regarding upcoming short course dates or scan the QR code above.

On-Demand Training There are a variety of subjects that we cover through our online webinars that feature applications such as porosimetry, anisotropy, Mueller matrices, and infrared ellipsometry. For those interested in online training, we’ve developed the CompleteEASE training series. For more information, visit www.jawoollam.com/resources or scan the QR code above.

Infrared Ellipsometry Course

Anisotropy Course

Session 1: Introduction to Ellipsometry Session 2: IR-VASE Sample Preparation & Data Acquisition Session 3: Transparent & Absorbing Substrates in the IR Session 4: Transparent & Absorbing Films in the IR Session 5: Free Carrier Effects (Doping) & the Drude Model Session 6: Non-ideal Samples and Measurements Session 7: Combined Analysis of IR and UV-Vis Data Session 8: Anisotropic Materials in the IR

Session 1: Transparent Uniaxial Thin Films Session 2: Absorbing Uniaxial Thin Films Session 3: Generalized Ellipsometry & Retardance Session 4: Mueller Matrix SE & Depolarization Session 5: Reflection SE for Anisotropic Surfaces Session 6: Approaching Anisotropic Substrates Session 7: Coatings on Anisotropic Substrates Session 8: Anisotropic EMAs & GLAD Structures Session 9: Liquid Crystals Session 10: Review J.A. Woollam Newsletter | 29

Customized Instruments for Revolutionary Research Explore your options when it comes to our industry-leading spectroscopic ellipsometers.

With over 100,000 possible configurations, our ellipsometers can be tailored to meet your research goals. The M-2000 pictured above has been modified with the addition of our Environment Cell and includes DUV to NIR wavelengths, 300 mm mapping, and our Fast-Alignment Camera.

info@jawoollam.com | www.jawoollam.com | 402.477.7501 30 | J.A. Woollam Newsletter

Employee SpotlightS Our employees are the foundation of everything we do. From research and development of new products to manufacturing and the logistics that ensure on-time delivery, they make it happen. Each employee has an integral role in every ellipsometer shipped, and their combined efforts have a direct effect on the world-class products that we offer.

Dillon Fagan

lisa huff

Lucas brightwell

Technician

Administrative Assistant

Technician

Dillon has been a technician at J.A. Woollam since 2015. His responsibilities are alpha-SE and theta-SE assembly along with wiring and assembly for table systems. He also does modification of machine parts and design work for various projects. Dillon enjoys playing volleyball and softball. He also does antique tractor pulling as a hobby.

Lisa joined J.A. Woollam in 2007. She started as John’s assistant organizing office projects and helping with his ellipsometry class at UNL. Since then, her responsibilities include maintenance of databases, patent and trademark documentation, applications engineers support, maintaining our company library, organizing logistics for tradeshows, and assisting John with his last UNL engineering class this past spring (a 44 year teaching legacy). Lisa's free time is spent with family, grandkids, friends, jogging, gardening, reading, playing bridge, and of course, playing golf!

Lucas has been a technician at J.A. Woollam since 2011. He is responsible for building, aligning, calibrating, and testing of new systems, both M-2000 and RC2 ellipsometers. In addition, he provides customer support, performs repairs, and handles management of scheduling.

Lucas enjoys the outdoors, hiking, kayaking, and golfing with friends.

The strength of the team is each individual member.

The strength of each member is the team.” - Phil Jackson J.A. Woollam Newsletter | 31

J.A. Woollam Scholarship recipients J.A. Woollam is committed to the support and development of young students and is proud to be one of the contributors for the 2023 Amplify Scholarship that takes a dedicated role in the future of Black scientists. This scholarship is awarded to 10 Black undergraduate or master’s level students.

In addition to the funding, recipients gain access to our global network of mentors and supporting companies. J.A. Woollam has also established an endowment through the Society of Vacuum Coaters Foundation to help support students studying in a field related to vacuum coating and thinfilm technology. Featured below are the 2023 recipients of our sponsored SVC scholarship:

Aleksandra Pająk, Materials Engineering at Polytechnique Montréal I am extremely happy to have been awarded the 2023 J.A. Woollam Scholarship from the SVC Foundation, and I would like to express my sincere gratitude for funding this scholarship.

I am currently a research master’s student in Materials Engineering at Polytechnique Montréal working in the Functional Coating and Surface Engineering Laboratory (FCSEL) under the supervision of Prof. Ludvik Martinu and Prof. Jolanta Klemberg-Sapieha, and my goal is to soon undertake a doctoral program within this research group.

Physical vapor deposition techniques play a major role in my current research project on transparent flexible electrodes. I am investigating novel hybrid materials which, in combination with transparent conductive oxides prepared via high-energy-per-particle deposition processes such as magnetron sputtering, give rise to enhanced optoelectronic performance. Characterization of these thin films via ellipsometry allows me to have a more thorough understanding of the relationship between the structure of materials and their properties, as well as predicting how a small parameter change can affect their behavior.

Therefore, having been recognized by J.A. Woollam is particularly significant to me, and I wish to thank you again for such great support. I am thrilled to have been awarded so early in my career, and I am looking forward to continuing my research in the field of thin-film optics.

Ömer Yeşilyurt, Birck Nanotechnology Center at Purdue University I am writing this letter to express my heartfelt gratitude to J.A. Woollam for funding my scholarship through the Society of Vacuum Coaters Foundation. I am honored to receive this prestigious and distinguished award; it means a lot to me. The recognition that I have received is a great motivation for me to continue my studies and push the boundaries of our field.

I am a graduate research assistant in Prof. Alexander Kildishev’s group at the Birck Nanotechnology Center at Purdue University. My research focus is artificial-intelligence-based inverse design for photonics and quantum optics. My work often involves theory, simulation, and experimentation on photonic and plasmonic structures. Your support will be most helpful in acquiring new computational resources which will greatly aid my research to develop AI-based methods for fabrication and characterization of optical devices. Your prestigious award has also brought recognition, and it is an invaluable aid for my future career as a scientist.

Once again, I extend my sincerest gratitude for the scholarship. The generosity and philanthropy of individuals such as yourselves make scientific advancement possible. Knowing that there are individuals who care about my research serves as a significant source of motivation for me to continually strive for excellence. I have been truly touched by your generosity and hope to give back to the society just as you have.

32 | J.A. Woollam Newsletter

Featured International Rep:

Quantum Design Europe

Written by: Andrea Donohue

F

or more than 50 years, Quantum Design Europe (QDE) has been one of the leading distributors of high-tech systems and components for research and industry. With 120 employees in 20 European countries, they offer the broadest selection with an exciting mix of suppliers from both long-established corporations and innovative start-up companies.

Quantum Design Europe provides well-founded and independent advice catered to individual requirements and serves as agent between highly specialized manufacturers and science. All sales and service employees have scientific or engineering degrees. Quantum Design Europe began in 1970 as Oriel GmbH, a representative of Oriel Instruments, later becoming L.O.T., L.O.T.-Oriel, and LOT-QuantumDesign. Over the years, their product portfolio and international reach have expanded. Today, Quantum Design Europe is part of the globally active Quantum Design International Group and proud to be part of the first global, high-tech distribution network with subsidiaries worldwide.

Sales and service personnel and support staff at Quantum Design Europe (April 2023)

A Successful Team

Thomas Wagner

Thomas Wagner and Inga Potsch support and coordinate with a team of sales and service engineers all over Europe, with local representatives in Germany, BeNeLux, Czech Republic, Slovak Republic, France, Hungary, Portugal, Spain, Italy, Denmark, Finland, Norway, Sweden, Poland, Romania, Bulgaria, Switzerland, Turkey, and Russia.

QDE provides a robust network of support for all our European customers. The photo above shows just some of the team members QDE at a recent product training in Darmstadt.

Inga Potsch

The partnership between Quantum Design Europe and J.A. Woollam began over thirty years ago. Thomas Wagner, Product Manager – Ellipsometry & Surface Science, has been the central figure through it all. Dr. Wagner’s tenure at Quantum Design and dedication to customers and fellow team members have allowed successful distribution of J.A. Woollam ellipsometers in Germany and beyond.

He is well-known and reputed in the European community as a leading expert in ellipsometry. Dr. Wagner recently celebrated his 30th work anniversary at QDE! Working with someone you know and trust for so many years is extraordinary. Partnership with Thomas Wagner and QDE has been a tremendous asset to our company and our customers.

Another VIP within Quantum Design Europe for J.A. Woollam is Inga Potsch. Inga is a service technician who travels all over Europe to install systems and provide technical support to customers. She is friendly, knowledgeable, capable, and has over 14 years of experience working with J.A. Woollam ellipsometers.

J.A. Woollam Newsletter | 33

Worldwide Sales & Support Singapore

Korea WizOptics

Crest Technology Pte. Ltd. Ph: +65.6546.4811 marcus@crest-technology.com www.crest-technology.com

Japan J.A. Woollam Japan Corp.

Ph: +81.(3).3220.5871 info@jawjapan.com www.jawjapan.com

Germany & Europe Quantum Design GmbH Ph: +49.6151.8806.68 wagner@qd-europe.com www.qd-europe.com/de

India

Sinsil International Ph: +91.98330.11933 ramesh@sinsil.in www.sinsilinternational.com

China

Genuine Optronics Ltd. Ph: +86.(21).64325169 sales@gen-opt.com www.gen-opt.com

34 | J.A. Woollam Newsletter

Ph: +82.(31).477.3785 info@wizoptics.com www.wizoptics.com

USA

Taiwan

J.A. Woollam Co., Inc. 311 South 7th St. Lincoln, NE 68508 USA Ph: +1.402.477.7501 sales@jawoollam.com www.jawoollam.com

Titan Electro-Optics Co., Ltd. Ph: +866.(2).26552200 sales@teo.com.tw www.teo.com.tw

United Kingdom

Quantum Design S.A.R.L. Ph: +33.(01).69.19.49.49 caby@qd-europe.com www.qd-europe.com/fr

Quantum Design UK and Ireland Ltd. Ph: +44.(0).1372.378822 shayz@qd-uki.co.uk www.qd-uki.co.uk

Israel VST Service Ltd.

Ph: +972.(3).92477.10 angel@vacuumltd.com www.vacuumltd.com

Italy

Quantum Design s.r.l Ph: +39.(06).5004204 baratti@qd-europe.com www.qd-europe.com/it

France

Australia & New Zealand Scientific Solutions Ph: +61.(02).9543.7377 pbarras@scisol.com.au www.scisol.com.au

Mexico

Micra Nanotecnologia, S.A. de C.V. Ph: +52.(55).8502.50.00 csegovia@micra.com.mx www.micra.com.mx

Schedule of Events MRS Fall

November 28-30, 2023 Boston, MA

SPIE BiOS

January 27-28, 2024 San Francisco, CA

SPIE AR|VR|MR January 30-31, 2024 San Francisco, CA

SPIE Photonics West January 30-February 1, 2024 San Francisco, CA

SPIE Advanced Lithography + Patterning February 27-28, 2024 San Jose, CA

ACS

March 19-21, 2024 New Orleans, LA

MRS Spring May 7-9, 2024 Seattle, WA

SPIE Defense + Commercial Sensing April 21-25, 2024 Washington, D.C.

SVC

May 7-8, 2024 Chicago, IL

FCSE

June 2-5, 2024 Montreal, Canada

UGIM

June 23-26, 2024 Cambridge, MA

IEEE Photovoltaics June 9-15, 2024 Seattle, WA

SEMICON West July 9-11, 2024 San Francisco, CA

ALD

August 4-7, 2024 Helsinki, Finland

SPIE Optics + Photonics August 20-22, 2024 San Diego, CA

AVS 70

November 5-7, 2024 Tampa, FL

J.A. Woollam Newsletter| 35 | 35 J.A. Woollam Newsletter

To access the interactive version of of the J.A. Woollam Newsletter, scan the QR code below.

36 | J.A. Woollam Newsletter