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Defect Management for 300 mm and 130 nm Technologies Part 2: Effective Defect Management in the Lithography Cell Scott Ashkenaz, Ingrid Peterson, Paul Marella, Mark Merrill, Lisa Cheung, Anantha Sethuraman, Tony DiBiase, Meryl Stoller, Louis Breaux, KLA-Tencor Corporation

As lithography becomes more complex with thinner resists and sub-wavelength optics, the value of implementing an effective defect-management program has increased. Defect excursions in the photo cell can be corrected by reworking wafers, affording manufacturers the opportunity to fix problems without scrapping wafers, which further enhances the value of defect control in this area. The second in a three-part series, this article focuses on lithography defect reduction and control by implementing a straight forward methodology that combines backside inspection, photo cell monitoring (PCM), after-develop inspection (ADI) for macro and micro defects, and image qualification for reticle defect control.

Introduction

Technology advances within the lithography area are placing greater demands on defect management. The introduction of subwavelength, low-k1 lithography—critical for today’s high-performance devices—has shrunk the size of the focus-exposure process window, and thus has placed tighter constraints on absolute tool stability within the litho cell.

The litho cell is defined as the cluster of process equipment that accomplishes the coating (surface prep, resist spin, edge-bead removal, and soft bake), the alignment and exposure, and the develop (post-exposure bake, develop, rinse, and hard bake), of the resist. The latest processes involve spinning the new resists in extremely thin, uniform films, exposing the films under conditions of highly optimized focus and illumination, and finally removing the resists completely and cleanly. With new processes, under these strict operating conditions, effective defect management is critical.

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Adding to these technical advances are the market forces of strong competition, softer demand, and requirements for shorter product life cycles and faster return on investment. One of the tactics for addressing these pressures is to turn to 300 mm wafers. However, with all the economic benefits that 300 mm wafers confer, their larger diameter poses even greater challenges for uniform processing. This places further constraints on the process window and defect control.

Another means for tackling current economic pressures is to utilize more automation. While this affects all equipment within the litho cell, the primary gap in the inspection area has been automation of the macro inspection steps. The benefits of automated macro inspection include higher defect capture, better repeatability, and having a permanent record of the data for in, depth analysis and archival.

Today the semiconductor process itself contributes the largest number and variety of defects, and a significant portion of the total defects originates within the lithography cell. From a defect-management perspective, the lithography cell has some unique characteristics.

First, defects in the photo process module have the widest range of sizes, from full-wafer to sub-optical, and with the largest variety of characteristics. Figure 1

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Edge-Bead Removal • Missing • Wrong width • Miscentering

Hot Spots Contamination • Particles • Foreign materials Coatings • Comets • Striations • Spin • Lifting • Splashback & bubbles • No resist coat

Develop • Scumming • Developer spots • Resist collapse • No develop

Scratches • Handling errors • Tool misadjustment

Exposure • Missing fields • Focus error • Gross misalign • Gross blade errors • No exposure

F i g u r e 1. Lith ography process con trol re q u i res high capture of all yield -limit ing macr o defect types.

gives a summary of the most common kinds of lithography-related defects. These fall into the categories of coating problems, focus and exposure defects, developer defects, edge-bead removal problems, contamination, and scratches.

Second, photo is the only area of the fab besides CMP in which defect excursions can be corrected by reworking the wafers. The opportunity to fix defect problems without scrapping wafers is best served by a defectinspection strategy that captures the full range of all relevant defect types. In this paper we will show that a macro inspection combined with a high-numerical aperture (NA), high-resolution imaging inspection system is best suited to this application.

Third, to some extent, the lithography cell remains a defect frontier. In most areas of the fab, leading-edge defect-management tools and methodology have already been adopted, but in the lithography area defectivity is often under-managed. For example, recent studies have shown that replacing manual inspection for macro defects by automated inspection can result in an increase of one to two percent in real yield. This paper will show that further yield increases can be realized by implementing a straight forward methodology that combines backside

inspection, photo cell monitoring (PCM), after-develop inspection (ADI) for macro and micro defects, and image qualification to check reticle integrity.

Current technology advances and market pressures are re-emphasizing the need for effective defect management in the lithography area. Fabs must detect and identify the sources of defects, and correct tool issues before committing product wafers. In production, defectivity must be monitored tightly so that defect excursions can be acted upon immediately to minimize yield loss. In this paper we focus on lithography defect reduction and control by describing the tools and methodology for optimum defect management, and substantiating the recommendations with case studies and modeling.

Overview of Methodology and Strategy

Defect management can be broken down into three basic components: • Initial process optimization • Routine monitoring of the tools and processes • Monitoring and disposition of product wafers Fall 2001

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F i g u re 2. KLA -Te n c o r ’s i nsp ecton and metr ology tool set for l itho cel l monit ori ng.

Each of these components is associated with a set of inspection tools and sampling strategies that addresses its unique requirements. Figure 2 summarizes the inspection points and inspection tool set that monitor the lithography cell.

Process optimization When a new process is under development, defect sources are greatest in number and variety, and include both systematic and random types, many of which may be previously unknown. This is especially true at a new node or when significant new technology is introduced, such as copper dual damascene, a new wavelength-resist system, or advanced optical-enhancement techniques.

Systematic defects are characterized as baseline defects; random defect types as excursions. Systematic defects are those types that are caused by un-optimized processes and/or incompatibility of materials. Examples of systematic defects are residues originating from resist/developer interactions, or process-window failures.

Random defects types tend to re-occur from time to time and are typically caused by machine failures, 40

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batch-to-batch chemical variations, particles, and other environmental problems. For this reason, the recommended defect-management approach is to utilize the inspection strategy that provides the highest capture rate for the full range of defect type. This strategy requires inspections to be performed at high sensitivity, even at the expense of throughput. The goals during the process optimization phase are to: • Capture and characterize all defect types • Analyze the effect of each defect type on yield • Optimize the process for minimum defectivity During this phase the team learns the sources of the critical defect types, tunes the inspection systems to capture them efficiently, programs the automatic defect classification (ADC) systems to recognize them, and sets control limits based on the expected frequency and kill ratio of each defect type.

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In the lithography area, a high-NA, high-resolution imaging inspection system is recommended to provide the highest level of defect capture of the broadest range of defect types. A high-frequency sampling strategy is needed: typically, full-wafer inspections on enough wafers to capture wafer-to-wafer and lot-to-lot variations coming from different spin and develop cups. Since high defect-capture rate is desired in this phase, the full-wafer inspection mode, typically performed using a “random” mode inspection, should be supplemented with “array” mode inspection which typically provides higher sensitivity in dense design areas. On-board ADC will be supplemented heavily with offline review using optical and SEM-based review stations. Towards the end of this phase, a PCM process will also be established, providing the maximum sensitivity to patterning defects to establish and maintain a baseline.

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Slurry residue, particles, and other contamination on the backside of the wafer have been correlated to the gener-ation of hot spots on the front side of the wafer (Figure 3). This is particularly important for devices relying on 180 nm design rules and below, where the depth of focus is very narrow. During backside inspection, blank wafers are run through the cell and an unpatternedwafer inspection system is used to examine the backside of the wafer for contamination, scratches, and other defects. Backside inspection also may be employed before and after cleaning steps to detect contamination and residual slurry, monitoring process equipment chucks and end effectors.

In some fabs, unpatterned test wafers are also used to enable detection of micro defects on the front side, such as pinholes and microbubbles from the coating process.

Detection of developer-dispense errors and residue via their spatial signatures represent another application for front side inspection of unpatterned test wafers.

Tool and process monitoring

Backside inspection After the process has been optimized and transferred to production, the health of the litho cell must be monitored through periodic checks. A systematic check of the photo process equipment is typically performed once per shift. Part of this monitoring process includes backside inspection.

The characteristics that make an unpatterned inspection system suitable for this application include high sensitivity and uniform detection capability, and the power to detect the range of defect types of interest—which in turn requires a flexible optical system. The high sensitivity and uniform detection are not only possible due to the inspection technologies available, but also due to the lack of interference from previous processing. Because the back side of the wafer is rough on 200 mm wafers and below, detecting defects such as particles and scratches on the back side poses different system requirements from detecting microbubbles in a thin film of resist on the front side. Backside inspection also necessitates edge handling of the wafers during inspection, instead of resting them on a chuck or paddle.

PCM

F i g u re 3. Bac kside c huck marks identified by the KLA- Tencor Surfsca n SP1 D L S

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Another technique for ensuring the health of the litho cell is PCM. The introduction of patterned photo cell monitor wafers to the lithography defectmanagement system arose from a need to increase the capture rate of certain low-contrast defects that were being missed during inspection of product wafers.1 These resist-on-silicon or resiston-oxide-on-silicon wafers may use the Yield Management Solutions

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same reticle as product wafers, or they may use their own specially designed reticle. The value of PCM wafers is that they have only a single layer of patterned resist, which facilitates capture of defects that may be masked by noise from underlying layers on a product wafer.

Although the cost of these non-product wafers must be taken into account in determining the optimum defect-management strategy, PCM wafers can be recycled.

The experience of KLA-Tencor’s Yield Management Consulting Group has shown that greater than 90 percent of defect types seen on product wafers can be detected and managed using PCM. Often the detection of the defects is better on PCM and the fab, therefore, is better able to ascertain the defect source through experimentation and analysis of the spatial signatures. Inspectionsystem throughput is also higher on PCM wafers because the inspections can be set at a larger pixel size and still have the same capture rates as compared to smaller pixel sizes used on product wafers. In addition, defect classification and review is also more efficient, since defects on PCM wafers are limited to the photo cell, compared with the many previous layer defects present on product wafers. Typically, the lithography cell is checked using PCM once a shift or once a day.

If the inspection frequency is lower, the cost risked by missing excursions increases.

Highly sensitive, high-resolution imaging inspection of PCM wafers will capture very low topography and/or very small defects such as stains, microbridging, microbubbles, CD variation, and single, isolated missing or deformed contacts/vias. All of these defect types are difficult to detect on product wafers. Examples are shown in Figure 4. Defects such as amine contamination of deep UV resist can also be detected by high-resolution imaging micro inspection using a PCM wafer. Stains and minor color variations can be translated into blocked contacts, bridging, missing or extra-pattern defects, and CD variations after etch. The high-resolution imaging system also has the sensitivity to detect single missing contacts with a high capture rate, providing good information for quantifying and improving this elusive defect. When defectivity problems are discovered and fixed using PCM, valuable product wafers can be spared.

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or cause CD variations. Image qualification is a necessary process for qualifying image transferring for PSM (Phase Shift Mask) reticles. Its importance has increased in the photo defect area due to the wide use of the phase shift technology for sub-130 nm. In order to ensure complete transfer of the PSM image onto the wafer, it is not necessary to inspect the full wafer for this, but only to inspect sufficient fields to allow arbitration and repeater confirmation. Some fabs choose to extend this by printing at a range of focus settings and exposures to amplify the effect at the edges of the process window.

These wafers are then inspected on a high-resolution imaging inspection system and analyzed for repeating defects.

Another method for reticle management is direct inspection of the reticle itself using a reticle inspection system.

This is effective for detecting defects on the reticle or pellicle such as soft defects, effects from electrostatic discharge, crystal growth, or a number of other common problems.

Small pattern bridging Single distorted contact/via

Single distorted

Micro bubbles

Image qualification The process used for PCM is designed to optimize sensitivity while reducing cost. It may also be used to qualify reticles in the fab inventory prior to use. By printing wafers from the product reticle, it is possible to discover any defects that may print as pattern errors 42

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Missing single contact/via F i g u re 4. Photo defects detected using KLA-Te n c o r ’s 2351 High Res olution Ima ging Waf er Inspection.

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It is beyond the scope of this article to fully explore reticle defect control; it is a topic that is worthy of its own paper on methods, tools, strategies, and costs.

macro inspection systems came on the market in 1998, and have been rapidly adopted in place of manual inspections (Figure 5).

Monitoring and disposition of product wafers via macro and micro ADI

Many of the defects formed in lithography can be reliably found with automated macro inspection. Defects ranging in size from 50 µm to full-wafer are captured at high throughput, with capture rates and repeatability much higher than that of visual inspection. Archival storage of each inspection is provided—another benefit over using visual techniques. Wafer maps can be used for defect analysis, stacking, and generating Paretos. Instead of relying on subjective judgment, which changes with the operator, the shift, and the product, automated inspection provides objective data to drive effective wafer disposition. Because this information is also recorded like any other automated defect inspection result, it may be examined by a number of methods, including stacking of multiple wafers to identify subtle patterns.

After the health of the litho cell has been assured by backside inspection and PCM, product wafers are allowed to pass through. A small number of product wafers are monitored for macro defects using automated, simultaneous high-resolution imaging and highthroughput laser scanning technology, then for micro defects using broad-band high-resolution imaging technology. When defectivity problems are discovered before etch, the product wafers often can be reworked, instead of being scrapped at a later step or found at final test to have suffered yield loss. The cost savings from this control can be dramatic.

This inspection point is known as the after-develop inspection, or ADI. CD SEM and overlay metrology are also performed at this point, either before or after the inspections, depending upon the expected frequency of metrology versus defect problems. A high-resolution imaging after-etch inspection of the product wafers for micro defects completes the set of lithography-related inspections, as shown in Figure 2.

Often the first after-develop inspection is macro ADI. In the past, this inspection was done by trained operators using their eyes and a bright light—with results that varied widely among inspectors and over time. Automated

A case study from IBM showed significant increases in capture of several lithography-related defect types after automated macro-defect inspection was implemented (Figure 6a), and another study from NEC6 demonstrated an overall increase in defect capture rate of more than ten percent (Figure 6b). Evaluating eight layers on one product, weighting defects by their kill ratio—and not including savings realized by using fewer operators or through shorter time to decision—NEC’s study found a potential savings of $66,500 per month through using automated macro inspection. Other studies have shown potential annual benefits of $3.6M2 to $6.7M3, depending

F i g u re 5. As des ign rules app roach 130 n m and beyond, these figur es show the r ise in adoption o f KLA-Te n c o r ’s macro-def ect inspect ion syst em by i nst alled base and app lication.

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upon the device value, fab size, and other assumptions and details of the calculation.

Completing the scope of after-develop inspections is micro ADI. As with the PCM inspection, high-NA, high-resolution imaging inspection is the best technology to capture any micro defects that may be similar to the PCM defects or may be topography-related, process- integration defects. Micro ADI inspection has shown critical detection of 130 nm-node photo ADI defects such as pattern repeaters, line CD variations, and missing contacts/vias due to reticle and other process issues. These are critical defects that normally are not detected until after etch/strip/clean inspection (ASI or ACI). Capture of these defects allows rework of the resist and avoids scrapping the wafers.

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When the after-develop inspection is complete, a decision must be made whether to pass the wafers onto etch, re-work the lot, or scrap it. Lot disposition can be done automatically in many cases by utilizing an integrated ADC and analysis system to monitor defectivity by type.

In the lithography cell, defect classification and analysis methodology should be similar to that in other parts of the fab. Newest techniques are aimed at intelligent filtering of data: leveraging any quick, automatic binning of defects that reduces the sample size of defects requiring more thorough review. On-board real-time classification or inline ADC can separate nuisance defects from defects of interest before the wafer leaves the inspection system— and often without impact on the inspection throughput.

High-resolution ADC, either on the inspection system itself or on a review station, can then be limited to defects of interest which require further review. The analysis tool is an integral part of this “waterfall sampling” process, as it employs automatic defect-source analysis, and manages the data flow and presentation.

The simple methodology described above relies on only three kinds of defect-inspection systems: an unpatterned inspection system for backside inspection, a high-resolution imaging micro-defect inspector for PCM and ADI, and an automated macro-defect inspection system for ADI. Together with automated defect classification and analysis, this inspection tool set and methodology can provide leading-edge defect management for the lithography module.

Methodology Model

F i g u re 6a. Normalized comparison of man ual r ewo rk t o automated m a c ro inspection, (with KLA-Te n c o r ’s 2401) excluding wh ole-wafer events, showing signifi cant i ncreases in captur e of al l d efect types.

To supplement the knowledge gained from customer experience and by in-house experiments, a group at KLA-Tencor constructed a model for determining an optimized defect-management methodology for the lithography module. Leveraging the Sample Planner 3 cost model, the group analyzed a full range of defect-inspection technologies and sampling strategy combinations to determine the most cost-effective solution.

F i g u re 6b. Pass/fa il resul ts comparing visual inspection to 2401 aut omated macro inspect ion, for 213 lot s i nspected at ran dom, demon stra ting th at t he auto mated syst em h as a capture rate ten times that of visual in spection.

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For the model inputs, they used 300 mm wafer sizes and throughputs, assumed 5000 wafer starts per week, used a 12wafer lot size, 600 dice per wafer, and $35 average selling price per device. They used actual 200 mm production fab-cycletimes and modeled 31 typical defect types.

KLA-Tencor’s Tool Set for Lithography Defect Control Unpatterned Inspection for Backside Contamination KLA-Tencor’s unpatterned inspection system is the Surfscan SP1DLS. It features axially-symmetric collection optics for sensitive and uniform defect detection, with an oblique incident angle and polarization to optimize sensitivity on rough surfaces—such as the back side of the wafer. Already used heavily throughout most fabs, including in the litho area, the SP1DLS is an important piece of the strategy to monitor and maintain process quality. On-board defect classification is provided without discernible impact on inspector throughput.

Automated Macro Inspection for ADI KLA-Tencor’s 2430 features concurrent darkfield and brightfield optics to provide the breadth of technology required to capture all important macro defect types. Defects ranging in size from 50 µm to full-wafer are captured at more that 80 wph throughput. The capture rate is about ten times that of visual inspection, and repeatability is more than 90 percent. The 2430 also features on-board review and storage capability for root-cause analysis, defect map signatures, and a wafer gallery.

High-Resolution Imaging Inspection for PCM, ADI, and Image Qualification KLA-Tencor’s latest addition to their line of high NA high-

For inspection equipment, they included macro ADI, high-resolution imaging and high-throughput laser scanning micro ADI, (such as would be provided by KLA-Tencor’s AIT systems), and high-resolution imaging and high-throughput laser scanning PCM. For costs due to inspection operations, they included inspection-and review-tool capital depreciations, testwafer and process-tool time, direct and indirect labor, service contracts and parts, and facility costs. For costs due to defect excursions they included lost revenue opportunity due to increased lots at risk to excursions, and investigation and fixing costs. The plan was to achieve the optimum balance of total fab costs, the sum of operational expenses, and yield-related losses.

The results of this simulation are given in Figure 7. In Figure 7a, the benefits of using PCM and macro inspection are clearly shown. Using macro inspection alone reduced the overall yearly cost by nearly a factor of two, while using macro inspection together with PCM three times a day reduced the overall cost by more than a factor of two. In Figure 7b, the results of comparing high-throughput scanning with high-reso-

resolution imaging inspection systems is the 2351. This system combines broadband visible and UV light with different pixel sizes to meet sensitivity and throughput requirements. Special optical modes are available to suppress grain noise and enhance capture of low-contrast defects. Cost of ownership is minimized by employing massively parallel image processing, plus an updated image computer and stage to enable highest possible throughput for wafer sizes up to 300 mm. On-board inline automatic defect classification (iADC) provides the most useful information in the fastest time possible.

Defect Classification and Analysis For most of KLA-Tencor’s inspection systems, automatic defect classification (ADC) is provided on the inspector itself. These integrated ADC systems can provide binning of defect types, such as nuisance defects, using the inspection data only and therefore providing information without impact on the throughput of the inspection system. For those defects requiring higher-resolution review, some of the inspection systems also allow review and higher-resolution ADC on the tool itself. After on-board review classifies most of the defects, any remaining unclassified defects can be sent to a dedicated review station, such as KLA-Tencor’s optical CRS or SEM eV300. All of these systems are equipped with compatible ADC systems, so that all defects of interest are automatically located, reviewed-and classified.

lution imaging PCM are given. In all cases high-resolution imaging PCM provided superior overall cost, and performing PCM three times a day provided benefit over a twice-daily regime. In this case, the high-resolution imaging technology claimed a significantly higher capture rate of the defects of interest over the highthroughput scanning system, easily negating the higher cost of operating the high-resolution imaging system.

The key component of this result is the higher capture rate of all critical defect types. In Figure 7c, the ADI inspections are added to the mix. The largest difference between revenue saved and cost of inspection operations was given by a combination of high-resolution imaging PCM, three times a day; 100 percent macro ADI; and high-resolution imaging ADI with the relatively low sampling rate of 6.25 percent.

This study provided several important conclusions: • Macro ADI provided the highest return on investment, and allowed the micro ADI sampling rate to be reduced. Important to this result is the need to detect all critical litho defect types; any significant gap in sensitivity can have dramatic impact on the cost benefit.

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Stepper Qualification Using Automated Macro Inspection A robust tool-monitoring technique is required for steppers, since they are often the most critical tools in the line. Their high capital costs can result in a throughput bottleneck.

The current practice of a visual check for focus errors or “hot spots”, following preventive maintenance or before critical lots, is limited by the qualitative nature of the operator’s inspection, high operator-to-operator variability, complex wafer diffraction patterns, and the lack of physical records of the inspection.

This is an area where automated macro inspection can provide significant benefit. Recently ST Microelectronics conducted a study with KLA-Tencor’s 2401 and found that: • Regular stepper monitoring can reduce product exposure to yield killers: hot spots, leveling/focus/exposure errors; • Their largest gap currently is their use of visual inspection techniques; • Using an automated macro inspection method provided significant benefit via high sensitivity (full-field grating, post-reticle at lens resolution); and high consistency— effective sampling with an historical record.

Source: Martin, B. (ST Microsystems); Kent, E., DiBiase, T., Tamayo, N., Rutherford, I. (KLA-Tencor) “Stepper Qualification with Automated Macro Inspection,” SPIE Microlithography Conference, Santa Clara, California, February, 2001.

• High-resolution imaging PCM provided the second highest return. Sampling once per shift was critical, even when capacity had to be allocated from the after-develop micro inspection. It was found that it is important to do this with high-resolution imaging inspection to capture all defect types; other types of inspection have inadequate capture at this step.

• Test wafer costs were low compared with PCM savings, even using 300 mm wafers.

• Lot-rework ability increased the value of the difference in capture rate of high resolution imaging versus high-throughput scanning technology for defect types modeled in this study. Lot-rework ability also reduced the requirement for high lot-sampling frequencies.

Thus, overall, high-resolution imaging technology proved more cost-effective for micro ADI and PCM. In short, the recommended lithography defect inspection strategy is provided by a combination of macro ADI, 46

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F i g u re 7. Results of the Sampl e Planner 3 model showed (a) the significant cost benefit to using automated macro inspection and PCM; (b) the benefit of using high-resolution imaging PCM over high-throughput s c a nning; (c) the benefit of high-resolution imaging ADI over high-re s o l u t i o n i m a g i n g, p roviding the op timum solution of ma cro ADI, h i g h - re s o l u t i o n i m a g i n g PCM and h i g h - resolut ion imaging ADI with a sampling interv a l of 6.25%.

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high-resolution imaging PCM, and high-resolution imaging ADI.4 Summary

From a defect-management perspective, now is the right time to bring the lithography module up to the standards of the other process modules in the fab.

References 1.

Petersen, I., Thompson, G., DiBiase, T., Ashkenaz, S., Pinto, B., “Lithography Defects: Reducing and Managing Yield Killers through Photo Cell Monitoring,” Yield Management Solutions, Summer 2000.

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Reticle Qualification Complemented by High-Resolution Imaging Wafer Inspection As design rules approach 130 nm and below, the reticles used to produce these devices typically must rely on phaseshift technology. Guaranteeing 100 percent defect-free reticles is a difficult task, even with the advanced reticle inspection tools available on the market today. The amount of phase error found on a defective reticle can be multiplied by an order of magnitude at the wafer level, depending on the kind of resolution-enhancing technology used.

Defect management in the litho cell is an area where significant improvements can be realized. As lithography has become more complex with thinner resists and sub-wavelength optics, the value of implementing an effective defect-management program has increased. The ability to rework wafers when defects are captured before etch enhances the value of defect control in this area.

An effective defect-management system is comprised of three parts: process optimization, tool and process monitoring, and monitoring and disposition of product wafers in production. A mathematical model of the inspection systems, sampling strategies, and fab costs, supported in part by case studies from fabs, demonstrates that the combination of high-resolution imaging PCM, macro ADI and high-resolution imaging micro ADI together with backside inspection provides the most effective litho defect-management system. The replacement of visual inspection with automated macro ADI provides highest value, followed by introducing highresolution imaging PCM.

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In addition to naturally occurring defects on reticles, attempts at repairing defective reticles occasionally produce unexpected results on the wafers near the repair area, such as defect printability or CD variations.

Considering that advanced reticles cost upwards of $30K, it can be cost-effective to supplement reticle inspection by using a high-resolution imaging wafer inspection system to monitor the wafer. This is one area of the fab where finding most of the defects is not enough—just one repeater occurring in an unfortunate position in the die can affect yield.

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Yanof, A., Plachecki, V., Fischer, F. (Motorola); Cusacovich, M., Nelson, C., Merrill, M.(KLA-Tencor), “Implementation of Automated Macro After Develop Inspection in a Production Lithography Process,” Metrology, Inspection, and Process Control for Microlithography XIV, Proc. SPIE Vol. 3998, p 504-514, SPIE, Bellingham, WA, 2000.

3. I n t e rnal KLA-Tencor presentation. Contact Kanae Mukai for additional information.—kanae.mukai@kla-tencor.com 4. These results are expected to hold for 200 mm operations as well. The sampling frequency may be incre a s e d since the inspection costs are lower for 200 mm wafer inspection.

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