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Reticle Automation Pathways for 300 mm-Era Fabs

by Tony Bonora, Michael Brain and William Fosnight, Asyst Technologies, Inc.

As we advance further into the era of state-of-the-art fabs optimized for 300 mm wafers and the complex semiconductor products they contain, a sharper emphasis is being placed on reticles and their importance to the advancement of semicon ductor manufacturing. Defect sizes considered critical to semiconductors only a few years ago are now becoming critical for reticles. Moreover, the area of a reticle is much larger than that of a semiconductor die, resulting in a significantly lower allowable defect density. Thus, reticle manufacturing and handling methods need to advance to ensure that defects do not become yield-limiting.

Reticle manufacturing and handling

A reticle starts out as a “blank” of high-quality glass or quartz. From the blank supplier’s site, it must be transferred safely and cleanly to the reticle manufacturer for patterning.

Reticle manufacturing consists of most of the same processes used in manufacturing a single layer of an integrated circuit (IC): film, photo, develop, etch, strip/clean, and inspect.

After the reticle is manufactured, it must again be safely and cleanly transported to the IC manufacturer, where it will be stored, transported, and used within the facility.

Throughout this process, numerous opportunities exist for the reticles to be damaged, through dropping, breakage, contamination, electrostatic discharge (ESD), mishandling, etc. Thus, it has become critical to have a strategy for isolating reticles and automating their movements to ensure that reticles are delivered safely, cleanly, and economically to the correct location at the optimal time.

Most of today’s reticle handling is reminiscent of 150 mm-wafer manufacturing methodologies. Examples include manual substrate handling using “picks,” a vast array

of tool-loading requirements and orientations, tools that load the substrates in fixtures, and paper lot travelers.

Tool suppliers resort to operator loading of special fixtures or cassettes, making mask shops especially vulnerable, as defect-density requirements tighten with the advent of advanced reticle technologies such as phaseshift and 157 nm lithography.

Meanwhile, IC manufacturers have been subjected to ever-shortening life cycles of lithography technologies, which has forced them to endure the burden of using custom, and often expensive, reticle carriers that require custom automation and storage solutions.

However, a reticle-automation strategy can be pursued that does not necessitate customized components and includes a comprehensive collection of modular, fully integrated products.

Implementing reticle isolation and automation technology

Reticle isolation technology is fully analogous to the standard mechanical interface (SMIF) technology used to isolate wafers within IC manufacturing facilities.

The key components of a reticle system incorporating both SMIF and automation technology include pods (closed, contamination-free carriers), SMIF-based interfaces (I/Os) for reticles, as well as robots, sorters, tracking devices and transport technology.

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allows tool suppliers to have one solution capable of working with both pods.

Although IC manufacturers have opted for the smallerfootprint RSP-150 until the advent of 230 mm reticles, reticle manufacturers have decided to stay with the SRP, which can also contain any known reticle size format, including next-generation lithography (NGL), extreme ultraviolet (EUV) and scattering with angular projection electron-beam lithography (SCALPEL).

RSPs with 200 mm wafer supports have been provided to support these development efforts. The advantage of the RSP being able to handle all reticle sizes outweighs its larger footprint for reticle manufacturers since they require far less reticle storage than IC manufacturers.

F i g u r e 1. The Asyst Reticle SMIF-Pod (RSP) 20 0 mm p rovides conta minati on control by p rotecti ng r eticles durin g ha ndlin g and storage.

The Reticle SMIF Pod (RSP), capable of containing either a single 6-inch or a single 230 mm reticle, has been adopted by Semiconductor Equipment and Materials International (SEMI) as standard E100 and operates with the existing 200 mm SMIF interface standard (E19.4), which has been developed to fit myriad semiconductor tools. Asyst’s 200 mm RSP is shown in Figure 1.

The first reticle manufacturers to adopt SMIF are blazing the trail for “hands off” manufacturing. Their efforts are paying off for all reticle manufacturers as reticle equip ment becomes increasingly available with SMIF integrated by the equipment OEM. Equally important, reticle equipment suppliers are freed from having to focus on resource-consuming custom-automation requirements.

They can instead concentrate on improving and tuning the process and metrology technology that is their key source of differentiation.

IC manufacturers belonging to Sematech’s I300I consortium (on 300 mm technology implementation) also decided to adopt the RSP as the standard for all 300 mm facilities, but because 230 mm reticle introduction has been delayed, they have standardized, for the time being, on a smaller-footprint, single-reticle pod based on 150 mm SMIF. This pod is known as an RSP-150.

Some fabs intend to use 150 mm SMIF pods capable of storing up to six reticles. This pod is also being standardized and is known as an MRSP, or multiplereticle SMIF pod, such as Asyst’s MRSP-150. The RSP-150 and MRSP-150 (Figures 2 and 3) both work with the same 150 mm SMIF interface (E19.3). This 50

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F i g u r e 2. The singl e-reticle pod (SR P) is a smal ler-footprint RSP based on 150 mm SMIF.

F i g u re 3. The multi-ret icle pod (MRP) is a 150 mm SRP capable of storing up to six r e t i c l e s .

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Since reticle manufacturers are faced with many more types and configurations of equipment with which to integrate SMIF, the RSP offers an additional advantage.

The proliferation of SMIF at 200 mm has resulted in a greater number of 200 mm SMIF interface solutions being developed to accommodate the wide variety of tool configurations. These solutions enable existing and future reticle manufacturing equipment to be more easily provided with reticle SMIF. Numbers released by DuPont Photomask suggest the semiconductor industry loses $200 million per year due to reticle damage caused by electrostatic discharge (ESD), a key consideration during the development of the SEMI-standard reticle SMIF pods. Isolating the reticle from all unpredictable and variable means of handling is fundamental to an effective ESD control strategy. Reticle sorters allow the management and handling of reticles within an IC fab while isolating the reticles from this and other mechanisms of operator damage. The reticle sorter may also be used to transfer reticles from the RSP to the RSP-150 at the reticle manufacturer prior to shipment to the IC manufacturer.

Indexers, such as those in Asyst’s SMIF-INX family (Figure 4) include an integrated SMIF port to provide contamination control while minimizing equipment footprint.

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dard and allows device makers to access multiple reticle-carrier suppliers. Lithography functional areas, traditionally difficult to automate, will now integrate carriers that can be easily automated in a variety of ways. This offers opportunities for improving reticle management and equipment layouts.

Both reticle and IC fabs alike are trying to converge upon a single-reticle carrier design to facilitate equipment designs as well as lower costs for themselves and suppliers. A common carrier format for reticle and IC manufacturing facilities opens the door for a carrier that functions as a shipper between mask and IC fabs, simplifying operations and offering superior reticle protection. Furthermore, the common carrier can be maintained for shipper reuse, according to preliminary data presented by Intel and Asyst at SPIE 2000.

The overall cost of ownership for a standard reticle carrier will be comparable, if not lower than for custom boxes in use today. Furthermore, due to the stringent technical requirements of storing and transporting next-generation reticles, the move to a new carrier

Integrated reticle-handling vision

As leading-edge device manufacturers move toward using more sensitive 193 nm and 157 nm reticles, the industry-wide need for a more sophisticated reticle carrier has finally opened a window of opportunity to capitalize on the many benefits afforded by standardization and automation: 1. Standardized carriers improve factory efficiency and lower costs associated with reticle storage and management.

2. The move toward standard carriers helps simplify equipment design and removes much of the burden of carrier design, manufacture and support from lithography equipment suppliers. This frees supplier resources to concentrate on core technical competencies in support of meeting the demand for shorter development cycles.

3. A standard carrier enables equipment suppliers to order off-the-shelf configurations for tool interfaces based on the well-established SEMI E19 SMIF stan-

F i g u re 4. Asyst’s SMIF-INX family of indexers includes this unit, optimized fo r 150 mm reticle SMIF.

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architecture is unavoidable. Next-generation stockers will likely be required to maintain the reticles in an oxygen-depleted environment. Additionally, IC makers will be presented with new challenges in safely scheduling, managing, and transporting highly sensitive and costly next-generation reticles. These challenges, however, lead the way to operational improvements long sought after, but never realized, due to IC makers’ desires to minimize design impact on lithography equipment.

Automated reticle tracking

To protect a reticle is to ensure that it is not damaged during transport and handling. Utilizing industrystandard carriers facilitates the use of the automated tracking systems currently deployed in over a hundred semiconductor fabs. These automatic identification and tracking systems utilize a tag-device attached to each pod. The identity of the material is written into this tag using either infrared (IR) or radio-frequency (RF) communications. Some tags have a liquid crystal display for the operator to immediately see what is in the pod and where it should go next. When the pod arrives at a process or metrology tool or automated material handling system, the tag is read automatically, and software (the function of which is to ensure correct handling) prevents inadvertent loading of the wrong reticle into a reticle production tool or fab stepper.

Reticles in storage can be quickly located to ensure that they are at the right place at the right time.

Handling history can be recorded in the tag, much as history is often manually recorded on paper travelers, to automate functions such as controlling the re-certification of reticles in use. One such system is the Asyst SMART-Tag, shown on the MRSP-150 in Figure 4.

Automated material handling systems

The size of 300 mm wafers, their value, the increased number and complexity of process steps, the increased

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cost of the facility and equipment itself, and chipmakers’ competitive pressures to improve their own manufacturing economics, will place demands on a fab’s automated material handling system (AMHS) requirements that even today’s most advanced 200 mm fabs will be unable to fulfill.

A number of key issues will drive AMHS needs for 300 mm. One that is critical to productivity is photolithography bay automation. It does no good to get the right lot to a stepper on time if the reticles for that process step aren’t available. An AMHS that can also deliver the correct reticle to the correct stepper, at the correct time, will enhance tool productivity for any fab that has a broad variety of products.

Conclusion

As the semiconductor industry looks forward to the 300 mm era, IC manufacturers are looking to advance to the next level of automation: standard interfaces, closed carriers, auto-ID capabilities, and automated transport systems. All of these contribute to true hands-off manufacturing, which helps eliminate the possibility of operator-induced defects, random electro static discharge (ESD) damage, particle contamination, and misprocessing. The semiconductor industry made a big leap to automated material handling and product protection in obtaining cassette-to-cassette automation for 200 mm wafers. This enabled standard cassette loading, diminishing the need for direct wafer handling by operators who now handle only the cassettes in most fabs. The references to semiconductor manufacturing point up the opportunity for reticle and IC manufacturers to “leapfrog” the 200 mm-wafer era substrate automation and proceed directly to standardized, automated reticle transport and handling consistent with the isolation technology approach of 300 mm wafer facilities.