Product Handling and Automation

Analyzing trends in automated reticle manufacturing, transport, and handling

Stephen Sumner, Intel; and William Fosnight, Joshua Shenk, and Rick Zemen, Asyst Technologies

Standardized, automated reticle handling and transport will be essential in next-generation semiconductor facilities.

Increasing emphasis is being placed on reticles and their importance in advanced semiconductor manufacturing. Most reticle patterns are sized for 4x reduction. This means that the patterns on a mask are four times larger than the patterns imaged onto an integrated circuit. Defects considered critical on reticles are now as small as those that were considered critical on semiconductor devices only a few years ago. Moreover, the reticle area affected by such small defects is much larger than that of a semiconductor die. Because these factors increase the requirements and cost of ownership of reticle manufacturing, methods of manufacturing and handling reticles must be advanced. This article discusses how existing standards and technology are being leveraged to meet this need.

The State of Reticle Manufacturing and Handling

A reticle begins its life as a piece of high-quality glass or quartz at a blank supplier. From there it must be transported safely and cleanly to the reticle manufacturer for patterning. The reticle manufacturing process resembles the process by which a single IC layer is manufactured, including film, photo, developing, etch, stripping/cleaning, and inspection steps. After a reticle is manufactured, it must again be safely and cleanly transported, this time to the IC fab, where it will be stored, transported, and used.

There were very few standards covering the carriers and automation used to manufacture, transport, and handle reticles. Existing standards defined only the size of reticles (SEMI P1, P34) and pellicles (SEMI P5), which are used to keep particles out of the focal plane. No reticle standards have existed for carriers, tool interfaces, or automation systems, perhaps because of the variety of reticle sizes used in fabs and the current ability to control contamination. However, the emergence of the 6 x 6 x 0.250-in. reticle, which is coming to dominate the field, and current reticle defect requirements have presented an opportunity to establish appropriate standards.

Because of the lack of carrier and automation standards, a wide array of reticle containers, boxes, and shippers are in use throughout the reticle and IC manufacturing industries. Most of these devices are opened manually, thus exposing reticles to contamination and damage during handling.

Reticle Manufacturers. Many reticle manufacturing facilities face issues that are reminiscent of old 150-mm wafer-manufacturing facilities. Reticle facilities have manual substrate loading systems using picks, many tool-loading requirements and orientations, and often paper lot travelers. Like fab personnel in the 150-mm wafer era, operators in reticle facilities manually load special fixtures or cassettes. With the increasing defect density requirements of advanced reticle technologies such as phase shift and 157-nm masks, these old-fashioned methods will become particularly problematic.

IC Manufacturers. Because of the ever-shortening life cycles of lithography technologies, the pressure to rapidly deliver next-generation lithography equipment to IC manufacturers has often short-circuited attempts at standardization. IC manufacturers have long endured the burden of using custom—and often expensive—carriers that require custom automation and stockers. Nevertheless, several IC manufacturers have adopted the 150-mm standard mechanical interface (SMIF), which is specified in SEMI E19.3, for their lithography equipment. Although SMIF ports are offered by most stepper suppliers, only the base of the pod, which interfaces with the lithography tool, has been specified by the SMIF standard. Single- and multiple-reticle SMIF pods (which typically hold six reticles) are in use in IC fabs. The SMIF standard allows single- or multiple-reticle pods to be used interchangeably. Figure 1 is a photograph of a multiple-reticle pod loaded on the type of SMIF load port (indexer) that is typically integrated into lithography equipment.

Figure 1: Multiple-reticle pod loaded on a SMIF load port, or indexer.

The lack of a reticle pod standard has encouraged the emergence of several reticle support systems (cassettes) within pods. The use of these differing systems results in different reticle end-effector and sensor clearances, causing all reticle-handling tools other than steppers that drive the configuration to have multiple, custom end-effector and automation designs. The lack of a pod standard has been costly and frustrating to both users and suppliers. Moreover, the lack of standard automation features on reticle carriers has impeded the development of automated delivery.

Adapting the SMIF to Reticle Fabs

Recognizing the need for advanced contamination control and reticle isolation technology, three reticle manufacturers have adopted reticle SMIF systems. Reticle SMIF technology is completely analogous to that used to isolate wafers within IC manufacturing facilities. SMIF pods, interfaces, and minienvironments are the basic building blocks of a reticle SMIF system. Reticle manufacturers have the following requirements for transport and handling systems:

• Size flexibility to accommodate 5-in., 6-in., and 230-mm substrates and 200-mm wafers (EUV and SCALPEL).
• Limited contact areas so that reticles are contacted on chamfered edges only and do not slide within pods.
• Particle isolation to protect smaller pattern geometries and minimize fab costs.
• Operator isolation to prevent reticle mishandling, scratching, and ESD damage.
• Purged carrier capability for advanced resists and oxygen depletion.
• Process control to prevent the misprocessing of increasingly complex reticles.
• Low cost achieved by leveraging existing industry standards and equipment.

One surprising result obtained by evaluating various alternatives proposed to satisfy these requirements was that 230-mm reticles fit in the current design of the 200-mm SMIF wafer pod, whose internal dimensions, 250 x 260 mm, accommodate any reticle up to 230 x 230 mm. This fit, coupled with the systems' ability to meet other requirements, made it advantageous for reticle manufacturers to adopt a reticle isolation and automation strategy based on 200-mm SMIF systems (SEMI E19.4). A shortened 200-mm SMIF pod, referred to as a reticle SMIF pod (RSP), operates with all existing 200-mm SMIF interface automation mechanisms, which have been developed to accommodate the many semiconductor tools developed since the late 1980s and the early 1990s. Figure 2 shows an RSP with a 150-mm reticle.

Figure 2: Early version of reticle SMIF pod (RSP) containing a 150-mm reticle.

Although the SEMI standards required to integrate SMIF systems into reticle equipment already existed in the form of the load port (SEMI E15) and interface (SEMI E19.4) standards, a specific SEMI standard for RSPs had to be adopted to fully define the SMIF systems to be used in reticle manufacturing facilities. This standard, SEMI E100, was approved in July 1999. Since its adoption, reticle tool suppliers have expressed relief that automated reticle management has been standardized.

Reticle manufacturers using SMIF systems are leading the drive toward "hands-off" manufacturing and the availability of reticle equipment with OEM-integrated SMIFs. This development has enabled reticle toolmakers to concentrate on differentiating their process and metrology technologies instead of consuming their resources on custom automation requirements.

Adopting Reticle SMIFs in IC Fabs

IC manufacturers have recognized that the introduction of 300-mm wafer technology has created a rare opportunity to develop standards for reticle transport and handling. After reviewing the RSP that was being developed for use in reticle manufacturing facilities, International 300-mm Initiative (I300I) member companies decided unanimously to adopt the pod as the standard for all 300-mm facilities. IC manufacturers came to this conclusion for the same reasons as reticle manufacturers and:

• Because standards and equipment have kept pace with the 300-mm tool development schedules of member companies.
• Because SMIF systems can meet the requirements of single- and multiple-reticle transport.
• Because RSPs can hold next-generation 230-mm reticles.

Although the ability of RSPs to hold 230-mm reticles was seen as advantageous, the move to 230 x 230 x9-mm reticles has been delayed. Initially, it was believed that the move toward the larger reticle size would correspond with the move toward 300-mm wafers. Now it is expected that 230-mm reticles will not be used in semiconductor fabs until at least 2003. Because of this delay, the I300I and Japan 300 (J300) consortia decided that despite its ability to hold 230-mm reticles, the RSP footprint is larger than needed to hold the 150-mm reticles currently used in IC fabs. Pod footprint is a much more critical issue in IC manufacturing facilities, where thousands of reticles may be stored, than in reticle manufacturing facilities, where hundreds (or fewer) typically may be stored.

IC manufacturers sought the advantages of a pod standard, but one with a smaller pod footprint. It quickly became apparent that the 150-mm SMIF format (SEMI E19.3) satisfied this need. While offering many of the advantages of the RSP but with a smaller footprint, a 150-mm pod would use interfaces that had already been integrated into many lithography tools. Moreover, a new RSP-150 standard could accommodate standard end-effector designs. In the process of establishing this standard, the height of the pod was reduced from that of the nonstandard single-reticle pods in current use. The resulting RSP-150 standard (SEMI 3141) was accepted in March 2000. Figure 3 is a photograph of this pod containing a 150-mm reticle, while Figure 4 shows the RSP-150 (left) and a commonly used single-reticle pod (right). Both pods interface with the 150-mm SMIF defined by SEMI E19.3.

Figure 3: Standardized version of reticle SMIF pod—RSP-150—containing a 150-mm reticle.

Figure 4: RSP-150 (left) and another commonly used single-reticle pod (right).

The reticle supports in the RSP—e.g., the chamfered edge contact, simple supports, and the reticle lead-in for reliability—were standardized in the RSP-150. Standardizing the reticle supports for both RSP sizes ensures that lithography tool suppliers can design one end-effector to work with either an RSP or an RSP-150. The new standards enable a passive end-effector to safely retrieve either a 150- or 230-mm reticle from either pod. The schematic shown in Figure 5 illustrates an end-effector that is compatible with both the RSP and RSP-150 designs as well as 150- and 230-mm reticles.

Figure 5: Schematic of end-effector that is compatible with the RSP and RSP-150 designs as well as 150- and 230-mm reticles.

Many IC fabs (particularly ASIC and higher product-mix facilities) would prefer RSP-150s that can handle six reticles. A standard for this type of multiple-reticle SMIF pod (MRSP-150) is in development and will be balloted by SEMI for review at Semicon West 2000. This pod will be based on the same SMIF standard as the RSP-150 (E19.3). Table I provides a summary of applicable SEMI standards.

The automation requirements for lithography equipment in 300-mm IC fabs are included in section 6 of the I300I Factory Guidelines, Version 5.0.¹ This document provides additional information on the expectations of lithography equipment suppliers and how the RSP-150 will be used and transported in 300-mm facilities. When larger reticles are adopted, the RSP will remain the next-generation carrier for IC manufacturing facilities.

Although IC manufacturers have opted for the smaller footprint RSP-150, reticle manufacturers prefer the RSP primarily because it can hold any of the reticle-size formats, including those for next-generation lithography techniques such as extreme ultraviolet (EUV) and scattering with angular projection electron-beam lithography (SCALPEL) wafers, which are being developed on standard 200-mm wafers. Reticle manufacturers believe that the RSP's capacity to handle all reticle sizes outweighs the disadvantage of its larger footprint.

Reticle manufacturers use many types and configurations of equipment that must be integrated with SMIFs. The RSP helps them achieve this integration, because the proliferation of 200-mm SMIFs has encouraged the development of various 200-mm SMIF interface solutions to accommodate the myriad tool configurations. Consequently, existing and future reticle tools can readily be provided with reticle SMIFs.

The Need for Integrated Handling Methods

Reticle and IC manufacturers will soon face technical challenges for which current reticle boxes are inadequate. As leading-edge device manufacturers move toward using sensitive 193- and 157-nm reticles, the industrywide need for a more sophisticated reticle carrier has increased the need for standardization. Because a suitable pellicle material for 157-nm reticles has not yet been developed, pellicleless reticles may come into use for the first time. Pellicleless reticles, however, tremendously increase the danger of particle contamination. Another challenge facing reticle makers is the use of amine-sensitive resists for 193-nm reticles and oxygen-sensitive 157-nm reticles.

Standardized carriers are intended to improve factory efficiency and lower the costs of reticle storage and management. The move toward standard carriers will also simplify equipment design and relieve lithography equipment suppliers of much of the burden of designing, manufacturing, and supporting their own carriers. This will enable suppliers to concentrate their resources on core technical competencies, which, in turn, will help shorten development cycles. A standard reticle carrier will also enable equipment suppliers to order off-the-shelf configurations for tool interfaces based on the well-established SEMI E19.3 standard, offering device makers access to a broad range of reticle carrier suppliers. Furthermore, using standard carriers, it will be possible to automate lithography-functional areas that have been difficult to automate. This will help improve reticle management methods and equipment layouts.

Both reticle and IC fabs desire a single reticle carrier design to facilitate equipment designs and lower costs for themselves and their suppliers. The carrier can also function as a shipper between mask and IC fabs, thus simplifying operations and offering superior protection against particle contamination. Furthermore, the carrier should be maintainable for reuse. Preliminary data indicate that benefits will accrue from the transition to RSPs.²

Figure 6: Reticle sorter used to manage and handle reticles within IC fabs.

A standardized carrier suitable for use in both IC and reticle facilities may also have a beneficial impact on electrostatic discharge­related issues, the management of which was a key consideration in developing such a carrier. ESD damage to reticles costs the semiconductor industry an estimated $200 million per year, a sum that can only increase as the costs of advanced-technology reticles increases.³ Preventing all unpredictable and variable types of reticle handling is fundamental to an effective ESD control strategy. Reticle sorters, such as that shown in Figure 6, manage and handle reticles within IC fabs while isolating them from ESD and other operator-induced effects. Reticle sorters may also be used to transfer reticles from an RSP to an RSP-150 at the reticle fab before shipment to the IC fab.

Conclusion

In the 200-mm wafer era, the semiconductor industry made great strides in automated material handling and product protection by obtaining cassette-to-cassette automation systems. These systems enabled standard cassette loading and diminished the need for operators to handle wafers directly; today, only cassettes are handled in most fabs. As the semiconductor industry looks toward 300-mm manufacturing, IC fabs are hoping to advance to the next level of automation: standard interfaces, closed carriers, and auto-ID capabilities. All of these technologies will contribute to true hands-off manufacturing, which will further reduce the possibility of operator-induced defects, random ESD damage, particle contamination, and misprocessing. Given the current state of technology, reticle and IC manufacturers can hope to bypass the 200-mm wafer era of reticle automation and proceed directly to the standardized, automated reticle transport and handling methods that are consistent with the move by 300-mm wafer facilities to isolation technologies.

Because of the stringent technical requirements of storing and transporting next-generation reticles, the move to a new carrier architecture is unavoidable. Next-generation stockers will likely be bare-reticle containers purged with a highly stable inert gas. Additionally, chipmakers will be compelled to manage, use, and transport highly sensitive and costly next-generation reticles safely. These challenges, however, will lead to operational improvements that have been long desired but never realized because chipmakers have sought to minimize the impact of design changes on lithography equipment.

References

1. A Ghatalia, "I300I Factory Guidelines, Version 5.0," International Sematech Technology Transfer No. 97063311G-ENG (Sematech, April 2000) Austin, TX.
2. A Ramamoorhty and W Fosnight, "Reticle SMIF Pod (RSP) Evaluation" (paper presented to the 157-nm Lithography Working Group, SPIE 2000, Santa Clara, CA, March 2, 2000).
3. "DuPont Photomasks Develops New ESD Detection Tool Technology Aimed at Improving Wafer Yields," DuPont press release, September 15, 1999.

Stephen Sumner is a manufacturing systems engineer at Intel in Chandler, AZ, but is on assignment in Tokyo. Sumner concurrently serves in various leadership roles within SEMI from the task force level to the division level helping to guide 300-mm standards for interfaces and carriers. His background is in manufacturing simulation modeling, and he now works in a corporate group focusing on factory integration of 300-mm production and automation equipment. He received a BS in industrial engineering from North Carolina State University in Raleigh. (Sumner can be reached at 480/552-3276 or sumnersw@intel.co.jp.)

William Fosnight is director of engineering at Asyst Technologies in Austin, TX. His responsibilities include the development of wafer and reticle transport, storage, and handling products, including carriers, equipment interfaces, and automation systems. Before joining Asyst, he was with Digital Semiconductor in Hudson, MA, where his responsibilities included the development and implementation of strategies to meet the contamination control requirements of advanced microprocessor manufacturing. Prior to joining Digital, he was involved with contamination control and wafer isolation studies at IBM in Burlington, VT. Fosnight holds a BS in mechanical engineering from Ohio State University in Columbus and an MS in mechanical engineering from Rensselaer Polytechnic Institute in Troy, NY. (Fosnight can be reached at 512/342-2500, ext. 1080, or wfosnight@asyst.com.)

Joshua Shenk joined Asyst Technologies in 1997 as a product engineer and is working on pod and automation reliability and testing, as well as supporting SEMI standards development. He received his MS in mechanical engineering from the University of Texas at Austin. (Shenk can be reached at 512/342-2500, ext. 1015, or jshenk@asyst.com.)

Rick Zemen is reticle section manager at Asyst Technologies in Austin. His responsibilities include the development and implementation of reticle transport, storage, and handling products, including carriers, equipment interfaces, and automation systems. Before joining Asyst, he was with Photronics in Austin, where he was responsible for hiring and training the engineering team at the company's most advanced reticle manufacturing site. He received a BS in nuclear engineering from Purdue University in West Lafayette, IN, and an MS in nuclear engineering from the University of Michigan at Ann Arbor. (Zemen can be reached at 512/342-2500, ext. 1047, or rzemen@asyst.com.)

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