I300I and the transition to 300mm Lithography

		At a Glance
	Today, a few suppliers of 300 mm litho tools are clearly into the beta phase of their tool developments. A greater number remain at the alpha level. Some will reach production readiness in late 1998, with most suppliers achieving beta and production in 1999.

Exposure tools are generally perceived to be the limiting factor in the production conversion to 300 mm wafers. In 1998 it appears that most of the suppliers will build fewer than 10 tools. It is possible that one or two semiconductor companies will place large enough orders to exceed 10 orders for one or two suppliers. The preferred 0.25 µm technology 300 mm exposure tool appears to be the 248 nm DUV scanner, based on CD control, field size and wafer throughput expectations. Customers have expressed interest in i-line exposure tools as well. The International 300 mm Initiative (I300I) does not expect to demonstrate 193 nm DUV or i-line 300 mm exposure tools in 1998. The track market is very lively and competitive. Six companies are preparing 300 mm tools for the coat and develop market, two of them quietly. Three of these are new entries into the market.

Many innovative techniques are being employed to reduce resist consumption, a key differentiator in the cost-of-ownership calculations now being done by many customers. Track suppliers are interested in demonstrations of resists for 193 nm exposures as well.

Key challenges to 300 mm lithography The main challenges for 300 mm lithography tool suppliers come in three areas, all directly impacting productivity:

• Throughput,
• Factory floor space,
• Reticle management in the minienvironment factory.

For faster 300 mm throughput, exposure tool wafer stage technologists are faced with the dual challenge of higher acceleration and precise positioning of a larger, heavier stage. With factory floor space at a premium, reducing the footprint per wafer start per week (wspw) is a very high priority. The most cost-effective linked lithography systems will consider the floor space required for the integrated system and will have designs that do not waste either width or depth in their layout. Lastly, the existence of Class 1 cleanroom aisles, for product and reticle transport in future fabs, is considered a luxury by the I300I technical advisory group. The minienvironment fab is becoming the driving force, in addition to 230 mm reticles, for the shift to standardized reticle carrier pods.

Benefits of I300I demonstrations

I300I has offered the opportunity for suppliers to perform single, high-quality demonstrations for our 13 members. The demonstration test method (DTM), which can be viewed at www.i300i.org, provides a very consistent methodology based on statistically significant techniques. Benefits in addition to efficiency include access to a large set of metrology tools, and in the case of donations to our Process Support and Metrology Center (PSMC), a large amount of real utilization of the tool with the concurrent learning. In addition, suppliers get a chance to interact with a broad base of customers simultaneously. The demonstrations are run consistently, by following the DTM, and are a process for a supplier to clearly show their process and reliability performance as well as their service, communications skills and learning rate. Member companies have encouraged and coached their suppliers to submit high-quality demonstration proposals. A typical donated tool will stay at I300I for 12 months, perform the entire DTM sequence and process 50% of all the wafers running in the PSMC. Data gathered includes a mechanical dry cycle of 5000 wafers, a passive data collection to show stability, a four-variable designed experiment to characterize the process envelope and finally, a three-week marathon to show reliability and process stability under simulated high-volume production. In litho specifically, for 1998, we will at least demonstrate or operate a stepper, a scanner, two track systems and a DUV photostabilizer. All but one of those will be in Austin. The litho process here will use advanced reticles and structure provided by SEMATECH, Phillips, Intel and MIT. We plan to resolve 0.18 µm lines and spaces and 0.20 µm contact holes on a number of thin film substrates, including poly, USG oxide and a PVD metal stack. The largest challenge for our litho capability will be to generate the test wafers for up to seven etcher demonstrations, as well as the patterned wafer support of numerous other demonstrations.

0.18 µm equipment performance metrics.

I300I has published the first version of equipment performance metrics for 0.18µm generation 300 mm tools. This document represents the expectations of I300I member companies for 300 mm equipment performance for 0.18 µm technology in 1999. These metrics will be used as targets for I300I equipment demonstrations in 1998. They were developed and agreed upon in consensus by the I300I Pattern and Process Technical Advisory Councils and the Metrology and Factory Integration Work-ing Groups during international meetings in August. Assumptions used for generating the process metrics are in alignment with those of the 1997 Semiconductor Industry Association (SIA) National Technology Roadmap for Semiconductors. The metrics were based on the SEMATECH 0.18 µm flow, with extra modules added for some memory processes. We are soliciting feedback on the metrics from the supplier community. For litho, we created metrics for scanners, tracks and links of those and are preparing one for the photostabilizer. The format of the metrics was modified from the 0.25 µm set to align with SELETE, the Japanese 300 mm consortium. Tables 1 and 2 provide process metrics for 248 nm DUV scanner and track systems.

Table 1. DUV 248 nm Litho Stepper/Scanner and Track Link (6 in./9 in. reticle)

(DUV/use of ARC for non-via levels)

Demonstration test method

In most cases, the members are already familiar with the exposure optics on 200 mm tools. For the 300 mm exposure tools, the most desired items to be measured are the following:

• Stage performance,
• Synchronization,
• Vibration,
• Accuracy performances,
• Stage precision,
• Stage speed,
• Focus leveling,
• Throughput,
• Wafer particle contamination.

Suppliers of exposure tools will not be able to complete full demonstrations in 1998 because of lateness in development timing and high per tool cost. member companies are unanamously interested in seeing full DTM demonstrations of exposure tools as soon as possible and are not interested in partial demonstrations. For the track systems, the full DTM method is being applied, with all
0.18 µm metrics expected to be measured.

I300I litho production activities

I-line resist methods used in 1997 included wafer services from Nikon using a 200 mm i-line stepper using a quad mode (exposure of 1/4 wafer at a time) exposure method for coverage of the 300 mm wafer. I300I and Nikon jointly patterned the wafers. These wafers were used to measure etch rate and uniformity on oxide, poly and metal etchers. I300I also used SEMATECH's Interserv laser interference stepper to create 0.25 µm line and space patterned wafers and contact pattern wafers at 0.28 µm. These were used for CD measurement and profiles. Next year, hundreds of patterned wafers per month will be created with the recently installed TEL ACT-12 Track (donated by TEL) and Canon FPA-3000EX3L Stepper (donated by Intel).

Trends in 300 mm exposure and track systems

Most I300I companies are interested in scanners using 248 nm laser optics based on CD control, field size and wafer throughput expectations for 0.25 µm and 0.18 µm technology. These introduce some unique KrF gas and laser safety concerns into a fab. I300I is driving early completion of SEMI S2 equipment safety and ergonomic audits of all tools with planned demonstrations or PSMC donations. There is also strong interest in demonstration of an i-line exposure tool because of the opportunity for an
i-line mix-and-match strat-egy to lower costs. All lithography suppliers are paying close attention to the productivity guidelines (1.0X footprint/
wspw, 1.3X cost/wspw relative to same-generation 200 mm tools), especially on footprint/wspw as shown by the emergence of engineering tools followed by repackaged designs that targeting smaller footprint/wspw ratios. Most exposure tools are planned for linked operation to improve CD control on the DUV process, placing the burden for E15.1 standard front-opening unified pod (FOUP) loading on the track suppliers.

Reticle activity

Detailed discussions are taking place about the guidelines for 230 mm reticles and their reticle carrier pods (RCPs). RCPs are much like FOUPs for wafers, in that they are front opening and designed for minienvironment operations. The developing standard is borrowing heavily from the FOUP standard, intended for use in minienvironment fabs. The larger reticle would allow scanner field size to increase from 25-32 mm to 25-50 mm, allowing larger die or more die per exposure. Detailed financial and operations analysis is taking place at member companies to understand the timing and strategy needed to shift to 230 mm reticles. Issues include strategies for 6 in. reticles, utilization of the increased field size and synchronizing needs with the rest of the reticle management infrastructure.

Table 2. DUV 248 nm KrF Litho Track

(DUV/use of ARC for non-via levels)

Summary

The 300 mm litho area today has a few suppliers clearly into the beta (near final footprint, standards compliance well under way, link capable) phase of their tool developments. A greater number remain at the alpha level. Some will reach production readiness in late 1998, with most suppliers achieving beta and production in 1999. The track suppliers must primarily bear the burden of the FOUP interface and buffering questions. The reticle carrier pod architecture seems to be driven by the push for minienvironment fabs, faster than by the push for 230 mm reticles.

Daniel T. Enloe received his bachelor's degree in electrical engineering from the U.S. Naval Academy in 1979. He was nuclear trained and served in the submarine force for five years, and he is now a commander in the Navy Reserves. At Intel, he started as a fab litho engineer. From 1994 to 1997 he has represented Intel at the SEMATECH Materials and Bulk Processing FTAB. He is now director for patterning technology at I300I on assignment for Intel.
Fax: (512) 356-3305
E-mail: daniel.enloe@i300i.org

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