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Q&A
TSMC’s T ransition to 300 mm
An Interview with Dr. Nun-Sian Tsai, Senior Director of TSMC’s 300 mm Pilot Line Project Dr. Nun-Sian (NS) Tsai is senior director of TSMC’s 300 mm pilot line project. Dr. Tsai joined TSMC in 1989 as an R&D manager. He then went on to hold various positions at TSMC, including Fab 1 fab director and Fab 4 fab director. From 1997 to 1999 he was vice president of operations at Vanguard International Semiconductor Corporation, a TSMC-affiliated company. Prior to joining TSMC, Dr. Tsai worked for AT&T Bell Laboratories from 1983 to 1989. He obtained a Ph.D. in materials science from M.I.T. in 1983.
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What are the primary reasons and main drivers behind your decision to move to the 300 mm wafer size?
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There are three primary reasons that drive our decision. These include lower cost, higher capacity, and higher yield. With regards to cost, the expectation of the industry is that the unit IC cost will reduce by 30% within next two to three years. We have capacity installed with new technology and capabilities. If we continue to add capacity, 200 mm can take us to 0.13 µm, however, 300 mm can take us to 0.07 µm. The third reason is that we believe 300 mm yields will be significantly higher that 200 mm.
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The slow down in 2001 will not impact or slow down our 300-mm activity. We plan to continue with the pilot line, install technology, improve yield, and reduce the cost. TSMC’s strategy is to be ready for ramp up as quickly as possible once the business recovers. The timing of advanced 300-mm production is related to the business aspect. If the business climate is good, we can even run more aggressive technolo gies; if it is bad, we will stick to 0.13 µm design rules.
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In your opinion, what are the key challenges to transitioning to 300 mm?
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Our biggest challenge has been process integration defectivity. Currently, work is underway on
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0.13 µm technology, and there is no experience with 0.13 µm yet that can be shared. We do not see a major issue in transferring processes from 200 mm, 0.18 µm Al interconnect technology to the larger, 300 mm wafer size. Other key issues include fab production and automation. In introducing new process technologies such as sub-wavelength lithography, potential issues include mask OPC, focus exposure, etc. Defects in copper and low-k have been points of concern in 200 mm, and will continue to remain of concern in 300 mm. However, more work has to be done in these areas before key challenges can be clearly identified.
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What are the risks that you are most concerned about in transitioning to 300 mm?
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Yield is the number one risk. We can manage this risk if we are doing things right, and, therefore, get higher yield. Manufacturability for high volume production and process control is also a risk. In 200 mm you have issues like plasma conditions, chamber conditions, CMP dishing and erosion. When we transition to 300 mm we have been very careful to handle recipes. We are more interested in porting 200-mm recipes with long term high volume manufacturing history to 300-mm tools. With this methodology we believe the recipes and processes will be much more stable for processing thousands of wafers in high volume manufacturing. Our suppliers can also do much to mitigate these risks. Suppliers need to have better recipes when they design the 300-mm chamber. Some of them cannot scale up and that is a disaster. Better tool reliability tests for new 300-mm tool components and parts are also required.
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From a business perspective, how do you compare operating a 300-mm fab vs. a 200-mm fab?
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I believe 300-mm fabs will be more productive and have greater ROI than 200-mm fabs after 2002 because there is room for higher profitability and higher yield. Due to more die per wafer, time to volume requirements will be significant. Yield learning and process control are also very important. In this area KLA-Tencor can play an important role to help process parameter correlation to yield and get the process up very quickly.
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At 0.18 Âľm design rules the current 300-mm tools look good. Diffusion and wet bench tools require much improvement in productivity.
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What do you consider to be the major 300mm yield management and process control challenges?
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For 0.18 Âľm technology, to the first order, 1-sigma process uniformities and process windows are similar to 200-mm wafers. Systematic defects are primarily the integration defects, and will require some time to be really cleaned up. From photoresist to etch and strip we have some impact. These processes really need to be cleaned up and taken step by step. We are still studying them. Although the integration defects are only at a few percent, they are prevalent everywhere, both at front end and back end. From our first couple of lots we demonstrated we can achieve better yields than 200 mm, but there is still much room for improvement. We are now looking at improving these few percentages of yield loss resulting from systematic defects. Regarding our requirements for new capabilities and solutions for 300-mm yield management and process con trol, they are really tied to equipment parameter control. We should have the ability to collect data and use statistics, and develop the methodology to tie this to yield and sporadic scrap. The industry should focus on this. A significant level of hardware and software automation will be introduced in
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300 mm fabs. Could you share your thoughts on 300 mm fab automation issues?
How do you rate the process readiness and performance readiness of current 300 mm tools?
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Intra-bay automation is a must. To this end, TSMC has chosen overhead transport systems. Together with mini-environments, automation reduces yield variations. Automation capability is a key differentiator. Information technology should play a very prominent role in networking all the information together. Correlation of data is very important and a lot of work needs to be done in this area. Tools today provide a lot more valuable information and correlation of information such as electrical fault to physical defects is critical. This is an area that should grow in the semiconductor industry.
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What role did you feel that KLA-Tencor’s newest defect and metrology systems played in the success of your high yields on the first wafers out.
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Your brightfield inspection tool, the 2350, was instrumental in finding critical defects at STI and photo. Using this tool we were able to get high yields on our first 300-mm lots going out.
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Would you like to comment on any 300 mm topics or issues that we did not cover in our discussion?
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Silicon substrate shortage is a major concern. The companies in this infrastructure are not aggressive enough and investment is low. The whole industry should transition to 300 mm a lot faster. At the same time, I feel that the transition to 300 mm will occur much more rapidly than most expectations.
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