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450 mm Wafers: Contamination and Litho Focus
April 8, 2008
Although plenty of people will tell you that the switch from 300 to 450 mm wafers is going to have to happen at some point, and most likely around the 2012 timeframe, the conversation is far from over. I understand the reluctance to embrace this change from a tool manufacturer’s point of view, and probably even more so from a wafer supplier’s point of view, but I hadn’t thought about the impact that 450 mm wafers would have when it comes to particle contamination and the already shrinking lithography process window.
I was out at Sematech’s Surface Preparation and Cleaning Conference (SPCC) last week in Austin, and had an interesting conversation with a wet cleans engineer at a major memory manufacturer. The point he made was about how much more important it becomes with a 450 mm plate to avoid backside contamination.
Already, with 300 mm wafers, particles making their way between a wafer and a chuck can distort a wafer, bringing some regions out of best focus. With a bigger wafer, those problems would just be compounded. Say, for example, a particle gets under a wafer. By the time you reach the edge of the wafer, it could be pretty out of focus. If that wafer were a 450 mm rather than a 300 mm wafer, it would be even more out of focus. I put together a quick sketch of this example. Although this is a very simplistic view of the problem, I just wanted to illustrate the difference in height at the edge of the 450 mm wafer vs. the height at the edge of the 300 mm wafer.
Another issue the engineer mentioned was that throughput trumped everything for memory manufacturers, because DRAM is so cheap. The idea of scrapping a 450 mm wafer vs. a 300 mm wafer sounded horrifying to him.
What other issues are there on the 300 vs. 450 debate within the world of lithography? What are your thoughts and insights about wafer sizes, productivity, contamination, etc.? I’d really like to understand the issues more thoroughly, and would love to get your feedback.
Posted by Aaron Hand on April 8, 2008 | Comments (1)
