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Technology Stocks : Cymer (CYMI)
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To: James Word who wrote (4874)10/10/1997 1:45:00 AM
From: Ian@SI   of 25960
 
jw,

I don't follow your reasoning at all when you conclude that "Therefore a fab that is supposed to put out a given number of product will require fewer exposure tools at 300mm vs 200mm.

So let me type very slowly for you...

1. The 1 foot wafer (300 mm) has precisely 2.25 as much surface area as the 8" (200mm) wafer.

2. Lithography does not act upon the whole wafer. It is unlike a deposition step or a CMP step, for example. Thus, in the time that 1 wafer is processed in a stepper, perhaps 15-20 would be processed in a CVD tool. For example, not a precise number irrespective of device being made.

3. If fab had same number of steppers as CVD tools, the steppers would be a huge bottleneck. Thus multiple steppers are configured in the fab line relative to the number of other tool types. This allows the fab manager to maximize utilization of all the tool types and not just 1 of them.

4. Lithography tools are among the slowest (except for those fabs that grow their own wafers. ;-) ) Therefore, the fab needs more of them.

5. The stepper does not expose the whole wafer in 1 exposure. If there are 400 die on a 200mm wafer there would be 900 die on a 300mm wafer or thereabouts. If it took 400 "stepper steps" to expose the
200mm wafer, it would take 900 "stepper steps" to expose the 300mm wafer.

I do not know how to state things any more clearly than this.

Perhaps one of us should not be investing in anything having anything whatsoever to do with lithography. Maybe it's me...

Ian.
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