Douglas RE: "Extending i-line lithography"
"I have a question. If current optical light sources are adequate because of innovations in the masks or substrate materials or whatever, is there a danger from out in left field that companies wont order 248 nm laser steppers because innovations are extending the usefullness of thier current equipment."
There is a small ammount of danger, expecially from DRAM manufacturers. They are practically the only products that can benefit from phase-shift masks and the newer photoresists.
Most memory products, like DRAMs, are made of a single type of
cell that is repeated millions of times, forming a very highly
repetitive pattern. These patters have a high degree of symmetry,
and in some cases can be though of a diffraction gratings. Almost
as important is the fact that most of the features are densely packed
lines and holes.
On the other hand, a logic device like a microprocessor or DSP chip
is composed of a vast array of complex, non repetitive sturcutures.
If you look in a microscope at such devices it looks like a bowl of
spaghetti. The patterns are dense in some areas, some areas have
mostly isolated lines and holes, there are lots of bends and turns
etc.
Simple, densely packed, repetitive mask patterns lend themselves to phase shift masks and off axis illumination. BOth of these can extend
i-line down to 0.25um feature sizes. If you throw in complex features
or isolated lines into the mask the aforementioned trick become useless.
DRAM manufacturers have been pushing i-line beyond 0.35um for a few
years now. Logic manufacturers have been using DUV for 0.25um and
even some 0.35um processes. They are the ones driving wavelengths
down to 248nm and 193nm. So far use of optical tricks to extend
i-line for broad applications is next to impossible and probably
won't occur for a long time, if ever.
Hope that wasn't too much detail.
"Im asking this question because I really don't understand the collapse of this stock."
Me either. Nothing about the stock market makes sense to me.
James Word |
