In which direction are the prevailing microlithography winds blowing? This is always one of the most fascinating questions to ponder after attending the annual semiconductor lithography geek-fest that is the SPIE Microlithography Symposium. Almost every year some new trend can be detected. Sometimes it is subtle, as a new problem or solution starts to be explored. Sometimes it is blatantly obvious, as when a few years ago the litho crowds deserted all the other lithography talks to attend the first session on 193nm lithography. So how were the winds of change blowing this year? I detected two gentle breezes, not too stiff, but quite obvious.
The first was a breath of fresh air for EUV. Yan Borodovsky in his keynote speech probably didn’t reassure a skeptical audience by showing how Extreme UV Lithography needed to improve by “only” 11 orders of magnitude before it was ready for production. Intel may be the biggest cheerleader for this next generation lithography, but the facts are the facts despite the spin. However, the next day ASML made up for lost ground by giving a well-received review of their EUV scanner development program – not to the believers in the Emerging Lithography conference, but to the life-long skeptics in the Optical Lithography conference. Personally, I still think that EUV technology is the next X-ray Lithography, doomed to failure by unforgiving physical realities. But it won’t be due to lack of effort, and if anyone can make it work it will be the industrious Dutchmen at ASML.
The second breeze felt warmer on my skin (optical bigot that I am), for it flowed along a path that allows 193nm to keep going past the 45nm half-pitch. High index fluids and materials can get you so far. Then what? Double printing, where two larger pitch patterns as interspersed to create a smaller pitch pattern, is getting serious attention. Of course, nobody likes to even think about doubling the cost of an already expensive critical lithography step. And the overlay challenges are formidable. Still, double patterning may first prove valuable as a process development vehicle, enabling device and process learning before other lithographic alternatives are available. Then, efforts towards making the technique production worthy might be successful. There is always huge momentum behind incremental improvements to our existing technology. I am hopeful, if not optimistic, that double patterning will eventually become mainstream.