SPIE Advanced Lithography and Patterning Symposium 2022 – day 3

In the morning, the optical and EUV session included two very good talks on EUV pellicles.  Mark van de Kerkhof described ASML’s latest material, a composite made of metal silicide crystals (if I got that right) that performs just a little bit better than the prior polysilicon-based stack.  At almost 92% transmission (one pass), it is a few percent better than the previous best and survives up to 400W source power.  Is it good enough to be adopted in manufacturing?  I’m not sure.  The next talk by Lintec described a 95% transmitting carbon nanotube pellicle, quite a promising result.  Their pellicle is making progress but did not seem manufacturing ready, requiring a bit more time to mature.

In the metrology session, my colleagues Gian Lorusso and Mohamed Zidan from imec gave a pair of good talks on the metrology challenges for measuring very thin resists.  (Full disclosure – I was a coauthor on both papers.)  When the as-coated resist thickness reaches 10 nm, line/space patterns have almost no contrast in a SEM, making measurement of CD and LWR extremely difficult.  Lowering the SEM voltage to 300V, and even lower for some materials, improved things.  It looks like 15 or 20 nm thickness and above is manageable with the right SEM measurement conditions.

I was also very impressed by Nearfield Instruments and their high throughput AFM, described by Cornel Bozdog.  Using four AFM heads running in parallel they could measure 64 0.5micronX0.5micron regions per wafer and get a throughput of 12 wafers per hour.  While I’m sure the typical “your results may vary” caveat applies, it is still an order of magnitude faster than I would have expected.

Quite a few students are attending the conferences this year, and I’ve been able to meet some of them.  Seeing the look of these eager young people, drinking from the firehose of information pouring out in each of the sessions, makes me hopeful for the future of our industry.

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