SPIE Advanced Lithography Symposium 2017 – day 3

It is just me or is 8:00am too early for the first technical talk of the day?  At least on Wednesday the 8:00am talk was an excellent one.  Oktay Yildirim of ASML presented a basic but very useful roughness model.  Alas, I had to run out before the end of his paper to give my own paper in the metrology session.  The problem with stochastics becoming the major theme of this year’s conference is that there have been stochastics papers everywhere, often conflicting with each other.  The morning metrology session was all roughness measurement.  Of course, I was pleased with Barton Lane’s presentation of SEM errors and their impact on roughness measurements, but since I was a coauthor that is to be expected.  I also gave my own paper on a new method for roughness characterization – the level crossing method.  I was especially impressed with Dr. Serap Savari’s work on applying modern algorithmic techniques for power spectral density (PSD) estimation.  I guess I’m going to have to figure out what a discrete prolate spheroidal sequence is.

Ravi Bonan of IBM went back to an old idea that remains underutilized today – the programed roughness mask.  Similarly, Sergey Babin of aBeam created a metrology test structure with deterministic randomness.  Please don’t ask me to explain.  The core concept of both is the same – create small structures with programmed “roughness” to test our measurement and analysis capabilities.  More creative ideas in these regards will certainly be welcome.

A creative idea came from Harm Dillen of ASML.  He used an array of very dense contact holes to measure the field distortion of scanning electron microscope images.  His application was edge placement error measurement, but as Barton Lane described earlier it also impacts roughness measurements.  Modeling the distortion using a typical first-order overlay model allows the systematic contribution (about 0.6 nm RMS for his data) to be subtracted out.  This amount of distortion is enough to have a quite noticeable on line-edge roughness measurement.  I can’t wait to try this method out.

Alex Robinson of Irresistible Materials gave a talk on increasing the sensitivity of EUV resists.  I didn’t attend.  But he did corner me later and run through it with me.  His cartoon chemistry looked very interesting – a believable mechanism for achieving second order acid amplification chemistry.  Now that such chemistry looks possible, I’ll have to think about the roughness implications more carefully.  That’s the problem with stochastics – nothing is obvious the first time you think about it.

The evening ended with another round of excellent hospitality suites (thanks to all of the companies that feed me so well throughout the week), with the PROLITH party always being my favorite.  For all of you who have asked me if my new company (Fractilia) will revive the traditional bathtub party of my old company (FINLE), the answer is no.  The bathtub party must remain the stuff of lithography legend; Fractilia will create its own traditions.

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