SPIE Advanced Lithography Symposium 2019 – day 3

Finally, a day where my only responsibility was to go to papers!  Dan Sobieski of Lam Research described combined etch and hardening techniques that could reduce microbridging and microbreaks in lines and spaces, just not at the same time.  It would be interesting to try these techniques combined with Peter De Bisschop’s defect analysis to see how much the defect-free process window could be opened up.  Toshiharu Wada of TEL described an area-selective deposition to reduce low-frequency roughness.  A resist line is coated with some material such that the deposition rate is slower in a narrow space than a wider one.  If roughness made a space wider, higher deposition rates would tend to fill it in more.  If a space were narrower, slower deposition rates would fill it in less.  The result would be a space that varied less after deposition than before, even at low frequencies.  His unbiased PSD (power spectral density) data showed that it actually worked.  An important caveat is that it may work properly only at one pitch (Wada-san’s results were at 36nm pitch).  More work is required, and I look forward to seeing it.

Switching to the metrology session I heard several SEM talks.  Hitachi explained that one of their biggest priorities is tool matching among a fleet of 10 to 100 CD-SEM tools, where tool matching specs can be extremely challenging to meet.  Sample variation, tool variation, environmental variation, and tool calibration errors all contribute about equally to this overall budget.  Another Hitachi paper described progress in in-situ aberration measurement and adjustment in a prototype CD-SEM to shrink the spot size by about 2X, with subsequent resolution improvements.  They demonstrated the technology with a 100eV beam energy (since the spot size is pretty large at that voltage), but I hope to see results at 500V soon.

It was good to see STMicro back at the conference, and Bertrand Le-Gratiet gave a great talk on monitoring and controlling SRAM contact holes using massive CD measurements.  It is interesting that at the 28-nm node stochastic variations (local CDU) are by far the dominant source of variation.  Stochastics have been with us for a long time, but we are just now putting effort into seeing that.  Finally, I enjoyed Vassilios Constantoudis comparing an edge placement error (EPE) metric to a line-edge roughness metric for synthetic rough features, showing the important role of correlation length in EPE of short features.

For me, Wednesday always ends with a beer (or two) with my friends at the KLA PROLITH party.  Cheers!

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