SPIE Advanced Lithography Symposium 2021 – days 3&4

On Wednesday and Thursday there were several live events, and I went through many, many prerecorded talks.  There were three metrology keynotes.  The Samsung talk (on Tuesday, but I watched it later) was a broad overview of the challenges for metrology in the semiconductor industry (summary:  its challenging).  The KLA and Applied Material keynotes, while containing some interesting information, were mostly marketing presentations – not my favorite style for this conference.  The Novel Patterning keynote was given by a former lithographer that I was happy to see back at this conference – Mike Fritze, now at a Washington think tank.  He talked about the market for low-volume IC manufacturing, now dominated by the use of used equipment.  Since Moore’s Law scaling has dramatically slowed and will slow even more in the coming years, and since the latest generation of tools may be too expensive to operate at any time for anyone but the biggest volume fabs, will there be a market for special-built lithography tools (such as direct-write) to serve the long-term needs of a growing ASIC (application -specific integrated circuit) market?  Mike raised interesting questions, provided interesting speculations, and presented historical data in useful ways – a great talk.

Mike’s talk was interesting to watch just before Donis Flagello’s Optical Lithography keynote.  More than 10 years ago Nikon ceded the next-generation lithography landscape to ASML, then also lost considerable market share in 193-immersion tools.  What is Nikon’s growth strategy in lithography?  Donis showed us that it is mostly emerging new markets, either outside the semiconductor market or niches within the semiconductor industry.  Nikon has been working on an optical direct-write tool for some time (the so-called Digital Scanner), but also is getting into 3D manufacturing with a tool for additive and subtractive direct metal processing for both macroscopic and microscopic patterning.  The most interesting idea, for this community anyway, was a concept for a two-beam EUV imaging tool.  A combination of a grating phase mask and one-direction wafer scanning could produce sub-30nm pitch lines and spaces over an entire wafer.  The simplified optical design would have much higher optical transmission, enabling good throughput with only moderately ridiculous EUV sources.  At least in concept.  We shall see if Nikon will invest the HUGE amount of money it would take to bring a tool like this to market.

I presented what was called a live “tutorial and networking event”.  The topic was how to use the power spectral density to understand roughness (a prerecorded talk), and what made it a networking event was that viewers could turn on their cameras at the end and ask me questions directly, rather than through the Q&A feature of Zoom and relayed by the moderator.  I liked that format, and was surprised to find out that 20+ minutes for Q&A was not enough!  The second such event will be on Friday with Ralph Dammel, which I am very much looking forward to.

I attend both poster sessions for about 30 minutes each.  The same posters were available in each, and the two sessions (one morning, one late afternoon) were intended to enable Europe and Asia to participate in at least one.  They were very disappointing.  It is not because the software platform (Remo) did not work well – I actually liked it.  Each poster was set up at a virtual table, and attendees could move to any table, view the poster (as a “white board” that anyone at the table could point to), and interact with others at the table if they wanted.  This worked pretty well.  The problem was that very few of the poster authors actually showed up.  We can view the pasters any time we want on the digital library, so the whole point of the live poster session was to interact with authors.  None of the authors I wanted to talk to were there on either day.

There were a slew of good papers that I watched.  Jan Van Schoot gave a great overview of ASML’s progress on their high-NA EUV system (which was considerable).  Still, I find their timetable on deployment terribly optimistic, even given ASML’s considerable tool development prowess.  Eric Verhoeven described the NXE:3600 due out this summer, another useful and needed incremental advance of the core NA=0.33 EUV system.  Since the 250W sources have been out in the field for a while, and by all accounts working well, everyone is looking towards the next source power advance, possibly as high as 500W. 

There were many papers on EUV stochastic defectivity (a particular interest of mine).  So here is some blatant self-promotion.  Danilo De Simone in his talk on 28nm pitch single patterning with EUV showed CD and unbiased linewidth roughness measurements using MetroLER and said “There is a correlation between defectivity and roughness. This is also an important point to mention.”  The reason it is important is that roughness is easy to measure (with tens or hundreds of SEM images), but defectivity for a good process may require many thousands or millions of SEM images.  I authored or coauthored three papers this year, all of which I will claim are useful contributions to the field of stochastic measurements and their use (but I am biased, even if my measurements are not).  The paper by IBM that I coauthored (I only helped with some of the measurements) showed yet another example of how biased roughness measurements can produce incorrect trends and decisions as compared to unbiased measurements.

Have you ever heard of the Kullback-Leibler divergence?  Neither had I, but thanks to a paper by Zachary Levinson of Synopsys, I’m going to look it up.  Luke Long of UC Berkeley contributed nice simulation work on the impact of diffusion, development, and etch to the 3D mechanism of missing contact holes.  I also watched several good etch/patterning papers (helping to reduce, ever so slightly, my knowledge gap on that topic), covering selective deposition and atomic layer etch/deposition cycles.  These approaches can produce aspect-ratio dependent results, which enable healing of stochastic variations of line/spaces or contact holes.  Fascinating.  Nayoung Bae of TEL taught me about DRAM contact hole staggered array formation using crossed SADP or SAQP lines, and the multiple populations of holes that result.  Characterizing the stochastics of the lines and spaces helps to understand the LCDU of the resulting holes.

It was good, busy, and technically packed couple of days.  I’m looking forward to the final live events of Friday as the conference wraps up.

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