The final day of the conference! Zhingang Wang of Hitachi talked about CD-SEM tool matching, describing all of the sources of variation that affect matching. This year he added a new error source to his list: detection/image level variation. The variation of SEM image quality across the SEM image field is something that I have been discussing (related to Fractilia) for the past few years, and I am glad to see Hitachi start talking about it as well.
Jara Garcia Santaclara gets my vote for best paper title of the conference – “One metric to rule them all: new k4 definition for photoresist characterization”. I’m a sucker for Lord of the Rings references. Jara and Bernd Geh have made some good progress on the k4 factor introduced by Bernd last year (essentially trying to create a predictive scaling relationship that is more detailed than Gregg Gallatin’s original RLS formulation). Their work seems to be converging with my (still unfinished) approach to simple LER modeling that I discussed at the last two EUVL Symposiums. With some more effort, we all might get these scaling rules to a very useful place, so I hope we continue to work this topic.
There were several useful papers on measuring and modeling secondary electron blur radius in EUV resists, an important but difficult topic. But most of the Thursday papers were not as on-target to my interests as the earlier days. I did end the day with a fun paper on “Sub-Wavelength Holographic Lithography” (SWHL) by a Swiss startup of that name. Holographic lithography is an old approach with many very interesting characteristics (no projection lens, masks that are hard to make but insensitive to defects). There were other attempts to make this approach work 15 years ago and 25 years ago, but improvements in lasers, mask making, and computational capabilities seem to be enabling a renewed interest. I’ll be watching Nanotech SWHL to see how they do.
Looking back over the week I have two closing thoughts. This is, I believe, the first time I have been to SPIE Advanced Lithography without seeing Grant Willson, who retired last year. I saw him present at my first SPIE in 1985, met him at my second conference in 1986, and have been friends with him ever since. I’m glad he is enjoying his retirement, but we certainly miss him here. The week has also seen an escalating concern over the new coronavirus, COVID-19. Like everyone else I am monitoring developments with morbid fascination, but also to see how it will impact my immediate future. And it has. If there is any positive to the spreading fear over the spreading virus, it is that I will soon be traveling far less. I have started asking customers if we could schedule our meetings, demos, and courses using video conferencing rather than in-person, and they are readily agreeing. Maybe such accommodations will be a permanent trend, with the significant savings in time and resources that come with less travel (not to mention a better quality of life when I spend more time with my family). I will look to this thought as a small consolation.