61st International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication
Orlando, FL, May 30 – June 2, 2017

Unlike some conferences, the 3-beams conference moves to a new location each year.  This means that some years it is in a location I like better than other years.  Last year was Pittsburg (liked it), in the past it has been in Las Vegas (didn’t like it), and this year it was in Orlando, Florida.  I like Orlando, at least when I’m with my family and we are going to Disney or Harry Potter World.  But when your conference is at a resort (Disney’s Coronado Springs, in this case) and you’re not there with family, you become trapped.  It was a 20 minute cab ride to any restaurant or bar that wasn’t part of Disney.  So I ended up eating mediocre resort food and paying $11 for a beer.  The only redeeming factor was that the conference was good.

Historically, the core of the triple beam conference has been lithography (using electrons, ions, photons, and non-beams) along with correlated disciplines (resist, etch, deposition, elf-assembly, etc.).  The application of these fabrication techniques to make devices has always been important to the conference as well.  It is not a manufacturing conference (one presenter described electron-beam lithography as a “high throughput” option for nanopatterning), but that is what I like about it.  It is quite academic, with many students giving papers (a plus for someone like me who spends more time at industry-focused conferences).  Unfortunately, this year saw a larger than normal number of visa cancelations (students who couldn’t get visas to travel here to present).

One of my favorite papers of the conference was a plenary talk by D. Frank Ogletree of Lawrence Berkeley National Labs.  As our industry barrels towards implementing UEV lithography in manufacturing, we still lack answers to very fundamental questions about the exposure mechanisms for EUV resists.  Ogletree described one way to study the complicated interactions of a high-energy photon with a resist material by interacting those photons with model compounds in the gas phase.  Simplifying the interactions allows for much more detailed measurements and easier interpretation of results.  The surprising outcome was how high-energy EUV photons could cause massive fragmentation of the resist molecules.  The full implications for resist chemistry are still unknown.

Dr. Nishikawa of the University of Tokyo gave an interesting talk on directly exposing and cutting DSA (directed self-assembly) patterns using direct-write e-beam lithography.  The results looked very promising.  My favorite student paper was by Yao Luo of Texas A&M, who is working on my favorite topic – stochastic-induced line-edge roughness.  In a technique that I have also successfully employed, she used a Monte Carlo simulator to create simulated scanning electron micrographs of simulated rough features with known statistical characteristics.  She then examined the impact on SEM noise on the ability to properly measure feature roughness.  Great work.

The multi-beam maskwriter company IMS gave an update on their tool development.  They are currently shipping a maskwriter tool with 262,144 programmable electron beams, each with 20-nm resolution capability.  This enables the printing of a state-of-the-art photomask in about 10 hours, limited mostly by the data path (275 TB of data for one mask).  This is great progress for mask making, but we all want to know, how much faster can this tool become?

There were several interesting papers on DSA (from MIT and NIST, among others), but little progress on its application to the semiconductor industry.  Carolien Boeckx of Imec discussed the healing properties of DSA for contact holes.  Unfortunately, you still can’t heal a missing contact.

I gave the last paper of the last day of the conference.  My thanks to the 25 hearty souls who persevered to the end and sat through my talk on how SEM errors influence line-edge roughness measurements.  I then made a mad rush to the airport to catch the last plane to Austin.  I needn’t have rushed.  Thanks to weather my flight was canceled and I found myself captive in Orlando for one more night.

It is 10 days since the SPIE Advanced Lithography Symposium, and I have finally finished and submitted all my papers!  If you are interested in any of them, you can find them on the Fractilia website here:

https://www.fractilia.com/technology/

Note that for the tutorial talk I gave I will not be preparing a paper, but you can get a copy of the slides I presented.  And for those you who didn’t attend the talk, this is the way it ended:

In the second talk of the morning in the EUV session, Andrew Liang of Lam Research showed how much work it takes to optimize a new process, and how that work can pay off.  Local critical dimension uniformity (LCDU) is a term that refers to stochastic-induced variation in CD.  Conventionally, CDU looks at the variation of CD across a chip, exposure field, wafer, and lot caused by things like mask CD variation, film variations across the wafer, focus control across the exposure field, hotplate temperature uniformity, and many other factors.  The length scale of these variations tend to be quite large compared to the pitch of the patterns being printed, so that two feature next to each other are assumed to be largely affected in the same way by all of these variations.  Stochastic variations, on the other hand, have a length scale (called the correlation length) that is small compared to the feature size so that we can understand its impact by looking at any features, even ones right next to each other.  By measuring the CDU of a small group features (a 7X7 array of contact holes, for example) we can isolate the stochastic impact on CD uniformity from the other CDU factors.  This is the idea behind LCDU.

Liang optimized the hard mask below the resist by switching to a thinner PECVD film, optimized the lithography process to maximize the image log-slope, and optimized the etch process using atomic layer etching.  The last item is the most interesting to me, since it looks like it is possible to use an etch rate that varies as a function of aspect ratio to compensate for resist CD variation.  When the resist CD is too small, the aspect ratio of the hole is higher.  For a typical etch process, this higher aspect ratio would cause shadowing of the etchant and a reduction in etch rate, making the small hole even smaller.  But etching can also involve polymer deposition on feature sidewalls to slow etching down.  If that polymer deposition slows down with higher aspect ratio, maybe it is possible to increase the etch rate when contact holes are too small, thus improving the LCDU.  To me this seems like magic, but only in the sense of Arthur C. Clarke’s third law, “Any sufficiently advanced technology is indistinguishable from magic.”  Others have reported on this very exciting possibility, and I am looking forward to learning more.

Ravi Bonam of IBM collected a large amount of data from a programmed roughness mask, a mask that contained an added rectangle (jog) along the feature edge of varying size and frequency.  By measuring the mask and the wafer after printing, something can be learned about the optical transfer of roughness from the mask to the wafer, and the ability of wafer metrology to see roughness at specific frequencies.  Unfortunately his data analysis and presentation left me unable to grasp a single lesson learned from his data.  I’ll have to wait for the manuscript.

Tom Wallow gave a comprehensive overview of sources of metrology variation for the case of metrology used for OPC model calibration.  His two laments were the same as from every lithography model developer.  First, customers want models to fit the data better than the data uncertainty justifies.  Second, models that are based on physics require data that has accuracy, not just precision.  Historically, metrologists have focused on precision for the simple reason that accuracy is just too hard a problem to comprehend.  Tom, I hope people absorb your lessons, but don’t hold your breath.

I presented my last paper at 2pm, and then I was mostly done for the day.  After giving my last demo of Fractilia’s new MetroLER software, socializing with friends that I rarely see at other times throughout the year became my last priority of the conference.  I sampled only about 10 – 15% of the papers in the symposium, and I learned a tremendous amount from them.  I dub this year’s major theme to be stochastics, and I am glad for the attention that it is finally receiving.  I’ll go home with many ideas to investigate and try out.  For anyone interested in my papers and presentations, I’ll be posting them soon on my lithoguru website, and also on the new Fractilia website.  But first I’m going home to relax.

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.

Sunday was a beautiful day in San Jose, bright and sunny.  Just a few blocks away, though, last week’s flooding has devastated whole neighborhoods, causing possibly billions of dollars in damage and the evacuation of more than 10,000 people.  Though very close, that disaster seems far away as we begin the SPIE Advanced Lithography Symposium and shift our focus from what nature can do to us to what we can do to harness nature.

Attendance is again at about 2,200 people this year, similar to what it has been for the last eight years.  It’s hard to get a full sense of what this week will teach us, but just a cursory glance at the program reveals same major shifts in emphasis in the lithography world.  The Advanced Lithography Technologies conference, now renamed Emerging Pattern Technologies, has shrunk considerably over the last two years, from 71 orals and 27 posters in 2015, to 27 orals and 14 posters this year.  There are far fewer papers on DSA (directed self-assembly) this year, as well as fewer multibeam e-beam lithography and nanoimprint lithography papers.  DSA’s early promise of “resolution in a bottle” has given way to the hard reality of defectivity for a thermodynamically driven system.  Meanwhile, the EUV community is emphasizing their progress towards manufacturing readiness.  Some hard realities await them as well, though, and talks on line-edge roughness seem to be everywhere.

This gives me the opportunity to advertise my first talk, at 5:40pm on Monday, at the end of the first day of the EUV conference.  I have been invited to give a 40 minute tutorial talk on stochastic-induced roughness.  I believe this is the first time that we’ve had a tutorial talk at the Advanced Lithography symposium, and I am very excited to be giving it.  I hope everyone interested in line-edge roughness will endure the late hour and come and listen.

For those who are interested in the talk but can’t be at the Symposium, I’m excited about SPIE’s new program to capture each presentation on video.  SPIE will be filming the slides and recording the audio for each talk.  For presenters who have given SPIE permission, these talks will then be posted on the SPIE Digital Library as a permanent record of the presentation.  So, if you do miss my tutorial talk, look for it to show up in a few weeks on the Digital Library.

Let the Symposium begin!