MNE 2019

I have a confession to make.  Sometimes I choose to go to a conference mostly based on its location.  My core conference is SPIE’s Advanced Lithography, and I would go to that wherever it was (San Jose is nice, but it is not a “destination”).  But there are a number of conferences at the periphery of lithography, and in particular conferences that touch on lithography for the academic community.  Three conferences that fit this bill are the Electron, Ion, and Photon Beam Technology and Nanofabrication conference (EIPBN, often called 3-beams or triple beam) in the US, Microprocesses and Nanotechnology Conference (MNC) in Asia, and Micro and Nano Engineering (MNE) in Europe (thought of as sister conferences).  They can be interesting, informative, thought provoking, and even inspiring.  But often there is little of direct relevance to my current focus.  In other words, I don’t need to go, but sometimes I want to go.  How much I want to go depends on where it is.

This year, the MNE conference was on the island of Rhodes, Greece, and guess what?  I wanted to go.

These three conferences, EIPBN, MNC, and MNE, used to have a lot more lithography content, much of which was relevant to semiconductor lithography.  Today, however, semiconductor lithography has priced itself out of the academic market, and universities employee either vastly outdated lithographies, or high-resolution approaches that are so slow they could never be considered for the semiconductor industry.  Still, it is always nice to find out what the academic research community is up to in the world of lithography.

But frankly, for me, it is generally not worth traveling half-way around to world to go to one of these conferences.  Unless I want to.

And so I found myself this week in Rhodes, Greece, listening to interesting papers, presenting one myself, and enjoying the amazing beauty and heritage of the one of the Greek islands.

The MNE conference is extremely vibrant, with a lot packed into three days:  150 orals, 360 posters, and four evenings of social activities.  Student participation is huge (often the point of an academic conference), and as an old, cynical industry guy, it is refreshing to be around enthusiastic young people.

The plenary session started with an old friend – Yan Borodovsky, retired from Intel, who talked about Moore’s Law: Past, Present, and Future.  As he told me after, “I can’t believe I am still being asked to speak when in my 5th year of retirement!”  For a retired guy, he gave a great talk.  His “past” described the three pillars of microelectronics:  Von Neumann’s computer architecture of CPU, memory, and I/O, Moore’s Law of reducing transistor costs, and Dennard scaling that makes a transistor better when it is smaller.  One by one these pillars of microelectronics are falling away.  Dennard scaling ended in the mid-2000s when voltage scaling became increasingly difficult.  Smaller transistors are no longer better, we just hope they are not terribly worse.  Moore’s Law has dramatically slowed of late, and Yan made a bold prediction – the end of reduced cost per transistor would occur in 2021, coinciding with the attempt to bring EUV lithography into high volume (really high volume) manufacturing.  The last pillar, Von Neumann’s architecture, is the hardest to escape given its phenomenal success.  But current high-performance computing is limited both by the speed and power consumption associated with transferring data back and forth from memory to CPU.  New architectures, such as neuromorphic computing, could redefine these limits.

Yan’s main point was that lithography choices have always been based on the constraints of these three pillars.  He added one further important constraint:  that today’s logic chips (such as CPUs, GPUs, and Application Processors) are seriously defect intolerant.  One defect (for example, one missing contact hole) will kill an entire chip.  This reality rules out any lithography approach with defect densities greater than about 0.1 defect/cm^2.  That’s a shame, since lithographies such as directed self-assembly (DSA) and nanoimprint lithography (NIL) are high resolution and cheap, but don’t have the defect densities required for today’s logic devices.  A change to a computing architecture that is fundamentally defect tolerant would enable lower-cost lithography choices.  Since today’s chips have 50% or more of their cost coming from lithography, the impact would be huge.  It was clear that Yan is hoping for a defect-tolerant future, so that lower-cost lithography approaches become practical.  As am I.

There were only a few other talks specifically relevant to semiconductor folks like me.  B.T. Chan of imec talked about the etch challenges that come with making FinFETs with only one or two fins.  Michal Danek of Lam Research talked about atomic layer deposition and atomic layer etching as enablers to 3D NAND devices.

The social interactions of the conference were some of the highlights for me.  The reception Monday night before the start of the conference brought us to crusader-era architecture (the Knights of Saint John ruled the island from about 1300 to about 1500) in the old town of Rodos (Rhodes).  It was lovely, and included Homeric singing (what a treat).  Tuesday night was a beach party (we could see Turkey from the beach).  Wednesday night was the conference reception, and I had the honor of serving as a judge for the very popular Micrograph contest.  John Randall began the micrograph competition at the 3-beams conference in 1995, and he brought it to MNE in 2005.  This year there were over 60 entries, and the judging was hard.  You can find this year’s micrographs at

The conference ended Thursday night with a bus trip to Lindos, an ancient and beautiful city.  A fitting end to a conference defined, for me, by its location.

SPIE Photomask and EUVL Symposium 2019 – part 2

I love to see young people at conferences like this one.  They tend to be enthusiastic (not yet jaded), with a look on their faces that only comes from drinking information from a firehouse.  I still remember what that was like, wondering what a word like “pellicle” meant, or what some undefined acronym in a slide could possibly represent (EL? DOF?).  There was so much to learn, and I wanted to learn it all.  This week I have had the added privilege of bringing a brand new Fractilia employee, Jonathan, to his first conference and his first introduction to the lithography community.  These two conferences are a great place to start (587 people in attendance), as opposed to the SPIE Advanced Lithography Symposium (with closer to 2,000 people, twice as many parallel sessions, and ten times as many hospitality suites).  It looks like the lithography life will suit him.

On Wednesday there were more talks about a new absorber material to reduce the thickness, and the 3D mask effects, of features on an EUV mask.  The problem is, we could use that new mask now, but we are a long way from picking the new material(s).  As many people have noted, new material development typically takes at least 10 years, and often 20, before it is ready for manufacturing.

Weimin Gao of ASML gave a talk about extending 0.33 NA EUV single exposure patterning to the 3-nm node.  While a decent talk, he delivered the typical ASML message:  it is someone else’s fault.  To get to the 3-nm node specs for EPE (edge placement error), we need better masks, better resists, and better etch.  What was not mentioned was the need for a better scanner.  More dose, anyone?

Rik Jonckheere of imec gave a paper that I’m sure will become a standard reference point from now on.  He showed that small mask defects, too small to print, can increase the probability of a stochastic printing error (bridge or break).  He showed that mask defects of a variety of types and sizes produced a universal curve where the increased probability of a stochastic printing defect was controlled by the percent CD error caused by the mask defect.  It looks as if mask defects are an important contributor to stochastic defects.

We new it was coming, but still it was good to hear that Lasertec is ready to ship their new actinic patterned mask inspection tool.  This is great news, though there are still many unknowns about how to use this tool for mask manufacturing, repelliclization or requalification, etc. 

On the EUV pellicle front, Emily Gallagher showed impressively high transmittance from carbon nanotube (CNT) pellicles.  At least one more year of research is needed, though, before an industrialization effort for CNT pellicles can begin.

The Photomask Technology conference ended with a panel of mask experts talking about the EUV mask ecosystem for beyond-first-generation masks (I moderated the panel along with Harry Levenson).  Here is my take on the main messages of the panelists:

  1. * Everyone wants (and probably needs) a new high-k absorber material in order to reduce the absorber thickness and the 3D mask affects that are robbing our images of contrast.  But we don’t have sufficiently detailed specs on what we want from this absorber, and that is delaying material selection.  And material development always takes longer than one would expect, so we are unlikely to have new absorber masks ready for manufacturing in less than five years (and that is being very optimistic, in my opinion).
  2. * For the merchant mask makers, the cost of dedicated EUV-only tooling is too high.  It is not clear when (or if) the mask volumes to the merchants will rise to the level where paying for these tools is possible.
  3. * Moving from today’s EUV k1 of 0.45 to the k1 people want to be using (0.35) will be very hard.  It will mean tightening up the mask specs, but will also require a much better understanding of resist stochastic effects.  Mask blank quality will also have to improve, since smaller features will make it harder to cover up mask blank defects with the pattern (at least for metal patterns).
  4. * Local critical dimension uniformity (LCDU) on the masks will be very challenging to improve.
  5. * As EUV mask volumes begin to rise, the volume of returns to the mask shop will also rise dramatically (for repelliclization, cleaning, requalification, etc.).  Are the mask shops ready for this?

Thursday was a half-day of EUV-only talks.  Chris Anderson of Berkeley gave a talk on the MET5 that was great (and I don’t even care about the MET5).  He simply told a compelling story.  He also gets the “most beautiful slides” award (and there was no one else even close in the competition).  From Daniel Schmidt of IBM I learned how high-order overlay corrections, where the scanner stage takes on a curvy path to make these corrections, result in “image fading”, a blurring of the images similar to stage vibration.  For the cases he studied he saw something like a 2% worsening of the LWR as a result of these high-order corrections.  The last session was full of good stochastic papers, each one incrementally adding to our understanding.

As I prepare to leave beautiful Monterey, I’m going to Fieldwork for one last locally-made double IPA.  Till next year.

SPIE Photomask and EUVL Symposium 2019 – part 1

What could be better than spending a week in September in Monterey, California.  This is especially true if you are from Austin, Texas, where the temperatures are still reaching 100 F and we just came through one of the hottest Augusts on record.  Yesterday’s sunrise (experienced while out for a run along the coast) was spectacular, as is the beer at Fieldwork.  But what makes my week even better is that I get to spend it thinking, talking, and dreaming about lithography!  (Does that make me weird?)  I’m here for SPIE’s Photomask Technology + Extreme Ultraviolet Lithography conferences.

Since the late 80s I have been attending (irregularly) the Photomask Technology conference, which everyone calls the Bacus conference (long story).  Three years ago, the Extreme Ultraviolet Lithography Symposium was brought into the SPIE fold and collocated with Bacus, which has proven to be a great idea.  The critical challenges of EUV masks and related technology are getting the attention they deserve through joint sessions of the two conferences.  For the ten years prior to the merger I didn’t attend either conference.  But bringing them together has made it worthwhile for me, and since I have been coming every year.

The three and a half days of conference this week have 140 papers for both conferences (78 orals, 62 posters), including something new this year:  two sessions devoted to stochastics.  This topic is now well recognized as the primary challenge for the success of EUV lithography.  The joint plenary session featured a talk by Mark Phillips of Intel, where he provided a good review of the progress and remaining challenges for EUV lithography, including the growing effort to develop high-NA systems and infrastructure.  My favorite tidbit was the insight (obvious in hindsight) that the need for a pellicle in EUV manufacturing depends on your die size.  When there are many die on one reticle, living without a pellicle may make sense.  In this scenario, wafer (print die) inspections are used to find reticle defects (“repeaters” on the wafer) after they occur.  Despite efforts to keep the inside of the EUV scanner clean, 20% of the time reticles at Intel developed particle adders between inspections, killing yield for those die.  On the other hand, the use of a pellicle, which today has a one-pass transmission of 83%, results in a 30% loss of scanner throughput.  (Note that using a pellicle also requires the use of a membrane just above the wafer to block out-of-band radiation, and this membrane has about 90% transmission.  Overall light intensity is reduced by 0.9*0.83*0.83.)  Which is more expensive, the lost scanner throughput due to low pellicle transmittance, or the lost yield due to printing reticle defects?  That will depend on the die size.

Marcel Mastenbroek, ASML’s NXE:3400 product manager, gave a talk on that tool’s progress the way a proud parent talks about their children.  After 20 years of industrialization efforts at ASML, both Samsung and TSMC are now producing chips, being shipped to customers, with at least one layer printed with EUV.  Granted, this is “risk production”, with those same layers also being printed for some wafers with conventional 193i lithography, but that doesn’t take away from the importance of this accomplishment.  ASML deserves to be proud.  He noted that the next generation pellicle is spec’ed to have a one-pass transmission greater than 88%, to be available next year if all goes well.  We’ll hear more about pellicle progress later in the week.

One of my favorite quotes of the day came from Andreas Frommhold of imec:  “Schrodinger’s contact hole”.  This is a contact hole that, due to stochastic variations, looks good at the top of the hole but doesn’t develop all the way to the bottom (some middle region doesn’t get enough photons or doesn’t generate enough acids to make the resist soluble).  The top-down SEM image ADI (after develop inspect, meaning after lithography but before etch) looks normal, but after etch the hole is missing.  He also noted that etching both increases the number of missing holes observed and the number of merged holes observed compared to ADI.  More work on etch process optimization is obviously required.

On Tuesday I heard a talk by Claire van Lare of ASML on making attenuated phase-shifting masks (attPSM) for EUV.  It is interesting to watch a new generation of lithographers learn the lessons of the past as she grappled with the problems of “high reflectance” attPSM such as sidelobe printing and reticle barcode reading, things that were experienced 20 years ago with high-transmittance attPSM at the 248nm wavelength.  I shudder to think about how OPC will deal with stochastic sidelobe printing.

It is rare now days to have any semiconductor manufacturer give a technical talk at a conference like this.  So I was very happy to see Intel give two talks this week.  Robert Bigwood talked about the role of edge placement error (EPE) in process definition, and he illustrated the value to Intel and to the industry of giving such talks.  He described the thought processes used by Intel to develop an EPE budget and to make process choices based on that budget.  In doing so he was able to challenge the audience with his needs.  First on the list was a sufficiently predictive full-chip etch model, since not every litho EPE will transfer into a complex film stack.  I also learned that stochastic variations of resist feature height are a critical issue for them.  I had not given this issue much thought before, but I will now.

During the resist session three companies talked about increasing resist absorption as a way to reduce absorbed photon shot noise without increasing dose.  All three companies showed that this is easier said than done.  Zeon made the most progress, with a 30% reduction in dose-to-size for similar contact hole local critical dimension uniformity (LCDU, a good measure of contact hole printing stochastics).  Zeon still has a way to go, however, since their non-chemically amplified resist still uses a higher dose than the more conventional chemically amplified resists.  Still, their progress was quite impressive.

I gave a talk on Monday afternoon, going back to my roots and the ideas that got me interested in stochastics more than 13 years ago.  I’ve been trying to develop a simple, analytical framework for predicting how the major factors affect roughness.  For a long time I’ve been stymied by quencher, a complication that I could not overcome mathematically.  I made some progress (as always, by making a simplifying assumption), and I am hopeful that my new derivations will prove useful.

The conferences are halfway through, and I’ll report more at the end of the week.  But I’ll end this post with a tribute to Tony Vacca.  Veterans of the Photomask Technology conference know that the highlight of the week is always the Bacus enterainment, a series of skits with singing and dancing that make fun of the people and players in our industry.  The all-volunteer cast works for months writing and rehearsing, with a frantic push at the end to make the show come together just in time.  For the last ten years or so this crew of “Bacanalians” (as we are called) was led by the amazing Tony Vacca.  Starting four months out he would line up the volunteers, solicit skit ideas, cull the list, flesh them out, edit (mercilessly cutting to make each skit shorter and funnier), manage music and videos, and then rehearse.  For an amateur actor like myself it was immensely fun, though incredibly stressful at the end.  But the stress that Tony was under was always immense.  Last year at the end of the show I thought Tony was going to have a heart attack from the pressure, and he announced that he was retiring from the Bacus entertainment.  No one stepped up to replace him, and this year we have no entertainment.  So tonight, when the conference banquet goes to the Monterey aquarium, I will be raising a glass of wine silently to Tony, with a smile on my face for all the wonderful Bacus entertainment memories that he enabled. Thank you, Tony.

(And to help keep those memories alive, here is one skit from two years ago:  Mr. Pellicle.)

Quitting Your Job: How Hard Could It Be?

Almost everyone has had the experience of quitting a job.  It’s not that hard.  You just go to your boss and say “Take this job and … find someone who will better appreciate its benefits.”  But things are more complicated when that job is with the National Security Agency.

I joined NSA at Fort Meade, MD as my first job out of college, and worked there for nine years in the 80s and early 90s.  (These were the good old days of NSA, before they started spying on Americans.)  I was very proud of my work there, making semiconductor encryption chips.  Like most of the people there, I had the highest security clearance the government offered – Top Secret Special Intelligence.  We scoffed at those piddly Top Secret clearances that they gave away like candy over at the CIA – this was the real deal.  And when you agree to accept this clearance there are certain freedoms you voluntarily give up.

The most obvious freedom I gave up was being able to talk about my work.  I could only talk about work at work, and outside of work I would end up talking about the people at work, which is more interesting anyway.  But the strangest lifestyle difference was the inversion of what is private and what is public.  Work became private, and my personal life could only remain private if it was boring.  The security office at NSA worried about its employees being blackmailed, so the skeletons in each of our closets were actively exhumed through regular security reviews and polygraph tests.

In 1988 an organization called SEMATECH was started up in Austin, Texas.  For those of us working in chip manufacturing, this was a big deal – a consortium of the largest US semiconductor companies, Intel, IBM, Motorola, sending people and money to this new research lab, with the Department of Defense contributing 50% of the budget.  It was the cutting edge of my profession.  So I thought, maybe I could get assigned to SEMATECH for a year or two to work with these great people doing important research in the interest of US security.  And moving from Baltimore to Austin for a while could be fun.  Everyone at NSA agreed this would be a great idea, but there was one problem:  it had never been done before.  And the first rule of bureaucracy is “If it’s never been done before, it can’t be done.”

Bureaucrats have a bad reputation, mostly undeserved since they are the people that actually get things done in government.  After all, the other group of government employees is politicians, and we know how much good they do.  Government employees operate under an important constraint that most people don’t realize.  At your job, you have rules, and if you break those rules you get in trouble, unless breaking the rules makes your company a lot of money, and then you get a pat on the back and a promotion.  But in the government these rules go by a different name:  they’re called laws.  You don’t just break the rules, you break the law.  A guess what – government employees don’t like breaking the law, so they work very, very hard to make sure everything they do follows the huge and continuously growing set of regulations that apply to almost everything they do.

It was hard to figure out how to make the regulations work so that I could be temporarily assigned to SEMATECH, but I was determined, and I was a pretty good bureaucrat.  Through a lot of careful study of regulations and a lot of advocacy from my boss and my boss’s boss and my boss’s boss’s boss and a team of people from finance and legal at NSA, we created a plan and made it work. I left Maryland to come to Austin to work at SEMATECH.  It was great!  I did cool work with cool people, I wrote and published papers and presented at conferences, and we made a real difference.  And when my 16 month assignment was over, I decided I couldn’t leave.  I had fallen in love with Austin.  I had found my home.  So six weeks before I was supposed to go back, I told my boss I was going to resign.  Of course, she was disappointed, but she understood my decision.

For my last week of working for NSA, I flew back to Maryland and started the week-long debriefing process.  Quitting a job with a TSSI clearance is a lengthy process.  On Monday and Tuesday it was meetings with my boss and group about projects and hand-offs, cleaning out my desk, all the normal stuff.  On Wednesday I got the library to sign off that I had no overdue books.  On Thursday I went to finance to finish up with my final paycheck and expense reports and to get their sign-off before the final security debriefing on Friday.  And this is where things went horribly wrong.  When I handed finance my exit form for their signature, they said “Sorry, we can’t sign this because our records show you owe us for an expense overpayment we made.  Once you write us a check for the overpayment we can sign your form.”  Well that’s odd, I thought, but OK.  “How much do I owe?”  “$120,000.” 

What?!?!?  $120,000?  That was more than two years of my salary!

There must have been a mistake.  No, they assured me that they had been working on these calculations for over a week, all the numbers had been double checked and approved, and they had applied the rules pursuant to joint federal travel regulation §301-74.24 scrupulously.

Regulation 301 what?

They explained to me what this regulation meant.  Suppose you are on a TDY (that’s Temporary Duty, government speak for a business trip) and you fail to meet your obligations of the TDY.  For example, you are sent on a trip to attend a conference but instead you go to the beach all week.  The government can require reimbursement of their expenses in sending you on the trip, including your salary for the week.  I was on an extended TDY, and the claim was that my obligation for the 16 month trip was to bring everything I had learned at SEMATECH back to NSA for use there, and by not returning it was the same as if I had spent 16 months at the beach instead of working.

I knew this could not possibly be right, but I discovered that finance was just doing what they were told.  My boss’s boss, who had gone to the mat two years before to figure out how to send me to SEMATECH, was pissed!  He had written a memo to finance the week before invoking this regulation, and the bureaucratic wheels had begun to spin.  It didn’t matter that I was being crushed under them.  I tried to call him, my new nemesis, but he refused my calls.  I went to his office but a security guard was stationed there to keep me out.  That night I was angry, but also determined.  I would fight this, lawyer up if needed.  I was obviously in the right, and I was not about to let some petty paper pusher ruin my life.

On Friday I went to my all-day security debriefing.  At the end of the day I handed my exit form to the security officer for that final signature.  “I can’t sign this,” he said.  “It’s not signed by finance.  They have to sign it first before I can sign.”  OK.  But what does that mean?  “It means you can’t resign.”

Can’t.  “Can’t,” he said. I can’t quit my job.  That was a thought that had never occurred to me.  My first reaction was, “Oh yeah, watch me.”  I’ll just leave and never come back.  What’s that if not quitting?

But then the security officer said four words that froze me in my tracks:  “The 59 minute rule.”

I’m guessing none of you know what the 59 minute rule is, but I knew perfectly well what he meant.  In the 1960s two NSA mathematicians had gone on vacation together for a week.  On the following Monday they didn’t show up for work.  Their boss was surprised, but assumed they had just decided to extend their trip.  The next day goes by, and then the next.  They still don’t show up.  The supervisor was getting worried, but still didn’t do anything.  The following week the two mathematicians show up on Soviet television.  They had defected, taking everything they knew about NSA with them.

NSA reacted by improving their security processes, and the 59 minute rule was born.  This is it:  If you are going to be more than 59 minutes late for work, you must call your supervisor to inform them.  If you don’t, your supervisor must contact the security office.  A security officer will then try to contact you.  If they can’t get in touch with you, they will call the FBI, and the FBI will come looking for you.

The 59 minute rule.  Every NSA employee knew and lived by this rule every day.  I instantly grasped what this meant for me.  I could choose to never show up for work again.  But if I did not officially severe my employment with the NSA, then I would have to call in by 8:59am, Monday through Friday, every week, for the rest of my life.

I was trapped, and I knew it.  When the shock wore off, I took a deep breath.  Slowly I came to understood what must be done.  The only thing that can beat bad bureaucracy is better bureaucracy.  And I could do bureaucracy as well as anyone.  I would show up the next Monday, and work the system.  And that’s what I did.  I spent the weekend reading regulations, I set up meetings, provided documentation, wrote memos and got other people to write memos, and slowly the wheels of the system began spinning in my direction.  I met with finance, with legal, with a director who had 10,000 people working under him.  More memos were written.  Consensus was formed.  I never once saw or spoke to my nemesis, but his novel legal theory was discredited, and so was he.  NSA paid me for an extra week to quit.  By Friday I had my signature and became a free man.

It is easy to take for granted a freedom that has never been infringed.  After my experience at NSA, I have always appreciated the freedom to quit.

Vladimir Ukraintsev, 1955 – 2019

Vladimir Ukraintsev
Vladimir Ukraintsev

I’m sad to report that Vladimir Ukraintsev died last Saturday. He was 64. I knew Vladimir from his long involvement in the Metrology conference of SPIE’s Advanced Lithography Symposium. He was conference chair this year, but his illness kept him from attending.

I enjoyed his rigorous mind and kind demeanor. Here are the details from his SPIE profile:

Vladimir Ukraintsev has PhD in Solid State Physics. Before joining Qorvo, Inc. Vladimir founded Nanometrology International, Inc., directed Technical Marketing at Veeco Instruments and developed metrology solutions for 6 technologies at Texas Instruments. Vladimir published over 85 articles focusing on development of metrology and characterization solutions for industrial applications.

SPIE Advanced Lithography Symposium 2019 – day 4

Thursday, the final day of the conference, is always full of mixed emotions.  I’m exhausted and glad the end is coming since I don’t think I can absorb anything else and need time to process all that I have seen and heard.  But like a sugar rush that turns into a sugar crash, when the last paper is over and the halls start emptying out, I feel almost depressed.  The energy and pace of the week is entirely unsustainable, but it is intoxicating.

In the morning I saw another good paper by Bertrand Le-Gratiet of STMicro, this time on the uses of contour-based metrology.  Both of his talks were perfect illustrations of the power of the visual representation of data.  Sufficiently complex data sets can contain many important lessons, but pulling out the new and useful information from the background of the known and expected can be difficult.  The right graph or presentation of the data can make the important points excessively clear.  I also liked two imec papers showing PSD analysis of AFM data.  By running an AFM tip in a 1D stripe along the top of a photoresist line we can get important information not available in a top-down SEM image.  PSD analysis of the data proved a very useful representation of that top surface roughness.

I spent the entire afternoon in the Grant Willson Tribute Session.  On the occasion of Grant’s retirement, the Patterning Materials conference devoted three hours to honoring the most famous and most beloved resist chemist in the world.  The talks walked us through Grant’s career with heartwarming stories of how he has profoundly changed each of us.  Here is the list of speakers, covering many (but not all) of the important phases of Grant’s life in science and engineering:

Bob Allen (IBM Almaden)
Yan Borodovsky (retired from Intel)
Ralph Dammel (EMD)
Cliff Henderson (Univ. of South Florida)
Chris Mack (Fractilia)
Dave Medeiros (Globalfoundries)
Doug Resnick (Canon)
Mark Somervell (Tokyo Electron)

As almost every speaker emphasized, Grant’s massively important technical accomplishments are dwarfed by the personal influences he has had on so many people, but especially the 274 (+1) students that have graduated from his University of Texas research group.  This tribute was definitely the highlight of the week for me, with the love for Grant pouring out from each speaker, and palpably present throughout the room.  We will miss you, Grant.  (But not me, since I live in Austin and hope to continue seeing Grant just as often as before!)

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!

SPIE Advanced Lithography Symposium 2019 – day 2

Tuesday was stochastics day for me, but before I start talking about papers let me talk about the conference as a whole.  My technical area of interest – stochastics – is a cross-cutting technology, meaning that papers on this topic can be found in almost every conference at the Advanced Lithography Symposium.  That is great, but it is also problematic when two or more papers on this same topic are being presented simultaneously in different conferences.  Last year I pushed for better coordination among conferences for cross-cutting technologies and the conference organizers listened!  They came up with a really good solution:  define three cross-cutting technologies (stochastics, overlay, and machine learning), assign various papers in various conferences to these technologies as appropriate, then create “tracks” (sessions within various conferences with no overlap).  It is working great!  Of course, it is not perfect, but the number of conflicts for me so far have been far reduced.  Kudos to Will Conley and the rest of the conference organizers for making this happen.  I certainly hope it will be a permanent feature of future symposia.

The two morning stochastics sessions in the EUV conference were great.  There was a nice combination of theoretical studies and experimental work, with both wafer printing studies and more fundamental measurements.  The industry is (finally) putting serious scientific attention to this fundamental problem, including the announcement of imec’s new AttoLab facility to probe the fundamental mechanisms of EUV resist exposure.  Peter Di Bisschop’s paper (delivered expertly by Eric Hendrix) added more depth to his important stochastic defect studies.  Anuja De Silva of IBM also gave a talk full of interesting results.  I liked her decision to use a 30 nm pitch as a “canary in the coal mine”, an easy way to make stochastic defects and thus to try out ideas for reducing them.  Steven Grzeskowiak of SUNY CNSE used flood exposure of resist with 80eV electrons as a model for EUV exposures – a nice approach. Roberto Fallica of imec showed off some great fundamental studies (as he always does), this time using photoelectron spectroscopy.  I was intrigued by Mark Maslow’s idea of correlating stochastic defects with what he called “Tail CD”, mean plus three sigma, rather than mean CD.  It is a simple idea (after you have thought of it!) that seems to have value.  It is on my list of things to investigate carefully when I get back to the office.

In the afternoon I stayed on the stochastics track as it switched to the metrology conference.  I gave a talk about taking the SEM out of SEM measurements, and heard several other good talks on roughness metrology.  A full day of nothing but roughness and stochastics – just about heaven for me.

The evening ended with the all-conference panel discussion.  Regular readers of these conference diaries will know that I sometimes (OK, almost always) complain about panels being boring.  There are three things that make a panel boring:  a topic that is too narrow, a topic that is not controversial, and powerpoint.  Especially powerpoint.  So when Will Conley (Symposium Chair) asked Harry Levinson and I to put a panel together, we knew what we had to do.  We agreed on an all-conference panel with a major theme (Is this the end of scaling?).  We decided to use questions that might elicit some controversy, and then tried to make it fun so that it would be interesting.  Here are those questions

1) The technology for which conference at this Symposium is most responsible for bringing about this end of scaling?
2) How is the technology of your conference saving Moore’s Law?
3) If lithographically-driven scaling does come to an end, what topics will you list in your conference’s call for papers?
4) How will we redefine the meaning of Moore’s Law in order to keep its spirit alive?

Finally, we refused to let any panelist get even near powerpoint.  And it worked!  We started out with 400 people in the room, and a majority of them stayed through the biggest part of the time.  I’d be interested in getting more feedback, but the comments so far have all been positive.  Thanks to our great panelists for making it work so well:

Tony Yen (EUV Lithography)
John Petersen (Optical Microlithography)
Rob Aitken (Design-Process-Technology Co-optimization)
Ryan Callahan (Patterning Materials)
Rich Wise (Etch Technology)
Erik Hosler (Novel Patterning Technologies)
Phillipe Leray (Metrology, Inspection and Process Control)

We agreed to disagree on almost every point, except that progress in lithography and patterning will require cooperation by us all.

SPIE Advanced Lithography Symposium 2019 – day 1

The conference remains strong, with about 2100 total attendees (nearly constant over the last 10 years).  The plenary session Monday morning began as always with awards.  We recognized seven new SPIE fellows from our community:  Yasin Ekinci (Paul Scherrer Institut), Jo Finders (ASML), Lynford Goddard (University of Illinois), Stephen Hsu (ASML), Hakaru Mizogushi (Gigaphoton), David Ruzic (University of Illinois), and Martha Sanchez (IBM).  Congratulations!  The first annual Nick Cobb memorial scholarship was awarded to Haoyu Yang of Chinese University of Hong Kong.  The scholarship (sponsored by Mentor Graphics) is quite significant ($10,000).

The Zernike Award for Microlithography is an annual award and our community’s highest honor.  Last year it was not given as we chose instead to honor Nick Cob after his untimely death.  This year, to make up for that gap, two awards were given:  Obert Wood (Global Foundries) and Akiyoshi Suzuki (Gigaphoton).  Congratulations – two highly deserving honorees.  (Full disclosure:  I’m on the award selection committee so I am not an unbiased observer.)

The current president of SPIE, Jim Oschmann, was in attendance to give out SPIE’s President’s Award to Bill Arnold for his outstanding service to the society.  So far as I recall, this is the first time this award has been given to someone from the lithography community.  Since Bill was on the stage anyway, he was further commemorated on the occasion of his impending retirement from ASML (which happens April 1, as I understand).  I hope, however, that this will not be the last time we see Bill in our community.  Two other notable retirements were also mentioned:  Pat Wight (long-time SPIE staff representative to this symposium) and C. Grant Willson of the University of Texas at Austin (more on that later in the week).

We often have some very good plenary speakers at this symposium, but not always.  But it rare to have three very good ones the same year, so we were quite fortunate this year.  Dario Gil, former lithographer and now Director of IBM Research, gave a great overview of quantum computing and IBM’s efforts in building one.  I especially like their open-access model to allow the public to write and run code on their 5-qubit quantum computer.  As expected, he confirmed that error rates are the biggest limiter to scaling up quantum computations.  I have to admit that I still have a spooky feeling about quantum computing.  I’m not sure that I am wishing for its success.

The next two plenary talks dived into the details of 3D NAND manufacturing.  I learned much from both (and enjoyed the tag-team presentation format from Lam Research and ASML).  I liked learning about the tricks used to make the stair-step patterning practical, with 6 lithography steps plus 42 resist trim steps combined to make 48 stair-step patterns.  Cool. The level of vertical integration in 3D NAND is becoming quite staggering.  Over 100 layers of transistors!  With scaling up continuing into the foreseeable future (possibly to 512 layers)!  Wow.  Lots of patterning challenges.

I went to the EUV session for the two keynote talks, one by on old lithographer (Bernd Geh of Zeiss) and the other by a young lithographer (Ryoung-Han Kim of imec).  Actually, I don’t think of Bernd as old (he is too close in age to me), but that is how he described himself.  As for me, I was the grumpy old lithographer portrayed in a cartoon at the end of his talk.  I accept the characterization, though I am grumpy only sometimes.  The best bit from Bernd’s talk was his definition of “k4”, a scaling constant relating measured LCDU (local critical dimension uniformity) caused by stochastics to NILS (normalized image log-slope) and exposure dose.  Alas, he exhibited the standard physicist bias:  there is nothing we can do about photon shot noise (since we understand that), but since we don’t understand the ultimate stochastic limits within the resist, we just need a better resist.  Ryoung-Han Kim provided my favorite quote of the conference so far:  “We used to say EUV would simplify OPC.  Now we know that EUV complicates OPC.”

I shifted to the Metrology session to hear Ofer Adan talk about AMAT’s new SEM.  Or actually I heard him not talk about AMAT’s new SEM since he didn’t really say anything about it.  I gather that it is a higher electron voltage tool that collects and combines signals from new backscatter and secondary electron detectors.  But I’m not sure.  The goal was to see multiple layers of the device at once in order to measure within-device overlay.  Back at the EUV conference I heard the papers in the high-NA session.  But since high-NA EUV lithography is many years away, it was mostly plans and simulations.  The exception was Chris Anderson’s talk on the newly operational MET-5, a microfield EUV lithography tool with NA = 0.5 built by Lawrence Berkeley National Labs.  I’m sure this will serve as a very valuable resist testing platform, just as the MET-3 did.

I ended the conference day by giving a keynote talk at the Novel Patterning conference.  My talk was entitled “Will stochastics be the ultimate limiter for nanopatterning?”  If you missed the talk, I’ll give the abridged version:  Yes.

The evening involved a customer dinner for my day job at Fractilia, followed by staying out too late and drinking too much beer.  The first of many similar nights this week I am sure.

SPIE Advanced Lithography Symposium 2019 – day 0

Let’s call it like it is:  I’m a nerd.  In fact, I’m an uber nerd.  Other nerds say “I want to be nerdy like him.”  The easiest way you can tell I’m a nerd?  I love being in San Jose the last week in February.  It is my favorite week of the year!  The weather’s not too great (though I don’t get outside much to see it), and I certainly don’t get around to see the sites (except the new Uproar brewery down the street).  I’m here for only one thing – the SPIE Advanced Lithography Symposium.  And I love everything about it.  The people, the papers, teaching an exhausting course all day Sunday, committee meetings, standards meetings, free beer, the panel discussion (at least this year), last-minute presentation preparation, lots of coffee in the morning, giving talks, listening to talks, asking hard questions, seeing old friends and meeting new ones, hallway conversations, getting that one great idea that changes everything, seeing the next generation of lithographers take over from us old ones, seeing the old ones still hanging on, late nights, early mornings, more beer, and learning learning learning.  I absolutely love it all.  Let the week begin!

Musings of a Gentleman Scientist