SPIE Advanced Lithography Symposium 2016 – day 1

At 8 am on Monday, the conference begins with opening remarks and the plenary session.

Bill Arnold and Harry Levinson won a “Special Contribution Award to the Art and Science of Lithography” for their two-part paper “Focus: the Critical Parameter for Submicron Lithography” published in 1988.  I read and cited those papers frequently over the years, and I still recall the clarity of their arguments and the insightfulness of their approach.  Without a doubt, these were milestone papers in the development of modern microlithography thought and practice.

Dr.  Andreas Erdmann of the Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie IISB (Germany) became our newest fellow.  Kurt Ronse of Imec was also promoted to that rank, but he was unable to attend the symposium this year and will receive his recognition at a later conference.

The symposium awards were completed when Yan Borodovsky, recently retired from Intel, become the 13th Frits Zernike Award winner.  Congratulations to all of them!

Some years, the plenary speakers are chosen from outside the lithography community to bring perspective and breadth to the opening of the symposium.  This year, we heard from three of our own.  Harry Levinson of GlobalFoundries gave an historical perspective on research and developments in lithography.  He mentioned the low uptime (60-70%) of early excimer lasers and the immaturity of deep-UV resists (especially sensitivity to airborne contaminants) as motivations for the extension of i-line lithography in the early 1990s.  The obvious analogy to EUV lithography was left unstated.  Two good quotes from Harry’s talk:

“Computer programming became a required skill for leading-edge lithography” (discussing the importance of computational lithography).

“Issues at the molecular scale will need to be addressed to realize the optical resolution “entitlement” of EUV lithography.”

Richard Gottscho, EVP of Lam Research, discussed deposition and etching and how those technologies will evolve to improve control in the age of multiple patterning.  In particular, the move towards atomic layer deposition (ALD) and now atomic layer etching (ALE) are greatly improving uniformity and control, though at the cost of processing speed.  These processes work by saturating the wafer with a monolayer of reactive species, which then is reacted to produce the deposition or etching.  This saturation is self-limiting and so removes many process variables from being significant factors in the process rate, easing both the process development and process control burdens.

Tony Yen of TSMC gave a very nice historical perspective on the development of EUV, one that he believes has put EUV lithography on the “eve of manufacturing”.  The very first demonstration of EUV lithography (called soft x-ray lithography until 1993) was by Hiroo Kinoshita in 1986, followed soon by Obert Wood and his many collaborators at AT&T Bell Labs.  Significant government and industry funding began in 1992 and the EUV LLC was formed in 1997 to pool the growing industry and government efforts in EUV.  With the completion of an important prototype tool, the 0.1 NA Engineering Test Stand, development work on the exposure tool shifted to ASML.  They produced their alpha-demo tool (ADT) in 2006, the NXE:3100 in 2011, and shipped the NXE:3300 in 2013.  Tony finished his historical description by saying that their first NXE:3350 has recently arrived at the TSMC loading dock.

As for the current status of EUV lithography at TSMC, Tony confirmed that the plan of record is to exercise EUV at the 7-nm node and use it in production at the 5-nm node.  The remaining problems include mask blank defectivity (currently about 20/blank, too high to use for metal patterning, but maybe OK for contact holes) and the still unproven pellicle solution.  Resist sensitivity in now closer to an acceptable range (between 25 and 30 mJ/cm2 for lines and spaces and between 35 and 40 for contact holes), but with unacceptably high linewidth roughness (LWR).

The invited talks at the EUV lithography conference gave some further perspective from Intel and Samsung on the readiness of EUV for high volume manufacturing (HVM).  Apparently, one of the big issues last year was the reliability of the tin droplet generator, part of the EUV light source.  Both Intel and Samsung were very pleased about progress on that front, so that source reliability has reached 70%, enough to do real engineering work with the tools, though not enough for manufacturing.  Intel reported end-of-line yield loss due to particles added to the mask during use.  They saw an average of one killer defect added per 20 reticle-stage-load cycles, a level that makes manufacturing impossible without a pellicle.

Seong-Sue Kim also reported on the mixed successes and failures of EUV at Samsung in the last year.  They reported 3 particle adders on the mask for every 10,000 wafers printed, a number too high by an order of magnitude at least.  But more disturbing was his report of mask damage after 40,000 wafer exposures using the 80W source.  Blisters formed within the mask multilayer, some of which popped.  Not only was the mask ruined, but contamination travelled through the optical system and made its way to the wafer.  I worry that such chemical reactions induced by the energetic photons of EUV light will behave nonlinearly with intensity.  How bad will this become when using a 250W source?

On the resist front, everyone is talking about metal oxide resists for EUV.  For many years now, Inpria has used metal oxides as an EUV resist that could deliver high resolution and low LWR, but at doses of 80 mJ/cm2 – too high to be practical given the realities of low EUV source power.  The push to get sensitivities of these resists into the 30 mJ/cm2 range has now been successful but, surprise!, the LWR is much worse.  It seems that all attempts to defy the laws of physics through chemistry continue to be unsuccessful.  Yet, since we do not have a complete understanding of all aspects of LER formation, the physical limits of roughness are unknown.  If other problems can be solved, metal oxide resists may be the way to go.

Indulge me, if you will, on another rant.  Thirty years ago I would come to this conference and see papers by resist companies that all had a familiar pattern:  here is our new material, here is a cartoon of the mechanism of why it will work, and here are one or two SEM images of high resolution patterns.  Success is then claimed.  What we learned painfully over time is that high resolution demonstrations of a material are a necessary but not sufficient condition of success.  The reason is the simple fact that a very good aerial image can produce a decent image in a mediocre resist.  The projected image maters!  So how do you know if your material is any good?  You have to consider the development contrast of the resist and how it affects process latitude.  A high image contrast can produce a good single image in a low contrast resist, but cannot produce good exposure latitude.  One needs to compare exposure latitude (or better yet, the focus-exposure process window – see the mention of the Arnold and Levinson papers above) to the entitlement process latitude (that which could be obtained from an ideal, infinite contrast resist), or at least to the current resist of record.  This lesson was learned and over the next 20 years resist contrast was systematically raised until it become sufficiently high.  Today, we almost take high resist contrast for granted (at 193 immersion, at least).

It seems that this lesson has been forgotten.  Have we experienced high-contrast resists for so long that we have forgotten how a low-contrast resist behaves?  Have we forgotten how to measure or characterize resist contrast?  I almost never see a process window for an EUV resist.  I never see a comparison of the exposure latitude to the NILS (or the best exposure latitude possible).  People compare resists printed at different numerical apertures without considering the differences in the aerial images that exposure them, or don’t even mention the conditions at which the patterns were imaged, as if a 20-nm pattern is a function of the resist alone.  We need high sensitivity EUV resists.  We need low LWR.  But we also need high resist contrast.  Let’s start measuring and reporting that, please.

One of my favorite quotes of the day: “I never thought they would discover gravity waves before EUV made it into manufacturing.”  – Kenneth Goldberg (Note:  over $1B was spent over 40 years on the gravity wave effort.)

And my favorite mixed metaphor: “We have only scratched the tip of the iceberg.” – Alex Vaglio Pret

SPIE Advanced Lithography Symposium 2016 – a prologue

2016 will prove to be a pivotal year in the history of semiconductor lithography.  How do I know this?  Because every year proves to be a pivotal year in the history of lithography.  Why should 2016 be any different?  Our industry moves too fast to allow a slack year.

I am frequently reminded of Sturtevant’s Law, not just because it is cute and funny (though it is), but because behind the humor lies a profound truth.  Sturtevant’s Law says that the end of optical lithography is 6 – 7 years away.  Always has been, always will be.  When I started in the field of lithography way back in 1983, Sturtevant’s Law was as yet unformulated but nonetheless in full swing.  X-ray or e-beam lithography was sure to take over by 1990 since it was obvious that optical lithography could not cross the 1 micron barrier.

This was but one of many, many failed predictions of the end of optical lithography.  But the fundamental truth behind Sturtevant’s Law is this:  we always know what we are doing for the next node (in 2 – 3 years), and are pretty sure about the node after that, but we have almost no visibility into what comes next.  We know all of the unsolved problems looming beyond the 6 year horizon, and can’t quite picture the solutions.  Sturtevant’s Law is a statement about our research and development timelines and how they relate to the pace of Moore’s Law.

But while Sturtevant’s Law has been in force for over 30 years, I’m afraid that it may be coming to an untimely end.  The reason is simple:  we no longer have good visibility out to two nodes (6 years).  We have a just barely reasonable impression about what the next node will bring, and are sure that the node after that is impossible.  The end of optical lithography is no longer 6 -7 years away, it is 2 – 3 years away, and even that time frame seems impossibly distant and opaque.

Our angst is about more than just lithography.  Of course, we lithographers know that the industry moves to the pace that we set.  Still, it is disconcerting to believe that a slowdown in lithography means the end of Moore’s Law.  Yet that is what is at stake.  In 2016, we must discover a path that keeps Moore’s Law moving forward, or watch Moore’s Law fall flat.

But a slowdown of Moore’s Law has already begun.  Intel’s 14-nm node was a year late, and Intel has admitted that its 10-nm node will also be late, on a 3-year node pace rather than the historic 2-year cycle.  TSMC has not admitted the slow-down, but is experiencing it anyway.  They created a “faux” node, a 16-nm product line that has the same dimensions and density as the previous 20-nm node.  Revealingly, when the 16-nm node came online last year, they did not report the revenues of that node separately as had been their normal practice, but rather began to lump the 16 and 20-nm node revenues together in one bucket.  “Follow the money” was good advice coming from Deep Throat, and is good advice in the semiconductor industry as well.

Moore’s Law is slowing down because lithography is not keeping up.  Multiple patterning is expensive and process control is a serious problem.  No other solutions are available.  Now, this where EUV is supposed to come in and save the day, right?

Alas, EUV is late.  ASML has made very good progress in the last two years, but that progress has been enough to keep EUV late, not enough to catch up with the industry need.  Anyone who has read these conference blogs before knows that I have been and continue to be an EUV skeptic.  But for the first time in over 20 years of development, I finally see a glimmer of hope for EUV.

Time is the enemy of all lithography development programs.  The demands of lithography move at an unrelenting pace, and even the slightest schedule slip in a lithography development program is the kiss of death.  EUV is late, an almost unmistakable sign of failure, and yet finally there is hope.  And here is the reason.

EUV was supposed to save Moore’s Law.  But instead, the slowdown of Moore’s Law may save EUV.

The 10-nm node will be two years late compared to the original schedule (naming games aside), as we are now on a three-year Moore’s Law cycle.  But since EUV is more than two years late, it still could not impact that node.  How late will the 7-nm node be?  Could it be late enough to use EUV?  That is a distinct possibility.

The big picture of lithography is bigger than the picture we will see at the SPIE Advanced Lithography Symposium in 2016, since the big picture involves the macroeconomics of the semiconductor industry itself.  But what we will see here this week is still big and very important.  How painful is multiple patterning really?  How close is directed self-assembly to being production worthy?  What is the status of nanoimprint manufacturing for Flash production?  Has there been any progress in taming the roughness beast?  And of course, what about EUV source power?

There are always many questions coming into the start of the SPIE lithography conference.  I am excited to start learning the answers.

Running: I can still do it

Ten years ago I took up running as a sport, and found that I really liked it.  I ran two marathons, seven half marathons, and some 10Ks.  All was good; I was meeting my goals and improving my times, until I hurt my knee.  I had cartilage repair surgery, just before a major study showed that these surgeries worked no better than physical therapy alone.  Ah well.  That was five years ago, and I had several abortive attempts to start running again, always followed quickly by a re-injury of that knee.  Finally, a slow and deliberate recovery coupled with weight training of the muscles around the knee allowed a comeback.  This week I ran my first race in five years – the 3M Half Marathon.

I wasn’t sure what to expect.  My goal was to beat 2 hours, so I chose a pace just fast enough to make that time and very carefully stuck to that pace through the whole race.  I kept waiting to poop out, but the miles went by and I never did.  My last two miles were my fastest, and I finished the race at 1:58:35.  That’s only 4 minutes slower than my most recent 3M half of five years ago – an acceptable age-related slowdown!

Incidentally, I ran a 10K five years ago with the goal of running it in my age in minutes, something I accomplished to within three seconds.  For this week’s half marathon I ran two 10Ks back to back, and the second one had a time of 55:11.  That’s 30 seconds faster than my age!  I’m back.

Where’s My Flying Car?

Last Wednesday, Oct. 21, was Back to the Future Day.  I know this because I was invited to a Back to the Future party, where we watched the 1989 Micheal J. Fox movie Back to the Future Part 2.  It is the second of the movie trilogy and in it our heroes travel to the distance date of 10-21-2015.  The future (now three days in the past) is predicted to have clean streets (fairly true), ubiquitous television screens (very true), terrible fashion (absolutely true), and flying cars (not so true).

Predictions of flying cars are not restricted to the campy side of science fiction.  The marvelous Ridely Scott classic Blade Runner (1982) shows overcrowded cities, life-like androids, and flying cars.  It is set in 2019.  Will the next four years bring us flying cars, as well as androids indistinguishable from humans?

At least Star Trek had the wisdom to project 50 years into the future rather than 30 or 40. In its 1968 first season, we are introduced to the infamous Khan in the episode “Space Seed”.  Thanks to a Federation historian, we learn in this episode that Warp Drive, with the ability to travel at speeds greater than light, is invented in 2018.

Ah, if only reality could live up to science fiction.  I’d love a flying car. But I’d settle for self-lacing Nikes.

It’s a Global World

We all know we live in a highly interconnected world.  News travels at the speed of the internet, and a huge number of goods and services compete on a global scale.  But who’d have thought that the war in Ukraine would be significantly impacting semiconductor manufacturing, and lithography in particular?

Because of this, I’ve learned far more about neon than I thought I ever would.

Yes, neon, noble gas, element number 10.  70% of neon production comes from Ukraine and Russia (one company, Iceblick, makes 60% of the world’s supply, and all of that goes through its plant in Odessa).  Neon is a byproduct of steel production, but because it is a rare component of the waste gases, it only makes sense to recover it at extremely large steel plants.  This is where Ukraine and Russia come in, since they still operate the old-style massive manufacturing plants that have long since disappeared from Western countries.

But why is neon important in lithography?  Excimer lasers use gases like KrF and ArF to generate light, and those gases are regularly changed out during use.  But a charge of excimer laser gas is actually about 98% neon, a carrier gas that is essential to the laser’s operation.  With the Russian-supported separatists fighting in the Ukraine, supplies have become highly constrained.  The price of neon has increased 6X in the last year, to about $1/liter, but worse yet there are shortages.  And since a fairly large share of the world’s consumption of neon is used for excimer lasers, this has got the excimer companies worried, and their semiconductor customers as well.

What to do?  Gigaphoton has announced a “Neon Gas Rescue Program” to reduce neon consumption for ArF lasers by 50%, and Cymer is working to reduce neon consumption as well.  In the meantime, we wait and hope for a peaceful and speedy resolution to the crisis in Ukraine.  And I’ll never take neon for granted again.

Professor Arnost Reiser, 1920 – 2015

Dr. Arnost Reiser, chemist, photoresist researcher, professor, and Holocaust survivor, died on August 4, 2015 at the age of 95.  Since 1982 a professor at the NYU Polytechnic School of Engineering, Reiser died at the school’s Rogers Hall where he continued to visit regularly even after he stopped teaching.

In the lithography community, Reiser is best known for his development of KTFR (Kodak Thin Film Resist), the first commercially successful photoresist for semiconductor manufacturing.  He is also well known for his studies of Novolak-diazonaphthoquinone resist mechanisms.  Reiser worked at Kodak from 1960 – 1982, then left to start the Institute of Imaging Sciences at Polytechnic University.

I remember devouring his 1989 book Photoreactive Polymers: The Science and Technology of Resists, published at a time when there were far too few serious books on photoresists.  But what really intrigued me about his work was the topic of percolation and how it might be related to photoresist development.  Reiser pioneered this topic, and I have to admit that I am still trying to understand it.

But as remarkable as his professional career was, his personal life was even more inspiring.  A Jew born and raised in Prague, Reiser was sent to a Nazi concentration camp in Czechoslovakia before being sent to Auschwitz.  After the war he earned his degree in chemistry and went on to teach and write a popular Czech textbook, Physical Chemistry.  With his family, he escaped communism in 1960 by jumping from an East German boat off the coast of Denmark and swimming to shore.  He was arrested by the Danes, but released after Niels Bohr interceded on his behalf.

He lived a remarkable life, and I am glad I was able to know him.

Here are a few links with more details of his life story:

http://engineering.nyu.edu/news/2015/08/18/memoriam-arnost-reiser

http://engineering.nyu.edu/cable/issue/fall-2011/news/faculty/arno%C5%A1t-reiser-survivor-%C3%A9migr%C3%A9-author-groundbreaking-chemist

Reiser’s testimony about being sent to a Nazi concentration camp in 1942:

https://www.youtube.com/watch?v=KahKwbYoJnc

A short book on his life published in 2010:

http://vydavatelstvi.vscht.cz/knihy/uid_isbn-978-80-7080-754-5/978-80-7080-754-5_en.pdf

Goodbye, SEMATECH

In August of 1990 I joined SEMATECH for a one-year assignment that, among many benefits, brought me to Austin.  In those days, SEMATECH was a great place to work, full of energy and promise (and yes, too much politics as well).  The pre-competitive research consortium wasn’t very efficient at spending money to make a difference, but it most definitely made a difference.  It was what the US industry needed at a time of competitive uncertainty, and it attracted some really great people working in a uniquely collaborative environment.

Ten days ago SEMATECH announced its own dissolution, as it merges with SUNY Polytechnic Institute in its new home in Albany.  It saddens me to say that my first thought at hearing this news was “ten years too late”.  While SEMATECH was the right organization at the right time in the 1990s, it lost its way in the 2000s and never recovered.  As the semiconductor industry, and the world, changed to be more global, SEMATECH’s original mission of shoring up the US semiconductor industry became obsolete.  But instead of recognizing its fading value, SEMATECH proved the first law of organization:  organizations strive first and foremost for the survival of the organization.  With all due respect to the many good people that worked there over the years (and still do today), the survival of SEMATECH became the primary goal of SEMATECH, with helping the semiconductor industry a distant second.  They left Austin in 2010 chasing money that the State of New York dangled in front of them, and completed their slide into irrelevance.

So, it is with decidedly mixed feelings that I say goodbye to SEMATECH.  The last decade has been one of lost opportunity for the organization, but their accomplishments over the years are worth remembering.  Mostly, though, I’ll remember the many good people, and good friends, that SEMATECH brought my way.

Salute.

Moore’s Law turns 50

On April 19, 1965  Gordon Moore published a paper in Electronics magazine entitled “Cramming more components onto integrated circuits“.  Thus was born Moore’s Law, an observation that has driven the semiconductor industry ever since.

I have written a piece for IEEE Spectrum magazine that discusses the history of Moore’s Law and celebrates its impact on our industry, and the world.  You can find that article online here:

The Multiple Lives of Moore’s Law

Musings of a Gentleman Scientist