I had the occasion, again, last week, to spend an hour speaking to my laptop screen, otherwise known as giving a technical-topic-of-interest webinar (as opposed to seminar) to interested parties at Synopsys. I thought perhaps to summarize the webinar for this somewhat wider audience.
I have written earlier on how, when you are in the midst of an evolving technology and working in head-down mode for days, and then weeks, and then months, and then years, and then decades, you may miss the perspective. This was certainly the case in my now advanced career when discussing the impact of computers on optical design; this apparently also applies to optical lithography.
As I may have mentioned earlier, I came to optics by way of astrophysics. As an undergraduate I thought my degree was in physics, but, during the last quarter at the University of Minnesota’s Institute of Technology, I received a letter from the university noting should I send in another $50 for the certificate, since I could get two degrees at once: one in physics, and, one in astrophysics. This occurred because of one professor, Ed Ney, who taught some undergraduate physics courses I was required to take. It turns out he worked on the Manhattan Project at Los Alamos and told great stories. This was one of the major turning points in my life, inspiring my interest in the history of science and scientists. He also caused me to sign up for whatever he was teaching going forward, which turned out to be primarily graduate astrophysics. Chandrashekar’s Stellar Interiors was a memorable case.
Faced with the opportunity to be an astrophysicist, I paused. In the last quarter of undergrad, I had not actually considered any path other than getting a job in physics and toiling away. Admittedly a somewhat pathetic career plan. So, faced with no job offers, I considered becoming an astrophysicist. I learned that an astrophysicist typically spends one night collecting data in some obscure but interestingly remote place, and then a year trying to figure out how to write a paper to explain what was just learned. This was not getting my attention. Plan B – make instruments so astronomers would get more interesting and valuable data – was more interesting. Hence, I entered the optics program at the University of Arizona’s Optical Sciences Center (where all the big telescopes are) in 1976. I had no idea where OSC fit in the history of optics education, or, more specifically, that I was part of arguably the first or second actual class of students to come to OSC. I also had no perspective that it was in fact the laser that was inspiring most people to enter optics. Although I had actually taken a laser course as an undergraduate in 1974, with the green Yariv book and Siegman’s book, I had no particular fascination with them – rare, apparently. This turned out to be important as many of the professors at OSC were coming from traditional optics, with Wyant and Shannon joining as the CORONA program collapsed and Roland Shack, a founding faculty from 1968, firmly geometrical.
The above digression explains why I fell into (as opposed to entered) optics in 1976. 1976 is also, as we will learn, close enough to the year that the optical lithography industry was started. There were two primary paths in the US. IBM had Janus Wilczynski at the Watson Research lab, developing relatively conventional refractive lenses to image a mask to a wafer with magnification. His first lens of interest appeared in 1974, providing the then Holy Grail, 1 micron resolution with a mercury lamp sourced filtered to 405 nm (A1, from a presentation by Russ Hudyma, to International Sematech, in 2001 – hereafter referred to as [Hudyma, 2001] as it is a convenient source for historical graphics). In the same year, Perkin-Elmer entered the field with the Offner 1:1 (C1, [Hudyma, 2001]). Now, in 1978, I was selected by Prof. Roland Shack to join him in research. Prof. Shack had worked at Perkin-Elmer, and as a result, in the summer of 1978 I found myself in the office of Abe Offner and others, working with the optics design group. That summer I worked on the tolerance analysis of the Fine Guidance system for the space telescope, but I also interacted with Offner, David Shafer, Hoshang Unvala, and others in the department. Returning in 1980, with my PhD, I joined the Government Division, in Danbury, but I did venture down to Wilton on occasion, to help with the alignment of the M100, then M300, and then the ultimate 1:1 test, the M500 (D1).
In preparing the webinar, I realized my career is exactly overlapping the rise (and end) of projection optical lithography. I was there when the Offner M100 was introduced, and I was involved in the M500 alignment of the strong and weak shells, with Bernie and Teresa Fritz and Bill Chen, all of Optical Sciences. Although I joined ORA in 1986, by 1992 I had established SVGL (who acquired Perkin-Elmer lithography) as a primary engineering customer. I worked on the challenging alignment issues of the only David Shafer design to enter manufacturing, the Micrascan I. David had the challenge of introducing magnification (4:1) (A2, [Hudyma, 2001]) into the otherwise ideal 1:1 geometry of Offner. This Perkin-Elmer lineage is interesting in that historically they always had at least one reflection in their optical trains. David Shafer’s system was short lived due to alignment challenges and was followed by David Williamson’s “Cube,” which went on to form the basis for Micrascan II and III (B2, C2 [Hudyma, 2001]).
In other interesting points in my career, in 1986 I remember being called to come and visit a small startup company in San Diego (one of those classic 18-hour “day trips”) to help them understand why their lenses kept exploding (literally). The company, Cymer, developed one of the first excimer lasers in the world. This of course went on to define the course of lithography from about 1992 to the present.
While I was involved in introducing things like interferometric as-built system modeling to the production of these systems, by 1990 I was brought in, through Tanya Jewell at Bell Labs, to the “soft x-ray” projection optic program, and created one of the earliest patents with her and J. Michael Rodgers/ORA, in 1990 (A3). In 1992 (or was it ’94), Bill Sweatt (who was the first graduate student I met when I appeared at OSC in the fall of ’76, as he had the cubicle next to me) of Sandia Labs had envisioned a more than creative illuminator for a first generation EUV illuminator. The concept was transmitted as a sketch on a piece of paper and went on to become the first optical system modeled for real in LightTools (B3). LightTools was a design and simulation environment that I had initiated with Mike Hayford/ORA some years earlier as a new platform for optical design in 3 dimensions. That vision turned out to be a few decades ahead of its time, but, fortunately Mike, working with Tom Walker and Bill Cassarly, all of ORA, managed to successfully morph it into the field of illumination and nonimaging optics.
With a successful model of the first EUV illuminator, I went on, with Jim McGuire, now the lead of the optical engineering group, to support the creation of the first full-scale EUV system, with Don Sweeney, David Shafer, Henry Chapman, Russ Hudyma, and others at the Virtual National Lab (VNL). This system appeared in the April 2000 issue of Scientific American (C3).
From here, SVGL, with their passion for reflective lithography, jumped in with both feet to design the next-generation system, using a source based in a laser plasma technology from TRW and with the support of the top level scientists at Intel. Jim McGuire and I, joined by Joe Kunick and later Mark Wilder, went on to design the illumination optics for the Beta-tool (A4) and to support, with help from John Rogers who saw the opportunity to introduce the SVD methods of Chapman into CODE V, David Williamson’s 6-mirror design (B4). This was quite a time. However, it ended somewhat abruptly, when ASML purchased SVG Lithography. ASML had an exclusive optics design and engineering relationship with a company in Europe, who will go unnamed, and we were terminated within two weeks of the purchase.
However, the intervening decade has been somewhat stagnant for EUV. The source has continually failed to achieve the required power to go commercial and significantly, the optical design of Williamson appears to be both the being and the end for that form. In 12 years there has been no significant advance on the numerical aperture. Returning to the source, I must say the path that was finally led to a first attempt at introduction in a fab is itself very interesting. Having been through many of the meetings on the source problem, the current path is inspiring for its path. The answer, at least for now was: 1) admit that EUV is going to set a new price point, at least 5X current technology; 2) find a path that leverages existing technology and does not rebuild everything from the ground up.
Worth restating, for those looking for messages of experience in this series of writings, this is one of what I can see could become the “blue note message,” in that I’ve done it twice in a row,
Find a path that leverages existing technology
In the case of the EUV source, in case you missed (I did for a while), they are bringing in the really big commercial lasers used in laser welding of things like jet engines. The current EUV source is based around a couple of these commercial behemoths – or so I hear.
This brings us to today. As I wrote with Prof. Jannick Rolland in the June issue of Optics and Photonics News (C4), freeform optics (D4) is a big deal. And it is likely that it will finally create the next generation of projection lithography. Stay tuned.