The theme of this year’s SPIE Advanced Lithography Symposium may be stochastics, but the buzzphrase of the year is definitely machine learning. I counted 11 papers with that phrase in the title, not to mention one short course, two full sessions on the topic, and numerous mentions in other talks trying to boost their “cool” factor. I am happy to say I did not attend any of these papers.
I’m just now learning about a technique that I believe TEL introduced last year to help with the edge placement error problem of complementary lithography (which I often misspell as “complimentary”, though this approach is anything but free). In complementary lithography long lines and spaces are patterned in one lithography/etch step (SADP, for example) and then cut up into smaller segments using a second litho/etch step. Sometimes the cuts are so challenging that two or more cut patterning steps are required to make one final pattern. This is where edge placement error (EPE, though more correctly described as edge-to-edge overlay error) comes in. Each cut patterning step will have an overlay error relative to the other cut patterning steps and relative to the lines and spaces being cut. If the cut’s overlay error perpendicular to the line is too large, it could accidentally cut a neighboring line. For this reason the cuts are made short, becoming almost contact holes. It would be easier to pattern the cuts if they were rectangular shaped (long dimension perpendicular to the lines), but then we have these potential overlay problems.
This is where the “multi-color” SAxP approach comes in. If you make every other line in your long line/space pattern out of a different material, and those materials have different etch rates, it is possible to cut one line in an etch process without worrying whether the neighboring line is damaged by a misplaced cut pattern. Alas, this technique comes with increased processing steps (and cost) to create the “colors” (the lines of different material), but it is probably worth it if it enables easier lithography of the cuts.
Wednesday was the day when life as a working stiff got in the way of pretending I was still a Gentleman Scientist. I missed a large chunk of papers in the middle of the day due to customer meetings. Time is the only truly limited resource.
For me the highlight of the day, if not the week, was the special session on shot noise in the EUV conference. 2018 is the 100-year anniversary of the seminal paper by Walter Schottky where he coined the phrase “shot effect” and described the statistical properties of a then newly discovered noise in low-current vacuum tubes due to the discrete nature of electrical change. Since shot noise has become an integral part of our community’s vocabulary recently, I suggested to Ken Goldberg and Felix Nelson that they organize this special section in honor of this anniversary. I gave a tutorial talk on the history of shot noise, then Patrick Naulleau and Robert Brainard followed with two great talks on the topic. I loved the session, especially since I got to give a talk with no technical content (my favorite kind of talk). If you missed it, remember that SPIE is now recording the talks and will post them on the SPIE digital library in the coming weeks (for those authors who have given permission).
The poster session afforded me the opportunity to engage in one of my favorite conference activities – talking with Vassilios Constantoudis. It was enlightening and educational as always.
The late nights are starting to catch up with me, and Wednesday always makes things worse because of the KLA-Tencor party. There are always too many good friends there to catch up with. Still, I think I will be able to make an 8am talk on Thursday. I hope.