As expected, the first EUV session of the last day of the conference filled a large room. It was time to hear the status of EUV tool development, in particular the EUV sources. ASML started things off with a rosy recounting of the successes of 2011. After installing their sixth NXE:3100 preproduction tool, ASML bragged of the 5300 EUV wafers processed at customer sites by these six tools in 2011. I couldn’t help remembering the ASML press release from last month saying a single 193i tool processed 4000 wafers in a day. That, in a nutshell, is the gap between preproduction and high volume manufacturing. They have a long way to go.
The EUV source status reports made future progress to higher power sound inevitable. Today, customers have sources with 9W of power at the intermediate focal plane, a 20W upgrade is being qualified, 50W has been demonstrated, and getting to 100W by the end of the year is straightforward. What could be easier? Somehow, I remain skeptical. Maybe it is because neither source presentation mentioned the damage caused by tin debris – the 5kV shorts or the frequent replacements of $1M collector mirrors – which can only get worse as source power goes up. Maybe it is because the roadmaps made the optimistic assumption that doubling the input laser power would double the EUV source output. Maybe it is because every past source milestone has been missed and it seems likely that future progress will be harder than past progress. Maybe it is because nature does not like EUV.
Or maybe I am biased. I wish the source vendors luck in reaching their goals. They are under a lot of pressure. In contrast, there was frequent mention of significant progress in EUV photoresists. A demonstration of 16 nm lines and spaces looked promising, though the dose was 33 mJ/cm2 (most people are hoping for 20 mJ/cm2 eventually) and the LWR was 3.7 nm, 23% of the nominal CD. This is progress certainly, but I find it very hard to believe that both dose and LWR will be appreciably reduced by next year.
I enjoyed the session on roll-to-roll printing, especially the Rolith presentation on a cylindrical phase-shifting mask with a UV lamp inside. This world of super-high volume patterning on continuous rolls of low-cost substrates is so different from what I think of as lithography that I could do nothing but look on in amazement.
The day ended for me with the last optical lithography session, where Nikon and ASML presented the current status of the latest 193-nm scanners. While single-patterning resolution remains fixed, the rest of the tool is getting better: CD uniformity, overlay and throughput. Under ideal conditions, CD uniformity can be less than 1 nm, single machine overlay can be less than 2 nm, and throughput can be over 220 wafers per hour (with a roadmap to >270 wph). These tools are becoming optimized for double patterning.
My favorite quote of the day: “Math works.” – John Biafore, commenting on a presentation showing a successful simulation prediction.
My least favorite quote: Cymer, talking about their improved internal EUV source testing facilities, said they will “hopefully learn faster than [the chip companies] do.”
And so another SPIE Advanced Lithography symposium is over. Till next year.
I’m old enough to remember when I-line lithography was considered impossible (difficult source, absorption too high in the resist and optical glass), KrF was too risky (ditto), ArF will never happen (ditto).
F2 and high-index immersion didn’t happen; sometimes they don’t (we maybe gave up too quickly, with EUV just around the corner).
I remember seeing an early ArF laser, finding it hard to believe that such a bomb would be allowed in a wafer fab – and, even it is was, it would destroy the optics…
And so we are now with EUV.
This is a remarkable industry – maybe the most remarkable industry – heroic efforts from many people, under incredible pressure, with unrealistic deadlines. And when they succeed, ho-hum – 2nm overlay, down from 200nm twenty years ago. But why isn’t the overlay 1nm, or 0.1nm?
As with the previous wavelength changes, the last pieces of the EUV jigsaw to be developed are the source and resist – too late and too expensive, but maybe just in time.
Or maybe not, this time – physics may finally intervene – we shall see next year.
What makes EUV different from previous wavelength changes is it is ionizing, so it is not just photons, there are also charges, i.e., photoelectrons and secondary electrons, involved, adding more randomness to the LER issue.
We submitted a paper to this year’s SPIE (8326-96). It was shown that avoiding shot noise at 20 nm would require >47 mJ/cm2 dose of EUV, which makes the common expectation of 30 mJ/cm2 or less very misguided.