Bring me the rhinoceros: A Review of the 2013 SPIE Advanced Lithography EUVL Conference
1) Ushio, maker of laser-assisted discharge produced plasma (LDP) sources, showed that they now have > 80% availability for their 6 W source at IMEC’s 3100. They have now demonstrated 51 W at 80% DC for 1 hour and 74 W at 12% DC for couple of minutes. As it has taken them a long time to realize acceptable high availability of 6 W sources, we know that scaling is no small task. It was not clear if LDP will be used for first NXE3300B prototypes, as was done for NXE3100.
2) Gigaphoton had > 7 W in 2012 from their Sn laser produced plasma (LPP) sources but they noted the scaling challenge and went back to the drawing board to address the issues of reliable droplet generation, pre-pulse laser for high conversion efficiency (CE) and debris mitigation. After proof of principal of their new design, they are working now to scale up their source from a current 10 W at low duty cycle, using 20 micron drops and 5 kW CO2 laser. Their new approach looks technically solid and I am expecting good progress this year. For 250 W Sn LPP sources, they are working on a 40 kW CO2 laser module.
3) Cymer’s sources in the field are averaging 10 W today with > 65% availability. These sources have > 0.5% dose stability. For upgrades, they have a 40 W source with 0.2% dose stability that they have used for 100% duty cycle for six one-hour runs. They also had a one-hour run of a 55 W source and feasibility of 60 W was demonstrated. This technology is for NXE3100 sources and they expect it to be ready for the scanners by Q3 of this year. They still will need to transfer this technology to NXE3300B, so I am not sure when the 80 W sources needed for these scanners will be ready. I will be delighted if 40 -50 W sources are ready and in the field in 2014. The Cymer team has done good work and has a roadmap for 250 W; but inasmuch as they have talked for many years about delivering high levels of source power and have not been able to do so, there was some skepticism in the audience toward their roadmap.
1) A paper by Nissan Chemical (8682-9) titled, "The novel solution for negative impact of out-of- band (OBB) radiation and outgassing by top coat materials in EUVL," provided welcome news about OOB radiation and resist outgassing. Topcoat on resist was shown to eliminate OOB radiation from source as well as outgassing. It was a relief, as there has been ongoing discussion about the extent of OOB radiation, its effect on imaging and losses in a spectral purity filter (SPF). So now we may not have to worry about OOB radiation, SPF losses and contamination from resists may be a thing of the past.
2) It looks like resist suppliers are working hard to make EUV resists ready, with several good resist papers presented. Among them was a nice review by JSR Micro (#8682-28) titled, "Novel EUV resist materials and process for 20 nm half-pitch and beyond." EUVL resists need to simultaneously meet the requirements of sensitivity, line edge roughness (LER) and resolution. One challenge that has been pointed out repeatedly is that a higher-than-expected dose is needed for best possible performance from a given resist. High absorbing resists (hybrid resists and resists with metal oxide particles) were presented as options in several papers and may allow us to adequately deal with increasing dose demand. As these resists will be more sensitive, I think that they will provide some relief from the increase in the source power requirements coming from shot noise based limitations.
3) Directed self assembly (DSA) was presented by IMEC as an aid for improving EUV resists performance (8682-10). We can expect to see increasing use of DSA in EUV resists.
4) Mask blank defects have been a challenge that has consistently proven hard to mitigate. Lasertech (8679-17) showed data from their tool that can detect 1 nm high and 33 nm wide defects with 100% accuracy. As shown in many papers, the number of defects in mask substrates and mask blanks remains stubbornly high. However, in the last session of the conference, a paper by IBM (8679-53) delivered good news on mask defect repair for phase and amplitude by nano machining. By looking at mask defects using AIT (mask inspection tool from CXRO), they were able to model the number of multilayers (ML) that may need to be removed or added to the mask blank so that the Bossung curve for the resulting ML is what is expected for a defect-free ML! They presented many examples, and I believe that although this process seems laborious, it may get widely adopted along with mask blank defect reduction to address this leading challenge for EUVL.
5) As we move to higher NA, absorber thickness becomes a larger issue due to higher shadowing. One solution presented utilizes phase-shifted masks, which are a short stack of ML etched into the mask blank, and topped by thin absorber to provide destruction interference to enable thinner absorber layers. New materials choices of Ni and Ag were presented in papers as alternatives to the current set of mask absorbers.
6) As EUVL moves to the 10 nm node and below, one option for achieving increasingly smaller patterning is double patterning with EUV. Intel confirmed success for this process in their pilot line and in the last paper of the conference IMEC and AMAT demonstrated 9 nm HP dense L/S patterning using NXE3300B!
1) A paper by Harry Levinson titled "Considerations for high-numerical aperture EUV" (8679-41) was my first choice. He not only elegantly outlined the technical challenges, he also proposed a comprehensive set of business solutions and challenges to their implementation.
2) A paper by Luigi Scaccabarozzi of ASML, "Investigation of EUV pellicle feasibility" (8679-3), showed how quickly this supplier has addressed a critical challenge which could have been a showstopper.
3) A paper by Shannon Hill of NIST titled, "Relationship between resist outgassing and witness sample contamination in the NXE outgas qualification using electrons and EUV" (8679-19) was an excellent technical work looking into the mechanism of resist outgassing and contamination. His group has continued to lead in the basic work of understanding the mechanism of contamination in EUVL.
4) A paper that I would like to cite for its excellent presentation style was offered by Ken Goldberg of CXRO as "Commissioning a new EUV Fresnel zone plate mask-imaging microscope for lithography generations reaching 8 nm" (8679-44). His outstanding talk set the standard for how to present a complex topic and immense technical achievements in a very elegant way, and the audience was very impressed. I will recommend that SPIE post Ken’s paper on their website as a standard for SPIE authors wishing to make an excellent technical presentation.
450 mm was not mentioned once in any paper in the EUV sessions!
Although sources remain the biggest challenge in EUVL, discussion on this topic was limited pretty much to suppliers showing their roadmaps. I spoke to many people about the source power issue and the lack of funding for source R&D. All agreed, but acknowledged that no action by the industry has been taken yet. Part of the issue, as some mentioned, is that source R&D needs cannot be fully addressed until ASML’s acquisition of Cymer is final, as then it will be something for ASML to address.