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.
Tin vapor control for better EUV collection efficiency. He said ionic debris can be controlled via magnetic field, and proposed controlling neutral debris with laser resonant ionization of Sn.
Scaling of lasers to high power will need 25 kW CO2 laser modules. One of the toughest challenges in developing such lasers is windows, although diamond windows may be the answer.
After more than a year of peer reviews of submitted articles, we will publish the JM3 special issue in July, with 23 papers covering such topics as laser produced plasma (LPP) and discharge produced plasma (DPP) sources, mask metrology sources, modeling source components (debris mitigation, spectral purity filter [SPF] and lasers) and papers on many alternate concepts for EUV sources. Although all of them are well worth reading, I want to highlight papers that analyze technology limits, offer solutions on how to advance current technology, and provide alternate EUV source concepts.
DPP sources have some definite advantages. They are simpler and cheaper than LPP, and I can personally testify that they can run continuously for eight hours and more. However, since 2007, the power for installed DPP sources has remained in the 7-10 W range, although their reliability has improved. My guess is that thermal mitigation is still the issue. Over the last five years, I have seen convincing data on power scaling potential for these sources, and I see even more conclusive scaling data now. However, I will withhold judgment on how well these sources can scale in power, until end customers report on their long term operation at higher power.
A paper by Koshelev et al. on metal jet offers an interesting approach to DPP power scaling. It was shown to be more than a concept when he provided experimental results at the 2011 Source Workshop. Koshelev expects to soon scale his source power to 800 W at source (80 W at IF) by using 32 kW input and 2.5% conversion efficiency (CE), and details his new DPP approach in this issue. As with all new concepts, it will need engineering work to become a commercial product.
LPP source power has improved from the mW range in 2007 to ~10 W today. The physics of scaling seems straightforward for these sources as well. Now that many LPP sources are in the field, much more attention is paid to them today. But in fairness, I must withhold judgment on the power scaling potential of LPP sources as well, until I see more field data from customers.
Papers from Toshio Tomie and Gerry O’Sullivan provide excellent reviews of LPP technology and offer opinions on its limits. Also worthwhile is a theoretical paper from Koshelev et al. on distributed targeting for LPP (Akira Endo expanded on this concept in his talk at the 2011 Source Workshop). The distributed target approach is interesting and promises higher CE and better debris control, but it needs to be brought into practice and then into manufactured products.
Alternate concepts for EUV sources are explored in papers on EUV lasers, the Laser Compton effect, tabletop synchrotron, inverse laser Compton effect, EUV lasers, electron cyclotron resonance (ECR)-based plasma and free electron lasers (FEL) lasers. Of these approaches, FEL, tabletop synchrotrons, and ECR plasma papers claim the ability to scale up for high EUV source power requirements. Other alternate concept papers focus on metrology applications. All of these papers provide experimental proof at some level.
An FEL paper delivered by William Barletta at the 2012 SPIE Advanced Lithography conference claimed a 500 W source with an estimated cost of $100 million. I support serious examination of these concepts, most probably by a group of experts that include end users as well as scanner makers. Even so, it’s difficult to find funding for alternate technology development when conventional suppliers are claiming that such high source power capability lies within reach of their technology in the near future. But if we do not see significant power scaling results this year, a serious review (not development) of alternate technology would be desirable. We owe it to ourselves, and it is very much worth the effort, to at least do a serious assessment. In any case, I encourage you to read the papers on current and alternate concepts and share your comments with me.
- When will these HVM-level EUVL scanners be used to make products?
- What will trigger the industry-wide insertion of EUV scanners in HVM production lines?
- Will it be a certain source power level, throughput, yield, or cost that raises the confidence of users?
- Who will be the first users of EUVL in HVM, and for what products and which node?
Similar questions can be posed for EUVL mask defect metrology tools. With scanners, we have an approximate throughput model that is widely known, so we can estimate throughput and cost of ownership at a given source power level. This is not quite so for mask defection inspection tools, as they are still being designed and need brighter EUV sources. The leading option for sources for defect metrology tools (and the only one for a 24 x 7 operation) is the Energetiq Xe discharge-produced plasma (DPP) source. However, current performance levels for this source allow only development of prototypes.
In my opinion, memory makers probably will be the first adopters of EUVL technology. Throughput as high as 40 wafers per hour (WPH) will convince chip-makers that EUVL is a viable technology, and sales of EUVL scanners and associated tools and products will start soaring. Mask defect metrology tools will remain unready for HVM until a brighter source becomes available. We can expect a déjÃ vu: low throughout metrology tools waiting to be upgraded.
In the case of high-power sources, we have three major suppliers with the commitment and resources to continue development. Not so for metrology sources, and the end customers will have only themselves to blame this time. I have read that end users are spending up to $150 million on metrology tool development, but not a dime on developing EUV sources for metrology. A source supplier told me that promises of support for metrology source development have not materialized, even though EUV sources for metrology are the weakest link in the chain. With virtually all of the money going to engineering development of tools and none to this weakest link, the results are very predictable.
As the industry Roadmap moves to smaller nodes of resolution (10 nm and below), will we choose EUVL with double patterning, or change the wavelength once again and move toward Beyond EUV (BEUV)? Gadolinium (Gd) at 6.8 nm is the current leading option for BEUV source material, as we saw from the latest development results on source and optics in last year’s EUVL Source Workshop. Increased optical proximity correction (OPC), off-axis illumination (OAI), and double patterning may require more power at these nodes than 13.5 nm sources can provide, so it might make sense to move to BEUV. For BEUV, we have a leading source material for multilayer (ML) optics and resist development has already started. We also can apply lessons learned from 13.5 nm to BEUV tools, although more infrastructure work will be required.
These and related topics will debated by panelists from Intel, GlobalFoundries, Toshiba and Applied Materials (AMAT) at the 2012 EUVL Workshop being held June 4-8 in Maui, Hawaii. The panel will be moderated by Sushil Padiyar of AMAT. The Workshop also will feature many papers on BEUV and EUVL R&D from some of the world’s leading researchers. I will be blogging here about these new developments after the EUVL Workshop.