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Is the Chip Industry as Important as We Think? Depends on Whom You Ask

Vivek Bakshi, EUV Litho, Inc.

For me, 2014 started with a focus on moving into my new office on my ranch that will allow me to do more higher-quality, uninterrupted work. After I finally finished moving in, I sat down to catch my breath and to contemplate the world I work in. Immediately these questions popped up:

Are we as leading-edge industry making a difference in the world?

Are my efforts to promote EUVL and help its transition into fabs making a positive difference?

Are we as scientists and technologists making the world a better place?”

This is not the first time I have pondered these questions. Not long ago, I responded with the following logic:

The world as we know it cannot continue to exist without the latest computer chips. Taking away all the leading-edge chips would set humanity back faster than almost anything else.
Lithography is the main driver for producing leading-edge computer chips.
I work on developing advanced lithography techniques – especially the most critical issue, EUV sources – so my work has to be important!
Our industry is the bedrock on which the new civilization stands.

Unfortunately, not everyone recognizes this. I shared my view with a friend who had just returned to Austin after many years in Hollywood. It turned out he took all the new and better chip-driven gadgets for granted. Yes, we use computers, he said, but all industries think highly of themselves. He told me Hollywood thinks it drives the world. Since then I have talked to more people and have gotten similar feedback: we get better gadgets every year and expect to pay less for them every Christmas. Business as usual, they say.

Still, I can’t help thinking that we’re special. Our leading-edge chip industry is driven by innovation and competition and not by regulation. Do you ever hear Congress debating legislation to make 14 nm node technologies available in 2014 so we can have faster computers for the next-generation X-box or IPad? Not a chance! Instead, our industry self-innovates by trying to outdo our competitors. Our only price and performance guidelines come from competition– we deliver better products every year at lower cost, as driven by Moore’s Law and consumer demand. Which other industry does this?

However, when we read media coverage about the leading-edge chip business, much of it circles around the extension of Moore’s Law, when and if it will end, EUVL delays, source power, when we are going to have EUVL ready, etc. That is the end of the story. So how as an industry have we ended up here?

First of all, we are here because of how the chip industry conducts business. By trying to move to EUVL as next-generation lithography, we are changing more than one thing in the critical technology of lithography, which is very difficult to do and hence the delay. The current light sources are plasma-based and what industry has achieved for EUV sources is phenomenal. However, making high temperature devices (35K or more) for 24 x 7 operation is extremely difficult and we still have a way to go. To make faster progress, we need larger knowledge and innovation bases in research labs around the world, and we do not have them. Our industry now has at least half a dozen consortia, which are supposed to be working to generate a knowledge base to support solutions for difficult problems, such as those EUVL is facing today. However, their main focus has been on supporting suppliers in tool development, an important task to be sure – but no support has been given to EUV source research for a very long time, which is our number one issue. Last year major chip makers announced R&D support for EUVL via their investments, but did it go toward our number one issue of high power and metrology EUV sources? Work in other areas of EUVL is good, but sources are where we can expect the most benefit from R&D.

The second reason is how we share information in this industry. It is done by press releases, investor statements and mostly in formal large conferences – too large for any discussions or format to allow discussion or questioning of critical data. After many technical conferences, the presentations are not available for a while (if at all) or may appear in formal papers after a long time. This is why I organize biannual EUVL workshops that are small, allow discussions on the data provided, and make presentations available to all at no cost just a few days after the meetings end.

The third reason is the type of OEMs we have in our business. Some are leaders and risk-takers and as a result they win big and grow, like ASML. They “bet the farm” on EUVL and it is paying off for them. In the near future, there will be only one leading supplier for critical litho tools – ASML. As I say for any business, there are three critical elements – investment, core competency and risk. Some suppliers are not willing to take risks or make investments, but I believe that many lack the core competency for getting into EUVL as well. You can acquire knowhow by buyout, but not always. ASML via its network of R&D institutes and sub-suppliers has built a vast network of competency that has supported its EUVL tool development. Such networks are not built in years, but over a decade.

History Repeats Itself – Rescuing Moore’s Law

I would like to focus on the topic of light sources for lithography, which is of interest to many. If we look at the history of chip-making, we find that in the beginning of the current deep ultraviolet (DUV) based processing, around 1980, in order to stay on Moore’s Law, IBM wanted to move to shorter wavelengths. At that time there was also a shortage of photons in shorter ultraviolet light, as we are seeing in the industry’s transition to 13.5nm wavelength to stay on Moore’s Law. Then Grant Willson and his colleague discovered chemically amplified resist, which allowed us to do more with fewer photons. We are at a similar place today: while many are looking for more photons, the solution may come not from that direction (higher source power) but from being able to do more with the photons we have. I believe that Prof. Willson and his team, or someone else of that caliber, will once again come to rescue Moore’s Law by showing us how to do more with less. I hope our industry is exploring this option well.

Nobel Prize and Computer Chip Industry

Coming back to the perception of our industry, let’s talk about the Nobel prizes that have been given in chip-making. Although our industry can boast of a few Nobel prizes, there are not enough, considering its history of innovation and its contributions. Three have been awarded over the past 50 years – a 2000 Nobel prize in Physics to Jack S. Kilby for his part in the invention of the integrated circuit, a 1973 Nobel Prize in Physics to Leo Esaki and Ivar Giaever for their experimental discoveries regarding tunneling phenomena in semiconductors and superconductors, respectively, and a 1956 Nobel in Physics to William Bradford Shockley, John Bardeen and Walter Houser Brattain for their research in semiconductors and their discovery of the transistor effect. I certainly hope that there will be more in coming years.

Prof. Willson’s discovery of chemically amplified resist (CAR) has revolutionized modern computer chip-making. It stands among great discoveries and its implications have been vast – any leading-edge electronic device that you touch (IPhone or Kindle or laptop) has been made possible due to processing based using CAR – his invention. For what others inventions we can say this? For his work he has received many well deserved prizes, including the Japan Prize (similar to the Nobel) in 2013. I believe that his invention deserves recognition by the Nobel Committee for Chemistry. I certainly hope that leaders of our industry will write a recommendation for him to the Nobel Committee and share with us on the role of his invention and contributions. I will be happy to publish them in this blog.

Source Workshop Presents Data on Readiness of 50 W EUV Sources to Support EUVL Scanners

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Vivek Bakshi, EUV Litho, Inc.

The 2013 Source Workshop (Nov 3-7, 2013, Dublin, Ireland) brought together one of the world’s largest annual gatherings of EUV source experts. I will focus on highlights of the workshop in this review.

In his keynote talk, Vadim Banine of ASML reminded the audience of the advantages of EUVL over double and quadruple patterning. He said that 50 W EUV sources have now demonstrated good dose control and are now available for deployment in the field. (ASML earlier this year acquired Cymer, a maker of high-power EUV Sources.) ASML also presented data on the feasibility of source power of 175 W at the first focus (720 W at source), and utilizing new, protective cap layers to give collectors six months of life.

Gigaphoton, the only other supplier of high power EUV sources, presented results of their development efforts. Although their source power is only 15 W with 2.5 % conversion efficiency (CE), their Sn laser produced plasma (LPP) technology has some key advantages for power scaling: dual wavelength pre-pulse, magnetic mitigation of debris and IR reduction technology for collectors, which they have developed with Rigaku. Collector rejection of IR radiation (10 µm from lasers) works with only 10% loss of reflectivity of collectors. Gigaphoton also showed that picosecond prepulse improves CE and reduces mists. High power lasers remain the drivers for source power scaling for ASML and Gigaphoton, and Gigaphoton is working with Mitsubishi on transverse flow CO₂ laser development and on an axial flow CO₂ laser development with Trumpf.

Mark Phillips of Intel in his keynote talk offered a balanced criticism of progress in EUV source technology. He said that 40-80 W of stable sources with master oscillator power amplifier (MOPA) technology and prepulse, linked to production level EUVL scanners (NXE 3300B), are needed to reestablish confidence in EUVL and process development. He expects these power levels to be available in the first half of next year, in keeping with the timeline of HVM insertion in 2017 by his company.

As Intel now expects that a pellicle will be needed for EUVL scanners, this position will help resolve the issue of choosing of actinic vs. e-beam technology for mask defect inspection, as only photon-based inspections can be used with a pellicle. This will hopefully result in an increased engagement between metrology source suppliers and mask defect inspection tool makers. Various makers of EUV sources for metrology application presented the performance of their sources, including Adlyte, Energetiq, Naextstream and NewLambda technologies. In an interesting paper, Serguei Kalmykov of Ioffe Institute, Russia demonstrated a 30-60 % increase in CE of Xe LPP sources via application of pre-pulse technology.

In other interesting results:

V. M. Krivtsun of RnD-ISAN /EUV Labs presented the concept of power scaling via increase of pulse energy, instead of the current option of pulse frequency for power scaling. His group also demonstrated a closed tin system with tin jets at velocity of 5-15 m/s (max temperature of 350 C), with potential for power scaling for Sn LPP sources.

In another invited paper, Alexey Lopatin of the Institute for Physics, Russia presented his design of freestanding film elements for use as pellicles in an EUVL scanner. These films of merely 20 µm thickness have 84% transmission for EUV wavelength.

In the keynote on November 6^th, Margaret Murnane, University of Colorado, Boulder, talked about coherent X-Rays from tabletop femtosecond lasers for applications in nanometrology. She discussed the ability to take high harmonic generation into the keV region and potential metrology applications in the Zepto (1E-21) and Yocto (1E-24) second physics!

Many excellent papers on multi-layer optics, modeling, BEUV, XUV sources and XUV Application were presented in the workshop and can be downloaded at the workshop’s website at www.euvlitho.com.

Advancing EUV Source Technology – 2013 Source Workshop (November 3-7, 2013, Dublin, Ireland)

Still a Tale of Two Paths: Highlights of Lithography Panel from SEMICON West 2013

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This year, I moderated the industry’s Lithography Panel during SEMICON West 2013 to a standing room only crowd. This interest in Litho was not a surprise as Litho is the key enabler of Moore’s Law.

Currently, both 193 immersion multiple patterning (193i MP) and EUV Lithography (EUVL) are the leading contenders for next generation lithography for the 10 nm node and below. The SEMICON West 2013 panel was great as we had speakers on both 193i MP (Nikon and Synopsys) as well as EUVL (SEMATECH and ASML). TEL talked about directed self assembly (DSA) applicable to both approaches. Nowadays all large workshops and symposia have separate tracks that focus on one or the other, so it was good to have both of them together. The title of the lithography panel was “Still a Tale of Two Paths” and both sides essentially talked about the merits of their own approach and issues with the other’s approach. (ASML makes both EUVL and 193i scanners while Nikon makes only 193i scanners. Synopsys supports both approaches via their modeling software and TEL makes tracks for both types of scanners.)

The lithography session underscored the issues that we are having in the search for next generation lithography (NGL) technology. There were “two elephants” in the room that all speakers tried to ignore: 1) the cost, complexity and possible technical impossibility of 193i MP below 10 nm, and 2) delays for EUVL due to lack of source power. The “elephants” were not discussed but their presences were very much felt. 193i MP is getting very expensive and complicated and may not be able to support patterning below the 10 nm node without additional complexity that chipmakers are not willing to adopt. EUV lithography right now still remains in the pilot line due to lack of adequate power. Hence, if scaling required by Moore’s Law is no longer supported soon, there will be an historic cost increase. Before I give my opinion on what I think may happen, let me first summarize what I heard from speakers and otherwise at SEMICON West 2013.

Talk Summary

Nikon titled its first talk “EUV Revolution Has Been Postponed” and then described how to move forward with 193i MP. It is the most probable route if EUVL is absent in HVM to provide resolution scaling, control of CD uniformity and overlay, and flexibility with design and cost. However, it is known that flexibility is reduced in MP with design restrictions and I pointed out during Q & A that Nikon’s comparison of MP with EUVL was not correct. The cost for 193i MP must include all equipment needed to support this technique. A scanner in MP is not just a scanner but a “large composite tool” that contains tools for deposition, etch, ash and metrology, and cost of all these must be included. However, in the absence of EUVL in HVM, 193i MP remains the main choice for chip makers.

In the next talk, Stefan Wurm of SEMATECH pointed out the readiness of EUV resists for EUVL introduction. EUV resists have been ready in part due to the testing infrastructure provided by SEMATECH and other consortia. His consortium is now focused on getting EUV mask blanks ready for HVM introduction of EUVL. The next set of challenges is to reduce pits, bumps and scratches in the substrate, focus on mask lifetime issues during cleaning and handling and reduce damage of backside coatings. In response to a question, Stefan pointed out that an EUVL mask should be able to go through 100 clean cycles, compared to today’s performance of 30 to 40 cleans.

Skip Miller of ASML presented data on the progress of EUVL scanners. He reported the shipment of two NXE3300B scanners to customers. He pointed out 30-70 percent lower cycle time via EUVL scanners compared to 193i based scanners and a large process window for 14nm node and below. He also pointed out that at 10nm node EUVL allows 50 percent scaling, while only 25 percent is possible with 193i MP. Even for grided SRAM chip makers will prefer EUVL, as limited overlay makes MP very difficult. For NXE3300B, throughput targets are 50-125 WPH, based on indications that his power vs. throughput curve will correspond to 68 – 250 W of source power. Currently 40-50 W of sources have been run with good dose repeatability of <0.5 percent for total run time of 20 hours, consisting of many hourly runs. I am not sure if runs were at 100% duty cycle. The target for these scanners in 2014 is for 70 WPH, and he expects 250 W source power to be achieved in 2015.

Mike Rieger of Synopsys described the role of electronic design automation (EDA) in enabling scaling via 193i MP. Scaling is possible without EUVL but will entail increasing cost, process complexity and design rules restriction. He pointed out need to keep cost under control for these options.

Ben Rathsack of TEL presented collaborations in the area of directed self-assembling (DSA), an emerging technology area that can help 193i MP as well as EUVL. He described his collaboration efforts in the area of defect reduction metrology via continued research with universities and consortia as well as chip makers.

The EUV revolution has not been postponed – it is delayed. The advantages of EUVL due to relaxed k1 and cost competitiveness are well known to chipmakers and what they want are tools that can support HVM, and those are delayed due to low source power.

Industry’s Position and Critical Questions

“Lithography is one of the highest priorities of our industry” and “EUVL must happen” were some of the comments we heard from consortia leaders at SEMICON West in other panel discussions in the meeting. These industry consortia have a combined budget of few hundred million per year and most of it is focused on EUVL. They have done a wonderful job of supporting mask and resist research. As they are funded by chipmakers and some government support, one can assume the view of the consortia is the position of chipmakers as well.

“Suppliers will deliver the EUV sources” has long been repeated by all consortia and they reiterated their position in this meeting as well. Currently consortia support all but EUV source projects, while EUVL continues to slip due to lack of adequate source power. In the end it is the chip makers who pay for the delay and the consortia reflect their strategy, so one wonders why this is so. Perhaps human psychology it is at work here. People do what they are comfortable doing and generally avoid trying new things unless calamity strikes. Mask and resist is something chip makers know how to deal with and have experience in developing these technologies. However, they do not have a team of plasma experts or source experts to guide them. Neither do consortia, so one has to go with what suppliers can provide. It is interesting that we are ready to bet the future of Moore’s Law rather than do something to hedge our risk. Year after year source power roadmaps slip, but no additional action is taken except to wait for new supplier source power roadmaps that we know will slip again.

Some point out to me is that the critical question today for the industry is, “If EUV Sources will be ready, will mask infrastructure be ready?” I agree that this is an important point and will address it below briefly. However, I think the most important question is, “What we will do with ready EUVL masks and EUV resists, if sources delay EUVL sufficiently to push it out further on roadmaps?”

EUVL mask infrastructure challenges (as detailed in the 2013 EUVL Workshop by Intel, Toshiba and GlobalFoundries) are certainly very difficult but do not look like showstoppers. They can be addressed with significant efforts and investment. What is lacking in the mask area is the consensus on key topics such as choice for masks for High NA tools, need for pellicles, how to inspect patterned masks during manufacturing, and need for various mask metrology tools during manufacturing, usage and maintenance of masks. Mask defect metrology tools are still not ready mostly due to lack of high brightness (not high power) EUV sources. In the upcoming 2013 Source Workshop, I expect more discussions and ideas presented on how to advance source technology for metrology sources.

My Predictions

I may be biased toward EUVL, but 193i MP will get more expensive and complex than EUVL at every next node, but EUVL is not yet ready so chip makers have no choice but to go with what is available. ASML announced in their presentation that two NXE3300B tools have been shipped and nine more are on their way to chipmakers. I think 50 W sources will be ready and working in NXE3300B sometime in 2014, corresponding to 43 WPH throughput. 100 W sources will be ready in 2015 or 2016 corresponding to 73 WPH. The readiness of 250 W EUV sources cannot be safely predicted, unless we see 100 W sources ready and have identified the issues to ensure that they are no showstoppers. I am not convinced that present approaches can get to 500 W sources. It is easy to put them on roadmaps, but delivering them is another question.

With 73 WPH, one can start with EUVL in HVM, as that cost is going to be better than for multiple pattering. Below 10nm nodes, the cost for 193i MP is high due to 4x or 8x patterning and for EUVL due to lower throughput due to low source power. I am not as concerned about 450mm transition for EUVL tools. EUV sources will have to deliver 2.5 x source power to keep the same throughput as 300mm tools, and that does not seem to be out of question by 2018, when the competition will be 4x patterning with extreme design rule limitation.

Another question to ask is how far you can scale with 193i MP and what are the cost implications. If EUVL is still not ready in few years and 193i MP is not feasible due to cost and complexity, what do we do? Both are projection lithography and rate of transfer of information from mask to wafer cannot be beaten by direct write techniques? This topic needs continued discussion.

Epilogue

Getting out of SEMICON for my next meeting, I was stopped by a colleague, who reminded me that EUVL was dead. Of course, he has been telling me the same thing since 2006, even while his own NGL approaches have gone bust. It appears that industry has been split into pro- and anti-EUVL camps for some time. It is becoming something like a religious war and there is less of a dialogue between these two camps. EUVL has been proven to be capable but it is delayed and will not be ready for HVM for a few more years. 193i MP is getting to be very complicated and expensive so chip makers have to have a backup, and that is EUVL. In the end it may be a mix of EUVL and 193i MP that will enable continuation of feature size scaling. The industry must continue to follow Moore’s Law and will do whatever it takes to keep up the scaling, so NGL will remain a hot topic for many years to come.

“Taming of Pele – the Fire Goddess”: 2013 EUVL Workshop Highlights

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Keynote talks

The sixth EUVL workshop was held June 11, 14 in Maui, HI with participants from the US, Korea, Taiwan, Japan, Europe and China.

The first keynote talk was delivered by Sam Sivakumar, who is leading the EUVL pilot line for Intel Corporation. He showed the yield data from his EUVL pilot line, obtained since his SPIE Advanced Lithography symposium presentation, that lead him to believe that there appears to be no fundamental roadblock to EUV achieving yield parity with 193i; any qualifying issues, he said, are not related to EUVL. In Sivakumar’s opinion, we must make progress on key issues of source power and mask defectivity in the next 1- 1.5 years. Although power delivery is getting better for the ASML’s NXE3100 scanner being used in his fab, source power remains the main impediment to EUVL being placed in HVM.

Tatsuhiko Higashiki (Toshiba) in the second keynote talk emphasized that at nodes 1x nm and below, non EUVL choices are not only unattractive – they are, in fact, scary! EUVL remains the only alternative, supplemented by double patterning (DP) and directed self-assembly (DSA). He also cautioned that in comparing EUVL to other lithography options, one needs to think about not only cost but also cycle time – something many comparisons do not do include in their cost of ownership calculations, even though increased cycle time is inherent in double patterning techniques and adds significant cost to that technology.

Panel Discussion: EUVL Readiness and Insertion Timeline

Following the keynote talks, panelists gave their opinions on what will be available to support lithography in the near future and related challenges. Sivakumar pointed out that EUV is currently targeted as the primary option for the 7nm node (2015 development, 2017 high volume manufacturing [HVM]) by Intel.

Sushil Padiyar of Applied Materials (AMAT) pointed out for the 12- 8nm nodes, choices are 13.5nm with double patterning (DP), 13.5 nm with hyper NA, or going with 6.x nm. The 13.5nm with DP option seems to be the best candidate, as its feasibility has been already demonstrated. The best guesses for 5-7nm are EUV with self aligned DP, and a combination of 193i multi-patterning and EUV. He pointed out the current positional accuracy for DSA is ~ 3nm, so the 193i /EUV combination will most probably need to be teamed with a self aligned (SA) process.

Tatsuhiko Higashiki (Toshiba) said that the semiconductor business will mature if lithography and mask cost reduction is not achieved. He believes that 9 inch masks are preferred by memory makers and EUV and DSA combinations will be the leading choices for lithography in the future.

Pawitter Mangat of GlobalFoundries pointed out the urgent need for EUVL readiness in the next two years. In his opinion, the industry needs to decide soon on masks for high NA scanners due to long lead times for developing this technology.

In a survey distributed to workshop attendees on EUVL readiness and technical challenges, most respondents predicted HVM insertion in the 2015-17 timeframe. Source power, mask defect and pellicle readiness were considered to be the leading challenges.

Workshop highlights

Workshop presentations focused on R&D topics, with the following highlights:

Greg Denbeaux of the University at Albany described his experimental design to study electron chemistry of secondary electrons. This setup will allow direct measurement of electron penetration depth and direct measurement of electron blur. Results will be used to improve resist modeling software to enhance our understanding of the functioning of EUV resists.

Grace Ho of NUK University, Taiwan described “Outgassing, Photoablation and Photoionization of Organic Materials by the Electron-impact and Photon-impact Methods.” The question of equivalence of resist outgas testing via electron beam vs. EUV photons is still not fully answered and in some cases, per her work, one can get different outgassing results for these two methods. As the basic physics of these two processes is different, this is not a surprise. As e-beam testing is frequently conducted to qualify new EUV resists, this topic needs to be continued to be evaluated to ensure the accuracy of assessments.

Cameron Moore of XEI Scientific described damage to various EUV specific materials under plasma cleaning. As dry plasma cleaning shows advantages over wet cleaning of EUV related contamination due to reduced damage to EUV components, we need to understand the effects of plasma cleaning on various vacuum components as well.

Yuriy Platonov of RIT described results of normal incidence collector optics for laser produced plasma (LPP) with average collector reflectivity of 54.3 percent. He also reported that for his Illuminator optics, the central wavelength is within +/-0.8 percent for all five optics sets. For collector refurbishment, he has demonstrated loss of only ~1 percent after two refurbishment cycles. Increased collector reflectivity and stable central wavelength is essential for increasing EUVL scanner throughput. Moving forward, we can see an increased demand for refurbication of normal incidence collectors for Sn Laser produced plasma (LPP) sources, so these were important results.

The meeting included six representatives from China, reflecting that nation’s increasing efforts in EUVL R&D. Prof. Yanqiu Li of Beijing Institute of Technology showed her modeling efforts for 0.3 NA EUVL scanners.

Performance of Cymer sources was presented in the US region review by Greg Denbeaux of U Albany. Sn LPP source now has power of 50 W with 0.5 percent stability for master oscillator power amplifier (MOPA) operation with prepulse. These results were from several continuous one-hour runs, and operation time is expected to rise soon. Denbeaux also presented results from SEMATECH and CXRO, among others, actively involved in EUVL related research. Overall, six EUVL regional overviews were presented from the US, Europe, Taiwan, China, Korea and Japan, demonstrating strong commitment in development of EUVL infrastructure and R&D. However, R&D for the most critical issue of HVM sources is still mostly absent due to lack of funding.

Padraig Dunne of University College Dublin (UCD) pointed out that 6.x nm emission from gallium (Ga), which is a liquid at 30° C, and germanium (Ge) is possible with electron temperature of 50-60 eV. This is significant as 110 eV plasma is needed for gadolinium (Gd), a material currently being considered for light sources for 6.x nm based lithography. As the temperature of Ge plasma is less than that of Gd plasma, it will take less laser power for Ge based 6.x nm sources. In addition, he suspects that conversion efficiency (CE) may be greater for Ga and Ge plasma than that for Gd.

Akira Sasaki of JAEA pointed out that Sn mist targets, an alternative tin delivery system being currently considered for Sn LPP sources, will require new modeling techniques and shared initial results of his modeling. Modeling work is certainly needed to ensure that maximum benefit for CE increase is obtained with this new method.

Energetiq, ETH Zurich (together with their spin-off company, Adlyte) and NewLambda shared their continued efforts on development of metrology sources for supporting mask defect detection metrology tools. Currently, Energetiq’s sources are used in the first generation of mask defect metrology tools under development. ETH Zurich has started a new facility (ALPS II) for further development of their metrology sources.

Addressing the topic of Mask infrastructure readiness, Pawitter Mangat of GlobalFoundries pointed out that zero defect printability is not same as zero defectivity on masks. He presented an excellent summary of mask challenges, actions needed to address them and new opportunities of thinner absorber and pellicle development.

Hiroto Kudo of Kansai University described molecular resists based on Noria derivatives (Oligomer derivatives) for EUV resists. A smaller line edge roughness (LER) as compared to current resists is expected in future through use of these polymers.

Yoshi Hishiro, JSR Micro Inc., shared a wide variety of improvements achieved by his company in EUV resists for 16nm node. One example is LER improvement via shorter acid diffusion length and development of EUV topcoat to remove out of band radiation (OOB). As OOB increases LER of printed features from 4.6 to 6.8nm, topcoat was able to bring LER down to 5.0nm. He showed that firm rinse reduces pattern collapse and decreases LER by 15 percent. In the results on use of DSA, an EUV+DSA approach allowed an increase in sensitivity of resist and improved the CD uniformity (CDU) of patterning, resulting in 14nm line and spaces (L/S) and 18nm contact holes (CH).

Takahiro Kozawa of Osaka University gave an excellent talk on stochastic effects in chemically amplified resists for EUVL. In his study, he determined that the amount of chemical reaction required at 16nm half-pitch (HP) increases by 74 percent compared to 60nm HP, and the optimum diffusion length for 16nm L/S pattern is ~ 10nm. Such fundamental work provides insight into the working of EUVL resists will enable development of newer resists to reduce LWR.

Take Watanabe of Hyogo University presented his analysis using synchrotron radiation (SR) based absorption spectroscopy for the chemical reaction analysis for EUV resist to explain the difference in resist sensitivity of various EUV resists from increase the acid yield.

Sushil Padiyar of AMAT presented results of 9nm CH and 8nm L/S via EUV DP. This work emphasizes the role of DP in the extension of EUVL.

Awards

The workshop attendees voted to award Best Oral Paper to Prof. Takeo Watanabe of Hyogo University for his invited presentation, “Recent Activities of the Actinic Mask Inspection using the EUV Microscope at Center for EUVL.”

The audience also posted decisions for the best poster papers, with these awards limited to students this year. First place went to SeongChul Hong of Hanyang University, South Korea for his paper titled, “Attenuated PSM for mitigating PSN effect in EUVL.” He is a graduate student of Prof. Jinho Ahn.

Second place poster award was given to Hung-M. Lin of NUK, Taiwan for her paper, “Quantitative Outgassing Study of Photosensitive Films upon Irradiation at 13.5 and 6.7nm.” She is a graduate student of Prof. Grace Ho.

Summary

EUV source power is showing progress but remains the main issue for HVM insertion. Without innovations, progress in this critical area may remain slow. Intel plans pilots in 2015 and 2017 HVM at the 7 nm node. Mask issues still require industry coordination, but the industry can be expected to address them with significant efforts. EUV DP, maybe with help from DSA, seems to be the choice for going below 10nm node and remains preferred by chip makers over 193nm immersion multipattern based approaches. EUV Resist is showing good progress.

Prologue – Taming of Pele – the Fire Goddess

Looking at the history of optical projection lithography, it appears we have learned how to manipulate photons well but not how to generate them effectively from hot plasmas for plasma machines that can operate 24 x 7 at a power level that we need in factories. We do not know if we can support the levels of power that we will need in the near future via our current approach. We need new ideas and we need to think out of the box to improve current technology and identify strong alternative candidates. It comes down to learning more about the taming of hot plasma.

In Maui, site of the EUVL Workshop, there are stories about the taming of Pele – mythical goddess of fire – who with burning lava (the geological version of hot plasma) created the islands of Hawai’i, with controlling force delivered by the surrounding sea. Hawaiian poetry also tells us that the the same force also tamed her:

Huaka’i ihola ‘o Pelehonuamea i ke kai Ko’olau

ma’e’ele ‘o Pele i ke kai kapu o Kamohoali’l

Pele, who gave birth to the reddish earth, flows like the ocean to Ko’olau

But she is benumbed by Kamohoali’I’s sacred seas.

[Hawaiian poetry and translation taken from Na Wahi Kapu o, a beautiful book of photographs of Maui and poetry by Kapulani Landgraf, Native Books, 2003.]

As we lithographers struggle to transform hot tin plasmas into useful servants that will help us print circuits night and day, let us be guided by the tenacity of the Hawaiian seas, which tamed the seemingly uncontrollable energies of Pele herself!

2013 International Workshop on EUVL: Maui, Hawaii, June 10-14, 2013

List of Leading EUVL Technical Challenges

This year, based on the feedback of technical steering committee, we have created a list of leading technical challenges as suggested topics to be addressed by presenters in the 2013 EUVL Workshop. We encourage authors to review this list and choose one of the specific topics for their papers in the area of source, mask, optics, resist and BEUV.

Source

Power scaling for current Sn based DPP and LPP sources

Physics of high power plasma and non-plasma sources (100 W -1000 W)

High brightness EUV sources to support mask metrology

BEUV Sources

Source requirements for high NA scanners for 10 nm and smaller nodes

Source power requirements for 450 mm wafer scanners

Optics and Contamination

High NA optics manufacturing

High NA scanner design

Thermal management for LPP normal incidence collectors

High reflectivity BEUV optics

Source debris management strategy

Carbon contamination and low contamination materials and process

Strategies for optics contamination control

Mask

Strategies for low defect mask blanks

Mask technology to support high NA scanners, including transition to 9 inch masks

Mask defect metrology: New approaches

Mask pellicles

BEUV (6.x nm) masks

Resist

Meeting simultaneous requirements for LER, sensitivity and resolution for EUV resists

Post-processing approaches to reduce LER

Resist materials and process for 1x node

High absorption resists

Resists materials for BEUV (6.x nm)

Bring me the rhinoceros: A Review of the 2013 SPIE Advanced Lithography EUVL Conference

Vivek Bakshi, EUV Litho Inc., February 28, 2013

Technical Highlights

The 2013 SPIE Advanced Lithography EUVL Conference started with many of us looking forward to Sam Sivakumar’s kickoff presentation on results from Intel’s EUVL pilot line. Sivakumar pointed out that printing vias and cuts is the real advantage of EUVL over 193nm immersion based lithography (193i). In order to investigate the feasibility of extreme ultraviolet Lithography (EUVL), his group produced the same 22 nm products that Intel manufactures using 193i scanners. Products made using EUVL demonstrated equal or better performance, and most importantly lacked EUV-specific defect nodes. He noted source power and particles added to the mask during manufacturing as two major challenges for EUVL. The source power issue is not new, but particles on pellicles can make EUVL manufacturing prohibitive.

Surprisingly, in the third paper of the session, ASML presented elegant results on development of EUVL pellicles – with 86% transmission (against 90% needed) that meet imaging and mechanical requirements and only need some scaling. These pellicles have almost no effect on imaging, unless the particles are larger than 1 micron, and can be fully cleaned as well. Also, if the pellicle breaks by accident, ASML said they can clean the mask using a dry clean process.

Scanner Status by ASML

ASML is essentially an integrator and their update was full of continuous improvements. NXE3300B is a solid improvement over NXE3100. In their presentations, one sees ASML’s style of making innovation and improvement part of business as usual. What I like the most about ASML is that they do not play the "blame game." They never say in public, "if sources are ready, we will have the tool ready." If they become an EUVL source supplier through their acquisition of Cymer, we will see if this attitude changes.

The most important information that I got out of ASML’s presentation was how source power will relay to throughput, a relationship that will help us figure out the progress of EUVL. Scanner stages are ready for 100 wafers per hour (WPH) tools and if mask fields need to be split for higher numerical aperture (NA), I expect that they will be able to turn this knob a little to partially compensate for throughput loss. NXE3100 scanners are supposed to have a throughput range of 6 – 60 WPH and NXE3300B scanners of 50-125 WPH. The ratio of source power to WPH will increase from about 1 now (10 WPH for 10 W with NXE3000) to 1.25 (43 WPH at 55 W for NXE3100 in the near future). For NXE3300B, the ratio will rise to 1.6 (80 W for 50 WPH) and then to 2 (250 W for 125 WPH). I expect this to be due mostly to higher dose requirements, plus a few other factors such as availability and reduced scanner throughput at higher NA.

Source Technology Status

Some progress has been made, but a large gap remains. 40 W in 2014 from Cymer looks promising. I am also somewhat optimistic about 60 W with 100% duty cycle (DC) and long term operation by the end of next year, at least in non-integrated sources.

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.

New Technical Solutions

The conference presented a large number of solutions for EUVL challenges, and several were good news:

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!

New Challenges

The conference also delivered a list of new EUVL challenges. I already mentioned the challenge of particles added to the pellicles. As EUVL is readied for smaller nodes with high NA optics, the angle of incidence on the mask is going to increase. Options to address this issue include 1) breaking the exposure field into two or four parts, 2) adding two additional mirrors to the scanners and 3) increasing mask size from the current 6 inches to 9 inches.

Winfred Kaiser of Zeiss summarized various technical options for the industry. In his paper, he suggested "going with 6 inch masks with quarter field and 8x magnification" as the best option for 0.5 NA. However, breaking the pattern into many parts will further downgrade the throughput. Harry Levinson of Global Foundries offered "6 x magnification with 9 Inch masks" as the best solution for 0.5 NA. He also stressed the need to continue working with 6 inch masks as long as we can. Going to a larger mask means upgrading mask infrastructure tools to handle 9 inch masks, which will be very difficult and could take a couple of years. However, this approach may involve changing only the handling part of tools, while leaving the key technical core of the tools the same. In any case, moving to 9 inch masks will be painful for mask makers and we can expect to hear more on this topic from them.

Best Papers

The following four papers seemed outstanding to me:

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.

Other Observations

Despite moving the conference to a larger venue, there was still standing room only for key talks.

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.

Summary of HVM Readiness of EUVL

Hynix presented their 2009 cost of ownership (COO) calculations for various next-generation lithography (NGL) techniques. They indicated that COO for an EUVL scanner at about 35 WPH would be the same as COO for double patterning. They said the COO equation has not changed much since 2009, although I think it will change some for smaller nodes, since for them higher source power will be needed.

I expect 40 W sources in the field next year. I will be delighted if NXE 3300Bs are in the field by the end of 2014 with a source as well, but I am not sure if 80 W sources will be ready by then. I do not think we will have 100 W sources in field before 2015. However, I do not want EUVL HVM insertion to shift from 2014 to 2015, so I can win my bet with Lithoguru Chris Mack and claim his Lotus as my own!

Bring Me the Rhinoceros

Last month, I decided to take a three-month introductory course on Zen Koans in the local Zen Monastery. (For those not familiar with Buddhism, a koanis a question without a real answer, and is aimed at getting the student to think deeply.) The first Koan, which students can study many years in a traditional Zen monastery, is called the Mu Koan. It goes like this:

A monk asked his Master ZhaoZhou, "Does a Dog have the Buddha nature, or not?"

Master ZhaoZhou replied, "Mu" (Japanese for No).

One of the central ideas in Buddhism is that all things have Buddha nature, so this answer does not make sense. A pupil is supposed to work with this Koan for a long time. There is no standard answer and the master judges each pupil’s answer differently. I had the homework of applying this Koan to whatever was happening to me during the week, and report back what I learned. As I was at the SPIE Advanced Lithography conference, I decided to rephrase the Koan as "250 W is needed for HVM adoption of EUVL and EUVL will be in HVM in the next two years. Does that mean we will have 250 W sources ready?" Having spent over ten years in the EUVL source business, I think I will answer my own Koanwith a Mu, while still acknowledging EUVL as the leading technology in the next two years. I will continue to give a dialogue on this topic in my blog in coming weeks.

I would like to leave my readers with the second Koan from my class called "Bring Me the Rhinoceros," and invite you to contemplate how it relates to the "Art and Science of Making Computer Chips."

One day, Master Yanguan called to his assistant, "Bring me the rhinoceros fan."

The assistant said, "It is broken."

Master Yanguan replied, "In that case, bring me the rhinoceros."

Second Koan used here is from a book by John Tarrant titled "Bring Me the Rhinoceros," Shambhala Press, 2012.

Further comments on physics and engineering of EUV sources

I got good bit of feedback on my last blog in which I discussed the differences between physics and engineering of EUV Sources, and the implications of that difference. I was glad to see that it generated some re-evaluation of current thinking (as intended) and now would like to clarify few points.

First is the supplier commitment. One can have lots of great technical options backed by beautiful physics, but if there are no suppliers to turn ideas into commercial products, technology will go nowhere. EUV source technology will succeed as it has three large suppliers, each with current business experience in supplying light sources for scanners. In the end, we may not have this many suppliers due to business and/or technology consolidation, but right now we do. For EUV sources for metrology, there is an even larger number of potential suppliers who are working to find a way to meet industry requirements. With this backing and competition among suppliers to outperform one another, we ought to see success.

The real question is whether scanners that can produce ~40 wafers per hour (WPH), which I expect to be ready by 2014, will deliver cost of ownership (COO) sufficient to convince leading chip-makers to switch from 193nm based technology. The challenge is to estimate the point where the COO of EUVL will cross that of 193nm, making it more cost effective technology. Will it be at 15nm or 7nm? What product, what wafer size? I do not have sufficient information to make this prediction right now, but I expect some acceptance of EUVL in high volume manufacturing (HVM) by the end of 2014.

Just because a technology cannot scale up in power does not mean that it will poorly serve EUVL in the process of development. Last week I gave an example of synchrotrons. They have provided low throughput printing to support development of current EUVL technology, and will continue to do so for future versions of EUVL. So let us continue that very wise investment! Supplier Energetiq has 10W source technology that has aided EUVL very well so far. Present designs may not scale up to the required brightness for mask defect metrology tools, but this supplier is looking at new physics for scaling, as they demonstrated in the last two Source Workshops in Dublin.

So it is a matter of realizing what cannot be done with present physics, and finding new ways to achieve scaling. We have seen >5% conversion efficiency and high debris mitigation techniques at low rep rates. Let us see how far these approaches can scale up. If they do not (over a reasonable period), then we need to quickly pick up another potential solution from a host of possibilities. These will become available to us if we continue to look for new physics, including development of new materials and chemistry. We can research the physics of EUVL with a very tiny fraction of what we have spent on engineering development of the technology. I still believe in the power of innovation and competition to help us move forward, but for this effort we must engage universities, national labs and independent research organizations to generate new ideas leading to new solutions. Only then will we be in a position to solve the persistent problem of low throughput in EUVL scanners.

EUV source roadmaps: Physics vs Engineering

I am frequently asked by my consulting clients and colleagues when EUV sources will be ready to support high volume manufacturing (HVM) of semiconductors. It is a difficult question to answer, partly because readiness metrics have been a moving target, or the latest performance data is not very clear. For example, how many wafers per hour will make it cost-effective to adopt EUVL over the alternatives of triple or quadruple 193 nm immersion lithography for a given product at a specified feature size for 300 mm or 450 mm wafers? Is the latest data in pulse mode and integrated, and for how long an operation?

Even if the targets are clear, there is still uncertainty because source progress has not increased as much as predicted by supplier roadmaps. Last week in a press release (see http://optics.org/news/4/1/26), ASML was quoted as saying, “40 W sources are providing good dose controls and will be used in NXE3300B to be shipped in 2013. 60 W sources have been successfully tested with no sign of performance degradation from debris.” But can we take these numbers at face value and expect sources to be ready as promised in the supplier roadmaps?

As EUV source technology has been the main reason for the delay in EUVL for HVM, it is worthwhile spending some time pondering why this is so and what we know. When I look at what I know about source technology status, my only data is what is shown at industry conferences by source suppliers or chip-makers. Most presentations are about achievements which have been significant, but not sufficient. Unfortunately, no one talks much about what is not working, except to say "We’ll fix the problems and here is our roadmap."

Given the many delays in HVM-ready EUVL, we should know by now that looking at roadmaps and press releases may not be the best way to predict technology readiness. Presumably, customers who own the latest EUVL scanners get confidential updates on source readiness so they have a better idea of what needs to be fixed. But these are chip- makers and not source experts, and their information may end with predictions from roadmaps which I suspect are very close to those shown in public by source suppliers. Of course, I have no clue about what additional information source customers may have, except that all of them list EUV source as the #1 problem in their public presentations.

One of the most repeated statements I hear on this topic is, “The physics is known and it is just an engineering challenge.” In other words, it is all about figuring out how quickly solutions can be engineered. I tend to disagree with this statement, and here’s why:

Let’s start by defining physics and engineering. Per Webster’s dictionary, “Physics is science dealing with the properties, changes, interactions of matter and energy,” while “Engineering is concerned with putting scientific knowledge to practical uses and planning, designing, construction or management of machinery.”

In other words, something is not physically possible if the physics is not there. Even if something is possible at low repetition rates, it does not mean that physics will support power scaling without near-impossible engineering. Figuring out physics is like seeing our target in a forest. Yes, we can see it, but can we build a freeway to it for 24 x 7 traffic? Take nuclear fusion as an example: the physics is there, but we have yet to power a light bulb from a fusion reactor after more than 50 years of research. At least EUVL scanners are in the field and are printing wafers every day for process development. So how large is the remaining engineering challenge for EUV sources? Isn’t finding that out the real challenge in EUVL?

This assertion that "only engineering challenges remain for source technology” is usually backed by low to very low repeatable data, e.g.,: “Yes, we have 70 W and we got this for 10 s in standalone mode at 10% duty cycle, but it means we know the physics and all we have to do is to engineer this result into a 24 x7 product that can be integrated into a scanner.”

You may remember that Xe discharge produced plasma (DPP) sources worked very well but never went beyond 5 W, once we finally figured out that collectable power would never exceed 5 W due to etendue limits (i.e., one can collect light only from a very small part of the plasma). In addition, it is not possible to mitigate all the heat that higher power produces in Xe DPP sources. So we had to use different physics by changing the fuel to tin, which was easier to engineer for power scaling using DPP and eventually source suppliers have put more focus on tin based laser produced plasma (LPP). But LPP sources utilize different physics than DPP to heat the plasma, so we had to use slightly different physics to create new systems of LPP Sn. These systems were initially based on 1 micron (mm) lasers and today we are using 10 mm lasers, according to results from lab physics experiments. Now the focus is on other aspects of Sn LPP to achieve HVM targets, including 1) changing of the delivery system from droplet to mist targets, and 2) pulse shaping and pre-pulsing to increase conversion efficiency. With each new twist, slightly different physics are added to the mix. So I am not sure if Sn LPP will scale up without our introducing new designs based on somewhat different physics, such as going to ion beam targets or something else.

So the question comes down to this: do we have a physics solution that we can engineer? If so, how do we assess that solution? Surprisingly, the size of the machine is not necessarily an indication – we cannot say DPP is superior to LPP because it is more compact. Synchrotrons, which are rather large machines, very reliably generate EUV photons on 24×7 time scale. In fact, their contribution to EUVL development has been so immense, I do not know where we would be without them. In addition to their size, coherence and cost have been raised as issues for these very reliable sources of EUV photons. Can we reduce the size/cost to make synchrotrons a potential source for fabs? Have we looked at them seriously enough in the light of current source technology, recent developments in technology and our future needs? Not really, in my opinion, and we need to do this for both plasma and non-plasma based sources.

In short, we have not quite figured out the physics for EUV sources that can be quickly scaled up in power and engineered to make products. Some will disagree with me that this is not so for 100 W sources, but I think I am probably right for 250 W or 1000 W EUV sources – which will be needed as we go to higher NA scanners, smaller printed features and 450 mm wafers.

Doing more with Moore’s Law: Status report from 2012 Source Workshop

The 2012 Source Workshop was held Oct. 8-11 in Dublin, Ireland, in the Clinton Auditorium on the campus of University College Dublin. This is the industry’s largest annual gathering of EUV and soft X-ray source experts, who took the opportunity to discuss the latest results from their labs.

A keynote talk was given by Akira Endo of Waseda University and the HiLASE project. He focused on identifying technology areas that need immediate development to enable current sources of 100 to 250 W. These areas include droplet generation at 150 kHz via electrostatic acceleration; 500 W solid state lasers with picosecond pulses and mJ energy for pre- pulse; and the ability to focus on 10 µm droplets. He also outlined a roadmap for 1000 W source at 13.5 nm and 6.x nm.

Dr. Endo also identified other important focus areas, including:

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.

Vadim Banine of ASML (the EUVL scanner-maker that recently acquired EUV source supplier Cymer) outlined the state of source technology and a path to 1000 W sources. He also listed top areas that need R&D work to enable power scaling for sources utilizing discharge-produced plasma (DPP) and laser-produced plasma (LPP). Describing the current status of tin-based LPP and DPP sources, Dr. Banine said Sn LPP has demonstrated 50 W average power at 80% duty cycle, along with scaling to 158 W at 3% duty cycle.

As for Sn DPP, Jeroen Jonkers of Ushio said 74 W power is possible today at intermediate focus (IF) in burst mode for a one-hour run. Dr. Jonkers elaborated on this data and presented a development area that may allow DPP to scale to 250 W. Konstantin, et al. presented results on ISAN’s new DPP design to potentially scale up to even higher power than Ushio’s design. Such concepts need to be further investigated to enable power scaling of DPP-based sources.

Although the roadmaps for plasma sources are rather clear, we know that the goals for 1000 W scaling of EUV sources are not easily attainable. After all, suppliers are still working hard to ready 100 W sources with reliable performance.

It was noted in various presentations that scaling of power for beyond EUV (BEUV) sources may be even harder. The potential of free electron laser (FEL) based sources for delivering 1.7 kW of BEUV photons at 6.x nm was discussed in a paper by Diana Tuerke of Carl Zeiss. Source design was presented for a 3 MHz, 1.7 kW, and facility costing 200 M Euro, with annual operational cost of 20 M Euro.

Coherent sources are typically not used for lithography due to large loss in the process of making the beam incoherent. However, it was very interesting to hear Zeiss mention that they developed an invention allowing them to use all coherent light without loss! This was exciting news indeed, as it may further open doors to the feasibility of coherent sources for lithography.

Highlights of workshop

Ulrich Mueller of Carl Zeiss presented the source requirements for mask defect AIMS tools. For their tools, high source stability is required : <0.3% for position and <3.5 % for energy in pulse to pulse. Sources will need brightness of > 30W/mm²sr with a target of 100/mm²sr. Currently they have sources of 8 W/mm²sr for tool development.

Klaus Bergmann of ILT showed the champion data for his Xe DPP source for metrology, with brightness of 21 W/mm²sr, operation frequency of 3.3 KHz, conversion efficiency (CE) of 0.35 and source radius of 155 mm for 20 kW input. He sees potential scaling to >50 W/mm²sr with a maximum limiting value of 71 W/mm²sr.

Steve Horne of Energetiq proposed a 100 W/mm²sr high frequency xenon Z-pinch DPP source for mask metrology. He thinks that the physics can be tested in six months – and if successful, the system can be built within 2 years. Cost of this new system would be similar to that of the present system in the field.

Paul Sheridan of NewLambda Technology described his LPP source as having a CE >1% at 45 degree viewing angle, and source size of 250 x 400 mm² at intermediate focus (IF). For 1,000 hours of operation, he measured 80 W/mm²sr brightness. For his source, at stability at IF is 7% in position and 8% in size.

Larissa Juschkin of RWTH presented theoretical calculations for estimating source brightness requirements for EUV Microscopes.

Sergey Zakharov of EPPRA revealed a "plasma lens" design for the capillary discharge Xe DPP source. The workings of this discharge produced focused EUV beam had been the subject of speculation in the past, and Sergey finally described it for us!

Igor Makhotkin from FOM Institute DIFFER provided the results of using BEUV optics to support EUV lithography at 6.x nm. Reflectivity for LaN/B based multilayer mirrors, the material of choice for BEUV optics, was reported to be 53.6% for normal incidence and 175 periods of multilayers. So far, this is the highest experimental value reported for these mirrors.

Leonid Sjmaenok of PhysTeX presented Zr filters with one pass transmission of 84% for 25 nm thickness and 80 mm aperture frames. Such filters, he noted, now have no more than a 2 degree max deviation from flatness. These filters will be key elements key to controlling out of band radiation and debris in sources.

For BEUV lithography sources, Takeshi Higashiguchi of Utsunomiya University proposed a mixed complex target of Gd and Tb for 6.x nm photons. He proposed punch out targets (mist) for Gd, as droplet generation is very difficult due to the high melting point of Gd. He also suggested phosphorus as a candidate material for BEUV sources.

Soft X-ray (SXR) sources

The Workshop has been successful in bringing together a large gathering of source experts by inviting technologists from the EUV (13.5 nm), BEUV (6.x nm) and Soft X-ray (~ 1- 50 nm) regions. Due to a lack of funding for research on EUV sources (despite its being the #1 issue in EUVL), many source experts now work on non-lithography applications of EUV and SXR sources. In widening the scope of the Workshop, we were able to attract EUV source experts who could give us good insights on EUV source development, even though their work may not be focused on lithography.

Two of the keynote presenters for the Workshop were global leaders in soft X-ray source technology. They focused their talks on SXR sources and their potential for non-lithographic applications. Prof. Jorge Rocca of Colorado State University talked about desktop EUV laser and its applications. Prof. Alan Michette of King’s College London discussed biological applications of soft X-ray sources.

The Workshop also had many other excellent, oral presentations and poster sessions on SXR sources and their applications.

M. Selin of KTH Royal Institute revealed a high-brightness liquid-jet laser-plasma source that enables 10 second exposure for water-window cryo microscopy. He claimed that its brightness of 1.5 x 10¹² photons/ (second x mm² x mrad² x line), is the highest operating in a lab today. He said the 10s exposures that are now possible with the new system make this microscope comparable to microscopy based on early synchrotron sources.

James Evans of Pacific Northwest National Lab and University of California at Davis presented "Whole Cell Cryogenic Soft X-ray Tomography" with a laboratory light source from Energetiq. He pointed out that soft X-ray tomography of whole cells is now available commercially and said he is working on improved zone plates to get better resolution. A new standalone, higher brightness non- plasma source with a small footprint is planned. I think such non-plasma based sources may have potential EUVL applications, and I plan to investigate the feasibility of such sources.

Summary

The 2012 Source Workshop succeeded in its objective to bring together more than 80 source R&D experts for discussions and updates. We came away with a list of topics that need focus for scaling sources for current and future generation technology. The virtual lack of sales pitches may have induced participants to let down their guard a bit among colleagues to acknowledge the problems we still face today, while celebrating the progress made since last year’s Workshop in Dublin. The proceedings of this workshop are available for download at www.euvlitho.com. If your business is EUV or SXR sources, you won’t want to miss our next Source Workshop on Nov. 4-7, 2013, in Dublin.