At 8 am on Monday, the conference begins with opening remarks and the plenary session.<\/p>\n
Bill Arnold and Harry Levinson won a \u201cSpecial Contribution Award to the Art and Science of Lithography\u201d for their two-part paper \u201cFocus: the Critical Parameter for Submicron Lithography\u201d published in 1988.\u00a0 I read and cited those papers frequently over the years, and I still recall the clarity of their arguments and the insightfulness of their approach.\u00a0 Without a doubt, these were milestone papers in the development of modern microlithography thought and practice.<\/p>\n
Dr.\u00a0 Andreas Erdmann of the Fraunhofer-Institut f\u00fcr Integrierte Systeme und Bauelementetechnologie IISB (Germany) became our newest fellow.\u00a0 Kurt Ronse of Imec was also promoted to that rank, but he was unable to attend the symposium this year and will receive his recognition at a later conference.<\/p>\n
The symposium awards were completed when Yan Borodovsky, recently retired from Intel, become the 13th<\/sup> Frits Zernike Award winner.\u00a0 Congratulations to all of them!<\/p>\n Some years, the plenary speakers are chosen from outside the lithography community to bring perspective and breadth to the opening of the symposium. \u00a0This year, we heard from three of our own. \u00a0Harry Levinson of GlobalFoundries gave an historical perspective on research and developments in lithography.\u00a0 He mentioned the low uptime (60-70%) of early excimer lasers and the immaturity of deep-UV resists (especially sensitivity to airborne contaminants) as motivations for the extension of i-line lithography in the early 1990s. \u00a0The obvious analogy to EUV lithography was left unstated.\u00a0 Two good quotes from Harry\u2019s talk:<\/p>\n \u201cComputer programming became a required skill for leading-edge lithography\u201d (discussing the importance of computational lithography).<\/p>\n \u201cIssues at the molecular scale will need to be addressed to realize the optical resolution \u201centitlement\u201d of EUV lithography.\u201d<\/p>\n Richard Gottscho, EVP of Lam Research, discussed deposition and etching and how those technologies will evolve to improve control in the age of multiple patterning.\u00a0 In particular, the move towards atomic layer deposition (ALD) and now atomic layer etching (ALE) are greatly improving uniformity and control, though at the cost of processing speed.\u00a0 These processes work by saturating the wafer with a monolayer of reactive species, which then is reacted to produce the deposition or etching.\u00a0 This saturation is self-limiting and so removes many process variables from being significant factors in the process rate, easing both the process development and process control burdens.<\/p>\n Tony Yen of TSMC gave a very nice historical perspective on the development of EUV, one that he believes has put EUV lithography on the \u201ceve of manufacturing\u201d.\u00a0 The very first demonstration of EUV lithography (called soft x-ray lithography until 1993) was by Hiroo Kinoshita in 1986, followed soon by Obert Wood and his many collaborators at AT&T Bell Labs. \u00a0Significant government and industry funding began in 1992 and the EUV LLC was formed in 1997 to pool the growing industry and government efforts in EUV. \u00a0With the completion of an important prototype tool, the 0.1 NA Engineering Test Stand, development work on the exposure tool shifted to ASML.\u00a0 They produced their alpha-demo tool (ADT) in 2006, the NXE:3100 in 2011, and shipped the NXE:3300 in 2013.\u00a0 Tony finished his historical description by saying that their first NXE:3350 has recently arrived at the TSMC loading dock.<\/p>\n As for the current status of EUV lithography at TSMC, Tony confirmed that the plan of record is to exercise EUV at the 7-nm node and use it in production at the 5-nm node.\u00a0 The remaining problems include mask blank defectivity (currently about 20\/blank, too high to use for metal patterning, but maybe OK for contact holes) and the still unproven pellicle solution.\u00a0 Resist sensitivity in now closer to an acceptable range (between 25 and 30 mJ\/cm2 for lines and spaces and between 35 and 40 for contact holes), but with unacceptably high linewidth roughness (LWR).<\/p>\n The invited talks at the EUV lithography conference gave some further perspective from Intel and Samsung on the readiness of EUV for high volume manufacturing (HVM).\u00a0 Apparently, one of the big issues last year was the reliability of the tin droplet generator, part of the EUV light source.\u00a0 Both Intel and Samsung were very pleased about progress on that front, so that source reliability has reached 70%, enough to do real engineering work with the tools, though not enough for manufacturing.\u00a0 Intel reported end-of-line yield loss due to particles added to the mask during use.\u00a0 They saw an average of one killer defect added per 20 reticle-stage-load cycles, a level that makes manufacturing impossible without a pellicle.<\/p>\n Seong-Sue Kim also reported on the mixed successes and failures of EUV at Samsung in the last year.\u00a0 They reported 3 particle adders on the mask for every 10,000 wafers printed, a number too high by an order of magnitude at least.\u00a0 But more disturbing was his report of mask damage after 40,000 wafer exposures using the 80W source.\u00a0 Blisters formed within the mask multilayer, some of which popped.\u00a0 Not only was the mask ruined, but contamination travelled through the optical system and made its way to the wafer.\u00a0 I worry that such chemical reactions induced by the energetic photons of EUV light will behave nonlinearly with intensity.\u00a0 How bad will this become when using a 250W source?<\/p>\n On the resist front, everyone is talking about metal oxide resists for EUV.\u00a0 For many years now, Inpria has used metal oxides as an EUV resist that could deliver high resolution and low LWR, but at doses of 80 mJ\/cm2 \u2013 too high to be practical given the realities of low EUV source power.\u00a0 The push to get sensitivities of these resists into the 30 mJ\/cm2 range has now been successful but, surprise!, the LWR is much worse.\u00a0 It seems that all attempts to defy the laws of physics through chemistry continue to be unsuccessful.\u00a0 Yet, since we do not have a complete understanding of all aspects of LER formation, the physical limits of roughness are unknown.\u00a0 If other problems can be solved, metal oxide resists may be the way to go.<\/p>\n Indulge me, if you will, on another rant.\u00a0 Thirty years ago I would come to this conference and see papers by resist companies that all had a familiar pattern:\u00a0 here is our new material, here is a cartoon of the mechanism of why it will work, and here are one or two SEM images of high resolution patterns.\u00a0 Success is then claimed.\u00a0 What we learned painfully over time is that high resolution demonstrations of a material are a necessary but not sufficient condition of success.\u00a0 The reason is the simple fact that a very good aerial image can produce a decent image in a mediocre resist.\u00a0 The projected image maters!\u00a0 So how do you know if your material is any good?\u00a0 You have to consider the development contrast of the resist and how it affects process latitude.\u00a0 A high image contrast can produce a good single image in a low contrast resist, but cannot produce good exposure latitude.\u00a0 One needs to compare exposure latitude (or better yet, the focus-exposure process window – see the mention of the Arnold and Levinson papers above) to the entitlement process latitude (that which could be obtained from an ideal, infinite contrast resist), or at least to the current resist of record.\u00a0 This lesson was learned and over the next 20 years resist contrast was systematically raised until it become sufficiently high.\u00a0 Today, we almost take high resist contrast for granted (at 193 immersion, at least).<\/p>\n It seems that this lesson has been forgotten.\u00a0 Have we experienced high-contrast resists for so long that we have forgotten how a low-contrast resist behaves?\u00a0 Have we forgotten how to measure or characterize resist contrast?\u00a0 I almost never see a process window for an EUV resist.\u00a0 I never see a comparison of the exposure latitude to the NILS (or the best exposure latitude possible).\u00a0 People compare resists printed at different numerical apertures without considering the differences in the aerial images that exposure them, or don\u2019t even mention the conditions at which the patterns were imaged, as if a 20-nm pattern is a function of the resist alone.\u00a0 We need high sensitivity EUV resists.\u00a0 We need low LWR.\u00a0 But we also need high resist contrast.\u00a0 Let\u2019s start measuring and reporting that, please.<\/p>\n One of my favorite quotes of the day: \u201cI never thought they would discover gravity waves before EUV made it into manufacturing.\u201d\u00a0 – Kenneth Goldberg (Note:\u00a0 over $1B was spent over 40 years on the gravity wave effort.)<\/p>\n And my favorite mixed metaphor: \u201cWe have only scratched the tip of the iceberg.\u201d \u2013 Alex Vaglio Pret<\/p>\n","protected":false},"excerpt":{"rendered":" At 8 am on Monday, the conference begins with opening remarks and the plenary session. Bill Arnold and Harry Levinson won a \u201cSpecial Contribution Award to the Art and Science of Lithography\u201d for their two-part paper \u201cFocus: the Critical Parameter for Submicron Lithography\u201d published in 1988.\u00a0 I read and cited those papers frequently over the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-478","post","type-post","status-publish","format-standard","hentry","category-microlithography"],"_links":{"self":[{"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/posts\/478","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=478"}],"version-history":[{"count":2,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/posts\/478\/revisions"}],"predecessor-version":[{"id":480,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=\/wp\/v2\/posts\/478\/revisions\/480"}],"wp:attachment":[{"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=478"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=478"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lithoguru.com\/life\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=478"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}