LITHOGRAPHY Extreme Ultraviolet Lithography: status and challenges ahead Vivek Bakshi, Jerry Cullins, N.V. Edwards, Kevin Kemp, Pat Marmillion, Jan-Peter Urbach, Thomas White & Obert Wood, International SEMATECH, Austin, TX, USA focusing architectures that are similar 1997 the EUV Limited Liability ABSTRACT to those found in current optical Corporation (EUV LLC) consortium The purpose of this article is to exposure tools. was formed and eventually expanded to provide an update of the current According to the International include Intel, AMD, Motorola, Micron, status and most recent advances in Technology Roadmap for Semi- Infineon and IBM. From 1997 to 2002, each of the specific areas of sources, conductors (ITRS), EUVL will be the EUV LLC program at Lawrence masks, optics, photoresists and targeted for application at the 45-nm Berkeley, Lawrence Livermore, and microexposure tool for extreme lithography node, although recent plans Sandia National Laboratories achieved ultraviolet lithography. The article is by some IC manufacturers indicate its many significant milestones, including therefore organized according to implementation at the 32-nm node. demonstrations of 100 nm lithography these topics, with a brief discussion Based on International SEMATECH’s over a 24 mm × 32.5 mm scanning of the issues surrounding each, the (ISMT’s) current estimates of industry field using a fully integrated 0.1 current development status, and timing, volume production at this node numerical aperture (NA) exposure future outlook. A sustained study is likely to begin in approximately system known as the engineering test on the development of industry 2009.While exposure-tool suppliers are stand (ETS). infrastructure for EUVL is underway developing tools to be ready to meet Meanwhile, significant advances in at International SEMATECH. Although this demand, it is just as important that EUV technology were being made significant challenges remain, the supporting infrastructure also be under the Association of Super- progress is being made on various developed in time. Advanced Electronics Technologies technical fronts. In the case of EUVL, this means (ASET) consortium in Japan, and the that mask and mask blanks must be Microelectronic Developments for commercially available at production European Applications (MEDEA+) and specifications, EUV photoresists must PREUVE consortia in Europe. Today, Introduction be available with adequate resolution, exposure tool development is in Background sensitivity, line-edge roughness and progress at the “big three” of ASML, outgassing performance, and in-fab Extreme ultraviolet lithography Nikon, and Canon, while Exitech in (EUVL) is the exposure technology of support items such as reticle handling, Cambridge, England is building choice to succeed optical lithography inspection and storage must be readily microfield tools for multiple customers. for volume semiconductor manu- available. In addition to focused projects Six or more companies are in a race to facturing at feature sizes below 50 nm. designed to yield solutions for each of develop high-power EUV sources that EUVL uses radiation at 13.5 nm from a the above items, International will find their way into production plasma source to project an image using SEMATECH’s EUVL program is also exposure tools. EUV-mask and mask- reflective optics and a reflective mask. directed at supporting the development blank technology is being developed Compared with competing next- of key enablers to identify and resolve in the US, Europe, and Japan, generation lithography (NGL) options, remaining critical issues for the and International SEMATECH is such as X-ray proximity, electron technology.These include achieving establishing an advanced EUV Mask projection, ion projection and direct- reliable high-power EUV sources, and Blank Development Center and Resist write, EUVL offers the solution that is mitigating the degradation of optical Test Center in collaboration with the most likely to meet the most important components. Standards also play an University at Albany – SUNY in industry requirements, which include important role in the infrastructure Albany,NY. the following: for an emerging technology, and International SEMATECH is at the Overview • Minimum feature size resolution, forefront of efforts to establish key The above discussion has provided including critical dimension and standards in the areas of EUV masks, insight into some of the important overlay control. source metrology and calibration. topics relevant to EUVL. Since there • Throughput capable of supporting exists a wealth of technical literature as volume manufacturing. A brief history of EUVL well as numerous previously published • Compatibility with existing mask- Early concepts for EUVL emerged overview articles on EUVL, only a making and resist-manufacturing from research in Japan and the US brief explanation of the underlying infrastructure. during the 1980s, using so-called “soft technology is given here and the reader X-rays” in the 10 to 30 nm range. is invited to consult other sources for • Extensibility to at least three During the 1990s, research in the US more detailed information. generations to allow recovery of was focused at Lawrence Livermore and Instead, the purpose of this article development costs. Sandia National Laboratories in will be to provide an update of the In addition, EUVL tools have mask Livermore, CA, with industry support current status and most recent advances and wafer scanning, alignment and from AT&T, Intel, AMD, and others. In in each of the following specific areas: SEMICONDUCTOR FABTECH – 19TH EDITION 67 LITHOGRAPHY • Sources TABLE 1. EUV LITHOGRAPHY: CRITICAL ISSUES • Masks • Optics Source output • Photoresists and microexposure tool. Defect-free ML coated mask blank manufacturing, including inspection Source and condenser optics reliability The remainder of this article is therefore organized according to these Cost of ownership (CoO) of EUV lithography topics, with a brief discussion of the Defect-free patterned mask manufacturing/commercial availability issues surrounding each, the current Reticle defect protection (from inspection through exposure) development status, and future outlook. Effective contamination control of optical path (lifetime) EUV sources and source High NA optics manufacturing metrology Thermal management of reticle and projection optics at high throughput EUV sources Resist – high sensitivity at low power with low LER At this time, there are two prominent (Source: 1st International EUV Symposium, Dallas, TX, USA, October 2002). technologies for the generation of EUV light, both of which depend on the creation of highly ionized Xe plasma. In the first approach, that of gas-discharge- sources can generate power in the produced plasma (GDPP), a plasma excess of 60 W while the collector discharge is created and then transmits only 5–10 W of that power. In magnetically self-compressed to generate 2000, similar sources were capable of highly ionized Xe ions. Component generating approximately 0.1 W after lifetimes of electrodes and collectors are the collector. the issues for this technology. Can we achieve the required power The competing technology uses from EUV sources? The source power laser-produced plasma (LPP) to requirements, for a source operating at generate the EUV emission. Although 6 kHz, are reaching Planck limits for the overall conversion efficiency for this a black body radiating at 60 eV [1]. technology is much less than GDPP, At present, conversion efficiency more of the light generated can be (conversion of plasma energy into EUV collected. LPP systems are much more emission at 13.5 nm) for GDPP is complex and lifetimes of laser-diodes about 0.5% and for LPP is 0.80% for and collectors are the main challenges Xe, and there is a push to increase the for LPP. A key issue for EUV conversion efficiency. However, it is lithography is the achievement of generally believed that maximum sufficient source power to meet conversion efficiency (CE) for GDPP Figure 1. GDPP EUV source from Xtreme production throughput requirements. is about 0.7%, and for LPP technologies. Figure 1 shows an EUV source from it is close to 1.5%. This makes GDPP (Photo courtesy of Xtreme technologies). Xtreme technologies, which is being sources much more efficient because delivered to ISMT for its EUV micro- the electrical power does not have to be EUV source metrology exposure tool. Extreme is also converted into laser power (which is An EUV source assessment program delivering an EUV source to ASML for expected to be at 10% conversion called “Flying Circus” was first its alpha version of an EUV scanner. maximum). conducted by ASML in 2000 to review Description of these and other EUV There are also efforts by most EUV the status of the EUV sources. Now the sources is available online at source suppliers to study other, more Flying Circus II program, under a ISMT’s public web site (http:// efficient emitters, such as Sn, which contract with FOM institute, is being www.sematech.org/public/index.htm), has more than twice the conversion used by ISMT to drive the under the proceedings of EUV Source efficiency of xenon. However, the debris standardization of source metrology and workshop, a biannual workshop issue will be a bigger challenge with Sn. assess the progress and risk associated organized by ISMT to bring together Despite enormous challenges still ahead, with the EUV sources.Additional issues the EUV source community. EUV source suppliers are