Extreme Ultra Violet Lithography (EUVL) has been widely regarded as the lithography technology to succeed optical lithography. It is now considered as one of the most promising technologies below hp45nm node [1], following ArF immersion lithography considering trend of achievable process K1 factors shown in Fig. 1. In this paper we would like to present significant progress on the development of EUV exposure tool. There are several key important areas which should be developed to realize EUVL to be feasible such as reflective mask, resist, and tool itself. The reflective mask features such characteristics as pellicle-less, ultra-smooth blank flatness and defect free. The resist should be of high sensitivity and small line edge roughness (LER) as well as fine resolution. EUV exposure tool itself consists of major modules such as EUV light source, projection optics, vacuum body, vacuum stages, and so on. As far as EUVL optics development is concerned, through the development of high-NA small-field EUV exposure system (HiNA) in conjunction with EUVA (Extreme Ultraviolet Lithography System Development Association) projects, we have developed new polishing technologies such as ion-beam figuring and elastic emission machining, and new ultra high-precision interferometers for aspheric surface metrology. Wave front sensor system has been also developed partly in EUVA project. A new wave front sensor system which can be used for evaluating the projection optics with EUV light has already been installed in New SUBARU synchrotron facility in University of Hyogo. Our multi-layer coating technology has been also improved. High reflective Mo/Si multi layer coating has been successfully achieved and irradiation tests using synchrotron radiation have been conducted [8]. Successful achievement of those developments enables us to produce full-field projection optics for EUVL process development tool called EUV1. Proto-type development of full-field projection optics has been successfully completed and evaluated to be of enough performance. Preparation of complete set of production and metrology tools necessary for projection optics production was completed and all tools are now in full operation.Nikon has studied reticle protection method and developed Dual Pod Concept in cooperation with Canon. Nikon also has developed its own reticle cover to be implemented in EUV1 tool.Nikon has completed almost all module fabrication such as full-field projection optics module, illumination optics module, vacuum body module, vacuum compatible reticle/wafer stage modules, reticle/wafer loader modules, and EUV light source module. Nikon has already got into module integration production process to meet EUV1 development schedule. Nikon announced to start EUV1 tool installation in 1 st half of 2007 and has been proceeding it on schedule. Nikon also would like to announce that development of 1 st generation production EUVL tool dubbed EUV2 is now considered and that system concept design is under way.
Nikon has been developing the full field exposure tool called EUV1 for process development of 32nm hp node and beyond. The unique feature of EUV1 is the capability of variable illumination coherence and off-axis illumination. EUV1 was installed in Selete and used for EUV lithography process development. Nikon also has conducted continuous collaborative works with customers using EUV1. Since the last SPIE Symposium in 2009, many exposure results with EUV1 tools were obtained. They showed excellent resolution capability beyond 24nm L/S with off-axis illumination and stable overlay capability of 10nm (Mean + 3 sigma). Process development exposures of test chip patterns are ongoing. With regard to HVM tool development, imaging capability with high NA projection optics and throughput capability are reviewed.
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Electron projection lithography (EPL) is a realistic technology for the 65nm node and below, as a complementary technology of optical lithography especially for contacts and gate layers because of its high resolution and large process margin. Nikon has developed an EPL exposure tool as an electron-beam (EB) stepper and the first generation EB stepper; NSR-EB1A is now almost completed as an R&D tool for the 65nm technology node. Using a ϕ200mm reticle, a 20mm×25mm exposure field is realized. Full-field exposure performance of NSR-EB1A is shown. A 70nm isolated line and 1:1 nested lines are simultaneously resolved, as are 50nm 1:2 nested lines. 60nm contact holes are resolved with a depth of focus over a 10μm range and dosage window over ±6%. Stitching accuracy is about 20nm (3σ) and the single machine overlay is about 30nm (mean + 3σ). These data mean sufficient performance for device manufacturing of the 65nm technology node. The concept of a large subfield is one candidate for resolution and throughput enhancement in EPL production tool. The Coulomb blur is directly measured by an aerial image sensor for a large subfield and small beam half-angle, and the data show good agreement with simulations. It is shown that throughput over 20 wafers per hour (ϕ300mm) is realistic and achievable in a production tool of a 45nm technology node.
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