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18 January 2007 Halide etching for tin EUV optics cleaning
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Tin (Sn) has the advantage of delivering higher conversion efficiency than xenon. However, the use of a condensable fuel in a lithography system leads to some additional challenges for maintaining a satisfactory lifetime of the EUV optics. A critical issue leading to decreased mirror lifetime is the buildup of debris on the surface of the primary mirror optics that comes from the use of Sn in GDPP or LPP. This leads to a decreased reflectivity from the added material thickness and increased surface roughness that contributes to scattering. Reactive ion etching (RIE) with halide ions is one potential solution to this problem. Encouraging results were obtained using argon/chlorine and other gas mixtures in a PlasmaTherm SLR-770 inductively coupled plasma reactive ion etcher at the Micro and Nanotechnology Laboratory at the University of Illinois. The results showed that at low sample bias tin could be etched at a rate of 278 nm/min with a selectivity of tin removal rate to SiO2 removal rate over 9000. However, the use of the etcher at a multi-user facility did not provide adequate control over experimental parameters and reproducible cleanliness of the system. Moreover, the simulating the real optics in the PlasmaTherm SLR-770 was not allowed. Hence, a collector mock-up which can simulate the real collector optics was constructed. This work presents results for etch rate and selectivity for halide etching of tin in the Plasma-Material Interaction Group's new reactive ion etching experiment where control over important parameters such as gas mixture, RF power, sample bias, and sample temperature; as well as overall system cleanliness is maintained. The effect of these parameters on etch rate and selectivity will be presented. In addition, the results of our recipes in the optics mock-up will be shown.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hyung Joo Shin, Brian E. Jurczyk, D. N. Ruzic, and Robert Bristol "Halide etching for tin EUV optics cleaning", Proc. SPIE 6151, Emerging Lithographic Technologies X, 615133 (18 January 2007);


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