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1 January 1992 Reflective masks for 1X deep ultraviolet lithography
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Recent work has demonstrated the high resolution optical performance possible with simple IX mostly-reflective optics: using 248nm light from a mercury arc lamp, 0.25pm features were delineated across a 2mm radius semicircular field, and much larger fields are possible with a scaled up version.[1] The mask required for this system consists of a quartz substrate, a patterned thin film reflector and a non-reflective backing which also serves to protect the reflector film. The mask is reflective at the quartz/reflector interface so the substrate is part of the projection optical path and so acts as the pellicle. We have investigated chromium, silicon and aluminum for the reflector material; their reflection coefficients at 248nm at the quartz- reflector interface are 30, 55, and 90 per cent respectively. Silicon has been chosen because it has a practical combination of reflectivity and ease of deposition and etching. Moreover films as thin as 30?m provide the full (bulk-value) reflection and so precise etching is further facilitated. Among possible absorber materials, novolak photoresist is a practical choice having a quartz/film reflectivity of 1%. Features down to 0.25?m are regularly patterned for these masks with a MEBES I using Shipley SAL-601 or PMMA electron beam resist.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert L. Hsieh, Julienne Yu-Hey Lee, Nadim I. Maluf, Raymond Browning, Paul Jerabek, Roger Fabian W. Pease, and Gerry Owen "Reflective masks for 1X deep ultraviolet lithography", Proc. SPIE 1604, 11th Annual BACUS Symposium on Photomask Technology, (1 January 1992);

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