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Proceedings Paper

Adding grayscale layer to chrome photomasks
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Paper Abstract

Recent work has shown that bimetallic films, such as Bi/In and Sn/In, can create laser direct-write grayscale photomasks. Using a laser-induced oxidation process; bimetallic films turn transparent with variations in optical transparency that are a function of the laser power. The films exhibit transmittances <0.1% when unexposed and >60% when full laser exposed. A novel grayscale photolithography technique is presented that utilizes conventional chrome photomasks as the high resolution pattern-defining layer with a bimetallic thin film layer deposited on top as the grayscale-defining layer. Having the grayscale layer on top of the chrome, grayscale patterns can be aligned to the underlying chrome patterns. Laser power and bimetallic thin film thickness are carefully calibrated such that no chrome ablation or conversion occurs. The calibration ensures that during laser scanning, the bottom chrome layer defines the fine features of the underlying patterns and remains unchanged, while the bimetallic thin film layer is converted to provide grayscale tones. To further investigate the optical density (OD) properties of this type of mask, we measured the transient time response for pure chrome mask and Bi/In coated chrome mask to help fine tune the laser writing parameters. Using bimetallic Bi/In/Cr photomasks, we have successfully created continuous tone 3D structures with superimposed binary structures in SU-8 photoresist. By introducing this novel combined chrome-bimetallic mask, the fine detail features found in binary lithography may be combined with smoothly-varying 3D microstructures best suited to grayscale methods.

Paper Details

Date Published: 20 October 2006
PDF: 12 pages
Proc. SPIE 6349, Photomask Technology 2006, 634931 (20 October 2006); doi: 10.1117/12.686599
Show Author Affiliations
David K. Poon, Simon Fraser Univ. (Canada)
James M Dykes, Simon Fraser Univ. (Canada)
Chinheng Choo, Simon Fraser Univ. (Canada)
Jimmy T. K. Tsui, Simon Fraser Univ. (Canada)
Jun Wang, Simon Fraser Univ. (Canada)
Glenn H. Chapman, Simon Fraser Univ. (Canada)
Yuqiang Tu, Benchmark Technologies (United States)
Patrick Reynolds, Benchmark Technologies (United States)
Andrew Zanzal, Benchmark Technologies (United States)


Published in SPIE Proceedings Vol. 6349:
Photomask Technology 2006
Patrick M. Martin; Robert J. Naber, Editor(s)

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