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26 May 2010 Preserving the mask integrity for the lithography process
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Proceedings Volume 7748, Photomask and Next-Generation Lithography Mask Technology XVII; 77480E (2010)
Event: Photomask and NGL Mask Technology XVII, 2010, Yokohama, Japan
The optical performance stability of a photomask is one of the most critical factors in the photolithography process and stringent specifications create greater challenges with each advancing technology node. Throughout its lifetime, a photomask is exposed to a variety of cleaning cycles. It is essential that the integrity of the mask is preserved throughout each of these processes. Standard mask cleaning treatments include surface preparation with 172nm VUV for better wetting, organic resist/particle removal with aqueous ozone (DIO3) and residual ion removal for haze control. However, high energy radiations from 172nm VUV have been reported to cause overlay shift and wet oxidizing chemistries adversely affect mask CD and optical properties, ultimately influencing lithography performance. Previously, HamaTech APE successfully demonstrated an advanced cleaning method using photolyzed DIO3 with minimal metal layer damage. In this paper, performance of different media under the UV photolysis effect is explored for various steps in the cleaning process. Photolyzed DI water based surface preparation of photomask under atmospheric conditions without any overlay shift is demonstrated. Alternative chemicals with higher photolysis rates are explored for resist stripping applications. Phase/Transmission and CD change on a PSM (Phase Shift Mask) are compared between regular and modified processes. Potential improvements in residual ion removal using combination of radiation and hot DI water are also presented.
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Sherjang Singh, Peter Dress, and Uwe Dietze "Preserving the mask integrity for the lithography process", Proc. SPIE 7748, Photomask and Next-Generation Lithography Mask Technology XVII, 77480E (26 May 2010);

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