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17 December 2003 Improved phase uniformity control using a new AAPSM etch stop layer technique
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One of the major challenges in alternating aperture phase shift mask (AAPSM) production is the variability of the glass etch rate as a function of exposed area (pattern loading) on the mask. The lack of an endpoint system means that the etch is entirely based on time, and the result is increased variability in the mean etch depth as well as decreased yields against ever tightening phase specifications. If a transmissive etch stop layer were placed underneath an appropriate thickness of glass to obtain a 180-degree phase shift, the result is a forced endpoint at exactly 180 degrees every time. Such a film system also leads to many process advantages over conventional AAPSM processes. This paper discusses the film stack deposition and maskmaking at Photronics, Inc. and details the process advantages of using AAPSM blanks with etch stop layers.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Matthew Lassiter, Michael J. Cangemi, and Darren Taylor "Improved phase uniformity control using a new AAPSM etch stop layer technique", Proc. SPIE 5256, 23rd Annual BACUS Symposium on Photomask Technology, (17 December 2003);

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