3 October 2016 UDOF direct improvement by modulating mask absorber thickness
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Abstract
As the process generation migrate to advanced and smaller dimension or pitch, the mask and resist 3D effects will impact the lithography focus common window severely because of both individual depth-of-focus (iDOF) range decrease and center mismatch. Furthermore, some chemical or thermal factors, such as PEB (Post Exposure Bake) also worsen the usable depth-of-focus (uDOF) performance. So the mismatch of thru-pitch iDOF center should be considered as a lithography process integration issue, and more complicated to partition the 3D effects induced by optical or chemical factors. In order to reduce the impact of 3D effects induced by both optical and chemical issues, and improve iDOF center mismatch, we would like to propose a mask absorber thickness offset approach, which is directly to compensate the iDOF center bias by adjusting mask absorber thickness, for iso, semi-iso or dense characteristics in line, space or via patterns to enlarge common process window, i.e uDOF, which intends to provide similar application as Flexwave[1] (ASML trademark). By the way, since mask absorber thickness offset approach is similar to focus tuning or change on wafer lithography process, it could be acted as the process tuning method of photoresist (PR) profile optimization locally, PR scum improvement in specific patterns or to modulate etching bias to meet process integration request. For mass production consideration, and available material, current att-PSM blank, quartz, MoSi with chrome layer as hard-mask in reticle process, will be implemented in this experiment, i.e. chrome will be kept remaining above partial thru-pitch patterns, and act as the absorber thickness bias in different patterns. And then, from the best focus offset of thru-pitch patterns, the iDOF center shifts could be directly corrected and to enlarge uDOF by increasing the overlap of iDOF. Finally, some negative tone development (NTD) result in line patterns will be demonstrated as well.
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Tuan-Yen Yu, En Chuan Lio, Po Tsang Chen, Chih I Wei, Yi Ting Chen, Ming Chun Peng, William Chou, Chun Chi Yu, "UDOF direct improvement by modulating mask absorber thickness", Proc. SPIE 9985, Photomask Technology 2016, 99850Y (3 October 2016); doi: 10.1117/12.2234760; https://doi.org/10.1117/12.2234760
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