Reduction of diffraction effect of UV exposure on SU-8 negative thick photoresist by air gap elimination
- Cite this article as:
- Chuang, YJ., Tseng, FG. & Lin, WK. Microsystem Technologies (2002) 8: 308. doi:10.1007/s00542-002-0176-8
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This paper reports a novel way to compensate the air gap between photomask and photoresist for eliminating UV light diffraction on photoresist, which greatly increases the sidewall straightness of high-aspect-ratio resist structures. In this research, SU-8 negative tone photoresist was used for experiments, and glycerol was employed as an index match material for bridging air gap between photomask and photoresist during exposure. Results showed that a high aspect ratio wall structure of 156 μm thick and 25 μm wide had a 45% pattern width error when exposed under 100 μm air gap, while glycerol compensated process accomplished a straight resist wall without appreciable error. This method is simple and cheap to employ, compared to the usage of costly thick-photoresist-film spinner for resist planarization. Numerical simulation on the diffraction effect upon the structure wall has also been conducted. The calculated and experiment wall profiles showed similarity in trend.