24 August 2001 Reduction of internal stress in a SU-8-like negative tone photoresist for MEMS applications by chemical modification
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Abstract
The occurrence of internal stress of ultrathick photoresists, like SU-8 is a well known problem in lithographic processes. We investigated chemically modified SU-8-like photoresists to extend the processing latitude by reducing the internal stress of the resist images. Firstly, the composition of the polymeric binder and secondly that of the photoacidgenerator (PAG) was changed. The influence of these two variations on the stress behavior, the process conditions and the lithographic performance was studied in resist layers of 250micrometers and of 65-140 micrometers thickness, respectively. The chemical modification resulted in a drastic reduction of the internal stress occurring during the post exposure bake and by an additional hardbake. In comparison to SU-8, stress values of the modified resists reduced by 70% were achieved. With optimized process conditions for each test resist the improvement of stress behavior was linked with a lithographic performance yielding high-quality patterns with high resolution and a good aspect ratio.
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Ralf Ruhmann, Gisela Ahrens, Antje Schuetz, Jeanine Voskuhl, Gabi Gruetzner, "Reduction of internal stress in a SU-8-like negative tone photoresist for MEMS applications by chemical modification", Proc. SPIE 4345, Advances in Resist Technology and Processing XVIII, (24 August 2001); doi: 10.1117/12.436882; https://doi.org/10.1117/12.436882
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