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Journal of Micro/Nanolithography, MEMS, and MOEMS

Low-stress ultra-thick SU-8 UV photolithography process for MEMS
Author(s): Bo Li; Miao Liu; Quanfang Chen
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Paper Abstract

Patterning thick SU-8 with conventional photolithography facilities is important for fabricating various MEMS structures. However, the fabrication of thick SU-8 MEMS has experienced severe problems such as cracks, distortions, or delaminations during the fabrication process and/or postservices, due to the large internal stress generated during the photolithography process. In this work, an in-depth finite element analysis (FEA) is performed to investigate the causes and effects of the internal stresses. Analytical results show that the post-exposure bake (PEB) temperature is the main factor in developing the resulted internal stress. Under the guidance of analytical results, an optimized UV photolithography process for the fabrication of ultra-thick low-stress SU-8 patterns is developed with conventional (simple) equipment. A low PEB temperature of 55°C reduces the internal stresses by more than 70% compared to those fabricated with the recommended procedure. Experimental results indicate that cracks, distortions, and delaminations are eliminated from the fabricated SU-8 structures using the newly developed procedure. In addition, the patterned SU-8 has a Young's modulus of 2.5 GPa and an ultimate strength of 50 MPa, which is about 50% higher than previous reported values.

Paper Details

Date Published: 1 October 2005
PDF: 6 pages
J. Micro/Nanolith. 4(4) 043008 doi: 10.1117/1.2117108
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 4, Issue 4
Show Author Affiliations
Bo Li, Univ. of Central Florida (United States)
Miao Liu, Univ. of Central Florida (United States)
Quanfang Chen, Univ. of Central Florida (United States)

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