Low-stress ultra-thick SU-8UV photolithography process for MEMS

    Authors

    B. Li; M. Liu;Q. F. Chen

    Comments

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    Abbreviated Journal Title

    J. Microlithogr. Microfabr. Microsyst.

    Keywords

    low stress; thick SU-8; process optimization; post-exposure bake; adhesion; mechanical tensile testing; HIGH-ASPECT-RATIO; UV-PHOTORESIST; SYSTEMS; Engineering, Electrical & Electronic; Nanoscience & Nanotechnology; Materials Science, Multidisciplinary; Optics

    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. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

    Journal Title

    Journal of Microlithography Microfabrication and Microsystems

    Volume

    4

    Issue/Number

    4

    Publication Date

    1-1-2005

    Document Type

    Article

    Language

    English

    First Page

    6

    WOS Identifier

    WOS:000234859500026

    ISSN

    1537-1646

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