Chemically amplified, positive tone, cross-linkable thick-film polymer

Authors

  • Brennen K. Mueller,

    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100
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  • Paul A. Kohl

    Corresponding author
    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0100
    • School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332-0100. E-mail: kohl@gatech.edu

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Abstract

A new class of positive tone, permanent materials has been demonstrated, which are chemically amplified (CA), aqueous-developable, and cross-linkable. The intended purpose is a patterning and cross-linking method to create high sensitivity permanent dielectrics for microelectronic devices and packages. The photochemistry is based on traditional CA, acid-catalyzed deprotection of a protected organic functionality to yield an aqueous base soluble group such as a carboxylic acid or alcohol. This CA chemistry produces high contrast and high photo-speed patterning, which is especially valuable for thick-film applications where high UV exposure doses are required for non-CA materials. The photospeed is about an order of magnitude faster than commercial materials at a similar thickness. Subsequent to patterning, the remaining films or features can be cross-linked by a variety of chemical mechanisms. The working photo-patterning and cross-linking mechanisms are demonstrated on a random copolymer of tert-butyl methacrylate (TBMA) and 2-hydroxyethyl methacrylate (HEMA). The optical contrast (at 248 nm) was found to be 12.7 and the sensitivity, D100, was calculated to be 50.2 mJ/cm2 in a 9.07-μm-thick film. Undeveloped regions were cross-linked after patterning. The esterification reaction is much slower than the TBMA deprotection, so that the cross-linking reaction does not interfere with the photopatterning. Cross-linking was also evident by the change in thin film stress 6.2 to 17.9 MPa during a thermal cure. Other polymers for Fischer esterification are discussed with their advantages and disadvantages along with other cross-linking chemistries. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 759-765, 2013

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