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

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