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Research on fabrication of resist mold patterns for electroplating

Printing of thick resist patterns with a high aspect ratio and vertical side walls was investigated. Such resist patterns are required for using as molds of electroplating, and patterning feasibility in a small field of 2 mm square was verified in the past researches. However, it is necessary to print patterns homogeneously in an exposure field with a practical size of larger than 10 mm square, for example. As profiles of resist patterns for the use of electroplating molds, rectangular cross-sections are preferable. For this reason, patterns were printed in the negative resist SU-8 with a thickness of 50 μm using an exposure system with a field size of 15 mm square. Before using the thick SU-8, the best focus position of the exposure system was investigated. To find out the best focus position, line and space (LS) patterns were printed using a positive resist OFPR-800 with a thickness of approximately 1 μm. The focus position where patterns were most clearly formed on the wafer was decided to be the focus origin, and defocuses were controlled by moving wafers downward. Next, 50-μm LS patterns were printed in 50-μm thick SU-8. As a result, LS patterns with rectangular cross sections and a height of 40 μm were obtained when the defocus and the exposure time were set at 2000 μm and for 70 seconds, respectively. It was demonstrated that patterns with rectangular cross sections were printed in 3x5 mm2 exposure fields.