Characterization of low-temperature SU-8 photoresist processing for MEMS applications

In this paper, negative SU-8 photoresist processed at low-temperature has been characterized in terms of delamination. Based on a 3/sup 3/ factorial designed experiment, 27 samples are fabricated and the degree of delamination is measured. In addition, nine samples are fabricated for the purpose of verification. Employing a neural network modeling technique, a process model is established, and response surfaces are generated to investigate the degree of delamination associated with three process parameters: post exposure bake (PEB) temperature, PEB time, and exposure energy. From the response surfaces generated, two significant parameters associated with delamination are identified, and their effects on delamination are analyzed. The higher the post exposure bake (PEB) temperature at a fixed PEB time, the more delamination occurred. In addition, the higher the dose of exposure energy, the lower the temperature at which the delamination begins and the larger the degree of delamination. The results identify acceptable ranges of the three process variables to avoid the delamination of SU-8 film, which in turn might lead to potential defects in MEMS device fabrication.