Residual stress release for SU-8 structures by water assist ultrasonic

High aspect ratio capability leads to a successful use of SU-8 photo-resist in a diversity of micro-scale polymer devices as a construction material. However, SU-8 structures fabricated by conventional photolithography technique suffer from high residual stress which results in the collapse of the fabricated structures. In the present work, a water assist ultrasonic method was proposed to decrease the residual stress in SU-8 structures. The mechanism of this method and ultrasonic parameters (power, temperature, and duration) on the remaining rate of SU-8 structures was studied. The experiments showed that only ultrasonic duration was conducive to the reduction of residual stress and a lower residual stress was associated with a longer ultrasonic duration. The proposed method is a potential candidate for fabricating of high aspect ratio SU-8 structures without any damage.