Experimental study on ultrasonic stress relief for cured SU-8 photoresist layer

The purpose of this work is to reduce the internal stress in cured SU-8 photoresist layer by ultrasonic stress relief technology. The stress relief mechanism of SU-8 photoresist layer was presented. Based on improved Stoney’s formula, a theoretical calculation model for SU-8 internal stress was proposed. Profile method was used to measure the curvature radius of substrate. The effect of ultrasonic stress relief on SU-8 layers was studied by experiments. Meanwhile, some important factors, such as amplitude of vibration, power input and relief time, have been discussed. The values of internal stress before and after the ultrasonic stress relief process were compared. The experimental results show that the internal stress in cured SU-8 layers can be effectively reduced if the proper experimental parameters are chosen.