Experimental study of ultrasonic stress relief used in SU-8 photoresist

To relieve the internal stress in SU-8 photoresist by using ultrasonic stress relief technology, the theory of the stress relief is discussed. Based on the wafer curvature measurement, a profile method was used to calculate the internal stress in SU-8 layers. The effect of ultrasonic stress relief to SU-8 layers was studied by experiments. The experimental values of internal stress before and after the ultrasonic stress relief process were compared. The experimental results show that the internal stress in SU-8 layers can be reduced for 2 MPa, and the relief rate is about 23.17% after 10 min of ultrasonic stress relief. It is proved that the internal stress in SU-8 layers can be effectively reduced when the proper parameters of ultrasonic stress relief are chosen.