Residual stress control of Cu film deposited using a pulsed direct current magnetron sputtering

Abstract

Residual stress of 10 μm thick copper (Cu) film deposited using direct current (DC) magnetron sputtering system was analyzed for various pulsed DC power conditions. It is found that the increase of pulse frequency at a fixed duty ratio of 80% from continuous wave (CW) to 100 kHz while maintaining the time average power significantly decreased the residual stress of Cu film from 21.75 MPa to 1.8 MPa. The decrease of pulse duty ratio further decreased the residual stress by showing 0.7 MPa at 60% of duty ratio and 50 kHz pulse frequency. Therefore, compared to CW power, Cu film with ~1/30 lower residual stress could be deposited by using DC pulse power. The decrease of residual stress by pulsing and by decreasing the pulse duty ratio while keeping the same time average power was related to the denser film density and smaller grain size of deposited Cu film caused by increased instant sputter power during the pulsing.