Correlation between the Microstructures of Bonding Interfaces and the Shear Strength of Cu-to-Cu Joints Using (111)-Oriented and Nanotwinned Cu

Abstract

Highly (111)-oriented Cu pillar-bumps were bonded to highly (111)-oriented Cu films at temperatures ranging from 200 degrees C/100 degrees C to 350 degrees C/100 degrees C in N-2 ambient conditions. The microstructures of the bonded interfaces affected the shear strength performance of the bonded Cu joints. The bonded interfaces at 300 degrees C/100 degrees C and 350 degrees C/100 degrees C had far fewer voids than interfaces bonded at 200 degrees C/100 degrees C and 250 degrees C/100 degrees C. In addition, grain growth took place across the bonding interfaces at temperatures above 300 degrees C/100 degrees C. The corresponding orientation map (OIM) showed the preferred orientation of large grown grains to be <100>. Shear tests revealed that the fracture mode was brittle for joints bonded at 200 degrees C/100 degrees C, but became ductile after bonded above 300 degrees C/100 degrees C. Based on the results, we found that voids and grain growth behavior play import roles in the shear strength performance of bonded Cu joints.