Mechanical behavior of Cu/low-k stacks with different barrier layers

Abstract

We report the nanomechanical characterization of Cu/BD/Si and BD/Si stacks with Ta and TaN barrier layers, which are of interest in BEOL (Back end of the line) technology. The hardness, elastic modulus and adhesion strength of Cu/Ta/BD/Si, Cu/TaN/BD/Si, Ta/BD/Si and TaN/BD/Si stacks were measured using nanoindentation and nanoscratch techniques respectively. The Cu/TaN/BD/Si stack with higher modulus and hardness shows higher adhesion strength when compared to Cu/Ta/BD/Si stack. There is no significant difference in hardness, elastic modulus and adhesion strength observed in case of Ta/BD/Si and TaN/BD/Si stacks. Scanning electron microscopy (SEM) investigations of scratch profile on stacks reveal that the Cu/Ta/BD/Si stack shows severe damage than Cu/TaN/BD/Si stack. It is observed that the BD/Si stacks with barriers show brittle scratch failure as irregular cracks and chipping at the sides of the scratch length.