Reliability Assessment for Cu/Low-k Structure based on Bump Shear Modeling and Simulation Method

Bump shear is widely used to characterize interface strength of Cu/low-k structure. In this work, the blanket low-k structure was used to evaluate the reliability and strength of Cu/low-k structure using finite element modeling technique. The objectives of this work are to determine the critical stress parameters for low-k interfaces with different Cu/low-k structures for understanding the failure mechanism and to improve the low-k structure reliability by optimizing the some parameters. In this paper, the comprehensive parametric study was conducted including 3 different low-k structures, different shear ram height, high Pb solder vs. Pb-free solder, different UBM thicknesses, blok layer modulus effect. The simulation findings can be summarized as follows: The shear force decreases with shear ram height. The critical stress decreases with the number of layer of low-k structure. Higher shear force occurs for SnAg solder bump than SnPb one. Reducing UBM thickness can help to improve the low-k structure reliability.