Correlation of silicon wafer strength to the surface morphology

Abstract

The trend in microelectronic packaging is towards thinner and smaller packages. To achieve this, the die must be smaller and thinner as well, which means greater susceptibility to process related failures, especially in the front-end processes. Silicon strength has been recognized as an important parameter in wafer processing, packaging and die assembly due to process-induced stresses. The strength of the silicon wafer is heavily dependent on how the backside surface is prepared prior to metal deposition. Flaws such as small microcracks or etch pits can occur during backside processes, causing the strength of the silicon to decrease, leading to fracture. This paper investigates the effect of die strength on the surface morphology using a ball breaker test and atomic force microscopy (AFM). The die strength was characterized using the ball breaker test while surface morphology was characterized using AFM. The methodologies of the ball breaker test and AFM were documented. The evaluation was performed for wafers with wet etch, smooth grind and rough grind types of backside surface finish. It shows that wet etched wafers have the highest strength and rough grind have the lowest.