Effects of Wafer Thinning Condition on the Roughness, Morphology and Fracture Strength of Silicon Die

A systematic investigation on the effects of wafer thinning process on the surface roughness, morphology and fracture strength of silicon chips was conducted. The results of the study suggest that the fracture strength of the silicon chips was determined predominantly by the geometry and scratch tip sharpness of a few large and deep scratches formed during wafer thinning. Although additional polishing by dry-polishing technique after traditional mechanical coarse/fine grinding could greatly improve the average roughness of the die surface, it would not further strengthen the silicon chips because the dry polishing could not successfully remove large scratches or reduce the scratch size. Plasma etching was found to have a high effectiveness in fracture strength improvement. Mechanism study shows that plasma etching turned the very sharp and large scratches into U-grooves, leading to a reduced stress concentration, hence, a much improved fracture strength.