Study of chip strength due to backside grinding on wafer

The strength distribution of semiconductor chips on a wafer was studied for this paper using the three-point bending test method that complies with ASTM standard E855. It was found from thousands of testing results that a weak region in a wafer always exists when the wafer has been thinned by mechanical backside grinding method. This weak region was distributed in two sectorial regions 45 degrees wide and symmetric to the wafer center. The averaged chip strength in the weak region was found to be at least 30% lower than the averaged chip strength of the whole wafer, and was independent of chip aspect ratio, metallization, diameter of the wafer, and the equipment that the backside grinding process used. The existence of the weak region was due to the grinding mark produced by the equipment, and was physically explained by the experimental results in this study. This weak region was able to be eliminated by using either plasma etching or polishing after the mechanical backside grinding,