Investigations of the influence of dicing techniques on the strength properties of thin silicon

Thin silicon offers a variety of new possibilities in microelectronical, solar and micromechanical industries, e.g. for 3D-integration (stacked dies), thin microelectromechanical packages or thin single crystalline solar cells. The wafers in this investigation were thinned back by grinding and subsequent spin etching steps for stress relief followed by separation into single test dies by sawing or etching. In order to characterize and optimize relevant process steps in terms of quality and fabrication yield, the mechanical properties were investigated considering the defect formation and strength. In this paper the influence of three different dicing technologies on the mechanical strength of thin silicon samples was investigated by 3-point bending tests. Sawing, Dicing by-Thinning with sawn grooves and Dicing-by-Thinning with dry-etched trenches were used as dicing technologies. Analytical and numerical calculations were performed to calculate fracture stresses from fracture forces in 3-point bending tests taking into account the non-linear relationship of force and displacement during testing. Thus the fracture stress as a parameter of strength could be calculated for all tested samples. The results were statistically evaluated by the Weibull distribution based on the weakest link theory. This approach allows a more comprehensive under standing of the influence of the process on strength properties independently of geometric factors. Samples, being separated by Dicing-by-Thinning, have much higher strength than simply sawed samples. If trenches are fabricated by dry-etched process the strength can be increased tremendously.