Effects of subsurface damage layer on flexural properties and reliability of thinned silicon wafers

Abstract

Thinned single crystalline silicon (sc-Si) is receiving numerous attention as the substrate in electronic devices based on its high stability and flexibility. Due to the lack of research on the flexural properties of thinned silicon wafers, it is difficult to predict and improve the mechanical reliability problems of thinned silicon substrates. In this study, the flexural properties, such as flexural modulus and flexural fracture strength, and the mechanical reliability of thinned sc-Si wafers according to the thickness and crystallographic orientation were accurately measured using the three-point bending (TPB) test. The measured flexural modulus decreased as the thickness of the wafers decreased, and varied depending on the crystallographic orientation of the wafers. The difference between tensile and flexural modulus increased as thickness decreased, and did not change with the crystallographic orientation of the wafers. The mechanical reliability was evaluated through the Weibull modulus, and the reliability increased as thickness decreased, and did not change with the crystallographic orientation of the wafers. These results came from the cross-sectional area ratio of the subsurface damage (SSD) layer below the ground surface of the wafers. By considering the existence of the SSD layer and substituting the accurate mechanical properties, the predictability of warpage simulation was improved. Therefore, improving the reliability of electronic devices is expected with an understanding of the way the SSD layer of thinned silicon wafers affects the mechanical properties and mechanical reliability.