Molecular-dynamics simulations of void formation in Si wafer during stealth dicing processes

Stealth dicing is a process used in semiconductor manufacturing to cut wafers into individual chips. It involves focusing a laser beam inside a silicon wafer to produce a modified layer, which is then subjected to an external force. The modified layer consists of regions with high-density dislocations and voids. Since voids serve as the starting point for cutting, understanding their formation mechanism is of technological importance for developing highly controlled stealth dicing technology. In this study, we investigated the void formation process within the modified layer during stealth dicing using molecular dynamics simulations. We found that laser irradiation induces a disordered structural transition that propagates preferentially along the <110> directions. At the tips of these disordered regions, nanovoids were transiently generated. Furthermore, residual volume expansion of 1.5% was observed throughout sequential laser irradiation and subsequent cooling processes, capturing a key feature of the retained void structure. These results suggest that intense expansion pressure generated at the center induces irreversible structural deformation associated with plastic deformation in the surrounding crystalline matrix, which contributes to the retention and formation of the final void.