Modified Au/bulk Si eutectic bonding structure with reliable compatibility of KOH etching based on two-step local oxidation of silicon

摘要

KOH etching and Au/Si bonding are primarily cost-efficient technologies for the miniaturization and integration of 3D device fabrications. In view of the incompatibility between conventional Au/bulk Si bonding and KOH etching, a modified Au/bulk Si eutectic bonding structure is proposed and verified in this study. Inspired by the local oxidation of silicon processes, the Au/Si eutectic reaction interfaces, which are vulnerable in KOH etching, can be protected with the oxide layers by the two-step thermal oxidation processes. Based on IR, SEM and EDS analyses, different etching performances have been dissected at different process parameters, in which choosing the two-step oxidation thicknesses plays a critical role. Specifically, the first-step oxidation thickness should be 1.273 times larger than the second-step oxidation while considering the KOH etching ratio of Si to silica. Further, acquired from tensile tests, the average floor levels of bonding strengths (similar to 23 MPa) indicate considerable application potential of the modified Au/bulk Si bonding structure in packaging, structure supporting, etc. This study provides an analogical strategy for another Si-based eutectic bonding technique suitable for wet etching processes.