Enabling reliable, low temperature direct bonding of silicon via metastable polymorphs and micro-patterning

The shortcomings of conventional silicon-silicon bonding are evident in the need for eutectic gaskets, adhesives or bonding layers, and temperatures exceeding 800░C to achieve reliable bonds. A gentler approach is sought to integrate a more diverse set of devices, including micro-electromechanical systems (MEMS). EPIR, Inc. proposes the development of a low temperature, reliable direct silicon bonding method by optimizing materials and geometry parameters of the mating surfaces. Nanoscale bonding will be enhanced by inverse design strategies to improve interfacial bonding characteristics that utilize artificial intelligence (AI) topology optimization to explore the metastable polymorphs. Wafer-scale bonding reliability will be addressed by introducing etched structures that help mitigate bowing by interrupting long range distortion. Process variation tolerance will be improved by the introduction of interlocking micropatterns on the mating surfaces guided by finite element model (FEM)-based thermo-mechanical stress studies. Phase I will deliver optimized silicon polymorphs at the interface, and a full wafer-scale FEM with optimized material and geometry to reduce thermo-mechanical stresses over the full operation range of -55║C to 85║C. Optimized process modules for silicon etching, planarization, and surface activation to promote hydrophilicity will also be delivered. These demonstrations will be extended to large area wafers in Phase II.