SOI Inertial Switch Fabrication by Fusion Bonding: Case Study and Lessons Learned

Abstract

In this work, we investigate the critical fabrication challenges of a vertically integrated inertial MEMS impact switch, uniquely implemented using fusion bonding, with a focus on the chemical stability of wafer-level bonds. While fusion bonding provides the sub-micron precision necessary for defining accurate contact air gaps, we demonstrate that mid-fabrication bonding strategies are highly susceptible to “unzipping” during the sacrificial release phase. Specifically, vapor-phase hydrofluoric acid (vHF), used to remove the buried oxide (BOX) layer, migrates into the fused oxide-to-oxide interface, leading to catastrophic delamination during die singulation. Through a multi-parameter refinement—including aggressive standard clean (SC1), surface activation, high-force thermal annealing, and a single-substrate oxide-bonding strategy—we achieved a stable silicon-to-oxide interface with an 84% dicing yield. These results establish a robust framework for device fabrication and demonstrate that interfacial chemical compatibility is a primary design constraint for high-precision MEMS integration using wafer-level fusion bonding.[2026-0088]