Silicon Migration Seal for Wafer-Level Vacuum Encapsulation

Silicon Migration Seal (SMS) is proposed for wafer-level high vacuum encapsulation of MEMS. The sealing of vent holes is done based on silicon surface migration at 1100°C in pure hydrogen “clean” environment. Compared with the conventional “Epi-Seal” process, no deposition, and eventually no stress control is needed. A CAP wafer with vent holes is diffusion-bonded with a device wafer, and the vent holes are closed by hydrogen annealing, followed by sacrificial oxide etching. Hermetic sealing is possible by 1200 s SMS process, if the diameter of the vent holes is $0.6\ \mu \mathrm{m}$ or smaller.