Application of thin Au/Ti double-layered films as both low-temperature bonding layer and residual gas gettering material for MEMS encapsulation

Abstract

In this study, we evaluated the applicability of thin Au/Ti double-layered films as both bonding layers and gettering material for residual gases in micro-electromechanical system (MEMS) packaging. The thin Au/Ti films on Si substrates with thermal SiO2 films were annealed at a maximum temperature of 400 °C for 1 h in atmospheric air to examine getter activation by the diffusion of Ti atoms to the surface through the Au film. X-ray photoelectron spectroscopy measurements revealed that the Ti atoms under the Au film diffused to the surface by the getter activation annealing at temperatures above 200 °C. The bonding characteristics of the thin Au/Ti films on the Si substrates were inspected through tensile tests, scanning acoustic microscopy (SAM), and transmission electron microscopy (TEM). With pre-bond annealing at or below 200 °C, no significant voids were observed at the bonding interfaces using SAM, and peeling was not observed at the bonding interface after the tensile tests. By contrast, the films could not bond with pre-bond annealing at 300 °C. At the bonding interface prepared after pre-bond annealing at or below 200 °C, no significant void was observed using cross-sectional TEM even after post-bond annealing at 300 °C, which is the required temperature for activation as a gettering layer. The results confirm that the thin Au/Ti films are applicable as both bonding layers and getter materials for MEMS packaging.