Effect of Environment on Activation and Sorption of Getter Alloys and Multilayers for Hybrid Wafer-level Vacuum Packaging

A large set of micro- and nanodevices requires hybrid vacuum packaging at the wafer level to optimize their performance and lifetime. When the temperature of the packaging fabrication process is limited, getter films must be integrated into the packaging cavity to obtain a low and sustainable pressure. In this paper, gas generation and residual gases inside a wafer-level package, as well as the main getter alloy films and multilayers investigated previously, are reviewed. An emphasis is put on the effect of a gaseous environment on the physicochemical mechanisms involved in getter film activation and gas sorption. A large outgassing occurs during the packaging fabrication process. It produces a gas load larger than or similar to that generated during the entire lifetime of the device at room temperature. The resulting partial pressures of gases in a micropackage are quite different from those found in ultrahigh vacuum during characterization by surface analysis techniques and when getter films are used in accelerators. Consequently, in micropackages, activation and sorption steps can no longer be analyzed separately and surface oxidation and/or oxygen bulk diffusion during activation should be taken into account. It is thus recommended to use and develop complementary characterization techniques that enable the investigation of surface and bulk phenomena at various temperatures, pressures, and gas mixtures for the assessment of getter films for vacuum packaging.