Oxygen and hydrogen sorption in thermally activated yttrium-based getter thin films for MEMS vacuum packaging

Many microsensors need to operate in medium vacuum, which is obtained by low temperature vacuum packaging integrating a getter film. By a thermal activation during the sealing process, the getter film aims to compensate the outgassing of the inner surfaces of the micro-cavity and also leaks after sealing. Thin films of getter alloys were coevaporated under ultra-high vacuum on silicon wafers. They were activated by annealing at temperatures ranging from 225°C to 400°C, during one hour under Argon atmosphere with traces of oxidizing species. Three complementary ion beam analysis techniques were performed to obtain depth profiles and to quantify the number of atoms of the different gaseous species absorbed by the getter films: Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA). The results show that both oxygen and hydrogen diffuse inside the getter films. However, hydrogen tends to accumulate near the interface between film and substrate and starts to diffuse inside substrate as well. We demonstrated that the sorption of hydrogen by an yttrium-based getter film is tailored by its composition and depends on its degree of oxidation.