NEG thin films for under controlled atmosphere MEMS packaging

Non-evaporable getter (NEG) thin films for residual gases control in micro-electro-mechanical systems (MEMS) cavities after sealing are considered. For this study, several getters are deposited and analyzed in terms of sorption performances, microstructure and activation mechanism. Compared to single layer evaporated titanium reference, the addition of a chromium sub-layer is shown to decrease the activation temperature of the NEG. Moreover, when activated under 0.2 mbar of N2, nitrogen diffusion in the titanium layer is enhanced by sub-layer addition. Effective pumping of nitrogen is monitored by residual gas analysis (RGA). Transmission electron microscopy investigation of as-deposited thin film getters reveals Ti layer microstructure modification due to platinum sub-layer addition. Furthermore, activation under nitrogen atmosphere is shown to induce microstructure modifications for both getters. X-ray photoelectron spectroscopy (XPS) and depth profiling monitoring of NEG activation under high vacuum conditions (10−8 mbar) shows the dissolution of the NEG surface oxide in the getter bulk, along with the formation of carbide and nitride compounds. These results are in good agreement with already published results on getter alloys.