Temperature-Dependent in Situ Studies of Volatile Molecule Trapping in Low-Temperature-Activated Zr Alloy-Based Getters

The activation process and the gettering mechanisms of Zr-Co-rare earth metal alloy getters were investigated. The evolution of the surface composition prior to and upon exposure to volatile molecules (O-2, N-2, CO2) was monitored in situ using X-ray photoelectron spectroscopy under annealing conditions compatible with low processing temperature regimes. The thermally activated process of surface oxygen diffusion into the bulk was elucidated and found to involve an activation energy of 0.21 +/- 0.02 eV in the 200-350 C temperature range. This activation process was also found to reversibly transform ZrO2 into Zr(OH)(2) through the interaction with thermally desorbed hydrogen. Carbidic species form upon annealing at 250 C via the interaction with an adventitious carbon layer on the surface, which results in the decrease in the number of surface sites available for subsequent gettering. In situ studies of the material reactivity with high purity O-2, N-2, and CO2 were also investigated. O-2 was found to saturate the surface after single exposure, while CO2 dissociates into CO and O-, where O- is incorporated deeper in the material and CO forms an ad-layer on the surface of the getter. N-2 was found to weakly interact with the partially activated surface and to form ZrN only upon annealing the sample to 350 C indicating the poor reactivity of the material with N-2 at room temperature. The results display the importance of ridding systems of residual gases, especially N-2, by properly degassing the system prior to sealing to minimize and/or eliminate trapped gases within devices during operation.