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

Abstract

The activation process and the gettering mechanisms of Zr−Corare earth metal alloy getters were investigated. The evolution of the surface composition prior to and upon exposure to volatile molecules (O 2 , N 2 , CO 2 ) 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 ZrO 2 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 CO 2 were also investigated. O 2 was found to saturate the surface after single exposure, while CO 2 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.

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

“…3(a) shows an increase in C 1s concentration above 200 °C, which is attributed to hydrocarbon decomposition at the surface. (80) This decomposition is likely promoted by the catalytic effect of the cobalt content in this alloy. (96) The authors also reported in Ref.…”

“…However, in Ref. 80, the onset of activation was found at ~200 °C [ Fig. 3(a)] instead of about 300 °C for the co-evaporated Zr 48 Co 52 film (Fig.…”

“…x Fe y , and Zr x Co y RE z , where RE is a mixture of rare-earth metals (La, Ce, and Nd), are the most widely examined and applied. (38,54,56,57,60,(78)(79)(80)(81) For example, Zr x Ti y V z is the getter film used in many accelerators worldwide to improve the vacuum level.…”

“…A full and detailed in situ XPS analysis of the kinetics of activation and gas sorption kinetics of a sputtered Zr 80 Co 15 RE 5 film where RE is a mixture of rare-earth metals (Ce, La, and Nd) was reported in Ref. 80. The authors found a reduction in the intensity of the O1s peak (mainly bonded to Zr) and an increase in the intensity of the Zr3d peak as a function of annealing temperature [ Fig.…”

“…The corresponding activation energy for oxygen diffusion from the surface to the bulk, estimated from an Arrhenius plot, was found to be 0.21 eV. (80) Such a low value is expected for a diffusion occurring mainly along grain boundaries. Finally, Fig.…”