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

Abstract

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.

Electrical and ion beam analyses of yttrium and yttrium-titanium getter thin films oxidation

“…However the use of these getters for MEMS packaging was never reported and is then restricted to ultra-high vacuum (UHV) systems like particle accelerators. This must come from the great difference in specifications between UHV systems and MEMS packaging due to a different gaseous environment during activation 5 .…”

“…Getter films used in MEMS packaging are typically multilayers or alloys of highly reactive transition metals (Ti, Zr, V, Co…), eventually doped with rare earths, and eventually covered with a thin passivating overlayer and/or deposited on a sublayer 5 .…”

“…In this paper, we present preliminary results concerning a new generation of getter films containing yttrium. Contrary to its close neighbors in the periodic table Ti, Zr, or V, yttrium has received little attention as a getter material, despite it is an excellent nonreversible getter for hydrogen 12 and a material with a high oxygen diffusivity 5 .…”

“…In this work we investigated single metal yttrium and binary alloy Y-Ti thin films activation under a gaseous environment with high partial pressures of O2 and H2O. Titanium was chosen to be combined with yttrium because of its excellent gettering properties 14 and because it is complementary to yttrium in terms of oxygen diffusivity and solubility: titanium has a low oxygen diffusivity and a high oxygen solubility, while yttrium has a high oxygen diffusivity and a low solubility 5 . Y-Ti thin films have been also scarcely studied 15 .…”

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

“…Getter films previously investigated were mainly based on single element or alloys of transition metals of column IV (Ti, Zr, Hf) and V (V, Nb, Ta), respectively because of their high oxygen solubility or diffusivity [3]. Many of these films have already proved high performances for the sorption of oxygen.…”