Abstract
Effect of Environment on Activation and Sorption of Getter Alloys and Multilayers for Hybrid Wafer-level Vacuum Packaging
Highlights
A sustainable vacuum or well-controlled environment is required for various micro/nanodevices to reach optimal performance and increase their lifetime
In the ASTM 798-97 standard,(70) the getter film sorption capacity is defined as the quantity of sorbed gas beyond which the gettering rate decreases to 5% of its value 3 min after the start of the test
For the reasons discussed below, as for getters passivated by natural oxide, the activation and sorption processes of getter multilayers are expected to be very different under UHV conditions and at pressures found in wafer-level packages
Summary
A sustainable vacuum or well-controlled environment is required for various micro/. nanodevices to reach optimal performance and increase their lifetime. The pressure inside a cavity of a micropackage tends to rapidly increase with time because of (i) the outgassing of sealing rings, device materials, and internal walls during die/wafer bonding, getter thermal activation, thermal reliability tests, and the packaged device lifetime (10–20 years), (ii) real and virtual package air leaks, and (iii) gas permeation through sealing rings, SiO2 or glass films, caps, and substrates These phenomena impose the getter film pumping rate required to reach and maintain the desired vacuum level. Wafer bonding, and thermal activation steps, diffusion can be the limiting step, while at room temperature, the gas sorption process mainly depends on the initial pumping speed and surface coverage.[73] The pumping speed per unit surface for a given gas Sg is related to the impingement rate of molecules and the gas effective sticking coefficient. This can be used to estimate the amount of sorbed hydrogen
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