Abstract
The outgassing problem is solved numerically by molecular dynamics. A slit-shaped nanopore consisting of cavity and channel is built with an implicit tabulated wall potential that describes the water–silicon/silica interaction. A flexible three-point water model is used for the simulation. The effects of varying the system temperature, outlet pressure, geometry, and materials of the nanopore on the outgassing rate are investigated. The results show that the temperature plays an important role in the outgassing rate, while the effect of the outlet pressure is negligible as long as it is in the high to medium vacuum range. The geometry of the channel also has an influence on the outgassing rate, but not as much as the surface material. Three different types of silica materials are tested: silicon, silica-cristobalite (hydrophilic material), and silica-quartz (super hydrophilic material). The fastest outgassing rate is found for a silicon nanopore. It is also found that a thin water film is formed on the surface of the silica-quartz nanopore. This material shows hardly any outgassing of water.
Highlights
Outgassing refers to gaseous emissions from solids; these gases have been reported to be adsorbed previously (Jousten 1999)
For our simulation scale, it is noticeable throughout the studies and has an impact on the half-life: It changes by the outgassing factors
The main factors affecting outgassing of water molecules are studied by varying the system temperature, the outlet pressure, the geometry of the nanopore, and the materials of the nanopore
Summary
Outgassing refers to gaseous emissions from solids; these gases have been reported to be adsorbed previously (Jousten 1999). Wafer-level packaging is essential for miniaturization and high-level integration in the semiconductor industry It allows for the encapsulation of MEMS or integrated circuits (IC), before the standard IC packaging process takes place. Outgassing forms pressure, which may destroy the vacuum in the sealed microcavity This can degrade the reliability of a MEMS/NEMS device, and it can lead to a failure of the device (Charvet et al 2013). Fusion bonding of silicon is a very commonly used wafer bonding technology due to its simplicity and high bond strength (Lindroos et al 2009). During this bonding process, wafer surfaces are brought into contact (pre-bonded) in vacuum condition followed by high temperature annealing to strengthen the bond. Outgassing of water molecules, remaining in the wafer before the prebonding stage, is found to be the main reason for bonding failures since it can lead to bubbles on the wafer surfaces (Gao et al 2012)
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