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State various physical vapor deposition techniques. Explain in brief any one technique of PVD in MEMS fabrication.
written 5.2 years ago by | modified 2.1 years ago by |
physical vapor deposition [PVD] describes a variety of vacuum deposition methods which can be used to produce thin films and coatings.
PVD is characterized by a process in which the material goes from a condensed phase to a vapor phase and then back to a thin film condensed phase.
The most common PVD processes are sputtering and evaporation.
Evaporation :
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapour particles to travel directly to that target object [substrate] where they condense back to a solid state.
- In evaporation, source material is heated in high vacuum chamber [ p < $10^-5$ , hence the name vacuum deposition. High vacuum is required to minimize collisions of source. atoms with back ground species [light of site deposition] Heating is done by resistive or e.beam sources. surface interactions are physical can be very fast L > l $\mu$ m / min possible but film quality may suffer for R ? P typical 0.1 - Inm[sec]. High sticking [at low T, an atom stays wherever it hits with limited surface migration], leading to poor conformal coverage / significant shadow. But this also makes evaporation the most popular thin film deposition for nanofabrication using lift off process. Evaporation [also called vacuum deposition] Deposition rate is determined by emitted flux and by geometry of the source and wafer evaporation is not widely used by industry, sputter deposition is used in industry.
fig : Evaporation system
- During deposition when evaporation is performed in poor vacuum or close to atmospheric pressure, the resulting deposition is generally non-uniform and tends not to be a continuous or smooth film this is called as shadowing or step coverage
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