Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 10M

• 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 $L \gt 1 \mu m / min$ possible but film quality may suffer. For $R \propto P$ 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.

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