Physical Vapor Deposition (PVD)
Physical vapor deposition (PVD) is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces (onto semiconductor wafers). The coating method involves purely physical processes such as high temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment rather than involving a chemical reaction at the surface to be coated as inchemical vapor deposition. The term physical vapor deposition appears originally in the 1966 book Vapor Deposition by CF Powell, JH Oxley and JM Blocher Jr, but Michael Faraday was using PVD to deposit coatings as far back as 1838.
Variants of PVD include, in order of increasing novelty:
1. Cathodic Arc Deposition: In which a high power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the workpiece.
2. Electron beam physical vapor deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum and is transported by diffusion to be deposited by condensation on the (cooler) workpiece.
3. Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrically resistive heating in "low" vacuum.
4. Pulsed laser deposition: In which a high power laser ablates material from the target into a vapor.
5. Sputter deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
PVD is used in the manufacture of items including semiconductor devices, aluminized PET film for balloons and snack bags, and coated cutting tools for metalworking. Besides PVD tools for fabrication special smaller tools mainly for scientific purposes have been developed. They mainly serve the purpose of extreme thin films like atomic layers and are used mostly for small substrates. A good example is mini e-beam evaporators which can deposit monolayers of virtually all materials with melting points up to 3500°C.
The source material is unavoidably also deposited on most other surfaces interior to the vacuum chamber, including the work-holders.
Some of the techniques used to measure the physical properties of PVD coatings are:
-Calo tester: coating thickness test
-Nanoindentation: hardness test for thin-film coatings
-Pin on disc tester: wear and friction coefficient test
-Scratch tester: coating adhesion test