http://www.siliconfareast.com/sputtering.htm

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Note added at 4 hrs (2009-07-11 19:16:28 GMT)
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Physical Vapor Deposition (PVD) is a process by which a thin film of material is deposited on a substrate according to the following sequence of steps: 1) the material to be deposited is converted into vapor by physical means; 2) the **vapor** is transported across a region of low pressure from its source to the substrate; and 3) the vapor undergoes condensation on the substrate to form the thin film. In VLSI fabrication, the most widely-used method of accomplishing PVD of thin films is by sputtering.

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Note added at 4 hrs (2009-07-11 19:18:01 GMT)
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Sputtering is a mechanism by which atoms are dislodged from the surface of a material as a result of collision with high-energy particles. Thus, PVD by Sputtering is a term used to refer to a physical vapor deposition (PVD) technique wherein atoms or molecules are ejected from a target material by high-energy particle bombardment so that the ejected atoms or molecules can condense on a substrate as a thin film. Sputtering has become one of the most widely used techniques for depositing various metallic films on wafers, including aluminum, aluminum alloys, platinum, gold, TiW, and tungsten.



Sputtering as a deposition technique may be described as a sequence of these steps: 1) ions are generated and directed at a target material; 2) the ions sputter atoms from the target; 3) the sputtered atoms get transported to the substrate through a region of reduced pressure; and 4) the sputtered atoms condense on the substrate, forming a thin film.

Sputtering offers the following advantages over other PVD methods used in VLSI fabrication:
1) Sputtering can be achieved from large-size targets, simplifying the deposition of thins with unifrom thickness over large wafers;
2) Film thickness is easily controlled by fixing the operating parameters and simply adjusting the deposition time;
3) Control of the alloy composition, as well as other film properties such as step coverage and grain structure, is more easily accomplished than by deposition through evaporation;
4) Sputter-cleaning of the substrate in vacuum prior to film deposition can be done;
5) Device damage from X-rays generated by electron beam evaporation is avoided.