Sputtering is the bombardment of a target with energetic ions. In microfabrication, sputtering can be used as both a deposition and an etching method. When used as an etching method, the physical mechanism of sputtering is usually combined with a chemical reaction between the ions and the target substance. This combined process is known as reactive ion etching (RIE).
When sputtering is used as a deposition method, the target material--typically a metal--is positioned above a wafer. Inert ions (usually Ar+) are created in a plasma and are accelerated to the target by an electric field. These ions arrive at the target with high kinetic energy and break off atoms from the target. The removed atoms shower down onto the wafer and deposit a thin film on it.
A very common sputtering target is a 95% aluminum/4% copper/1% silicon alloy that is used as an interconnect layer by many integrated circuit companies. The aluminum is the dominant wiring material. The copper is added to improve aluminum's resistance to a phenomenon called electromigration, in which aluminum atoms move over an integrated circuit's lifetime, eventually creating catastrophic voids in the wires. The small amount of silicon is added to deal with a problem called aluminum spiking that can occur when aluminum contacts silicon devices.