Sputtering is a technique in which atoms are ejected from a target material after being bombarded with ions. The process can be physical, electrical, and even potential. It creates gaseous plasma, sometimes considered the fourth state of matter, which will then allow ions to accelerate from that plasma and into the target.
Physical sputtering is done through momentum exchange due to collisions by ions and atoms in the target. The initial collisions are set off by ions and flow into the target. When this reaches the surface of the target at an energy level above the binding energy of the surface, the atom may be ejected. A sputter yield is produced, calculated by the number of atoms ejected from the target per incident ion. It is dependant on the energy of the ion, the incident angle of the ion, the mass of the ion, and the surface binding energy of atoms in the target.
Electronic sputtering is similar to physical sputtering except it is induced by energetic electrons. These electronic excitations are what set off the sputtering rather than the collisions of ions. Potential sputtering is a type of electronic sputtering that occurs when various charged projectile ions recombine on the solid surface during collisions, thus freeing the potential energy within these charged particles.
Sputtering is done for various parts of the semiconductor fabrication process. Film deposition is its main use, in which the thin film is deposited onto the substrate. Atoms in this process are not at thermodynamic equilibrium and will deposit onto all surfaces of the vacuum chamber, allowing the wafer to be coated with a thin film during this time.
Sputtering is also done during etching, but is referred to as ion milling instead. It is also involved in reactive ion etching which is a plasma process. Other applications include analysis by etching away the target material or space weathering.