ION PLATING
ION PLATING is a generic term applied to film deposition processes in which the substrate surface and the growing film
are subjected to a continuous or periodic flux of energetic massive bombarding particles (ions, radicals, atoms, or
molecules--reactive or inert) sufficient to cause changes in the film formation process and the properties of the deposited
film (Ref 1, 2, 3, 4). The bombarding species and the depositing species can be from a number of sources. Bombardment
can take place in a plasma or vacuum environment. When a beam of energetic particles is used in vacuum, the process is
often called ion-beam-assisted deposition (IBAD).
A vacuum can be defined as an environment where the gas density is low and the mean free path for collision is very
long. In vacuum-barrel deposition processing, this means that the pressure is lower than about 1.3 mPa (1 × 10-5 torr). A
plasma is a low-pressure gas that contains enough ions and electrons to have an appreciable electrical conductivity. This
requires a gas pressure of greater than 13 mPa (1 × 10-4 torr). Plasmas can be low-pressure (less than about 0.4 Pa, or 3
mtorr) or higher-pressure (greater than about 0.4 Pa, or 3 mtorr), depending on whether or not collisions in the gas phase
are sufficient to "thermalize" high-energy particles leaving a source (Ref 5, 6). This differentiation is important when
using sputtering as a source for deposition because reflected high-energy neutrals from the target can have an important
effect on the growing film. Figure 1 shows the distance traveled by particles of differing masses (12 and 400 atomic mass
unit, or amu) and energies (5 eV, or 0.8 aJ, and 1 keV, or 160 aJ) in argon before becoming thermalized. It should be
noted that the gas density in a plasma system can vary with position due to preferential gas motion and particle
temperature distribution

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