Ion plating — past, present and future

Ion plating is an atomistic vacuum coating process in which the depositing film is continuously or periodically bombarded by energetic atomic-sized inert or reactive particles that can affect the growth and properties of the film. The source of depositing atoms can be from vacuum evaporation, sputtering, arc vaporization or from a chemical vapor precursor. Bombarding species are generally either ions accelerated from a plasma in the deposition chamber (‘plasma-based’ ion plating) or ions from an ‘ion source’ (‘vacuum-based’ ion plating). The stages of ion plating can be differentiated into surface preparation, nucleation and interface formation, and film growth. Ion plating was first described in the early 1960s and was initially used to enhance film adhesion and improve surface coverage. Later it was shown that controlled bombardment could be used to modify film properties such as density, morphology, index of refraction, and residual film stress. More recently the bombardment has been used to enhance chemical reactions in reactive and quasireactive deposition processes. Presently, ionization and acceleration of the depositing film atoms (‘film ions’) is being used for ‘directed deposition’ to improve filling of surface features in semiconductor processing. This paper will review the history of the development of the ion plating process and how it has affected vacuum coating technology. Potential developments using the ion plating concept will be discussed.