New vapour deposition technique

Abstract

THERE are various techniques of vapour deposition for putting down thin films, or thicker coatings and deposits of one material on another^1,2, which are of interest to a growing number of industries. The techniques range from chemical vapour deposition at relatively high gas pressure and temperature to physical vapour deposition based on thermal evaporation in a high vacuum for deposition on to hot or cold substrates. In recent years interest has grown in several intermediate techniques in soft vacuum (10⁻³ to 1 torr) which may be physical and/or chemical in nature^3–5. Gas discharges are sometimes used to influence both the physical and chemical aspects of the process—to generate vapour by sputtering, to cause chemical reactions among vapour species, or to encourage bonding to the substrate. Here I outline the basic features of a new ‘intermediate’ technique which depends simply on evaporation into a heated gas. The aim is to cause the vapour species to diffuse to the substrate while avoiding conditions favouring homogeneous nucleation in the gas phase. Chemical reactions may or may not occur depending on the choice of gas and gas discharges can be employed for substrate cleaning, or other purposes if required.