Chapter 6 - Vacuum Evaporation and Vacuum Deposition

Abstract

Vacuum deposition or vacuum evaporation is a PVD process in which the atoms or molecules from a thermal vaporization source reach the substrate without collisions with residual gas molecules in the deposition chamber. Vacuum deposition normally requires a vacuum of better than 10–4 Torr in order to have a long mean free path between collisions. At this pressure, there is still a large amount of concurrent impingement on the substrate by potentially undesirable residual gases that can contaminate the film. Thermal vaporization requires that the surface and generally a large volume of material be heated to a temperature at which there is an appreciable vapor pressure. Common heating techniques for evaporation/sublimation include resistive heating, high-energy e-beams, low energy e-beams, and inductive (rf) heating. In the vacuum environment, the vapor travels from the source to the substrate in a straight line with few collisions with residual gas molecules. Thermally vaporized atoms may not always condense when they impinge on a surface; instead, they can be reflected or re-evaporate. Re-evaporation is a function of the surface temperature and the flux of depositing atoms.