20.1 Introduction

All deposition processes provide a heat load onto the substrate. There is the latent heat of condensation, which is the energy lost when the condensing atom stops moving about on the surface and nucleates and cools. The other sources of energy tend to be source dependent. Resistance-heated boats will run at 1400 C and the whole boat will radiate heat, which is seen by the substrate.[1] The magnetron sputtering sources tend to run much cooler and so do not radiate as much of a heat load. They do however have energetic species in the plasma that are a source of heat load. ^[2 ^,3 ^,4 ^] The resistance-heated boats do not produce these energetic particles. Electron beam guns fall somewhere in between the above two sources. The crucible is often cooled and it is only the molten pool that radiates heat, making it similar to the resistance-heated sources; however, they also produce some secondary electrons that can bombard the substrate, although this is much less than for the sputtering sources.[5]

There can be an additional source of heating in some reactive processes such as the oxidation of aluminum. The chemical reaction of converting aluminum metal to aluminum oxide is an exothermic reaction and liberates heat. Where the whole metal layer is converted to oxide, rather than the surface oxidation of only the top few monolayers, the heat that is liberated, in addition to the other heat sources, can be of significance.

In production, it is...