How evaporation material effect physical vapor deposition coating
The coating material used should be specifically designed for thin film deposition. This includes not just the purity of the material but its structure and behavior during deposition as well-all of which affect the final thin film quality.
The so-called "out-gassing" phenomenon may stem from various sources: remnant air inside the evaporation material, oxides and fluorides that dissociate during deposition, remnant moisture inside the chamber, and even gasses released by equipment inside the chamber. The tendency for out-gassing depends not just on the physical properties of the evaporation material but also on its structure.
"Spitting" is a critical problem often encountered during evaporation, and is difficult to prevent. Spitting may be invisible to the naked eye, or may appear as pinholes or other surface defects on the thin film surface. The tendency for spitting depends on the intrinsic properties of the evaporation material, itself, but can be minimized to acceptable levels by using suitable materials and appropriate deposition conditions. Spitting is related to not only to the physical properties of the material but also its form, grain size, density, purity, and the various deposition conditions.
"Hole-drilling" is another problem that can decrease the production efficiency and also sometimes causes defects. When irradiating the material with an e-beam, unexpected deep holes may be drilled through the melted surface of the pellet or tablet. The point of evaporation will change suddenly and this will affect the distribution of the thin film. Unexpected hole-drilling is also one cause for spitting.
When using tablet- or pellet-type evaporation materials, the material itself may crack under the irradiation. This phenomenon often spoils the tablet or pellet, halting the production process.