Deposition

Plasma deposition processing is typically used for deposition of thin films when temperature sensitivity is an issue. In semiconductor processing, this issue often arises because of the material properties of complex devices being fabricated.

The fundamental principles of plasma deposition are similar to plasma etching, except that instead of removing material, a thin film of new material is deposited:

• Formation of active gas species.
• Transport of active species to the surface.
• Reaction at the surface.
• Removal of reaction products.

Films commonly deposited include silicon dioxide, silicon nitride, silicon carbide, and amorphous silicon. The gases used in processing determine the film composition. To deposit silicon oxide, dichlorosilane or silane is combined with an oxidizer such as nitrous oxide. Silicon nitride can be deposited using silane and ammonia or nitrogen. The process parameters, including gases, pressure, and RF power, determine the properties of deposited films.

For deposition, the process chamber may have a simple parallel-plate arrangement with capacitive coupling of the RF power. Or, the chamber may have coils to create a higher density, inductively coupled plasma. In either case, the gas delivery system plays an important role in the resulting film uniformity.