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.