The name says it all: ChemicalVapor
deposition. CVD depends on the availability of a volatile chemical
which can be converted by some reaction into the desired solid
film. We've already discussed how the vapors, once produced,
can be transported to the
substrate and heated up when they get there. Next we need to
think about what makes the vapors in the first place (that is,
volatility) and how these vapors can react in the gas phase or
on the surfaces to be converted into the film.
We'd like to emphasize that in every CVD
process, there is of necessity some reaction path that converts
the vapors to a solid. Part of the task of designing the reactor
and process is always to force this reaction to happen only where
and when it is desired (typically on the substrate), and not
everywhere else. Undesired reactions result in particles which
can fall onto the substrates, coating of chamber walls, and clogging
of exhaust openings. The approaches to achieving this selectivity
typically rely on four levers: temperature, time, pressure, and
surface specificity.
In a brief tutorial we can't possibly hope
to cover the vast field of how atoms interact with each other.
The tutorial material is highly selective; we hope to at least
provide enough familiarity with the most relevant terminology
and concepts to help the reader negotiate the technical literature
with confidence, and perhaps remind them of material they studied
in school but haven't used since.
We'll start by recalling some of the basic
concepts of how electrons and nuclei interact to produce atoms
and bonds between them...
