Every CVD process requires that precursors
be transported from the location where gases are supplied
(inlet manifold, showerhead, injector) to the surface on which
deposition must occur (substrate, wafer): that is, masstransport must occur. As we described in our consideration
of zero-dimensional
reactors, the rate of deposition can be controlled by the surface
reaction rate (surface limited) or the mass transport rate (transport
limited). The latter is frequently the case in commercial reactors,
where high rate is desirable to reduce costs.
in the case where transport is important,
it often determines not merely the rate but also the uniformity
of deposition, frequently critical in practical applications
Many processes also require control of temperature
of gases and substrates. To control temperature we need to understand
heat transport to and from the objects of interest.
We will find that convection (the
bulk motion of a fluid or gas) and diffusion (the random
motion of molecules down gradients in concentration) play important
roles in transport of mass and energy (heat). In addition, heat
can be transported by the motion of photons: radiative
transport.
