Diamond growth mechanism in chemical vapor depostion systems

[BULLDAWG]

In the past decade, massive effort has been directed to making
thick (greater than 100 um) diamond films. The current leader is
Crystallume at GE. THey have succeded in growing films on the order
of 600 um using an unknown (i.e. proprietory) method in an unknown span
of time. My research has centered in the past year in growing thick films
along the lines of GE.

What makes this problem interesting is that the *engineering* of the
growth of diamond is fairly well understood. What is not known is the
growth dynamics and the chemical species involved.

One starts in a diamond CVD process (and I will limit myself to one
particular method, high power microwave plasma depostion) with a carbon
containing specie and hyper-dilute this in hydrogen (1% to 99%). Then one
heats the substrate to high (900 C) temperature under a microwave discharge
of this mixture. The diamond grows at 0.1 um / hour if one is lucky.
To grow a 100 um film (sort of the minimum that you need to charaterize the
film with bulk properties) one obviously needs 1000 hours. A long time.

On to the theory.

First theory. Amorphous carbon (soot) is laid down in much faster
rate than diamond carbon. The hydrogen atoms produced in the discharge
serve very little more than to react with soot more so than with the diamond
so that there is a net growth of diamond. Presumably the carbon species
interacts with the surface and due to the high temperatures involved is able
find energy minima on the surface and crosses over a barrier and reacts with
dangling bonds on the surface to produce new diamond / soot and new bonds.

I would call that theory the "eat-crud-faster-than-the good-stuff".

Second theory. CH3 radical is produced in the gas phase and then
reacts with surface. Still in development in the liturature.

Third theory. Enough energy is avalable in the form of fast atoms,
ions etc to activate gas phase chemistry which then deposits directly down on
the surface.

Well, I will elaborate in much more detail if there is any interest
from anyone.

My present research will be to go into the gas phase with a probe
tunable laser and actually measure the concentrations of particular species
present to try to deduce the mechanisms.

Ken Pearce
The Ohio State University