From: "bob" <nomail@nospam.com>
Newsgroups: sci.physics.plasma
Subject: Need help with a microwave plasma deposition problem.


Hello,
I have a bit of a problem with a NIRIM style cvd diamond deposition system
and am looking for advice. Before I go any further please let me state that
I'm a laser jock and DONT have any formal experience with this hardware.
It's a project my company picked up on the cheap, and were just in the
'fooling around' stages...

For the sake of reference, a NIRIM cvd reactor is essentially little more
than a quartz tube that has been 'stabed' through a waveguide connected to a
2.45 gig microwave soucre and tuner. the tube is pumped down to 10 to 100
torr and process gasses are maintained by mass flow controllers. The MW
radiation sustains an arc and allows for the deposition of diamond while at
the same time free hydrogen etches any graphite phase carbon that may be
deposited onto a heated substrate holder in the plasma column.

Now for my problem. I have noticed silicon inpurities in diamond films
produced by this reactor. As I understand it these types of reactors are
known to have impurity problems due to etching of the reactor wall tube by
the MW plasma. In an effort to reduce this problem, why cant the tube be
centered in a solinoid that squeezes the plasma into the central portions of
the process tube (if etching of the process tube isnt stopped, it should at
least be lessened I would think). I checked into the literture, and the only
such arraingments I could find related to ECR style systems where very low,
large area dischages (in other reactor designs, NOT an NIRIM reactor) lead
to a non-isothermal plasma and the magnetic feild only serves to aid in
energy transfer from hot electrons to the heavier gas species.

So.. What am i missing here? Is there some reason I'm overlooking that would
inhibit me from making use of such a magnetic feild to reduce this
contamination issue?

Thanks in advance for any help!



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