From: "merle hirsh" <plasma@frontiernet.net>
Newsgroups: sci.physics.plasma
References: <bfsjhb$f486$1@saturn.cs.uml.edu>
Subject: Re: Need help with a microwave plasma deposition problem.


Hi, Bob,

You might try an Al2O3 tube to replace the quartz. Al is not very
sputterable, and at least the impurity would be changed.

As far as magnetic confinement is concerned, I would guess the Lorentz force
(F = v x B) would be weak since v would essentially be the gas flow
velocity - but it may be worth the try. You may have some undesirable
interaction between the solenoid windings and the microwave circuitry,
though.

Merle Hirsh
Chemistry Department
Rochester Institute of Technology
"bob" <nomail@nospam.com> wrote in message
news:bfsjhb$f486$1@saturn.cs.uml.edu...
>
> 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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