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Julia:<br>
<br>
Fouad is correct that things like epitaxial reactors and MOCVD
equipment run pure hydrogen at high temperatures. They also have
careful pre- and post-run purging to remove residual air before
hydrogen is introduced and typically also have some form of hydrogen
burning/scrubbing at the exhaust end. In short, epi reactors and
MOCVD systems go to great lengths to make sure that oxygen and
hydrogen NEVER mix at high temperatures. I certainly wouldn't want
to be in the room if you tried to run pure hydrogen at 800 C in a
typical horizontal annealing furnace. I suspect that Fouad would
agree that this would be a very bad idea. Long ago, when running an
oxidation furnace with a hydrogen torch to generate steam, I learned
why you want to make sure that the ratio of hydrogen to oxygen is
safely less than 2.0: I turned a cassette of wafers into fine
glitter all over the laboratory floor.<br>
<br>
But, back to the issue of forming gas anneals:<br>
<br>
For a comparatively open forming gas anneal setup, I believe that
your numbers of 5% forming gas at 400 C or slightly higher are right
in the proper ball park. I'll be surprised if others aren't very
close to this range in their own usage.<br>
<br>
We at Stanford run 4% forming gas and the great majority of our lab
members likely do their annealing at either 400 or 450 C typically
for about 30 minutes. The furnace used for this typically idles
close to 400 C so there isn't too much of a ramp up/down even if
the actual anneal will be at 450 C.<br>
<br>
At 450 you probably get slightly better annealing of interface traps
than you would at 400 C ... but you can also see more in the way of
hillock formation if you have aluminum or aluminum-alloy
metalization on your wafers.<br>
<br>
Good luck,<br>
<br>
John<br>
<br>
<br>
On 11/13/2012 2:07 PM, Fouad Karouta wrote:
<blockquote cite="mid:002a01cdc1eb$4cbc5a20$e6350e60$@anu.edu.au"
type="cite">
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Hi
Julia,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Pure
H2 is commonly used in epitaxy reactors at temperature well
above 600°C. MOCVD of GaAs/AlGaAs is performed at T=600-800C.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">In the
past I did liquid phase epitaxy of GaAs/AlGaAs around 800C in
pure H2.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Moreover
Flammability of H2 in air is between 4 to 80%. So in inert gas
like N2 the flammability are different.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Hope
this would help.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Fouad
Karouta<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
</blockquote>
<br>
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