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On 8/9/2012 4:44 AM, Siva Penmetsa wrote:<br>
<br>
You are talking about an atmospheric pressure pre-deposition
correct? While it's been many, many years, we used to use diborane
as a predeposition source and my failing memory recalls that we
would expect a sheet resistance of about 45-50 ohms/square following
a 30 minute predep at 1000 degrees C prior to drive in.<br>
<br>
I trust that you are actually using fairly dilute diborane in a
carrier gas, correct? What is the diborane concentration of your
source gas and what is the carrier gas?<br>
<br>
While my recommendations might vary somewhat depending on those
answers, one thing jumps off the page at me when I read your process
details: 2 SLPM of oxygen is a very large flow oxygen when your
total flow is about 5 SLPM.<br>
<br>
While you need enough oxygen to fully oxidize the amount of diborane
injected to convert it into B2O3 ... which is ultimately what does
the doping, too much oxygen is a bad thing because it creates an
ever increasing oxide layer at the silicon surface that tends to
isolate the B2O3 layer (that is deposited on top of that oxidizing
surface) from the silicon surface. I believe that it is likely that
you would see lower sheet resistance and better reproducibility if
you lowered your oxygen flow significantly .... while I can't quite
recall details from my youth, I'm guessing that an oxygen flow of
100-200 SCCM is probably a lot closer to where you want to be to
fully oxidize the diborane but not have such a high concentration of
oxygen that the thermally grown oxide prevents the glassy B2O3 layer
from doping your silicon surface.<br>
<br>
You need to look carefully at how much diborane you are actually
flowing at various flow conditions .... assuming that you are using
a comparatively low concentration of diborane. As I recall, for
example, we used to use something on the order of 1000 ppm diborane
in nitrogen as our source .... certainly well less than 1%. If you
are using a comparable concentration, it only takes a few SCCM of
oxygen to fully oxidize your diborane. Rather than adjusting
diborane flow, I'd fix your diborane flow at 40 SCCM and then back
down your oxygen flow significantly. I suspect that you'll see
lower sheet resistance and better reproducibility because the
oxidation of the silicon surface will no longer be "winning".<br>
<br>
This is all from many years ago from someone whose memory is not
that great, but that is where I would start.<br>
<br>
Good luck,<br>
<br>
John<br>
<br>
<blockquote
cite="mid:CAHmH2YTaKeqT05Jp7HYfG4JJ-K=xjxDGeT8irRE0115dcNqCyg@mail.gmail.com"
type="cite">
<div>Hi All,</div>
<div> </div>
<div>We are trying to optimise Diborane furnace in a new CVD
equipment.</div>
<div> </div>
<div>We have performed few trials(all the souces are gases) at </div>
<div> </div>
<div>Temperature 1000 C </div>
<div>Diborane Flow rate in the range 40 sccm to 100 sccm</div>
<div>Oxygen flow rate 2 SLPM</div>
<div>Nitrogen flow rate is 3 SLPM</div>
<div>Time 30 minutes</div>
<div> </div>
<div>Instead of decrese in resistance we observed that the
resistance incresed to around 500 ohm/sq from around 50 ohm/sq</div>
<div> </div>
<div>We apprecite your experience and inputs on how we can resduce
the resisitivity with better Diborane diffussion.<br clear="all">
<br>
-- <br>
</div>
<div>Thanks & Regards,</div>
<div><strong>Siva Prasad Raju Penmetsa</strong></div>
<div><em>Senior Facility Technologist</em></div>
<div>National Nano Fabrication Center</div>
<div><em>Indian Institute of Science(IISc)</em></div>
<div>Bangalore, India 560 054</div>
</blockquote>
<br>
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