: Tylan Ox Furnaces: TCA System Upgrade

Jim McVittie mcvittie at cis.Stanford.EDU
Thu Aug 29 00:19:04 PDT 2002

Tylan Furnace Users,

Over the last few months in doing contamination studies in the lab using
TOF SIMS, we found that the Fe level in our thermally grown oxides was
higher than expected (low E 11 /cm2).  Last week, we finally traced down
the source of this Fe to a programming error in the TCACLEAN process used
to clean the tubes. We were not getting the benefit the chlorine from TCA
and essentially only doing steam cleans of the tubes. Some low level of
TCA did make into the tube but the low flow allowed HCl from the TCA
decomposition to diffusion back up the delivery line and reach the
stainless steel section of the line. The result was that there was some
corrosion of the stainless steel. We believe that this corrosion is the
source of the low level Fe found in our oxides.

So what are we doing to correct the problem?

1. The TCACLEAN program has been corrected.

2. On tubes #1, #2, #3 and #4, all the stainless steel fittings and lines
showing any corrosion have been replaced. On tube #7, the stainless steel
should be replaced in the next day or so. I will send a note out when this
has been done.

3. In doing the testing to solve this problem, there is a small
possibility that we increased the Fe level in tubes #1, #2, #3 and #4. To
correct for this possibility, we are running TCA cleans on these tubes and
will be pulling each of these tubes over the week to wet clean or replace
the tube. Tube #1 was shut down today (Thursday) and a new tube will be
installed tomorrow.  I am asking the techs to send out notes to keep you
updated on the status of each tube.

4. To make sure that the corrosion problem can not occur again, we will be
replacing the stainless steel tubing, fittings and valves with Teflon
replacements.  This will be accomplished as the parts become available
over the next few weeks.

5. Finally, we will be doing TOF SIMS testing of oxides to confirm that
the problem is gone.

I am sorry if any of your work has been inconvenienced or compromised by
this problem. It is our goal to keep the lab at the highest standard
possible. We are looking ways to make something like this does not happen

	Thanks,			Jim 	
James P. McVittie	                Senior Research Scientist
Allen Center for Integrated Systems     jmcvittie at stanford.edu
Stanford University             	Tel: (650) 725-3640	
Rm. 336, 330 Serra Mall			Fax: (650) 723-4659
Stanford, CA 94305-4075	

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