Silane for the LP tubes

Dick Crane rcrane at snf.stanford.edu
Tue Aug 6 18:27:11 PDT 2002


It is with great embarrassment that I am writing this email concerning
running out of silane late Sunday night. How could this happen? When it
happened several months ago I instituted some changes in our method of
monitoring the process gases. Cylinder weight or pressure was checked
and recorded daily. Trends were plotted. Arrangements with purchasing
were made to insure replacement product would be here in a timely
fashion. We haven't had an another oops until now. What happened? As of
last week the projected run out time was next week. After-the-fact
calculations suggest there was enough silane to go into this week. The
cylinder supplies BPSG, SiGe, Poly, and Tystar tubes. The multiple user
aspect further complicates predicating use rates. Two sources of error
are being pursued: 1.The cylinder pressure gauge may have an offset
and/or be non-linear. The gauge will be replaced at next cylinder
change. 2. The gas volume vs. pressure curve may be non-linear at low
pressures.

More important is how to not have this happen again. Action items: 1. I
am pursuing an automatic changeover, two cylinder manifold which would
allow a second cylinder of silane to come on line when the first
cylinder reaches a predetermined level. This change would also make the
24 hr leak test invisible to users. Because of permits and construction
issues, this upgrade will take a few months to implement. 2. For the
time being, when the cylinder reaches the 25% volume remaining level, a
"Silane Budget Sheet" will be posted near the cleanroom entrance and a
notice will be sent to users. Silane users will need to sign up for the
number of ccs to be used. The procedure will allow users with critical
runs to chose between running now, close to the end, or waiting for a
cylinder change in a few days. The budget sheet should answer the
question of "Is there enough silane to complete my run this evening (or
weekend)?" and help coordinate use between users of different tubes.

Gas data is taken every weekday morning before 0700. Please feel free to
ask me, Ted, Ray, or Mike Dickey what the silane level at any time
during the day. I would also like to ask for your help. If you have run
scheduled which uses a large amount of silane, please notify us ahead of
time.

My apologies to the two users who ran out this weekend,

Dick




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