PQ after clean 5-18-08
jimkruger at yahoo.com
Fri Apr 18 12:41:00 PDT 2008
PQuest check 4-18-08
After the chamber clean and Turbo pump scare, I
checked the Leak-up rate and the He blow-by on
The leak-up rate was 2.2 mTorr/minute, but this was
after a GaAs recipe chamber conditioning and only one
day after the Wet Clean. The Best Ever leak-up
rate, expected after ~ days since wet lcean and after
an O2 chamber clean is about 1.0 mTorr / min. I judge
~2 to be OK, 5 or 10 is a problem.
The back-side wafer He blow-by is very good right now.
The issue is that the there is a high flow impedance
between the pressure monitor and the chuck so the
pressure behind the wafer is lower for high blow-by
flows and thermal impedance is raised.
For Chuck Temperature = 11 C (chiller at 0, set point
= 13 C), the no wafer flow was 11.1 sccm . With a
new carrier wafer in place it was 5.5 sccm. This
gives a delta of 5.6 sccm, very good.
I judge a He blow-by delta of 3 or 4 to be good, 2
marginal, 1 or less poor.
The flows are all temperature dependent (lower for
higher Chuck temperature) so you need to characterize
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