PQ after clean 5-18-08

jim kruger 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
PQuest.

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
your recipe.

jim



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