Problem epi2 SNF 2010-03-25 00:46:46: DOP2 Deviation by 57%
maurice at stanford.edu
Thu Mar 25 10:40:59 PDT 2010
The Dopant line has an MFC of 500 sccm
the hydrogen line has an MFC of 20 slm
For your 2% mixture we are asking for 2% of the dopant 500sccm mass flow
controller (MFC) and 98% of the H2 20slm MFC:
10 sccm Dopant2
19.6 slm H2
Generally, you don't want to operate an MFC in the upper 95% or the
lower 5% of their range.
I ran your flows and got the same results that you did...a deviation
error..it gave a value of 4.6sccm. We are asking the 500sccm MFC to
give you a value of 10sccm...that is a little tough. I didn't have a
problem with 5% or even 3%.
Ted Kamins wrote:
> For a single flowmeter, the manufacturers of the latest flowmeters CLAIM that 2% is OK. Even if that claim is valid, 50% of 2% is an even smaller number, and assuming that no momentary deviations occur is probably too hard. That's for a single flowmeter.
> If you are refering to the mixing ratio in the header of the recipe, that's more complicated. The mixing ratio appears to control two flowmeters (called source and diluent in other reactors), and proper operation also requires that the pressure at an internal node is correct. I'm concerned that operating at the limit of the MFC and then compounding that with the need for the proper pressure at that node (and probably some complex software) is too hard.
> Can you obtain the same dopant flow by using a higher mixing ratio and a lower dopant 2 inject flow?
> ----- Original Message -----
> From: jasonlin at snf.stanford.edu
> To: epi2-pcs at snf.stanford.edu
> Sent: Thursday, March 25, 2010 12:46:46 AM GMT -08:00 US/Canada Pacific
> Subject: Problem epi2 SNF 2010-03-25 00:46:46: DOP2 Deviation by 57%
> Same problem as 3/22/2010. Went into Isolated state. LLA could not be closed normally and had to be manually shut (same as last time).
> Was running the same recipe. In the header of that recipe (Jason-NP2), I set DOP2 to 2%. Is that too low and causing this problem?
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