is residual psg dopant in tube a problem?

Chris McGuinness cmcg at
Tue Jun 15 11:52:56 PDT 2010

I take it that no responses from users mean this is not a concern to anybody else, and no response from staff to mean nobody really knows the degree of psg contamination after a psg run.  For now I will be sure to do a dummy run after any psg runs in order to coat the tube with a layer of undoped oxide.  Though it would be reassuring to know this is a sufficient solution.

----- Original Message -----
From: "Chris McGuinness" <cmcg at>
To: "tylanbpsg" <tylanbpsg at>
Sent: Monday, June 7, 2010 12:44:45 PM
Subject: is residual psg dopant in tube a problem?

Hi all,
It seems the vast majority of the users use tylanbpsg for undoped LTO
depositions. Occasionally a user runs a recipe with PSG doping. Have
there been any studies done on the effect of running PSG prior to an
undoped LTO run? Is there significant residual PSG in the tube to
significanlly affect the quality or type of oxide deposited on
subsequent runs?

The reason that I ask is there have been two situations which I have had
a hard time understanding. In both cases one thought was that residual
doping was affecting the properties of the oxide. The first situation
was never resolved, though it did not reoccur and there was not a
correlating PSG run prior to it, so I assumed it was unrelated. The
second situation was found to be due to other causes, so cannot be
blamed on residual dopant in the tylan tube.

The concern that both of these issues raise is that this was a
possibility. It does not seem clear to me whether there is any residual
dopant left in the tube after an PSG run that could affect successive
LTO runs. Maybe I am unaware of any studies done on this, but I did
notice a quartz tube that had a significant yellow tinge, and a few
boats that seemed to be coated in yellow. Is this from PSG? Should I be
afraid to put wafers with 3 months of hard work into a tube with strange
yellow coating? With all the clean/dirty distinctions and effort to keep
contaminants out this seems like an important issue if PSG contaminant
are as fatal to optical structures as metals are to electronic ones.

Thanks for any information or feedback on this.


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