is residual psg dopant in tube a problem?

Chris McGuinness cmcg at
Mon Jun 7 12:44:45 PDT 2010

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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