[Fwd: Uniformity results Oct 28 &29]

Ted Berg tberg at snf.stanford.edu
Wed Oct 30 08:44:36 PST 2002


John,
    JUst an update on what we have done this morning.   Tube 4 Oxidation Issues

This morning we did the following:
· checked the packing-it looked tight but we pushed it in farther.
· Measured the quartz position on three tubes and set the position of # 4 equal to #2
· Checked all TC positions- all looked fine
· Closed the damper to the position it was for the pre-tube clean
Additional info:
· The torch was replaced during the tube pull for possible contamination issues.  It was
pulled this morning and inspected no visual defects
·


John Shott wrote:

> Friends of Tylan 4:
>
> Keith has been following the saga of tylan 4 and has sent me the following
> message related to the health/alignment of the torch assembly.  He points out
> that torch problems can result in non-uniform wet oxide thickness ... but
> should show uniform dry oxidation results.
>
> As the tube was just pulled/cleaned can anyone comment on the alignment or
> wear of the torch assembly?
>
> Thanks,
>
> John
>
> Here are Keith's comments ...
>
> John, Nancy -
>    I hope you don't mind me chiming in but I thought of another possibility.
> Has
> there been a uniformity test done on this tube with a dry oxidation lately?
> Were
> the results better than the wet? If so and the results are better this more
> than
> likely points to a faulty or mis-aligned torch. If the center bore of the
> torch is
> mis-aligned with the outer bore the flame produced will not be uniform and
> will
> cause uniformity variations. (Thicker where the flame is actually pointing). I
> know there is a baffle in the rear of the tube that is supposed  to take care
> of
> this problem but doesn't always do it. A dry ox test run would take this
> variable
> (steam) out of the equation but would point out any temperature variations. My
> guess is the dry ox is probably good and you need to replace the torch with
> one
> that is properly aligned or not worn. (I would always visibly check the
> torches to
> make sure the center bore was aligned with the outer)
>    Hope this helps -
>         Keith
>
>   ------------------------------------------------------------------------
>
> Subject: Re: Uniformity results Oct 28 &29
> Date: Wed, 30 Oct 2002 07:34:57 -0800
> From: Keith Gaul <gaul at ee.stanford.edu>
> To: John Shott <shott at snf.stanford.edu>
> References: <3DBF2553.FBDA45C3 at snf.stanford.edu> <3DBF333D.13DA4B8B at snf.stanford.edu>
>
> John, Nancy -
>    I hope you don't mind me chiming in but I thought of another possibility. Has
> there been a uniformity test done on this tube with a dry oxidation lately? Were
> the results better than the wet? If so and the results are better this more than
> likely points to a faulty or mis-aligned torch. If the center bore of the torch is
> mis-aligned with the outer bore the flame produced will not be uniform and will
> cause uniformity variations. (Thicker where the flame is actually pointing). I
> know there is a baffle in the rear of the tube that is supposed  to take care of
> this problem but doesn't always do it. A dry ox test run would take this variable
> (steam) out of the equation but would point out any temperature variations. My
> guess is the dry ox is probably good and you need to replace the torch with one
> that is properly aligned or not worn. (I would always visibly check the torches to
> make sure the center bore was aligned with the outer)
>    Hope this helps -
>         Keith
>
> John Shott wrote:
>
> > Nancy et al:
> >
> > Nancy, thanks for collecting and posting this information ...
> >
> > Yes, this doesn't look good ... in fact, I would say that it is rather unusual
> > to see an oxidation with that much variation!
> >
> > There are two disturbing things (over and above the fact that the average
> > overall thickness isn't as great as it should be ...):
> >
> > 1. The top to bottom uniformity on each wafer really stinks.  In fact, I don't
> > think that this is easily explained by cantilever position in the same way
> > that it would be in a LPCVD situation.  To me, particularly given the fact
> > that these two runs are just after a tube pull, this is a symptom of a
> > temperature uniformity problem.  The first thing that I would ask, would be:
> > was all thermal blocking/glass wool installed properly ... I'm thinking that
> > maybe we are drawing air out the vestibule that is being drawn along the
> > length of the tube by leakage near one side of the tube. If cool air is
> > flowing along the one side of the tube (and not along the other), this could
> > affect the top to bottom uniformity. Also, are the spike thermocouples
> > positioned properly and in good thermal contact?
> >
> > 2. We seem to see a pretty significant increase in thickness near the torch
> > end of the tube.  This would lead me to think that we don't have a set of
> > calibration numbers that are properly set for the "torch on" condition.  Can
> > we double check this?
> >
> > Lastly, I'm a bit surprised that when we saw these problem yesterday ...
> > particularly a top to bottom uniformity problem ... that a more comprehensive
> > search wasn't launched at that point.  As I understand it, the conjecture was
> > that a door interlock problem was at fault ... can anyone explain to me how a
> > door interlock can affect top to bottom uniformity?  I think that we probably
> > wasted a day re-running an experiment that was bound to produce bad results
> > again today ....
> >
> > Thanks,
> >
> > John
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