[labnetwork] Problems with ALD system

[Matthew Oonk]

Hi David
I think Mac has the right idea : are you sure it backstreaming oil that is
leading to you nucleation issue and if so changing oil would be the easiest
of solutions.      With a hot chamber and chuck, I might be tempted to run
a longer pre-dep Ar purge to see if it changes the behavior.

Unfortunately our OpAL is hooked up to a dry pump about 30 feet away so I
don't have insight on that.

Matt Oonk (Michigan LNF)

On Friday, April 18, 2014, Hathaway, Malcolm <hathaway at cns.fas.harvard.edu>
wrote:

>  Hi David,
>
> This is Mac Hathaway, at Harvard CNS.  I'm not familiar with A155, but the
> oil should be of a sort that is inert and appropriate for O2 service.  This
> usually mean Fomblin, or some other perfluorinated oil of that type.  If
> you go with fomblin, you have to make sure the pump seals are of the
> appropriate type, as you mentioned.
>
> To provide a place for our excess precursors to "wet out" and react before
> they reach our pump, we put a plain old mist filter on our Cambridge
> Nano/Ultratech Savannah unit.  I should think you could do something
> similar and have a positive effect on your backstreaming.  If the Opal has
> pressure monitoring, the pressure spikes associated with precursor pulses
> will be softened by the presence of the mist filter.
>
> Have you done any XPS on your film to see if there is any carbon/pump oil
> in it?
>
> "Dirty" wafers would presumably have nucleation issues, but if you really
> see copious oil in your chamber, that would seem to be the most likely
> cause of dirty wafers...
>
> Does the Opal have a constant N2 purge?
>
> Last thing (or perhaps first thing!):  Check with Oxford to see what they
> recommend.  If your unit is stock, they will almost certainly have seen
> this before, and have good suggestions...
>
>
> Mac
>  ------------------------------
> *From:* labnetwork-bounces at mtl.mit.edu<javascript:_e(%7B%7D,'cvml','labnetwork-bounces at mtl.mit.edu');>[
> labnetwork-bounces at mtl.mit.edu<javascript:_e(%7B%7D,'cvml','labnetwork-bounces at mtl.mit.edu');>]
> on behalf of David Frankel [frankel at maine.edu<javascript:_e(%7B%7D,'cvml','frankel at maine.edu');>
> ]
> *Sent:* Friday, April 18, 2014 1:25 PM
> *To:* labnetwork at mtl.mit.edu<javascript:_e(%7B%7D,'cvml','labnetwork at mtl.mit.edu');>
> *Subject:* [labnetwork] Problems with ALD system
>
>  We have an Oxford Opal ALD system we use primarily for Al2O3 deposition
> using TMA. It is a thermal system, no plasma.  It is pumped by a rotary
> vane pump with a synthetic di-ester oil (A155), same as originally supplied
> by Oxford. There is no trap between the pump and chamber. We are having
> problems getting consistent good film quality.  We often see films with
> poor quality, micron-sized pin holes etc...  We think the problem may be
> related to contamination of the chamber with back-streaming pump oil as we
> often find considerable quantities of oil in the chamber.
> Some questions:
> 1) The A155 oil has a fairly high vapor pressure, is there a lower vapor
> pressure oil you can suggest that would stand up to the process gas that
> would work with our present pump?  (switching to a dry pump is cost
> prohibitive at this time, switching to Fomblin may be possible but would
> also presumably be expensive as it may require a pump rebuild or exchange)
> 2) Can a molecular sieve trap be added in the fore-line without creating
> any further problems?  If so, can a standard one be used or must it have
> some special features (high conductance...)?  Are there other types of
> traps that would work in this application?
> 3) With a trap in the line what safety measures are needed, for instance
> when venting to air?
> 4) Are there other issues that could be causing poor film quality?
>
> Thanks for your help on this,
> David
>
> --
> David J. Frankel - Senior Research Scientist
> LASST - University of Maine
> 5708 Barrows Hall
> Orono, ME 04469-5708
> 207-581-2256frankel at maine.edu <javascript:_e(%7B%7D,'cvml','frankel at maine.edu');>
>
>

-- 
Matthew Oonk
Research Engineer
Lurie Nanofabrication Facility
University of Michigan
734-646-1275
mwoonk at umich.edu
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