[labnetwork] Problems with ALD system

[David Frankel]

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
207-581-2256
frankel at maine.edu

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mtl.mit.edu/pipermail/labnetwork/attachments/20140418/34cfb1e3/attachment.html>