(RE: dry vs wet pumps for an ECR etcher)
The Microlab at the University of California - Berkeley has both wet (oil
filled) and dry pumps in use. Our dry pumps are Edwards DP80's. Our wet
pumps come from a variety of manufacturers; however, Edwards is our
preferred pump. Mechanical pumps are rebuilt in-house by a dedicated
pump technician. We have apx. 80 mechanical pumps in use.
Edwards Drystar DP & QDP80 pumps have proven reliable with chlorine
based etch chemistry. The DP80 on our polyetcher has been in service for
3 years. It has not given us any trouble. I see prodigious numbers
of Edwards brand mechanical pumps when I visit Applied Materials and Lam
Research.
Our Lam 690 aluminum etcher uses an Edwards blower/wet pump package with
Fomblin oil. The chemistry is Cl2. This pump package has been in service for
more than 6 years. Thus far we have replaced the shaft oil seal.
We currently operate an ECR system for PECVD/oxide. This system uses SiH4/O2
chemistry and operates with a blower/wet pump combination. The pump package
has not been problematic.
My advice would be to choose a dry pump if your budget can afford it. For
etch, dry pumps are appropriate technology; however, I do not have experience
with dry pumps in PECVD. As you point out, dry pumps present less problem
with oil backstreaming.
Alternatively, a wet pump will probably do everything you want for less
money. Backstreaming can be virtually eliminated by injecting a
controlled amount of nitrogen gas at the top of the mechanical pump, between
the turbo and the mechanical pump. This N2 can be toggled off during
process runs for best throughput.
Ultimately, the choice of wet vz. dry is significantly influenced by the
process. For instance, we have found wet pumps the most appropriate technology
for LPCVD, giving much better performance than dry pumps used by colleagues
in CVD applications.
Given our experience, I certainly endorse Edwards mechanical pumps.
Sincerely,
Bob Hamitlon
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| University of California at Berkeley |
| Department of Electrical Engineering and Computer Sciences |
| Bob Hamilton |
| Senior Development Engineer |
| Maintenance Supervisor | bob@eecs.berkeley.edu |
| EECS/ERL Microfabrication Laboratory | fax: (510) 642-2916 |
| 406 Cory Hall # 1770 | phone: (510) 642-2716 |
| Berkeley, CA 94720-1770 | preference: e-mail |
| www http://argon.eecs.berkeley.edu:8080 |
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