[labnetwork] Cryopump configuration on a CVD tool

[Robert M. Hamilton]

Errol Porter,

Sidestepping the safety issues of trapping pyrophorics in a 
confined spare (see my last paragraph about this): I suspect 
a cryopump would not perform well unless one could assure 
residual H2 levels were minimized. A good deal of H2 is 
produced in the disassociation of hydrides. Cryopumps use an 
activated carbon-array (aka "Christmas tree") as the ~12 K 
stage to physio-adsorb and trap non-condensible gases (such 
as H2). Thus, they have finite limitation on the total 
volumes for such gases. It is often the H2 capacity of a 
cryo that drives the need for regenerations. Besides CVD, H2 
is a product of in PVD processes because sputtered (or 
evaporated) metals react with residual water vapor inherent 
on surfaces producing both an oxide and H2.

Cryopumps have the option of equipping the vent with a gas 
tight overpressure/vent port so effluents are properly 
routed  to a fume exhaust system and remediation equipment. 
This prevents the vent from discharging to an area an area 
with personnel.

More importantly, your query begs the question why not use 
the turbo to maintain base pressure when the system is in 
standby? To present a corollary, I would not want to operate 
our lab with a pump that might inadvertently become the 
equivalent of a silane cylinder, out of a gas cabinet, 
connected to a tool. One failure of gate valves are flakes 
getting onto the o-ring resulting in a leak across the seat. 
Such flakes are common in deposition systems. Such a leak 
would result in a reactive load within the cryo.

Bob Hamilton

Bob Hamilton
Marvel NanoLab
University of CA at Berkeley
Rm 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
bob at eecs.berkeley.edu
(e-mail preferred)
510-809-8600
510-325-7557 (mobile - emergencies)

On 12/6/2012 8:31 AM, Errol V. Porter wrote:
>
> Greetings members,
>
> I wanted to see if there are any members currently using a 
> cryopump on a CVD tool utilizing any of the following 
> gases; germane, hydrogen, methane, silane, diborane or 
> phosphine. Note the main pump being used during processing 
> is a turbopump with the cryopump being used to keep the 
> tool under vacuum while the tool is not being operated. If 
> there are any users using  a similar configuration, how 
> was the pump installed specifically to deal with the 
> effluent that is released during a normal regeneration cycle.
>
> Regards,
>
> Errol Porter
>
> University of Arkansas / HiDEC
>
> 700 W. Research Center Blvd
>
> Fayetteville, AR 72701
>
> Tel. 479 575-2519
>
> Fax 479 575-2719
>
> email:evporte at uark.edu <mailto:evporte at uark.edu>
>
> http://www.hidec.uark.edu
>
>
>
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