[labnetwork] cryopump maintenance

Thu Dec 19 15:17:02 EST 2013

Xiaojin,

    After reading your note and relating it to past experiences with cryo
pumps over the years you could be experiencing numerous problems.  There are
numerous things that could cause your issue you should inspect the arrays in
the pump and numerous other things but the easiest check that you can do to
start is to take a look at your helium pressure, you should have a send and
return gauge on your compressor and they should be operating within limits
that are required by the manufacturer.  Check those gauges first and see if
they are within the specified tolerance, you may be either low on helium or
of the Delta P is to great you may have a dirty adsorber.   If your helium
pressure has dropped below what the manufacturer recommends you can simply
recharge it and perform a regeneration and you should be fine (given you
don't have a helium leak somewhere), make sure to use 6.0 grade helium and
the proper helium gas filling manifold and recharging procedure.  I have
pasted a troubleshooting guide for you from a CTI system but a lot of the
principles will apply to your pump.  If you still have problems feel free to
give me a call at the numbers below.

Table 4-1: Troubleshooting Procedures

Problem

Possible Cause

Corrective Action

High base pressure of vacuum system, and a cryopump tem- perature below 20K.

High base pressure of vacuum system, and a cryopump tem- perature above 20K.

Air-to-vacuum leak in vac- uum system or in cryopump.

Check cryopump relief valve for proper seating.

Check cryopump for leaks.

Check vacuum chamber and Hi-Vac valve for leaks.

High partial pressure of non- condensables (helium, hydrogen, or neon)
within the cryopump because the 15K array has reached full capacity.

Regenerate the cryopump as described in Section 3 - Regeneration.

One of the arrays is loose, which is preventing good thermal contact with
the cold station.

Warm the cryopump to ambi- ent temperature and retighten the array mounting
screws to 15 - 20 in. lbs.

Decrease in cryopump cold head performance.

If the helium return pressure gauge reads below the nor- mal-operating
return pres- sure 60-85 psig (415-590 kPa), add gas as described in the
appropriate Compressor manual.

High partial pressure of non- condensables (helium, hydrogen, or neon)
within the cryopump because the 15K array has reached full capacity.

Regenerate the cryopump as described in Section 3 - Regeneration.

Excessive thermal load on frontal array.

Reduce the thermal radiation load by 1) shielding the cry- opump or 2)
lowering the temperature of the radiating surface.

Table 4-1: Troubleshooting Procedures (Continued)

Problem

Possible Cause

Corrective Action

Cryopump fails to cool down to the required operating tem- perature or takes
too long to reach that temperature (20K).

Low helium supply pressure.

Add gas as described in the appropriate Compressor manual.

Compressor problems.

Refer to Troubleshooting sec- tion of the appropriate Com- pressor manual.

Vacuum leak in vacuum sys- tem or cryopump.

Check the cryopump relief valve for proper seating.

Check cryopump for leaks.

Check vacuum system for leaks.

Incomplete regeneration may not have fully cleaned the adsorbing array.
Partial pres- sures of non-condensables (hydrogen, neon or helium) may
remain.

Regenerate the cryopump as described in Section 3 - Regeneration.

Thank you,

Craig Cheney

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From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu]
On Behalf Of Wang,Xiaojin
Sent: Thursday, December 19, 2013 10:05 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] cryopump maintenance

Dear colleagues:

We have a cryo-torr 8F pump on our sputtering system PVD75 manufactured by
Kurt J.Lesker. It has experienced a very strange incidence lately. During
the weekend, the gate valve between process chamber and cropump shut off
itself and the pressure in the chamber went up to several torrs while the
gate valve is supposed to open and let cropump pump the system to 10^-7
torr. The temperature of cropump went up to 215K and it was still pumping.
After we regenerated the cryopump the cooling time for it to be below 20K
has been doubled and the lowest temperature it can reach is 18K while it
used to be 13K. 

Did anyone run into this kind of incidence before and what could possibly
cause it?

What do we need to do to prevent it from happening again?

Is there anyway to bring the good performance back to the pump again? 

We also have a cryopump on e-beam system. Generally, what kind of
maintenance need to be done on these cryopumps so that we can maximize their
lifetime?

Your valuable suggestions are very appreciated.

Best wishes

Xiaojin Wang

Senior process engineer

Micro/nano technology center

University of Louisville

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