[labnetwork] STS DRIE Multiplex Lip Seal failures

Fri Mar 8 15:29:59 EST 2019

Let me tag on to the topic of STS Multiplex tools with another question.

We are in the process to bring up a tool that has been running the Bosch etch process.  We noticed some build-up of white coating inside the vacuum lines and valves from the chamber.  Can someone recommend a best practice to remove and clean surfaces of this material?  Are there any particular cautions or safety concerns?

Thanks in advance.

Larry A Rehn
Technical Lab Manager
AggieFab Nanofabrication Facility
Texas A&M University
979 845-3199
lrehn at tamu.edu<mailto:lrehn at tamu.edu>
[cid:image001.jpg at 01CEC37D.FAF8C9E0]

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Kevin Owen
Sent: Thursday, March 07, 2019 12:45 PM
To: Paolini, Steven <spaolini at cns.fas.harvard.edu>
Cc: Fab Network <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] STS DRIE Multiplex Lip Seal failures

We don't have lip seals on our SPTS systems, but I do agree that Kalrez is the way to go for o-rings. All of the source o-rings for the Pegasus were Kalrez to begin with. Well, except for a couple that were called out in the BOM as Kalrez but weren't... this was remedied. I also replaced our lid seals with Kalrez about a year ago and it was definitely a Good Decision.

I wound up going with the 9300 series for the Bosch process equipment. Used to source them through Bay Seal, who was even able to make the custom size for the lid seal (it's not actually a 280, just seems like it should be), without the crazy tooling cost for most custom sizes. Recently, they suggested I find a distributor closer to my area, and I went with James Walker in Chicago, which seemed to work well for my last order.

The one case I've found where this did not work as expected was the lid o-ring in our APS tool. I think it is because we tend to excessively over-clean the chamber to accommodate some "dirtier" processes, the Kalrez o-ring actually got substantially eaten away after only about 6 months. I wonder if this could also be related to some of the lip seal issues (not saying they didn't switch to a "cheaper" material also), but it might be that over-using O2 cleans could shorten the life further like it did to my o-ring.

-Kevin

On Wed, Mar 6, 2019 at 7:51 PM Paolini, Steven <spaolini at cns.fas.harvard.edu<mailto:spaolini at cns.fas.harvard.edu>> wrote:
My $0.02,
Black marks on the back of a wafer are not normal. I agree that there must have been a material change by the supplier perhaps to “value engineer” there consumables. What IS normal is O-rings growing a black crud on their surfaces. This is simply O2 attacking organics regardless of the O-rings being out of the “ line of sight” of the plasma. A downstream etcher (two 90 degree gas shifts), will experience the same effect at a slower rate. We inspect them and if not cracked, we clean them up until the wipes show minimum crud and put them back in for more service.
Oh yeah, I wholeheartedly agree with Julia that we should not forget that the LUR with backside He is the overall LUR of the chamber and you could be mislead by some other fine leak not associated with the He seal.

Steve Paolini
Principal Equipment Engineer
Harvard University Center for Nanoscale Systems
11 Oxford St.
Cambridge, MA 02138
617- 496- 9816
spaolini at cns.fas.harvard.edu<mailto:spaolini at cns.fas.harvard.edu>
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From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> <labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>> On Behalf Of Mark Weiler
Sent: Wednesday, March 06, 2019 10:18 AM
To: Noah Clay <nclay at upenn.edu<mailto:nclay at upenn.edu>>
Cc: Fab Network <labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>>
Subject: Re: [labnetwork] STS DRIE Multiplex Lip Seal failures

Hi Noah,

We have the first version of the 100mm STS Multiplex DRIE whereby the wafer is mechanically clamped with weighted ceramic fingers, and the wafer is lifted with a tripod.  Our LUR is 0.00 mTorr/min when new, but rises to 15-20 mT/m within a week.  We have an older HBC controller that indicates 6.5 for pressure at 2.33 flow rate... I apologize but don’t know the units for either.  If these values are incorrect, it could be because they were adjusted to ensure a leak rate would pass.  I will need to go back over a decade in the logs to see if any changes were made over time...but, our rates and results have been consistent.

I believe the issue is material related, because we have our chamber lid o-ring and bottom ceramic o-ring failing with the same symptoms.

Thanks,

Mark

Mark Weiler
Equipment & Facilities Manager
Claire and John Bertucci Nanotechnology Laboratory
Electrical and Computer Engineering | Carnegie Mellon University
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On Mar 6, 2019, at 09:19, Noah Clay <nclay at upenn.edu<mailto:nclay at upenn.edu>> wrote:
Mark,

I have seen blackening on the back of the wafer when clamping is poor.  Most recently, this was due the e-chuck having been etched excessively and/or polymer redep on the chuck from the endpoint clean step (cleans used to be run without a wafer; we now use SiC).

What are your backside He leak rate set points and actual values?  We run our etch process at -5C...(SPTS Rapier platform).

Thanks,
Noah
Sent from my iPhone

On Mar 5, 2019, at 15:44, Mark Weiler <mweiler at andrew.cmu.edu<mailto:mweiler at andrew.cmu.edu>> wrote:
Hello Everyone,

We have gone through seven new lip seals purchased form Orbotech/SPTS.  They are often failing before we even finish qualifying the system, or within a month thereafter.

Our our process is stable with power and parameters not deviating over the past decade.  However, I ordered the most recent batch of lip seals because the wafer seals we had been using were coming out with black residue after only a few runs… however, the current ones do the same.  Not only have the lips seals disintegrated, but the chamber lid o-ring and bottom ceramic spool o-ring have also failed with black rubber material shedding off.  It’s as if they are made of Buna and not meant for this application.

Our process is typical Bosch with 100 sccm C4F8 and 20 sccm O2 for etching switching off with ~50 Sccm SF6 for passivation at a processing pressure of 15 mTorr, Coil power 600-800W,  Platen power 100-150W, Bias voltage 50-100v (up to 200 peak-to-peak), Platen temp at 19 degrees, Lid temp 41 degrees.  Qual wafers are new bare Silicon.  Etch rates are normal and stable with 10+ years of data…. we just can’t complete the work due to failing seals.

Our chamber base pressure is between 1E-8 and 5E-8 Torr each morning.  When we put in a brand new seal and run only the LUR, it passes with 0.00 mTorr/minute leak rate.  That jumps to 3.00 mTorr/m after only 30 minutes of the SPTS recommended O2 Clean… then rises as time and more runs progress.  Wafers are coming out with black rings on their backsides.

This should not be happening, and I believe it is due to incorrect material of the lip seals and o-rings.  I am pinging the network, though, to see if there might be a parameter change we need to effect that may assist us.

Have any of you seen this before?

Best regards,

Mark

________________________________________________________________

Mark Weiler
Equipment & Facilites Manager
Clair and John Bertucci Nanotechnology Laboratory
Eden Hall Nanofabrication Cleanroom
Carnegie Mellon University
P:  412-268-2471
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--
Kevin Owen
Senior Engineer in Research
Operations Group, Lurie Nanofabrication Facility
University of Michigan
(734) 545-4014
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