[labnetwork] STS DRIE Multiplex Lip Seal failures

Thu Mar 7 03:40:47 EST 2019

For what it is worth we used to run an SPTS Pegasus deep RIE etcher years ago, there is a Plasmatherm Versaline in its place now. I think we sold it ~6 years ago. We had many problems with it towards the end of its life but o-ring seals were with regards to chamber or He leak rate were not one. We used the same set for possibly years at a time. I recall being advised on an official training course to boil them for a couple of hours in water to remove the flatted edge before re-sealing the chamber which I never did, but always found to be quite interesting advice. I did have to rebuild the lower platen once due to a coolant leak and it did take me a about a day to get it to seal due to the complex arrangement of o-rings.

If the black circle on the rear of the wafer is not the material breakdown of the o-ring itself, it could be micro-masking from rear wafer deposited polymer/spontaneous etching of Si radicals giving a rough Si surface? Do not ask me why this would be the case but we find it is often the cause of unexpectedly blackened Si wafers removed from etch chambers.

O.

From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> On Behalf Of Paolini, Steven
Sent: 06 March 2019 22:32
To: Mark Weiler <mweiler at andrew.cmu.edu>; Noah Clay <nclay at upenn.edu>
Cc: Fab Network <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] STS DRIE Multiplex Lip Seal failures

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>
www.cns.fas.harvard.edu<http://www.cns.fas.harvard.edu>

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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