HgTe/CdTe in Raith

Mary Tang mtang at stanford.edu
Thu Apr 22 16:11:40 PDT 2010

Hi Jim, Ed  --

I also followed up with Jim Kruger who said much the same thing.  He 
brought up the additional concern that even if users had their own 
chimney and quartzware, they would have to store it and clean it in a 
safe place.  And me, I'm worried about the pump oil. 

As for the Raith, James has been routinely allowing II-VI compounds in.  
Rationale is that the samples are largely cooled, and maybe only locally 
heated where the beam strikes -- and that's going to be covered in 
resist anyway -- and as Paul has indicated, the total energy is 
extremely low.  James says these materials were fairly routinely 
processed in ebeam at HP (they even deposited them in a sputter tool, 
during the last few days before a monthly pm.)

I'd like to propose that we OK this for the Raith.  As for the MRC, I 
would suggest we voice these concerns and offer to help them -- advice 
on getting an etcher for their own lab, due diligence with EH&S, 
alternatives on campus, etc.

What do you think?


Jim McVittie wrote:
> Mary,
> If it was just a small sample once in a while I doubt there would not be
> much of a safety issue. But if we allow it, the use would grow and safety
> issues would have to be addressed, so we have to look at the safety issues
> up front. At present the all our toxic etch byproducts are volatile so
> they go out the exhaust although I think it is best to assume vacuum oils
> coming from the etchers are toxic and should be handled as such.  It is
> not clear to me that all the etch products from HgTe/CdTe are volatile.  
> The etching/sputtering process will likely fragement this material into
> its components and other products. Since Hg, Cd and Te are all toxic,
> there could be a problem for users opening the chamber and for the techs
> working on the chamber and pumps. I doubt we have the time to work out the
> details to insure that the system is safe after etch this material. I
> suggest they get their own etch system in their lab and let them work out
> the procedures for keeping its use safe.
> 	Jim   
> On Wed, 21 Apr 2010, Mary Tang wrote:
>> Hi all --
>> I don't believe there is any reason that he should not be able to 
>> process these materials in the Raith, since the temperatures would not 
>> be expected to be very high. It isn't likely the beam would be directed 
>> at the material itself, but just the resist on top. And I can't imagine 
>> the vapor pressure would be higher than for resist.
>> As for the MRC request, I caught part of the conversation between Jim 
>> McV and Jim K about this -- at that time, I think both were in agreement 
>> that if they had their own complete, dedicated set of quartzware and 
>> shields, we could minimize the possible risk of off-gassing in 
>> subsequent runs. The concern, I believe, was not the individual piece or 
>> two, but coming up with a broader, workable solution in case this work 
>> expands or similar materials are introduced. I think the one thing that 
>> had not been resolved was how to handle the diffusion pump oil (not a 
>> user issue, but a maintenance staff safety concern.) I suspect the 
>> safest solution (unless we ban the material from etchers) would be to 
>> require staff wear PPE while performing pump oil changes.
>> What does everyone else think?
>> Mary
>> Matthias Baenninger wrote:
>>> Dear Special Materials Committee,
>>> In addition to my inquiry about using the MRC etcher (see separate 
>>> email), I'd also like to check if I could use the Raith to do ebeam 
>>> lithography on HgTe/CdTe devices. The material is identical, i.e. 
>>> Hg_0.3Cd_0.7Te/HgTe heterostructures grown on a CdTe (Zn 4%) 
>>> substrate. Spinning of the resist and developing would be done 
>>> externally, so the device would be covered in PMMA during the entire 
>>> process done at SNF.
>>> Many thanks,
>>> Matthias Baenninger
>>> Coral login: mbaennin
>>> -----------------------------------
>>> Matthias Baenninger, PhD
>>> Goldhaber-Gordon Group
>>> Stanford University
>>> McCollough Bldg., Room 224
>>> 476 Lomita Mall
>>> Stanford
>>> CA 94305-4008
>>> USA
>>> Phone: +1 (650) 723-5892
>>> -----------------------------------

Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at stanford.edu

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