Funny smell at Metalica

Mary Tang mtang at
Thu Dec 9 10:28:27 PST 2004

Hello SpecMat’ers and others with vested interest in metal dep tools –

First, a summary:

There was a strong smell reported emanating from metalica, Wednesday on 
Coral. Knowledgeable noses identified the smell as sulfurous. Zheng Wang 
(wangz) had deposited ZnCdS on this system on Tuesday. However, several 
people (Jeannie, Rafael Aldaz) had noted that the smell was noticed 
before her deposition.

Zheng is using Jim McV’s RF modification to deposit her materials. Jim 
McV set this up over a year ago, intially for MgO deposition, I believe. 
She has all her own hardware, which is labeled as contaminated and kept 
separately. She has been depositing ZnCdS since about February. Her 
deposition time is about 30 minutes and has not changed and she deposits 
this fairly frequently. (Jim H. noticed a strong smell on the cryopump, 
when he replaced this in September. However, up until this week, no 
unusual smells were noted by other users of metalica.)

After speaking with Zheng this morning, we now know that she also used 
the system to deposit GeSe on Friday. Because it is tricky to sputter 
Ge, she says she inadvertently boiled off the target.

We now believe that the smell is actually selenium.

Zheng is depositing ZnCdS this morning again. Once she is done, Jim H 
will take the system down and replace all the hardware. I don’t know if 
additional precautions need to be taken to clean out the bell jar. I 
would certainly think that we would need to take some extra precautions 
the next time the cryopump is taken care of.

Second, issues that we should address:

   1. The staff responsible for the metalica were unaware that these
      materials were being used.
   2. Although only certain people were trained to use these new
      capabilities and new materials, it is not clear there is a method
      for ensuring that these practices do not propagate to other users
      in an uncontrolled fashion.
   3. Are there any special safety precautions we need to take, given
      that Zn, Cd, S, Se are low vapor pressour compounts that are being
      used at metalica? There is no loadlock on this system which might
      expose users, and certainly, maintenance might be more of a problem.

Should we make this a topic for our next SpecMat meeting?


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

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