SpecMat Logsheet, Dec. 5, 2006

Ed Myers edmyers at stanford.edu
Mon Dec 4 15:42:01 PST 2006

SpecMat Members,

I have a conflict for tomorrow's meeting.  We only have a couple of 
items, so I am canceling the meeting.

New Items:

1) Bismuth/Antimony Telluride is not listed in the standard 
materials, and I would like to know if I can use it in a limited way 
in the lab.  The material would be brought into the lab as patterned 
films on the order of 10 um thick on 4 inch silicon wafers or smaller 
chips.  Initially I will be doing SEM work.  Later I will be 
depositing metals, thereby encapsulating the Bi/Sb-Te, and patterning 
the metals.  I do not know the specifics of the equipment that would 
be used but they would be the 'contaminated' class of tools.

Recommendation:  The MSDS seems viable.  There is concern about 
vapors which can form by water, acids or oxidizers.  My initial 
impression is the request can be approved, but we should get more 
detail the process flow first.

2) I am requesting approval of the following: 1. application of 
polycarbonate plastic film in Innotech. 2. Bring in outside wafer 
after CMP. The surface at this stage surface contains SiO2 and 
carbon. 3. SiO2 etch in drytek 4 of a wafer having both SiO2 and 
carbon on the surface. 4. PECVD SiO2 dep on a wafer that has carbon 
nanotube exposed.  My process flow is the following: 1. Silicon 
Nitride deposition on Si wafer (clean) 2. Litho to pattern the 
nitride 3. Ni (10nm) and Fe (3nm) deposition through a polycarbonate 
membrane and SS shadow mask in Innotech. (cont) 4. PECVD SiO2 
deposition (cont) 5. CMP (outside lab) 6. Drytek 4 etch of SiO2 
(cont) 7. PECVD SiO2 dep (cont) 8. Cr dep (cont)

Recommendation: Approve the process.  The question I have regards 
post-CMP cleans.   Do we have a recommended clean process for each 
equipment category?  Any suggestions.

3) I need to etch silicon isotropically with a high selectivity to 
oxide and nitride. I was planning on doing it in the new XeF2 but it 
is a gold-contaminated equipment. After this step, I need, among 
other things, to do wet oxidation and DRIE.  Is there any way to 
decontaminate a wafer that has gone through the XeF2 machine or 
should I just drop the idea of using XeF2 in this process (in which 
case are there alternatives to do a highly slective isotropic Si etch)?

Recommendation:  The question is, can we use the Xactix as both a 
semiclean and gold contaminated equipment?  The wafers or samples set 
on a removable stainless steel platen.  If we dedicate the platens to 
the appropriate clean category, can this tool serve a dual 
purpose?  Initially it was my plan to use the Xactix for all 
categories (silicon), but the Xactix VP told me a story about having 
gold evaporate off the sample and coat the chamber.  The etch process 
is exothermic and under certain conditions, vaporization of the 
material is possible.  I think this has a low chance of occurring.  I 
would like to suggest we take the risk, fabricate multiple platens 
and open the tool up to both semiclean and gold contaminated samples.

Please respond with your comments by Thursday, Nov. 14th.


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