[Fwd: Lampoly with Aluminum]

[Mary Tang]

Hi all --

Think of this as another tangible test case.  What do you think?

Mary

-------- Original Message --------
Subject: 	Lampoly with Aluminum
Date: 	Thu, 2 Oct 2008 17:14:02 -0700
From: 	Joey Doll <jcdoll at stanford.edu>
To: 	Mary Tang <mtang at stanford.edu>
CC: 	Bryan Petzold <petzold at stanford.edu>



Hi Mary -
Here's a paragraph re: metal in lampoly:

In order to release microcantilevers fabricated on SOI wafers, a 
frontside silicon etch is required. Ideally this etch would be uniform 
within a few % across the wafer, stop on the buried oxide and have 
vertical sidewalls without scalloping (as in DRIE) for low noise. In 
order to minimize the topography on the wafer for lithography steps, it 
is best to release the cantilever as one of the last steps, after the 
deposition and patterning of aluminum bondpads. We propose allowing the 
introduction of wafers with standard metals (Al, Ti, W) into lampoly if 
the metal is protected by photoresist and not exposed to the plasma, 
much like the policy on STSEtch. As in the case of STS, the etch chamber 
is aluminum already, so keeping aluminum at least out of the chamber is 
somewhat of a moot point, and the wafer is cooled on the backside, 
keeping temperatures down and the metals at the surface of the wafer so 
that they can be removed by a subsequent diffusion clean. However, the 
metal on the wafer would not be exposed to the plasma under normal 
operation, and again much like STS and drytek2, it should be possible to 
keep the tool in the clean/semiclean category so that clean wafers 
coming into it could still go back into the tubes afterwards while 
semiclean wafers coming in remain semiclean going out.

Let us know what you think. We have wafers with some aluminum on them 
right now that we would be interested in etching as soon as possible, 
but titanium is something we'll be using in about two weeks.

Thanks,
Joey

-- 
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at stanford.edu
http://snf.stanford.edu