Request to use lampoly or p5000 to etch semi-clean wafers

Nahid Harjee nharjee at
Thu Oct 8 21:08:53 PDT 2009


I am designing a process to fabricate single crystal silicon cantilevers
that are 3 um thick. The narrowest cantilevers are 14 um wide and have 4
"legs" at the clamped end that are 2 um wide. I am trying to select a tool
to etch the 3 um of silicon to define the cantilever that will produce
straight sidewalls. In the past, I have used stsetch to define wider
cantilevers. However, I am concerned that the scalloping resulting from this
tool will make it difficult to etch the 2 um legs of the new design. Thus, I
am writing to propose that I perform this etch with HBr/Cl2 chemistry in
lampoly or p5000. What makes this process non-standard is that my wafers
will be semi-clean at this point. The step prior to defining the cantilevers
is deposition of 1500 A of Al in gryphon which is then patterned with a wet
etch in Al-11. During the Si etch, the Al will never be exposed to the
plasma (it will be covered by 3 um of resist). However, there is a chance
that there will be trace Al on the exposed Si from the Al-11 bath. At the
most recent process clinic, Keith Best raised the point that there may be
exposed Al in the EBR region of my wafers. In order to minimize this
possibility, I can use 5 mm EBR for the Al litho and 2 mm EBR for the
cantilever litho, ensuring there's a buffer of 3 mm of resist with no Al
below it.

I look foward to hearing your decision on the proposed process or if there
is a tool that is better suited for this process, I welcome any suggestions.



Nahid Harjee
Ph.D. Candidate
Electrical Engineering
Stanford University
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