[labnetwork] Challenging Oxide Etch Process

[Pilar Herrera-Fierro]

Hello Ronald,
This is Pilar, from LNF. First thank you for the help with the vapor HF.
What we sometimes do is to deposit Ti on top of the Au, because some
plasma  tools do take Ti. Ti is easily wet etched from gold. Now, I am not
sure if there will be surface tension issues with such a small cavity but
good thing is silicon dioxide is hydrophilic...
Hope it helps,

Pilar

On Wed, Feb 17, 2021 at 3:50 PM Reger, Ronald K <rreger at purdue.edu> wrote:

> Dear Colleagues,
>
>
>
> One of our faculty members has a process he needs to run in which
> nano-scale oxide definition is required to expose a gold contact pad.  With
> our shared-use RIEs we are very concerned about Au contamination in our
> etch tools, particularly for our electron device researchers.  We’re
> seeking your input from your facilities whether you may have etch tools
> that allow Au processing for these specialty kinds of processes, and if you
> have a procedure for dealing with such contamination.  A generic sketch
> about what our faculty member needs is shown below.
>
>
>
> So, have you dealt with this contamination issue with your multi-use tools
> before, and how do you deal with mitigating the contamination?  Do any of
> you have a tool that could be used by this research group?
>
>
>
> Thanks very much in advance.
>
>
>
> Ron Reger
>
> Birck Nanotechnology Center
>
> Purdue University
>
>
>
>
>
> *Generic process steps*:
>
>
>
> Fabrication need: metal connection to a sub-micron-size metal pad buried
> under <=50nm ALD oxide (HfO2 or Al2O3).
>
> Conventional fabrication steps (see sketch attached):
>  (1) cover metal pad with etch-resistive metal, e.g. Au,
>  (2) ALD-grow oxide (20-50nm),
>  (3) define a sum-micron PMMA mask using e-beam lithography,
>  (4) dry etch oxide with Au serving as a stop-etch layer (ICP-assisted
> etch using BCl3 or SF6 gases),
>  (5-6) subsequent standard e-beam lithography to connect the exposed Au
> pad to the outside circuit.
>
> Problem: Au (or any other metal which forms non-volatile compounds in RIE
> system) may be problematic for some electron device processes and is
> restricted from being used in shared-use RIE oxide etchers.
>
> Current work-around: for large (>10 micron) pads steps (3-4) can be
> performed by optical lithography + wet etch in HF. e-beam resists like PMMA
> are attacked by HF and this work-around cannot be used if sub-micron
> lithography is needed.
>
>
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-- 
Pilar Herrera-Fierro, Ph.D.
LNF User Services Director
Lurie Nanofabrication Facility
University of Michigan

RM 1239 EECS Building
1301 Beal Ave.
Ann Arbor, MI 48109-2122

*Cell* 734 646 1399

(734) 646 1399

www.lnf.umich.edu
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