Hi Mehmet,

I normally use 5nm Cr as adhesion layer which works quite nice. 5nm and less
should also work for your etchant not to attack. Usually I obtain continuous
films (5nm). So, try 5nm or even less, 2-3nm to be safe of underetching.

The CrOx in the crucible should not be a problem, normally you evaporate the
Cr.

Success!
Daniel

* Dr. Daniel Grimm
* IFW Dresden
*            - Institute for Integrative Nanosciences -
* E-Mail:  d.grimm@ifw-dresden.de
* Phone: +49 351 4659-314
* Mobile: +49 177 4926561

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Mehmet Yilmaz
Sent: Freitag, 28. August 2009 17:54
To: mems-talk@memsnet.org
Subject: Thinnest Cr layer that can still successfully adhere Au to Si

Hello all,

I am trying to stick Au on Si substrates.
I am using 10nm Cr as adhesion layer between Au and Si.

But I am not sure if the layer that I am depositing is pure Cr, or some
Cr Oxide is also there. The crucible that I am using seems to be
contaminated with Cr Oxide before I start my e-beam evaporation of Cr.
Instead of having the gray shiny color of Cr, at some regions of the
crucible I see a greenish color which is probably Cr Oxide...

I do not see any serious adhesion problems after further processing of
my wafers except the last release step to have free standing Au thin
films. I see a problem when I insert my wafers into a Cr etchant. I am
inserting my wafers into this Cr etchant to get rid of some of the Cr
layer which is not covered with Au (This Au patterning is done in
previous steps). But, during this etching process, I realized that the
Cr etchant that I am using penetrates so fast from the Au-Si interface,
the Au structure that I want to keep on top of my substrate peels.

I suspect that, the capillary forces in the Au-Si interface are playing
a strong role during that process and Cr adhesion layer is etched
extremely fast because of that.

I wonder whether 10nm Cr adhesion layer is a continuous film or not
continuous?

If 10nm Cr is a continuous layer, then I wonder how thin should be the
Cr layer that I need to evaporate in order NOT to have a continuous Cr
layer? This way, I believe I will be able to keep Au layer on my
substrate because the Cr etchant that I am using will not be able to
penetrate through the whole Au-Si interface because Cr adhesion layer
will not be continuous... But, I am not sure if something less than 10nm
Cr will be enough to have good adhesion between Au and Si...

Do you have any suggestions?

Thanks in advance,

Mehmet Yilmaz
Mechanical Engineer