Adhesion of evaporated gold on silicon oxide is very poor. You have to
deposit an adhesion layer. A few nm of Chromium or Titanium works well. They
react with the oxigen of silicon oxide and present a metallic bond with
gold. I use 5 nm of Cr for 150 nm of Au. It is important to deposit Cr and
then immediately Au. If you open the vacuum chamber in between the surface
of Cr (or Ti) will be oxidised and the adhesion is poor. In this case you
need to heat the wafer at almost 250 - 300 C to obtain some adhesion.

If you need to deposit Au directly on silicon you must remove the native
silicon oxide with a deep in diluted HF immediately before loading the wafer
in the evaporation chamber. After the deposition you have to heat the wafer
to have some Au - Si  diffusion and improve the adhesion. I never do that
but probably 200 -300 C will work
Remember that at 363 C there is an eutectic point  and a liquid Au-Si  phase
will be formed.

Regards

Flavio

__________________________________________________________
Flavio Giacomozzi
ITC-irst                                  Tel +39 - 0461 314432
Via Sommarive 18                     Fax +39 - 0461 314591
38050 Povo  Trento                   E-mail [email protected]
Italy                                         Internet: http://www.itc.it/
http://mis.itc.it
__________________________________________________________



----- Original Message -----
From: Chen-Han Lee 
To: Mems-Talk 
Sent: Tuesday, August 31, 2004 4:07 PM
Subject: [mems-talk] adhesion between Si wafer and gold film


>
>
>
> Dear all,
>
> could anyone help me please.
> I am doing some electroplating using SU-8 mould.
> gold is evaporated before SU-8 is deposited.
> after the developing step,
> many SU-8 parts fall off of the wafer with gold film attached to them,
> how do i improve the adhesion between Si and the gold film,
> so that i have a a complete patterned wafer??
>
> thanks for the help.
>
> Chen han
>
> ///////////////////////////////////
> Chen-Han Lee
> Research Student
> School of Manufacturing and Mechanical Engineering,
> University of Birmingham,
> Birmingham, B15 2TT
> United Kingdom,
> Phone :  +44 121 4144245
> Fax :    +44 121 4143958
> E-Mail : [email protected]
> ///////////////////////////////////
>
>
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