Good morning,

In case of Si/W/Au, I have tried to deposit a very thin layer of Titanium on W.
A 10nm Ti layer works since if create a diffusion barrier to adhere W and 500nm
Au. I dont know what is the thickness of Au film you need but the best thickness
of Ti layer can be differed according to the Au film thickness.

The same thing will happen when you deposit Au on the Si wafer but remember, if
you deposit with sputtering, do not use a slow velocity of deposition since it
will create the very high grains developed on the surface of thin film.

Furthermore, there're some kind of photoresist that can stay on tungsten not
very bad. But for the substrate of W, normally, you cannot have a thick layer of
photoresist. My suggestion is that you etch the surface by the sputtering plasma
after you deposit W. It can better the result.

Good luck.

Kim-Anh BUI-THI

Stagiaire de ThalC(s Recherche et Technologie
91767 - Palaiseau Cedex

Portable : + 33 6 37 955 998
--Forwarded Message Attachment--
From: [email protected]
To: [email protected]
Date: Fri, 13 Jun 2008 10:10:39 -0400
Subject: Re: [mems-talk] Gold pad bonding problem

I have a similar issue when I tried to place photoresist on top of
tungsten metal.  Adhesion was poor and the photoresist flaked more than
usual.  I used HF which removed the oxide layer and allowed for better
adhesion of my photoresist.  HF removed tungsten oxides, but does not
etch the W metal.  Here are some refs to that effect.

Hockett, L. A.; Creager, S. E. Review of Scientific Instruments 1993,
64, 263-264.
Paparazzo, E.; Moretto, L.; Selci, S.; Righini, M.; Farne, I. Vacuum
1999, 52, 421-426.

Also, we electrically deposited gold onto tungsten microwires.  The HF
helped the adhesion of the gold as well.  That reference is

Hermans, A.; Wightman, R. M.  Langmuir; 2006; 22(25); 10348-10353.

Just an idea.  Good Luck.

-Richard