Hi Joachim,
Your peeling problem is most likely due to chrome diffusion up through the
gold. At temperatures above 150 C at atmosphere, or slightly higher
temperatures under vacuum, the chrome will diffuse right through gold. Does
your gold surface look tarnished or hazy at all once the 1000W O2 plasma is
completed?
What you need is a barrier layer between your chrome and gold. Or you need
to use a different adhesion layer other than chrome, such as titanium, if
your device would allow it.
In any case, what you can do prior to evaporation to further reduce the risk
of delamination of the film is to do a light O2 plasma clean to the SiN
surface you mentioned. This will help ensure there are no organic
contaminants on the surface. On some other applications, an Argon plasma or
Ar-O2 plasma could also be used.
Regards,
Justin
Justin C. Borski
MEMS Program Manager
Advanced MicroSensors Inc.
jborski@advancedmicrosensors.com
www.advancedmicrosensors.com
-----Original Message-----
From: Oberhammer Joachim [mailto:joachim.oberhammer@s3.kth.se]
Sent: Friday, November 22, 2002 10:18 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] adhesion-layers for Au evaportation onto SiN
Hi researchers,
I have adhesion problems of evaporated Au (150 nm) to PECVD SiN (300
degC, 1 um). I'm using a Cr (50 nm) layer as adhesion. Both
evaporation processes (Cr+Au) are done in the same machine together.
I don't use any surface treatment of the SiN before the evaporation.
After exposure of the structures to O2 plasma (1000 W, 100 mTorr, 700
sccm O2) for 15 min, the Cr/Au layer is pealing off. The temperature
during the O2 plasma etch is between 150 and 200 degC.
Questions:
(1) is the off-pealing caused by the temperature during O2 treatment,
due to stress?
(2) how can I improve the adhesion? What kind of surface preparation
of the SiN do you recommend before the evaporation of Cr/Au (like O2
plasma ...)?
Thanks very very very much for any comment,
Joachim Oberhammer/KTH Stockholm.
--
----------------------------------------------------------------------------
--
Joachim Oberhammer, Dipl.-Ing.
Royal Institute of Technology (KTH) Phone: +46/(0)8 790 6250
Dept. of Signals, Sensors and Systems Fax: +46/(0)8 10 0858
Microsystem Technology (MST) Mobile: +46/(0)70 692 1858
e-mail:
joachim.oberhammer@s3.kth.se
Osquldas väg 10 homepage: http://www.s3.kth.se/mst/
SE-100 44 Stockholm, Sweden
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