I'd add that Pt is capable of withstanding high post-deposition
temperatures.  Pt/Ti/SiO2/Si stacks were developed for use as a bottom
electrode for ferroelectric film capacitors that often require a post
deposition anneal at T>600C.  There is a wealth of information on Pt/Ti
interdiffusion, adhesion, stress development, microstructure, etc. in the
ferroelectrics literature.  For a start check out the MRS proceedings
Ferroelectric Films (I think there are now something like 13 volumes over
the past 15+ years).

Charles D.E. Lakeman, Ph.D
Senior Scientist
TPL Inc.
3921 Academy Parkway North, NE
Albuquerque, NM 87123
505/342-4427 (Tel)
505/343-1797 (FAX)


-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
David Nemeth
Sent: Tuesday, December 09, 2003 9:14 AM
To: General MEMS discussion
Subject: RE: [mems-talk] Why Choose Platinum

It depends on the purpose.

A thin layer of platinum is an excellent diffusion barrier (Ti is not so
good at this) to prevent interdiffusion of metal into Silicon and vise
versa.  For example, if you want a conductive layer, you might use thin Ti,
thin Pt, and thick gold.  The platinum prevents the gold from diffusing into
the silicon, and prevents the silicon from diffusing into the gold.

If you are making a temperature sensor, platinum has a nice, linear
resistance versus temperature down to very low temperatures (about 10
Kelvin).

David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On
Behalf Of cindy seah
Sent: Tuesday, December 09, 2003 1:48 AM
To: [email protected]
Subject: [mems-talk] Why Choose Platinum


Hi,
    I know that platinum is used during the fabrication of silicon wafer.
And an adhesion layer of Ti/Tiox is used.
Can i know why is platinum (beside using gold) used instead of other metals?
If it is because of conductivty, why aren't silver (one that have the best
conductivity),copper, alumnium which have better conductivity then platinum
used?

It is due to the reaction between Ti/Tiox or does it have anything to do
with Si3n4?

Thank you...
Cindy Seah



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