Dan W Chilcott@DELCO on 06-17-98 02:18:17 PM
Dear MEMS experts,
I have a Si wafer coated with a LPCVD silicon nitride thin film
200nm thick. I need to bond this silicon nitride coated wafer to
another Si wafer. Are there any good methods for bonding a silicon
nitride coated surface to another surface? I am flexible about the
surface coating of the second Si wafer.
If there exists such a bonding method, does it matter whether the
silicon nitride coating was deposited by LPCVD, PECVD or
sputttering???
Thanks,
Richard Koba
Foster-Miller, Inc.
195 Bear Hill Road
Waltham, MA 02154-1196
781-684-4197
fax: 781-290-0693
Richard-
Direct bonding of silicon nitride has been reported. UC Davis has
done some good work in this area.
Like any direct bond the surface roughness is the most important
issue. The surface roughness of prime silicon wafers
is barely good enough for direct bonding. Thus, deposited films are
usually too rough for a good repeatable direct
bonding process. LPCVD is favored over PECVD or sputtering for this
reason. The solution to direct bonding
deposited films is CMP or some other method of leaving a smooth
surface.
Surface treatments have been studied for modifying the bond surfaces.
Both wet and plasma treatments have been used.
These treatments are usually aimed at producing a hydrophilic surface
for good room temperature contacting of the
wafers. Hydrophobic treatments have also been used to obtain
electrical contacts at silicon to silicon bonded interfaces
at the expense of room temperature contacting.
There are other silicon wafer bonding methods but they use
intermediate layers. These layers are usually not compatible
with further fab processing.