Deep silicon etching is often done using the Bosch process, but this does
not give 70-80 degree wall profiles; in fact it often gives negative wall
profiles (i.e. greater than 90 degrees) which are bad for filling.  There
are two alternatives.  It is possible to etch isotropically using an ICP
system with only SF6, at rates over 20 microns/minute.  This gives a better
profile for filling, but is only appropriate for quite large holes.  As this
is a recently developed technique, there are not any datasheets on the web
yet describing this.  Contact me if you want more information.

Smaller holes (and other 'filling' applications that require positive
profiles) can be created using a cryogenic process, with the sidewall
protection achieved using low volatility oxy-fluorides.  This process can
achieve similar etch rates to the Bosch process, but has a wider range of
profile control.  An example of this can be seen at
http://www.oxford-instruments.com/PLMAPP621.htm.

Alternatively, if rate is not an issue, the cheaper way of producing these
holes is by RIE (both the previously mentioned processes need ICP) and
SF6/O2.  Again, I can supply details for anyone who wants more information.

Martin (mailto:[email protected])

>dear all,
>
>i'm looking for information about deep silicon etching for
>via holes fabrication (side wall 70 or 80 degrees for further
>metallization).
>
>I would be grateful for any suggestions.
>
>Ngo

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