Shortening the etch cycles will improve roughness.  If you have the means to
cryogenically cool the substrate during the etch, a smooth, anisotropic sidewall
can be achieved using conventional (SF6/O2) RIE.  A sharp bend in the anisotropy
vs. substrate temperature curve occurrs at -40 deg (C/F).  This allows for a
straight sideawll without the cyclic sidewall scallopping characteristic of the
Bosch proces.

Neal





Jobert van Eisden  wrote:
Dear all,

We are trying to etch vias (3-10 um) to a depth of 5 um with sidewall
roughness under 30 nm. The mask we use is 1 um thermal oxide. I would
like to ask you all if there is any way the Bosch process can be
adapted, or if there is a gas chemistry we can use to do a RIE process
that gives us these smooth sidewalls. There should be little or no mask
undercut.

We have tried running a Bosch like recipe using very little ICP power
and short cycles, which gave us too much sidewall roughness.
The available chemistries are CHF3, CF4, O2 and N2 on the dieletrics
chamber and SF6, C4F8, O2 and Ar on the Bosch chamber.

I would very much appreciate ideas and suggestions.

Regards,

Jobert van Eisden
Graduate student
SUNY Albany

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