can you control the bias? Try larger bias.

Ar should help your etch rate. And O2 would give your anisotropy.

The doping in your SOI might be different from your bare Si. That could be
the reason.

Jie

On Thu, Dec 4, 2008 at 11:20 AM,  wrote:

> Hello all,
>
> I have just started working with SOI wafers and I just come across my
> first frustrating problem:
>
> I can't etch with our RIE two SOI wafers, and I have to.
> Strange, but I etched other SOI wafers (with different device layer
> thickness) and bare silicon wafers without problems with the same RIE
> recipe.
>
> But, when I try with these two wafers, the etching rate decreases as
> much as ten times, and then the resist thickness is not enough to etch
> the device layer.
>
> The device layer is 300 nm thick of silicon.
>
> I tested different parameters:
>
> SF6: from 7 to 26 sccm (and also with small amounts of O2 and Ar, but
> they decreased the selectivity),
> RF Power: from 20 to 75 W,
> Pressure: from 0.02 mbar to 0.2 mbar (= 15-150 mtorr).
> Resist: 500 nm ZEP520 (I also tried PMMA, but the selectivity was worst)
>
> In the deepest etch, I only get 200 nm etch before the resist
> disappears.
>
> The recipe should work for 300 nm Silicon, so I started to suspect that
> either something strange happens with the wafers, or I am missing
> something important in the procedure.
>
> Until now I worked with the wafers without cleaning (just as clean as
> they come from the box). Do you think that this could be the problem?
> Should I clean them with acid before processing? How?
> Do you think that it is possible that a thin film of oxide, or
> whatever, in the surface of the wafer could be the problem? Or do you
> think that the cause could be another reason?
>
> I would appreciate any suggestion, because I really need to etch these
> wafers.
>
> Thanks,
> Jose Marques

*  Zou Jie (Jay)
*  Department of Physics
*  University of Florida
*  Tel: +1-352-846-8018
*  Email: [email protected]
*  Homepage: http://plaza.ufl.edu/zoujie/