Hi Peng,
Selectivity between silicon nitride and silicon is not good in most dry
etch systems. You can etch with CF4/SF6 but the selectivity typically
will be close to 1:1.

Michael Pedersen
The MEMS Exchange

Peng Yao wrote:

> Hi,
> I am going to etch silicon using silicon nitride as the mask. But I only
> have CF4, SF6, O2 and He... I am not sure if those gases are enough for my
> application or I need to order some new gases.
> Thanks.