Dear Y.C. Lin,

I think that you have a problem with the silicon nitride. Both KOH and TMAH
should be
masked easily with 1500 A LPCVD silicon nitride. Check the refractive index. It
should be
somewhere around 2.05 to 2.10 ( I don't rememer the exact figures). Otherwise,
you could
have too many pinholes in the film.

As mask material you could use thermal grown silicon oxide instead. The
selectivity of
silicon to silicon oxide is around 100 for 30 wt.% KOH at 80C. In TMAH the
selectivity is
generally much higher (> 1000), but I don't know the exact figure for an 8 %
concentration. Low concentrations of TMAH gives rough surfaces, but high etch
rates. For
better surface quality, concentrations above 15% are preferred.

Regards,
Gert Eriksen




On 1 May 2004 at 22:37, g915705@oz.nthu.edu.tw wrote:

> Dear all:
>
> I have questions about the TMAH and KOH etching.
> I use a layer of LPCVD nitride with 1500A thick.
> After 3 hours KOH etching (30% w.t., 80C), the nitride layer is etched
seriously.
> Similarly, the nitride layer cannot survive in TMAH (8% w.t., 90C) for more
than 5 hours.
> Is there any method or material that can be used as the etching mask in TMAH
and KOH for
> at least 11 hours? Please give me some advice. I really appreciate it.
>
> Regards,
>
> Y.C. Lin
>
> Dept. of Power Mechanical Engineering,  National Tsing Hua University, Taiwan.
>
>
>
>
>
>
>
>
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