You should use silicon Nitride. It offers better resistance to KOH than oxide.
With oxide, TMAH is a better choice, slower Si ER though.

Matthieu

Le 2012-01-23 à 12:00, 
 a écrit :

> -----Original Message-----
> From: mems-talk-bounces+shay=mizur.com@memsnet.org
> [mailto:mems-talk-bounces+shay=mizur.com@memsnet.org] On Behalf Of H V
> Balachandra Achar
> Sent: Sunday, January 22, 2012 10:03 AM
> To: mems-talk@memsnet.org
> Subject: [mems-talk] Pin holes in thermal oxide
>
> Dear All,
>
> I am using 1 micron thick thermal oxide, grown using dry-wet-dry sequence,
> as the mask during bulk etching of silicon using KOH solution. After
> oxidation I notice pin holes in oxide surface. Because of these pin holes,
> silicon is getting etched in KOH at places where I don't want to etch.
>
> Please suggest a remedy.
>
> Note: I am using (100) p-type 1-10 ohm-cm Si wafer.
> Cleaning sequence: TCE, acetone, nitric acid, dilute HF Dry-wet-dry
> durations: 20 min - 4 hrs - 20 min, followed by 30 min annealing in N2
> ambient.
>
> Thank you
>
> --
> H V Balachandra Achar