Dear Kagan,

I echo Om's statement regarding the robustness of thermally grown SiO2 in
wet anisotropic Si etchants.  The majority of my experience is with TMAH
etching, and I routinely used ~500 nm of "wet" thermal oxide as an etch mask
to etch 500µm of Si in concentrated TMAH at 90C.  I observed an oxide etch
rate on the order of ~10 nm/hr and a Si etch rate on the order of 50µm/hr,
with a Si:SiO2 selectivity of 5000:1.  In my limited experience with KOH, I
found that concetrated KOH solutions typically had lower Si:SiO2 selectivity
than concentrated TMAH solutions for comparable temperatures and Si etch
rates.  While I have no first-hand experience with deposited oxides, it is
my understanding that LPCVD oxides withstand wet etching better than PECVD
oxides, and thermally grown oxides are generally more robust than deposited
oxides.

Good luck,

Brian C. Stahl
Graduate Student Researcher
UCSB Materials Research Laboratory
[email protected] / [email protected]
Cell: (805) 748-5839
Office: ò_Ó MRL 3117A


On Wed, May 5, 2010 at 10:48 PM, Om Suwal  wrote:

> Dear Kagan,
>
> In my experience, the use of thermally grown oxide does stand well as etch
> mask for both TMAH . The oxide etch rate is ~2A/min for TMAH @80C.
> Thermally
> grown >3000 A oxide is sufficient as etch mask to etch for 500 um
> Si substrate of SOI.
>
> Regards
> Om
>
> On Thu, May 6, 2010 at 3:44 AM, Kagan Topalli <
> [email protected]> wrote:
>
> > Hi,
> >
> > PECVD nitride and oxides cannot withstand several hours of KOH or TMAH
> > etching. LPCVD nitride or thermally grown oxide might be the choices for
> > masking KOH or TMAH etching.
> >
> > Regards.
> >
> > Kagan Topalli