> I etched the substrate about 2 min.
If you etched around 80C, 2 min etching in KOH should give you an etched
substrate.


> 1). Etch rate is so small that the substrate is not etched.
Depending on your etch emperature. If you say RT, no way.

> 2). The nature oxide on the substrate is prohibit the
>     etching of the substrate.
I do not think so. The native oxide can not sustain in KOH for 2 min at
80C.


I gues the problems are (1) your exposing was not enough,
                     or (2) your PMMA was a little bit thick,
                     or (3) your soft baking was done at high temp, or so
                            long.


Good luck.


============================================
Kiyotaka Mori (Graduate Student)

Dept.of Materials and Nuclear Engineering,
BLDG.090,
University of Maryland at College Park,
College Park, MD 20742
Tel: 301-405-5229
Fax: 301-314-9467
E-mail: mori@eng.umd.edu
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