Hi Vinit,

54.7 is the angle between (111) plane to the wafer surface(100).  Due
to the atomic sturcture of silicon, the (111) plane is etched slowest
almost in every anisotropic etchant.  So you cann't get rid of 54.7
degrees.

However,  you can get vertical sidewalls if you align your opening to
(100) direction, not the wafer flat, then the (111) planes only occur
on the corner of the opening.  If you align your opening to other
directions, other angles will be possible, depending on the ER profile
of the etchant.

Another way is using (110) wafer, then you can get vertical sidewalls
which are (111) planes.  What kind of method you use, and what kind of
mask you should design will be related to your objective.

All these information can be in the literatures or the book
"fundamentals of MICROFABRICATION".

Good luck.

Duan

On 6/14/05, [email protected]  wrote:

> Is there any Si-etch method which etches anisotropically at angles lesser
> than 54 degrees ? I've looked around but the KOH-etch giving the steep
> 54.7 degree inclines is all that I've found.  I am looking to etch ~200
> microns deep.