Paul,

The holes are quite big and the aspect ratio small so you shouldn't have
any problems getting an angle less than 1 degree.  If you are prepared
to do some development you may even get vertical walls.  On the other
hand it is much more difficult to get positive profiles.

Start with the standard deep etch recipe that came with your etcher and
from there control the angle by changing the etch cycle time or the
platen power.

Bear in mind, you need to be careful what to use as an etchstop.  It's
best not to etch to oxide to avoid footing so you could mount the wafer
or, as the exposed area is very small in this case, use a metal layer.


Ian Johnston


Subject: [mems-talk] DRIE sidewall angle

What is the expected tolerance for sidewall angle when DRIE 'etching a
Si
substrate 500um thick?

I need to etch an arrayed die pattern consisting of two holes 125um and
155um diameter.  The two holes are spaced 150 um apart and the die are
~1mm
apart.  I want to etch 125 um diameter hole through the 500um thick
wafer
and obtain a negative sidewall profile no greater than 1 degree and a
backside hole diameter of 125um +17um / -0um.  Likewise, I need the
155um
diameter hole to have a negative sidewall profile no greater than 1
degree
and a backside hole diameter of 155um +17um / -0um.

Thank you in advance for any guidance,

Paul