Pavan

Your PEB temperature will play a very imp role in deciding the side wall
profile. For  measuring the undercut you can see it under a microscope, but it
is more of a qualitative estimate. You can cleave the wafer and measure the
undercut in a SEM would be better, but if you choose to section the wafer with
PR only, make sure you sputter some gold or else the resist will charge up like
a christmas tree in the SEM.

Factors such as exposure time  and develop time will ensure that your features
are clear, i would suggest you first fix your exposure dose and develop time and
then tweak your PEB temp to get the dersire undercut.

Your idea for measuring the undercut on a glass wafer will also work, just make
sure the the type of glass (borofloat or Pyrex) has a CTE close to Si. In
addition the manner of baking your wafer will also effect the result, .i.e if
you using a hot plate these might be some descripancy in the results as the heat
transfer is through conduction, but if you are baking your sample in a oven you
results should be pretty close as heat transfer is a combination of conduction
and convection.

Hope it helps