Priyank:

Are you just trying to rie etch the silicon with some undercut or are you trying
to produce vertical profiles? If you have an rie diode reactor you can try the
following for a silicon etch
Power 150 watts
Gas: SF6
Flow  20 sccm
Pressure: 250 mtorr

For a more vertical profile try
Power 150 watts
Gas: SF6
Flow: 20sccm
Gas: O2
Flow 10 sccm
Pressure 200 mtorr

Good luck Bob Henderson