A set of 4 µm wide windows are to be etched into a SiO2 film of thickness 0.8µm.
a) Find the dimension of the window, as measured at the top of the oxide, after ideal isotropic etching (i.e. no overetch). Draw a cross section of the window opening with the resist still on.
b) What is the dimension of the window at the oxide substrate interface.
c) Find the average slope of the window edge.
d) Repeat the above question a), b) and c) if the process was done with a 20% over-etch, assuming that the silicon is etched at 2% of the oxide etch.
e) what type of Si wafer (orientation) and chemical etchant would be needed to make a perfectly vertical wet etch for these 4 µm wide windows? Comment on the practicality of such an etch.