It is desired to etch out a region of a silicon dioxide film on the surface of a silicon wafer. The SiO2 film is 100 nm thick. The width of the etched-out area is specified to be 650 nm.
(a) If the degree of anisotropy for the etchant in the process is known to be 1.25, what should be the size of the opening in the mask through which the etchant will operate?
(b) If plasma etching is used instead of wet etching, and the degree of anisotropy for plasma etching is infinity, what should be the size of the mask opening?