A method for production testing includes receiving a wafer including a
semiconductor substrate and a non-conducting layer formed over the
substrate, following etching of contact openings through the
non-conducting layer to the substrate, the contact openings including an
array of the contact openings arranged in a predefined test pattern in a
test area on the wafer. An electron beam is directed to irradiate the
test area, a specimen current flowing through the substrate responsive to
the electron beam is measured. The specimen current is analyzed so as to
assess a dimension of the contact openings.