Detecting registration marks with low energy electron beam

Abstract

For electron beam wafer or mask processing, a registration mark is capacitively coupled to the top surface of an overlying resist layer on a substrate to form a voltage potential on the surface of the resist layer directly over the registration mark. The registration mark is directly connected to an electrical lead that produces an AC voltage on the registration mark, which is capacitively induced on the surface of the resist layer. Alternatively, the registration mark itself is capacitively coupled to a conductive plate placed on the bottom surface of the semiconductor substrate. An AC voltage is then applied to the conductive plate that induces a charge on the registration mark, which then capacitively induces a charge on the surface of the layer of resist. An electron beam scanning across the surface of the resist layer generates secondary electrons. The secondary electrons have a low energy and are affected by the voltage potential created at the surface of the resist layer. Thus, by detecting the secondary electron signal generated by the electron beam the voltage potential on the surface of the resist layer is detected in contrast with surrounding areas. Consequently, the registration mark is detected by an electron beam, such as a low energy electron beam produced for example by an electron beam microcolumn, that does not have sufficient energy to penetrate the resist layer.