Metrology of high-resolution resist structures on insulating substrates

Abstract

One of the main problems in the field of ultra-large-scale integration is the accurate use of metrological tools to provide information for critical dimension control of insulating material structures. In particular, for the inspection of high-resolution resist structures with a scanning electron microscope, it is necessary to choose the relevant working parameters, such as voltage and current, to take into account the electrical charging of the resist. Charging may influence the secondary electron (SE) signal that is used for metrology. In this article, the SE signal, collected while inspecting a resist structure on silicon substrates with an electron beam, is studied both theoretically and experimentally. Cold-cathode tungsten field emission microscopes, Hitachi S6100 and Hitachi S900, have been used for this study. Low-voltage signals are computed by direct simulation of low energy SE emission, using Monte Carlo (MC) calculations. The charging effect is evaluated as a function of beam energy and beam current for poly(methylmethacrylate) resist on a silicon substrate, by means of extensive calculations combining MC methods with the Poisson equation. The study of the signal profile is fundamental to the development of a precise metrological algorithm for high-resolution linewidth measurements. In previous articles calculations of the backscattered electron signal have been described from conducting materials derived using an analytical function that is the convolution of probe beam function and the specimen transfer function. In this work, the algorithm is extended to the SE signal obtained by e-beam inspection of insulating materials at voltages between 1 and 2 keV and currents of a few pA. It was found that linewidth variations are negligible for quarter micron structures when the working parameters, such as voltage and beam current, are chosen in accordance with MC calculations.