METROLOGY OF HIGH-RESOLUTION RESIST STRUCTURES ON INSULATING SUBSTRATES

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 parti cular, for the inspection of high-resolution resist structures with a scanning electron microscope, it is necessary to choose the relevant w orking parameters, such as voltage and current, to take into account t he electrical charging of the resist. Charging may influence the secon dary electron (SE) signal that is used for metrology. In this article, the SE signal, collected while inspecting a resist structure on silic on substrates with an electron beam, is studied both theoretically and experimentally. Cold-cathode tungsten field emission microscopes, Hit achi S6100 and Hitachi S900, have been used for this study. Low-voltag e 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(methylmethacry late) resist on a silicon substrate, by means of extensive calculation s combining MC methods with the Poisson equation. The study of the sig nal profile is fundamental to the development of a precise metrologica l algorithm for high-resolution linewidth measurements. In previous ar ticles calculations of the backscattered electron signal have been des cribed from conducting materials derived using an analytical function that is the convolution of probe beam function and the specimen transf er function. In this work, the algorithm is extended to the SE signal obtained by e-beam inspection of insulating materials at voltages betw een 1 and 2 keV and currents of a few pA. It was found that linewidth variations are negligible for quarter micron structures when the worki ng parameters, such as voltage and beam current, are chosen in accorda nce with MC calculations.