Diffraction gratings for submicron linewidth measurement

摘要

A test structure and a method of using it for measuring submicron linewidths. Diffraction gratings are made with lines having an unknown linewidth. The grating has a pitch comprises of multiple lines and multiple spaces. This permits a wider "effective pitch" resulting in an increased number of observable diffraction orders. Each order provides an intensity measurement, which can be substituted into a diffraction intensity equation in which intensity is a function of linewidth and other unknown variables. At least as many intensity measurements are obtained as are unknown variables so that a system of equations can be solved for the linewidth. In practice, if the grating lines are made in the same manner as other lines of a product, the width of the latter can be inferred.