Patent ID: 6912056

Claim:
An apparatus for measuring a thickness of a multilayer on a substrate, comprising: a measuring unit for measuring reflected light to generate a measured spectrum of the reflected light, the reflected light being reflected from the substrate on which the multilayer is formed; an input unit for inputting a plurality of recipe data, each of the plurality of recipe data corresponding to one of a plurality of hypothetical multilayers, one of the hypothetical multilayers being initially assumed as the multilayer actually formed on the substrate; a first storing unit for storing the measured data; a second storing unit for storing the plurality of recipe data; an output unit for outputting a thickness of the multilayer on the substrate; and a control unit connected to the measuring unit, the input unit, the first and second storing units and the output unit, wherein the control unit calculates a plurality of theoretical spectra, each of which indicates at least a thickness of each component layer of the hypothetical multilayer assumed to be the multilayer actually formed on the substrate, using one of the plurality of recipe data, compares the measured spectrum with the plurality of theoretical spectra, thereby determining a temporary thickness of the multilayer, estimates whether a reliability of the temporary thickness is within an allowable range, and transfers the temporary thickness to the output unit when the reliability is within the allowable range or repeats the selection of the temporary thickness after changing the recipe data when the reliability is outside of the allowable range.