Laser micrometrology for integrated circuits

Abstract

The optical microscope measurement of micrometer and submicrometer linewidths during integrated-circuit fabrication utilizes a wide variety of optical microscope system designs including bright-field, dark-field, and focused laser beam scanning systems. Previous papers have dealt with the problem of accurate edge detection on lines as small as 0.5 μm using partially coherent or effectively coherent imaging. The present paper deals with the “principle of equivalence” in optical system design of both conventional microscope imaging systems and focused-spot scanning systems. It is shown both theoretically and experimentally that, for the case of measurement of lines patterned in thin films like those found on integrated-circuit wafers, the principle of equivalence does not hold because of the angular dependence of the optical parameters that characterize the line object. It is concluded that accurate linewidth measurements require both the angle of incidence and the wavelength to be well defined in a manner analogous to the requirements for accurate ellipsometric measurement of film thickness.The optical microscope measurement of micrometer and submicrometer linewidths during integrated-circuit fabrication utilizes a wide variety of optical microscope system designs including bright-field, dark-field, and focused laser beam scanning systems. Previous papers have dealt with the problem of accurate edge detection on lines as small as 0.5 μm using partially coherent or effectively coherent imaging. The present paper deals with the “principle of equivalence” in optical system design of both conventional microscope imaging systems and focused-spot scanning systems. It is shown both theoretically and experimentally that, for the case of measurement of lines patterned in thin films like those found on integrated-circuit wafers, the principle of equivalence does not hold because of the angular dependence of the optical parameters that characterize the line object. It is concluded that accurate linewidth measurements require both the angle of incidence and the wavelength to be well defined in a manner ...