Thin-film thickness profile measurement using a Mirau-type low-coherence interferometer

Abstract

White-light interferometry has been spotlighted for years in the field of microelectronics as a 3D profiling tool but its application was limited to only opaque surfaces. Recently many approaches using white-light extended sources have been performed to measure the top and bottom surfaces of a thin-film structure simultaneously. When the film thickness is less than the coherence length of the light source, two waves reflected from the top and bottom surfaces of the film overlap and the interference signal become more complicated than for an opaque surface. Thus, it is an essential issue to cleanly separate the film thickness and surface height information from the complex interferograms. In this paper, we describe a Mirau-type low-coherence interferometer for measurements of the film thickness and top surface height profile with a simple measurement procedure. Our proposed method is verified by simulating the measurement errors according to the film thickness and measuring a SiO2 patterned film structure.