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Development of confocal-based techniques for shape measurements on structured surfaces containing dissimilar materials

Optical metrology
Vice-president Software, Ph.D. in Physics (Optical Engineering), Technical Engineering in Telecommunications, Electronic Engineering at Sensofar Metrology | Other articles

Partner at Sensofar since 2004.
Experienced Research & Development Specialist, Cristina works at CD6 as R&D Engineer since 1996 and she is Software Manager at Sensofar Tech SL since it’s foundation in 2001 and VP Software since 2017. The research interests include optical metrology, surface metrology, image processing and computing sciences. Since 2010 she is developing the use of three-dimensional (3D) topographical analysis in firearms analysis.

Abstract

One of the applications, which is considered to be very difficult to carry out with most optical imaging profilers, is the shape and texture measurements of structured surfaces obtained from the superposition of various micro or sub-micrometric layers of dissimilar materials. Typical examples are the architectures of microelectronics samples made up of Si, SiO2, Si3N4, photoresists and metal layers. Because of the very different values of the index of refraction of the involved materials, visible light is reflected in the various interfaces. As a result, some reflected wavefronts are superposed giving rise to interference patterns, which are difficult to understand in terms of surface topography and layer thickness. In this paper we introduce a new method based on non-contact confocal techniques to measure the shape of structured samples. The method is based on the comparison of the axial responses obtained in areas of the surface where there is a layer and in other areas where there is just the substrate. To our knowledge, this approach enables the confocal profilers to measure the thickness of layers on the sub-micrometric scale for the first time.

3D shape and texture measurements