APPARATUS FOR AND A METHOD OF DETERMINING CHARACTERISTICS OF THIN-LAYER STRUCTURES USING LOW-COHERENCE INTERFEROMETRY

摘要

In respective measurement operations on a first sample surface area having a layer structure (81) and a characterised second sample surface area (82), light reflected by the region of the sample surface and the reference surface interfere and a sensing device (10) senses light intensity representing interference fringes at intervals during the relative movement along a measurement scan path to provide first intensity data in the form of a first series of intensity values resulting from a measurement operation on the first sample surface area and second intensity data in the form of a second series of intensity values resulting from a measurement operation on the second sample surface area. A layer structure determiner (100) determines a frequency transform ratio corresponding to a ratio between the first and second intensity data and fits a layer structure model having variable model parameters related to the layer thicknesses and refractive indices of the layers of a layer structure to the determined ratio by adjusting the model parameters, thereby obtaining for the model parameters values representing the layer thicknesses and refractive indices of the layers of the sample layer structure.