Patent Document ID: 20070188768
Application ID: 11653700
Patent Flag: 0

Claim One:
1. Apparatus for determining information relating to a sample layer structure, the apparatus comprising: a light director operable to direct light along a sample path towards a region of a surface of a sample and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere; a mover operable to effect relative movement along a measurement scan path between the sample and the reference surface; a sensing device operable to sense light representing the interference fringes produced by a sample surface region during relative movement along the measurement scan path; a controller operable to carry out a measurement operation by causing the mover to effect relative movement while the sensing device senses light intensity at intervals to provide a series of intensity values representing interference fringes produced by a region of a sample surface during the relative movement; and a data processor operable to receive and process first intensity data comprising a first series of intensity values resulting from a measurement operation on a first sample surface area having a layer structure and second intensity data comprising a second series of intensity values resulting from a measurement operation on a characterised second sample surface area, the data processor comprising: a frequency transform ratio determiner operable to determine a frequency transform ratio corresponding to a ratio between the first and second intensity data; and a data fitter operable to fit 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 ratio determined by the ratio determiner 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.