Patent ID: 7385707

Claim:
Surface profiling apparatus for obtaining surface profile data for a sample surface, the apparatus comprising: a light director operable to direct light along a sample path towards a region of a sample surface 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 between the sample surface and the reference surface along a measurement path; a sensor operable to sense light representing the interference fringes produced by a sample surface region during the relative movement; a controller operable to carry out a measurement operation by causing the mover to effect the relative movement while the sensor 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 process the intensity values, the data processor comprising: a receiver operable to receive intensity values from the sensor during a measurement operation; a first processor operable to carry out processing on intensity values as the intensity values are received by the receiver during a measurement operation to produce data indicating the position of a coherence peak; and a second processor operable to, after completion of a measurement operation, use the data produced by the first processor to obtain data indicative of a height of the surface region; wherein: the second processors comprises: a correlator operable to correlate intensity values with correlation function data representing a correlation function to provide correlation data for that sample surface region to enable a position of a coherence peak in the intensity values for a sample surface region to be identified, the correlation function having first and second periodically varying wave functions with the first and second wave functions being of different phase and being bounded by an envelope; and a surface height determiner operable to determine a height of a sample surface region from data related to the position of the coherence peak; the first processor comprises a determiner operable to determine a range of the intensity values that includes an intensity value representing a coherence peak and to identify that range of intensity values to the correlator; and the determiner comprises a further correlator.