Patent ID: 8077324

Claim:
Surface characteristic determining apparatus for determining a characteristic of a sample surface, the apparatus comprising: a first light source to provide light of one of a plurality of first wavelengths; a second light source to provide light of a second wavelength; a combiner to combine light from the first and second light sources to produce combined light; a director to diffract the combined light to cause one order of diffracted light to be directed be incident on a location of the sample surface dependent upon wavelength and zeroth order light to be incident on a reference surface such that light reflected by the sample surface and light reflected by the reference surface interfere to provide interference light, a first detector to detect interference light of the first wavelength; a second detector to detect interference light of the second wavelength; a path controller to control the relative locations of the reference and sample surfaces on the basis of interference light detected by the second detector to compensate for phase variation due to environmental effects; a determiner to determine a characteristic of a sample surface on the basis of interference light detected by the first detector; and a light source controller to change the wavelength of the first light source to change the location of the sample surface on which light from the first light source is incident to enable the surface characteristic to be determined for different sample surface locations.