Patent ID: 7369234

Claim:
A method of performing a measurement on a sample to determine a thickness of a film on the sample including: irradiating the sample with a polarized irradiation beam; linearly polarizing a return beam from the sample; modulating the irradiation or return beam with a birefringence modulator in accordance with a primary modulation signal; generating a secondary modulation signal which has a predetermined phase relationship with the primary modulation signal; directing the return beam onto a multichannel detector, the multichannel detector having a plurality of detection elements; simultaneously generating a detection value at each detection element; processing the simultaneously generated detection values to determine a plurality of measurements, each measurement corresponding with a respective detection element and being indicative of a change induced by the film on the sample on the irradiation beam; modulating the irradiation or return beam in accordance with the secondary modulation signal, or controlling the generation or processing of the detection values in accordance with the secondary modulation signal; and using at least the plurality of measurements to determine the thickness of the film.