Patent ID: 7505143
Filing Date: 2009-03-17
Classification: G01B,G11B

Abstract:
1. A method of dynamic reference plane compensation, comprising: impinging radiation from a first radiation source onto a surface of an object; generating an uncompensated measurement signal from radiation reflected from a first location on the surface and a second location; generating a compensation signal from radiation reflected from a third location and a fourth location on the surface; and generating a compensated measurement signal using the uncompensated measurement signal and the compensation signal; wherein the compensated measurement signal comprises a corrected phase signal calculated using the formula: where: θ θ is the phase difference measured between the measurement beams; θ d is the distance between the point of incidence of the first portion of the measurement beam and the point of incidence of the second portion of the measurement beam; d λ is the wavelength of the radiation used for the measurement beam λ