The present invention is directed to a
heterodyne reflectometer
system and method for obtaining highly accurate phase shift information from heterodyned optical signals, from which extremely accurate film depths can be calculated. A
linearly polarized light comprised of two linearly polarized components that are orthogonal to each other, with split
optical frequencies, is directed toward a film causing one of the
optical polarization components to
lag behind the other due to an increase in the
optical path in the film for that component. A pair of detectors receives the beam reflected from the film layer and produces a measurement
signal, and the beam prior to incidence on the film layer and generates a reference
signal, respectively. The measurement
signal and reference signal are analyzed by a
phase detector for phase shift. The detected phase shift is then fed into a thickness
calculator for film thickness results. A
grating interferometer may be included with the
heterodyne reflectometer
system with a
grating, which diffracts the reflected beam into zeroth- and first-order bands, which are then detected by separate detectors. A
detector receives the zeroth-order beam and generates another measurement signal. Another
detector receives the first-order beam and generates a
grating signal. The measurement signal from the grating and reference signal may be analyzed by a
phase detector for phase shift, which is related to the thickness of the film. Conversely, either measurement signal may be analyzed with the grating signal by a
phase detector for detecting a grating phase shift. The
refractive index for the film may be calculated from grating phase shift and the
heterodyne phase shift. The updated
refractive index is then used for calculating thickness.