Rotating-compensator ellipsometer

Abstract

Plane polarized light is reflected from a surface of a sample film to produce an elliptically polarized reflected beam. The reflected beam is passed sequentially through a rotating one-quarter wave plate and a fixed analyzer which transmits a beam whose intensity varies as a function of the rotational angle of the plate. The transmitted beam impinges upon a photodetector which produces an electric signal proportional to the intensity of the transmitted light. The rotating one-quarter wave plate cyclically varies the polarization of the beam, so that the electrical signal, when numerically Fourier analyzed, provides Fourier coefficients having both sin .DELTA. and cos .DELTA. terms, where the ellipsometric parameter .DELTA. is the instantaneous phase difference between the parallel (R.sub.p) and perpendicular (R.sub.s) components of the electric vector of the elliptically polarized reflected beam; therefore, the phase difference .DELTA. is uniquely and unambiguously defined in a single measurement. Furthermore, the presence of both sin .DELTA. and cos .DELTA. terms permits .DELTA. to be determined more accurately than is possible with the prior art rotating-analyzer ellipsometer. Since the ellipsometric parameter .psi. is also uniquely defined (tan.psi.=R.sub.p /R.sub. s), properties of the sample film can be computed. Alternatively, the rotating quarter-wave plate may be placed in the path of the incident plane polarized beam.