Effect of nonpolarizing beam splitter on measurement error in heterodyne interferometric ellipsometers

Abstract

The nonlinear error of the ellipsometric parameters (EP) has been investigated by many researchers in terms of the imperfection of polarizing beam splitters (PBS), the elliptical polarization and nonorthogonality of the light beams produced by the laser source and wave plates. To our knowledge, the effect of the nonpolarizing beam splitters (NPBS) on the EP errors has not been reported before. Aiming at the heterodyne interferometric ellipsometer with two acousto-optical modulators we proposed before, the EP errors produced by the NPBS are analyzed and calculated with the Jones matrix algebra in this paper. The theoretical analysis indicates that the misorientation of the NPBS has a major effect on the errors; it must be smaller than 0.02° for obtaining nanometer accuracy. Furthermore, the first NPBS which separates the measurement arm from the reference arm has more important contribution to the EP errors than the second NPBS, which recombines the measurement light and the reference light. In addition, the slight variation of the reflectivity and transmissivity of NPBS has a direct and serious influence on the amplitude ratio error; however, it almost has no effect on the phase difference error. As another important source of error, the influence of NPBS on the measure accuracy needs more emphasis.