Investigation of a half-wave method for birefringence or thickness measurements of a thick, semitransparent, uniaxial, anisotropic substrate by use of spectroscopic ellipsometry

A half-wave method of measurement of wafer birefringence that is based on i nterference fringes recorded from a uniaxial wafer by use of a standard pha se-modulated spectroscopic ellipsometer is investigated. The birefringence of uniaxial wafers is calculated from the extremal points in the recorded o scillating intensities. A formalism is developed to incorporate the change in birefringence with wavelength as a correction factor. The correction exp lains the overestimation of the birefringence from previous similar researc h on thick uniaxial sapphire substrates. The enhanced derivative of the bir efringence that is due to polarization-dependent intraconduction band trans itions is detected. Furthermore, for well-characterized wafers it is shown that this method can be used in wafer-thickness mapping of 4H-SiC and simil ar uniaxial high-bandgap semiconductors. (C) 2000 Optical Society of Americ a OCIS codes: 260.1180, 260.1446, 260.2130, 260.5430, 160.1190.