PHASE-SHIFTING ELLIPSOMETER

A new type of automatic ellipsometer based on a phase-shifting techniq ue is described, where an electrooptic modulator made of ADP (ammonium dihydrogen phosphate) crystals is used for phase shifting; thus we ca ll it the phase-shifting ellipsometer. The light source is a 5 mW He-N e laser. The intensities changed as the phase retardation Gamma was sh ifted by 0, pi/2 and pi. The design, alignment, and calibration of the system are discussed in detail. Once the optical system is aligned, a ll components are free from mechanical movement, hence the precision i s high. The accuracy of the results has been evaluated, and the errors introduced on Psi and Delta are <0.032 degrees and 0.19 degrees, resp ectively. The inaccuracy of the phase shift can only introduce an erro r on Delta, and the degree of error on Delta is the same as that on Ga mma, so it is very easily to modify.