Null ellipsometer with multi-wavelength

A multi-wavelength null ellipsometer with variable incident angle has been developed recently. The ellipsometer consists of five parts, mainly including a source set with three semiconductor lasers, a rotating component with step motor, sample stage of variable incident angle, detector, and the system of computer control procedure and data processing procedure. The light source set is composed of three semiconductor lasers at a wavelength of 635nm, 532nm, and 780nm respectively and prisms used for dividing a beam of laser into two beams. An improved formula of ellipsometric parameters (named psi and delta) has been adopted to obtain more accuracy data, as a quarter-wave plate at the wavelength of 635nm is used as the compensator for the multi-wavelength null ellipsometer. In order to make the instrument meet the need of ellipsometric parameters measurement of different types of substrate samples, a novel iterative algorithm is presented. Experimental results show that the accuracy of the ellipsometric parameters can reach to 0.01°, and the precision of film thickness is 0.1nm.