DETERMINATION OF THE SIGN OF DELTA IN SPECTROSCOPIC ELLIPSOMETRY WITHOUT A QUARTER-WAVE PLATE - CALCULATION AND APPLICATIONS

For several years spectroscopic ellipsometry (SE) has been widely used in semiconductor or optical coatings technology to characterize the t hicknesses and indices of thin layer deposited or grown on various sub strates. In the case of a spectroscopic ellipsometer modulated by mech anical rotation of the polarizer or analyser, it is impossible to dete rmine directly for each wavelength the phase retardation DELTA of the signal. Only cos DELTA can be measured. Until now, the usual approach to determine the sign of DELTA in this configuration has been to intro duce in the optical axis a compensator plate (quarter-wave plate). Thi s method has some disadvantages such as the optical alignment of the p late itself, the transmission coefficient and the exact compensation f or one wavelength only. To avoid these problems, a mathematical treatm ent of the measured data can be performed. SE measures the complex rat io R(p)/R(s), so it is possible to apply the Kramers-Kronig analysis t o this complex function. The measurement of the real part of this rati o tan PSI cos DELTA and the use of this theorem allows the determinati on of the imaginary part tan PSI sin DELTA and finally the knowledge o f the sign of DELTA without a compensator. The ability of the method i s shown on simulations and its limitation is discussed on a real spect rum. It is interesting to note that this approach is general and witho ut any consideration of the structure of the sample itself.