ELLIPSOMETRIC DETERMINATION OF OPTICAL-CONSTANTS FOR SILICON AND THERMALLY GROWN SILICON DIOXIDE VIA A MULTISAMPLE, MULTIWAVELENGTH, MULTI-ANGLE INVESTIGATION

Optical constant spectra for silicon and thermally grown silicon dioxi de have been simultaneously determined using variable angle of inciden ce spectroscopic ellipsometry from 0.75 to 6.5 eV. Spectroscopic ellip sometric data sets acquired at multiple angles of incidence from seven samples with oxide thicknesses from 2 to 350 nm were analyzed using a self-contained multi-sample technique to obtain Kramers-Kronig consis tent optical constant spectra. The investigation used a systematic app roach utilizing optical models of increasing complexity in order to in vestigate the need for fitting the thermal SiO2 optical constants and including an interface layer between the silicon and SiO2 in modeling the data. A detailed Study was made of parameter correlation effects i nvolving the optical constants used for the interface layer. The resul ting thermal silicon dioxide optical constants were shown to be indepe ndent of the precise substrate model used, and were found to be approx imately 0.4% higher in index than published values for bulk glasseous SiO2. The resulting silicon optical constants are comparable to previo us ellipsometric measurements in the regions of overlap, and are in ag reement with long wavelength prism measurements and transmission measu rements near the band gap. (C) 1998 American Institute of Physics.