THICKNESS DETERMINATION OF LOW DOPED SIC EPI-FILMS ON HIGHLY DOPED SIC SUBSTRATES

The room temperature infrared reflectance of low doped SiC epi-films, both 4H and 6H polytypes, deposited by chemical vapor deposition on hi ghly doped SiC: substrates has been measured. The epi-film doping leve ls are in the 10(15) cm(-3) range while the substrate doping levels ar e in the 10(18) to 10(19) cm(-3) range. Interference fringes from the epi-films are often observed in the frequency region below the reststr ahl band in SiC (200-600 cm(-1)) and they can be used to determine the thickness of these epi-films. The fringes arise due to the difference in free carrier concentration between the epi-film and substrate whic h causes differences in their frequency dependent dielectric functions . The epi-film thickness determinations were made by comparison of the measured infrared reflectance spectra to calculated spectra based on a frequency dependent dielectric function modeled with Lorentz oscilla tors using only bulk input parameters. The effects of film and substra te anisotropy and off normal incidence are included in the calculation .