THE DETERMINATION OF THE THICKNESS OF ULTRATHIN METAL AND SEMICONDUCTOR-FILMS ON CONVENTIONAL SEMICONDUCTOR SUBSTRATES

In order to measure the thickness or area mass density of ultrathin metal or semiconductor films in the range from about 1 to 15 nm deposited on a conventional semiconductor substrate Si (Z//s equals 14) or GaAs the electron backscattering rate is investigated. The primary energy of the electrons used is 18 kev. Metal films are studied both for Z//f greater than Z//s and Z//f less than Z//s. It is shown empirically that the relative backscattering rate can be represented in this low thickness limit by the sum of a constant backscattering background due to the substrate and a contribution proportional to the thickness of the metal layer obeying approximately the Rutherford backscattering formula. Based on these investigations, a method is developed for the rapid and precise determination of the effective thickness of ultrathin metal or semiconductor films on Si or GaAs substrates.