Thickness measurement of light elemental films

Abstract

A non-destructive method for measuring the thickness of films composed of light elements has been developed. The method utilizes a conventional electron microscope equipped with a windowless energy-dispersive X-ray spectrometer. The film thickness is determined from the intensity of a characteristic X-ray line from one element in the film after comparison with the intensity of the same X-ray line from a bulk standard. This means that only one standard is needed. The method includes the necessary corrections to obtain the film thickness as a function of the X-ray intensity. The accuracy of this method was checked experimentally by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). Hydrogen-containing amorphous carbon films (60 nm to 2.0 μm thick) deposited on Si(100) wafers from a CH 2I 2+Ar reaction gas mixture served as test samples. The atomic concentration of hydrogen was 10%±5%. The error in the thickness using measurements based on the X-ray signal was found to be less than 5% which was comparable with the accuracy of the TEM, SEM, NRA and RBS methods. By optimization of the method a thickness range of 15 nm to 5.6 μm could be covered.