Spectroscopic Ellipsometry Investigation of Amorphous Silicon Nitride Thin Films

It has been reported earlier that the attenuation lengths of photoelectrons from very thin amorphous ilicon nitride films (3 to 11 nm) increase with film thickness. These changes were attributed to systematic variations in the film density. Spectroscopic elllpsometry has been used here as an independent technique to evaluate the refractive indexes of several of the same films. The ellipsometric results are consistent with the earlier finding that the relative densities of these films vary with thickness. The density variations may be attributed to either structural changes in the films or differences in the oxygen content of the films with film thickness. Amorphous ilicon nitride thin films are widely used in the microelectronlcs industry as dielectric films in various devices, and as passivation or masking films to protect devices during processing. An understanding of very thin silicon nitride films (3 to 10 nm) is of great interest as the dimensions of the devices become smaller and smaller. Previous investigation of such thin films by x-ray photoelectron spectroscopy (XPS) and high resolutio