Suppressing the surface roughness and columnar growth of silicon nitride films

The growth and structure evolution of silicon nitride films prepared by radio frequency magnetron sputtering at low pressure were investigated for thickness changes. Grazing-incidence X-ray reflectivity, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to study the structure, surface roughness and composition, respectively, of the films. It was found that with an increase in thickness from 5 to 830 nm, the silicon nitride films have a similar surface structure and their surface roughness only slightly increases. The surface roughness of all the silicon nitride films is only a little more than 0.2 nm, much less than previously reported results. AFM measurement of the fractured film surface indicated that thin silicon nitride films with a thickness below approximately 300 nm have a dense, smooth and uniform structure, and columnar structures gradually appear only in thick films. These results are mainly attributed to the special design of the sputtering system and the energetic particle bombardment of the growing surface, by which the surface roughness and columnar growth were suppressed.