Small-area XPS depth profiling and AFM investigation on plasma-enhanced CVD SiNx films grown on GaAs (100) surfaces

Silicon nitride thin films prepared by plasma enhanced chemical vapour deposition (PE-CVD) are widely used for interlevel insulator and as encapsulator layer on ion implanted GaAs surfaces. Encapsulant silicon nitride thin films have been first grown by plasma-enhanced chemical vapour deposition (PECVD) on GaAs (100) surfaces using a mixture of silane-ammonia-nitrogen as rectant gas and then, annealed in a N2+H2 mixture at 1123 K. The influence of some deposition parameters such as the pressure, the substrate temperature, the radio frequence power and the flow ratio of the gases as well as the annealing treatment, on the surface microstructure, the roughness, the chemical composition of the SiNx films and the SiNx-GaAs interface, have been studied by means of the combined use of small-area X-ray photoelectron spectroscopy (SA-XPS) depth profiling and atomic force microscopy (AFM) techniques. In order to study the variation of the SiNx chemical composition and the SiNx-GaAs interface, the Ar+ sputtering conditions have been first optimized on reference materials by varying the ion energy and current density and then, the SA-XPS depth profiling analysis have been extended to the SiNx/GaAs materials. In particular, the attention has been focused on the sharpness and the micro chemistry of the SiNx/GaAs interface considering the As 3d, Ga 3d, As 3p, Ga 3p, Ga 2p3/2 and As 2p3/2 signals that are photoemitted from different depths. The SA-XPS and AFM results have shown that stoichiometric Si3N4 films characterized by a low roughness ranging from 0.8 nm to 1.5 nm, and a sharp SiNx-GaAs interface is obtained by increasing the substrate temperature up to 673 K and the flow of N2 in the reactant gases as well as by annealing the materials at 1123 K for 30 s. The paper describes the small-area XPS depth profiling and AFM investigation on plasma-enhanced CVD SiNx films grown on GaAs (100) surfaces.