X-ray photoelectron spectroscopy observations of argon-ion bombardment effects on phase separated structures such as SiNx alloys or Si/Si3N4 interfaces

Abstract

SiNx layers have been prepared in an ultrahigh vacuum (UHV) system by reactive electron beam evaporation of Si under NH3 ambient. In situ x-ray photoelectron spectroscopy (XPS) measurements show that films formed in this way consist essentially of a Si/Si3N4 mixture on a microscopic scale with the Si and Si3N4 clusters embedded in a subnitride compound. Upon mild Ar-ion bombardment (ion energy ∼1 keV), the analysis of the Si 2p core level lines for various stoichiometries reveals enhanced subnitride local atomic arrangements. This demonstrates the growth, by atomic redistribution, of the intermediate domains connecting the Si-rich and nitride domains. With increasing ion energy it is found that the phase separation progressively disappears and finally, within the probed depth, the whole film may be thought of as an homogeneous random bonding alloy. A similar behavior observed on a planar Si/Si3N4 interface, probably explains, for the main part, the diffuse nature of the interface observed in sputter profiling experiments. Evidence for preferential nitrogen sputtering as well as modifications of the XPS valence band upon ion bombardment is presented: Thus ion etching of initially heterogeneous structures results in drastic changes in film composition and structure. The present finding may account for a more homogeneous growth in plasma deposited films where ion bombardment is used during the growth.