Evolutions and distributions of Si nanocrystals and other Si oxidation states in Si-implanted SiO2 films

Abstract

In this study, X-ray photoelectron spectroscopy (XPS) is used to study the annealing effects on the structure and chemical states of Si-rich SiOx (x<2) films. The analysis of the XPS Si 2p peaks shows the existence of the five chemical structures corresponding to the Si oxidation states Si n+ (n =0, 1, 2, 3, and 4) in the SiOx films. The XPS results clearly show the evolution of various chemical structures and the formation of Si nanocrystals (corresponding to the oxidation state Si 0 ) in the SiOx films as a function of annealing temperature and annealing time. The results are explained in terms of the thermal decompositions of the suboxides Si 2 O, SiO and Si 2 O 3 (corresponding to the oxidation states Si 1+ , Si 2+ and Si 3+ , respectively). The thermal decompositions lead to the growth of SiO2 (corresponding to the oxidation state Si 4+ ) as well as the formation of Si nanocrystals in the SiOx films. On the other hand, the depth profiling experiment was carried out with ion sputtering. The relative concentration of each oxidation state at various depths is determined quantitatively from the XPS analysis. In addition, annealing effects on both the oxidation states and their depth distributions are studied as well.