Composition, structure and annealing-induced phase separation in SiO x films produced by thermal evaporation of SiO in vacuum

Abstract

SiO x thin films with various oxygen contents (1.1⩽ x⩽1.7) have been prepared by thermal evaporation of silicon monoxide in vacuum. The film composition is controlled by changing both deposition rate (between 0.2 and 6 nm/s) and depositing the films at two different residual pressures, (2×10 −4 or 1×10 −3 Pa). Long-term stability of all films is ensured by a post-deposition anneal at 520 K for 30 min and this is explained with reference to the annealing-induced decrease of the volume fraction occupied by pores in the film. The oxygen content, x, of each film is determined using both infrared absorption and Rutherford backscattering measurements and the x-values obtained in each case are quite different. The observed difference is related to the low density of the films, particularly those deposited at high residual pressure and high deposition rates, which, in addition to the oxygen deficiency, decreases the frequency of the TO stretching mode. An increase of the oxygen content of the films is observed upon annealing at 970 K accompanied by formation of amorphous silicon particles. Phase separation is completed after annealing at 1300 K and Si nanocrystals embedded in SiO 2 matrix are produced, but the infrared absorption results show that the level of chemical disorder in the matrix is appreciably higher than that in ‘pure’ SiO 2 thin films.