Evolution of silicon nanoclusters and hydrogen in SiNx:H films: Influence of high hydrostatic pressure under annealing

Hydrogenated silicon-rich nitride (SRN) films of various stoichiometry (SiNx:H, 0.7<x <= 1.3) were deposited on single-crystalline Si substrates with the use of plasma enhanced chemical vapor deposition at a temperature of 100 degrees C. Furnace annealing for 5 h in ambient Ar at 1130 degrees C under atmospheric and enhanced hydrostatic pressure (HP - 11 kbar, 1.1 GPa) was applied to modify the structure of the films. The properties of as-deposited and annealed films were studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL), as well as high-resolution transmittance electron microscopy (HRTEM). According to the Raman data, the as-deposited film, in which the stoichiometry parameter x is below 1.0, contains amorphous silicon nanoclusters. Furnace annealing leads to crystallization of the nanoclusters. From the HRTEM and Raman data, the average size of the Si nanocrystals in the annealed films was 6-7 nm. No silicon nanoclusters were observed in the as-deposited films with relatively low concentration of excessive silicon atoms (the case of SiNx:H, x>1); furnace annealing leads to segregation of the Si and Si3N4 phases, so, the amorphous Si clusters were observed in annealed films according to Raman data. Surprisingly, after annealing with such high thermal budget, according to the FTIR data, the SRN film with parameter x close to that of the stoichiometric silicon nitride contains hydrogen in the form of Si-H bonds. From analysis of the FTIR data of the Si-N bond vibrations one can conclude that silicon nitride is partly crystallized in the films with x>1 after annealing for 5 h. No influence of HP on the structure of Si nanoclusters was observed in the case of SRN films with x <= 1.1. Dramatic changes in the PL spectra of the SRN films with the x parameter close to that of the stoichiometric silicon nitride (x approximate to 1.3), annealed under atmospheric pressure and HP, were observed. HP stimulates the formation of very small hydrogenated amorphous nanoclusters. The size of amorphous Si nanoclusters determined from the quantum size effect model describing the PL spectra, should be 2-4 nm in this case. (C) 2012 Elsevier B. V. All rights reserved.