Effect of Hydrogen Dilution on Growth of Silicon Nanocrystals Embedded in Silicon Nitride Thin Film by Plasma-Enhanced CVD

Abstract

An investigation was conducted into the effect of hydrogen dilutionon the microstructure and optical properties of silicon nanograinsembedded in silicon nitride (Si/SiNx) thin film depositedby the helicon wave plasma-enhanced chemical vapour depositiontechnique. With Ar-diluted SiH4 and N2 as the reactant gassources in the fabrication of thin film, the film was formed at ahigh deposition rate. There was a high density of defect at theamorphous silicon (a-Si)/SiNx interface and a relative lowoptical gap in the film. An addition of hydrogen into the reactantgas reduced the film deposition rate sharply. The silicon nanograinsin the SiNx matrix were in a crystalline state, and thedensity of defects at the silicon nanocrystals (nc-Si)/SiNxinterface decreased significantly and the optical gap of the filmswidened. These results suggested that hydrogen activated by theplasma could not only eliminate in the defects between the interfaceof silicon nanograins and SiNx matrix, but also helped thenanograins transform from the amorphous into crystalline state. Bychanging the hydrogen dilution ratio in the reactant gas sources, atunable band gap from 1.87 eV to 3.32 eV was obtained in theSi/SiNx film.