Role of hydrogen on the deposition and properties of fluorinated silicon-nitride films prepared by inductively coupled plasma enhanced chemical vapor deposition using SiF4∕N2∕H2 mixtures

Abstract

Fluorinated silicon-nitride films have been prepared at low temperature (250°C) by remote plasma enhanced chemical vapor deposition using mixtures of SiF4, N2, Ar, and various H2 flow rates. The deposited films were characterized by means of single wavelength ellipsometry, infrared transmission, resonant nuclear reactions, Rutherford backscattering analysis, and current-voltage measurements. It was found that films deposited without hydrogen grow with the highest deposition rate, however, they result with the highest fluorine content (∼27at.%) and excess of silicon (Si∕Nratio≈1.75). These films also have the lowest refractive index and the highest etch rate, and exhibit very poor dielectric properties. As a consequence of the high fluorine content, these films hydrolize rapidly upon exposure to the ambient moisture, forming Si–H and N–H bonds, however, they do not oxidize completely. The addition of hydrogen to the deposition process reduces the deposition rate but improves systematically the stability and insulating properties of the films by reducing the amount of both silicon and fluorine incorporated during growth. All the fluorinated silicon-nitride films deposited at hydrogen flow rates higher than 3.5sccm resulted free of Si–H bonds. In spite of the fact that films obtained at the highest hydrogen flow rate used in this work are still silicon rich (Si∕Nratio≈1.0) and contain a considerable amount of fluorine (∼16at.%), they are chemically stable and show acceptable dielectric properties.