Hot filament activated chemical vapor deposition of nitride and carbide thin films.

Abstract

A novel method of Hot Filament activated Chemical Vapor Deposition (HFCVD) has been explored for the deposition of nitride and carbide thin films. This method was employed to obtain silicon nitride, titanium nitride and boron carbide thin films. This hot filament assisted activation of stable molecules helps in reducing the deposition temperatures and in obtaining thin films at high rates. In this method, the stable precursor gases, such as ammonia, methane and hydrogen, are decomposed at the surface of a resistively heated tungsten filament (1500$\sp\circ$C to 1850$\sp\circ$C). These activated precursors further downstream react with the source gases to form the desired film on a temperature controlled substrate. Various thin film characterization techniques were used to evaluate the properties of these films. Elemental composition of the films was determined by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). The film thicknesses were measured by single-wavelength ellipsometry, RBS and cross sectional scanning electron microscopy. The microstructure was studied with X-ray diffraction and electron microscopy. The bonding configuration in the films was analyzed with Fourier transformed infrared and Raman spectroscopies. Very high deposition rates (up to 2000 A/min) were obtained for silicon nitride at low substrate temperatures (245-370$\sp\circ$C). The silicon nitride films were amorphous and had low hydrogen content. They also showed very low etch rates in buffered hydrofluoric acid solution. These silicon nitride films also showed strong visible photoluminescence (PL). The PL in these films has been characterized in detail and a qualitative model is proposed for the origin of PL. The titanium nitride films were polycrystalline with grain sizes between 300 and 1000 A. The substrate temperature had a strong influence on the grain orientation. These films showed low resistivity, good conformality and diffusion barrier properties. The diffusion barrier performance was tested for both aluminum and copper films. We also performed preliminary studies on low temperature (450$\sp\circ$C) deposition of boron carbide films for hard protective coating applications. The films were amorphous as determined by transmission electron microscopy. Preliminary wear testing showed that these films adhere well and have high hardness.