Plasma processes affecting etching and growth of nitride materials

Abstract

The main goal of this research was to determine the key reagents during the highly Si3N4/SiO2 selective etching. The experiments were conducted, where both Si3N4 and SiO2 samples were etched by NF3/O2 and NF3/O2/N2/H2 plasmas. The sources of the plasmas were removed from the etched sample to exclude a damaging from UV emission and ion bombardment. Optical emission spectroscopy and mass-spectroscopy were used during the etching. The reaction mechanisms were studied using quantum chemistry methods. It was suggested analytical models, which quantitively describe dependence of Si3N4 and SiO2 etch rate on the fluxes of key reactants in NF3/O2 and NF3/O2/N2/H2 downstream plasmas. The densities of the kye reagents were measured and calculated using plasma simulation. Thus, the Si3N4 etch rate curve in NF3/O2 mixture has a peak, where NO density peaks. The high and narrow Si3N4/SiO2 selectivity peaks, which appears in NF3/O2/N2/H2, correlates with high and narrow density peak of vibration excited HF(v1) molecule. Also, this research was aimed to study a mechanism of precursor formation of boron nitride nanotubes growth during high temperature synthesis. It was shown that boron consumption (it is the main impediment to large scale production) occurs through the reactions of N2 dissociative adsorption on small boron clusters (N2 fixation) resulting in generation of B4N4 and B5N4 chains. The liquid boron is only source of the small boron clusters. A subsequent formation of longer chains occurs via collisions of B4N4 and B5N4 with each other. It was also shown that slow gas cooling rate and high pressure enhance liquid boron consumption during the synthesis, creating a good condition to large scale production of high purity and quality BNNT.