  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.
