The process of r.f. diode sputtering from a Si3N4 target was investigated at various partial pressures of oxygen P(O) in argon sputter gas. It was shown by IR spectroscopy that Si3N4, SiO(x)N(y) and SiO2, films can be produced depending upon the P(O) value. For each case the corresponding intervals of oxygen pressures were determined. Refractive index and chemical etching rates of the prepared films in BHF were measured.