Low temperature-low hydrogen content silicon nitrides thin films deposited by PECVD using dichlorosilane and ammonia mixtures

Low hydrogen content silicon nitride thin films have been obtained by direct plasma enhanced chemical vapor deposition at relatively low temperature (250 °C), using different NH3/SiH2Cl2 flow rate ratios and RF powers. Deposition rates and refractive indices of the films, determined from ellipsometric measurements, were in the range from 13 to 19 nm/min, and from 1.763 to 2.35, respectively. Optical emission spectra of plasmas sustained at low RF powers (20-30 W) show a continuous band related to H2, SiCl2 emitting species and peaks related to N2, SiH and SiH2, indicating an incomplete decomposition of the SiH2Cl2 precursor. However, at high RF powers (60-80 W), the continuous band and most of the peaks related to molecular species are suppressed, meanwhile the other lines related to atomic species are intensified. According to infrared spectroscopy the samples deposited at high RF powers and a NH3/SiH2Cl2 ratio equal to 2.5 present a low total content of hydrogen and are free of Si-H bonds. Current-voltage measurements revealed that these films have dielectric breakdown fields higher than 5 MV/cm and conductivities lower than 5 × 10−13 (Ω cm)−1, and are resistant to oxidation, even if they are immersed in water for long period of time.