Since Sterling and Swan [1] first reported, in 1965, the growth of silicon nitride films utilizing plasmaenhanced chemical vapour deposition (PECVD) for passivation of silicon devices, PECVD-grown silicon nitride films have been extensively studied and used in microelectronics circuits manufacture. The properties of deposited films, such as the refractive index, deposition rate, density, etching rate, stress and hydrogen content, have been investigated by varying deposition parameters including the reactant gas ratio, gas flow rate, gas pressure, substrata temperature, r.f. power and geometric configuration of the reactor chamber [2-5], In this letter we report the growth of silicon nitride films utilizing an in-house designed PECVD apparatus and the dependences of the deposition rate, hydrogen content and refractive index of the films on the partial pressure ratio of the reactant gases, substrate temperature and r.f. power. In particular, we found a peculiar behaviour of the refractive index dependence on the r.f. power at low ratios of partial pressures, PNH~ /PsiH4, and attribute it to a heating effect in the glow discharge. The deposition apparatus consisted of a reactor, assorted pumping systems, gas lines and an r.f. power source. The reactor was a hot-wall capacitively coupled type PECVD equipment. The upper electrode (cathode) was 10.4 cm in diameter and had double layer with inlets of a matrix form separated by 1 cm on each layer to obtain a uniform flow of reactant gas mixture. The lower electrode was 19 cm in diameter and separated from the cathode by 4 cm. The r.f. generator had a frequency of 13.56 MHz and a maximum output power of 1000 W. The reflected power was kept less than 5 W at operation powers below 160 W by using a matching box. The flows of reactant gases were controlled by the valve at the gas cylinder and the mass-flow controllers. The pressures of the reactant gases were monitored by a commercial capacitance manometer (PDR-C-2C, MKS). For oxygen4ree silicon nitrate films, the reactor was heated to 300 °C and purged with dry N 2 gas flow for 1 h before plasma deposition. We used diluted silane (5% Sill 4 in H2), and high-purity NH3 (99.999%) and N 2 (99.9999%) as reactant gases. We varied the substrate temperature (240-360 °C), ratio of partial pressures (PNH~ /PsiH4 0.14-1.80) and r.f. power (20-160 W) as deposition parameters. The deposition was performed on a *Author to whom all correspondence should be addressed. bare silicon wafer and the formation of silicon nitride and the hydrogen content were determined by Fourier-transform infrared (FTIR) spectroscopy. The refractive index and the thickness of the film were measured utilizing an ellipsometer (Garternes Ll17). The thickness was also checked by a Nanospec (AFT-210) and spectroscopic ellipsometer (Rudolph, $2000). Fig. 1 shows the temperature dependence of the properties of the deposited films at an r.f. power of 60 W and the partial pressure ratio, PNH3/PsiH4, Of 0.14. The deposition rate showed a minimum at a temperature around 300-330 °C, whereas the hydrogen content decreased and then saturated at around 330 °C as we increased the temperature. The hydrogen content was determined by calibrating the infrared absorption bands corresponding to the Si-H (2160 cm -1) and N-H (3350 cm -I) stretching frequencies [6]. The refractive index increased from 1.8 to 2.1 as we increased the temperature from 240 to 360 °C, indicating that the Si/N ratio [3] and/or the Si-H/N-H ratio [4, 7] of the film increase with the substrate temperature. This has been observed and explained [8] as being due to the decrease of N-H bonds at higher temperatures. The saturation of Sill 4 decomposition fraction [8] and the decrease