Two series of amorphous silicon nitride layers (a-SiNx:H) were formed with Radio Frequency Chemical Vapor Deposition method (13.56 MHz) from a NH3/SiH4 gas mixture: the first one on Si (001) and the second on glass. The deposition process was repeated at various [NH3]/[SiH4] ratios, while the other parameters (pressure, plasma generator power, substrate temperature, total gas flow, and time) were kept constant. It has been confirmed in optical measurements that the refractive indexes decrease for the layers obtained at increasing [NH3]/[SiH4] ratios. Simultaneously, the position of the band assigned to Si-H stretching vibrations (at about 2100 cm(-1)) shifts towards higher frequencies. The observed dependencies were applied in evaluation of nitrogen and hydrogen contents in the respective layers. It has been shown that when [NH3]/[SiH4] increases from 0 (no silane flow) to 0.2 then the a-SiNx:H layers of x-[N]/[Si] increasing between 0 and nearly 1.4 may be obtained. The obtained layers have the refractive indexes higher than 2.1 and lower than 2.7 which make them good materials for antireflective coatings on crystalline and multicrystalline silicon solar cells. (C) 2011 Elsevier B. V. All rights reserved.