Silicon nitride (SiNx:H) films were deposited on both InP and Si substrates at temperatures ranging from room temperature to 400 °C by electron cyclotron resonance (ECR) plasma chemical-vapour deposition. The silicon source used was ditertiary butyl silane (SiH2(C4H9)2) that was activated by ECR plasmas composed of nitrogen alone or in combination with hydrogen or argon. The effects of various deposition parameters on the film properties are reported. The film indices of refraction ranged from 1.85 to 2.0, while the buffered HF etch rates were as low as 6 Å min−1 (1 Å = 10−10 m). Si/N ratios of the films ranged from 0.70 to 2.5, while the total hydrogen content was found to be approximately 20 to 25 at.%. Incorporation of carbon from the organic silicon source was efficiently suppressed (< 1%) by the addition of a small amount of H2 to the ECR plasma gas. To study the electrical properties of the SiNx:H films, metal–insulator–semiconductor structures were fabricated. Film resistivities as high as 2 × 1015 Ω cm and insulator dielectric constants from 4 to 5 were measured.