Polycrystalline boron carbon nitride (BCN) films are synthesized at various temperatures by plasma-assisted chemical-vapor deposition. BCN films are characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, and transmission electron diffraction. The dielectric constant is estimated from the accumulation region of capacitance-voltage (C-V) characteristics of Au/BCN/p-Si samples. Reduction in the crystal grain size and increase of the amorphous region of the BCN film are observed with decreasing growth temperature. The dielectric constant is found to decrease with decreasing growth temperature. A dielectric constant as low as 2.4 is achieved for the BCN film. © 2002 American Institute of Physics.