As a coating material for silicon field emitters, amorphous carbon nitride (a-C:N) by helical resonator plasma enhanced chemical vapor deposition has been proposed. Thermal annealing in nitrogen ambient up to 600 degrees C was carried Out to investigate the effects of heat treatment on the field emission. The structural and compositional modifications induced by the annealing were followed by several analytical techniques : Fourier transformation infrared (FTIR) spectroscopy, elastic recoil detection analysis (ERDA), and x-ray photoelectron spectroscopy. FTIR and ERDA analyses indicate that hydrogen loss occurs for annealing temperatures higher than 300 degrees C. Amorphous-C:N films significantly lowered the turn-on voltage and increased the emission current of the silicon emitters. After annealing at 600 degrees C, the field emission property was further enhanced presumably due to the efficient conduction through the a-C:N films induced by an increase of the number and/or the size of the graphitic domains.