The dependence of the deposition rate on the radius of the synchrotron radiation (SR) beam, on the incident angle to the substrate and on substrate configuration to SR-excited chemical vapor deposition of silicon nitride films. Through the experimental results and related analyses, the contribution of gas-phase excitation near the substrate surface to deposition is clarified. In addition, by evaluating the numbers of photoelectrons and secondary electrons emitted from the SR-irradiated substrate, the contribution of low-energy secondary electrons to the excitation of gas-phase and adsorbed molecules is discussed. Finally, a reaction model including the excitation of the core electrons of substrate constituent atoms and the contribution of the interaction between generated low-energy secondary electrons and gas-phase molecules and adsorbates near/at the surface is proposed to explain the material dependence of the film composition observed in the SiH4 + NH3, gas system.