Novel CVD precursors for SiB_xC_yN_z film deposition such as HCCB[N(SiMe₃)₂]₂, MeB[N(SiMe₃)₂]₂ and Me₃SiCCB[N(SiMe₃)₂]₂ were synthesized. The structure and composition of the compounds were investigated with NMR, FTIR, Raman spectroscopies and CHN-analysis. Comparison of theoretical and experimental FTIR and Raman data was performed. Thermogravimetric analysis and the static tensimetry method with a glass membrane null manometer demonstrated that Me₃SiCCB[N(SiMe₃)₂]₂ is the most suitable CVD precursor. The formation of SiB_xC_yN_z films was predicted using thermodynamic modelling at a temperature below 1600 K in the total pressure range of 0.27-1333 Pa. The films of chemical composition Si_23.7B_8.3C_51.4N_9.6O₇ were deposited by low-pressure chemical vapour deposition (LPCVD) and their morphology and mechanical properties were investigated. The amorphous SiB_xC_yN_z films with a smooth surface exhibited hardness, Young's modulus and elastic recovery equal to 17.5 ± 0.9 GPa, 176 ± 11 GPa and 61 ± 2%, respectively.