Carbon-silicon-nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by a RF nitrogen plasma source. Up to about 30 at% nitrogen and up to 20 at% silicon were found in the hard amorphous thin films by RES, XPS, and SNMS in dependence on the composition of the mixed graphite/Si3N4-PLD target. Due to incorporation of 10% Si3N4 to the PLD graphite target the CSixNy films show slightly increased universal hardness value of 23 GPa (at 0.1 mN load force, reference value for silicon substrate 14 Gpa), increased plastic hardness (67 instead of 61 GPa), but strongly decreased elastic modulus (from 464 to 229 GPa) compared to the corresponding carbon nitride him without silicon. The internal compressive stress of the CSixNy films showed a maximum of 5.5 GPa at a film thickness below 50 nm and decreased down to about 1.5 GPa for film thickness exceeding 100 nm. X-ray photoelectron spectroscopy (XPS) of CSixNy film surfaces shows clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to composition of the graphite/Si3N4 target and to nitrogen flow through the plasma sourer, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Increasing carbon double and triple bonding of the CSixNy films in dependence on the deposition process as identified by FTIR and Raman spectroscopy correlates with decreasing nanohardness. The results demonstrate the capability of the plasma assisted PLD process to deposit hard amorphous CSixNy films with variable chemical binding structure and corresponding mechanical properties.