Carbon silicon nitride (CSixNy) thin films have been grown by pulsed laser deposition (PLD) of various [C(1-z)(Si3N4)(z)]-targets using an additional nitrogen RF plasma source on [1 0 0] oriented silicon substrates without additional heating. At the beginning of the deposition the resulting microstructure is amorphous with some embedded microcrystals of approximate to 30 nm diameter, which induce increasing internal stress. After less than 200 nm thickness the growth of the films is changing, resulting in an amorphous microstructure with textured nanocrystallites. In this growth-mode the internal stress is decreasing. Due to the resulting low internal stress, CSixNy films can be grown to a thickness above 3 mum, in contrast to DLC films. The microstructure of the films is found as textured graphitic planes of small size connected to each other by fullerene-like three-dimensional CNx-structures. This three-dimensional bonding network leads to high nanohardness of up to 20 GPa. Most of the silicon is bonded to carbon, which results in anisotropic hardness properties.