The present invention relates to methods of forming silicon nitride thin films on a substrate in a reaction chamber by plasma enhanced atomic layer deposition (PEALD). Exemplary methods include the steps of (i) introducing an octahalotrisilane Si3X8 silicon precursor, such as octachlorotrisilane (OCTS) Si3Cl8, into a reaction space containing a substrate, (ii) introducing a nitrogen containing plasma into the reaction space, and wherein steps (i), (ii) and any steps in between constitute one cycle, and repeating said cycles a plurality of times until an atomic layer nitride film having a desired thickness is obtained.