The invention relates to a process for obtaining thin films with a content of amorphous stoichiometric and non-stoichiometric silicon nitride, in high vacuum conditions, on flexible temperature-sensitive substrates to be used in microelectronics and for generating energy, as anti-reflective protective layer. According to the invention, the process consists in the pre-preparation of the vacuum precinct and the use of a plasma source Thermionic Vacuum Arc for Compounds, so as to obtain an advanced vacuum of 3 x 10mbar at the most, followed by the injection of Nin controlled flow, in the range of 0.5 … 2.5 sccm, resulting in a localized Si + Nplasma which does not come into direct contact with the substrate.