In this work we report the results of a theoretical and experimental study on the lattice deformation induced by the deposition of a stoichiometric Si3N4 straining layer on silicon photonics coupling structures. Simulations of stress and strain distribution have been performed together with strain measurements on the nanofabricated structures employing convergent beam electron diffraction (CBED) technique. Good agreement between simulations and measurements have resulted and strain values of the order of mɛ have been obtained.