Non-stoichiometric silicon nitride SiNx, enriched with silicon, is a promising material for the non-volatile resistive memory development. The current studies devoted to investigation of the optical properties of SiNx synthesized in a low-pressure reactor at 800 oC at different ratios of dichlorosilane (SiH2Cl2) to ammonia (NH3). It was found that for films synthesized at SiH2Cl2/NH3 ratio =1/1, 1/2 and 1/3, the corresponding bandgap values are 3.83, 4.17 and 4.40 eV. At the same time, the corresponding values of the parameter x, found according to the theoretical dependence of the bandgap value on x for SiNx calculated from the first principles, are 1.26, 1.30 and 1.32. Thus, by increasing the SiH2Cl2/NH3 ratio, it is possible to create non-stoichiometric SiNx films with a controlled silicon enrichment degree with high uniformity of chemical composition and thickness.