Due to the continuous scaling down of equivalent oxide thickness requested for inter-poly dielectric material in the next technology nodes, the Oxide-Nitride-Oxide structure is not able anymore to guarantee charge retention because of high leakage current. An alternative stack with higher dielectric constant is needed in order to have lower EOT together with higher physical thickness which fulfils retention requirements. With this purpose we have studied nitrided Hf-silicates (k=15÷20) grown by Atomic Layer Deposition at 350ºC starting from HfCl4, SiCl4 and H2O. The attention has been focused on how the thermal stability of these materials is improved when nitrogen is inserted in the film by NH3 annealing. Their chemical properties have been studied by Time of Flight-Secondary Ion Mass Spectrometry and X-ray Photoemission Spectroscopy, while their morphological evolution has been followed by means of X-Ray Reflectivity, X-Ray Diffraction and Transmission Electron Microscopy.