A thermodynamic study of titanium nitride formation on a patterned oxidized silicon substate in the TiCl4-NH3-H-2 gaseous phase was carried out. Calculations were performed in the temperature range of 700-1300 K and in the total pressure range of 27-133 Pa. On a silicon oxide surface, TiN formation occurs according to a three-step mechanism involving TiCl3 formation as an intermediate compound. On a TiN surface, the deposition occurs in the same manner. On a silicon surface, titanium disilicide or silicon nitride are the only condensed phases obtained at equilibrium in the TiCl4-rich and NH3-rich cases, respectively. Because silicon diffusion is allowed through TiSi2 and not through Si3N4, TiN can only grow on a Si3N4 surface. In spite of the fact that Si3N4 is not conductive, the formation of a thin Si3N4 covering layer is necessary for TiN growth. Calculations show that the best TiN yield is obtained with an ammonia-rich gaseous phase at a deposition temperature of about 1100 K.