Titanium monophosphide (TiP) layers as potential diffusion barriers

By annealing titanium nitride (TiN) layers in phosphine (PH3) at 450 degrees C, top layers of pure titanium monophosphide (TiP) could be deposited. The phase TiP and the structure as a double layer of TiP on TIN could be identified unambiguously by AES, XRD and cross-sectional TEM. TiN was deposited on silicon by means of an RTCVD-process (Rapid thermal CVD) with titanium tetrachloride (TiCl4) and ammonia (NH3) as precursors. The subsequent annealing step in PH3 followed immediately in the same reactor. The TiCl4-precursor required for the additional deposition is assumed to be delivered by the fraction adsorbed at the reactor walls during the previous deposition step of TiN. The synthesis of TiP at temperatures as low as 350 degrees C is unique so far. Processes for the preparation of TiP, as far as are described in the literature, presuppose temperatures above 750 degrees C and the presence of catalysts. The TiP top layer has a very low resistivity compared with TiN, it seals the whole stack against oxygen uptake and its roughness is lower than that of TiN. These properties suggest an excellent suitability of the bilayers as a potential diffusion barrier for Al/W-metallization.