X-ray diffraction, high resolution transmission electron microscopy, and resistivity measurements were used to demonstrate a modification of the Ti/Si reaction path consisting of direct nucleation followed by diffusion limited growth of low resistivity C54 TiSi2 without nucleation of high resistivity C49 TiSi2, for the reaction of Ti with Mo doped polycrystalline or Mo doped amorphous Si by rapid thermal processing at 650 °C. We also report the mechanism of early C54 nucleation. We demonstrate that MoSi2 and an unidentified silicide phase lattice matched to C54 TiSi2, with spacings of 4.15 and 2.26 Å, nucleate along the Ti/Si interface at early stages of the reaction and act as templates on which C54 TiSi2 nucleates and grows epitaxially. In contrast, the conventional phase sequence, nucleation and growth of C49 TiSi2 preceding nucleation of C54 TiSi2, was observed for the Ti/Mo doped single crystal (100) Si reaction and for all samples without Mo.

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The phase sequence of the rapid thermal processing induced reaction at T=650 °C has been studied by a combination of high resolution transmission electron microscopy and image simulations. We found that pre-amorphization of poly-Si substrates does not change the reaction path, i.e., Ti5Si4 and C-49 TiSi2 phases were formed with the latter growing upon further annealing. In the Mo doped poly-Si/Ti system the C-54 TiSi2 phase forms along with Ti5Si4 and two Mo silicide phases, MoSi2 and Mo5Si3; no C-49 TiSi2 was observed. We provide direct evidence that the Ti–Si reaction in the Mo doped system follows the template mechanism with MoSi2 and Mo5Si3 based phases acting as template phases for accelerated growth of C-54 TiSi2. Direct formation of C-54 TiSi2 at lower temperatures bypassing C-49 TiSi2 is very promising for application of the Ti salicide process in the future generation of deep-submicron complementary metal–oxide–semiconductor devices.

The mechanism and evolution from the early stages of the Ti/Si reaction by rapid thermal processing (RTP) at 650°C in the presence of Mo doping was studied and compared to the case without Mo doping; for amorphous, polycrystalline and single crystal (100) Si substrates. It was found that for Mo doped polycrystalline Si or Mo doped amorphous Si, the low resitivity C54 TiSi2 phase nucleates at the Ti/Si interface and grows following diffusion limited kinetics, bypassing the nucleation of the high resistivity C49 TiSi2 phase. The conventional phase sequence, with C49 TiSi 2 nucleation and growth, was observed on Mo doped (100) Si and all samples without Mo. The mechanism of early C54 nucleation was identified by high resolution transmission electron microscopy (HRTEM): at early stages of the reaction, precursor silicide phases lattice matched to C54 TiSi2 nucleate at the Ti/Mo doped Si interface, and act as templates for epitaxial nucleation of C54 TiSi2. Two such phases were observed, MoSi2 and a phase with spacings of 2.26 Å and 4.2 Å. Image simulations suggest that the structure of the second template phase is based on Mo5Si3. Similar kinetics were observed on large structures and narrow lines for Mo doped Si (except for the case of (100) Si), indicating that this growth mechanism eliminates the linewidth dependence. Implementation on a 0.10 μm CMOS technology of a process combining Mo doping with pre-amorphization (PAI) achieves low source/drain (S/D) sheet resistance, and the first Ti salicide process with low gate sheet resistance down to 0.06 μm.

The phase sequence of the RTP induced reaction at T=650°C has been studied. We found that pre-amorphization of poly-Si substrates does not change the reaction path. i.e. Ti5Si4, and C-49 TiSi2 phases were formed_ with the latter growing upon further anneal. In the Mo doped poly-Si/Ti system the C-54 TiSi2 phase has formed along with Ti5Si4 and two Mo silicide phases, MoSi2 and Mo5Si3; no C-49 TiSi2 was observed. We show that the reaction in the Mo doped system follows the template mechanism with MoSi2 and Mo5Si3 based phase acting as template phases for accelerated growth of C-54 TiSi2.