Abstract
Interfacial reactions of non-ultrahigh vacuum deposited 30-nm-thick Ti films with an interposing 0.5-nm-thick Mo layer on (001)Si and implanted Si have been studied by transmission electron microscopy (TEMP), x-ray diffractometry, energy dispersion analysis of x-ary (EDAX) and secondary ion mass spectroscopy (SIMS). X-ray diffraction (XRD) and sheet resistance data revealed that C49- to C54-TiSi2 phase transformation occurred in 650℃ annealed samples. A Ti-Mo-Si ternary silicide was found to form. In the XRD spectra of the 650℃ annealed implated samples containing Mo, a ternary phase containing Ti, Mo and Si atoms was also found. Substantial amount of C54-TiSi2 phase already forms at this temperature. Therefore, with a thin interposing Mo layer, the formation temperature of C54-TiSi2 was lowered by about 100℃ compared to the what is usually needed for the C49- to C54-TiSi2 transformation. From EDAX and SIMS data, the redistribution of Mo atoms in TiSi2 layer was found. The enhancement of the formation of C54-TiSi2 is attributed to the presence of Mo atoms which provies more heterogeneous nucleation sites needed for thetransformation from C49 to C54 phase. Effects of nitrogen ion implantation on TiSi2 contacts on shallow junctions have been investigated. Nitrogen ion implantation was found to suppress the B and As diffusion in silicon. For Ti on 30 keV BR＋2 ＋ 20 keV, 1 x 1015/cm2 N＋2 implanted samples, a continuous low-resistivity TiSi2 layer was found to form in all samples annealed at 650-950℃ from TEM observations. For Ti on 20 keV, 1 x 1015/cm2 N＋2 ＋ 30 keV As＋ implanted samples, end-of-range (EOR) defects were completely climinated in all samples annealed at 650-900℃. The results indicated that with appropriate control, a thin interposing Mo layer and N＋2-implantation can be successfully implemented in forming low-resistivity TiSi2 contacts and enhancing the thermal stability of TiSi2 layer on shallow junctions in deep submicron devices. In a polycrystalline structure, grain boundary nucleation is generally the dominant mode. In the present study, the Mo atoms and/or the (Ti, Mo)Si2 ternary phase were proposed to provide more nucleation sites to enhance formation of C54-TiSi2. On the other hand, the effect of grain boundary for decreasing transformation temperature was found to be less crucial.