Quantitative investigation of titanium/amorphous-silicon multilayer thin film reactions
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K. N. Tu IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (Received 26 June 1989; accepted 16 November 1989) Growth of amorphous-titanium-silicide and crystalline C49 TiSi2 in titanium/amorphous-silicon multilayer films was investigated using a combination of differential scanning calorimetry (DSC), thin film x-ray diffraction, Auger depth profiling, and cross-sectional transmission electron microscopy. The multilayer films had an atomic concentration ratio of ITi to 2Si and a modulation period of 30 nm. In the as-deposited condition, a thin amorphous-titanium-silicide layer was found to exist between the titanium and silicon layers. Heating the multilayer film from room temperature to 700 K caused the release of an exothermic heat over a broad temperature range and an endothermic heat over a narrow range. The exothermic hump was attributed to thickening of the amorphous-titanium silicide layer, and the endothermic step was attributed to the homogenization and/or densification of the amorphous-silicon and amorphous-titanium-silicide layers. An interpretation of previously reported data for growth of amorphous-titanium-silicide indicates an activation energy of 1.0 ± 0.1 eV and a pre-exponential coefficient of 1.9 x 10"7 cm2/s. Annealing at high temperatures caused formation of C49 TiSi2 at the amorphous-titanium-silicide/amorphous-silicon interfaces with an activation energy of 3.1 ± 0.1 eV. This activation energy was attributed to both the nucleation and the early stages of growth of C49 TiSi2. The heat of formation of C49 TiSi2 from a reaction of amorphous-titanium-silicide and crystalline titanium was found to be -25.8 ± 8.8 kJ/mol and the heat of formation of amorphous-titanium-silicide was estimated to be -130.6 kJ/mol.
I. INTRODUCTION
Titanium/amorphous-silicon thin film reactions have generated interest in the scientific community due to applications of titanium silicides in integrated circuits1 and due to the formation of a metastable amorphous titanium silicide phase.2"4 In previous studies Rutherford backscattering, transmission electron microscopy, and x-ray photoelectron spectroscopy have been used to study growth of amorphous-titaniumsilicide and crystalline TiSi2.2"4 Recently, Clevenger et al.5'6 have demonstrated that differential scanning calorimetry can also ~be used to study the nucleation and growth of both metastable amorphous and stable crystalline silicides in nickel/amorphous-silicon and vanadium/amorphous-silicon multilayer thin films. In investigating metal/amorphous-silicon reactions, differ-
a'Permanent
address: Departamento de Ciencia dos Materiais e Metalurgia, Pontificia Universidade Catolica, 22452-Rio de Janeiro, RJ-Brazil. "'Current address: IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598. J. Mater. Res., Vol. 5, No. 3, Mar 1990
ential scanning calorimetry has two major advantages over Rutherford backscattering and transmission electron microscopy. First, differential scanning calorimetry is sensitive to both compositional and struct
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