| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 90 === Interfacial reactions of Ti on strained Si epitaxially grown on Si0.7Ge0.3 have been investigated.
35-nm-thick strained Si films were epitaxially grown on 300-nm-thick Si0.7Ge0.3 at 500℃ by solid source molecular beam epitaxy(MBE). The stress measurements of top strained Si layer were carried out by Raman spectra and high resolution X-ray diffraction (rocking curves). 30-nm-thick Ti thin films were evaporated by an electron beam evaporation system on the strained Si substrates at room temperature. The solid-phase reactions were induced in a rapid thermal annealing (RTA) system by annealing at temperatures ranging from 600 to 850 ℃ for 30 seconds. The resulting films were characterized by transmission electron microscopy (TEM), Rutherford backscattering spectrometry, glancing-angle x-ray diffraction method, energy dispersive x-ray spectrometry, and four-point probe method.
The stresses of top strained Si layer determined by high resolution x-ray diffraction (rocking curves) and Raman spectra were about 2.5 to 3.0 GPa and tensile. From cross-sectional high-resolution TEM micrograph of as-deposited Ti/strained Si samples, it was found that the amorphous interlayer of as-deposited Ti/strained Si sample ( tstrained Si≒3.0 nm ) is thicker than that of as-deposited Ti/bare Si sample ( tbare Si≒2.0 nm ). A sharp drop in sheet resistance was found for Ti on the tensily stressed samples at 700 °C. On the other hand, for Ti on stress-free samples a sharp drop in the sheet resistance was found as the annealing temperature was increased to 750 ℃. It indicated that appreciable high-resistivity C49—TiSi2 to low-resistivity C54—TiSi2 transformation occurred. The phases of annealed samples were characterized by glancing-angle x-ray diffraction method. The C54 TiSi2 phase was found to be present in 700 ℃ annealed Ti/strained Si samples. The activation energy of Ti/Si/Si0.7Ge0.3 system (∼0.8 ± 0.2 eV) is lower than that of Ti/Si system (∼1.0 ± 0.2 eV). The results clearly showed that in Ti/Si/Si0.7Ge0.3 system the tensile stress reduces the activation energy for the growth of Ti/Si amorphous interlayer.
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