Enhanced Growth of Low-Resistivity Metal Silicides and Self-Assembled Silicides Quantum Dot Arrays on Epitaxial Si-Ge Alloys on Silicon
| Autor: | Wen-Wei Wu, 吳文偉 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 Enhanced growth of low-resistivity metal silicides and self-assembled NiSi and CoSi2 quantum dot arrays on epitaxial Si-Ge alloys have been studied by sheet resistance measurement, glancing incidence X-ray diffractometry (GIXRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and energy dispersion analysis of X-ray (EDAX). The formation of Co silicides on (001) Si with an interposing Ni layer has been investigated. For Co(20 nm)/Ni(7 nm)/Si(001) samples, CoSi2 and NiSi phase were observed to form at 400-500 ºC. AES analysis indicated that Ni diffused from the Co/Si interface to disperse in CoSi2 layer during annealing. Above 700 ºC, (Co,Ni)Si2 was the only silicide phase present. The presence of Ni was found to decrease the formation temperature of CoSi2 by about 100 ºC, prevent oxygen contamination from the annealing ambient, and improve uniformity of CoSi2 compared to that without Ni interlayer. In addition, the resulting (Co,Ni)Si2 layer has good thermal stability up to 1000 ºC and has a preferential epitaxial orientation with respect to the Si substrate. Formation of Co silicides on Si0.7Ge0.3 alloys with a thin interposing Au layer and capping Ti layer has been investigated. CoSi2 was observed to be the only silicide phase in Si0.7Ge0.3 samples annealed at 650-950 ℃ with a thin interposing Au layer and capping Ti layer. The sequence of phase formation is the same as the reaction of Co with (001)Si. The presence of Au was found to decrease the formation temperature of CoSi2 by about 300 ℃ compared to that of Co(30nm)/Si0.7Ge0.3 samples. In addition, a thin capping Ti layer improves the uniformity and thermal stability of CoSi2 layer. For Ti(5nm)/Co(30nm)/Au(1nm)/Si0.7Ge0.3 system, the process window of CoSi2 was extended to 650-950 ℃. SIMS analysis indicated that a large amount of Au diffused from the Co/Si0.7Ge0.3 interface to disperse in the CoSi2 layer during annealing. Enhanced growth of low-resistivity self-aligned CoSi2, C54-TiSi2, and NiSi on epitaxial Si0.7Ge0.3 has been achieved with an interposing amorphous Si (a-Si) layer. The a-Si layer was used as a sacrificial layer with appropriate thickness to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming CoSi2, C54-TiSi2, and NiSi on Si0.7Ge0.3 grown by molecular beam eptiaxy. The process promises to be applicable to the fabrication of high-speed Si-Ge devices. Self-assembled NiSi and CoSi2 quantum dot arrays have been grown on relaxed epitaxial Si0.7Ge0.3 on (001)Si. The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001)Si direction. The two-dimensional, pseudo-hexagonal structure was achieved under the influence of repulsive stress between nanodots. Since the periodicity of surface bunching can be tuned with appropriate vicinality and misfit, the undulated templates promise to facilitate the growth of ordered silicide quantum dots with selected periodicity and size for utilization in nanodevices. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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