Metallic thin film on SiGe/Si substrates
In this thesis, in-situ XPS and ex-situ AFM have been employed to probe the thermal stability of Si0.8Ge0.2(001) virtual substrate (VS), the interfacial reaction and growth mode of Ni thin film on Si0.8Ge0.2 VS at room temperature (RT), and the germanosilicide phase transformation at high temperatures. Similar studies on Si(001) and Ge(001) substrates were also carried out for comparison. The Si0.8Ge0.2 VS remained stable in composition and unchanged in surface morphology below 500oC. Above 500oC, Ge desorbed from surface, leading to a decrease in Ge concentration and formation of macroscopic pits on the surface. Ni growth proceeded via a pseudo-layer-by-layer mode on H-terminated Si, Ge, Si0.8Ge0.2 and clean Ge surfaces, while it changed to small close-packed island growth on the clean Si and Si0.8Ge0.2 surfaces. The ultra-thin Ni films (~2-6A) reacted strongly with the Si, Ge and Si0.8Ge0.2 substrates to form thin, amorphous NiSi-like, NiGe-like and NiSi0.8Ge0.2-like layers at RT on both clean and hydrogen terminated surfaces. Upon annealing, they transformed to NiSi2, NiGe and Ni(Si1-yGey)2 (y<0.2) phases, respectively. Continuous films at RT became 3D rectangular islands on all three substrates when annealed beyond 400oC.
Ni, Si1-xGex, Virtual substrate, Growth mode, Interfacial reaction, XPS
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