As conventional Si based device structures are approaching their physical limits, Ge epitaxial film on Si (100) substrate becomes more attractive for virtual substrates, on which advanced channel engineering techniques to be applied, or integrated Ge photonic devices to be formed. Low threading dislocation density and smooth surface are key features to realize such applications of the Ge/Si virtual substrate. To date, growth methods for Ge epitaxial film on Si (100) substrate involve at least one of thick (micrometer order) Si x Ge 1-x buffer growth process, high temperature annealing steps or Chemical mechanical polishing (CMP) process, any of which could compromise reliability and suitability for production.In this study, feasibility of ultra thin (in the order of 10 nm) Si x Ge 1-x buffer layer for pure Ge epitaxial growth was investigated with regard to Ge layer's crystallinity, threading dislocation density, and surface roughness, as well as suitability for production.As a result, Ge epitaxial film that has low threading dislocation density with very smooth surface (root mean square (RMS) = 0.44 nm) was successfully grown in shorter process time by using SiGe buffer layer 1/1000 thinner than that of previously known methods without using CMP or high temperature annealing.

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Low-temperature epitaxial Si, SiGe, and SiC films were grown in a 300mm cold-wall UHV/CVD reactor on (100) silicon wafers (bulk and SOI) at temperatures ranging from 300 to 800 °C using disilane, germane and methylsilane. Four key advantages of UHV/CVD over RPCVD are demonstrated: (i) higher structural quality of epitaxial Si using disilane as a precursor, (ii) highly controlled growth of ultra-thin Si down to ~ 6 Å, (iii) planar growth of SiGe at ultra low temperature (< 375 ºC), and (iv) planar growth of germanium at temperatures of less than 350 ºC.

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A 300mm cold-wall UHV/CVD reactor was used to grow epitaxial silicon layers on (100) SOI wafers at 500 to 800 °C using disilane, silane, and mixtures thereof. Spectroscopic ellipsometry was utilized to measure the deposition rates and wafer uniformities after growth, and high-resolution atomic force microscopy was employed to extract surface roughness and assess step flow growth. In the massflow controlled deposition region, both disilane and silane resulted in a linear dependence of growth rate on gas flow where disilane dominated over silane. In the reaction-limited regime, both precursors exhibited a perfect rate limitation with activation energies of ≈ 2 eV. Unlike in RPCVD, the deposition rate of disilane was found to approach twice that of silane at lowest temperatures. Step-flow growth was maintained even after 1μm of silicon was deposited under high-rate conditions. Additionally, continuous epitaxial films with thickness as low as 4 Aå were also obtained.