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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In this study, we introduced another very thin SiGe layer that was selectively grown on the Si buffer layer prior to the ultra- thin Si0.5Ge0.5 buffer growth. As a result, selective epitaxial growth of Ge film with good crystalline quality was realized without increasing intermediate layer thickness or thermal budget significantly. This technique is expected to be applicable for the Ge channel formation and other application that require selective Ge film formation with low thermal budget. The mechanism of selectivity enhancement by the first SiGe layer as well as its influence on crystalline quality of the Si0.5Ge0.5 buffer layer and Ge epitaxial layer above will be discussed in the presentation.