Atomic-order thermal nitridation of group IV semiconductors for ultra-large-scale integration

One of the main requirements for ultra-large-scale integration (ULSI) is atomic-order control of process technology. Our concept of atomically controlled processing for group IV semiconductors is based on atomic-order surface reaction control in Si-based CVD epitaxial growth. On the atomic-order surface nitridation of a few nm-thick Ge/about 4 nm-thick Si_0.5Ge_0.5/Si(100) by NH₃, it is found that N atoms diffuse through nm-order thick Ge layer into Si_0.5Ge_0.5/Si(100) substrate and form Si nitride, even at 500 °C. By subsequent H₂ heat treatment, although N atomic amount in Ge layer is reduced drastically, the reduction of the Si nitride is slight. It is suggested that N diffusion in Ge layer is suppressed by the formation of Si nitride and that Ge/atomic-order N layer/ Si_1-xGe_x/Si (100) heterostructure is formed. These results demonstrate the capability of CVD technology for atomically controlled nitridation of group IV semiconductors for ultra-large-scale integration.