An intermediate Si1–yCy layer in the Si1–xGex film, replacing the conventionally graded buffer layer, was used to form the high-quality relaxed SiGe substrate. With the 700nm-thick Si0.8Ge0.2 overlayer, such a Si1–xGex/Si1–yCy/Si1–xGex (x = 0.2, y = 0.014) heterostructure had a threading dislocation density of 5.5 x 105/cm2 and a residual strain of only 2%. The surface roughness was measured to be about 4.2nm. The long-range misfit dislocation array was formed mainly at the interface of top Si1–xGex and Si1–yCy. Strained-Si n-channel metal-oxide-semiconductor transistors with various buffer layers were fabricated and examined. Effective electron mobility for the strained-Si device with this substrate technology was found to be 95% higher than that of Si control device. The scheme for the formation of the relaxed Si1–xGex film serving as a virtual substrate shall be applicable to high-speed strained-Si devices.

Growth of Strained Si on High-Quality Relaxed Si1-xGex with an Intermediate Si1-yCy Layer. S.W.Lee, Y.L.Chueh, L.J.Chen, L.J.Chou, P.S.Chen, M.H.Lee, M.J.Tsai, C.W.Liu: Journal of Vacuum Science & Technology A, 2005, 23[4], 1141-5