Abstract
An intermediate Si1-y Cy layer in the Si1-x Gex film, replacing the conventionally graded buffer layer, was used to form the high-quality relaxed SiGe substrate. With the 700 nm thick Si0.8 Ge0.2 overlayer, such a Si1-x Gex Si1-y Cy Si1-x Gex (x=0.2, y-0.014) heterostructure has a threading dislocation density of 5.5× 105 cm-2 and a residual strain of only 2%. The surface roughness was measured to be about 4.2 nm. The long-range misfit dislocation array was formed mainly at the interface of top Si1-x Gex and Si1-y Cy. 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-x Gex film serving as a virtual substrate shall be applicable to high-speed strained-Si devices. c 2005 American Vacuum Society.