Growth of strained Si on high-quality relaxed Si1−xGex with an intermediate Si1−yCy layer

Abstract

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 700 nm thick Si0.8Ge0.2 overlayer, such a Si1−xGex∕Si1−yCy∕Si1−xGex (x=0.2, y−0.014) heterostructure has a threading dislocation density of 5.5×105cm−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−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.