The effects of buffer layers on the growth of smooth relaxed SiGe thin films

Abstract

The smooth relaxed SiGe films were fabricated on Si(001) substrate using 30nm thick buffer layers by molecular beam epitaxial (MBE). The buffer layers were fabricated as followings: first deposited 20nm thick SiGe alloy layer at 550°C, then 10nm Si buffer was deposited at 400°C. After the buffers were finished, the top SiGe layer with the thickness of 200nm was deposited at 500°C. The deposition quality, thin film structure and residual strain in the film were characterized by high-resolution X-ray diffraction (HRXRD). We found that the surface morphology and crystal quality of SiGe thin film can be improved obviously. It was shown that SiGe top layer was relaxed and smooth by comparing the measured and simulated (004) rocking curves. The peak range and relative position of the SiGe epilayer with respect to the Si substrate in high-resolution reciprocal space map(HRRSM) described clearly the high crystal quality and the strains relaxation. The surface morphologies of thin films were also observed by atomic force microscopy (AFM). The surface is very smooth with RMS less than 7 a.