Smooth and high quality epitaxial strained Ge grown on SiGe strain relaxed buffers with 70–85% Ge

Further improving complementary metal oxide semiconductor (CMOS) performance beyond the 15nm generation likely requires the use of high mobility materials like Ge for pMOS devices. However, Ge pMOS devices made in relaxed Ge do not out-perform current state-of-the-art uni-axially strained Si pMOS devices. This explains the current interest in compressively strained Ge like bi-axially strained Ge grown on top of SiGe strain relaxed buffers. From a device integration point of view, the surface smoothness of the strained Ge layer is an important parameter, which has so far not widely been reported in literature, in contrast to other parameters like the material quality (crystallinity) and the threading dislocation density. In this paper we report the capability of chemical mechanical polishing (CMP) to reduce the surface roughness of the SiGe strain relaxed buffers and the post-CMP and pre-epi cleans, which are required to obtain contamination free SiGe surfaces and to enable nearly defect free strained Ge growth without re-occurrence of the surface roughening. We will demonstrate the epitaxial growth of fully strained 20–40nm-thick Ge epitaxially grown on top of SiGe strain relaxed buffers with 85% Ge with a surface roughness as low as 1.6Å (measured on areas of 10×10μm2).