Formation of Uniaxially Strained Si/Ge Channels on SiGe Buffers Strain-Controlled with Selective Ion Implantation

2013 
The uniaxial strain induced in Si/Ge heterostructures can significantly widen the possibility of band engineering and consequently enhance the device performances compared to the biaxial strain. Particularly, the uniaxial compressive stress induced along the channel length direction is highly expected to effectively increase the hole mobility. New technologies to induce the uniaxial stress are, therefore, strongly desired to be developed. We proposed selective ion implantation technique to induce uniaxial strain into the SiGe layer [1]. In this method, strain of the SiGe is locally relaxed in the region where ions are implanted into the Si substrate prior to the SiGe growth. Implantation induced defects are responsible for this facilitation of the strain relaxation. In proper configurations of the selective implantation, the anisotropic strain can be introduced into SiGe layers in the unimplanted regions, where the neighboring relaxed SiGe on the ion-implanted region provides the shear stress and causes the anisotropic strain to the unrelaxed SiGe in the unimplanted region. In previous works [1, 2], we attained Si0.73Ge0.27 buffer layers where the strain relaxation around 40% took place only one direction and almost no relaxation did along the orthogonal direction. In this study, we attempt to grow the uniaxially strained SiGe channel layers with higher Ge concentrations on the SiGe buffers containing anisotropic strain states.
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