Fabircation And Molelling Of The Thin SiGe Virtual Substrate

The shrink of transistor dimensions and the higher integration of integrated circuits are driven by the Moore’s law. As the feature size of transistors comes into nanometer level, the performance of transistors begins to suffer from small size effects. Strained Si technology including SiGe material has so many advantages that it has been a new kind of technology to maintain Moore’s law and boost transistor performances.The strained channel on SiGe virtual substrates is caused by the lattice mismatch between SiGe and Si. Therefore, a high-quality SiGe relaxed film is required for the realization of high performance strained Si/SiGe device. The high-quality of SiGe virtual substrates means higher degrees of relaxation, lower defect densities, lower surface roughness and thinner thicknesses of that. However, these indicators may affect and even against each other. This thesis aims to the realization of thin and high-quality SiGe virtual substrate. By studying the mechanism of the relaxation of strained SiGe, a thin SiGe virtual substrate is designed and fabricated successfully, and the process of strain-relaxation induced by Ar+ ion implantation is modeled for this thin virtual substrate.The reason that strain isinduced in SiGe is demonstrated from the perspective of the lattice mismatches between SiGe and Si. The mechanism of strain-relaxation of epi-SiGe film is demonstrated from the perspective of the mismatch dislocation at SiGe/Si interface. And the critical thickness models are also discussed in this thesis.Based on the relationship between dislocation and relaxation, the fabrication of SiGe alloy and the basic design of virtual substrate is demonstrated. Then two thin SiGe virtual substrates are designed, and the one via Ar+ ion implantation is chosen and fabricated. After studying the experimental techniques, the fabricated virtual substrate is tested and analyzed. The result shows that the Ge composition is 19.93%, and the degree of relaxation is up to 81.51%.The process of strain-relaxation induced by Ar+ ion implantation is modeled for this thin virtual substrate. For the elastic multilayer systems, a strain distribution physical model is built based on the lattice mismatch, and the analytical expressions are deduced. Furthermore, the interfacial defects induced by ion implantation are put into the strain distribution model of elastic multilayer systems, and the analytical expression is given for the relationship between the interfacial defects density and the degrees of relaxation. This model can make a good description for the fabricated thin SiGe virtual substrate. In addition, the effect on Young’s modulus caused by ion implantation is investigated, and thus a mathematical model is built.