Effects of group-V impurities on the elastic properties of silicon

Besides reduction in device size the application of strained silicon in transistor design plays a crucial role in improving device speed and power consumption. Microscopic investigations are fundamental to understand the mechanical behaviour of strained Si layers, especially in combination with impurity atoms. In the present work, the influence of group-V impurities on strain fields in silicon was studied by means of the perturbed angular correlation method using the acceptor 111In as probe. This nuclear technique is well suited for studying strain on an atomic scale. After ion implantation of the group-V atoms and subsequent annealing the Si samples were bent along the <1 1 0> crystal axis resulting in a uniaxial tensile strain. For nitrogen-implanted silicon the response of the crystal lattice to mechanical stress shows no difference to undoped samples, which means that nitrogen has no influence on strain fields in silicon. However, after implantation of the donors P, As and Sb a significant strain relaxation is observed which is probably due to dislocations. We show that this relaxation caused by n-doping also extends to undoped areas which are adjacent to the implanted region.