Influence of impurities on mechanical strength of silicon crystal

Abstract

The change in the mechanical strength of silicon wafers due to the impurity atoms introduced as dopants in them was investigated by a three-point bending test and finite element method (FEM) simulation. As representatives of p-type and n-type dopant species, boron and phosphorus were used. Stress-strain curves were obtained with samples having three levels of impurity concentrations, and the upper yield stresses were evaluated to investigate the influence of the impurities on the mechanical strength. In the case of boron in the experimental results, there was no change in the strength with the doping concentration, and the upper yield stress remained constant. Contrastingly, the phosphorus-doped samples showed a decrease in the upper yield stress with the doping concentration increase. FEM simulation of the three-point bending test and analysis of the simulation results showed that the dislocation velocity, i.e., the activation energy of the dislocation motion, varies according to the concentration. This suggested that the dislocation velocity changed based on the concentration of the added impurities strongly influenced the mechanical strength of silicon.