INFLUENCE OF LOCAL MECHANICAL STRESSES ON THE SILICON SPUTTERING YIELD BY ION BEAM

Abstract

A review of scientific publications and modeling of the effect of mechanical stresses on the sputtering yield of silicon by an ion beam is carried out. It is shown that the flux of atoms (from the depth to the surface) through interstitial or vacancy mechanisms due to the stress gradient caused by the limiting bending of the plate is insufficient to explain the increase in the sputtering coefficient. Calculations show that even the limiting elastic deformations do not significantly change the energy of atom detachment from the site, and an increase in the drift velocity of atoms due to the enrichment of the near-surface region with vacancies is insufficient to increase the sputtering rate. Consequently, it is necessary that the elastic deformation is transformed into plastic with the formation of mobile weakly bound atoms. The calculated stress distribution in a loaded silicon wafer using the COMSOL Multiphysics software package showed that the key driving force behind the increase in the silicon sputtering coefficient is the concentration of compressive and tensile stresses in the vicinity of the simulated crater during sputtering. The created crater is a stress concentrator, the gradients of which significantly exceed the values obtained by bending a plate without a crater. It is demonstrated that the generated stresses exceed the ultimate strength of the material in the vicinity of the crater, which begins to relax due to the expulsion of "excess" atoms in the tension region. The appearance of additional deformation-stimulated fluxes of weakly bound surface atoms at the bottom and walls of the crater provides an increase in the concentration of knocked-out atoms in the process of ion sputtering. Simulations predict an increase in sputtering yield of up to 40%. It is also shown that closely spaced craters, due to elastic interaction with each other, compensate each other's elastic fields, which has an effect on the value of the sputtering coefficient.