Amorphization and stress kinetics in ion implanted crystalline solids

Abstract

Nowadays, ion implantation is widely used for doping and modification of semiconductors. Ion bombardment induced amorphization, strain and stress of semiconductors is the subject of many articles dealing with ion implantation. Dependence of the stress (or strain) on the ion dose, energy, kind of ions, stress relaxation processes are the key problems that are solved in the recent articles on this subject. Usually stress in the crystalline silicon increases with the dose of ion irradiation and maximum values of stress (108 - 109 Pa) are reached in the region of the dose close to the amorphization dose. After initial growth of the stress in ion implanted region further irradiation induces relaxation of the stress and maximum of the stress-dose can be found for many ion combinations. If the mass of ions increases the maximum usually is shifted to the lower dose region. Stresses in the plane for thin samples depend on the biaxial strain. On the other hand, strain in the perpendicular direction to the plane is measured experimentally. Poisson relation is used to express strain in plane using the values of strain in the perpendicular direction. It should be mentioned as well that plastic flow of the material can contribute to the strain in plane if the crystal is saturated by radiation defects. As the result, some errors in the determination of the real values of strain can be induced. To avoid these uncertainties analytical expression directly for the stress in plane can be constructed. Strain in plane in the present paper expressed using elementary volume related to the point defect and stress-strain dependence is defined taking in account relaxation processes in the ion irradiated solid.