Some Features of the Structure of Silicon Single Crystals Irradiated by Large Fluences of Fast Light Ions of Gases

Abstract

Structural study of silicon irradiated by large fluences of light gas ions has shown how the degree of damage in Si, both in the ion passage region and in the braking area, increases and become more complicated with increasing energy and mass of ions. For hydrogen ions the stress line in the braking region is narrowest and its width grows almost linearly with energy. For ions of deuterium and helium, this dependence is weaker and deviates from linear. Additional stress lines depended on the value of ion current (intensity of irradiation) were observed in the pictures of selective etching. For current densities up to 0.45 μA/cm2, the second etched line of stresses appeared at the distance equal to the twice length of the run of protons from the surface. With an increase in the current density up to 1 μA/cm 2 , this line was not observed, at 3 μA/cm2 the part of Si (with thickness that corresponds to the ion path depth) in the irradiation process was exfoliated from main volume. The number of extra etched lines is maximal for helium and depends on the temperature of irradiation. Increase in the temperature (over 100 oС) leads to disappearance of additional stress lines. Detail study with gradual selective etching (in the step of 30 μm) from an irradiated surface has shown the distribution of structural defects in the plane of the proton braking region of silicon, irradiated with fluence 10 17 cm –2 at T ≤ 100 оС and annealed for 0.5 h at 580 оC. With deepening into Si volume the irradiated region associated with radiation defects was gradually decreasing and completely disappeared at the depth of 150 μm behind the braking line. At the depth of nearly 35 μm behind the braking line, the growth layers of matrix Si were detected.