Characterization of defects by the Helium and Hydrogen implantation using a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Tran, D. T.*

The irradiation defect and induced structure which are formed by helium ion irradiation into silicon were observed by the positron annihilation method. The positron trapping to the helium bubbles has not been confirmed. Helium ions were implanted to the silicon (irradiation dose: 210/cm at room temperature) with the energy of 50200 keV. The peak intensities of annihilation rays (S parameter) and its annealing behaviors were measured. S parameter decreased after 300 C annealing. This means that positrons are trapped to the irradiation defects filled up with the helium atoms. S parameter slightly increased rapidly at 900 C. This caused by the growth of helium bubbles and subsequent desorption of helium atoms. From the comparison with the experimental result and first principle calculation, positrons are trapped at the defect cluster of approximately 1 nm filled up with 36 helium atoms, which is considered the helium bubble.