Characterization of the ion-beam induced structure probed by a positron annihilation spectroscopy

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

The irradiation defect and induced structure 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 50-200 keV. The peak intensities of annihilation rays (S parameter) and its annealing behaviors were measured. S parameter decreased after 300C annealing. This means that positrons are trapped to the irradiation defects filled up with the helium atoms. S parameter slightly increased with 800C annealing and increased rapidly at 900C. This is caused by the growth of helium bubbles and subsequent desorption of helium atoms. From the first principle calculation, positron trapping at the defect cluster of approximately 1nm filled up with 36 helium atoms is suggested.