The changes which were introduced into single crystals by implanting He were investigated by using ion-beam techniques. The damage was detected by means of 2MeV 4He+ back-scattering under channelling conditions, and the He depth distribution was monitored by means of 7 or 8MeV 15N2+ elastic recoil scattering. Wafer samples were prepared by implanting 20keV He ions to 2 x 1016/cm2 at 77K or 300K, and were heat-treated for 2h at 100 to 800C. In the case of the former samples, the damage maximum was originally at 130nm and moved to 180nm after annealing at 200C. In the case of the latter samples, the damage maximum was already at 180nm. At 250 to 500C, both types of sample exhibited the same annealing behavior; with only slight differences in the temperatures. In both cases, the de-channelling signal increased and attained a maximum number, of non-registered Si atoms, of between 2.2 x 1022 and 2.5 x 1022/cm3. Within the same temperature range, the He signal became narrower, built up in a region that was centered on 220nm, and no appreciable loss of He could be detected. The increase in damage was consistent with the creation of cracks and a heterogeneous distribution of bubbles which were filled with high-pressure He which stressed the lattice. Their effect was similar to that of Si interstitials, with regard to channelling Rutherford back-scattering. At temperatures above 500C, He was released from the samples. This process was associated with a decrease in the damage and with the formation and increase in size of voids. Empty voids with a diameter of about 20nm were found at 900C.

High-dose helium-implanted single-crystal silicon R.Tonini, F.Corni, S.Frabboni, G.Ottaviani, G.F.Cerofolini: Journal of Applied Physics, 1998, 84[9], 4802-8