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A. van Veen, H. Schut, A. Rivera, A.V. Fedorov, IRI Delft University of Technology, Mekelweg 15, 2629JB, Delft, The Netherlands

ABSTRACT

Annealing experiments of deuterium implanted silicon have been performed while positron beam analysis was used for monitoring the cavity growth. The experiments indicate up to annealing temperature 5000 C similar defect evolution for both the low dose of 10 16cm-2 as for a 3 times higher dose. At this temperature the deuterium stabilized vacancy clusters dissociate and only in the case of the high dose micro-cavities are formed. Monte Carlo simulations of vacancy cluster growth in silicon based on vacancy cluster dissociation energies, calculated with the Stillinger Weber potential, have been performed. The results indicate that for low initial defect concentrations vacancy clusters might be hindered to grow because the vacancy binding energy of the clusters does not increase monotonically with the cluster size. Only a high concentration guarantees that growth barriers will be overcome.

INTRODUCTION

By implantation of silicon with helium or hydrogen ions vacancy agglomerates are formed which during thermal annealing may develop to gas bubbles. At certain temperature the gas is released and small cavities remain [1,2]. The cavities act as effective sinks for metallic impunities.Earlier it has been observed that a critical threshold dose is required to allow the formation of cavities during post-irradiation annealing. Keionen et al [3] observed removal of the damage created by 35 keV H- in two stages at 250'C and at 5500 C respectively. The dose amounted to 1016 cm 2 . Williams et al [4] observed with XTEM the presence of microcavities after annealing to 650 'C of silicon irradiated with 100 keV IT -ions at a dose of 3 x 10 "6cm -2. Brusa et al [5] observed with positron techniques the survival of defects after annealing to 600 °C for 31 keV -12 ions. They implanted at a temperature of 77 K. It appears that the critical dose for formation of cavities is at about 10 "6cm2 for energies ranging from a few keV to 100 keV. In this article we present the results of an annealing study for 30 keV D '-ions at a dose beyond the critical dose. Since deuterium defect interactions are similar to hydrogen defect interactions regarding binding and dissociation energies annealing results for deuterium can be compared well with results obtained for hydrogen. Positron depth profiling of the defects is used to monitor the vacancy clustering process.

EXPERIMENTAL

The deuterium implantations have been carried out by a mass analyzed ion beam from an 30 keV ion implanter. Two samples were prepared one with a dose of 3x i0' 6 cm-2 and the other one with 10"6 cm2 D '. The samples were annealed in a vacuum oven during periods of 25 minutes. Defects have been studied by positron beam depth profiling [6]. Characterization of the defects was improved by monitoring two positron annihilation parameters which describe the Doppler 155 Mat. Res. Soc. Symp. Proc. Vol. 396 0 1996 Materials Research Society

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