Effect of the Ge preamorphisation dose on the thermal evolution of End of Range defects
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Effect of the Ge preamorphisation dose on the thermal evolution of End of Range defects B. Colombeau1, F. Cristiano2, J-C. Marrot2, G. Ben Assayag1 and A. Claverie1 1 CEMES/CNRS, 29 rue J.Marvig, 31055 Toulouse Cedex, France 2 LAAS/CNRS, 7 av. colonel Roche, 31077 Toulouse Cedex, France ABSTRACT In this paper, we study the effect of the Ge+ preamorphisation dose on the thermal evolution of End of Range (EOR) defects upon annealing. Amorphisations were carried out by implanting Ge+ at 150 keV to doses ranging from 1x1015 ions/cm2 to 8x1015ions/cm2. Rapid Thermal Annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Plan view transmission electron microscopy under specific imaging conditions was used to measure the size distributions and densities of the EOR defects. We found that for a fixed thermal budget, the increase in the Ge ion dose results in an increase in the defect density but has no effect on the defect size distribution. This invariance of the mean size of defects with respect to the initial supersaturation introduced in the matrix is an expected characteristic of a conservative Ostwald ripening mechanism. Moreover, the total number (Nb) of Si interstitial atoms bound to the EOR defects is a monotonically increasing function of the Ge ion dose. Furthermore, we found that Nb is directly proportional to the number of Si atoms in excess of the vacancies found below the a/c interface as calculated by Monte Carlo simulations. This is consistent with the “excess interstitial” model which explains the origin of the EOR defects.
INTRODUCTION In order to realise ultra-shallow junctions compatible with advanced CMOS technology, it is now admitted that preamorphisation of the wafer prior to low energy dopant implantation has several advantages [1]. After annealing of such preamorphised implants, End of Range (EOR) defects are formed below the a/c interface. As these defects strongly influence dopant diffusion [2], it is necessary to know how process parameters such as the preamorphisation ion dose affect their thermal evolution. The goal of this paper is to study the effect of the Ge+ preamorphisation dose on the thermal evolution of End of Range (EOR) defects upon annealing. In other words, we investigate the influence of the amplitude of the initial supersaturation of Si interstitial atoms (Si(int)s) located below the a/c interface on the kinetics of EOR defects. Indeed, previous studies [3,4] have investigated the effect of the preamorphisation dose on the defect density of EOR defects, but no conclusions have been drawn on the separate evolution of the mean size and defect density upon annealing. Moreover, until now, no publications have clearly shown the so-called “initial supersaturation effect” [5]. To this purpose, we have studied by TEM samples implanted with various Ge amorphisation doses. The thermal evolution of the EOR defects from these analyses has been compared to the Ostwald ripening theory. Finally, these results have been explained following the “excess inte
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