Damage to Crystalline Silicon Following Implantation by Low Energy Silicon Ions
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DAMAGE TO CRYSTALLINE SILICON FOLLOWING IMPLANTATION BY LOW ENERGY SILICON IONS. Y. LEVINt, N. HERBOTSt and S. DUNHAMt. tBoston University, Electrical, Computer and Systems Engineering Department, Boston, MA 02215 tArizona State University, Department of Physics and Astronomy, Tempe, AZ 85287 ABSTRACT. A new approach to investigate low energy defect formation and annealing in a crystal is developed, based on experimental observations of the total number of interstitials. The model is applied to damage in crystalline silicon caused by low energy implantation of Siatoms during 40eV implants at 300°Kand 685*K. The model has two versions, analytical and computational, and includes two kinds of diffusing species, self-interstitials and vacancies, their interaction, surface motion of the growing crystal, and a constant source of defects. The source was calculated using a modified TRIM code (TRIMCSR). The focal point of the analysis is the number of interstitials per ion dose surviving at the end of the deposition time (damage to dose ratio or DDR),which is found to be an informative quantity and can be calculated for more sophisticated models including precipitation.
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INTRODUCTION
Observations of damage in crystalline silicon following low energy silicon ion bombardment [1] show that, after deposition, the interstitials tend to accumulate well beyond the crystal region where they have been produced. The total number of these interstitials has been measured by ion channeling [1] and the results are shown in Table 1. Based on these measurements, we have developed a new, global approach, calculating the number of interstitials (damage) and damage to dose ratio (DDR) rather than defect profiles. This quantity is very descriptive and its analysis gives a better understanding of implantation damage annealing processes. In this work, we analyze DOSE atoms/cm x 1016 13.0 5.7 6.1 6.2 6.3 7.0 7.4 7.8 7.9
TEMPERATURE 2
DDR
K
DEPOSITION TIME sec
300 685 685 685 685 685 685 685 685
13000 5700 6100 6200 6300 7000 7400 7800 7900
0.157 0.320 0.333 0.327 0.273 0.276 0.264 0.239 0.208
0
Table 1: Experimentally measured damage obtained by Si-ion scattering and cross-section TEM on ion beam deposition layers of Si on Si . The damage to dose ratio is listed as a function of temperature and dose at Si-ion energy of 40eV [1]. a model for annealing of damage to crystalline silicon caused by low energy Si ions and compare them to the data for 40 eV implants at 300*K and 685*K "Themodel includes interstitials and vacancies, their recombination, the surface motion of the growing crystal, and a constant source of interstitials and vacancies. The source is calculated using a modified TRIM code, TRIMCSR (TRansport of Ions in Matter including Collision cascade, Sputtering and Replacement events) [2]. Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
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In the analytical version of the model, the number of interstitials per ion surviving at the end of the deposition time (DDR), was evaluated and compared to measure
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