Raman study of irradiation damage in silicon

We have studied irradiation damage in a single-crystal silicon wafer prepared parallel to (100) by micro-Raman spectroscopy. Surficial structural damage in areas ~150 µm in size was produced by irradiation with a microbeam loaded with 600 keV Si⁺ ions at a 3MV Tandetron accelerator, Rossendorf (GRAMBOLE et al., 2007). Several implantations were done with a uniform fluence of 5 × 10¹⁴ cm^-2, however, at different temperatures to produce areas with different degrees of damage. Full amorphisation was reached at implantation temperatures below 140 °C (NASDALA et al., 2007). Monte Carlo simulations using the SRIM code (ZIEGLER et al., 1985) predict that trajectory lengths of implanted ions are below 1 µm. This still exceeds the low penetration depth of light in silicon and, with that, the depth probed by Raman spectroscopy. Spectra obtained from partially amorphised areas virtually consist of an overlap of the two Raman spectra of amorphous and crystalline silicon, i.e., the LO=TO band of crystalline silicon at ~ 521 cm^-1 shows only minor band broadening and shift when compared to the spectrum of the unirradiated host wafer. This indicates that the majority of the structural damage is located in amorphous clusters whereas the remnant crystalline silicon fraction shows only low levels of point defects as caused by atomic displacements.

References
GRAMBOLE, D., HERRMANN, F., HEERA, V. & MEIJER, J. (2007): Nucl. Instr. Meth. Phys. Res. B (in press).
NASDALA, L., GRAMBOLE, D., KRONZ, A. & TRULLENQUE, G. (2007): Am. Mineral. (accepted).
ZIEGLER, J. F., BIERSACK, J. P. & LITTMARK. U. (1985): The Stopping and Range of Ions in Solids.
Pergamon, New York.