Study of ion beam induced chemical effects in silicon with a downsized high resolution X-ray spectrometer for use with focused ion beams

Abstract

A downsized wavelength dispersive X-ray spectrometer, employing a flat crystal and a CCD detector for use with focused ion beams has been constructed and employed to study ion beam induced chemical effects in Si K X-ray spectra from silicon and its selected compounds. By using ADP, PET and LiF(110) diffraction crystals, the spectrometer can measure X-rays in the energy range between 1.2 and 8.4 keV, with the energy resolution E/ΔE(FWHM) = 1850 on Al Kα and 1580 on Si Kα achieved with 2 MeV protons. This energy resolution enables the study of secondary effects in the K X-ray spectra of light elements, L-shell spectra of medium Z elements and M-shell spectra from heavy elements. The K X-ray spectra of silicon and selected silicon compounds were measured after excitation with 2 MeV protons and 20 MeV carbon ions focused to micrometer size. The results obtained for peak relative intensities were analyzed to study their dependence on the silicon oxidation states and effective charge on Si. The results were compared with the existing data obtained by proton, electron and photon induced ionization mechanisms, and clear differences between the ionization sources were observed. Si Kα multiple ionization satellites were studied with 20 MeV carbon ions on Si, SiO₂ and SiC. The variation of apparent average L vacancy fraction p_L^x with effective charge on Si was studied. It has been shown that, for ionization by 20 MeV carbon ions, the relative KαL² intensity is more sensitive to the chemical environment compared to p_L^x values.