Strain and SiC crystallite formation in carbon implanted silicon

SiC formation by implantation of C ions into silicon is not a single-step process [1]. The implantation results in an elastic distortion of the Si host lattice and in a formation of crystalline SiC particles or their prestages depending on ion fluence and thermal conditions.
One part of the samples was prepared by implantation of C ions with an energy of 195 keV into Si (001) wafers at fluences varying from 5E15 ions/cm2 to 4E17 ions/cm² and temperatures between room temperature and 800°C. The other part was produced by implantation of 3.25E17 /cm² of C (45 keV) ions at 500 °C and a subsequent annealing at 1200°C for 2 h. The whole fluence was applied as well in one step as in three steps, respectively. The maximum of the carbon content lies in a depth of 130 nm for ions with an energy of 45 keV and at 570 nm for ions with an energy of 195 keV, respectively.
The growth of the SiC particles and the strain in the Si matrix and its relaxation were studied with different x-ray scattering techniques: high-resolution diffraction, wide-angle diffraction for the phase identification [2], grazing incidence diffraction for particle size determination, reciprocal space mapping (RSM) and texture studies for revealing the orientation alignment of the particles to the matrix. Mostly the use of Synchrotron radiation was necessary in order to have a clearly detectable signal in spite of the very small volume part of SiC. Furthermore, high resolution diffraction for strain studies requires radiation with a low divergence. The material research goniometer of the Rossendorf Beamline (ROBL) at the ESRF Grenoble [3] enables such studies which allow to follow the early stage of phase formation.
From the measurements it can be stated:
1. At the lowest ion fluence a significant Si lattice expansion on the order of 1E-3 is observed. However, no crystalline SiC precipitates were found.
2. Intermediate ion fluences and temperatures generate very small SiC particles (pre-stages) with enhanced lattice spacings in relation to the value of 3C-SiC. Due to the SiC particle formation the strain in the Si lattice is reduced.
3. Finally, for the highest fluences and temperatures crystalline 3C-SiC particles are found. The SiC lattice itself is only negligible strained if the phase formation occurs during a high-temperature implantation process.
4. As it was revealed by RSM and texture studies the SiC crystallites are aligned to the Si host lattice in such a way that the cubic crystallographic axes of matrix and particles coincide within an accuracy of 2.5° to 5°. A narrower distribution of the SiC crystallite orientation is formed by implantation at higher temperatures. Elevated temperature during implantation is supposed to be more effective in forming an aligned crystallite distribution than a subsequent annealing even at higher temperature.
[1] M. Deguchi et al., Jap. J. Appl. Phys. 31, 343 (1992)
[2] F. Eichhorn et al., J. Appl. Phys. 86, 4184 (1999)
[3] W. Matz et al., J. Synchrotron Rad. 6, 1076 (1999)