Characterization of ion implanted silicon: correlation of optical measurements with microstructural observations

Abstract

Laser, electron and ion beam techniques were used to probe the near surface crystallography of silicon implanted with various ion species. Optical third harmonic radiation (THR) generated in reflection with short laser pulses was found to be a sensitive monitor of lattice damage. The isotropic part, or the part of the third harmonic signal which does not vary with crystalline orientation, reaches a minimum value at a critical ion dose and increases slightly at higher doses. The anisotropic part, or the part which exhibits the symmetry of the lattice, becomes negligible at the critical dose and remains so at higher doses. The critical dose depends on the mass and energy of the implanted ion. The consquences of making the measurements in air as opposed to making them in vacuum are discussed. Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and ion channeling were used to correlate the nonlinear optical response (the intensity and polarization of the generated THR) with the near surface microstructure. Samples with the critical ion dose exhibited an amorphous layer containing residual crystalline particles near the surface. As the dose increases above the critical level the residual crystallites disappear and the surface layer becomes completely amorphous. Further implantation has no effect on the nonlinear response.