Characterization of carbon in heteroepitaxial Si1-x-yGexCy thin films via combined ion channeling and nuclear resonance analysis

The amount and substitutionality of carbon in Si1-x-yGexCy heteroepitaxial thin films on Si(100) with thicknesses ranging between 100 and 500 nm are characterized via combined ion channeling acid nuclear resonance analysis (NRA). To measure carbon concentrations as small as 2.5 X 10(20) atoms/cm(3) the C-12(alpha,alpha)C-12 nuclear resonance at 4.265 MeV with He-4(2+) is used since the resonance enhances the elastic cross section by a factor of 128, However, the NRA signal from carbon surface contamination is of the same order of magnitude as the signal from the carbon within the film. The two signals can be separated by increasing the angle between the normal to the sample surface and the incident beam. Bulk signal crystal cubic SiC was used for calibrating NRA combined with ion channeling. The chi(min) was found to be 4.5% along the [111] direction for both carbon and silicon, Because SiC is used, a higher energy than the carbon resonance energy can be used to resonate C inside the crystal to maximize the signal from the resonance of carbon at the surface. The carbon signal of the film cannot be separated from the surface signal in the [111] channeling direction in films that are 100 nm thick, but can be separated in thicker films. Experiments were also conducted to determine the effectiveness of surface carbon removal via wet chemical etching, The surface carbon was reduced but not eliminated. This study was complemented by depth profiling with SIMS and microstructural analysis from HRTEM and FTIR techniques.