Effect of Boron Doping on High-Resolution X-Ray Diffraction Metrology

Abstract

The effect of boron (B) doping on high-resolution X-ray diffraction (HXRD) metrology has been investigated. Twelve samples of Si1–xGex films were epitaxially grown on Si (100) substrates with different thicknesses, germanium (Ge) concentrations and with/without B dopants. Secondary ion mass spectroscopy (SIMS) and HXRD were employed for measurements of B doping, Ge concentration, strain, and thickness of the layers. The SIMS results show the absence of B in two samples while the rest of the samples have B doping in the range of 8.40 × 1018–8.7 × 1020 atoms/cm3 with Ge concentration of 13.3–55.2 at.%. The HXRD measurements indicate the layers thickness of 7.07–108.13 nm along with Ge concentration of 12.82–49.09 at.%. The difference in the Ge concentration measured by SIMS and HXRD was found to deend on B doping. For the undoped samples, the difference is ~0.5 at.% and increases with B doping but with no linear proportionality. The difference in the Ge concentration was 7.11 at.% for the highly B-doped (8.7 × 1020 atoms/cm3) sample. The B doping influences the Si1–xGex structure, causing a change in the lattice parameter and producing tensile strains shifting Si1–xGex peaks towards Si (100) substrate peaks in the HXRD diffraction patterns. As a result, Vegard’s law is no longer effective and makes a high impact on the HXRD measurement. The comparison between symmetric (004) and asymmetric (+113, +224) reciprocal space mappings (RSM) showed a slight difference in Ge concentration between the undoped and lower B-doped samples. However, there is a change of 0.21 at.% observed for the highly doped Si1–xGex samples. RSM’s (+113) demonstrate the small SiGe peak broadening as B doping increases, which indicates a minor crystal distortion.