X-ray diffraction characterization of multilayer semiconductor structures*

The analysis of double-crystal x-ray rocking curves of single-crystal layered structures can give valuable information on layer strains, displacement of atoms from normal lattice sites (which reduces the structure factor), crystallographic misorientations, and crystal defects. Both strains and misorientations cause shifts in the Bragg angle. These two effects are readily separated using two or more rocking curves with appropriate hkl reflections. The thickness of a layer and its structure factor affect the integrated intensity of a shifted Bragg peak while the width of the peak is affected by the thickness of the layer and its defect content. Calculation of the x-ray rocking curve of a crystal with strain, structure factor, and damage (displaced atoms) is done using the kinematical or single-scattering theory for thin layers or the dynamical theory for thick strongly diffracting layers. The problem of uniqueness of the rocking curve calculated for a given structure is discussed. Application of the rocking curve technique to the characterization of multilayer semiconductor structures is presented. The applications include Si homoepitaxy and heteroepitaxy, metal silicide on Si, GaAs implanted with 0.3-15 MeV ions, quaternary compound laser structures, AlGaAs/GaAs and HgCdTe/CdTe superlattices, and strains in polycrystalline or noncrystalline films on a thin single crystal.