Structural Defects in p/p+ Silicon Vapor Phase Epitaxy
H. Fukuto, P. Feichtinger, M.S. Goorsky, T. Magee*, D. Oster*, and J.
*Wacker Siltronic Corporation
7200 Northwest Front Avenue
Portland, OR 97283
We investigated the origin of misfit dislocations and the state of strain relaxation in p/p+ boron-doped silicon wafers. The samples were 6 inch Czochralski grown wafers with the substrate resistivity of 4 mW × cm and the epitaxial layer resistivity of 10 W × cm. The epitaxial layers were deposited by vapor phase epitaxy at 1050-1100 ° C and the thichnesses ranged from 2.5 m m to 20 m m. We employed Lang transmission x-ray topography and double-crystal x-ray topography for defect imaging, triple-axis x-ray diffraction for quantifying strain relaxation, and Secco etch to reveal the interfacial defects for defect density measurements. The images from Lang and double-crystal x-ray topography reveal two orthogonal <110> type dislocations. The misfits are observed in a ring-shape around the wafer periphery, with the longest misfit segments observed adjacent to the wafer flat and the shorter misfit segments in the regions where both orthogonal segments overlap. There is a distribution of misfit dislocation length, suggesting more than one misfit dislocation nucleation event. The misfit dislocation length is found to increase with increasing epitaxial layer thickness. Triple-axis x-ray diffraction measurements were performed at the wafer periphery, corresponding to the regions where the misfit segments were observed from the x-ray topography images. No quantifiable strain relaxation is measured in the samples with the epitaxial layer thicknesses of 2.5, 5, and 10 m m, however, (need to redo)% relaxation is measured in the sample with the epitaxial layer thickness of 20 m m. The misfit densities at the wafer periphery are approximately 500, 600, 1500, and 2000 cm-1 for the epitaxial layer thicknesses of 2.5, 5, 10, and 20 m m, respectively. The results from the x-ray topographs and Secco etch show higher misfit densities near the wafer periphery. Triple-axis x-ray diffraction measurements show more diffuse scattering near the wafer periphery, suggesting that there is more crystal damage in the region. All results suggest that a potential misfit nucleation source is the crystalline damage at the wafer periphery.