Correlating Template Properties with the Quality of Epitaxially Grown Silicon Wafers
Epitaxially grown silicon wafers (EpiWafers) are a promising alternative to conventional wafers. High lifetimes are already reported for EpiWafers but still defects limit their quality. The properties of the reorganized porous silicon template affect the crystal defects in final EpiWafers. Therefore, the influence of reorganization temperature on template properties has been investigated. Atomic force microscopy (AFM) measurements reveal an increase of surface waviness of reorganized porous silicon layers with an increasing process temperature. A reduced distortion of the crystal lattice of the porous layers is measured for the higher temperature using high resolution X-ray diffraction (HRXRD). Though both properties have the potential for reducing the quality of subsequently grown epitaxial layers, measured defect densities and local minority charge carrier lifetimes suggest that there are other causes which are quality limiting. Thermal stress in combination with the mechanical weakness of the porous layers is identified as one decisive factor. Impurities in form of residual native oxide on pore walls are suspected to increase crystal defect formation as well.