Investigation of the Substrate/Epitaxial Interface of Si/Si_1-xGe_x Layers Grown by LPCVD

Abstract
The paper reports a study of the quality of the substrate/epilayer interface. Before growing the Si or Si/Si_1-xGe_x structures by low pressure chemical vapour deposition, Si(100) substrates were cleaned by a modified RCA-cleaning and just before epitaxy different ex-situ and in-situ processes were applied to remove the oxide layer grown on the wafer substrates in the last step of the RCA-cleaning. The effect of interfacial contamination on electrical and optical properties were studied. By a wet-chemical removal of the oxide layer an interfacial oxygen level of 1.3x10₁₃ atoms/cm₂ is found, while a thermal removal leads to an interfacial oxygen level below 6x10₁₂ atoms/cm₂. In both cases carbon levels of (1-2)x10₁₄ atoms/cm₂ have been detected. By electrochemical capacitance-voltage profiling it was found that these contaminations are connected with electrically active donors. According to our investigations, electrochemical capacitance-voltage profiling is suitable to give a quick indication on the quality of the substrate/epitaxial interface. In addition, the removal of the oxide layer was investigated by high resolution electron energy loss spectroscopy on cleaned Si-surfaces.