Investigation of the substrate/epitaxial interface of Si/Si1−xGex 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-x Ge 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 1.3 x 10 13 atoms/cm 2 is found, while a thermal removal leads to an interfacial oxygen level below 6 x 10 12 atoms/cm 2 . In both cases carbon levels of (1-2)x10 14 atoms/cm 2 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.