Charge-transfer dipole moments at the Si–SiO2 interface

Abstract

A first-order model has been developed to calculate the magnitude of the dipole moment at the Si–SiO2 interface resulting from partial charge transfer that takes place upon the formation of interface bonds. The charge transfer occurs because of the difference in electronegativity between the two species across the interface, namely silicon atoms and SiO2 molecules. This approach is similar to that introduced to describe the modification of band lineup at the Si–SiO2 interface by means of an intralayer of H or Cs. The charge-transfer estimation uses the principle of electronegativity equalization, and results obtained for (100) and (111) silicon substrates indicate that the magnitude of the interface dipole is orientation dependent. Dipole moments at the Si–SiO2 and gate–SiO2 interfaces should be included in the definition of the flatband voltage VFB of metal-oxide-semiconductor structures. The metal-semiconductor work function difference φms determined from capacitance-voltage measurements on (100) and (111) silicon oxidized in dry oxygen and metallized with Al agree well in magnitude and sign with the predictions of this model. Other types of interface dipoles and their processing dependence will be examined.