Properties of silicon-anodic oxide interfaces

The study of the complex capacitance C*mos of MOS capacitors has shown the important influence of the moisture on the properties of anodic oxide MOS structures. Two behaviours have been pointed out: the “dry” type and the “wet” type. The unambiguous determination of surface state parameters from the variations of C*mos as a function of frequency, temperature, and applied bias is discussed. A method of characterizing the distribution of surface states is proposed. The utilization of this method permits to explain some apparently contradictory results published in the literature, and shows that: 1. whatever the oxide (“wet” or “dry”) and silicon (n or p) types may be, the silicon-oxide interfaces are characterized by the same energy distribution of surface states, whose density is high (about 1013 eV−1 cm−2) and nearly symmetrical with respect to the middle of the gap, 2, the mobile protons contained in “wet” oxide have no influence on the distribution of surface states, 3. in order to reduce the density of surface states by thermal treatments at low temperatures (about 150 °C) the oxide must be of “wet” type.