Chemistry Reference
In-Depth Information
1. It cannot be charged or discharged over a wide range bending of the silicon
energy band.
2. It is located within 20 nm of the Si/oxide interface and its density is on the
order of to depending on the oxidation conditions.
3. Its density is not significantly affected by the oxide thickness or by the type
and concentration of impurities in the silicon.
4. The density is independent of doping type and concentration in the silicon in
the range from to but is a strong function of silicon crystal orienta-
tion. The ratio of the density values for silicon oriented along the (111), (110),
and (100) directions is approximately 3:2:1, which follows the variation of
the oxidation rate constants for these directions.
5. Its density is independent of band bending over the middle 0.7 eV of the silicon
energy gap, indicating that the energy levels of the surface states are located
within the forbidden gap of the oxide.
6.The density strongly depends on oxidation and annealing conditions and
regardless of the previous treatments of the oxide, the final heat treatment
determines the density. Its density decreases with heat treatment in inert gas
and increases with increasing negative field.
7. The surface state charge is due to the excess ionic silicon present in the oxide
during the oxidation, waiting to react with the oxidizing species that has
diffused across the oxide/silicon interface as illustrated in Fig. 3.27.
495
The change of potential due to the surface state charge can be calculated from
High-quality films can have a resistivity exceeding The high resistiv-
ity of the film is a consequence of the large band gap, which preclude thermally
or optically excited carriers from entering the oxide. The conduction of thin dielectric
films can be due to bulk-limited processes and electrode-limited processes. In general,
electronic conduction, space charge-limited conduction, ionic conduction, and impu-
rity conduction are bulk limited whereas Fowler-Nordheim tunneling and Schottky
emission are electrode limited.
309
The dominant source of dc conduction is that associ-
ated with the motion of impurity ions through the oxide.
