Anodic oxidation in an ethylene glycol solution of potassium nitrate is shown to be capable of forming uniform amorphous
SiO2
layers on hydrogenated amorphous silicon (a‐Si:H) films at room temperature at a rate of 5.5 Å/V up to the maximum thickness of about 2500Å. The process is stable, reproducible, and electrically controllable. The oxidation process and the properties of the anodic oxide films are described, and a detailed comparison is made with the anodization of single‐crystal silicon. The anodization accompanies electroluminescence. The effect of illumination of the anode and the behavior of luminescence from the anode are discussed in detail in an attempt to clarify the electrical behavior of the anode during anodization. The anodic oxide of a‐Si:H displays resistivity of
1×1012 normalΩ normalcm
, breakdown strength of
9–10×106V/normalcm
and a refractive index of 1.46 (at 6328Å).
The technology of forming silicon oxide film at low temperature was developed and the application of the oxide film to electronic devices was investigated. Silicon oxide was formed by anodic oxidation of silicon at room temperature. The anodic oxide was Si‐rich in the as‐grown state.
When the anodic oxide film was annealed at 600°C in hydrogen atmosphere, followed by annealing at 450°C in the same ambient, the film became stoichiometric SiO2 and the SiO2/Si interface condition was improved because of the saturation of the unsaturated Si atoms at the interface. These mechanisms were evaluated by IR, AES, and SIMS analyses. The SiO2/Si interface was investigated by the degree of atomic dimension using TEM. As a result, it was found that the overall interface could be regarded as flat but it had local dents.
After annealing, a transition region of one or two atom layers in thickness existed at the interface. It was found that the electrical properties of the annealed anodic oxide were comparable with those of an oxide film grown thermally by the MOS C‐V measurement. The input/output characteristics of an MOSFET with a gate oxide formed by this anodic oxide indicated that the anodic oxide formed at low temperature could be used for electronic devices.
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