Negative Ion Assisted Silicon Oxidation in Downstream of Microwave Plasma

For one application of negative ions in plasma, silicon oxidation at low temperatures was studied by employing the oxygen negative ions. In the downstream region of microwave oxygen plasma, the silicon oxidation was examined under DC bias. The oxidation depth was much larger under the positive bias than under the negative. It was found that the oxidation depth became maximum at a certain distance in downstream, and this was consistent with the distance at which the probe saturation current ratio showed a local minimum, suggesting a maximum negative ion density at that point. An in-depth analysis by X-ray photoelectron spectroscopy (XPS) showed that the oxidation proceeded almost linearly with the substrate bias voltage, and this voltage dependence was also found for the Si substrate at a temperature of 200°C. The repetition of the short time application of the substrate bias was found to be effective for further oxidation.