Theoretical and experimental studies for nano-oxidation of silicon wafer by ac atomic force microscopy

In the present study, all the oxidational experiments were carried out by using the function of the electrochemical chemical atomic force microscopy. The theory for the growth rate of the oxide film thickness is derived to be the combined effect of the alternating current (ac) voltage applied to the system and the charges entrapped in the oxide film formed on silicon wafer. Part of the space charges that accumulated in the oxide film can be removed by the negative part of the ac voltage. The residual proportion of the space charges was first determined by the force-displacement curves obtained from the experiments of the kelvin force microscopy. Then, the formula for the growth rate of the oxide film thickness was slightly modified by weighting this residual proportion at the term related to the space charges. The comparisons between the theoretical and experimental results in the oxide height as a function of different controlling factors were made. The behavior exhibited in the experimental results of the oxide height due to the change in the oxidation time is quite consistent with that predicted by the present model if the applied voltage is not high enough to oxidize the probe. The height of the oxide film was generally increased by elevating the positive electrical voltage. The increase in the modulation number (or the applied voltage frequency) was within a fixed time period of the oxide height.