Surface Second Harmonic Generation as a Probe of Anodic Oxidation of Si[001]

Anodic oxidation of Si(001) has been well studied by traditional electrochemical techniques. A detailed description of the process is however lacking due to insufficient knowledge of the state of the silicon surface during the course of the reaction. In the present work, we employ surface second harmonic generation (SHG) to monitor the oxidation process in situ. Our recent work has clearly shown that the variation of the SHG signal during oxidation is largely determined by the evolution of the space charge field in the silicon. This result is consistent with the experiments of previous workers that demonstrate that the nonlinear optical response of Si-SiO₂ interfaces is sensitive to the presence of electric fields in the space charge region (SCR) of silicon. By enabling us to monitor the surface potential in the Si during oxide growth, these in situ optical experiments reveal details of the oxidation mechanism that are difficult or impossible to study by using purely electrochemical methods