Non uniformities of silicon oxide films grown in peroxide mixtures

Abstract

The growth kinetics of silicon chemical oxides in H 2O 2-containing solutions at various pH values and temperatures was studied by electrochemical impedance spectroscopy (EIS), ellipsometry and X-ray photoelectron spectroscopy (XPS). Infrared (IR) spectroscopy was also used to investigate the evolution of the surface chemistry from the initial Si–H hydrogen coverage to the subsequent oxidation states by analysing the Si–O–Si stretching vibration modes. Successive EIS diagrams obtained in SC1 solutions (NH 3 + H 2O 2 + H 2O) as a function of time constituted a series of semicircles indicating that the semiconductor/oxide/electrolyte (SOE) junction can be modelled as an RC circuit, in which the R term increased to almost 1 MΩ cm 2 after 3 h. It is generally known that, in alkaline solutions such as SC1, the oxidation rate rapidly reaches a steady regime controlled by the interfacial charge transfer reaction and the subsequent dissolution of the generated chemical oxide. Accordingly, we propose a mechanism involving a diffusion process of reactants through the oxide barrier followed by a simultaneous dissolution of the layer. Moreover, in acidic media such as SC2 (HCl + H 2O 2 + H 2O), even though the solubility is extremely low, we have extended our model based on the competition between the oxidation rate at the surface and the dissolution on the nanoscopic scale of the built-up oxide. Both EIS and IR spectroscopy of the residual Si–H x bonds lead to a non-uniformity of the surface oxide growth proceeding from island nuclei. In addition, thickness measurements by ellipsometry together with the observed gradual change in the IR spectrum of the Si–O–Si vibration mode were interesting parameters revealing that the oxide growth proceeds simultaneously with an evolution of the structure leading to a more compact and insulating dielectric layer.