Transport Processes in the Thermal Growth of Metal and Semiconductor Oxide Films

Abstract

The transport problems involved in the thermal growth of thick oxide films are reexamined on the basis of a semiconductor model of the oxide film, in which the electron and hole concentrations are assumed to be in local thermodynamic equilibrium. The coupled transports of ions and of electrons or holes required in the Wagner electrochemical model of film growth are related separately to the electrostatic and Fermi potential gradients in the oxide film. The electrostatic potential difference across the oxide film is shown to be fixed by the free energy of formation of the oxide and by the transport coefficients of the several migrating species. The effect of externally applied fields on the thermal growth process is discussed. Anomalies pointed out by Raleigh are shown not to be inconsistent with the electrochemical model of film growth. The question of local electroneutrality in the film relative to the parabolic growth law is also examined.