MOBILE SODIUM ION PASSIVATION IN HCL OXIDES

Chlorine has been incorporated into SiO2 thin films by thermal oxidation of Si in a mixture of O2 and HCI gases. Controlled amounts of mobile sodium ions were adsorbed on the SiO2 free surface and drifted to the Si-SiO2 interface to study Na+ neutralization in these HCI oxides. Passivation, defined as the neutralized fraction of total mobile Na charge, was determined by electrical measurements. Passivation was measured over a variety of oxide growth conditions (temperature = 1100°-1300'C, time = 15-120 min, and HCI partial pressure in the oxidation ambient = 0-0.1 atm) and drift conditions (Na contamination = 0.05-1 x 1013 cm-2 and temperature = 100°-250'C). We demonstrate that pasivation P was essentially independent of drift conditions, but varied linearly with nCi, the CI content of the oxide film, and with renormalized growth temperature Tox: P nCi/(Tox - t). A variation of P with growth time is also demonstrated. We suggested that the controlling process in Na+ neutralization is a simple capture process (Na+ is immobilized at neutral CI species at the Si-SiO2 interface). © 1979, The Electrochemical Society, Inc. All rights reserved.