THERMAL DIFFUSION OF SODIUM IN SILICON NITRIDE SHIELDED SILICON OXIDE FILMS

The ability of silicon nitride layers deposited on silicon oxide-passivated silicon to act as contamination barriers has been measured through the use of a radioisotope, sodium-22. Transport studies at 500°C have shown that the concentration of sodium reaching the silicon oxide-silicon interface was re duced one thousandfold when a 1000Å shield of silicon nitride was present. These nitride films which may be deposited by any one of several techniques act not only as mechanical barriers against sodium penetration, but also as sodium getters. The amount of sodium retained by the silicon nitride film depends mainly on the film deposition temperature. For example, silicon ni tride films deposited at 850°C trap more sodium than those deposited at 1100°C. The presence of moisture in the ambient atmosphere during any annealing process of a silicon nitride shielded silicon oxide film will release some of the sodium trapped in the nitride layer and allow it to move to the silicon oxide-silicon interface. © 1969, The Electrochemical Society, Inc. All rights reserved.