ROLE OF HYDROGEN IN SIO2-FILMS ON SILICON

This review discusses within a unified framework various phenomena occurring in thermally grown SiO2 films on silicon with hydrogen as the most important contaminant or additive. The possible sources of hydrogen are (i) H2O in the oxidizing ambient, deliberately introduced or resulting from permeation through hot furnace tubes, (ii) hydrogen in the room ambient oxide film on silicon, and (Hi) deliberate or unintentional H2 or H2O in the ambient of postoxidation heat-treatments. The “critical oxide thickness,” which separates the linear oxidation regime from the parabolic one, is a very sensitive indicator of H2O present in the oxidizing ambient. There is plenty of evidence, both direct and indirect, of hydrogen in SiO2 films. In particular, infrared spectroscopy shows that OH and SiH groups are present whose concentration and distribution depend strongly on preparation conditions. These groups can be H-bonded to an oxygen; this feature and the presence of SiH distinguishes SiO2 films from fused SiO2 which is another form of noncrystalline SiO2. The H-bonded OH groups in grown SiO2 films may be preferentially aligned along structural channels and responsible for various transport processes characterized by ~0.3 eV activation energy. Hydrogen greatly affects the properties of the Si/Si02 interface, particularly its behavior under negative bias stress and irradiation. In fact, practically all properties of Si/Si02 interface structures depend so strongly on hydrogen that its proper control and the understanding of its complicated role are probably the most important problems associated with these structures. This is particularly true for silicon-based chemical sensors whose operation is basically determined by hydrogen in the SiO2 film. Various aspects of the hydrogen in Si/SiO2 interface structures are similar to the role of hydrogen in Si3N4 and SiHx polymer films as well as in passivating films on metals. © 1979, The Electrochemical Society, Inc. All rights reserved.