SOL-GEL LOW-TEMPERATURE PREPARATION OF SILICA FILMS - RBS, TEM AND MOS C-V CHARACTERIZATION

Low-temperature preparation of oxide layers or oxide coatings is of interest in many fields, such as optical coating, or encapsulation of compound semiconductors which suffer no elevated temperature during processing. In this study silica films with thicknesses of some hundred Å have been prepared onto doped silicon wafers using the sol-gel technique. The films are deposited by dipping the substrate, under controlled conditions and at room temperature in a silica-gel solution. Polymerization, drying and densification of films are enhanced by a 500 ° C, 1 h annealing in pure oxygen. The layers have been characterized by backscattering of α particles in order to check the stoichiometry and homogeneity. No impurities are detectable at this level. Transmission electron microscopy on the edge of the film helped us in trying to determine the actual thicknesses, the density and the structure of the silica layers. MOS devices have also been fabricated on the above wafers, and capacitance-voltage measurements were performed. The studied samples evidence fixed charged in the oxide ranging between 5 X 1010 and 2 X 1011 cm-2. Few mobile charges are found. All three techniques show a high quality of the silica layer, if we consider the low annealing temperature (500 ° C) used to densify the film. © 1990.