A reliability comparison of RTO and furnace thin SiO2 layers:: effect of the oxidation temperature

Three thermal oxidation methods aimed at growing thin SiO2 films have been considered: Low temperature oxidation, O-2-diluted oxidation, and Rapid Thermal Oxidation (RTO). These procedures differ not only in their oxidation temperature but also in the thermal uniformity that is possible to achieve across the wafer. The electrical evaluation of the test capacitors show that longer times-to-breakdown are attained by the RTO samples for thicknesses down to 50 Angstrom. The observed behaviour is explained in terms of the different mechanical stress levels in the different samples due to their different oxidation temperatures according to viscoelastic relaxation considerations and is further confirmed by the analysis of their FTIR spectra. Despite their better intrinsic breakdown features, RTO oxides exhibit more defect related failures that arise from wafer stress related problems due to the spatial thermal gradients that are characteristics of RTO operation. (C) 1998 Elsevier Science B.V. All rights reserved.