Highly concentrated ozone gas supplied at an atmospheric pressure condition as a new oxidizing reagent for the formation of SiO₂ thin film on Si

We have investigated the characteristics of silicon oxidation by concentrated ozone gas through the comparison of the oxidation by oxygen molecules. A sophisticated high-concentration ozone generator, which exploits the ozone/oxygen gas separation technique with silica gel, has been developed for the study. The generator can continuously supply ozone-oxygen mixtures with ozone concentrations up to 30 at.% at one atmospheric pressure. Ozone gas with a concentration of 25 at.% from the generator formed SiO₂ films as thick as 2 nm and 6 nm on Si for a 30 min. exposure at 200°C and 600°C, respectively. On the other hand, oxygen gas by itself could form SiO₂ films with only 1 nm and 3 nm thickness, respectively, at the same conditions. Moreover, in the oxide film formation at 600°C, the oxide film growth by ozone was proceeded with an oxidation time in excess of 240 min., while it saturated within very short time in the oxidation by oxygen. These phenomena verify the strong oxidation power of ozone. In addition, we confirmed that the growth rate of the silicon oxide with ozone dramatically changed when the substrate temperature was over 500°C, and this suggested the change of oxidation mechanism at this point. However, such a characteristic was not found in oxidation with oxygen.