High-concentration ozone generator for oxidation of silicon operating at atmospheric pressure

A high-concentration ozone generator operating at atmospheric pressure was developed to produce ozone for use in fabrication of ultrathin silicon oxide films. A technique for adsorption onto silica gel, in which ozone has adsorption priority over oxygen, was adopted to obtain concentrated ozone. An ozone-oxygen mixture gas generated by a commercial ozonizer is fed in turn to three parallel adsorption columns that are kept at -60°C. After the adsorption process, the ozone-enriched gas is desorbed by a slow warming of the columns from -60 to 0°C and is stored in a storage vessel. Finally, the condensed ozone, at concentrations up to 30 vol % can be supplied continuously to a silicon oxidation chamber at atmospheric pressure and a constant flow rate. Moreover, highly concentrated ozone above 70 vol % can be produced in a batch process by using an additional purification procedure prior to the desorption. We confirmed that even with 25 vol % ozone gas, SiO₂ film as thick as 6.3 nm grew on a Si substrate at 600°C and 15 Torr in a 30 min exposure, while under the same experimental conditions only a 3.1 nm thick SiO₂ film could be formed on the same substrate with pure oxygen.