A method and apparatus for oxidizing materials used in semiconductor integrated circuits, for example, for oxidizing silicon to form a dielectric gate. An ozonator is capable of producing a stream of least 70% ozone. The ozone passes into an RTP chamber through a water-cooled injector projecting into the chamber. Other gases such as hydrogen to increase oxidation rate, diluent gas such as nitrogen or O2, enter the chamber through another inlet. The chamber is maintained at a low pressure below 20 Torr and the substrate is advantageously maintained at a temperature less than 800° C. Alternatively, the oxidation may be performed in an LPCVD chamber including a pedestal heater and a showerhead gas injector in opposition to the pedestal.