Highly concentrated ͑Ͼ93 vol %͒ ozone (O 3) gas was used to oxidize silicon for obtaining high-quality SiO 2 film at low temperature. Compared to O 2 oxidation, more than 500°C lower temperature oxidation ͑i.e., from 830 to 330°C͒ has been enabled for achieving the same SiO 2 growth rate. A 6 nm SiO 2 film, for example, could be grown at 600°C within 3 min at 900 Pa O 3 atmosphere. The temperature dependence of the oxidation rate is relatively low, giving an activation energy for the parabolic rate constant of 0.32 eV. Furthermore, a 400°C grown SiO 2 film was found to have satisfactory electrical properties with a small interface trap density (5ϫ10 10 cm Ϫ2 /eV) and large breakdown field ͑14 MV/cm͒.

We have grown SiO 2 films on polycrystalline Si using excited ozone produced by ultraviolet light irradiation of ozone, and characterized their electrical properties in the metal-insulator-semiconductor capacitor configuration. SiO 2 films of ϳ8.5 nm thickness on poly-Si layers were grown in 60 min even at room temperature. The leakage current density across the SiO 2 film fitted well the Fowler-Nordheim tunnel current behavior and breakdown occurred at above 12 MV/cm, showing that the film was of device quality. The rate of Si oxidation by excited ozone was similar for both Si͑100͒ and Si͑111͒ wafers, as was the interface trap density ͑D it ͒. These results indicate that excited ozone can form a homogenous SiO 2 film on poly-silicon. We conclude that excited ozone is one of the most efficient reactive species for SiO 2 film formation on poly-Si at room temperature.

A reactive oxygen beam generation system is described for the formation of high-quality and high-precision films. This system utilizes pulsed laser evaporation of highly concentrated solidified ozone (O3). The equipment for safely generating and handling a large amount of high-purity liquid and solid O3 was also developed for this purpose. The beam is characterized by its high concentration of oxygen atoms in an excited state [O(1D)], constant flux per laser shot (4×1017 molecules cm−2 shot−1), appropriate level of kinetic energy (KE) for enhancing the surface reaction (mean KE of 0.4 eV, maximum KE of 2 eV) and small angular spread (6°). These characteristics enabled us to precisely control the SiO2 film thickness by the number of laser shots, and achieve an enhanced Si oxidation rate and new local oxidation process.

A system is described which can continuously generate/supply highly concentrated (HC) ozone gas to satisfy the future need for practical low-temperature oxidation. This system comprises four ozone vessels, each with independent temperature control. The system can supply a constant flow of HC ozone gas by allocating one of four modes of operation, i.e., accumulation/storage, vaporization (supply), evacuation, and cooling, to each of the ozone vessels so that all the modes can be simultaneously addressed. The maximum flow rate is 60 sccm with a flux stability of ±1.1%, and an ozone concentration of over 99.5 vol % can be achieved at the system outlet. The system was applied to the formation of an ultrathin SiO2 film on a 4 in. diameter silicon wafer substrate.

New processing technologies are demanded which produce hyperfine structures for electronic devices and which do not exacerbate environmental problems. We specifically examined photoresist removal technology for this study. Ozone gas of nearly 100% concentration was applied to various photoresists and ion-implanted-photoresists. Results showed that reactivity with ozone gas differs between a novolac resist, which has a benzene ring structure on a main chain, a KrF resist with this structure on a side chain, and an ArF resist which has no such structure. The activation energy of the KrF resist indicates a value close to that of the novolac resist; the value for the ArF resist was larger than these. Irrespective of the ionic species, the ion-implanted-photoresist of amount 1e16 cm -2 of the dose can be removed with 0.7 µm/min or less in the ashing of 400°C in processing temperature. Additionally, results showed that the removal speed slows in order of B, As, and P.