Decomposition Characteristics of Organics Dissolved in Water under Irradiation of Diffuse Light Including Far UV Light and Excimer Light

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In line with the research on process developments of recycle use of ultrapure water for cleaning semiconductor elements, we firstly examined the possibilities of a process which could decompose a trace amount of organics dissolved in oxygen-free water by irradiating far UV (ultaviolet) 185nm light, and UV 354nm light with a low-pressure mercury lamp. We secondly tried evaluating the effect of far UV light by comparing the above-mentioned results to the one with far UV 172nm excimer light irradiation. Complete decomposition of TOC has been achieved even in the absence of oxygen with methanol as an initial reactant. Direct decomposition of organics is dominant here in comparison with the case of irradiation in the presence of oxygen where a hydroxyl radical plays an important role.We thirdly aimed at modelling kinetics of far UV degradation of TOC in the presence of oxygen, a far (vacuum) UV oxidation process, because a quantitative interpretation of decomposition characteristics in the presence of oxygen is also important from a practical point of view. As described in the present report, precise data have been accumulated with good use of a TOC analyzer and an excimer lamp respectively purchased under the grant-in-aid ; especially the sole effect of far UV light was clearly evaluated with the excimer lamp. Simulation of the decomposition hehavior observed is now being conducted with reaction-rate equations based on the stoichiometric equations governing methanol, formaldehyde, and formic acid decomposition to form hydrogen peroxide. Results will soon be reported.