A bakeout procedure is effective for reducing outgassing of a vacuum chamber. But it is difficult and so long times are needed for the large and complicated chambers such as the recent fusion machines to heat up and down uniformly. So if possible, it is desired not to heat the chamber and to reach our needed outgassing level as fast as possible.
Recently, new surface cleaning method which simultaneously irradiates ultraviolet ray and ozone to be cleaned surface in room atmosphere is successively used, mainly in a semi-conductor processing. So we examined to turn on a low pressure mercury lamp which mainly emitted 184.9 and 253.6 nm in a vacuum chamber, and investigated these outgassing characteristics. Graphite liners were installed inside of the chamber.
It was found that the total pressure increased during turning on the lamp, and simultaneously, the outgassing of H2, CO, CO2, CH4, etc also incleased, while H2O and O2 were slightly reduced. Weakly bonded gas molecures on the surface were desorbed by the energy of ultra-violet ray, and particularly, in part of adsorbed H2O molecures were dessociated.
