Charged particle beam exposure apparatus and method of cleaning the same

A charged particle beam exposure apparatus having an interior within which a charged particle beam is projected along an optical axis and onto a member thereby to oppose a pattern on the member, said charged particle beam exposure apparatus comprising:

• a plurality of electrodes disposed around the optical axis of the charged particle beam and within said interior of said apparatus;
• first means for introducing a gas containing oxygen as a main component into the interior of the apparatus and for holding said interior of the apparatus at a degree of vacuum between 0.1 Torr and 4 Torr;
• and
• second means for applying a selected one of a high-frequency signal, having a frequency between 100 kHz and 800 kHz, and a reference signal to each of said plurality of electrodes and thereby for generating a plasma radical state of the gas in said interior of the apparatus so that the high-frequency signal is applied to at lest one electrode and the reference signal is applied to at least one other electrode, of the plurality of electrodes, and so that a deposition present in the apparatus can be eliminated.