Oxidative cleaning method and apparatus for electron microscopes using UV excitation in an oxygen radical source

A method of cleaning a vacuum chamber, the method comprising:

• flowing an oxygen-containing gas into a irradiation chamber to expose it to vacuum ultra violet (VUV) radiation having a wavelength less than about 193 nm;
• maintaining the oxygen-containing gas at a pressure below atmospheric that fully absorbs the VUV radiation to photo-disassociate the oxygen molecules into Oxygen radicals, but does not favor the formation of Ozone;
• differentially pumping the oxygen radical containing gas from the irradiation chamber into a separate vacuum chamber at a pressure lower than the irradiation chamber and below 100 milli Torr to prevent recombination of oxygen radicals, wherein the oxygen radicals oxidize hydrocarbon contaminants and clean a surface in the vacuum chamber of the hydrocarbon contaminants, wherein VUV radiation does not reach the surface;
• and
• evacuating the oxidized hydrocarbon contaminants from the vacuum chamber.

A method for cleaning and removing hydrocarbons from a region of a vacuum chamber comprising the steps of:

• activating a vacuum pump in fluid communication with the vacuum chamber;
• flowing, using the vacuum pump, a gas mixture including a majority of molecular oxygen and molecular nitrogen gases into a separate irradiation chamber for photo disassociation of oxygen;
• irradiating the flow of the gas mixture in the irradiation chamber with ultraviolet light of at least one wavelength selected to generate oxygen radicals, the ultraviolet light containing no wavelength that disassociates or ionizes nitrogen-containing molecules from the mixture, wherein exposure of the vacuum chamber to ultraviolet light is minimized;
• maintaining the irradiation chamber at a pressure selected to promote complete absorption within the chamber of all of the ultraviolet light capable of generating oxygen radicals;
• maintaining the vacuum chamber at a pressure lower than the irradiation chamber and below 100 milli Torr to minimize the recombination of the oxygen radicals and low enough to permit operation of a charged particle beam while removing hydrocarbons;
• flowing the irradiated gas mixture through the region of the vacuum chamber to be cleaned to remove hydrocarbons oxidized by the oxygen radicals from the vacuum chamber without the presence of ultraviolet light;
• and
• exhausting the gas mixture with the oxidized hydrocarbons from the vacuum chamber using the vacuum pump.