| 摘要 |
Super clean air having therein chemical components-such as hydrocarbons, organic halogens, acidic gases, basic gases, aldehydes, nitrogen oxides, and H2O (that is, all components other than oxygen, nitrogen, and noble gases-the types of chemical components differ depending on the source of the air)-in concentrations no more than 1 ppb and a dew point lower than -40° C., is obtained from the atmosphere by low-temperature adsorption treatment in stages at temperatures ranging from -40° C. to -180° C. Material air collected from the atmosphere is pretreated in a room-temperature adsorption step to remove moisture and carbon dioxide. The pretreated air is then low-temperature adsorption treated by absorbents in a plurality of steps to adsorb the gaseous chemical components, the treatment temperature being lower in each succeeding step. Treatment at -40° C. may remove, for example, HF, SO2, and/or NH3. Treatment at -100° C. may remove, for example, SF6, C2F6, H2S, and/or N2O. Treatment at -150° C. may remove, for example, CF4, NO, CH4, and/or CO. The last treatment step produces super clean air suitable for use in processing semiconductor wafers.
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