Clean aluminum oxide formation on surface of aluminum cylinder in an ultraclean gas-sampling system

Because it is difficult to obtain enough space for a gas-analysis system in semiconductor manufacturing lines, gas purity is usually confirmed by an e x situ analysis of gas sampled inside the gas-sampling cylinders (samplers) . In order to analyze trace impurities, it ts necessary to significantly su ppress contaminants generation in samplers and to fabricate surfaces and/or materials with extremely low outgasing rates. We have produced a sampler m ade of pure aluminum (Al) carried out plasma oxidation in 3% oxygen (O-2)/a rgon (Ar) after the extrusion-lathing process. Nevertheless, the hydrogen ( H-2) concentration in nitrogen (N-2) or At sealed at 0.58 MPa in the sample r increased from below 1 to 8 ppb after 168 h. The carbon monoxide (CO) and carbon dioxide (CO2) concentration in O-2 also increased. Wet cleaning was carried out in the sampler by deionized water for 72 h at a flow rate of 2 L/min. After wet cleaning, the sampler was annealed at 423 K for 72 h in N -2 without exposure to air. We have observed that the H-2 concentration in N-2 was maintained below 1 ppb, the detection limit of the gas chromatograp h for 168 h. The CO and CO2 concentrations in O-2 were also sufficiently lo w. We have confirmed that amorphous gamma-aluminum oxide (Al2O3) film with a thickness over 0.5 mu m was formed on the inner surface of the sampler us ing cross-sectional transmission electron microscopy observation, These res ults suggest that the amorphous gamma-Al2O3 film formed by a series of trea tments mentioned above functions as a gas-barrier film with an anticatalyti c property. (C) 1999 American Vacuum Society. [S0734-2101(99)21504-7].