As amounts of metallic impurities on a Si wafer surface have a profound effect on the performance and reliability in semiconductor devices, the ultraclean Si wafer surface, on which metal impurities are not, is strongly required in the current semiconductor fabrication processes. Therefore, the adhesion mechanism of metallic impurities to the surface has been revealed and many kinds of method to remove metallic impurities from the surface have been developed by a lot of study. In particular, it was well-known that noble metals, such as Cu, could adhere to the surface by taking electrons from the surface to form direct chemical bonds with Si and not remove from the surface easily using some kinds of chemical solutions, because noble metals have a lower electronegativity than Si. On the contrary, it was reported that the bulk Cu was etched by an electrochemical machining using OH ions in ultrapure water. We supposed that even Cu contaminants on the Si wafer surface were removed by OH ions in ultrapure water, of which the concentration was 10-7mol/L (at 298K, 1atm), taking into account the previous report. In this study, we have developed the cleaning system to remove Cu contaminants from Si wafer surface, with which OH ions in ultrapure water were in direct with the contaminants using high-speed shear flow of ultrapure water along the substrate surface, and found that this cleaning system could clean up the contaminants from it below the level of detection limit of TRXF (total reflection X-ray fluorescence).
