Dry Cleaning of Si Surface Contamination by Reactive Sputter Etching

A dry cleaning method is needed at present in Si wafer processing. We investigated the removal of Na contamination from an Si surface by a reactive sputter etching method. The surface contamination was analyzed by SIMS, AES and ESCA, and the results showed that this dry cleaning technique can decrease Na contamination under low gas pressure and high RF power if a CF₄+O₂ gas mixture is used. However, a saturated Na contamination value exists because of reattachment of Na atoms sputtered from the surface of the sample, the cathode and the chamber walls. Fluorine plays an important role in removing the Na. Na atoms combine with F atoms, and are then sputtered from the surface in this cleaning method. F and C atoms are removed from the surface as CO_x and COF_x as the relative flow rate (O₂/CF₄) increases.