TRANSITION-METAL CLEANING USING THERMAL BEAMS

The cleaning of transition metals including copper, nickel and iron fr om silicon surfaces at ambient temperature was demonstrated using vari ous thermal beams. Sputter-deposited copper was found in two forms on silicon surfaces: uniformly dispersed copper and copper islands. At ro om temperature, a ClF3 beam removed the uniformly dispersed copper, bu t not the copper islands. Since copper-halides are not volatile at roo m temperature, the observation of uniformly dispersed copper removal s uggested the formation of a volatile silicon-copper-halogen species. T o remove the copper islands, a hot thermal dichlorosilane SiCl2H2 (DCS ) beam which pyrolytically produces SiCl2 was used as a reactive silic on source. The DCS beam alone deposited SiClx on wafer surfaces suppre ssing complete copper removal. Exposure of this surface to ClF3 remove d the SiClx deposition and copper islands from the wafer surface at ro om temperature. Beams containing DCS + Cl-2 or DCS + F-2 in which the F-2 or Cl-2 was also pyrolytically dissociated at 1000 degrees C to fo rm F and Cl atoms, were tested. The combination of DCS with Cl-2 at a beam temperature of 1000 degrees C reduced the deposition rate, but di d not remove all of the copper islands from the wafer surface. A F-2 b eam at 1000 degrees C alone did not remove the SiClx deposition as ClF 3 did; however, the mixed DCS + F-2 beam at 1000 degrees C removed cop per to below the detection limit of x-ray photoelectron spectroscopy w ithout any observable deposition. These results validated the proposed copper removal mechanism in which a volatile copper-halogen-silicon c ompound was formed. The mixed DCS + F-2 beam was also capable of remov ing other transition metals such as nickel and iron at room temperatur e. (C) 1997 American Vacuum Society. [S0734-2101(97)01506-6].