Abstract: An apparatus for chemically conditioning a surface of a planarizing substrate while a semiconductor wafer is planarized on the substrate. The conditioning apparatus has a conditioning solution dispenser that deposits a conditioning solution onto the substrate, and a conditioning solution barrier that removes the conditioning solution from the substrate to prevent the conditioning solution from contacting the wafer or diluting the planarizing solution. The conditioning solution dispenser is positioned over the planarizing substrate down-stream from the wafer with respect to the path along which the substrate travels. The conditioning solution barrier is positioned down-stream from the conditioning solution dispenser and upstream from the wafer to remove the conditioning solution from the surface of the substrate. The conditioning solution barrier accordingly cleans the surface of the substrate so that planarizing solution may be dispensed onto a surface relatively free from other fluids or particles.