The present invention provides a method for in-situ cleaning of walls of a reaction chamber, e.g. reactive ion etching chamber, to remove contamination, e.g. copper comprising contamination from the walls. The method comprises converting the contamination, e.g. copper comprising contamination into a halide compound, e.g. copper halide compound and exposing the halide compound, e.g. copper halide compound to a photon comprising ambient, thereby initiating formation of volatile halide products, e.g. volatile copper halide products. The method furthermore comprises removing the volatile halide products, e.g. volatile copper halide products from the reaction chamber to avoid saturation of the volatile halide products, e.g. volatile copper halide products in the reaction chamber in order to avoid re-deposition of the volatile halide products, e.g. volatile copper halide products to the walls of the reaction chamber.