A method of descumming a dielectric layer is provided. In an embodiment the dielectric layer is deposited over a substrate, and a photoresist is applied, exposed, and developed after the photoresist has been applied. Once the pattern of the photoresist is transferred to the underlying dielectric layer, a descumming process is performed, wherein the descumming process utilizes a mixture of a carbon-containing precursor, a descumming precursor, and a carrier gas. The mixture is ignited into a treatment plasma, and the treatment plasma is applied to the dielectric layer in order to descum the dielectric layer.