A method for removing impurities (e.g., atomic sulfur) from a reticle for use in photolithography is provided. In one embodiment, a reticle (or photomask) comprising a plate, a first layer over the plate, and a photoresist layer over the first layer is provided. The photoresist layer is removed with a first chemistry comprising a sulfur-containing compound. At least a portion of the first layer is removed with a second chemistry comprising a sulfur-containing etchant, thereby exposing portions of the plate. Removing the photoresist layer and/or at least a portion of the first layer leaves sulfur on at least portions of the reticle. In a cleaning step, the reticle is contacted with one or more excited species of oxygen to remove residual sulfur and other contaminants, such as carbon, sulfur and oxygen-containing species. Methods of embodiments can be used to clean, e.g., binary photomasks, attenuated phase shift masks (APSMs) and high transmission attenuated photomasks.