A method of treating a substrate includes directing first ions over a first range of angles to one or more photoresist features disposed on the substrate, the first ions effective to generate an altered layer in the one or more photoresist features, the altered surface layer encapsulating an inner portion of the one or more photoresist features, and directing second ions different from the first ions over a second range of angles to the one or more photoresist features, the second ions effective to generate gaseous species in the inner regions of the one or more photoresist features.