An apparatus for processing a substrate may include a processing module including at least one process chamber for performing a desired process on a substrate and an index module transferring the substrate into the processing module from an outside. The at least one process chamber may include a housing providing a process space therein, a supporting unit disposed in the housing to support a substrate, the supporting unit including a focus ring having a plurality of rings, a gas supply unit providing a process gas into the process space, and a plasma generating unit generating a plasma from the process gas in the process space. The focus ring may include a stepped structure having a plurality of stepped portions downwardly provided toward the substrate.