In an apparatus and method for removing a photoresist structure from a substrate, a chamber for receiving the substrate includes a showerhead for uniformly distributing a mixture of water vapor and ozone gas onto the substrate. The showerhead includes a first space having walls and configured to receive the water vapor, and a second space connected to the first space so that the water vapor is supplied to and partially condensed into liquid water on one or more walls of the first space. Ozone gas and water vapor without liquid water may be supplied to the second space to form the mixture therein. The showerhead may be heated to vaporize the liquid water on a given surface of the first space.