A method of forming an etch mask includes: providing a substrate having thereon a material layer to be etched; forming a hard mask layer consisting of a radiation-sensitive, single-layer resist material on the material layer; exposing the hard mask layer to actinic energy to change solvent solubility of exposed regions of the hard mask layer; and subjecting the hard mask layer to water treatment to remove the exposed regions of the hard mask layer, thereby forming a masking pattern consisting of unexposed regions of the hard mask layer.