A method includes forming a photoresist layer over a substrate, where the photoresist layer includes a polymer blended with a photo-acid generator (PAG), exposing the photoresist layer to a radiation source, and developing the photoresist layer, resulting in a patterned photoresist layer. The PAG is bonded to one or more polarity-enhancing group (PEG), which is configured to increase a dipole moment of the PAG. The exposing may separate the PAG into a cation and an anion, such that a PEG bonded to the cation and a PEG bonded to the anion each increases a polarity of the cation and the anion, respectively.