Abstract: A film (e.g., silicon polymer film, photoresist film) may be removed by applying a composition including a quaternary ammonium hydroxide, a sulfoxide compound, a dialkylene glycol alkyl ether, and/or water to the film. A silicon polymer film (e.g., hard mask layer) and a photoresist film, for example, may be removed by the composition using an in-situ process. Additionally, the composition may remove the silicon polymer film and the photoresist film while preventing or reducing damage to an underlying layer and the generation of particle-type etch residue.