A photoresist processing method includes treating a substrate with a sulfur-containing substance. A positive-tone photoresist is applied on and in contact with the treated substrate. The method includes selectively exposing a portion of the photoresist to actinic energy and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate. The treating with a sulfur-containing substance reduces an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating.