A method of forming a thin film pattern includes providing a thin film on a substrate, providing a photoresist on the thin film, forming a first photoresist pattern having a first packing density by exposing and developing the photoresist, etching the thin film by using the first photoresist pattern as a mask, processing the first photoresist pattern to convert the first photoresist pattern into a second photoresist pattern having a second packing density, which is lower than the first packing density, and stripping the second photoresist pattern by spraying steam onto the second photoresist pattern.