Abstract: A photo mask structure used during a twice-performed photo process and methods of using the same. The photo mask structure may include first mask patterns that correspond to first photoresist patterns during a first photo process performed on a first photoresist layer and second mask patterns that correspond to second photoresist patterns during a second photo process performed on a second photoresist layer. A method of using a photo mask structure may include performing a first photo process on a first photoresist layer using first mask patterns of the photo mask structure to form first photoresist patterns on a semiconductor substrate, and performing a second photo process on a second photoresist layer using second mask patterns of the photo mask structure to form second photoresist patterns on a semiconductor substrate, wherein the second photoresist patterns are interposed between the first photoresist patterns and overlap the first photoresist patterns.