A photo mask includes a transparent substrate and a mask pattern. The mask pattern is disposed on the transparent substrate. The mask pattern includes a blocking portion for blocking light and a transmitting portion for transmitting the light. The transmitting portion is adjacent to the blocking portion. The blocking portion includes a first blocking layer, a photo guide layer and a second blocking layer. The first blocking layer is disposed on the transparent substrate. The first blocking layer transmits a portion of the light. The first blocking layer includes a plurality of blocking patterns including a first blocking material. The photo guide layer is disposed on the first blocking layer. The photoguide layer guides the transmitted portion of the light to a side surface of the photoguide layer. The second blocking layer reflects the transmitted portion of the light.