The present invention discloses a method of manufacturing a thin film transistor, including: preparing a substrate and a mixed solution, the mixed solution having a reductant and a first metal; forming a photoresist pattern on the substrate; etching a portion of the substrate to form a groove using the photoresist pattern as a mask; depositing a second metal on the substrate, a height of the second metal being smaller than a depth of the groove; removing the photoresist pattern on the substrate and the second metal on the photoresist other than in the groove; and forming the first metal on the second metal in the groove by submerging the substrate in the mixed solution.