A producing method includes a sealing agent disposing process of preparing substrates one of which has thin film patterns thereon and disposing sealing agent portions on the one substrate to surround the thin film patterns, respectively, a bonding process of bonding the substrates via the sealing agent portions and forming a bonded substrate after the sealing agent disposing process, a cutting process of cutting the substrates being included in the bonded substrate and outside the sealing agent portions after the bonding process, and a grinding process of grinding collectively the substrates and the sealing agent portions of the bonded substrate along the outline after the cutting process such that overlapped portions of the substrates and the sealing agent portion are partially ground collectively and ground surfaces of the substrates and the sealing agent portion are aligned with each other.