Thin-film semiconductor device, display apparatus, and method for manufacturing thin-film semiconductor device

A method for manufacturing a thin-film semiconductor device having a thin-film semiconductor element for driving a display device, the method comprising:

• simultaneously forming, on a substrate, a first gate line through which a control signal is applied to the thin-film semiconductor element, and a first gate electrode of the thin-film semiconductor element, the first gate electrode extending from the first gate line;
• simultaneously forming a second gate line on and along the first gate line and a second gate electrode extending from the second gate line;
• forming, on the first gate line, an area in which the second gate line is not formed;
• forming a gate insulating film on the second gate electrode;
• forming a semiconductor layer on the gate insulating film;
• forming an insulating layer in the area on the first gate line in which the second gate line is not formed;
• and
• simultaneously forming a metal line which crosses the first gate line on an area in which the insulating layer is formed, and a metal electrode of the thin-film semiconductor element on the semiconductor layer, the metal electrode extending from the metal line,
• wherein when forming the insulating layer in the area on the first gate line, the insulating layer is formed in a crossing area in which the first gate line and the metal line cross, to secure a space between the first gate line and the metal line,
• the metal line is formed on the insulating layer,
• the second gate line and the second gate electrode are thicker than the first gate line and the first gate electrode, and
• an interface between the metal line and the insulating layer is positioned above a top surface of the second gate electrode, in a cross section above the first gate line and the second gate line and in a direction in which the first gate line and the second gate line extend.