1. An integrated circuit design method applied to a plurality of library cells having a first library cell and a second library cell, where both the first library cell and the second library cell respectively have a plurality of metal layers, and a metal track direction of the odd metal layers of the first library cell is perpendicular to that of the odd metal layers of the second library cell, the integrated circuit design method comprising: rotating the second library cell to make the metal track direction of the odd metal layers of the rotated second library cell be parallel to that of the odd metal layers of the first library cell; and placing the first library cell and the rotated second library cell in an identical integrated circuit design.