The present invention provides a method to prevent an ITO from opening. A dummy material layer with tapered edges is formed on a substrate. A first insulating layer is formed on the dummy material layer. Then a metal layer is formed on the first insulating layer, wherein one edge of the metal layer corresponds to any part of one of the tapered edges of the dummy material layer and the other tapered edge is situated away from the metal layer. After a second insulating layer is formed on the metal layer, an ITO layer is formed thereon without opening.