A stacked structure includes a lower structure and an upper structure. The lower structure includes at least one lower dielectric layer and at least one lower metal layer in contact with the lower dielectric layer. The upper structure includes at least one upper dielectric layer and at least one upper metal layer in contact with the upper dielectric layer. The upper dielectric layer includes a first upper dielectric layer attached to the lower structure. The first upper dielectric layer includes a first portion and a second portion. A difference between a thickness of the first portion and a thickness of the second portion is greater than a gap between a highest point of a top surface of the first upper dielectric layer and lowest point of the top surface of the first upper dielectric layer.