A method includes forming a buffer lower metal line over a semiconductor substrate for absorbing an external impact, forming a pre-metal-dielectric layer which covers the buffer lower metal line, the pre-metal-dielectric layer having a via hole formed therein to expose a portion of the buffer lower metal line, forming a seed layer over a surface of the pre-metal-dielectric layer having the via hole formed therein, forming polyimide which exposes the via hole and the seed layer formed over the pre-metal-dielectric layer in the vicinity of the via hole, growing an upper metal line over the exposed seed layer, subjecting the semiconductor substrate having the upper metal line formed thereon to a thermal process, removing the polyimide by dry etching, and bonding a bonding portion onto the upper metal line.