The disclosure relates to fabrication of to a metal pillar. An exemplary method of fabricating a semiconductor device comprises the steps of providing a substrate having a contact pad; forming a passivation layer extending over the substrate having an opening over the contact pad; forming a metal pillar over the contact pad and a portion of the passivation layer; forming a solder layer over the metal pillar; and causing sidewalls of the metal pillar to react with an organic compound to form a self-assembled monolayer or self-assembled multi-layers of the organic compound on the sidewalls of the metal pillar.