Method of fabricating a wafer structure having a pad and a first protection layer and a second protection layer

A method of fabricating a wafer structure, comprising:

• providing a wafer having a pad and a first protection layer covering the wafer, the first protection layer having a first opening that exposes part of the pad;
• forming a second protection layer on the first protection layer, the second protection layer having a second opening that exposes part of the pad and the first protection layer, wherein the second opening is larger than the first opening, and the edges of the first opening and the second opening construct a step structure;
• forming an adhesion layer on the pad, the step structure and the second protection layer;
• forming a photo-resist layer on the adhesion layer, wherein the photo-resist layer has a third opening located over the pad, and the third opening exposes part of the adhesion layer;
• electroplating a barrier layer onto the adhesion layer by using an electroplating solution, wherein the barrier layer completely covers the exposed part of the adhesion layer, and the barrier layer and the third opening substantially have a same width;
• forming a wetting layer on the barrier layer;
• removing the photo-resist layer;
• removing part of the adhesion layer exposed outside the barrier layer;
• and
• printing a solder layer on the wetting layer.