Bump manufacturing method

A method of forming bumps on a silicon wafer having an active surface with a passivation layer and a plurality of bonding pads thereon, wherein the passivation layer exposes the bonding pads, the method comprising the steps of:

• forming an adhesion layer over the active surface of the wafer, wherein the adhesion layer covers both the bonding pads and the passivation layer;
• forming a barrier layer over the adhesion layer;
• forming a wettable layer over the barrier layer;
• conducting a photolithographic process to form a plurality of photoresist blocks over the wettable layer;
• conducting an etching operation to remove the wettable layer, the barrier layer and the adhesion layer outside the photoresist blocks so that only the wettable layer, the barrier layer and the adhesion layer underneath the photoresist blocks remain;
• removing the photoresist blocks;
• attaching a plurality of first solder blocks to the upper surface of the wettable layer through a bonding operation, wherein each first solder block has an upper surface and a lower surface such that the lower surface of the first solder block bonds with the wettable layer;
• planarizing the upper surface of the first solder blocks;
• attaching a second solder block to the upper surface of each first solder block through a bonding operation;
• and
• conducting a reflux operation.