Bump manufacturing method

A method of forming bumps over a silicon wafer having an active surface thereon, the method comprising the steps of:

• forming a first under-bump metallic layer over the active surface of the wafer;
• forming a second under-bump metallic layer over the first under-bump metallic layer;
• conducting a first photolithographic process to form a plurality of photoresist blocks over the second under-bump metallic layer;
• conducting a first etching operation to remove the second under-bump metallic layer outside the photoresist blocks so that only the second under-bumpl metallic layer underneath the photoresist blocks remains;
• removing the photoresist blocks;
• conducting a second photolithographic process to form a photoresist layer over the second under-ball layer, wherein the photoresist layer has a plurality of openings that exposes the second under-bump metallic layer;
• conducting a metal-filling operation by depositing metallic material into the openings in the photoresist layer to form solder bumps that cover the second under-bump metallic layer;
• removing the photoresist layer;
• and
• conducting a second etching operation to remove the exposed first under-bump metallic layer so that only the first under-bump metallic layer underneath the second under-bump metallic layer remains.