Patent ID: 6486054
Filing Date: 2002-11-26
Classification: H01L

Abstract:
A process for solder bump formation, comprising:on an upper surface of a semiconductor wafer, depositing, and then sputter cleaning, a seed layer; applying a layer of negative photoresist, having a first thickness, on said seed layer and then exposing said layer of photoresist through a first pattern that defines a first mold having a first inside diameter and a floor; developing said layer of photoresist in such a manner as to form said first mold while leaving a layer of unexposed photoresist, having a second thickness that is less than said first thickness, fully covering said floor; then exposing said layer of unexposed photoresist through a second pattern that defines a second mold located inside said first mold and having a second inside diameter that is less than said first inside diameter; then fully developing all photoresist, thereby forming a final mold; by means of electroplating, growing a layer of UBM and then a layer of solder inside said final mold until said final mold is filled with solder; removing all photoresist, thereby forming a solder bump having the form of a cylinder, having said first diameter, coaxially disposed above a cylinder having said second diameter; then removing all exposed UBM; and heating said wafer whereby said solder bump assumes the shape of an oblate spheroid whose long axis extends vertically upwards from said upper surface.