Dual layer photoresist method for fabricating a mushroom bumping plating structure

A method of forming a bump structure, comprising the steps of:

• providing a structure having an exposed first conductive structure;
• the first conductive structure being a bonding pad;
• forming an under bump metal (UBM) layer over, and in electrical communication with, at least a portion of the exposed first conductive structure;
• forming a first photoresist layer over the UBM layer;
• the first photoresist layer being dry resist film (DFR);
• forming a second capping photoresist layer over the first photoresist layer;
• the first photoresist layer being unexposed;
• the second capping photoresist layer being liquid photoresist;
• patterning the first and second photoresist layers to form an opening through the first and second photoresist layers and exposing at least a portion of the UBM layer over the first conductive structure;
• wherein the second capping photoresist layer prevents excessive formation of first photoresist layer residue during processing;
• forming a second conductive structure within the opening and in electrical communication with the UBM layer;
• stripping the first and second patterned photoresist layers;
• etching a portion of the UBM layer not under the second conductive structure;
• and
• reflowing the second conductive structure to form the bump structure.

A method of forming a bump structure, comprising the steps of:

• providing a structure having a conductive structure exposed through a passivation layer;
• forming an under bump metal (UBM) layer over the passivation layer and over, and in electrical communication with, at least a portion of the exposed conductive structure;
• forming a DFR layer over the UBM layer;
• forming a spin-on liquid photoresist layer over the DFR layer;
• the DFR layer being unexposed;
• patterning the liquid photoresist layer and the DFR layer to form an opening through the liquid photoresist layer and the DFR layer and exposing at least a portion of the UBM layer over the conductive structure;
• wherein the liquid photoresist layer prevents excessive formation of DFR layer residue during processing;
• forming a mushroom shaped conductive structure within the opening and in electrical communication with the UBM layer;
• stripping the liquid photoresist layer and the DFR layer;
• etching a portion of the UBM layer not under the mushroom shaped conductive structure;
• and
• reflowing the mushroom shaped conductive structure to form a bump structure.