Conductive pillar structure for semiconductor substrate and method of manufacture

A semiconductor die comprising:

• a substrate;
• a first passivation layer having a metal contact opening over the substrate;
• a bond pad having a first portion and a second portion, the first portion inside the metal contact opening, the second portion overlying the first passivation layer and having a first width;
• a second passivation layer overlying the first passivation layer, partially covering second portion of the bond pad and leaving a surface of the bond pad exposed;
• a buffer layer overlying the second passivaton layer and a part of the second portion of the bond pad, the buffer layer having a pillar contact opening with a second width over a part of the exposed surface of the bond pad;
• and
• a conductive pillar having a first portion and a second portion, the first portion inside the pillar contact opening of the buffer layer, the second portion above the first portion having a third width,
• wherein a ratio of the second width to the first width is between about 0.35 and about 0.65 and a second ratio of the second width to the third width is between about 0.35 and about 0.65.

A method of forming a conductive pillar structure, said method comprising:

• forming a passivation layer over the substrate, the passivation layer having a metal contact opening;
• forming a bond pad over the passivation layer, the bond pad having a first portion inside the metal contact opening and a second portion with a first width above of the first portion;
• forming a buffer layer overlying the bond pad, the buffer layer having a pillar contact opening with a second width to partially expose the second portion of the bond pad;
• and
• forming a conductive pillar in the pillar contact opening and overlying a portion of the buffer layer, wherein the conductive pillar overlying the buffer layer has a third width,
• wherein a ratio of the second width to the first width is between about 0.35 to about 0.65,
• and a second ratio of the second width to the third width is between about 0.35 and about 0. 65.