Chip structure and method for forming the same

A chip structure, comprising:

• a substrate;
• a first conductive line and a second conductive line over the substrate and spaced apart from each other, wherein a first lower surface of the first conductive line is substantially level with a second lower surface of the second conductive line;
• a conductive pillar over the first conductive line and the second conductive line, wherein the conductive pillar is formed in one piece, the conductive pillar has a third lower surface and a bottom protruding portion protruding from the third lower surface, the bottom protruding portion is in direct contact with the first conductive line, and a first linewidth of a first portion of the first conductive line under the conductive pillar is less than a width of the conductive pillar;
• and
• a solder bump on the conductive pillar, wherein the solder bump is in direct contact with the conductive pillar.

A method for forming a chip structure, comprising:

• forming a first conductive line over a substrate;
• forming an insulating layer over the substrate and the first conductive line, wherein the insulating layer has a through hole exposing a first portion of the first conductive line;
• forming a conductive pillar over the insulating layer and in the through hole, wherein the conductive pillar is formed in one piece, the conductive pillar has a bottom protruding portion in the through hole, the bottom protruding portion is in direct contact with the first conductive line, and a first linewidth of a second portion of the first conductive line under the conductive pillar is less than a width of the conductive pillar;
• and
• forming a solder bump on the conductive pillar, wherein the solder bump is in direct contact with the conductive pillar.