Semiconductor structure comprising up-narrow and down-wide openings and forming method thereof

A method of forming a semiconductor structure, comprising:

• providing a semiconductor chip, a plurality of protruded metal pillars and a solder bump on a top surface of each of the plurality of protruded metal pillars being formed on the semiconductor chip;
• providing a substrate, a plurality of metal pads being formed on a surface of the substrate;
• forming, on the substrate, a first covering film covering the plurality of metal pads and the surface of the substrate, a plurality of up-narrow and down-wide openings being formed in the first covering film, and a bottom of each of the plurality of up-narrow and down-wide openings correspondingly exposing a surface of the plurality of metal pads;
• and
• flipping the semiconductor chip onto the substrate, such that the solder bump on each of the plurality of protruded metal pillars is correspondingly located in the plurality of up-narrow and down-wide openings through the first covering film, and the solder bump fills a corresponding one of the plurality of up-narrow and down-wide openings inside with an up-narrow and down-wide shape.