Chip package structure with buffer structure and method for forming the same

A method for forming a chip package structure is provided. The method includes removing a first portion of a substrate to form a first recess in the substrate. The method includes forming a buffer structure in the first recess. A first Young's modulus of the buffer structure is less than a second Young's modulus of the substrate. The method includes forming a first wiring structure over the buffer structure and the substrate. The method includes bonding a chip package to the first wiring structure. The chip package has an interposer substrate and a chip structure over the interposer substrate, and a first corner of the interposer substrate and a second corner of the chip structure overlap the buffer structure in a top view of the chip package and the buffer structure.