Semiconductor structure and forming method thereof

Semiconductor structures and methods of forming the same are provided. An exemplary semiconductor structure includes a contact pad over a substrate, an under bump metallization (UBM) layer over the contact pad, a metal pillar over the UBM layer and electrically coupled to the contact pad via the UBM layer, and a solder cap over the metal pillar. The metal pillar includes copper, and the percentage of the (111) crystal orientation of the copper is 90% or more. 提供了半导体结构及其形成方法。示例性半导体结构包括位于衬底上方的接触焊盘，位于接触焊盘上方的凸块下金属化(UBM)层，位于UBM层上方并且经由UBM层电耦接至接触焊盘的金属柱，以及位于金属柱上的焊料帽。金属柱包括铜，并且铜的(111)晶向的百分比为90％或更大。