Method for manufacturing semiconductor structure and planarization process thereof

A method for manufacturing a semiconductor structure, comprising steps of:

• providing a substrate having a first surface;
• forming at least one trench on the first surface of the substrate, wherein a bottom surface and a plurality of side walls of the substrate are configured along an outer periphery of the at least one trench;
• performing a first planarization process comprising annealing the substrate with the at least one trench thereon in an annealing ambient comprising a gas selected from one of argon and hydrogen to flatten at least one of the bottom surface and the side walls of the at least one trench;
• conformally disposing a composite-material layer to cover the first surface of the substrate, the bottom surface and the side walls of the at least one trench;
• disposing a polysilicon material layer in the at least one trench, wherein the polysilicon material layer covers the composite-material layer on the bottom surface and the side walls;
• removing the composite-material layer on the first surface;
• forming a multilayer metal interconnection structure on the first surface and the polysilicon material layer, wherein the multilayer metal interconnection structure comprises a micro-electromechanical system (MEMS) frame structure and a plurality of through holes;
• removing the polysilicon material layer and the composite-material layer in the at least one trench;
• and
• performing a second planarization process, in which a plasma treatment is used to process the at least one trench to flatten the bottom surface and the side walls thereof, wherein the plasma treatment comprises a plasma comprising inert gas and hydrogen.