Methods for chemical mechanical polishing and forming interconnect structure

A method for chemical-mechanical polishing (CMP), comprising:

• forming a first metal layer in a dielectric structure and a second metal layer covering the first metal layer;
• removing a portion of the second metal layer to expose the first metal layer;
• forming a protecting layer over the second metal layer and etching the first metal layer, wherein a top surface of the etched first metal layer is lower than a top surface of the protecting layer;
• removing the protecting layer to expose the second metal layer;
• and
• removing a portion of the first metal layer, a portion of the second metal layer and a portion of the dielectric structure, wherein a top surface of the first metal layer, a top surface of the second metal layer and a top surface of the dielectric structure form a flush surface.

A method for forming an interconnect structure, comprising:

• receiving a dielectric structure having an opening formed therein;
• forming a liner covering a bottom and sidewalls of the opening and covering a top surface of the dielectric structure;
• filling the opening with a conductive layer, wherein the conductive layer covers the liner;
• removing a portion of the conductive layer to expose the liner;
• applying a mixture to etch the liner from the top surface of the dielectric structure and form a protecting layer over the conductive layer during the etching of the liner, wherein a top surface of the etched liner is lower than a top surface of the protecting layer;
• and
• removing a portion of the conductive layer, a portion of the liner and a portion of the dielectric structure to form an interconnect structure in the dielectric structure, wherein a top surface of the conductive layer, a top surface of the liner and a top surface of the dielectric structure form a flush surface.