Semiconductor structure and manufacturing method thereof

A semiconductor structure, comprising:

• a metal layer comprising a first lateral side, a second lateral side and a middle portion between the first lateral side and the second lateral side;
• an etch-resistant layer disposed above the metal layer, the first lateral side, the middle portion and the second lateral side comprising a same material across an entire range covered by the etch-resistant layer;
• and
• a dielectric layer surrounding the metal layer and the etch-resistant layer, the dielectric layer contacting the metal layer;
• and
• a spacer surrounding a portion of the metal layer and a portion of the etch-resistant layer,
• wherein a first thickness of the middle portion is greater than a second thickness of the metal layer at the first lateral side or the second lateral side.

A method of forming a semiconductor structure, comprising:

• forming a dummy gate over a substrate, a spacer over a substrate and surrounding the dummy gate, and an interlayer dielectric layer over the dummy gate and the spacer;
• performing a planarization operation on the interlayer dielectric layer to expose the spacer;
• forming a recess over the substrate by removing the dummy gate;
• depositing a dielectric layer on a bottom of the recess;
• forming a first layer covering the dielectric layer and sidewalls of the recess, the first layer comprising a recessed surface;
• depositing a metal layer above the first layer and confined by the recessed surface;
• and
• forming a second layer from the metal layer by oxidizing at least a portion of the metal layer,
• wherein the second layer comprises a first lateral side, a second lateral side and a middle portion between the first lateral side and the second lateral side, and the middle portion has a thickness less than a thickness of at least one of the first lateral side and the second lateral side;
• and
• wherein an entirety of non-oxidized portions of the metal layer comprise a third lateral side, a fourth lateral side and a second middle portion between the third lateral side and the fourth lateral side, and the second middle portion comprises a thickness greater than a thickness of the third lateral side, and the third lateral side is thicker than the fourth lateral side.