Method for manufacturing semiconductor device

A method, comprising:

• etching a dummy gate to form a gate trench in a dielectric structure, wherein a channel portion of a first semiconductive fin and a first isolation structure are exposed by the gate trench, and the first isolation structure is adjacent to the first semiconductive fin;
• depositing a gate dielectric layer over the channel portion of the first semiconductive fin and the first isolation structure;
• depositing a first work function layer over the gate dielectric layer, wherein the first work function layer has a first portion directly over the channel portion of the first semiconductive fin and a second portion directly over the first isolation structure;
• depositing a second work function layer over the first work function layer;
• etching the second work function layer to expose the first portion of the first work function layer, wherein the second portion of the first work function layer is covered by a remaining portion of the second work function layer after etching the second work function layer;
• and
• filling the gate trench with a gate metal after etching the second work function layer.

A method, comprising:

• etching a dummy gate to form a gate trench in a dielectric structure, wherein a channel portion of a first semiconductive fin, a channel portion of a second semiconductive fin, and an isolation structure are exposed by the gate trench, and the isolation structure is between the first semiconductive fin and the second semiconductive fin;
• depositing a gate dielectric layer over the channel portion of the first semiconductive fin, the channel portion of the second semiconductive fin, and the isolation structure;
• forming a work function structure over the gate dielectric layer, wherein the work function structure has a first portion directly over the channel portion of the first semiconductive fin, a second portion directly over the isolation structure, and a third portion directly over the channel portion of the second semiconductive fin, the first portion of the work function structure is thicker than the second portion of the work function structure, and the second portion of the work function structure is thicker than the third portion of the work function structure;
• filling the gate trench with a coating layer;
• etching the coating layer to expose the third portion of the work function structure;
• etching the third portion of the work function structure;
• and
• filling the gate trench with a gate metal after etching the third portion of the work function structure.