Metal gate structure and method of fabricating the same

A fabricating method of a gate structure, comprising:

• providing a substrate divided into a N-type transistor region and a P-type transistor region, an interlayer dielectric covering the N-type transistor region and the P-type transistor region, a first trench disposed in the interlayer dielectric within the N-type transistor region, a second trench disposed in the interlayer dielectric within the P-type transistor region, and a gate dielectric layer covering the first trench and the second trench;
• forming a P-type work function layer covering the second trench;
• performing a first removing process to remove the P-type work function layer at a upper portion of the second trench;
• after performing the first removing process, forming a N-type work function layer covering the first trench and the second trench;
• forming a metal layer on the N-type work function layer on the first trench and the second trench;
• performing a second removing process to remove part of the gate dielectric layer, part of the metal layer, part of the N-type work function layer to make a topmost surface of the gate dielectric layer, a topmost surface of the metal layer and a topmost surface of the N-type work function layer lower than the top surface of the interlayer dielectric;
• and
• performing a third removing process to remove part of the N-type work function layer to make the metal layer protrude out of the N-type work function layer, and make the metal layer in the first trench become a bullet-shaped profile under a cross-sectional view and the metal layer in the second trench become a mushroom-shaped profile under a cross-sectional view.