US Patent 9209273 Method of fabricating metal gate structure

A method for fabricating a metal gate structure includes providing a substrate on which a dielectric layer, a first trench disposed in the dielectric layer, a first metal layer filling up the first trench, a second trench disposed in the dielectric layer, a second metal layer filling up the second trench are disposed, and the width of the first trench is less than the width of the second trench; forming a mask layer to completely cover the second trench; performing a first etching process to remove portions of the first metal layer when the second trench is covered by the mask layer; and performing a second etching process to concurrently remove portions of the first metal layer and portions of the second metal layer after the first etching process.