Manufacturing method for semiconductor device having metal gate

A manufacturing method for a semiconductor device having a metal gate, comprising:

• providing a substrate having a first semiconductor device and a second semiconductor device formed thereon, the first semiconductor device having a first gate trench therein and the second semiconductor device having a second gate trench therein;
• forming a first work function metal layer in the first gate trench and the second gate trench;
• forming a first shielding layer on the substrate;
• performing a first removing step to remove a first portion of the first shielding layer, so that the remaining first shielding layer is located at a bottom of the second gate trench and fills up the first gate trench;
• performing a second removing step to remove a second portion of the remaining first shielding layer, so that the remaining first shielding layer is located at a bottom of the first gate trench to expose the first work function metal layer at a sidewall of the first gate trench and in the second gate trench;
• removing a portion of the first work function metal layer not covered by the remaining first shielding layer by using the remaining first shielding layer as a mask, so that the remaining first work function metal layer is only located at the bottom of the first gate trench;
• and
• removing the remaining first shielding layer.