Semiconductor device and formation method thereof

A method of forming a semiconductor device, comprising:

• forming a first fin and a second fin in a first device region and a second device region on a substrate, respectively, each of the first fin and the second fin comprises alternately stacked first semiconductor layers and second semiconductor layers;
• removing the first semiconductor layers to form spaces each between the second semiconductor layers;
• forming a gate dielectric layer wrapping around each of the second semiconductor layers;
• filling the spaces with a dummy layer;
• removing a first portion of the dummy layer in the second device region using an etchant while leaving a second portion of the dummy layer in the first device region intact;
• forming a first p-type work function metal layer wrapping around the second semiconductor layers in the second device region;
• forming a second p-type work function metal layer on the first p-type work function metal layer;
• removing the second portion of the dummy layer;
• and
• after removing the second portion of the dummy layer, forming an n-type work function metal layer over the second p-type work function metal layer.

A method of forming a semiconductor device, comprising:

• forming a fin over a substrate, the fin comprising alternately stacking first semiconductor layers and second semiconductor layers;
• removing the first semiconductor layers to form spaces each between the second semiconductor layers;
• forming a gate dielectric layer wrapping around each of the second semiconductor layers;
• forming a first p-type work function metal layer between the adjacent second semiconductor layers;
• thinning the first p-type work function metal layer;
• forming a second p-type work function metal layer over the thinned first p-type work function metal layer;
• and
• forming an n-type work function metal layer over the second p-type work function metal layer.