Semiconductor device fabrication methods and structures thereof

A method comprising:

• providing first channel layers and second channel layers over a substrate;
• forming a first dipole layer wrapping around the second channel layers but not the first channel layers;
• forming an interfacial dielectric layer wrapping around the first dipole layer and the first channel layers;
• forming a high-k dielectric layer wrapping around the interfacial dielectric layer;
• forming a second dipole layer wrapping around the high-k dielectric layer over the second channel layers but not the high-k dielectric layer over the first channel layers;
• performing a thermal process to drive at least some dipole elements from the second dipole layer into the high-k dielectric layer over the second channel layers;
• removing the second dipole layer;
• and
• forming a work function metal layer wrapping around the high-k dielectric layer over both the first and the second channel layers.

A semiconductor structure, comprising:

• a substrate;
• semiconductor channel layers over the substrate;
• a p-dipole material around the semiconductor channel layers;
• an interfacial dielectric layer over the p-dipole material and the semiconductor channel layers;
• an n-dipole material over the interfacial dielectric layer;
• a high-k dielectric layer over the n-dipole material and the interfacial dielectric layer;
• and
• a work function metal layer over the high-k dielectric layer and wrapping around each of the semiconductor channel layers.