Semiconductor devices with varying threshold voltage and fabrication methods thereof

A method for fabricating a semiconductor device, the method comprising:

• providing a structure with at least one region and including a dielectric layer disposed over a substrate. wherein the at least one region is present in an opening located in an interlaver dielectric material that is disposed directly on the substrate;
• forming a multilayer stack structure comprising a threshold-voltage adjusting layer over the dielectric layer, the multilayer stack structure comprising a first threshold-voltage adjusting layer in a first region of the at least one region, and a second threshold-voltage adjusting layer in a second region of the at least one region;
• and
• annealing the structure to define a varying threshold voltage of the at least one region, the annealing facilitating diffusion of at least one threshold-voltage adjusting species from the first threshold-voltage adjusting layer and the second threshold-voltage adjusting layer into the dielectric layer, wherein a threshold voltage of the first region is independent of the threshold voltage of the second region.