Semiconductor device and methods of formation

A semiconductor device, comprising:

• a first source/drain region in a substrate layer of the semiconductor device;
• a second source/drain region in the substrate layer;
• a gate structure, laterally between the first source/drain region and the second source/drain region, comprising:
• a gate electrode;
• and
• a work function metal layer between the gate electrode and the substrate layer, and between the gate electrode and a dielectric layer above the substrate layer;
• and
• a gate dielectric layer between the work function metal layer and the substrate layer, and between the work function metal layer and the dielectric layer,
• wherein a first segment of the gate dielectric layer extends along a first side of the gate electrode facing the first source/drain region,
• wherein a second segment of the gate dielectric layer extends along a second side of the gate electrode facing the second source/drain region, and
• wherein a first height of the first segment of the gate dielectric layer is greater than a second height of the second segment of the gate dielectric layer.

A method, comprising:

• forming a first source/drain region and a second source/drain region of a transistor structure in a substrate layer of a semiconductor device;
• forming a dielectric layer above the first and second source/drain regions;
• forming a gate dielectric layer of the transistor structure in a recess in the dielectric layer laterally between the first and second source/drain regions,
• wherein the gate dielectric layer is formed on a first sidewall, a second sidewall, and a bottom surface of the recess;
• forming a work function metal layer of a gate structure of the transistor structure on the gate dielectric layer;
• forming a gate electrode of the gate structure on the work function metal layer;
• and
• performing an etch operation to etch a first portion of the work function metal layer on the first sidewall and a second portion of the work function metal layer on the second sidewall,
• wherein a first vertical height of the first portion of the work function metal layer and a second vertical height of the second portion of the work function metal layer are different vertical heights after the etch operation.