Semiconductor device and method for fabricating the same including re-growth process to form non-uniform gate dielectric layer

A method for fabricating a semiconductor device having a gate structure with a non-uniform gate dielectric layer, the method comprising:

• forming the gate structure over a substrate, wherein the gate structure including a dielectric layer and a columnar crystal grain layer is stacked over the substrate;
• adding a first chemical species only on a first side of the gate structure;
• performing a re-growth process on the dielectric layer to form the non-uniform gate dielectric layer;
• and
• forming a source region and a drain region in the substrate on both sides of the gate structure, after the re-growth process,
• wherein a first side of the gate dielectric layer is thicker than a second side of the gate dielectric layer, and
• wherein the source region and the drain region are formed to laterally extend to overlap with the first side and the second side of the gate dielectric layer, respectively.