Method and multi-channel devices with anti-punch-through features

A method, comprising:

• receiving a semiconductor substrate having a semiconductor surface of a first semiconductor material;
• performing a prebaking process to the semiconductor substrate with a first temperature;
• epitaxially growing an undoped semiconductor layer of the first semiconductor material on the semiconductor substrate at a second temperature, the undoped semiconductor layer having a first thickness;
• epitaxially growing a semiconductor layer stack over the undoped semiconductor layer at a third temperature less than each of the first and second temperatures, wherein the semiconductor layer stack includes first semiconductor layers and second semiconductor layers stacked vertically in an alternating configuration, each of the first semiconductor layers having a second thickness greater than the first thickness, and each of the second semiconductor layers having a third thickness greater than the first thickness;
• patterning the semiconductor substrate, and the semiconductor layer stack to form a trench, thereby defining an active region being adjacent the trench;
• filling the trench with a dielectric material layer and a solid doping source material layer containing a dopant;
• and
• driving the dopant from the solid doping source material layer to the active region at a fourth temperature greater than the third temperature.

A method, comprising:

• receiving a semiconductor substrate having a semiconductor surface of a first semiconductor material;
• performing a prebaking process to the substrate with a first temperature;
• epitaxially growing an undoped semiconductor layer of the first semiconductor material on the substrate at a second temperature, the undoped semiconductor layer having a first thickness;
• forming a diffusion blocking layer on the undoped semiconductor layer;
• epitaxially growing a semiconductor layer stack over the undoped semiconductor layer at a third temperature less than the second temperature, wherein the semiconductor layer stack includes first semiconductor layers of the first semiconductor material and second semiconductor layers of a second semiconductor material stacked vertically in an alternating configuration, each of the first semiconductor layers having a second thickness greater than the first thickness, and each of the second semiconductor layers having a third thickness greater than the first thickness, the diffusion blocking layer having a fourth thickness greater than each of the second thickness and the third thickness, and the second semiconductor material being different from the first semiconductor material in composition;
• forming a dummy gate structure over the semiconductor layer stack;
• forming a first source/drain feature and a second source/drain feature in the semiconductor layer stack;
• removing the dummy gate structure from the top and the sidewall surfaces of the semiconductor layer stack;
• removing the second semiconductor layers such that the first semiconductor layers remain and form semiconductor sheets connecting the first source/drain feature and the second source/drain feature to each other;
• and
• forming a gate structure wrapping around each of the first semiconductor layers.