Semiconductor gate-all-around device having an anti-punch-through (APT) layer including carbon

1. A semiconductor device, comprising:

a substrate;

a first well over the substrate, the first well including dopants of a first conductivity-type;

a first anti-punch-through (APT) layer at an upper section of the first well, the first APT layer including the dopants of the first conductivity-type and further including carbon;

a source feature and a drain feature adjacent the APT layer and being of a second conductivity-type opposite to the first conductivity-type;

multiple channel layers over the APT layer and connecting the source feature to the drain feature, wherein the multiple channel layers are vertically stacked one over another; and

a gate wrapping around each of the channel layers, wherein a first portion of the gate is disposed between a bottommost one of the channel layers and the APT layer,

wherein the first well is fully doped with carbon.

2. The semiconductor device of claim 1 , wherein a bottom surface of the source feature is deeper, with respect to the substrate, than an interface between the gate and the first APT layer, by about 5 nm to about 25 nm.

3. The semiconductor device of claim 2 , wherein a bottom surface of the drain feature is deeper, with respect to the substrate, than the interface between the gate and the first APT layer by about 5 nm to about 25 nm.

4. The semiconductor device of claim 3 , wherein the first APT layer is below the interface between the gate and the first APT layer by about 5 nm to about 25 nm.

5. The semiconductor device of claim 1 , further comprising:

an isolation feature over the substrate and adjacent to the upper sections of the first well and adjacent the first APT layer.

6. The semiconductor device of claim 5 , further comprising:

a second well over the substrate, the second well including dopants of the second conductivity-type; and

a second APT layer at an upper section of the second well, the second APT layer including the dopants of the second conductivity-type and further including carbon.

7. The semiconductor device of claim 6 , further comprising:

an isolation feature over the substrate and adjacent to the upper sections of the first and second wells and adjacent the first APT layer and the second APT layer.

8. The semiconductor device of claim 6 , wherein the second well is fully doped with carbon.

9. The semiconductor device of claim 1 , wherein the multiple channel layers are epitaxially grown silicon germanium.

10. The semiconductor device of claim 1 , wherein the multiple channel layers are interleaved by a plurality of inner dielectric spacers to space the gate apart from the source feature and the drain feature.

11. The semiconductor device of claim 1 , further comprising:

a top spacer disposed along a sidewall of the gate and over the channel layers; and

a gate top dielectric layer disposed on top surfaces of the top spacer and the gate.

12. The semiconductor device of claim 11 , further comprising:

a contact feature disposed over the source feature,

wherein the contact feature is electrically coupled to the source feature by way of a silicide layer.

13. A semiconductor device, comprising:

a substrate;

a first well over the substrate doped throughout with an n-type dopant and with carbon, the first well including a first anti-punch-through (APT) layer at an upper section of the first well;

a second well over the substrate doped throughout with a p-type dopant and with carbon, the second well including a second APT layer at an upper section of the second well;

a first source feature and a first drain feature over the first APT layer and including a p-type dopant;

a second source feature and a second drain feature over the second APT layer and including an n-type dopant;

a first group of multiple channel layers suspended over the first APT layer and connecting the first source feature to the first drain feature, wherein the first multiple channel layers are vertically stacked one over another;

a second group of multiple channel layers suspended over the second APT layer and connecting the second source feature to the second drain feature, wherein the second multiple channel layers are vertically stacked one over another;

a high-k metal gate wrapping around three sides of each of the first and second groups of multiple channel layers,

a plurality of inner dielectric spacers disposed between the high-k metal gate and the first and second source features and the first and second drain features; and

a top dielectric disposed over sidewalls of the high-k metal gate and over a topmost one of the channel layers of each group.

14. The semiconductor device of claim 13 , further comprising:

an isolation feature over the substrate, adjacent to and between the upper sections of the first and second well, and adjacent the first and second APT layers,

wherein portions of the first and second wells are under the isolation feature.

15. The semiconductor device of claim 13 , wherein the n-type dopant is phosphorus and the p-type dopant is boron.

16. The semiconductor device of claim 15 , wherein the first well has a dopant concentration of phosphorus and carbon in a range of about 1E16 atom/cm 3 to about 1E19 atom/cm 3 .

17. The semiconductor device of claim 16 , wherein the second well has a dopant concentration of boron and carbon in a range of about 1E16 atom/cm 3 to about 1E19 atom/cm 3 .

18. The semiconductor device of claim 13 wherein

the first source feature and the first drain feature extend into the first well a first amount; and

the second source feature and the second drain extend into the second well a second amount, different from the first amount.

19. A semiconductor device, comprising:

a substrate;

a first well over the substrate doped throughout with an n-type dopant, the first well including a first anti-punch-through (APT) layer at an upper section of the first well that is also doped with carbon, wherein there is substantially no carbon in the first well except at the first APT layer;

a second well over the substrate doped throughout with a p-type dopant, the second well including a second APT layer at an upper section of the second well that is also doped with carbon, wherein there is substantially no carbon in the second well except at the second APT layer;

a first source feature and a first drain feature over the first APT layer and including a p-type dopant;

a second source feature and a second drain feature over the second APT layer and including an n-type dopant;

a first group of multiple channel layers suspended over the first APT layer and connecting the first source feature to the first drain feature, wherein the first multiple channel layers are vertically stacked one over another;

a second group of multiple channel layers suspended over the second APT layer and connecting the second source feature to the second drain feature, wherein the second multiple channel layers are vertically stacked one over another;

a high-k metal gate wrapping around three sides of each of the first and second groups of multiple channel layers,

a plurality of inner dielectric spacers disposed between the high-k metal gate and the first and second source features and the first and second drain features; and

a top dielectric disposed over sidewalls of the high-k metal gate and over a topmost one of the channel layers of each group,

wherein the first source feature and the first drain feature extend into the first well a first amount and the second source feature and the second drain extend into the second well a second amount different from the first amount.

20. The semiconductor device of claim 19 , wherein the first amount is greater than the second amount.