Transistor with low leakage currents and manufacturing method thereof

1. A transistor with low leakage currents, comprising:

a substrate;

a gate formed above a gate dielectric layer, wherein the gate dielectric layer has a first dielectric constant and has a bottom directly contacted with the substrate;

spacers having a second dielectric constant;

pad dielectric layers formed under the spacers and having a third dielectric constant, wherein a bottom of each sublayer of the spacers completely contacts with a corresponding pad dielectric layer of the pad dielectric layers, wherein the gate dielectric layer further has curved corners contacted with the pad dielectric layers, and a maximum width between two most lateral edges of the curved corners of the gate dielectric layer is not greater than a width between two most lateral edges of sidewalls of the gate dielectric layer; and

a source and a drain, wherein the source and the drain are adjacent to the spacers and installed in two opposite directions of the gate, wherein the source and the drain are formed in a first concave of the substrate and a second concave of the substrate respectively.

2. The transistor of claim 1 , wherein the gate dielectric layer is formed above a fin-like active region, the fin-like active region is formed above a surface of the substrate, the fin-like active region comprises a semiconductor material, and the pad dielectric layers are formed between the spacers and the fin-like active region.

3. The transistor of claim 2 , wherein the source and the drain are coupled to the fin-like active region, and top surfaces of the source and the drain are higher than a top surface of the fin-like active region.

4. The transistor of claim 3 , wherein a bottom of at least one concave of the first concave and the second concave is filled with an isolator, and an isolator-substrate junction exists between the isolator and the substrate.

5. The transistor of claim 3 , further comprising:

a first contact formed above the source, wherein a first distance exists between the first contact and a corresponding spacer of the spacers; and

a second contact formed above the drain, wherein a second distance exists between the second contact and another corresponding spacer of the spacers, and the second distance is larger than the first distance;

wherein top surfaces of the first contact and the second contact are higher 5 nm to 400 nm than the top surface of the fin-like active region.

6. The transistor of claim 3 , wherein at least one of the source and the drain has a controllable doping concentration distribution, and a distribution direction of the controllable doping concentration distribution is vertical or horizontal.

7. The transistor of claim 6 , wherein the controllable doping concentration distribution comprises a first doping concentration and a second doping concentration, the first doping concentration corresponds to a first region of the at least one and the second doping concentration corresponds to a second region of the at least one, the second doping concentration is between 10 17 atom/cm 3 to 10 21 atom/cm 3 and the first doping concentration is two times or more times higher than the second doping concentration, and a first resistivity of the first region is lower than a second resistivity of the second region.

8. The transistor of claim 2 , wherein the gate dielectric layer is formed between the gate and the fin-like active region, and further between the gate and the spacers.

9. The transistor of claim 2 , wherein the gate dielectric layer is formed between the gate and the fin-like active region, and further between the gate and the spacers, wherein at least one of the pad dielectric layers has multiple thicknesses.

10. The transistor of claim 1 , wherein the fin-like active region is a channel of the transistor.

11. The transistor of claim 1 , wherein the gate has sidewalls directly coupled to one or more of the spacers, and the gate dielectric layer has a rounded shape at edge sides between the gate and the spacers, wherein in an outer curvature radius of the rounded shape is greater than a thickness of the gate dielectric layer.

12. The transistor of claim 1 , wherein the first dielectric constant is greater than the second dielectric constant, and the second dielectric constant is greater than the third dielectric constant, wherein the third dielectric constant is between 1 and 4.

13. The transistor of claim 1 , wherein a thickness of each pad dielectric layer is less than a thickness of each spacer of the spacers.

14. The transistor of claim 1 , wherein the gate is comprised of a p+ or n+ doped polysilicon containing material or a metal containing material.

15. The transistor of claim 1 , wherein a thickness of at least one spacer of the spacers is controllable, a dimension of the source is controllable, and a dimension of the drain is controllable, wherein the dimension of the source is different from the dimension of the drain.

16. The transistor of claim 1 , wherein a thickness of each pad dielectric layer of the pad dielectric layers is between 1 nm to 15 nm.

17. A transistor with low leakage currents, comprising:

a substrate;

a gate formed above a gate dielectric layer;

a spacer, wherein the spacer comprises at least two sublayers;

a pad dielectric layer formed under the spacer, wherein a bottom of each sublayer of the spacer completely contacts with the pad dielectric layer; and

a source region or a drain region, wherein the source region or the drain region is adjacent to the spacer;

wherein the gate dielectric layer has a bottom directly contacted with the substrate and has a curved corner contacted with the pad dielectric layer, and a maximum width between two most lateral edges of the curved corners of the gate dielectric layer is not greater than a width between two most lateral edges of sidewalls of the gate dielectric layer.