Superjunction structure, superjunction MOS transistor and manufacturing method thereof

1. A superjunction structure, comprising a first-type epitaxial layer and a plurality of second-type pillars formed therein, a part of the first-type epitaxial layer between each two adjacent second-type pillars serving as a first-type pillar, so as to form alternately arranged first-type pillars and second-type pillars, wherein:

each second-type pillar consists of at least two sections in a vertical direction, a second section from the top down having a groove formed in its top, the groove having a profile wider at the top and narrower at the bottom, a first section from the top down being formed in the groove and also having a profile wider at the top and narrower at the bottom;

each section of the second-type pillar includes a second type impurity, doping concentrations of the second type impurity in the respective sections decreasing from the top down;

each first-type pillar includes first-type impurities distributed in the vertical direction, a doping concentration of the first-type impurities in a lower portion of the first-type pillar being greater than or equal to a doping concentration of the first-type impurities in an upper portion of the first-type pillar;

in a bottom of the first-type epitaxial layer, a total quantity of the second-type impurity in the second-type pillars is less than a total quantity of the first-type impurities in the first-type pillars;

in a top of the first-type epitaxial layer, a total quantity of the second-type impurity in the second-type pillars is greater than a total quantity of the first-type impurities in the first-type pillars,

further wherein, the first-type is N-type and the second-type is P-type, or the first-type is P-type and the second-type is N-type.

2. The superjunction structure according to claim 1 , wherein:

in each second-type pillar, the first section from the top down forms an additional structure of the second-type pillar, and remaining sections of the second-type pillar form a main body of the second-type pillar;

a distance between a bottom of the main body and a bottom of the additional structure is from 25 μm to 30 μm, and a height of the additional structure is from 2 μm to 8 μm.

3. The superjunction structure according to claim 2 , wherein in each second-type pillar, a doping concentration of the second type impurity in the main body is lower than or equal to an even doping concentration of the second-type pillar, while a doping concentration of the second type impurity in the additional structure is greater than the even doping concentration of the second-type pillar,

further wherein the even doping concentration of the second-type pillar is defined as a doping concentration of the second-type pillar measured when the second-type pillar is evenly doped with the second-type impurity and a total quantity of the second-type impurity in the second-type pillar is equal to a total quantity of the first-type impurities in a first-type pillar.

4. The superjunction structure according to claim 3 , wherein the doping concentration of the second type impurity in the main body is 0.5˜1 time of the even doping concentration of the second-type pillar, and the doping concentration of the second type impurity in the additional structure is 3˜10 times of the even doping concentration of the second-type pillar.

5. The superjunction structure according to claim 2 , wherein in each second-type pillar, a doping concentration of the second type impurity in the main body is greater than an even doping concentration of the second-type pillar but lower than a maximum doping concentration within the first-type pillar, while a doping concentration of the second type impurity in the additional structure is greater than the even doping concentration of the second-type pillar,

further wherein the even doping concentration of the second-type pillar is defined as a doping concentration of the second-type pillar measured when the second-type pillar is evenly doped with the second-type impurity and a total quantity of the second-type impurity in the second-type pillar is equal to a total quantity of the first-type impurities in a first-type pillar.

6. A method of manufacturing the superjunction structure according to claim 1 , comprising:

providing a first-type epitaxial layer and forming a plurality of trenches in the first-type epitaxial layer by etch, wherein a doping concentration in a lower portion of the first-type epitaxial layer is greater than or equal to a doping concentration in an upper portion of the first-type epitaxial layer;

filling the trenches with a second-type silicon by conducting at least two filing steps from the bottom up, each latter filing step adopting a greater doping concentration of the second-type silicon than its former filing step, wherein the second-type silicon filled by the second last filing step in each trench has a groove formed in its top, the groove having a profile wider at the top and narrower at the bottom, the second-type silicon filled by the last filing step in each trench being formed in the groove; and

removing the second-type silicon above a surface of the first-type epitaxial layer.

7. A superjunction MOS transistor, comprising:

a first-type heavily doped substrate;

a first-type epitaxial layer formed on the first-type heavily doped substrate; and

a plurality of second-type pillars formed in the first-type epitaxial layer, wherein:

a part of the first-type epitaxial layer between each two adjacent second-type pillars serves as a first-type pillar, so as to form alternately arranged first-type pillars and second-type pillars;

each second-type pillar consists of at least two sections in a vertical direction, a second section from the top down having a groove formed in its top, the groove having a profile wider at the top and narrower at the bottom, a first section from the top down being formed in the groove and also having a profile wider at the top and narrower at the bottom;

each section of the second-type pillar includes a second type impurity, doping concentrations of the second type impurity in the respective sections decreasing from the top down;

each first-type pillar includes first-type impurities distributed in the vertical direction, a doping concentration of the first-type impurities in a lower portion of the first-type pillar being greater than or equal to a doping concentration of the first-type impurities in an upper portion of the first-type pillar,

further wherein, the first-type is N-type and the second-type is P-type, or the first-type is P-type and the second-type is N-type.

8. The superjunction MOS transistor according to claim 7 , wherein in each second-type pillar, the first section from the top down forms an additional structure of the second-type pillar, and remaining sections of the second-type pillar form a main body of the second-type pillar; a distance between a bottom of the main body and a bottom of the additional structure is from 25 μm to 30 μm; and a height of the additional structure is from 2 μm to 8 μm.

9. The superjunction MOS transistor according to claim 8 , wherein in each second-type pillar, a doping concentration of the second type impurity in the main body is lower than or equal to an even doping concentration of the second-type pillar, while a doping concentration of the second type impurity in the additional structure is greater than the even doping concentration of the second-type pillar,

further wherein the even doping concentration of the second-type pillar is defined as a doping concentration of the second-type pillar measured when the second-type pillar is evenly doped with the second-type impurity and a total quantity of the second-type impurity in the second-type pillar is equal to a total quantity of the first-type impurities in a first-type pillar.

10. The superjunction MOS transistor according to claim 9 , wherein the doping concentration of the second type impurity in the main body is 0.5˜1 time of the even doping concentration of the second-type pillar, and the doping concentration of the second type impurity in the additional structure is 3˜10 times of the even doping concentration of the second-type pillar.

11. The superjunction MOS transistor according to claim 8 , wherein in each second-type pillar, a doping concentration of the second type impurity in the main body is greater than an even doping concentration of the second-type pillar but lower than a maximum doping concentration within the first-type pillar, while a doping concentration of the second type impurity in the additional structure is greater than the even doping concentration of the second-type pillar,

further wherein the even doping concentration of the second-type pillar is defined as a doping concentration of the second-type pillar measured when the second-type pillar is evenly doped with the second-type impurity and a total quantity of the second-type impurity in the second-type pillar is equal to a total quantity of the first-type impurities in a first-type pillar.

12. The superjunction MOS transistor according to claim 7 , further comprising:

gate oxide layers of bowl-shapes, each being in contact with a top of a first-type pillar;

polysilicon gates, each being surrounded by a gate oxide layer;

second-type wells, each being in contact with a top of a second-type pillar and parts of the tops of the first-type pillars adjacent to the second-type pillar;

first-type heavily doped source regions and second-type heavily doped contact regions, formed under surfaces of the second-type wells;

a dielectric layer, formed above the gate oxide layers and the polysilicon gates;

contact hole electrodes, formed above the first-type heavily doped source regions and the second-type heavily doped contact regions;

a surface metal layer, formed on the dielectric layer and the contact hole electrodes;

a source electrode, picked up from the surface metal layer;

gate electrodes, picked up from the polysilicon gates;

a backside metal layer, formed on a backside of the first-type heavily doped substrate; and

a drain electrode, picked up from the backside metal layer.