Silicon carbide semiconductor device and method for manufacturing the same

• US 20060097268A1
• Filed: 11/08/2005
• Published: 05/11/2006
• Est. Priority Date: 11/08/2004
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Takeuchi, Yuichi, Kumar, Malhan Rajesh
• Granted Patent: US 7,582,932 B2
• Time in Patent Office: Days
• US Class Current: 257/77
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/66666 Vertical transistors H01L29/66712, H01L29/66742 take precedence
• CPC Class Codes: H01L 29/7391 Gated diode structures
• CPC Class Codes: H01L 29/7397 and a gate structure lying on a slanted or vertical surface or formed in a groove, e.g. trench gate IGBT
• CPC Class Codes: H01L 29/7828 without inversion channel, e.g. vertical ACCUFETs, normally-on vertical MISFETs
• CPC Class Codes: Y10S 438/931 Silicon carbide semiconductor

Abstract

A silicon carbide semiconductor device includes: a semiconductor substrate having a silicon carbide substrate, a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer; a trench penetrating the second and the third semiconductor layers to reach the first semiconductor layer; a channel layer on a sidewall and a bottom of the trench; an oxide film on the channel layer; a gate electrode on the oxide film; a first electrode connecting to the third semiconductor layer; and a second electrode connecting to the silicon carbide substrate. A position of a boundary between the first semiconductor layer and the second semiconductor layer is disposed lower than an utmost lowest position of the oxide film.

Claims

1. A silicon carbide semiconductor device comprising:

a semiconductor substrate including a silicon carbide substrate having a first conductive type or a second conductive type, a first semiconductor layer made of first conductive type silicon carbide and having an impurity concentration lower than that of the silicon carbide substrate, a second semiconductor layer made of second conductive type silicon carbide, and a third semiconductor layer made of the first conductive type silicon carbide, which are stacked in this order;

a trench disposed in a cell region of the semiconductor substrate and penetrating the second and the third semiconductor layers to reach the first semiconductor layer;

a channel layer having the first conductive type and disposed on a sidewall and a bottom of the trench;

an oxide film disposed on the channel layer in the trench and including a part for functioning as a gate oxide film;

a gate electrode disposed on a surface of the oxide film in the trench;

a first electrode electrically connecting to the third semiconductor layer; and

a second electrode electrically connecting to the silicon carbide substrate, wherein

a position of a boundary between the first semiconductor layer and the second semiconductor layer is disposed lower than an utmost lowest position of the oxide film in the trench.

2. The silicon carbide semiconductor device according to claim 1, wherein

an impurity concentration of a second conductive type impurity in the second semiconductor layer is gradually reduced from a height of a position of the oxide film disposed on a bottom of the trench to a boundary between the first semiconductor layer and the second semiconductor layer, and

an impurity concentration of a first conductive type impurity in the channel layer is higher than an impurity concentration of the first conductive type impurity in the first semiconductor layer.

3. The silicon carbide semiconductor device according to claim 1, further comprising:

a low resistance layer having the first conductive type and disposed under the oxide film on a bottom of the trench, wherein

a length from the utmost lowest position of the oxide film to the bottom of the trench corresponds to a sum of a film thickness of the low resistance layer and a film thickness of the channel layer.

4. The silicon carbide semiconductor device according to claim 3, wherein

an impurity concentration of a second conductive type impurity in the second semiconductor layer is gradually reduced from a height of a position corresponding to a bottom of the low resistance layer to a boundary between the first semiconductor layer and the second semiconductor layer, and

an impurity concentration of a first conductive type impurity in the channel layer is lower than an impurity concentration of the first conductive type impurity in the low resistance layer, and higher than an impurity concentration of the first conductive type impurity in first semiconductor layer.

5. The silicon carbide semiconductor device according to claim 1, wherein

a plane orientation of the sidewall of the trench is a (1-100)-surface or a (11-20)-surface, and

a thickness of a part of the channel layer disposed on the bottom of the trench is larger than that disposed on the sidewall of the trench.

6. The silicon carbide semiconductor device according to claim 5, wherein

the thickness of the part of the channel layer disposed on the bottom of the trench is once to five times larger than that formed on the sidewall of the trench.

7. The silicon carbide semiconductor device according to claim 5, wherein

a dopant concentration of a first conductive type impurity in the part of the channel layer disposed on the sidewall of the trench is five times larger than that disposed on the bottom of the trench.

8. The silicon carbide semiconductor device according to claim 1, wherein

the silicon carbide substrate has the first conductive type,

a plurality of second trenches are disposed in the silicon carbide substrate, each second trench being disposed from a backside of the silicon carbide substrate to the first semiconductor layer,

the second trenches are embedded with an impurity layer having the second conductive type, and

the second electrode contacts the silicon carbide substrate and the impurity layer.

9. The silicon carbide semiconductor device according to claim 1, wherein

the silicon carbide substrate has the second conductive type,

a plurality of second trenches are disposed in the substrate, each second trench being disposed from a backside of the silicon carbide substrate to the first semiconductor layer,

the second trenches are embedded with an impurity layer having the first conductive type, and

the second electrode contacts the silicon carbide substrate and the impurity layer.

10. A method for manufacturing a silicon carbide semiconductor device comprising the steps of:

preparing a semiconductor substrate including a silicon carbide substrate having a first conductive type or a second conductive type, a first semiconductor layer made of first conductive type silicon carbide and having an impurity concentration lower than that of the silicon carbide substrate, a second semiconductor layer made of second conductive type silicon carbide, and a third semiconductor layer made of the first conductive type silicon carbide, which are stacked in this order;

forming a trench in a cell region of the semiconductor substrate, the trench penetrating the second and the third semiconductor layers to reach the first semiconductor layer;

forming a fourth semiconductor layer having the first conductive type in the trench by an epitaxial growth method in such a manner that a part of the fourth semiconductor layer disposed on a bottom of the trench is thicker than that on a sidewall of the trench;

forming an oxide film on an inner wall of the trench by a thermal oxidation method in such a manner that the oxide film includes a part for functioning as a gate oxide film, which contacts the fourth semiconductor layer, so that the fourth semiconductor layer provides a channel layer;

forming a gate electrode on a surface of the oxide film in the trench;

forming a first electrode electrically connecting to the third semiconductor layer; and

forming a second electrode electrically connecting to the silicon carbide substrate, wherein

in the step of forming the oxide film, the thermal oxidation method is performed so that a position of a boundary between the first semiconductor layer and the second semiconductor layer is disposed lower than an utmost lowest position of the oxide film in the trench.

11. The method for manufacturing the silicon carbide semiconductor device according to claim 10, further comprising:

forming a fifth semiconductor layer on the fourth semiconductor layer on the sidewall and on the bottom of the trench, the fifth semiconductor layer having a dopant concentration of the first conductive type impurity higher than that of the fourth semiconductor layer, wherein

in the step of forming the oxide film, the thermal oxidation method is performed until a part of the fifth semiconductor layer formed on the sidewall of the trench is completely oxidized so that the oxide film is formed, and that a low resistance layer having the first conductive type is formed under the oxide film on a bottom of the trench by maintaining the fifth semiconductor layer without oxidation.

12. The method for manufacturing the silicon carbide semiconductor device according to claim 10, wherein

in the step of forming the trench, a plane orientation of the sidewall of the trench is set to be a (1-100)-surface or a (11-20)-surface.

13. The method for manufacturing the silicon carbide semiconductor device according to claim 11, wherein

in the step of forming the fourth semiconductor layer, the thickness of the part of the fourth semiconductor layer formed on the bottom of the trench is set to be once to five times larger than that formed on the sidewall of the trench.

14. The method for manufacturing the silicon carbide semiconductor device according to claim 11, wherein

in the step of forming the fourth semiconductor layer, a dopant concentration of a first conductive type impurity in the part of the fourth semiconductor layer formed on the sidewall of the trench is set to be once to five times larger than that formed on the bottom of the trench.

15. The method for manufacturing the silicon carbide semiconductor device according to claim 10, wherein

the step of preparing the semiconductor substrate, in a case where the silicon carbide substrate has the first conductive type, including the steps of:

forming a plurality of second trenches on a backside of the substrate, each second trench reaching the first semiconductor layer; and

embedding the second trenches with an impurity layer having the second conductive type.

16. The method for manufacturing the silicon carbide semiconductor device according to claim 10, wherein

the step of preparing the semiconductor substrate, in a case where the silicon carbide substrate has the second conductive type, including the steps of:

forming a plurality of second trenches on a backside of the substrate, each second trench reaching the first semiconductor layer; and

embedding the second trenches with an impurity layer having the first conductive type.