SILICON CARBIDE SEMICONDUCTOR ELEMENT AND METHOD FOR PRODUCING THE SAME

• US 20130140586A1
• Filed: 06/25/2012
• Published: 06/06/2013
• Est. Priority Date: 06/27/2011
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Takahashi, Kunimasa, Niwayama, Masahiko, Uchida, Masao, Kudou, Chiaki
• Granted Patent: US 8,686,439 B2
• Time in Patent Office: Days
• US Class Current: 257/77
• CPC Class Codes: H01L 29/045 by their particular orientation of crystalline planes
• CPC Class Codes: H01L 29/1033 with insulated gate, e.g. characterised by the length, the width, the geometric contour or the doping structure with channel and gate aligned in the lengthwise direction H01L29/42376; with buried channel H01L29/7838
• CPC Class Codes: H01L 29/1041 with a non-uniform doping structure in the channel region surface
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/4236 within a trench, e.g. trench gate electrode, groove gate electrode
• CPC Class Codes: H01L 29/42368 the thickness being non-uniform
• CPC Class Codes: H01L 29/66068 the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
• CPC Class Codes: H01L 29/66666 Vertical transistors H01L29/66712, H01L29/66742 take precedence
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236
• CPC Class Codes: H01L 29/7827 Vertical transistors H01L29/7802, H01L29/78642 take precedence
• CPC Class Codes: H01L 29/7828 without inversion channel, e.g. vertical ACCUFETs, normally-on vertical MISFETs

Abstract

This silicon carbide semiconductor element includes: a body region of a second conductivity type which is located on a drift layer of a first conductivity type; an impurity region of the first conductivity type which is located on the body region; a trench which runs through the body region and the impurity region to reach the drift layer; a gate insulating film which is arranged on surfaces of the trench; and a gate electrode which is arranged on the gate insulating film. The surfaces of the trench include a first side surface and a second side surface which is opposed to the first side surface. The concentration of a dopant of the second conductivity type is higher at least locally in a portion of the body region which is located beside the first side surface than in another portion of the body region which is located beside the second side surface.

Claims

1-15. -15. (canceled)

16. A silicon carbide semiconductor element comprising:

a semiconductor substrate of a first conductivity type;

a drift layer of the first conductivity type which is located on the principal surface of the semiconductor substrate;

a body region of a second conductivity type which is located on the drift layer;

an impurity region of the first conductivity type which is located on the body region;

a trench which runs through the body region and the impurity region to reach the drift layer;

a gate insulating film which is arranged on surfaces of the trench;

a gate electrode which is arranged on the gate insulating film;

a first electrode which contacts with the impurity region; and

a second electrode which is arranged on the back surface of the semiconductor substrate,

wherein the surfaces of the trench include a first side surface and a second side surface which is opposed to the first side surface,

wherein a portion of the gate insulating film which is arranged on a part of the body region that is exposed on the first side surface is thinner than another portion of the gate insulating film which is arranged on a part of the body region that is exposed on the second side surface, and

wherein the concentration of a dopant of the second conductivity type is higher at least locally in a portion of the body region which is located beside the first side surface than in another portion of the body region which is located beside the second side surface.

19. The silicon carbide semiconductor element of claim 16, wherein a body concentration adjusting region including the dopant of the second conductivity type in a higher concentration than the body region is provided at least in some depth range of the portion of the body region which is located beside the first side surface.

20. The silicon carbide semiconductor element of claim 16, wherein a body concentration adjusting region including the dopant of the second conductivity type in a lower concentration than the body region is provided at least in some depth range of the portion of the body region which is located beside the second side surface.

21. The silicon carbide semiconductor element of claim 16, wherein the semiconductor substrate is a 4H—

SiC substrate, of which the principal surface defines a tilt angle of 2 to 10 degrees with respect to either a (0001) Si plane or a (000-1) C plane.

22. The silicon carbide semiconductor element of claim 16, wherein the first and second side surfaces are arranged substantially perpendicularly to the direction in which the principal surface of the semiconductor substrate tilts with respect to the (0001) Si plane or the (000-1) C plane.

23. The silicon carbide semiconductor element of claim 16, wherein the principal surface of the semiconductor substrate tilts in a <

11-20>

direction with respect to the (0001) Si plane or the (000-1) C plane and wherein the first and second side surfaces are arranged substantially perpendicularly to the <

11-20>

direction.

25. The silicon carbide semiconductor element of claim 16, wherein a difference in threshold voltage between the two opposing sidewall surfaces of the trench is equal to or smaller than 0.1 V.

26. The silicon carbide semiconductor element of claim 16, wherein when viewed perpendicularly to the principal surface of the semiconductor substrate, the trench has the shape of a rectangle on a plan view, and

wherein the first and second side surfaces form the longer sides of the rectangle.

17. A silicon carbide semiconductor element comprising:

a semiconductor substrate of a first conductivity type;

a drift layer of the first conductivity type which is located on the principal surface of the semiconductor substrate;

a body region of a second conductivity type which is located on the drift layer;

an impurity region of the first conductivity type which is located on the body region;

a trench which runs through the body region and the impurity region to reach the drift layer;

a gate insulating film which is arranged on surfaces of the trench;

a gate electrode which is arranged on the gate insulating film;

a first electrode which contacts with the impurity region;

a second electrode which is arranged on the back surface of the semiconductor substrate; and

a channel layer of the first conductivity type,

wherein the surfaces of the trench include a first side surface and a second side surface which is opposed to the first side surface,

wherein the channel layer is arranged between the first and second side surfaces of the trench and the gate insulating film,

wherein a portion of the channel layer which contacts with a part of the body region that is exposed on the first side surface is thicker than another portion of the channel layer which contacts with another part of the body region that is exposed on the second side surface, and

wherein the concentration of a dopant of the second conductivity type is higher at least locally in a portion of the body region which is located beside the first side surface than in another portion of the body region which is located beside the second side surface.

24. The silicon carbide semiconductor element of claim 17, wherein the channel layer of the first conductivity type has been formed by epitaxial growth.

18. A silicon carbide semiconductor element comprising:

a semiconductor substrate of a first conductivity type;

a drift layer of the first conductivity type which is located on the principal surface of the semiconductor substrate;

a body region of a second conductivity type which is located on the drift layer;

an impurity region of the first conductivity type which is located on the body region;

a trench which runs through the body region and the impurity region to reach the drift layer;

a gate insulating film which is arranged on surfaces of the trench;

a gate electrode which is arranged on the gate insulating film;

a first electrode which contacts with the impurity region;

a second electrode which is arranged on the back surface of the semiconductor substrate; and

a channel layer of the first conductivity type,

wherein the surfaces of the trench include a first side surface and a second side surface which is opposed to the first side surface,

wherein the channel layer is arranged between the first and second side surfaces of the trench and the gate insulating film,

wherein a portion of the channel layer which contacts with a part of the body region that is exposed on the first side surface includes a dopant of the first conductivity type in a higher concentration than another portion of the channel layer which contacts with another part of the body region that is exposed on the second side surface, and

wherein the concentration of a dopant of the second conductivity type is higher at least locally in a portion of the body region which is located beside the first side surface than in another portion of the body region which is located beside the second side surface.

27. A method for producing a silicon carbide semiconductor element, the method comprising the steps of:

(a) providing a semiconductor substrate, of which the principal surface is already covered with a drift layer of a first conductivity type;

(b) forming a body region of a second conductivity type on the drift layer;

(c) forming, in the drift layer, a body concentration adjusting region of the second conductivity type which includes a dopant of the second conductivity type in a different concentration from the body region;

(d) forming an impurity region of the first conductivity type on the body region;

(e) subjecting the semiconductor substrate to an annealing process for activation;

(f) forming a trench which runs through the body region and the impurity region by etching;

(g) forming a gate insulating film on the surface of the trench;

(h) forming a gate electrode in contact with the gate insulating film;

(i) forming a first electrode in contact with the impurity region; and

(j) forming a second electrode on another surface of the semiconductor substrate that is opposed to the principal surface,

wherein the step (f) includes forming a trench which has a first side surface and a second side surface, which is opposed to the first side surface, so that the body concentration adjusting region is exposed on the first side surface, and

wherein a portion of the gate insulating film which is arranged on a part of the body region that is exposed on the first side surface is thinner than another portion of the gate insulating film which is arranged on a part of the body region that is exposed on the second side surface.

30. The method for producing a silicon carbide semiconductor element of claim 27, wherein the step (c) includes forming the body concentration adjusting region of the second conductivity type by implanting ions of the second conductivity type into the body region.

31. The method for producing a silicon carbide semiconductor element of claim 27, wherein the step (c) includes forming the body concentration adjusting region of the second conductivity type by implanting ions of the first conductivity type into the body region.

28. A method for producing a silicon carbide semiconductor element, the method comprising the steps of:

(a) providing a semiconductor substrate, of which the principal surface is already covered with a drift layer of a first conductivity type;

(b) forming a body region of a second conductivity type on the drift layer;

(c) forming, in the drift layer, a body concentration adjusting region of the second conductivity type which includes a dopant of the second conductivity type in a different concentration from the body region;

(d) forming an impurity region of the first conductivity type on the body region;

(e) subjecting the semiconductor substrate to an annealing process for activation;

(f) forming a trench which runs through the body region and the impurity region by etching;

(g) forming a gate insulating film on the surface of the trench;

(h) forming a gate electrode in contact with the gate insulating film;

(i) forming a first electrode in contact with the impurity region; and

(j) forming a second electrode on another surface of the semiconductor substrate that is opposed to the principal surface,

wherein the step (f) includes forming a trench which has a first side surface and a second side surface, which is opposed to the first side surface, so that the body concentration adjusting region is exposed on the first side surface,

wherein the method further includes, after the step (f) and before the step (g), the step of forming a channel layer of the first conductivity type between the first and second side surfaces of the trench and the gate insulating film, and

wherein a portion of the channel layer which contacts with a part of the body region that is exposed on the first side surface is thicker than another portion of the channel layer which contacts with another part of the body region that is exposed on the second side surface.

29. A method for producing a silicon carbide semiconductor element, the method comprising the steps of:

(a) providing a semiconductor substrate, of which the principal surface is already covered with a drift layer of a first conductivity type;

(b) forming a body region of a second conductivity type on the drift layer;

(c) forming, in the drift layer, a body concentration adjusting region of the second conductivity type which includes a dopant of the second conductivity type in a different concentration from the body region;

(d) forming an impurity region of the first conductivity type on the body region;

(e) subjecting the semiconductor substrate to an annealing process for activation;

(f) forming a trench which runs through the body region and the impurity region by etching;

(g) forming a gate insulating film on the surface of the trench;

(h) forming a gate electrode in contact with the gate insulating film;

(i) forming a first electrode in contact with the impurity region; and

(j) forming a second electrode on another surface of the semiconductor substrate that is opposed to the principal surface,

wherein the step (f) includes forming a trench which has a first side surface and a second side surface, which is opposed to the first side surface, so that the body concentration adjusting region is exposed on the first side surface, and

wherein the method further includes, after the step (f) and before the step (g), the step of forming a channel layer of the first conductivity type between the first and second side surfaces of the trench and the gate insulating film, and

wherein a portion of the channel layer which contacts with a part of the body region that is exposed on the first side surface includes a dopant of the first conductivity type in a higher concentration than another portion of the channel layer which contacts with another part of the body region that is exposed on the second side surface.