SILICON CARBIDE SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME

• US 20150048382A1
• Filed: 04/17/2013
• Published: 02/19/2015
• Est. Priority Date: 04/19/2012
• Status: Active Grant

• Current Assignee: DENSO Corporation, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: DENSO Corporation, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Takeuchi, Yuichi, Soejima, Narumasa, Watanabe, Yukihiko, Chida, Kazumi
• Granted Patent: US 9,673,288 B2
• Time in Patent Office: Days
• US Class Current: 257/77
• CPC Class Codes: H01L 21/044 Conductor-insulator-semiconductor electrodes
• CPC Class Codes: H01L 21/0465 using masks
• CPC Class Codes: H01L 21/26513 of electrically active species
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/324 Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering H01L21/20 - H01L21/288 and H01L21/302 - H01L21/322 take precedence
• CPC Class Codes: H01L 29/0623 Buried supplementary region, e.g. buried guard ring multi-RESURF H01L29/0634
• CPC Class Codes: H01L 29/1095 Body region, i.e. base region, of DMOS transistors or IGBTs cell layout H01L29/0696
• 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 29/66734 with a step of recessing the gate electrode, e.g. to form a trench gate electrode
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

In a silicon carbide semiconductor device, a p-type SiC layer is disposed in a corner of a bottom of a trench. Thus, even if an electric field is applied between a drain and a gate when a MOSFET is turned off, a depletion layer in a pn junction between the p-type SiC layer and an n⁻ type drift layer greatly extends toward the n⁻ type drift layer, and a high voltage caused by an influence of a drain voltage hardly enters a gate insulating film. Hence, an electric field concentration within the gate insulating film can be reduced, and the gate insulating film can be restricted from being broken. In this case, although the p-type SiC layer may be in a floating state, the p-type SiC layer is formed in only the corner of the bottom of the trench. Thus, the deterioration of the switching characteristic is relatively low.

Claims

1. A silicon carbide semiconductor device comprising:

a first or second conductivity type substrate that is made of silicon carbide;

a drift layer that is disposed on the substrate, and made of a first conductivity type silicon carbide lower in impurity concentration than the substrate;

a base region that is disposed on the drift layer, and made of a second conductivity type silicon carbide;

a source region that is disposed on the base region, and made of a first conductivity type silicon carbide higher in impurity concentration than the drift layer;

a contact region that is connected to the base region, and made of a second conductivity type silicon carbide higher in impurity concentration than the base layer;

a trench that extends to a position deeper than the base region from a surface of the source region;

a second conductivity type layer that is disposed in a corner of a bottom of the trench, made of a second conductivity type silicon carbide, and has a triangular round shape in cross-section taken along a depth direction of the trench;

a gate insulating film that is disposed on an inner wall surface of the trench on the second conductivity type layer;

a gate electrode that is disposed on the gate insulating film within the trench;

a source electrode that is electrically connected to the base region through the source region and the contact region; and

a drain electrode that is disposed on a rear side of the substrate,

wherein the silicon carbide semiconductor device is provided with a semiconductor switching element with an inversion type switching element that forms an inversion type channel region on a surface portion of the base region located on a side surface of the trench by controlling an application voltage to the gate electrode, and allows a current to flow between the source electrode and the drain electrode through the source region and the drift layer.

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

the trench defines a longitudinal direction in one direction, and has a bottom with a predetermined width, and

the second conductivity type layer is disposed in the corner on each of sides of the trench in a width direction, and spaced away from each other in the width direction.

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

the trench defines a longitudinal direction in one direction, and has a triangular shape with a pointed taper bottom, and

the second conductivity type layer is disposed in a tip end of the trench.

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

at least a part of the side surface of the trench is provided with a coupling layer made of a second conductivity type silicon carbide, and the base region and the second conductivity type layer are coupled with each other by the coupling layer.

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

an impurity concentration of the second conductivity type layer and an impurity concentration of the coupling layer are same as each other, and 1×

10¹⁷/cm³ or higher.

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

the impurity concentration of the coupling layer is higher than an impurity concentration of the base region.

7. A method of manufacturing the silicon carbide semiconductor device according to claim 1, comprising:

forming the trench to a position deeper than the base region from the surface of the source region; and

after the forming of the trench, conducting a heat treatment under a hydraulic atmosphere mixed with a second conductivity type dopant gas to subject the inner wall surface of the trench to hydrogen etching, and to form the second conductivity type layer in the corner of the bottom of the trench by epitaxial growth taking the second conductivity type dopant gas.

8. The method of manufacturing the silicon carbide semiconductor device according to claim 7, further comprising activation-annealing to activate an ion implantation layer including the contact layer, wherein

the activation-annealing is conducted simultaneously by the heat treatment for conducting the hydrogen etching.

9. The method of manufacturing the silicon carbide semiconductor device according to claim 7, wherein

a TMA is used as the second conductivity type dopant gas.

10. The method of manufacturing the silicon carbide semiconductor device according to claim 7, wherein

a B₂H₆ is used as the second conductivity type dopant gas.