Short gate high power MOSFET and method of manufacture

• US 8,084,813 B2
• Filed: 12/03/2007
• Issued: 12/27/2011
• Est. Priority Date: 12/03/2007
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Konstantinov, Andrei, Harris, Christopher, Svederg, Jan-Olov
• Primary Examiner(s): Warren, Matthew E
• Assistant Examiner(s): Lin, John
• Application Number:
  US11/949,221
• Publication Number:
  US 20090140326A1
• Time in Patent Office: 1,485 Days
• Field of Search: 257/E29.001, 257327-332, 257/335, 257/E29.257, 257/E29.259, 257/E29.26, 257/E29.262, 438/270, 438/212, 438/268
• US Class Current: 257/330
• CPC Class Codes: H01L 29/0696 of cellular field-effect devices, e.g. multicellular DMOS transistors or IGBTs
• CPC Class Codes: H01L 29/0847 of field-effect transistors with insulated gate H01L29/0653 takes precedence; with a passive supplementary region between source or drain and substrate related to punch-through, capacity or isolation phenomena H01L29/1079; with LDD or DDD structure H01L29/7833; for thin film transistors H01L29/78618
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/41766 with at least part of the source or drain electrode having contact below the semiconductor surface, e.g. the source or drain electrode formed at least partially in a groove or with inclusions of conductor inside the semiconductor H01L29/41733 - H01L29/41758 take precedence
• CPC Class Codes: H01L 29/4236 within a trench, e.g. trench gate electrode, groove gate electrode
• CPC Class Codes: H01L 29/66666 Vertical transistors H01L29/66712, H01L29/66742 take precedence
• CPC Class Codes: H01L 29/7828 without inversion channel, e.g. vertical ACCUFETs, normally-on vertical MISFETs

Abstract

A short gate high power metal oxide semiconductor field effect transistor formed in a trench includes a short gate having gate length defined by spacers within the trench. The transistor further includes a buried region that extends beneath the trench and beyond a corner of the trench, that effectively shields the gate from high drain voltage, to prevent short channel effects and resultantly improve device performance and reliability.

Claims

1. A semiconductor device comprising:

a substrate of a first conductivity type;

a region of a second conductivity type within the substrate, the region extending from an upper surface of the substrate into the substrate, the second conductivity type opposite the first conductivity type;

a first layer of the first conductivity type over the substrate and the region;

a trench extending into the first layer, a bottom of the trench is within the first layer and directly over the region,

a portion of the first layer is intermediate between the bottom of the trench and the region, the portion is a current conducting channel; and

a gate within the trench.

2. The semiconductor device of claim 1, wherein the substrate and the first layer are silicon carbide epitaxial layers.

3. The semiconductor device of claim 1, wherein the first conductivity type is n-type, and the second conductivity type is p-type.

4. The semiconductor device of claim 1, wherein the region is an implanted region.

5. The semiconductor device of claim 1, wherein the gate is polysilicon.

6. The semiconductor device of claim 1, having a gate length in a range of about 0.3 to 1.5 μ

m.

7. The semiconductor device of claim 1, wherein the region has a dopant concentration that is graded in the vertical direction.

8. The semiconductor device of claim 1, further comprising:

a plurality of additional regions of the second conductivity type within the substrate, the plurality of additional regions extending from the upper surface of the substrate into the substrate;

a plurality of additional trenches extending into the first layer and having respective trench bottoms within the first layer,

respective portions of the first layer are intermediate between the trench bottoms and the additional regions, the respective portions are current conducting channels; and

a plurality of additional gates within the additional trenches.

9. A vertical field effect transistor comprising:

a first layer of a first conductivity type;

an implanted region of a second conductivity type extending into the first layer, the second conductivity type opposite the first conductivity type;

a second layer of the first conductivity type on an upper surface of the first layer and an upper surface of the implanted region;

a trench extending into the second layer directly over the implanted region, a portion of the second layer is disposed intermediate between a bottom of the trench and the implanted region, the portion is a current conducting channel; and

a gate within the trench.

10. The vertical field effect transistor of claim 9, wherein the first and second layers are silicon carbide epitaxial layers.

11. The vertical field effect transistor of claim 9, wherein the first conductivity type is n-type, and the second conductivity type is p-type.

12. The vertical field effect transistor of claim 9, wherein the gate is polysilicon.

13. The vertical field effect transistor of claim 9, wherein the implanted region has a dopant concentration that is graded in the vertical direction.

14. The vertical field effect transistor of claim 9, having a gate length in a range of about 0.3 to 1.5 μ

m.