Silicon carbide bipolar junction transistor with overgrown base region

• US 6,815,304 B2
• Filed: 02/22/2002
• Issued: 11/09/2004
• Est. Priority Date: 02/22/2002
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Semisouth Laboratories, LLC
• Inventors: Sankin, Igor, Dufrene, Janna B.
• Primary Examiner(s): Pham, Long
• Assistant Examiner(s): Farahani, Dana
• Application Number:
  US10/079,893
• Publication Number:
  US 20030160302A1
• Time in Patent Office: 991 Days
• Field of Search: 438/335, 438/336, 438/337, 438/338, 438/339, 438/340, 438/364, 438/365, 438/366, 438/367, 438/345, 438/348
• US Class Current: 438/348
• CPC Class Codes: H01L 29/0619 with a supplementary region doped oppositely to or in rectifying contact with the semiconductor containing or contacting region, e.g. guard rings with PN or Schottky junction
• CPC Class Codes: H01L 29/0661 specially adapted for altering the breakdown voltage by removing semiconductor material at, or in the neighbourhood of, a reverse biased junction, e.g. by bevelling, moat etching, depletion etching
• CPC Class Codes: H01L 29/1004 Base region of bipolar transistors
• CPC Class Codes: H01L 29/1608 Silicon carbide
• 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 29/732 Vertical transistors

Abstract

Silicon carbide bipolar junction transistors having an overgrown base layer are provided. The bipolar junction transistors can be made with a very thin (e.g., 0.3 μm or less) base layer while still possessing adequate peripheral base resistance values. Self aligning manufacturing techniques for making the silicon carbide bipolar junction transistors are also provided. Using these techniques, the spacing between emitter and base contacts on the device can be reduced. The silicon carbide bipolar junction transistors can also be provided with edge termination structures such as guard rings to increase the blocking capabilities of the device.

Claims

1. A method of making a SiC bipolar junction transistor comprising:

providing a collector comprising SiC doped with a donor material, the collector having first and second major surfaces;

optionally forming a drift layer on the first major surface of the collector, the drift layer comprising SiC doped with a donor material;

forming a first base layer on the first major surface of the collector or on the drift layer, the first base layer comprising SiC doped with an acceptor material;

forming an emitter layer on the first base layer, the emitter layer comprising SiC doped with a donor material;

etching through the emitter layer and the first base layer to expose the collector or drift layer and to form at least one raised emitter region having an upper surface defined by regions of etched emitter and first base layer, the etched regions comprising bottom and sidewall surfaces;

forming a second base layer comprising SiC doped with an acceptor material, wherein the second base layer covers the bottom and sidewall surfaces of the etched regions and the upper surfaces of emitter regions;

forming emitter contact openings through the second base layer on upper surfaces of the emitter regions to expose emitter material, the emitter contact openings having bottom and sidewall surfaces;

forming base contacts on surfaces of the second base material in the etched regions; and

forming emitter contacts on surfaces of the emitter material in the emitter contact openings.

2. The method of claim 1, wherein the step of forming the drift layer comprises epitaxially growing the drift layer on an exposed surface of the collector and wherein the step of forming the first base layer comprises epitaxially growing the first base layer on an exposed surface of the drift layer.

3. The method of claim 1, wherein the collector layer is doped with a donor material at a first doping level and the drift layer is doped with a donor material at a second doping level and wherein the first doping level is higher than the second doping level.

4. The method of claim 3, wherein the first doping level is 10¹⁸ atoms·

cm<sup>−

3</sup> or greater and the second doping level is 10¹⁵ atoms·

cm^{31 3} or less.

5. The method of claim 2, wherein the step of forming the emitter layer comprises epitaxially growing the emitter layer on the first base layer.

6. The method of claim 5, wherein the emitter layer is doped with a donor material during epitaxial growth.

7. The method of claim 6, wherein the emitter layer is doped at a doping level of 10¹⁸ atoms·

cm<sup>−

3</sup> or greater during epitaxial growth.

8. The method of claim 5, wherein the step of forming the second base layer comprises epitaxially growing the second base layer on an exposed surface of the emitter layer.

9. The method of claim 8, wherein the second base layer is doped with an acceptor material during epitaxial growth.

10. The method of claim 9, wherein the second base layer is doped at a doping level of 10¹⁸ atoms·

cm<sup>−

3</sup> or greater during epitaxial growth.

11. The method of claim 1, further comprising:

forming a plurality of raised guard rings in the overgrown base layer, the raised guard rings circumscribing the raised emitter regions.

12. The method of claim 11, wherein the guard rings are formed simultaneously with the formation of the emitter contact openings.

13. A method of making a SiC bipolar junction transistor comprising:

providing a collector comprising SiC doped with a donor material, the collector having first and second major surfaces;

optionally forming a drift layer on the first major surface of the collector, the drift layer comprising SiC doped with an donor material;

forming a first base layer on the first major surface of the collector or on the drift layer, the first base layer comprising SiC doped with an acceptor material;

forming an emitter layer on the first base layer, the emitter layer comprising SiC doped with a donor material;

etching through the emitter layer and the first base layer to expose the collector or drift layer and to form at least one raised emitter region defined by regions of etched emitter and first base layer, the etched regions comprising bottom and sidewall surfaces;

forming a second base layer comprising SiC doped with an acceptor dopant, wherein the second base layer covers the bottom and sidewall surfaces of the etched regions;

forming a base contact layer on the second base layer;

forming emitter contact openings through the base contact layer on surfaces of the raised emitter regions to expose the second base layer,

etching emitter contact openings through the second base layer on surfaces of the raised emitter regions using the base contact layer as a mask to expose emitter material;

forming emitter contacts on the emitter material in the emitter contact openings.

14. The method of claim 13, wherein:

the step of forming the drift layer comprises epitaxially growing the drift layer on the first major surface of the collector;

the step of forming the first base layer comprises epitaxially growing the first base layer on the drift layer or on the first major surface of the collector;

the step of forming the emitter layer comprises epitaxially growing the emitter layer on an exposed surface of the first base layer; and

the step of forming the second base layer comprises epitaxially growing the second base layer on an exposed surface of the emitter layer;

wherein dopant materials are incorporated into each of the layers during growth.

15. The method of claim 13, wherein the collector is doped with a donor material at a first doping level and the drift layer is doped with a donor material at a second doping level.

16. The method of claim 15, wherein the first doping level is 10¹⁸ atoms·

cm<sup>−

3</sup> or greater and the second doping level is 10¹⁵ atoms·

cm<sup>−

3</sup> or less.

17. The method of claim 14, wherein the emitter layer is doped at a doping level of 10¹⁸ atoms·

cm<sup>−

3</sup> or greater during epitaxial growth.

18. The method of claim 14, wherein the second base layer is doped at a doping level of 10¹⁸ atoms·

cm<sup>−

3</sup> or greater during epitaxial growth.

19. The method of claim 14, further comprising:

forming a plurality of raised guard rings in the base contact layer, the raised guard rings circumscribing the one or more raised emitter regions and etched regions; and

etching a plurality of raised guard rings in the second base layer using the base contact layer as a mask.

20. The method of claim 19, wherein the guard rings and emitter contact openings are formed simultaneously in the base contact layer and/or etched simultaneously in the second base layer.