Low resistance power MOSFET or other device containing silicon-germanium layer

• US 6,239,463 B1
• Filed: 08/28/1997
• Issued: 05/29/2001
• Est. Priority Date: 08/28/1997
• Status: Expired due to Term

• Current Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Original Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Inventors: Cornell, Michael E., Williams, Richard K., Darwish, Mohamed, Grabowski, Wayne
• Primary Examiner(s): MINTEL, WILLIAM A
• Application Number:
  US08/919,386
• Time in Patent Office: 1,370 Days
• Field of Search: 257/341, 257/342, 257/329, 257/330, 257/332, 257/331, 257/334, 257/328, 438/206, 438/212
• US Class Current: 257/328
• 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 29/0873 Drain regions
• 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 29/165 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/7378 comprising lattice mismatched active layers, e.g. SiGe strained layer transistors
• CPC Class Codes: H01L 29/7395 Vertical transistors, e.g. vertical IGBT
• CPC Class Codes: H01L 29/74 Thyristor-type devices, e.g. having four-zone regenerative action two-terminal thyristors H01L29/87
• CPC Class Codes: H01L 29/7802 Vertical DMOS transistors, i.e. VDMOS transistors
• CPC Class Codes: H01L 29/7809 having both source and drain contacts on the same surface, i.e. Up-Drain VDMOS transistors
• 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 29/7816 Lateral DMOS transistors, i.e. LDMOS transistors
• 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
• CPC Class Codes: H01L 29/7835 with asymmetrical source and drain regions, e.g. lateral high-voltage MISFETs with drain offset region, extended drain MISFETs
• CPC Class Codes: H01L 29/872 Schottky diodes

Abstract

A power MOSFET or other semiconductor device contains a layer of silicon combined with germanium to reduce the on-resistance of the device. The proportion of germanium in the layer is typically in the range of 1-40%. To achieve desired characteristics the concentration of germanium in the Si-Ge layer can be uniform, stepped or graded. In many embodiments it is desirable to keep the germanium below the surface of the semiconductor material to prevent germanium atoms from being incorporated into a gate oxide layer. This technique can be used in vertical DMOS and trench-gated MOSFETs, quasi-vertical MOSFETs and lateral MOSFETs, as well as insulated gate bipolar transistors, thyristors, Schottky diodes and conventional bipolar transistors.

Claims

1. A power MOSFET comprising:

an epitaxial layer formed on a surface of a substrate;

a source region of a first conductivity type formed in said epitaxial layer;

a body region of a second conductivity type opposite to said first conductivity type formed in said epitaxial layer, said body region being located adjacent said source region and including a channel region;

a drain region of the first conductivity type comprising said substrate layer and at least a portion of said epitaxial layer;

a gate, said channel region being separated from said gate by a dielectric layer; and

a Si-Ge layer comprising germanium atoms, said Si-Ge layer being formed in at least a portion of said epitaxial layer and extending to a surface of said epitaxial layer, said Si-Ge layer being substantially thicker than said channel region.

2. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms is constant throughout most of said vertical section.

3. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along most of said vertical section.

4. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along most of said vertical section.

5. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is constant throughout most of said vertical section.

6. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along most of said vertical section.

7. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along most of said vertical section.

8. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is constant throughout most of said vertical section.

9. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along most of said vertical section.

10. The power MOSFET of claim 1 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along most of said vertical section.

11. The power MOSFET of claim 1 comprising a vertical current flow device fabricated in said epitaxial layer.

12. The power MOSFET of claim 1 wherein the content of germanium in said Si-Ge layer is between 2% and 40%.

13. The power MOSFET of claim 1 wherein said Si-Ge layer is more than 2 μ

m thick.

14. The power MOSFET of claim 1 wherein a gradient of the germanium content in said Si-Ge layer is less than or equal to 4%/μ

m.

15. The power MOSFET of claim 1 comprising a lateral current flow device fabricated in said epitaxial layer.

16. The power MOSFET of claim 15 wherein the content of germanium in said Si-Ge layer is between 2% and 40%.

17. The power MOSFET of claim 15 wherein said Si-Ge layer is more than 2 μ

m thick.

18. The power MOSFET of claim 15 wherein a gradient of the germanium content in said Si-Ge layer is less than or equal to 4%/μ

m.

19. A power MOSFET comprising:

an epitaxial layer formed on a surface of a substrate;

a source region of a first conductivity type formed in said epitaxial layer;

a body region of a second conductivity type opposite to said first conductivity type formed in said epitaxial layer, said body region being located adjacent said source region and including a channel region;

a drain region of the first conductivity type comprising said substrate layer and at least a portion of said epitaxial layer;

a gate, said channel region being separated from said gate by a dielectric layer; and

a Si-Ge layer comprising germanium atoms, said Si-Ge layer being formed in a portion of said epitaxial layer and not extending to a surface of said epitaxial layer.

20. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms is substantially constant along a vertical section of said Si-Ge layer.

21. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along a vertical section of said Si-Ge layer.

22. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is constant throughout most of a vertical section of said epitaxial layer which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along a vertical section of said Si-Ge layer.

23. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is constant along a vertical section of said Si-Ge layer.

24. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along a vertical section of said Si-Ge layer.

25. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type varies gradually along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along a vertical section of said Si-Ge layer.

26. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is substantially constant along a vertical section of said Si-Ge layer.

27. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms varies gradually along a vertical section of said Si-Ge layer.

28. The power MOSFET of claim 19 wherein a dopant concentration of atoms of said first conductivity type is stepped along most of a vertical section which does not transect either said body region or said source region and a concentration of germanium atoms is stepped along a vertical section of said Si-Ge layer.

29. The power MOSFET of claim 19 comprising a vertical current flow device fabricated in said epitaxial layer.

30. The power MOSFET of claim 29 wherein the content of germanium in said Si-Ge layer is between 2% and 40%.

31. The power MOSFET of claim 29 wherein said Si-Ge layer is more than 2 μ

m thick.

32. The power MOSFET of claim 29 wherein a gradient of the germanium content in said Si-Ge layer is less than or equal to 4%/μ

m.

33. The power MOSFET of claim 19 comprising a lateral current flow device fabricated in said epitaxial layer.

34. The power MOSFET of claim 33 wherein the content of germanium in said Si-Ge layer is between 2% and 40%.

35. The power MOSFET of claim 33 wherein said Si-Ge layer is more than 2 μ

m thick.

36. The power MOSFET of claim 33 wherein a gradient of the germanium content in said Si-Ge layer is less than or equal to 4%/μ

m.

37. The power MOSFET of claim 19 comprising an oxide layer on a surface of said epitaxial layer, said oxide layer being substantially free of germanium atoms.

38. The power MOSFET of claim 19 wherein said dielectric layer comprises a gate oxide layer, said gate oxide layer being substantially free of germanium atoms.

39. The power MOSFET of claim 38 wherein said gate is formed in a trench.

40. The power MOSFET of claim 39 wherein said trench does not extend into said Si-Ge layer.

41. The power MOSFET of claim 39 wherein said Si-Ge layer does not extend into said body region.

42. The power MOSFET of claim 39 comprising a diffusion of said second conductivity type which forms a clamping diode with a portion of said epitaxial layer of said first conductivity type, said Si-Ge layer extending into said diffusion.

43. The power MOSFET of claim 39 comprising a diffusion of said second conductivity type which forms a clamping diode with a portion of said epitaxial layer of said first conductivity type, said Si-Ge layer not extending into said diffusion.

44. The power MOSFET of claim 19 comprising:

a trench extending downward from a top surface of said epitaxial layer, a wall of said trench being lined with said dielectric layer, said gate being formed in said trench;

wherein said source region is formed adjacent said top surface of said epitaxial layer and

said channel region is separated from said gate by said dielectric layer.

45. The power MOSFET of claim 44 wherein a concentration of germanium atoms in said Si-Ge layer is substantially constant throughout said Si-Ge layer.

46. The power MOSFET of claim 44 wherein a concentration of germanium atoms in said Si-Ge layer varies at different levels of said Si-Ge layer.

47. The power MOSFET of claim 44 wherein said Si-Ge layer extends to said top surface of said epitaxial layer.

48. The power MOSFET of claim 44 wherein said Si-Ge layer does not extend to said top surface of said epitaxial layer.

49. The power MOSFET of claim 44 comprising a MOSFET cell bounded on at least two sides by said trench and a deep diffusion of said second conductivity type located substantially at a center of said MOSFET cell and extending to a level below a bottom of said trench.

50. The power MOSFET of claim 49 comprising a plurality of said MOSFET cells, each of said MOSFET cells being bounded on at least two sides by said trench, and a diffusion of said second conductivity type spaced apart from said MOSFET cells, a PN junction at a border of said diffusion forming a clamping diode.

51. The power MOSFET of claim 49 comprising a plurality of said diffusions, said diffusions being located at periodic intervals across a surface of said trenchFET.

52. The power MOSFET of claim 49 wherein said MOSFET cell is bounded on all sides by said trench.

53. The power MOSFET of claim 49 wherein said MOSFET cell is in the form of an elongated strip.

54. The power MOSFET of claim 44 wherein said body region is fully depleted.

56. The power MOSFET of claim 19 wherein said power MOSFET comprises a planar vertical double-diffused MOSFET and wherein:

said epitaxial layer is of a first conductivity type;

said source region is formed in said epitaxial layer adjacent a top surface of said epitaxial layer;

said body region is adjacent said top surface of said epitaxial layer and encloses said source region and said channel region extends parallel to said top surface.

57. The power MOSFET of claim 56 wherein a concentration of germanium atoms in said Si-Ge layer is substantially constant throughout said Si-Ge layer.

58. The power MOSFET of claim 56 wherein a concentration of germanium atoms in said Si-Ge layer varies at different levels of said Si-Ge layer.

59. The power MOSFET of claim 56 wherein said Si-Ge layer extends to said top surface of said epitaxial layer.

60. The power MOSFET of claim 56 wherein said Si-Ge layer does not extend to said top surface of said epitaxial layer.

55. An ACCUFET comprising:

an epitaxial layer formed on a surface of a substrate;

a trench extending downward from a top surface of said epitaxial layer, a wall of said trench being lined with a dielectric layer, a gate being formed in said trench;

a mesa formed between at least two segments of said trench;

a first region of the first conductivity type comprising said substrate layer and at least a portion of said epitaxial layer; and

a second region of a first conductivity type formed adjacent said top surface of said epitaxial layer in said mesa, said second region being doped more heavily than said first region;

a Si-Ge layer comprising germanium atoms, said Si-Ge layer being formed in at least a portion of said epitaxial layer.