DMOS-transistor with lateral dopant gradient in drift region and method of producing the same

• US 7,064,385 B2
• Filed: 09/20/2004
• Issued: 06/20/2006
• Est. Priority Date: 09/19/2003
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Germany GmbH (Microchip Technology Incorporated)
• Inventors: Graf, Michael, Dudek, Volker
• Primary Examiner(s): Prenty, Mark V.
• Application Number:
  US10/946,547
• Publication Number:
  US 20050062102A1
• Time in Patent Office: 638 Days
• Field of Search: 257/335, 257/336, 257/343, 257/347, 257/655, 257/657, 438/197
• US Class Current: 257/335
• CPC Class Codes: H01L 21/26586 characterised by the angle between the ion beam and the crystal planes or the main crystal surface
• CPC Class Codes: H01L 29/0653 adjoining the input or output region of a field-effect device, e.g. the source or drain region
• 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 29/0878 Impurity concentration or distribution
• CPC Class Codes: H01L 29/66659 with asymmetry in the channel direction, e.g. lateral high-voltage MISFETs with drain offset region, extended drain MISFETs
• CPC Class Codes: H01L 29/66681 Lateral DMOS transistors, i.e. LDMOS transistors
• CPC Class Codes: H01L 29/7824 with a substrate comprising an insulating layer, e.g. SOI-LDMOS transistors
• 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

Abstract

A DMOS-transistor has a trench bordered by a drift region including two doped wall regions and a doped floor region extending along the walls and the floor of the trench. The laterally extending floor region has a dopant concentration gradient in the lateral direction. For example, the floor region includes at least two differently-doped floor portions successively in the lateral direction. This dopant gradient in the floor region is formed by carrying out at least one dopant implantation from above through the trench using at least one mask to expose a first area while covering a second area of the floor region.

Claims

1. A DMOS-transistor in a semiconductor body comprising:

a trench in said semiconductor body bounded by a source-side wall, a drain-side wall, and a floor extending in a lateral direction between bottom ends of said walls; and

a drift region including a doped source-side wall region in said semiconductor body along said source-side wall, a doped drain-side wall region in said semiconductor body along said drain-side wall, and a doped floor region in said semiconductor body extending in said lateral direction along said floor;

wherein said floor region exhibits a dopant concentration gradient, in said lateral direction, of an implanted dopant that is implanted into said floor region to establish a higher dopant concentration in a first floor portion of said floor region and a lower dopant concentration in a second floor portion of said floor region.

2. The DMOS-transistor according to claim 1, wherein said implanted dopant is not implanted into said second floor portion so that said lower dopant concentration is a zero concentration of said implanted dopant.

3. The DMOS-transistor according to claim 1, wherein said first floor portion with said higher dopant concentration is proximate to said drain-side wall, and said second floor portion with said lower dopant concentration is proximate to said source-side wall.

4. The DMOS-transistor according to claim 1, wherein said floor region further has a third floor portion with a dopant concentration of said implanted dopant that is lower than said higher dopant concentration of said first floor portion, said first floor portion is between said second and third floor portions in said lateral direction, said second floor portion is proximate to said source-side wall, and said third floor portion is proximate to said drain-side wall.

5. The DMOS-transistor according to claim 1, wherein said first floor portion and said second floor portion laterally adjoin one another and together make up all of said floor region, which does not include further differently-doped portions.

6. The DMOS-transistor according to claim 1, wherein said floor region further includes at least one additional floor portion in addition to said first and second floor portions, said at least one additional floor portion respectively has a respective dopant concentration of said implanted dopant different from said dopant concentrations of said implanted dopant in others of said floor portions, and said floor portions are contiguous with one another in succession in said lateral direction.

7. The DMOS-transistor according to claim 1, wherein said source-side wall region, said floor region, and said drain-side wall region extend continuously and successively without gaps therebetween along all of said source-side wall, said floor, and said drain-side wall respectively, to form a continuous drift length of said drift region.

8. The DMOS-transistor according to claim 1, wherein said semiconductor body further comprises a first well region of a first conductivity type and a second well region of a second conductivity type, and wherein said trench and said drift region are at least partially within said second well region.

9. The DMOS-transistor according to claim 8, wherein said trench and said drift region are located entirely within and completely surrounded by said second well region.

10. The DMOS-transistor according to claim 8, wherein said floor region has said second conductivity type.

11. The DMOS-transistor according to claim 8, wherein said wall regions and said floor region have respective total dopant concentrations higher than a total dopant concentration of said second well region.

12. The DMOS-transistor according to claim 8, wherein said wall regions and said floor region have respective total dopant concentrations higher than a total dopant concentration of said first well region.

13. The DMOS-transistor according to claim 8, wherein a PN-junction is formed at an interface between said first and second well regions, and said PN-junction laterally extends below said floor region in a direction having at least a component in said lateral direction.

14. The DMOS-transistor according to claim 1, wherein said semiconductor body further comprises a drain region spaced apart from said drain-side wall by a spacing distance in a range from 0.5 μ

m to 4.0 μ

m.

15. The DMOS-transistor according to claim 1, wherein said trench has a width in a range from 0.5 μ

m to 4.0 μ

m and an aspect ratio greater than 0.5.

16. The DMOS-transistor according to claim 1, wherein said trench is a shallow trench having a width greater than a depth thereof.

17. The DMOS-transistor according to claim 1, wherein said trench is a tapering trench having a width at said floor smaller than a width at a surface of said semiconductor body.

18. The DMOS-transistor according to claim 1, wherein said semiconductor body comprises an insulating intermediate layer and a surface layer consisting of a semiconducting substrate disposed on said insulating intermediate layer, and wherein said DMOS-transistor is formed in and/or on said surface layer.

19. The DMOS-transistor according to claim 18, wherein a remaining thickness of said surface layer between said floor of said trench and said insulating intermediate layer is from one half to five times a depth of said trench.

22. A method of producing the DMOS-transistor according to claim 1, said method comprising the steps:

a) providing said semiconductor body;

b) forming in said semiconductor body said trench bounded by said source-side wall, said drain-side wall, and said floor extending in said lateral direction between said bottom ends of said walls; and

c) doping said semiconductor body to form said drift region including said doped source-side wall region along said source-side wall, said doped drain-side wall region along said drain-side wall, and doped floor region extending in said lateral direction along said floor;

wherein said doping in said step c) to form said floor region includes at least a first dopant implantation directed through said trench into said floor after said step b), so as to implant said implanted dopant into only said first floor portion and not said second floor portion of said floor region and thereby produce said dopant concentration gradient in said lateral direction in said floor region.

23. The method according to claim 22, further comprising, before said first dopant implantation, providing a mask on said semiconductor body to cover said second floor portion and leave exposed said first floor portion of said floor region, and then carrying out said first dopant implantation while using said mask to spatially limit said first dopant implantation.

24. The method according to claim 23, further comprising, after said first dopant implantation, shifting an edge of said mask in said lateral direction to expose a third floor portion of said floor region that had been covered by said mask during said first dopant implantation, and then carrying out a second dopant implantation into said third floor portion of said floor region, so that said first, second and third floor portions of said floor region respectively have different dopant concentrations.

25. The method according to claim 23, wherein said providing of said mask is achieved in a self-adjusting mask process step.

26. The method according to claim 25, wherein said providing of said mask comprises forming said mask by a structural or shape transfer through lithography and etching steps.

27. The method according to claim 25, wherein said providing of said mask comprises forming a positive or a negative of said mask with a photoresist layer.

28. The method according to claim 23, further comprising, before said providing of said mask and before said forming of said trench, providing a hard mask with an opening that defines a location, shape and size of said trench, and then forming said trench by etching through said opening, and then providing said mask on said hard mask.

29. The method according to claim 22, further comprising performing a LOCOS oxidation in said trench after said steps b) and c).

30. The method according to claim 22, wherein said forming of said trench is carried out by performing an STI etching process, and further comprising filling said trench with an insulating material after said steps b) and c).

20. A DMOS-transistor in a semiconductor body comprising:

a trench in said semiconductor body bounded by a source-side wall, a drain-side wall, and a floor extending in a lateral direction between bottom ends of said walls; and

a drift region including a doped source-side wall region in said semiconductor body along said source-side wall, a doped drain-side wall region in said semiconductor body along said drain-side wall, and a doped floor region in said semiconductor body extending in said lateral direction along said floor;

wherein said floor region exhibits a dopant concentration gradient, in said lateral direction, of an implanted dopant that is implanted into said floor region to establish a higher dopant concentration in a first floor portion of said floor region and a lower dopant concentration in a second floor portion of said floor region;

wherein said semiconductor body comprises an insulating intermediate layer and a surface layer consisting of a semiconducting substrate disposed on said insulating intermediate layer, and wherein said DMOS-transistor is formed in and/or on said surface layer;

further comprising, in said surface layer, a first well region of a first conductivity type, a second well region of a second conductivity type, a source region disposed within and surrounded by said first well region, a drain region of the second conductivity type disposed within and surrounded by said second well region;

further comprising a gate region disposed on a surface of said surface layer of said semiconductor body, wherein said gate region, beginning from said source region, extends laterally over at least a portion of said trench over an entire lateral extension of said first well region; and

wherein said floor region has a first concentration value of a total dopant concentration of a dopant of the second conductivity type therein, said source-side wall region has a second concentration value of a total dopant concentration of a dopant of the second conductivity type therein, and said drain-side wall region has a third concentration value of a total dopant concentration of a dopant of the second conductivity type therein.

21. The DMOS-transistor according to claim 20, wherein said first, second and third concentration values are all different from one another.