Semiconductor device and method for manufacturing the same

• US 6,469,345 B2
• Filed: 01/12/2001
• Issued: 10/22/2002
• Est. Priority Date: 01/14/2000
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Aoki, Takaaki, Kuroyanagi, Akira, Suzuki, Mikimasa, Soga, Hajime, Tomatsu, Yutaka
• Primary Examiner(s): Prenty, Mark V.
• Application Number:
  US09/758,377
• Publication Number:
  US 20010008291A1
• Time in Patent Office: 648 Days
• Field of Search: 257/330, 257/333, 257/411
• US Class Current: 257/330
• CPC Class Codes: H01L 21/28202 in a nitrogen-containing ambient, e.g. nitride deposition, growth, oxynitridation, NH3 nitridation, N2O oxidation, thermal nitridation, RTN, plasma nitridation, RPN
• CPC Class Codes: H01L 29/42368 the thickness being non-uniform
• CPC Class Codes: H01L 29/511 with a compositional variation, e.g. multilayer structures H01L29/516 takes precedence
• CPC Class Codes: H01L 29/513 the variation being perpendicular to the channel plane
• CPC Class Codes: H01L 29/518 the insulating material containing nitrogen, e.g. nitride, oxynitride, nitrogen-doped material
• CPC Class Codes: H01L 29/66348 with a recessed gate
• CPC Class Codes: H01L 29/7397 and a gate structure lying on a slanted or vertical surface or formed in a groove, e.g. trench gate IGBT
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

A trench-gate type transistor has a gate insulating film formed on an inner wall of a trench. The gate insulating film is composed of a first portion disposed on a side wall portion of the trench and a second portion disposed on upper and bottom portions of the trench. The first portion is composed of a first oxide film, a nitride film, and a second oxide film. The second portion is composed of only an oxide film and has a thickness thicker than that of the first portion. Accordingly, electric field concentration on upper and lower corner portions of the trench can be mitigated, and a decrease in withstand voltage at that portions can be prevented.

Claims

1. A trench-gate type transistor, comprising:

a semiconductor substrate having a trench formed thereon; and

a gate insulating film disposed on an inner wall of the trench, the gate insulating film including a first portion and a second portion respectively locally disposed on the inner wall of the trench and having different structures from each other, the first portion being composed of a first oxide film, a nitride film, and a second oxide film which are layered.

2. The trench-gate type transistor according to claim 1, wherein a first region of the inner wall where the first portion of the gate insulating film is disposed includes a side wall portion of the trench in which a channel region is provided, and the first region excludes a bottom portion of the trench.

3. The trench-gate type transistor according to claim 2, wherein the first region excludes an opening portion of the trench.

4. The trench-gate type transistor according to claim 2, wherein a second region of the inner wall where the second portion of the gate insulating film is disposed includes at least one of an opening portion and the bottom portion of the trench.

5. The trench-gate type transistor according to claim 4, wherein the second portion of the insulating film disposed on the one of the opening portion and the bottom portion of the trench has a thickness thicker than that of the first portion disposed on the side wall portion of the trench.

6. The trench-gate type transistor according to claim 1, wherein:

the first portion of the gate insulating film is disposed on a bottom portion of the trench; and

the second portion consists of an oxide film and is disposed on a side wall portion of the trench.

7. The trench-gate type transistor according to claim 1, wherein the second portion consists of an oxide film.

8. A semiconductor device, comprising:

a semiconductor substrate having a main surface in which a trench is formed; and

an insulating film located on an inner wall of the trench, wherein the insulating film includes;

a first portion composed of a first oxide film, a nitride film, and a second oxide film,

wherein the first portion is located on the side wall of the trench; and

a second portion consisting of an oxide film, wherein the second portion is located on both the upper portion and the lower portion of the trench, and the thickness of the second portion is larger than that of the first portion.

9. A semiconductor device, comprising:

a semiconductor substrate having a main surface in which a trench is formed, wherein the semiconductor substrate is composed of a first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, and a first conductivity type third semiconductor layer, wherein the trench penetrates the first semiconductor layer and the second semiconductor layer to reach the third semiconductor layer; and

an insulating film located on an inner wall of the trench, such that the semiconductor substrate provides a transistor in which the second semiconductor layer serves as a channel region, and the insulating film serves as a gate insulating film, and the insulating film includes;

a first portion composed of a first oxide film, a nitride film, and a second oxide film, wherein the first portion is located on the side wall of the trench, and the nitride film of the first portion of the insulating film has an upper end located at a position closer to the main surface than a boundary between the first semiconductor layer and the second semiconductor layer; and

a second portion consisting of an oxide film, wherein the second portion is located on at least one of the upper portion and the lower portion of the trench, and the thickness of the second portion is larger than that of the first portion.

10. A semiconductor device, comprising:

a semiconductor substrate having a main surface in which a trench is formed; and

an insulating film located on an inner wall of the trench, wherein the insulating film includes;

a first portion composed of a first oxide film, a nitride film, and a second oxide film, wherein the first portion is located on the bottom portion of the trench; and

a second portion consisting of an oxide film, wherein the second portion is located on the side wall of the trench.

11. The semiconductor device according to claim 10, wherein:

the semiconductor substrate is composed of a first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, and a first conductivity type third semiconductor layer;

the trench penetrates the first semiconductor layer and the second semiconductor layer to reach the third semiconductor layer; and

the nitride film has an upper end that is located such that the distance from the main surface to the upper end of the nitride film is greater than the distance from the main surface to a boundary between the second semiconductor layer and the third semiconductor layer.

12. A trench-gate type transistor, comprising:

a semiconductor substrate in which a trench is formed; and

a gate insulating film located on an inner wall of the trench, wherein the gate insulating film includes;

a first portion, which is located on a side wall of the trench, wherein the first portion is composed of a plurality of insulating films; and

a second portion, which is located at least on an opening portion and a bottom portion of the trench, wherein the second portion is composed of only a single insulating film and the thickness of the second portion is greater than that of the first portion.

13. A trench-gate type transistor, comprising:

a semiconductor substrate in which a trench is formed; and

a gate insulating film located on an inner wall of the trench, wherein the gate insulating film includes;

a first portion, which is located only on a bottom region of the trench, wherein the first portion is composed of a plurality of insulating films; and

a second portion, wherein the second portion is composed of only a single insulating film and the thickness of the second portion is greater than that of the first portion.

14. A semiconductor device comprising:

a semiconductor substrate having a main surface, wherein a trench is formed in the main surface;

an insulating film located on an inner wall of the trench, wherein the insulating film includes;

a first portion composed of a first oxide film, a nitride film, and a second oxide film, wherein the first portion is located on a sidewall of the trench; and

a second portion consisting of an oxide film, wherein the second portion is located at least on an upper inlet portion the trench, and the thickness of the second portion is greater than that of the first portion.

15. The semiconductor device according to claim 14, wherein the second portion is located on both the upper inlet portion and a bottom portion of the trench.

16. The semiconductor device according to claim 15, wherein the substrate includes a trench gate type transistor structure that comprises:

a first semiconductor layer of a first conductivity type, wherein the first semiconductor layer is located at the main surface;

a second semiconductor layer of a second conductivity type, wherein the second semiconductor layer encompasses the first semiconductor layer, and wherein the trench penetrates the first and second semiconductor layers, and an upper boundary between the first portion and the second portion located at the upper inlet portion of the trench is located above a boundary between the first and second semiconductor layers;

a third semiconductor layer of the first conductivity type, wherein the third semiconductor layer is located under the second semiconductor layer, and a lower boundary between the first portion and the second portion located at the bottom portion of the trench is located below a boundary between the second and third semiconductor layers; and

a gate electrode buried in the trench, wherein the insulating film serves as a gate insulating film.

17. The semiconductor device according to claim 14, wherein the substrate includes a trench gate type transistor structure that comprises:

a first semiconductor layer of a first conductivity type, wherein the first semiconductor layer is located at the main surface;

a second semiconductor layer of a second conductivity type, wherein the second semiconductor layer encompasses the first semiconductor layer, wherein a boundary between the first portion and the second portion of the insulation film is located at the upper inlet portion of the trench and above a boundary between the first and second semiconductor layers;

a third semiconductor layer of the first conductivity type, wherein the third semiconductor layer is located under the second semiconductor layer, wherein the trench is formed from the main surface into the third semiconductor layer and penetrates the first and second semiconductor layers; and

a gate electrode buried in the trench, wherein the insulating film serves as a gate insulating film.

18. The semiconductor device according to claim 14, wherein oxide film of the second portion is formed by thermal oxidation that is performed for forming the second oxide film of the first portion after the first oxide film and the nitride film are formed on the side wall.