Semiconductor device and method for manufacturing the same

Abstract

A semiconductor device A1 comprises: a semiconductor layer 11 that has a trench 10; an insulating film 12 that covers an inner surface 10a of the trench; a conductor 13 that is buried in the trench covered by the insulating film; and a Schottky junction layer 15 that forms a Schottky junction with a semiconductor layer surface 11a which is adjacent to the trench. A surface 13a of the conductor is positioned lower than the semiconductor layer surface. The semiconductor layer surface has, in a section thereof adjacent to an inner wall surface 10a1 of the trench, an inclined section 11a1 that is displaced further downward as the proximity of the semiconductor layer surface to the inner wall surface increases.

Description

[Technical field]

[0001] The present disclosure relates to a semiconductor device and a method for manufacturing a semiconductor device. [Background technology]

[0002] Conventionally, a semiconductor device having a Schottky junction has been manufactured as described in JP 2012-9756 A. In this semiconductor device, an insulating film is formed on a surface of a semiconductor layer having a trench, a conductor is embedded in the trench, the insulating film on the surface of the semiconductor layer adjacent to the trench is removed by etching to expose the surface of the semiconductor layer, and a Schottky junction is formed on the surface of the semiconductor layer. In JP 2012-9756 A, the upper surfaces of the insulating film and conductor at the upper opening of the trench are concave, and the upper surfaces of the insulating film and conductor and the surface of the semiconductor layer are covered with a barrier metal. Summary of the Invention

[0003] A semiconductor device according to one embodiment of the present disclosure includes a semiconductor layer having a trench, an insulating film covering an inner surface of the trench, a conductor embedded in the trench covered with the insulating film, and a Schottky junction layer forming a Schottky junction with a semiconductor layer surface adjacent to the trench, the surface of the conductor being located below the semiconductor layer surface, and the semiconductor layer surface having an inclined portion adjacent to an inner wall surface of the trench that is displaced downward as it approaches the inner wall surface. The upper end surface of the insulating film covering the inner wall surface is continuous with the inclined portion, inclined in the same direction as the inclined portion, and has a convex curved shape in which the inclination angle gradually increases as it approaches the conductor. .

[0004] A method for manufacturing a semiconductor device according to one embodiment of the present disclosure includes forming an insulating film on a surface of a semiconductor layer having a trench, filling the trench with a conductor, removing the insulating film on the surface of the semiconductor layer adjacent to the trench by etching to expose the surface of the semiconductor layer, and forming a Schottky junction on the surface of the semiconductor layer. In the etching, the upper end surface of the insulating film covering the inner wall surface of the trench is lowered below the surface of the semiconductor layer, and the R of the corner formed by the surface of the semiconductor layer and the inner wall surface is increased by anisotropic etching. [Brief description of the drawings]

[0005] [Figure 1] 1 is a schematic cross-sectional view illustrating a semiconductor device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is an enlarged view corresponding to FIG. [Diagram 3] 2A to 2C are schematic cross-sectional views for explaining a manufacturing process of the semiconductor device shown in FIG. [Figure 4] FIG. 4 is an enlarged view corresponding to FIG. 3. [Diagram 5] 4 is a schematic cross-sectional view for explaining the manufacturing process following FIG. 3. [Figure 6] FIG. 6 is an enlarged view corresponding to FIG. [Figure 7] FIG. 1 is a schematic cross-sectional view showing a semiconductor device of a comparative example. [Figure 8] 1 is a graph showing reverse voltage-current characteristics of an example of the present disclosure and a comparative example. [Figure 9] FIG. 9 is a partially enlarged view of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings. [Semiconductor Device] 1, a semiconductor device A1 according to an embodiment of the present disclosure includes a semiconductor layer 11 having a trench 10, an insulating film 12, a conductor 13, and a Schottky junction layer 15. The insulating film 12 covers an inner surface 10a of the trench 10. The conductor 13 is embedded in the trench 10 covered with the insulating film 12. The Schottky junction layer 15 forms a Schottky junction with a semiconductor layer surface 11a adjacent to the trench 10. For example, polysilicon may be used as the conductor 13. For example, silicon may be used as the semiconductor layer 11, and a silicon oxide film may be used as the insulating film 12. For example, the Schottky junction layer 15 is a barrier metal such as nickel, molybdenum, or platinum.

[0007] As shown in FIG. 2, a surface 13a of the conductor 13 is located below a surface 11a of the semiconductor layer. The semiconductor layer surface 11a has an inclined portion 11a1 adjacent to the inner wall surface 10a1 of the trench 10, which is displaced downward as it approaches the inner wall surface 10a1. This improves the step coverage of the surface of the underlying layer of the Schottky junction layer 15. This also alleviates electric field concentration during application of a reverse voltage and the resulting stress concentration, making it possible to suppress the leakage current to a low level.

[0008] The upper end surface 12a of the insulating film 12 covering the inner wall surface 10a1 is continuous with the inclined portion 11a1 and is inclined in the same direction as the inclined portion 11a1. That is, when tracing from the center of the semiconductor layer surface 11a to the surface 13a of the conductor 13, the inclined portion 11a1 and the upper end surface 12a are inclined downward. This improves the step coverage of the surface of the underlying layer of the Schottky junction layer 15 around the Schottky junction. This also alleviates the electric field concentration during application of a reverse voltage and the resulting stress concentration, making it possible to suppress the leakage current to a low level.

[0009] The inclined portion 11a1 has a convex curved shape with an inclination angle that gradually increases toward the inner wall surface 10a1. The inclination angle is an angle between a tangent at a point on the inclined portion 11a1 and a tangent at the top (flat portion) of the semiconductor layer surface 11a in a cross section perpendicular to the inner wall surface 10a1 shown in Figures 1 and 2. This improves the step coverage of the underlying layer surface of the Schottky junction layer 15. Furthermore, electric field concentration during application of a reverse voltage and the resulting stress concentration are alleviated, making it possible to suppress leakage current to a low level.

[0010] Moreover, the upper end surface 12a of the insulating film 12 covering the inner wall surface 10a1 has a convex curved shape whose inclination angle gradually increases toward the conductor 13. This improves the step coverage of the surface of the underlying layer of the Schottky junction layer 15 around the Schottky junction. This also alleviates electric field concentration during application of a reverse voltage and the resulting stress concentration, making it possible to suppress the leakage current to a low level.

[0011] [Method of manufacturing a semiconductor device] An example of a manufacturing method for obtaining the above-mentioned semiconductor device A1 will be described. (Insulating film formation, conductor embedding process) 3 and 4, an insulating film 12 is formed on a surface of a semiconductor layer 11 having a trench 10, and a conductor 13 is embedded in the trench 10. The surface of the conductor 13 is etched so that a surface 13a of the conductor 13 is positioned below a surface 11a of the semiconductor layer.

[0012] (Insulating film etching process) Next, the insulating film 12 on the semiconductor layer surface 11a adjacent to the trench 10 is removed by etching to expose the semiconductor layer surface 11a as shown in Figs. 5 and 6. At this time, the insulating film 12 is over-etched to fully expose the semiconductor layer surface 11a. As a result, the upper end surface 12a of the insulating film 12 covering the inner wall surface 10a1 of the trench 10 is etched deeper. As shown in Figs. 5 and 6, the upper end surface 12a is located below the semiconductor layer surface 11a. In this case, the insulating film on the semiconductor layer surface 11a is sufficiently removed. Note that in the description of the present semiconductor device and its manufacturing method, the up and down refer to the direction in which the trench 10 is dug down from the surface of the semiconductor layer 11 as down, and the opposite direction as up, and do not refer to the up and down direction (gravity direction) during the manufacturing or use of the present semiconductor device.

[0013] In the above etching, the upper end surface 12a of the insulating film 12 covering the inner wall surface 10a1 of the trench 10 is lowered below the semiconductor layer surface 11a, and the R of the corner formed by the semiconductor layer surface 11a and the inner wall surface 10a1 is increased by anisotropic etching. When the semiconductor layer 11 is silicon and the insulating film 12 is a silicon oxide film, an etching gas species capable of etching these and having strong anisotropy, such as CF4, CF3, etc., may be used. As the etching progresses, the semiconductor layer surface 11a is exposed from the insulating film 12, and then the corner formed by the semiconductor layer surface 11a and the inner wall surface 10a1 is exposed to the etching gas. However, due to the strong anisotropy, the etching also progresses in the lateral direction. As a result, the curved inclined portion 11a1 as described above is formed. Similarly, the curved upper end surface 12a as described above is formed by anisotropic etching.

[0014] (Schottky junction formation process) Thereafter, a Schottky junction layer 15 is formed on the semiconductor layer surface 11a to form a Schottky junction, thereby obtaining the semiconductor device A1 having the structure shown in Figures 1 and 2. Other necessary steps are then carried out to complete the semiconductor device A1.

[0015] [Comparison of reverse characteristics] 7 shows a semiconductor device B1 of a comparative example, which is different from the semiconductor device A1 of the above-described embodiment only in that it does not have the inclined portion 11a1 and the semiconductor layer surface 11a is flat, but is otherwise the same. When the reverse voltage-current characteristics were simulated for the semiconductor device A1 of this embodiment and the semiconductor device B1 of the comparative example under common conditions, the results were as shown in Fig. 8. A portion 80 of the graph shown in Fig. 8 is enlarged and shown in Fig. 9. As shown in FIGS. 8 and 9, the semiconductor device A1 of this embodiment was able to suppress the reverse current lower than the semiconductor device B1 of the comparative example, and the reverse characteristics were improved. It was confirmed that the step coverage of the surface of the underlayer of the Schottky junction layer 15 described above was improved, and the electric field concentration during application of a reverse voltage and the resulting stress concentration were alleviated, thereby making it possible to suppress the leakage current to a low level.

[0016] [Summary, etc.] According to the semiconductor device of the above embodiment of the present disclosure, leakage current at the edge of the Schottky junction can be suppressed to a low level when a reverse voltage is applied. Furthermore, the insulating film on the semiconductor layer surface 11a is sufficiently removed, and the Schottky junction characteristics are excellent. According to the manufacturing method of the embodiment of the present disclosure, the step coverage of the surface of the underlayer of the Schottky junction layer 15 is improved, and a semiconductor device can be manufactured in which the leakage current during application of a reverse voltage can be kept low. Furthermore, in the manufactured semiconductor device, the insulating film on the semiconductor layer surface 11a is sufficiently removed, and the Schottky junction characteristics are excellent.

[0017] Although an embodiment of the present disclosure has been described above, this embodiment is shown by way of example only, and the present disclosure can be embodied in various other forms, and components can be omitted, substituted, or modified without departing from the spirit of the invention. [Industrial Applicability]

[0018] The present disclosure can be utilized in a semiconductor device and a method for manufacturing a semiconductor device. [Explanation of symbols]

[0019] 10. Trench 11 Semiconductor layer 11a Semiconductor layer surface 11a1 Inclined section 12 Insulating film 13 Conductors 15 Schottky junction layer A1 Semiconductor device

Claims

1. a semiconductor layer having a trench; an insulating film covering an inner surface of the trench; a conductor buried in the trench covered with the insulating film; a Schottky junction layer forming a Schottky junction with a surface of the semiconductor layer adjacent to the trench; Equipped with the surface of the conductor is located below the surface of the semiconductor layer; the surface of the semiconductor layer has an inclined portion adjacent to an inner wall surface of the trench, the inclined portion being displaced downward as it approaches the inner wall surface, A semiconductor device in which an upper surface of an insulating film covering the inner wall surface is continuous with the inclined portion, inclined in the same direction as the inclined portion, and has a convex curved shape in which the inclination angle gradually increases as it approaches the conductor.

2. 2. The semiconductor device according to claim 1, wherein the inclination angle is the angle between a tangent at a point on the inclined portion in a cross section perpendicular to the inner wall surface and a tangent at the top of the semiconductor layer surface, and the inclination angle is a convex curved shape in which the inclination angle gradually increases as it approaches the inner wall surface.

3. 1. A method for manufacturing a semiconductor device, comprising the steps of: forming an insulating film on a surface of a semiconductor layer having a trench; burying a conductor in the trench; removing the insulating film on the surface of the semiconductor layer adjacent to the trench by etching to expose the surface of the semiconductor layer; and forming a Schottky junction on the surface of the semiconductor layer, In the etching, the upper surface of the insulating film covering the inner wall surface of the trench is lowered below the surface of the semiconductor layer, and the R of the corner formed by the surface of the semiconductor layer and the inner wall surface is increased by anisotropic etching.

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