Semiconductor device

Abstract

The present invention raises withstand voltage by reducing the concentration of an electric field at an end of a field plate 7 provided in a termination region 102. A semiconductor device 100 comprises an active region 101 having a semiconductor element, and a termination region 102 surrounding the active region 101. The termination region 102 has a first conductivity type drift layer 1, a second conductivity type field limiting layer 3 formed on a part of the surface of the drift layer 1, a field insulating film 8 covering the drift layer 1 and the field limiting layer 3, and a field plate 7 electrically connected to the field limiting layer 3. The field plate 7 is formed on the surface of the field insulating film 8 so as to extend to the outside of the field limiting layer 3. The field insulating film 8 is gradually thicker toward the end of the field plate 7 in a region overlapping the field plate 7.

Description

Semiconductor Devices

[0001] The present invention relates to a semiconductor device.

[0002] In semiconductor devices, a structure for alleviating the electric field in the termination region is provided to ensure a sufficient breakdown voltage. One example of such a structure is a field limiting layer and a field plate electrically connected to the field limiting layer. The field plate is formed to extend beyond the edge of the field limiting layer to avoid electric field concentration at the edge of the field limiting layer.

[0003] Such a technique is disclosed, for example, in FIGS. 1 and 2 of Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2003-158258

[0005] The longer the distance between the edge of the field limiting layer and the edge of the field plate, the stronger the effect of the field plate in alleviating the electric field at the edge of the field limiting layer.

[0006] However, the longer this distance is, the smaller the radius of curvature of the equipotential lines that wrap around the edge of the field plate becomes, which makes it easier for the electric field to concentrate at the edge of the field plate, resulting in a problem of reduced breakdown voltage.

[0007] The problem to be solved by the present invention is to provide a semiconductor device that can reduce the concentration of an electric field at the end of a field plate provided in a termination region and increase the breakdown voltage.

[0008] In order to solve the above-mentioned problems, a semiconductor device of the present invention is a semiconductor device having an active region having a semiconductor element and a termination region surrounding the active region, wherein the termination region has a drift layer of a first conductivity type, a field limiting layer of a second conductivity type formed on a part of the surface of the drift layer, a field insulating film covering the drift layer and the field limiting layer, and a field plate electrically connected to the field limiting layer, wherein the field plate is formed on the surface of the field insulating film and extends to the outside of the field limiting layer, and the thickness of the field insulating film increases in a region overlapping with the field plate as it approaches an end of the field plate.

[0009] According to the semiconductor device of the present invention, the concentration of the electric field at the end of the field plate provided in the termination region can be alleviated, and the breakdown voltage can be increased.

[0010] 1A and 1B are a top view and a cross-sectional view of a semiconductor device according to a first embodiment of the present invention, respectively, and are cross-sectional views of a semiconductor device according to a second embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing and each embodiment, the same or similar components are designated by the same reference numerals, and redundant explanations will be omitted.

[0012] 1 is a top view of a semiconductor device according to Example 1. FIG. 2 is a cross-sectional view taken along line AA' in FIG.

[0013] The semiconductor device 100 of this embodiment has an active region 101 having a semiconductor element, and a termination region 102 surrounding the active region 101 .

[0014] Examples of semiconductor elements that can be used include an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a diode, etc. In this embodiment, an example in which the present invention is applied to an IGBT will be described.

[0015] In this embodiment, the conductivity types of the semiconductor layers will be described by taking as an example a case where the first conductivity type is n-type and the second conductivity type is p-type. However, this is not limited thereto, and the first conductivity type may be p-type and the second conductivity type may be n-type. Furthermore, the impurity concentration of the semiconductor layers will be described by taking as an example, but is not limited thereto and can be changed as appropriate within the range in which the intended operation of the embodiment can be realized.

[0016] The active region 101 includes a drift layer 1 of a first conductivity type, a well layer 2 of a second conductivity type, a first main electrode 5, a collector layer 9 of a second conductivity type, and a second main electrode 10. In the case of an IGBT, the first main electrode 5 is an emitter electrode, and the second main electrode 10 is a collector electrode. The active region 101 also includes a gate electrode, a gate insulating film, an emitter layer of the first conductivity type, a channel layer of the second conductivity type, a body layer of the second conductivity type, and the like, all of which are not shown. The impurity concentrations of each semiconductor layer are, for example, low concentration n- for the drift layer 1, medium concentration p for the well layer 2, high concentration p+ for the collector layer 9, high concentration n+ for the emitter layer, medium concentration p for the channel layer, and medium concentration p for the body layer. The configuration of the active region 101 is similar to that of a general semiconductor element, and therefore a detailed description thereof will be omitted.

[0017] Termination region 102 has drift layer 1 of a first conductivity type, field limiting layer 3 of a second conductivity type formed on part of the surface of drift layer 1, field insulating film 8 covering drift layer 1 and field limiting layer 3, and field plate 7 electrically connected to field limiting layer 3. Note that, although field limiting layer 3 and field plate 7 are insulated from each other by field insulating film 8 at the location shown in Figure 2, they are electrically connected at a connection portion shown in Figure 4, which will be described later.

[0018] The field limiting layer 3 is, for example, a field limiting ring. The impurity concentration of the field limiting layer 3 is, for example, a medium concentration of p. The field insulating film 8 is, for example, an oxide film.

[0019] In this embodiment, the case where there is one pair of field limiting layer 3 and field plate 7 is illustrated, but this is not limited to this, and a configuration may also be used in which a plurality of field limiting layers 3 are provided side by side, and a field plate 7 is provided corresponding to each of them.

[0020] Field plate 7 is formed on the surface of field insulating film 8, extending to the outside of field limiting layer 3. The longer the distance L between the end of field limiting layer 3 and the end of field plate 7, the stronger the electric field relaxation effect of field plate 7 at the end of field limiting layer 3. However, the longer this distance L, the smaller the radius of curvature of equipotential lines 11 that wrap around the end of field plate 7, which makes it easier for the electric field to concentrate at the end of field plate 7, posing a problem of reduced breakdown voltage.

[0021] Therefore, in this embodiment, the field insulating film 8 is configured so that, in the region overlapping the field plate 7, the thickness increases as it approaches the edge of the field plate 7. More specifically, in the region overlapping the field plate 7, the surface of the field insulating film 8 becomes higher in a stepped manner as it approaches the edge of the field plate 7. This type of shape for the field insulating film 8 can be achieved, for example, by repeatedly forming and etching an insulating film using multiple masks. The number of stepped steps is preferably three or more. Furthermore, in the region overlapping the field plate 7 and outside the field limiting layer 3, the surface of the field insulating film 8 preferably becomes higher as it approaches the edge of the field plate 7.

[0022] According to this embodiment, the equipotential lines 11 are inclined along the lower part of the stepped field plate 7 (the surface of the field insulating film 8), and therefore the radius of curvature of the equipotential lines 11 that wrap around the end of the field plate 7 is increased, thereby alleviating the concentration of the electric field at the end of the field plate 7 and increasing the breakdown voltage.

[0023] FIG. 3 is a cross-sectional view of a semiconductor device of a comparative example.

[0024] In the semiconductor device 100 of the comparative example, the surface of the field insulating film 8 and the field plate 7 have a flat shape at least outside the field limiting layer 3. Therefore, it can be seen that the radius of curvature of the equipotential lines 11 that wrap around the end of the field plate 7 is smaller than in this example.

[0025] As can be seen from the comparison between this embodiment and the comparative example, this embodiment can alleviate the concentration of the electric field at the end of the field plate 7 provided in the termination region 102, thereby increasing the breakdown voltage.

[0026] As shown in FIG. 2, in this embodiment, the termination region 102 also includes a channel stopper 4 of the first conductivity type, a field stopper electrode 6, and an interlayer insulating film 12.

[0027] The channel stopper 4 is formed on a part of the surface of the drift layer 1, and is arranged outside the field limiting layer 3 and the field plate 7. The field stopper electrode 6 is electrically connected to the channel stopper 4.

[0028] Interlayer insulating film 12 is formed to cover field plate 7 and field insulating film 8 .

[0029] FIG. 4 is a cross-sectional view of a connection portion according to the first embodiment.

[0030] At the connection portion electrically connecting the field limiting layer 3 and the field plate 7, the field insulating film 8 has a contact hole 13 at a position overlapping the field limiting layer 3 for electrically connecting the field limiting layer 3 and the field plate 7. Note that the contact hole 13 is also formed in the field plate 7 and the interlayer insulating film 12. The field limiting layer 3 and the field plate 7 are electrically connected using a connection electrode 14. The connection electrode 14 can be formed simultaneously with the first main electrode 5 and the field stopper electrode using the same material. Note that the connection electrode 14 is not shown in FIG. 1 . The structure of the connection portion is not limited to the structure shown in FIG. 4 .

[0031] FIG. 5 is a cross-sectional view of a semiconductor device according to a second embodiment.

[0032] Example 2 is a modification of Example 1. In this example, in the region overlapping with the field plate 7, the surface of the field insulating film 8 becomes higher in a curved shape as it approaches the end of the field plate 7. Such a shape of the field insulating film 8 can be achieved by, for example, isotropic wet etching.

[0033] According to the present embodiment, the field plate 7 is curved, and therefore the radius of curvature of the equipotential lines 11 that wrap around the end of the field plate 7 can be made larger than in the first embodiment, thereby alleviating the concentration of the electric field at the end of the field plate 7 and increasing the breakdown voltage more than in the first embodiment.

[0034] Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible within the scope of the technical concept of the present invention. In addition, some or all of the configurations described in each embodiment may be combined and applied.

[0035] 1: Drift layer 2: Well layer 3: Field limiting layer 4: Channel stopper 5: First main electrode 6: Field stopper electrode 7: Field plate 8: Field insulating film 9: Collector layer 10: Second main electrode 11: Equipotential line 12: Interlayer insulating film 13: Contact hole 14: Connection electrode 100: Semiconductor device 101: Active region 102: Termination region

Claims

1. A semiconductor device having an active region with a semiconductor element and a termination region surrounding the active region, wherein the termination region includes a drift layer of a first conductivity type, a field limiting layer of a second conductivity type formed on a part of the surface of the drift layer, a field insulating film covering the drift layer and the field limiting layer, and a field plate electrically connected to the field limiting layer, the field plate is formed to extend to the outside of the field limiting layer on the surface of the field insulating film, and the field insulating film is thicker as it approaches the end of the field plate in a region overlapping the field plate. A semiconductor device characterized by this.

2. In claim 1, in a region overlapping the field plate, the surface of the field insulating film becomes stepwise higher as it approaches the end of the field plate. A semiconductor device characterized by this.

3. In claim 2, the number of steps of the stepwise shape is three or more. A semiconductor device characterized by this.

4. In claim 1, in a region overlapping the field plate, the surface of the field insulating film becomes curved higher as it approaches the end of the field plate. A semiconductor device characterized by this.

5. In claim 1, in a region overlapping the field plate and outside the field limiting layer, the surface of the field insulating film becomes higher as it approaches the end of the field plate. A semiconductor device characterized by this.

6. In claim 1, the field insulating film has a contact hole for electrically connecting the field limiting layer and the field plate at a position overlapping the field limiting layer. A semiconductor device characterized by this.

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