Semiconductor device

Abstract

Semiconductor device comprising: a semiconductor substrate of a first conductivity type and consisting of a semiconductor material with a larger band gap than silicon; a control electrode (5) which is provided on a first main surface of the semiconductor substrate; an output electrode (7) which is provided on a second main surface and a side surface of the semiconductor substrate and forms a Schottky contact with the second main surface of the semiconductor substrate; and a layer (20) which is provided at least at an outer circumferential edge (20a) of the semiconductor substrate and reduces a residual current arising from at least the outer circumferential edge (20a), wherein the layer (20) which reduces the residual current is a second semiconductor region (26) of a second conductivity type, is provided in a surface layer of the second main surface of the semiconductor substrate and comes into contact with the output electrode (7) at the second main surface and the lateral surface of the semiconductor substrate.

Description

Area

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

[0002] In recent years, the use of bidirectional switching elements for direct conversion circuits, such as matrix converters, has received considerable attention in semiconductor power conversion devices. Matrix converters can perform AC / AC conversion, AC / DC conversion, and DC / AC conversion, for example. Much attention has been paid to the use of bidirectional switching elements for direct conversion circuits because their use can reduce the size and weight of a circuit, improve efficiency and performance, and reduce costs.

[0003] The matrix converter has a higher power conversion efficiency than an inverter / converter. While the inverter / converter generates an intermediate DC voltage from an AC power supply and converts this intermediate voltage into an AC voltage, the matrix converter generally does not generate the intermediate voltage, but instead generates the AC voltage directly from the AC power supply.

[0004] In addition, the service life of the inverter / converter is determined by the service life of an electrolytic capacitor, since the electrolytic capacitor is used as a capacitor for generating the intermediate voltage. In contrast, the capacitor for generating the intermediate voltage between the AC power supply and an AC output unit in the matrix converter does not need to be provided. Therefore, it is possible to circumvent the problems of the inverter / converter.

[0005] Fig. Figure 11 is an equivalent circuit diagram illustrating the matrix converter. Fig. 12 is an equivalent circuit diagram illustrating a prior art reverse blocking semiconductor device. Fig. Figure 13 is a characteristic diagram illustrating the electrical behavior of the reverse blocking semiconductor device according to the prior art. As shown in Fig. 12 is a for the in Fig. 11, the power semiconductor element 101 used in the matrix converter is a reverse blocking semiconductor device having a structure in which two transistors 102 having a reverse breakdown voltage are connected in antiparallel. As shown in Fig. 13, the reverse blocking semiconductor device has a general forward breakdown voltage (a positive voltage is applied to the drain terminal based on the source potential) and also has a reverse breakdown voltage (a negative voltage is applied to the drain terminal based on the source potential) with the same value as that of the forward breakdown voltage.

[0006] Fig. 14 is a sectional view illustrating a reverse blocking semiconductor device according to the prior art. Fig. The reverse blocking semiconductor device illustrated in Figure 14 has a MOS gate structure including a p-well region 202, an n +-source region 203, a gate oxide film 204, a gate electrode 205, and a source electrode 206 on a front surface of a semiconductor substrate, which is an n-type drift region 201. A p-type region (hereinafter referred to as a field plate (FP)) 207 is provided at the end of the front surface of the semiconductor substrate. A p-type region 208, which comes into contact with the FP 207 and extends from the front surface to the back surface of the semiconductor substrate, is provided on the side surface of the semiconductor substrate. A drain electrode 209, which is connected to the n- - -Drift region 201 is provided on the back surface of the semiconductor substrate.

[0007] As the reverse blocking semiconductor device of the prior art, a device has been proposed in which a MOS gate structure including a gate electrode and an emitter electrode is formed in a surface layer of an n - -drift layer, which is a semiconductor substrate with a GaN semiconductor or a SiC semiconductor as the main semiconductor crystal, is provided, a cross section for making a chip, a p-protection region, which is the front surface and the back surface of the n - -drift layer and a collector electrode which is connected to the back surface of the n - -drift layer, contains a Schottky metal film (see, for example, the following Patent Literature 1).

[0008] As another prior art reverse blocking semiconductor device, a device has been proposed that includes a silicon substrate, a buffer layer formed on the silicon substrate, a gallium nitride semiconductor layer formed on the buffer layer, a trench groove formed from the back surface of the silicon substrate through the silicon substrate and the buffer layer to a depth reaching the gallium nitride semiconductor layer, and a metal film formed in the trench groove. In the device, the metal film and the gallium nitride semiconductor layer form a Schottky junction (see, for example, the following Patent Literature 2). Another generic semiconductor device is disclosed in Patent Literature 3. List of publicationsPatent literature Patent literature 1: JP 2009-123 914 A Patent literature 2: JP 2010-258 327 A Patent literature 3: JP 2002-299 624 A Short descriptionTechnical problem

[0009] However, in the method disclosed in Patent Literature 1, it is difficult to form, for example, by ion implantation and annealing, a semiconductor region of a conductivity type different from the conductivity type of the semiconductor substrate with a desired width and depth in the cross-section (hereinafter referred to as the side surface) of the semiconductor substrate cut into a chip shape. Therefore, it is necessary to develop a semiconductor device with a structure capable of easily achieving a reverse breakdown voltage. Furthermore, in the method disclosed in Patent Literature 1, there is a concern that a reverse leakage current increases in the outer peripheral parts of the front and back surfaces of the semiconductor substrate when a reverse voltage is applied to the drain electrode. When the reverse leakage current is induced, the reverse breakdown voltage decreases.

[0010] An object of the invention is to provide a semiconductor device with a high reverse breakdown voltage to solve the above-mentioned problems in the prior art. Furthermore, another object of the invention is to provide a semiconductor device capable of reducing leakage current to solve the above-mentioned problems in the prior art. Problem solving

[0011] To solve the above-mentioned problems and to achieve the object of the invention, according to a first aspect of the invention, there is provided a semiconductor device according to claim 1. According to a second aspect of the invention, there is provided a semiconductor device according to claim 2. Further aspects of the invention are the subject of the dependent claims, the drawings, and the following description of embodiments.

[0012] In the semiconductor device according to the above aspect of the invention, the first semiconductor region may form an ohmic contact with the output electrode.

[0013] In the semiconductor device according to the above aspect of the invention, the layer that reduces the leakage current may be a second semiconductor region that is of a second conductivity type, is provided in a surface layer of the second main surface of the semiconductor substrate, and comes into contact with the output electrode.

[0014] In the semiconductor device according to the above aspect of the invention, the output electrode may extend from the second main surface to the first main surface of the semiconductor substrate and may be laid over the outer peripheral edge of the first main surface.

[0015] In the semiconductor device according to the above aspect of the invention, the semiconductor substrate may be made of silicon carbide or gallium nitride.

[0016] According to the invention, a depletion layer spreads from both the interface between an n-type drift region, which is the semiconductor substrate, and the output electrode provided on the back surface of the semiconductor substrate, and the interface between the n-type drift region and the output electrode provided on the side surface of the semiconductor substrate. Therefore, unlike the prior art, it is possible to form a reverse-blocking semiconductor device with a structure capable of maintaining the reverse breakdown voltage without the p-type region (which is Fig. 14) in the side surface of the semiconductor substrate. As a result, it is possible to form a semiconductor device with a reverse breakdown voltage more easily than the prior art semiconductor device.

[0017] The leakage current reduction layer covers the n- type drift region exposed from the front surface of the semiconductor substrate and is provided in the outer peripheral part of the semiconductor substrate. Therefore, when the reverse voltage is applied to the drain electrode, it is possible to reduce the reverse leakage current.

[0018] Since the semiconductor substrate made of a semiconductor material (hereinafter referred to as wide band gap semiconductor material) having a wider band gap than silicon is used, it is possible to improve the reverse breakdown voltage maintained by the Schottky contact between the n- type drift region and the output electrode compared to the case where the semiconductor substrate made of silicon is used. Advantageous effects of the invention

[0019] According to the semiconductor device of the invention, it is possible to improve the reverse breakdown voltage. Furthermore, it is possible to reduce the leakage current. Brief description of the drawings Fig. 1 is a sectional view illustrating a semiconductor device according to an embodiment; Fig. 2 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 3 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 4 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 5 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 6 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 7 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 8 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 9 is a sectional view illustrating another example of the semiconductor device according to the embodiment; Fig. 10 is a characteristic diagram illustrating the electrical behavior of the semiconductor device according to the embodiment; Fig. 11 is an equivalent circuit diagram illustrating a matrix converter; Fig. 12 is an equivalent circuit diagram illustrating a prior art reverse blocking semiconductor device; Fig. 13 is a characteristic diagram illustrating the electrical behavior of the reverse blocking semiconductor device according to the prior art; and Fig. 14 is a sectional view illustrating the reverse blocking semiconductor device according to the prior art. Description of embodiments

[0020] A semiconductor device according to an exemplary embodiment of the invention will be described in detail below with reference to the accompanying drawings. In the description and the accompanying drawings, in the layers or regions with an "n" or "p" appended, an electron or a hole represents a majority carrier. Furthermore, symbols "+" and "-" added to n or p indicate that the impurity density is higher and lower than that of the layers without the symbols. In the description of the following embodiment and the accompanying drawings, like components are denoted by the same reference numerals, and their descriptions will not be repeated. (Embodiment)

[0021] Fig. 1 is a sectional view illustrating a semiconductor device according to an embodiment. Fig. The semiconductor device illustrated in Figure 1 includes an active region 10, in which a current flows when the semiconductor device is turned on, and a breakdown voltage structure portion 11 surrounding the active region 10. The breakdown voltage structure portion 11 is provided in an outer peripheral portion of an n- (first conductivity type) semiconductor substrate, which will be an n--drift region 1. The breakdown voltage structure portion 11 is in the Fig. 1, are arranged on the left and right sides of the active region 10. The semiconductor substrate consists of a semiconductor material (a so-called "wide bandgap semiconductor material") with a larger bandgap than silicon.

[0022] Specifically, it is preferable that the semiconductor substrate be made of, for example, silicon carbide (SiC) or gallium nitride (GaN). When the semiconductor substrate made of the wide-band-gap semiconductor material is used, it is possible to improve the reverse breakdown voltage maintained by a Schottky junction, which will be described later, compared to the case where a semiconductor substrate made of silicon is used. Furthermore, when the semiconductor substrate made of the wide-band-gap semiconductor material is used, it is possible to manufacture a semiconductor device with low loss and high efficiency compared to the case where the semiconductor substrate made of silicon is used.

[0023] In the active region 10, a p-well region 2 is selectively provided in a surface layer of the front surface (the first main surface) of the semiconductor substrate. A gate electrode 3 is selectively provided in a surface layer of the p-well region 2. A gate electrode 5 is provided on the surface of the p-well region 2, which is exposed from the front surface of the semiconductor substrate between the n- type drift regions 1 and 3, with a gate oxide film 4 interposed therebetween.

[0024] A source electrode 6 comes with the p-well region 2 and the n +-Source region 3. Furthermore, the source electrode 6 is insulated from the gate electrode 5 by an interlayer insulating film (not shown). In the active region 10, a MOS gate structure, including, for example, the p-well region 2, the gate electrode 3, the gate electrode 5, and the source electrode 6, is provided on the front surface of the semiconductor substrate.

[0025] A drain electrode (output electrode) 7, which is connected to the n -The drain electrode 7, which contacts the drift region 1, is provided on the cut surface (hereinafter referred to as a side surface) of the semiconductor substrate, which is cut into a chip shape from the back surface (the second main surface) of the semiconductor substrate. The drain electrode 7 is provided so as to extend from the active region 10 to the breakdown voltage structure part 11, and is also provided on the entire back and side surfaces of the semiconductor substrate.

[0026] The drain electrode 7 is provided to form a Schottky junction with the n-type drift region 1, which is the semiconductor substrate. The Schottky junction between the drain electrode 7 and the n-type drift region 1 is formed on the entire back and side surfaces of the semiconductor substrate. Thus, when a reverse bias is applied to the drain electrode 7, a depletion layer spreads from the interface between the n-type drift region 1 and the drain electrode 7 to the back and side surfaces of the semiconductor substrate. Therefore, it is possible to maintain the reverse breakdown voltage of the semiconductor device.

[0027] For example, the side surface of the drain electrode 7 may be inclined such that the width of the semiconductor substrate gradually increases from the back surface (drain) to the front surface (source) (tapered shape). Furthermore, the side surface of the drain electrode 7 may, for example, be inclined such that the width of the semiconductor substrate gradually increases from the front surface (source) to the back surface (drain) (tapered shape), or the side surface may be perpendicular to the front surface of the semiconductor substrate.

[0028] As in Fig. 1, as the breakdown voltage structure part 11, a layer (hereinafter referred to as a leakage current reducing layer) 20, which reduces a leakage current from the outer peripheral edge of the semiconductor substrate, is provided at least on the outer peripheral edge of the semiconductor substrate. As shown in the sectional view in Fig. As shown in Figure 1, the leakage current reducing layer 20 is provided at least between the left and right outer peripheral edges of the breakdown voltage structure portion 11 and the active region 10. A plurality of p-type guard rings or field confinement rings may be provided on the surface of the breakdown voltage structure portion 11. The p-type guard rings or field confinement rings make it possible to reduce the width of the breakdown voltage structure portion 11.

[0029] When the leakage current reducing layer 20 is provided between the outer peripheral edge of the breakdown voltage structure part 11 and the active region 10, the n - -Drift region 1 in the breakdown voltage structure part 11 is not exposed from the front surface of the semiconductor substrate. Therefore, no charge carrier enters the n -The drift region 1 of the breakdown voltage structure part 11 on the front side of the semiconductor substrate is formed when a negative voltage (reverse voltage) based on the source potential is applied to the drain electrode 7. In this way, it is possible to reduce the leakage current (hereinafter referred to as reverse leakage current) when the reverse voltage is applied.

[0030] In addition, an outer peripheral edge 20a of the leakage current reducing layer 20 is provided so as to come into contact with an upper end 7a of the drain electrode 7. When the outer peripheral edge 20a of the leakage current reducing layer 20 is provided so as to come into contact with the upper end 7a of the drain electrode 7, there is no gap from which the n - -Drift region 1 is exposed, formed between the outer peripheral edge 20a of the residual current reducing layer 20 and the upper end 7a of the drain electrode 7.

[0031] In this way, no charge carrier enters the n - -Drift region 1 is formed in the vicinity of the outer peripheral edge of the semiconductor substrate when the reverse voltage is applied to the drain electrode 7. Therefore, it is possible to reduce a leakage current (hereinafter referred to as reverse leakage current) when the reverse voltage is applied. For example, the leakage current reducing layer 20 may be provided to cover the front surface of the semiconductor substrate, or may be provided in the semiconductor substrate. The leakage current reducing layer 20 surrounds the active region 10, which is in Fig. 1 is not shown.

[0032] Now, with reference to Fig. 2 to 4 different examples of the structure of the with reference to Fig. 1 described residual current reducing layer 20. Fig. 2 to 4 are sectional views illustrating other examples of the semiconductor device according to the embodiment. Fig. 2 and Fig. 4 illustrate examples in which the leakage current reducing layer 20 is provided on the front surface of the semiconductor substrate. Fig. 3 illustrates an example in which the leakage current reducing layer 20 is provided in a surface layer of the front surface of the semiconductor substrate. In the following, the leakage current reducing layer 20 is the Fig. 2 to 4 shows an example of the semiconductor device shown in Fig. 1 shown residual current reducing layer 20 (correspondingly, in the Fig. 5 to 9, the residual current reducing layers 20 of the semiconductor devices are examples of the semiconductor devices shown in Fig. 1 shown residual current reducing layer 20).

[0033] In the Fig. 2, the leakage current reducing layer 20 is an insulating film 21 which covers the n exposed from at least the outer peripheral part of the front surface of the semiconductor substrate. - -drift region 1. The outer peripheral part is a part outside the active region 10 and characterizes the breakdown voltage structure part 11. In the Fig. In the structural example shown in Figure 2, there is no gap from which the n - -Drift region 1 is exposed between the outer peripheral edge 21a of the insulating film 21 and the upper end 7a of the drain electrode 7.

[0034] Fig. 2 shows the semiconductor device in which the insulating film 21 is provided as the leakage current reducing layer 20. In the Fig. 2, the arrangement of the n - -drift region 1, the p-well region 2, the n +-Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0035] As such, since the insulating film 21 is provided as the leakage current reducing layer 20 in the breakdown voltage structure part 11, it is possible to expose the n exposed from the front surface of the semiconductor substrate - -drift region 1. Therefore, when the reverse voltage is applied to the drain electrode 7, the generation of charge carriers in the outer peripheral part of the semiconductor substrate is prevented, and it is possible to prevent an increase in the reverse leakage current.

[0036] In the Fig. In the semiconductor device shown in Figure 3, the leakage current reducing layer 20 is a first p-type region (a first semiconductor region of a second conductivity type) 22, which is provided in a surface layer of the outer peripheral part of the front surface of the semiconductor substrate and comes into contact with the drain electrode 7 provided on the side surface of the semiconductor substrate. The first p-type region 22 is provided so as to be exposed from the outer peripheral edge of the front surface of the semiconductor substrate. In the semiconductor device shown in Fig. In the structural example shown in Figure 3, there is no gap from which the n - -drift region 1 is exposed, between the outer peripheral edge 22a of the first p-region 22 and the upper end 7a of the drain electrode 7.

[0037] Since the first p-type region 22 is provided in the outer peripheral part of the semiconductor substrate, the first p-type region 22 protrudes in a direction opposite to the direction in which the depletion layer spreads from the active region to the breakdown voltage structure part under a forward bias voltage. Therefore, the first p-type region 22 prevents the spread of the depletion layer and functions as a channel stopper. Under a reverse bias voltage, the first p-type region 22 protrudes in the forward direction in which the depletion layer spreads from the drain electrode to the active region. Therefore, the depletion layer spreads to reduce the electric field strength. It is preferable that the junction between the first p-type region 22 and the drain electrode 7 provided on the side surface of the semiconductor substrate be an ohmic contact to stabilize the potential of the drain electrode 7.

[0038] In the Fig. 3, the first p-type region 22 is provided as the leakage current reducing layer 20 and the arrangement of the n - -drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1. Furthermore, an insulating film (not shown) may be provided on a portion of the semiconductor substrate between the first p-type region 22 and the p-well region 2.

[0039] As such, when the first p-region 22 is provided, the depletion layer spreads from the pn junction part between the first p-region 22 and the n --drift region 1. Therefore, when the reverse voltage is applied to the drain electrode 7, it is possible to prevent the generation of a reverse leakage current from a corner portion 41 of the front surface of the semiconductor substrate, where the reverse leakage current is likely to arise. When the first p-type region 22 is provided in the front surface of the semiconductor substrate, the corner portion 41 of the front surface of the semiconductor substrate is the interface between the first p-type region 22 and the drain electrode 7 at the outer peripheral edge of the front surface of the semiconductor substrate.

[0040] In the Fig. In the semiconductor device shown in FIG. 4, a drain electrode 23 is provided from the side surface of the semiconductor substrate to the front surface of the semiconductor substrate and is laid over the outer peripheral edge of the front surface. The drain electrode 23 is provided on the entire back and side surfaces of the semiconductor substrate and a part of the front surface of the semiconductor substrate. The width of a bent part 23a of the drain electrode 23 provided on the front surface of the semiconductor substrate may vary depending on the design conditions of the semiconductor device and may be a value sufficient to cover at least the corner part 41 of the front surface of the semiconductor substrate.In this case, a part (a bent part 23a) of the drain electrode 23 covering the outer peripheral part of the front surface of the semiconductor substrate is the leakage current reducing layer 20.

[0041] In the Fig. 4, the bent part 23a of the drain electrode 23 is provided as the leakage current reducing layer 20 and the arrangement of the n--drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 23, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0042] In the Fig. In the semiconductor device shown in FIG. 4, it is preferable that the bent portion 23a of the drain electrode 23 be provided to cover a portion of the outer peripheral portion including the outer peripheral edge of the front surface of the semiconductor substrate. Furthermore, an insulating film (not shown) may be provided on a portion of the semiconductor substrate between the p-well region 2 and the bent portion 23a of the drain electrode 23.

[0043] In the outer peripheral part of the semiconductor substrate, since the width of a part of the n-type drift region 1, which is located from the end of the bent part 23a of the drain electrode 23 near the active region 10 to the end of the p-well region 2 near the breakdown voltage structure part 11 and is exposed from the front surface of the semiconductor substrate, is reduced, the intensity of the electric field increases in the vicinity of the end of the active region 10 near the breakdown voltage structure part 11. Therefore, the width of the bent part 23a of the drain electrode 23 may vary depending on the design conditions of the semiconductor device.

[0044] The bent portion 23a of the drain electrode 23 causes the depletion layer to spread from the interface between the n--type drift region 1 and the bent portion 23a of the drain electrode 23 on the front surface of the semiconductor substrate when the reverse voltage is applied to the drain electrode 23. Therefore, when the reverse voltage is applied to the drain electrode 23, it is possible to prevent the generation of a reverse leakage current from the corner portion 42 of the front surface of the semiconductor substrate, where the reverse leakage current is likely to be generated. When the n- type drift region 1 is exposed from the entire outer peripheral part of the front surface of the semiconductor substrate, the corner part 42 of the front surface of the semiconductor substrate is the interface between the n- type drift region 1 and the drain electrode 7 at the outer peripheral edge of the front surface of the semiconductor substrate.

[0045] The leakage current reducing layer 20 may be composed of various combinations of the insulating film 21, the first p-type region 22, and the bent portion 23a of the drain electrode 23 provided from the side surface of the semiconductor substrate to the outer peripheral portion of the front surface. Fig. 5 to 9 are sectional views illustrating other examples of the semiconductor device according to the embodiment.

[0046] In the Fig. 5, the leakage current reducing layer 20 includes an insulating film 21 covering a portion of the n- type drift region 1 exposed from at least the outer peripheral portion of the front surface of the semiconductor substrate, and a first p-type region 22 exposed from the outer peripheral edge of the front surface of the semiconductor substrate. In the embodiment shown in Fig. 5 shown semiconductor device are the n --drift region 1 and the first p-region 22 in the outer peripheral part of the semiconductor substrate are exposed from the front surface of the semiconductor substrate.

[0047] Therefore, the insulating film 21 can - -drift region 1 and the first p-region 22, which are exposed from the front surface of the semiconductor substrate. In the Fig. 5, the outer peripheral edge 22a of the first p-region 22 may be provided so that there is no gap from which the n - -Drift region 1 is exposed, between the outer peripheral edge 22a of the first p-type region 22 and the upper end 7a of the drain electrode 7. The outer peripheral edge 21a of the insulating film 21 may be provided such that there is no gap from which the first p-type region 22 is exposed, between the outer peripheral edge 21a of the insulating film 21 and the upper end 7a of the drain electrode 7.

[0048] In the Fig. 5, the insulating film 21 and the first p-type region 22 are used as the leakage current reducing layer 20, and the arrangement of the n - -drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0049] In the Fig. In the semiconductor device shown in Figure 5, since the insulating film 21 and the first p-type region 22 are provided, the insulating film 21 prevents the generation of carriers in the outer peripheral part of the semiconductor substrate, making it possible to prevent an increase in the reverse leakage current. Furthermore, when the reverse voltage is applied to the drain electrode 7, the first p-type region 22 makes it possible to prevent the generation of the reverse leakage current from the corner part 41 of the front surface of the semiconductor substrate, where the reverse leakage current is likely to arise.

[0050] In the Fig. 6, the leakage current reducing layer 20 includes the first p-type region 22 exposed from the outer peripheral edge of the front surface of the semiconductor substrate, and the bent portion 23a of the drain electrode 23 provided from the side surface of the semiconductor substrate to the outer peripheral portion of the front surface. Fig. 6 shown semiconductor device are the n - -drift region 1 and the first p-region 22 in the outer peripheral part of the semiconductor substrate are exposed from the front surface of the semiconductor substrate.

[0051] Therefore, a part (a bent part 23a) of the drain electrode 23 provided on the front surface of the semiconductor substrate covers the first p-type region 22 exposed from the front surface of the semiconductor substrate. In the Fig. 6, the outer peripheral edge 22a of the first p-region 22 is provided so that the n - -Drift region 1 comes into contact with the bent part 23a of the drain electrode 23 without an intermediate gap.

[0052] In the Fig. 6, the first p-type region 22 and the bent part 23a of the drain electrode 23 are provided as the leakage current reducing layer 20, and the arrangement of the n - -drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 23, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0053] When the first p-type region 22 and the bent portion 23a of the drain electrode 23 are provided, the first p-type region 22 per se makes it possible to prevent the generation of a reverse leakage current from the corner portion 41 of the front surface of the semiconductor substrate, where the reverse leakage current is likely to occur. Furthermore, when the reverse voltage is applied to the drain electrode 23, the bent portion 23a of the drain electrode 23 makes it possible to prevent the generation of the reverse leakage current from the corner portion 42 of the front surface of the semiconductor substrate, where the reverse leakage current is likely to occur.

[0054] In the Fig. 7, the leakage current reducing layer 20 includes the insulating film 21 which covers the n exposed from at least the outer peripheral part of the front surface of the semiconductor substrate. --drift region 1, and an auxiliary electrode 24, which comes into contact with the drain electrode 7. In the Fig. In the semiconductor device shown in Figure 7, the insulating film 21 covers at least the corner portion 42 of the front surface of the semiconductor substrate. The auxiliary electrode 24 comes into contact with the drain electrode 7, extends from the drain electrode 7 to the surface of the insulating film 21, and covers a portion of the insulating film 21. The auxiliary electrode 24 cannot form the Schottky contact because it is not connected to the n - -Drift area 1 comes into contact.

[0055] In the Fig. In the semiconductor device shown in Figure 7, the auxiliary electrode 24 functions as a field plate and lowers the electric field strength of the front surface of the semiconductor substrate when the reverse voltage is applied to the drain electrode 7. Therefore, it is possible to easily maintain the reverse breakdown voltage of the semiconductor device. In the semiconductor device shown in Fig. 7, the outer peripheral edge 21a of the insulating film 21 is provided so that there is no gap from which the n - -Drift region 1 is exposed, between the outer peripheral edge 21a of the insulating film 21 and the upper end 7a of the drain electrode 7. The auxiliary electrode 24 is contacted to the upper end 7a of the drain electrode 7 such that there is no gap between the auxiliary electrode 24 and the upper end 7a of the drain electrode 7.

[0056] In the Fig. 7, the insulating film 21 and the auxiliary electrode 24 are provided as the leakage current reducing layer 20, and the arrangement of the n--drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0057] When the insulating film 21 and the auxiliary electrode 24 are provided, the insulating film 21 itself prevents the generation of charge carriers in the outer peripheral part of the semiconductor substrate, and it is possible to prevent an increase in the reverse leakage current. Furthermore, the auxiliary electrode 24 reduces the electric field strength of the front surface of the semiconductor substrate when the reverse voltage is applied to the drain electrode 7. Therefore, it is possible to easily maintain the reverse breakdown voltage of the semiconductor device.

[0058] In the Fig. In the semiconductor device shown in Figure 8, the leakage current reducing layer 20 includes the insulating film 21 covering a part of the n-type drift region 1 exposed from at least the outer peripheral part of the front surface of the semiconductor substrate, the first p-type region 22 exposed from the outer peripheral edge of the front surface of the semiconductor substrate, and an auxiliary electrode 25 electrically connected to the drain electrode 7. In the embodiment shown in Fig. 8 shown semiconductor device are the n - -drift region 1 and the first p-region 22 in the outer peripheral part of the semiconductor substrate are exposed from the front surface of the semiconductor substrate.

[0059] In the Fig. In the semiconductor device shown in Figure 8, the insulating film 21 may cover a portion of the first p-type region 22. The auxiliary electrode 25 is provided from the outer peripheral edge of the front surface to the surface of the insulating film 21. A portion of the first p-type region 22 not covered by the insulating film 21 is covered by the auxiliary electrode 25.

[0060] The Fig. The semiconductor device shown in Figure 8 differs from that shown in Fig. 7 is characterized in that it includes the first p-type region 22, and the auxiliary electrode 25 comes into contact with the first p-type region 22 exposed from the front surface of the semiconductor substrate. The auxiliary electrode 25 comes into contact with the first p-type region 22, is provided so as to extend from the first p-type region 22 to the surface of the insulating film 21, and has, for example, a step shape in a sectional view. The auxiliary electrode 25 is electrically connected to the drain electrode 7, which is provided via the first p-type region 22 on the side surface of the semiconductor substrate.

[0061] Therefore, the auxiliary electrode 25 may come into direct contact with the drain electrode 7 provided on the side surface of the semiconductor substrate or may not come into contact with the drain electrode 7. In the Fig. 8, the outer peripheral edge of the first p-region 22 is provided so that there is no gap from which the n - -drift region 1 is exposed, between the outer peripheral edge of the first p-region 22 and the upper end 7a of the drain electrode 7.

[0062] In the Fig. 8, the insulating film 21, the first p-type region 22 and the auxiliary electrode 25 are provided as the leakage current reducing layer 20, and the arrangement of the n - -drift region 1, the p-well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0063] In itself, in the Fig. 8, when the insulating film 21, the first p-type region 22, and the auxiliary electrode 25 are provided, the generation of charge carriers in the outer peripheral part of the semiconductor substrate is prevented by the insulating film 21, and it is possible to prevent an increase in the reverse leakage current. Fig. 8, the first p-type region 22 also makes it possible to prevent the generation of the reverse leakage current from the corner part 41 of the front surface of the semiconductor substrate in which the reverse leakage current is likely to be generated.

[0064] In the Fig. 8, the auxiliary electrode 25 makes it possible to reduce the electric field strength of the front surface of the semiconductor substrate when the reverse voltage is applied to the drain electrode 7. In fact, according to the Fig. 8, it is possible to effortlessly maintain the reverse breakdown voltage of the semiconductor device.

[0065] The Fig. 9 contains, in addition to the components of the semiconductor device shown in Fig. 8, a second p-type region (a second semiconductor region of a second conductivity type) 26 serving as the leakage current reducing layer 20 is provided in a surface layer of the back surface of the semiconductor substrate so as to come into contact with the drain electrode 7 provided on the side surface of the semiconductor substrate.

[0066] The second p-type region 26 is provided in a corner portion 43 of the back surface of the semiconductor substrate and comes into contact with the drain electrode 7 provided on the side and back surfaces of the semiconductor substrate. The corner portion 43 of the back surface of the semiconductor substrate is the interface between the n-type drift region 1 and the drain electrode 7 at the outer peripheral edge of the back surface of the semiconductor substrate when the second p-type region 26 is not provided.

[0067] In the Fig. 9, the insulating film 21, the first p-type region 22, the auxiliary electrode 25 and the second p-type region 26 are provided as the leakage current reducing layer 20, and the arrangement of the n- type drift region 1, the p-type well region 2, the n + -Source region 3, the gate oxide film 4, the gate electrode 5, the source electrode 6 and the drain electrode 7, which are separated from the components in the Fig. 1 shown semiconductor device are different components, the same as that in the Fig. 1 shown semiconductor device.

[0068] Since the second p-type region 26 is provided, a depletion layer per se also spreads from the pn junction part between the second p-type region 26 and the n-type drift region 1. Therefore, when the reverse voltage is applied to the drain electrode 7, it is possible to prevent the generation of the reverse leakage current from the corner part 43 of the back surface of the semiconductor substrate, in which the reverse leakage current is likely to arise.

[0069] Each of the Fig. 5 to 8 includes two or more components from the group of components consisting of the insulating film 21, the first p-type region 22 and the bent part 23a of the drain electrode 23, which are shown in Fig. 2 to 4 are provided as the leakage current reducing layer 20. Therefore, the semiconductor devices shown in Fig. 5 to 8, a variety of combinations of the semiconductor devices shown in Fig. 1 to 4. Specifically, in each case, it is possible to achieve the following effects.

[0070] In the case where the insulating film 21 covering the n--drift region 1 exposed from at least the outer peripheral part of the front surface of the semiconductor substrate is provided ( Fig. 5, Fig. 7 and Fig. 8), when the reverse voltage is applied to the drain electrode 7, it is possible to prevent the generation of charge carriers in the outer peripheral part of the semiconductor substrate and to prevent an increase in the reverse leakage current.

[0071] When the first p-type region 22 exposed from the outer peripheral edge of the front surface of the semiconductor substrate ( Fig. 5, Fig. 6 and Fig. 8), and when the bent part 23a of the drain electrode 23 is provided so as to extend from the side surface of the semiconductor substrate to the outer peripheral part of the front surface ( Fig. 6), the depletion layer spreads from the pn junction portion between the first p-type region 22 and the n-type drift region 1 and from the interface between the n-type drift region 1 and the bent portion 23a of the drain electrode 23. Therefore, when the reverse voltage is applied to the drain electrode 7, it is possible to prevent the generation of the reverse leakage current from the corner portion 41 of the front surface of the semiconductor substrate.

[0072] In the case where the auxiliary electrodes 24 and 25 electrically connected to the drain electrode 7 are provided ( Fig. 7 and Fig. 8), when the reverse voltage is applied to the drain electrode 7, the auxiliary electrodes 24 and 25 can reduce the electric field strength of the front surface of the semiconductor substrate. Therefore, it is possible to easily maintain the reverse breakdown voltage of the semiconductor device.

[0073] The Fig. 1 to 7, the second p-type region 26 provided as the leakage current reducing layer 20 may be formed in the corner part 43 of the back surface of the semiconductor substrate in the manner shown in Fig. 9. When the second p-type region 26 is provided in the corner part 43 of the back surface of the semiconductor substrate ( Fig. 9), the depletion layer spreads from the pn junction portion between the second p-type region 26 and the n-type drift region 1. Therefore, when the reverse voltage is applied to the drain electrode 7, it is possible to prevent the reverse leakage current from the corner portion 43 of the back surface of the semiconductor substrate.

[0074] It is preferable that the front and back surfaces of the semiconductor substrate forming the Schottky contact are smooth and clean to reduce the reverse leakage current arising from the surface of the semiconductor substrate.

[0075] The side surface of the semiconductor substrate according to each of the above-mentioned structural examples may be perpendicular to the front surface of the semiconductor substrate, or it may have a tapered shape. Fig. In the structural examples shown in Figures 1 to 9, the side surface of the semiconductor substrate is inclined so that the width of the semiconductor substrate gradually increases from the back surface (drain) to the front surface (source). The interface of the semiconductor substrate that contacts the Schottky barrier electrode must be processed into a smooth and clean surface. When the side surface of the semiconductor substrate has a tapered shape, it is easy to form the drain electrodes 7 and 23 on the back and side surfaces of the semiconductor substrate by means of a sputtering method or an evaporation method, compared to the case where the side surface of the semiconductor substrate is perpendicular to the front surface.

[0076] Therefore, when the side surface of the semiconductor substrate has a tapered shape, it is easy to uniformly form metal films that will be the drain electrodes 7 and 23 on the entire side surface of the semiconductor substrate, compared to the case where the side surface of the semiconductor substrate is perpendicular to the front surface. Furthermore, after the metal films that will be the drain electrodes 7 and 23 are formed on the side surface of the semiconductor substrate, it is possible to uniformly anneal the metal films that will be the drain electrodes 7 and 23. Therefore, it is possible to form the drain electrodes 7 and 23 on the side surface of the semiconductor substrate with high controllability.

[0077] If the metal films that will be the drain electrodes 7 and 23 can be uniformly formed on the side surface of the semiconductor substrate and then uniformly annealed, the side surface of the semiconductor substrate can be perpendicular to the front surface. Furthermore, if the Schottky contact can be formed by the drain electrodes 7 and 23 in the side surface of the semiconductor substrate, the side surface of the semiconductor substrate can be perpendicular to the front surface.

[0078] The level of the leakage current of the semiconductor device according to the embodiment was checked. Fig. 10 is a characteristic diagram illustrating the electrical behavior of the semiconductor device according to the embodiment. Fig. 10 shows the reverse residual current curves of the Fig. 1 to 9. In Fig. 10, the horizontal axis is a voltage Vsd, which is based on the source potential and is applied to the drain terminal. In Fig. In Figure 10, the vertical axis represents the leakage current Isd, which flows when the voltage Vsd is applied to the drain terminal. The voltage Vsd is positive when a negative voltage is applied to the drain terminal. The leakage current Isd flowing from source to drain is positive.

[0079] In Fig. 10, a first curve 31 indicates the profile of the reverse leakage current of the semiconductor device without the leakage current reducing layer 20. The semiconductor device without the leakage current reducing layer 20 serves to check the effect of the leakage current reducing layer 20 provided in the semiconductor device according to the embodiment. A second curve 32 indicates the profile of the reverse leakage current of the semiconductor device in Fig. 1 to 8. A third curve 33 indicates the reverse leakage current of the semiconductor devices shown in Fig. 9 shown semiconductor device.

[0080] As in Fig. 10 is shown in the Fig. 1 to 9 (second curve 32 and third curve 33), the reverse leakage current was smaller than that in the semiconductor device (first curve 31) without the leakage current reducing layer 20. This showed that the generation of the reverse leakage current was prevented in the outer peripheral part of the semiconductor substrate or in the corner part 43 of the back surface.

[0081] In the Fig. 9 (third curve 33), the reverse leakage current is smaller than that in the semiconductor device shown in Fig. 1 to 8 (second curve 32). This showed that the reverse leakage current in the Fig. 9 is smaller than that in the semiconductor device shown in Fig. 1 to 8 shown semiconductor devices.

[0082] As described above, according to the embodiment, the drain electrode 7 is provided from the back surface to the side surface of the semiconductor substrate. The drain electrode 7 and the n-type drift region 1, which is the semiconductor substrate, form the Schottky contact. In this way, the depletion layer spreads from both the interface between the n-type drift region 1 and the drain electrode 7 provided on the back surface of the semiconductor substrate and the interface between the n-type drift region 1 and the drain electrode 7 provided on the side surface of the semiconductor substrate. Therefore, unlike the prior art, it is possible to form a reverse-blocking semiconductor device capable of maintaining the reverse breakdown voltage without damaging the p-type region (which is Fig. 14) on the side surface of the semiconductor substrate.

[0083] In the semiconductor device according to the embodiment, unlike the prior art semiconductor device, it is not necessary to form the p-type region on the side surface of the semiconductor substrate. Therefore, compared to the prior art semiconductor device in which the p-type region is formed on the side surface of the semiconductor substrate by ion implantation and annealing, for example, it is possible to easily achieve a reverse blocking semiconductor device by forming only the drain electrode 7 using a sputtering method or an evaporation method.

[0084] According to the embodiment, it is possible to realize a reverse blocking semiconductor device compared to the case where the semiconductor device (see Fig.14) according to the prior art. Furthermore, since the side surface of the semiconductor substrate has a tapered shape, according to the embodiment, it is possible to manufacture a reverse blocking semiconductor device with a structure in which it is easy to connect the drain electrode 7.

[0085] The semiconductor device according to the embodiment includes the n - -Residual current reducing layer 20 covering the drift region 1 exposed in the outer peripheral part of the semiconductor substrate from the front surface of the semiconductor substrate. Therefore, when the reverse voltage is applied to the drain electrode 7, it is possible to reduce the reverse residual current.

[0086] Since the semiconductor substrate made of a semiconductor material with a wide band gap is used, it is possible to reduce the reverse breakdown voltage generated by the Schottky contact from the n -The aim of the invention is to improve the breakdown voltage maintained between the drift region 1 and the drain electrode 7 compared to the case where the semiconductor substrate made of silicon is used. Specifically, the breakdown voltage maintained by the Schottky contact is approximately 200 V when the semiconductor substrate made of silicon is used. On the other hand, when the semiconductor substrate made of a wide band-gap semiconductor material is used, the breakdown voltage maintained by the Schottky contact can increase to approximately 1200 V.

[0087] The invention is not limited to the above-described embodiment, but the insulating film, the first p-type region, and the bent-over part of the drain electrode and the second p-type region constituting the leakage current reducing layer can be combined in various ways. For example, the insulating film and the bent-over part of the drain electrode can be provided as the leakage current reducing layer, and the bent-over part of the drain electrode can cover part of the surface of the insulating film. In the above-described embodiment, the first conductivity type is an n-type and the second conductivity type is a p-type. However, in the invention, the first conductivity type may be a p-type and the second conductivity type may be an n-type. In this case, the same effect as described above is achieved. Industrial applications

[0088] As described above, the semiconductor device according to the invention is applicable to a power semiconductor device used in, for example, a direct conversion circuit such as a matrix converter. List of reference symbols 1 n - -DRIFT AREA 2 p-tub area 3 n + -SOURCE AREA 4 GATE OXIDE FILM 5 GATE ELECTRODE 6 SOURCE ELECTRODE 7 DRAIN ELECTRODE 10 ACTIVE AREA 11 BREAKDOWN VOLTAGE STRUCTURE AREA 20 RESIDUAL FLOW REDUCING LAYER

Claims

[1] A semiconductor device comprising: a semiconductor substrate which is of a first conductivity type and consists of a semiconductor material with a wider band gap than silicon; a control electrode (5) provided on a first main surface of the semiconductor substrate; an output electrode (7) provided on a second main surface and a side surface of the semiconductor substrate and forming a Schottky contact with the second main surface of the semiconductor substrate; and a layer (20) which is provided at least on an outer peripheral edge (20a) of the semiconductor substrate and reduces a residual current arising from at least the outer peripheral edge (20a), wherein the layer (20) which reduces the leakage current is a second semiconductor region (26) which is of a second conductivity type, is provided in a surface layer of the second main surface of the semiconductor substrate and comes into contact with the output electrode (7) at the second main surface and the side surface of the semiconductor substrate. [2] A semiconductor device comprising: a semiconductor substrate which is of a first conductivity type and consists of a semiconductor material with a wider band gap than silicon; a control electrode (5) provided on a first main surface of the semiconductor substrate; an output electrode (7) provided on a second main surface and a side surface of the semiconductor substrate and forming a Schottky contact with the semiconductor substrate; and a layer (20) which is provided at least on an outer peripheral edge (20a) of the semiconductor substrate and reduces a residual current arising from at least the outer peripheral edge (20a), wherein the layer (20) which reduces the leakage current is a first semiconductor region (22) which is of a second conductivity type, is provided in a surface layer of the first main surface of the semiconductor substrate and comes into contact with the output electrode (7) on the lateral surface of the semiconductor substrate. [3] A semiconductor device according to claim 2, wherein the first semiconductor region (22) forms an ohmic contact with the output electrode (7). [4] A semiconductor device according to claim 1, wherein the output electrode (7) extends from the second main surface to the first main surface of the semiconductor substrate and is laid over the outer peripheral edge (20a) of the first main surface. [5] A semiconductor device according to any one of claims 1 to 4, wherein the semiconductor substrate is made of silicon carbide or gallium nitride.

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