JP2015002259A - Silicon carbide semiconductor device, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the strength of a silicon carbide semiconductor substrate while reducing the ON resistance of the silicon carbide semiconductor device, and to prevent the occurrence of warpage of the silicon carbide semiconductor substrate.SOLUTION: A silicon carbide semiconductor device comprises: a silicon carbide semiconductor substrate 10; a silicon carbide semiconductor layer 20 formed on the silicon carbide semiconductor substrate 10; and an electrode 50 provided on the silicon carbide semiconductor layer 20. A group of recess part 15 having a plurality of recess parts 16 formed by applying the laser light L, is provided only in a region that contains a lower side in a vertical direction of the electrode 50 and is a lower surface of the silicon carbide semiconductor substrate 10.

Description

  The present invention relates to a silicon carbide semiconductor device using silicon carbide and a method for manufacturing the silicon carbide semiconductor device.

  Conventionally, a silicon carbide semiconductor device using silicon carbide (SiC) is known. In such a silicon carbide semiconductor device, reducing the thickness of the silicon carbide semiconductor substrate is very effective in reducing the ON resistance of the silicon carbide semiconductor device.

  In this regard, it is conventionally known that the lower surface (back surface) of a substrate of a semiconductor device is ground by back grinding, mechanical polishing, or the like. For example, Patent Document 1 discloses a wafer grinding method in which the lower surface of a semiconductor wafer having a plurality of embedded electrodes embedded at a predetermined depth is ground so that all embedded electrodes are exposed on the lower surface of the wafer. Yes.

JP 2011-40511 A

  However, silicon carbide is hard and brittle, and when the silicon carbide semiconductor substrate 10 is thinned by grinding such as back grinding or mechanical polishing, a knife-shaped edge (hereinafter referred to as “knife”) is easily damaged at the edge of the lower surface of the silicon carbide semiconductor substrate 10. Edge ") is formed (see FIG. 9), and such a knife edge may be damaged. Further, when the entire silicon carbide semiconductor substrate 10 is thinned, the amount of warpage of the silicon carbide semiconductor substrate 10 is increased.

  The present invention has been made in view of such points, and while reducing the ON resistance of the silicon carbide semiconductor device, the strength of the silicon carbide semiconductor substrate is increased, and further, warpage occurs in the silicon carbide semiconductor substrate. The present invention also provides a silicon carbide semiconductor device and a method for manufacturing the silicon carbide semiconductor device.

A silicon carbide semiconductor device according to the present invention includes:
A silicon carbide semiconductor substrate;
A silicon carbide semiconductor layer formed on the silicon carbide semiconductor substrate;
An electrode provided on the silicon carbide semiconductor layer;
With
A recess group having a plurality of recesses formed by irradiating a laser beam is provided only on a lower surface of the silicon carbide semiconductor substrate and including a region below the vertical direction of the electrode.

In the silicon carbide semiconductor device according to the present invention,
A plurality of recesses and a plurality of electrodes are provided;
Each recess group may be provided vertically below each electrode.

In the silicon carbide semiconductor device according to the present invention,
Each recessed part of the said recessed part group may be provided in the grid | lattice form in the horizontal direction.

In the silicon carbide semiconductor device according to the present invention,
Each recess of the recess group may be provided with a honeycomb structure in the horizontal direction.

In the silicon carbide semiconductor device according to the present invention,
In the recess group, the width in the horizontal direction of the recess located on the center side of the electrode may be larger than the width in the horizontal direction of the recess located on the peripheral side of the electrode.

In the silicon carbide semiconductor device according to the present invention,
In the recess group, the width in the horizontal direction of the recess positioned on the peripheral side of the electrode may be larger than the width in the horizontal direction of the recess positioned on the center side of the electrode.

In the silicon carbide semiconductor device according to the present invention,
The vertical cross-sectional shape of the recess may be U-shaped.

In the silicon carbide semiconductor device according to the present invention,
The recess may be formed in the silicon carbide semiconductor substrate, and an upper end thereof may not reach the silicon carbide semiconductor layer.

In the silicon carbide semiconductor device according to the present invention,
The energy of the laser beam may be 0.5 J / cm ² or more.

In the silicon carbide semiconductor device according to the present invention,
A carbon conductive layer may be formed on the exposed surface of the recess by the laser beam.

A method for manufacturing a silicon carbide semiconductor device according to the present invention includes:
Forming a silicon carbide semiconductor layer on the silicon carbide semiconductor substrate;
Providing an electrode on the silicon carbide semiconductor layer;
A recess group having a plurality of recesses is formed by irradiating a laser beam limited to a region on the lower surface of the silicon carbide semiconductor substrate and including a region below the electrode in the vertical direction or a region below the electrode in the vertical direction. And a process of
Is provided.

  According to the present invention, a recess group having a plurality of recesses is provided below the electrodes in the vertical direction. For this reason, the thickness of the silicon carbide semiconductor substrate below the electrodes in the vertical direction can be partially reduced, and the ON resistance of the silicon carbide semiconductor device can be reduced.

  Further, in the present invention, since the recess of the recess group is formed using laser light, unlike the grinding by back grinding, mechanical polishing, etc., the knife edge is not formed on the lower surface of the silicon carbide semiconductor substrate, The strength of the silicon carbide semiconductor substrate can be increased. Furthermore, since the recess group is provided only in the region including the lower part in the vertical direction of the electrode without thinning the entire silicon carbide semiconductor substrate, it is possible to prevent the silicon carbide semiconductor substrate from being warped.

FIG. 1 is a cross-sectional view for illustrating an overall configuration of a silicon carbide semiconductor device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view for illustrating the configuration of the silicon carbide semiconductor device according to the first embodiment of the invention. FIG. 3 is a cross-sectional view for illustrating a step of manufacturing the silicon carbide semiconductor device according to the first embodiment of the invention. FIG. 4 is a plan view showing the lower surface (back surface) side of the silicon carbide semiconductor substrate used in the first embodiment of the present invention. FIG. 5 is a plan view showing the lower surface (back surface) side of the silicon carbide semiconductor substrate used in the modification of the first embodiment of the present invention. FIG. 6 is a cross-sectional view for illustrating a configuration of a silicon carbide semiconductor device according to another modification of the first embodiment of the present invention. FIG. 7 is a cross-sectional view for illustrating the configuration of the silicon carbide semiconductor device according to the first aspect of the second embodiment of the present invention. FIG. 8 is a cross-sectional view for illustrating the configuration of the silicon carbide semiconductor device according to the second aspect of the second embodiment of the present invention. FIG. 9 is a cross-sectional view for illustrating a knife edge formed when a silicon carbide semiconductor substrate is thinned by grinding such as back grinding or mechanical polishing.

First Embodiment << Configuration >>
Hereinafter, embodiments of a silicon carbide semiconductor device (SiC semiconductor device) and a method for manufacturing a silicon carbide semiconductor device according to the present invention will be described with reference to the drawings. Here, FIG. 1 to FIG. 6 are diagrams for explaining a first embodiment of the present invention. Although the silicon carbide semiconductor device of this invention is not specifically limited, For example, it is a Schottky barrier diode (SBD), MOSFET, etc. Hereinafter, a Schottky barrier diode will be described as a semiconductor device. However, it should be noted that this Schottky barrier diode is merely an example of a semiconductor device.

  As shown in FIG. 1, the silicon carbide semiconductor device of the present embodiment includes a silicon carbide semiconductor substrate (SiC semiconductor substrate) 10 and a silicon carbide semiconductor layer (SiC semiconductor layer) 20 formed on the silicon carbide semiconductor substrate 10. And a Schottky electrode (corresponding to an “electrode” described in claims) 50 provided on silicon carbide semiconductor layer 20.

  More specifically, the semiconductor device of the present embodiment includes a high concentration n-type silicon carbide semiconductor substrate (first conductivity type silicon carbide semiconductor substrate) 10 and a high concentration n-type silicon carbide semiconductor substrate 10. Low-concentration n-type silicon carbide semiconductor layer (first conductivity type silicon carbide semiconductor layer) 20 and p-type carbonization formed in a ring shape in low-concentration n-type silicon carbide semiconductor layer 20 And a silicon semiconductor layer (second conductivity type silicon carbide semiconductor layer) 30. The n-type silicon carbide semiconductor substrate 10 has an upper surface (hereinafter also referred to as “front surface”) and a lower surface (hereinafter also referred to as “back surface”) facing away from the upper surface. The low-concentration n-type silicon carbide semiconductor layer 20 described above is formed on the surface side of the silicon carbide semiconductor substrate 10. As shown in FIG. 2, an ohmic electrode 80 is formed on the back side of the n-type silicon carbide semiconductor substrate 10 along the shape of the back side of the silicon carbide semiconductor substrate 10. Although not shown, a semiconductor chip is mounted on the ohmic electrode 80 via solder, Al or the like. In FIG. 1, the ohmic electrode 80 is not shown.

  As shown in FIG. 2, a Schottky electrode 50 is provided on the low-concentration n-type silicon carbide semiconductor layer 20 and the p-type silicon carbide semiconductor layer 30 so as to straddle them. A lead electrode 55 is provided on the Schottky electrode 50. Further, an insulating layer 60 is provided in a ring shape so as to surround the Schottky electrode 50 and the extraction electrode 55. Examples of the material of the Schottky electrode 50 include Ti, Mo, Ni, and the like. Examples of the material of the extraction electrode 55 include Al, Ni, Au, and the like. Examples of the material of the insulating layer 60 include silicon oxide, silicon nitride, and polyimide.

  The thickness of the n-type silicon carbide semiconductor substrate 10 where the later-described recess 16 is formed is about 250 μm, for example, and the thickness of the silicon carbide semiconductor device including the Schottky electrode 50 and the extraction electrode 55 is about 350 μm, for example. It is. For this reason, in this example, the depth of the recess 16 is about 100 μm.

A recess group 15 having a plurality of recesses 16 formed by irradiating the laser beam L is provided only on the lower surface of the silicon carbide semiconductor substrate 10 and including the area below the Schottky electrode 50 in the vertical direction. Yes. The energy of the laser beam L used in the present embodiment is, for example, 0.5 J / cm ² or more. In addition, a conductive layer of carbon (C) is formed on the exposed surface of the recess 16 in the present embodiment, with silicon (Si) flying by the laser light L. This is because silicon is generally more likely to fly than carbon. That is, when the concave portion 16 is formed using the laser light L, carbon and silicon fly, but on the surface finally formed, a conductor layer is formed by carbon after the silicon has blown.

  Incidentally, the laser beam L is irradiated with a spot of, for example, 50 μm, and the concave portion 16 is formed by shifting by one spot or overlapping each spot. The wavelength of the laser beam L is, for example, 555 nm or less. According to an experiment by the inventor of the present application, when the wavelength of the laser beam L is longer than 555 nm, the laser beam is transmitted through the silicon carbide semiconductor substrate 10 and the recess 16 cannot be formed in the silicon carbide semiconductor substrate 10. When the wavelength of the laser beam L is 555 nm or less, the recess 16 can be formed in the silicon carbide semiconductor substrate 10. As the laser light having such a wavelength, a green laser (wavelength is about 532 nm), an excimer laser, or the like can be used. In general, a machine that irradiates a laser beam having a long wavelength (for example, a laser beam having a wavelength of 400 nm or more) such as a green laser is low-priced. It is beneficial in that it can be done.

  The recesses 16 of the recess group 15 can be provided in various arrangements and shapes. As an example, as shown in FIG. 4, the recesses 16 are provided in a grid pattern in the horizontal direction. Can do. Further, unlike such an embodiment, as another example, as shown in FIG. 5, there is a structure in which each recess 16 of the recess group 15 is provided with a honeycomb structure (honeycomb shape) in the horizontal direction. it can.

  As described above, the ohmic electrode 80 is formed on the back side of the silicon carbide semiconductor substrate 10. And as a material of this ohmic electrode 80, Ni, Mo etc. can be mentioned, for example. Incidentally, silicon carbide has high thermal conductivity and excellent heat dissipation, has thermal conductivity similar to copper, etc., and higher thermal conductivity than solder, Ni, Al, and the like.

  As shown in FIG. 2, the horizontal width W2 of the recess group 15 is larger than the horizontal width W1 of the Schottky electrode 50. Further, the silicon carbide semiconductor device of the present embodiment is provided with a plurality of recess groups 15 and a plurality of Schottky electrodes 50 (see FIG. 1). Each concave group 15 is provided vertically below each Schottky electrode 50, and the Schottky electrode 50 and the concave group 15 are formed in a one-to-one relationship. Note that the recess 16 of the present embodiment has a U-shaped vertical cross-sectional shape. Incidentally, in the present embodiment, as shown in FIG. 2, in the recess group 15, the width of each recess 16 in the horizontal direction is uniform and has the same length.

  As shown in FIG. 2, recess 16 of the present embodiment is formed in silicon carbide semiconductor substrate 10, but upper end 16 t does not reach n-type silicon carbide semiconductor layer 20. That is, the upper end 16t of the recess 16 is positioned below the lower end of the low-concentration n-type silicon carbide semiconductor layer 20 in the vertical direction.

  Incidentally, in the drawing of the present embodiment, each recess 16 has the same depth and uses an aspect, but the present invention is not limited to this, and the depth of the recess 16 may be different. As an example, the depth of the recess 16 positioned on the center side of the electrode is deeper than the depth of the recess 16 positioned on the peripheral edge side of the electrode, and the upper end of the recess 16 positioned on the center side of the electrode and the silicon carbide semiconductor layer. The distance between the lower end of 20 and the lower end of the silicon carbide semiconductor layer 20 may be shorter than the distance between the upper end of the recess 16 located on the peripheral side of the electrode. Also, unlike such an embodiment, the depth of the recess 16 located on the peripheral side of the electrode is deeper than the depth of the recess 16 located on the center side of the electrode, and the upper end of the recess 16 located on the peripheral side of the electrode And the lower end of silicon carbide semiconductor layer 20 may be shorter than the distance between the upper end of recess 16 located on the center side of the electrode and the lower end of silicon carbide semiconductor layer 20.

"Manufacturing process"
Next, the manufacturing process of the semiconductor device of the present embodiment having the above-described configuration will be described mainly with reference to FIG.

  First, a high concentration n-type silicon carbide semiconductor substrate 10 is prepared (see FIG. 3A).

  Next, a low-concentration n-type silicon carbide semiconductor layer 20 is formed on the high-concentration n-type silicon carbide semiconductor substrate 10 by epitaxial growth (see FIG. 3A). The low-concentration n-type silicon carbide semiconductor layer 20 has an impurity concentration and thickness necessary to ensure a withstand voltage.

Next, Al, B, or the like is ion-implanted on the low-concentration n-type silicon carbide semiconductor layer 20, and a p-type silicon carbide semiconductor layer 30 is formed, for example, by performing a heat treatment at 1500 ° C. or higher (FIG. 3 (b)). More specifically, SiO ₂ is deposited on the surface of the low-concentration n-type silicon carbide semiconductor layer 20 by CVD. Next, a photoresist is formed on the SiO ₂ , and a portion corresponding to the formation position of the p-type silicon carbide semiconductor layer 30 is removed from the photoresist. By performing an etching process in this state, the portion of SiO ₂ corresponding to the formation position of the p-type silicon carbide semiconductor layer 30 is removed, and the low-concentration n-type silicon carbide semiconductor layer 20 in the portion is exposed. Thereafter, the remaining photoresist is removed. Thereafter, for example, Al or B is ion-implanted from the exposed portion of the low concentration n-type silicon carbide semiconductor layer 20. Then, after removing the remaining SiO ₂ , a heat treatment at 1500 ° C. or higher is performed to activate the implanted impurities.

  Next, a Schottky electrode 50 made of Ti, Mo, Ni or the like is formed on the low-concentration n-type silicon carbide semiconductor layer 20 and the p-type silicon carbide semiconductor layer 30 by, for example, sputtering. (See FIG. 3C).

  Next, an extraction electrode 55 made of Al, Ni, Au or the like is provided on the Schottky electrode 50 (see FIG. 3C).

  Next, an insulating layer 60 made of silicon oxide, silicon nitride, polyimide, or the like is provided so as to surround the Schottky electrode 50 and the extraction electrode 55 (see FIG. 3C).

As described above, after or before the Schottky electrode 50, the extraction electrode 55, and the insulating layer 60 are provided, the vertical direction of the Schottky electrode 50 on the lower surface (that is, the back surface) of the silicon carbide semiconductor substrate 10. By irradiating the laser beam L limited to the area including the lower part or the lower part in the vertical direction of the place where the Schottky electrode 50 is to be arranged, the concave group 15 having a plurality of concave parts 16 is formed (see FIG. 3D). . In the embodiment shown in FIG. 3, after the Schottky electrode 50, the extraction electrode 55, and the insulating layer 60 are provided, the back surface of the silicon carbide semiconductor substrate 10 is irradiated with the laser light L to form the recess groups 15. ing. In addition, the energy of the irradiated laser beam L is, for example, 0.5 J / cm ² or more.

  As an example of the arrangement and shape of the recesses 16 in the recess groups 15 formed in this way, one in which the respective recesses 16 are provided in a lattice shape in the horizontal direction can be cited (see FIG. 4). As another example, there can be mentioned one in which each recess 16 of the recess group 15 is provided in a honeycomb structure (honeycomb shape) in the horizontal direction (see FIG. 5).

  The horizontal width W2 of the recess 15 formed in this manner is larger than the horizontal width W1 of the Schottky electrode 50 (see FIG. 2). Moreover, the longitudinal cross-sectional shape of each recessed part 16 is U-shaped. Moreover, the recessed part 16 is formed in the silicon carbide semiconductor substrate 10, The upper end 16t has not reached the silicon carbide semiconductor layer 20 (refer FIG. 2).

  Each recess group 15 is formed corresponding to the lower part of each Schottky electrode 50 in the vertical direction, and the Schottky electrode 50 and the recess group 15 are formed in a one-to-one relationship (see FIG. 1). Incidentally, a carbon (C) conductive layer is formed on the exposed surface of the recess 16.

  Next, ohmic electrode 80 is formed on the lower surface (back surface) of silicon carbide semiconductor substrate 10 (see FIG. 3E). More specifically, a metal such as Ni or Mo is deposited on the lower surface (back surface) of the silicon carbide semiconductor substrate 10, or the lower surface (back surface) of the silicon carbide semiconductor substrate 10 is plated with a metal such as Ni or Mo. Thereafter, the ohmic electrode 80 is formed, for example, by performing a heat treatment for 2 minutes at a temperature of about 1000 degrees in a vacuum. Thereafter, a semiconductor chip is mounted on the ohmic electrode 80 via solder or the like.

"effect"
Next, effects of the present embodiment configured as described above will be described.

  According to the present embodiment, the recess group 15 having the plurality of recesses 16 is provided below the Schottky electrode (electrode) 50 in the vertical direction (see FIGS. 1 and 2). Therefore, the thickness of silicon carbide semiconductor substrate 10 below the Schottky electrode (electrode) 50 in the vertical direction can be partially reduced, and the ON resistance of the silicon carbide semiconductor device can be reduced.

  In the present embodiment, since there is a portion where silicon carbide semiconductor substrate 10 remains below the Schottky electrode 50 in the vertical direction, ohmic electrode 80, solder, and the like are present at the portion where silicon carbide semiconductor substrate 10 remains as described above. Compared with metals such as, the electrical conductivity is reduced. However, since silicon carbide has high thermal conductivity and excellent heat dissipation, it can prevent an increase in electrical resistance by having heat.

  For this reason, in the present embodiment, a combination of partially reducing the thickness of the silicon carbide semiconductor substrate below the Schottky electrode 50 in the vertical direction and preventing the electrical resistance from increasing due to generated heat is used. , ON resistance can be reduced.

  In addition, since the recess 16 of the recess 15 is formed using the laser beam L, a knife edge is formed on the lower surface of the silicon carbide semiconductor substrate 10, unlike grinding by back grinding, mechanical polishing, or the like. The strength of the silicon carbide semiconductor substrate 10 can be increased. Furthermore, since the concave group 15 is provided only in the region including the lower part in the vertical direction of the Schottky electrode 50 without making the entire silicon carbide semiconductor substrate 10 thin, warping of the silicon carbide semiconductor substrate 10 is also prevented. be able to.

  These points will be described.

  Reducing the thickness of the silicon carbide semiconductor substrate 10 is very effective in reducing the ON resistance of the silicon carbide semiconductor device. However, silicon carbide is hard and brittle, and when it is thinned by grinding such as back grinding or mechanical polishing, a knife edge that is very easily damaged is formed on the edge of the lower surface of the silicon carbide semiconductor substrate 10. It may be damaged (see FIG. 9). Further, when the entire silicon carbide semiconductor substrate 10 is thinned, the amount of warpage of the silicon carbide semiconductor substrate 10 is increased.

  In this regard, in the present embodiment, since the thickness of the silicon carbide semiconductor substrate 10 is reduced only to the region including the lower part of the Schottky electrode 50 in the vertical direction, it is possible to prevent the silicon carbide semiconductor substrate 10 from warping. can do.

  Further, since recess 16 is formed using laser light L, a knife edge is not formed on the lower surface of silicon carbide semiconductor substrate 10, and the strength of silicon carbide semiconductor substrate 10 can be increased. . Incidentally, when the concave portion is formed by physical polishing without using laser light, a damaged layer is formed on the silicon carbide semiconductor substrate 10, but in the present embodiment, such a damaged layer is generated. It can also be prevented.

  In the present embodiment, the horizontal width W2 of the recess group 15 is larger than the horizontal width W1 of the Schottky electrode 50 (see FIG. 2). For this reason, the recessed part 16 can be intermittently formed over the whole vertical direction lower part of the Schottky electrode 50, and the thickness of the silicon carbide semiconductor substrate 10 can be made thin intermittently. Incidentally, since the current flowing from the electrode such as the Schottky electrode 50 toward the lower surface (back surface) of the silicon carbide semiconductor substrate 10 has a certain spread, the horizontal width W2 of the recess group 15 is the horizontal of the Schottky electrode 50. It is preferable that the horizontal width W2 of the recess group 15 is larger than the horizontal width W1 of the Schottky electrode 50 instead of being equal to the width W1 in the direction.

  In the present embodiment, each recess group 15 is provided vertically below each Schottky electrode 50, and each recess group 15 is provided corresponding to each Schottky electrode 50 (see FIG. 1). ). For this reason, there is no portion where the thickness of silicon carbide semiconductor substrate 10 is not intermittently thinned vertically below Schottky electrode 50, and the thickness of silicon carbide semiconductor substrate 10 is intermittently below each Schottky electrode 50. Therefore, the ON resistance of the silicon carbide semiconductor device can be more reliably reduced. In addition, since concave portion 16 is not provided vertically below the portion where Schottky electrode 50 is not provided, the portion where thickness of silicon carbide semiconductor substrate 10 is reduced can be reduced as much as possible. It is possible to prevent the occurrence of warpage as much as possible.

  Moreover, in this Embodiment, the longitudinal cross-sectional shape of the recessed part 16 is U-shaped, and the recessed part 16 is not the shape where it was square (refer FIG.1 and FIG.2). In this regard, when the concave portion has an angular shape, inconvenience may occur due to difficulty in attaching metal to the upper corner when performing vapor deposition, plating, die bonding, etc. When the longitudinal cross-sectional shape of the recessed part 16 is U-shaped like a form, it can prevent that the situation where a metal does not adhere easily arises in this way.

  Moreover, in this Embodiment, the recessed part 16 is formed in the silicon carbide semiconductor substrate 10, and the upper end 16t has not reached the silicon carbide semiconductor layer 20 (refer FIG. 2). For this reason, it can prevent that the silicon carbide semiconductor layer 20 for ensuring a proof pressure becomes thin, and a high proof pressure can be maintained by extension.

  Incidentally, after the ohmic electrode 80 is formed of a metal such as Ni in the recess 16, solder or the like enters. However, silicon carbide has a higher thermal conductivity than Ni and solder. Heat can be released through the silicon semiconductor substrate 10.

Modification In the above-described embodiment, the description has been made using the aspect in which the vertical cross-sectional shape of the recess 16 is a U-shape. However, this aspect is merely an example, and another aspect can be used. As an example of another aspect, as shown in FIG. 6, there can be mentioned one in which the longitudinal section of the recess 16 ′ is rectangular. Incidentally, “16′t” in FIG. 6 indicates the upper end of the recess 16 ′.

  In the rectangular recess 16 ′ according to such a modification, it is possible to uniformly thin the lower part of the Schottky electrode 50 (electrode) in the vertical direction, so that it can be expected to reduce the ON resistance of the silicon carbide semiconductor device.

Second Embodiment Next, a second embodiment of the present invention will be described.

  In the first embodiment, the width in the horizontal direction of each recess 16 is uniform in the recess group 15, but in the second embodiment, in each recess 16, The width in the horizontal direction is different.

  In the second embodiment, other configurations are substantially the same as those in the first embodiment. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  Also in this embodiment, the same effects as those of the first embodiment can be obtained. Since it has been described in detail in the first embodiment, the description of the effects in this embodiment will be made only for the parts unique to this embodiment.

  As a first aspect of the present embodiment, as shown in FIG. 7, in the recess group 15, the horizontal width of the recess 16 c located on the center side of the Schottky electrode (electrode) 50 is the Schottky electrode 50. It is larger than the width in the horizontal direction of the concave portion 16p located on the peripheral edge side. More specifically, the width in the horizontal direction of the recess 16 c located closest to the center of the Schottky electrode 50 is larger than the width in the horizontal direction of the recess 16 p located closest to the peripheral edge of the Schottky electrode 50. It is getting bigger. In the embodiment shown in FIG. 7, the width of the recess 16 is gradually reduced from the center of the Schottky electrode 50 toward the periphery.

  According to such an aspect, the amount of metal such as the ohmic electrode 80 and solder embedded in the recess 16 is increased on the center portion side vertically below the Schottky electrode 50, and the peripheral edge on the vertically lower side of the Schottky electrode 50 is increased. The current can be reduced on the part side, and the current can be concentrated on the center part side of the recess group 15.

  As a second mode of the present embodiment, as shown in FIG. 8, in the recess group 15, the width in the horizontal direction of the recess 16 p located on the peripheral side of the Schottky electrode 50 is the center side of the Schottky electrode 50. It is larger than the width in the horizontal direction of the recess 16c located at the position. More specifically, the horizontal width of the recess 16p located closest to the peripheral edge of the Schottky electrode 50 is greater than the horizontal width of the recess 16c located closest to the center of the Schottky electrode 50. It is getting bigger. In the embodiment shown in FIG. 8, the width of the recess 16 gradually increases from the center of the Schottky electrode 50 toward the periphery.

  According to such an aspect, the amount of the metal such as the ohmic electrode 80 and solder embedded in the recess 16 is increased on the peripheral side on the vertically lower side of the Schottky electrode 50, and the center of the Schottky electrode 50 on the lower side in the vertical direction is increased. The current can be reduced on the part side, and the current can be concentrated on the peripheral part side of the recess group 15.

  Note that whether to use the first aspect or the second aspect described above depends on the design of the silicon carbide semiconductor device. In general, a silicon carbide semiconductor device is broken when a current is concentrated in a state where the temperature is high. Therefore, a structure that can release a current in a state where the temperature is high is preferable. As described above, according to the first aspect, the current can be concentrated on the central portion side of the recess group 15. On the other hand, according to the second aspect, the current can be concentrated on the peripheral edge side of the recess group 15. In this regard, it is better to concentrate the current on the center side of the recess group 15 or to concentrate the current on the peripheral side of the recess group 15 in order to allow the current to escape when the temperature is high. Since it depends on how the silicon carbide semiconductor device is designed, it cannot be generally stated. For this reason, depending on the design content of the silicon carbide semiconductor device, it is selected that the current is concentrated on the central portion side of the concave group 15 or the current is concentrated on the peripheral side of the concave group 15, and the temperature is appropriately increased. In this state, the silicon carbide semiconductor device can be prevented from being destroyed by letting off the current.

  Lastly, the description of each embodiment described above, the description of modified examples, and the disclosure of the drawings are merely examples for explaining the invention described in the claims, and the description of the embodiment described above. The invention described in the scope of claims is not limited by the disclosure of the description or the drawings.

DESCRIPTION OF SYMBOLS 10 Silicon carbide semiconductor substrate 15 Recessed part 16 Recessed part 16 'Recessed part 16t Recessed part upper end 16't Recessed part upper end 16p Recessed part 16c located on the peripheral side Recessed part 20 located on the center side Silicon semiconductor layer 50 Schottky electrode (electrode)
L Laser light W1 Horizontal width W2 of Schottky electrode Horizontal width of recess group

Claims (11)

A silicon carbide semiconductor substrate;
A silicon carbide semiconductor layer formed on the silicon carbide semiconductor substrate;
An electrode provided on the silicon carbide semiconductor layer;
With
Limited to the lower surface of the silicon carbide semiconductor substrate and including the lower part in the vertical direction of the electrode, a recess group having a plurality of recesses formed by irradiating laser light is provided. A silicon carbide semiconductor device. A plurality of recesses and a plurality of electrodes are provided;
2. The silicon carbide semiconductor device according to claim 1, wherein each recess group is provided below each electrode in the vertical direction.   3. The silicon carbide semiconductor device according to claim 1, wherein each of the recesses in the recess group is provided in a lattice shape in the horizontal direction.   3. The silicon carbide semiconductor device according to claim 1, wherein each of the recesses of the recess group is provided with a honeycomb structure in a horizontal direction.   5. The width in the horizontal direction of the concave portion located on the center side of the electrode in the concave group is larger than the width in the horizontal direction of the concave portion located on the peripheral side of the electrode. 2. A silicon carbide semiconductor device according to claim 1.   5. The width in the horizontal direction of the concave portion located on the peripheral side of the electrode in the concave group is larger than the width in the horizontal direction of the concave portion located on the center side of the electrode. 2. A silicon carbide semiconductor device according to claim 1.   The silicon carbide semiconductor device according to claim 1, wherein a vertical cross-sectional shape of the concave portion is a U-shape.   The silicon carbide semiconductor device according to claim 1, wherein the recess is formed in the silicon carbide semiconductor substrate, and an upper end thereof does not reach the silicon carbide semiconductor layer. 9. The silicon carbide semiconductor device according to claim 1, wherein the energy of the laser beam is 0.5 J / cm ² or more.   10. The silicon carbide semiconductor device according to claim 1, wherein a conductive layer of carbon is formed on the exposed surface of the concave portion by the laser light. Forming a silicon carbide semiconductor layer on the silicon carbide semiconductor substrate;
Providing an electrode on the silicon carbide semiconductor layer;
A recess group having a plurality of recesses is formed by irradiating a laser beam limited to a region on the lower surface of the silicon carbide semiconductor substrate and including a region below the electrode in the vertical direction or a region below the electrode in the vertical direction. And a process of
A method for manufacturing a silicon carbide semiconductor device, comprising:

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