Semiconductor device

Abstract

The invention provides a semiconductor device. An RFC diode in which secondary breakdown is difficult to occur can be obtained. On the rear surface side, n-type cathode layers (12) and p-type cathode layers (13) are alternately formed in plan view, and the n-type cathode layers (12) and p-type cathode layers (13) are connected to a cathode electrode (21). The front surface-side semiconductor region is provided with: a first p-type anode layer (15) formed at substantially the same depth from the front surface; and a plurality of second p-type anode layers (16) which are formed so as to be dispersed in the first p-type anode layer (15) in plan view and which are formed deeper than the first p-type anode layer (15). In a plan view, the n-type cathode layer (12) is formed so as to be wider than each of the second p-type anode layers (16) directly below each of the second p-type anode layers (16) so as to include each of the second p-type anode layers (16), and is formed so as to correspond to each of the second p-type anode layers (16).

Description

Technical Field

[0001] This disclosure relates to a semiconductor device that functions as a diode. Background Technology

[0002] Among diodes utilizing pn junctions, the RFC (Relaxed Field of Cathode) diode is known as a diode with a structure that rapidly cuts off the current to suppress ringing during the reverse recovery period (the transition period from conduction to off).

[0003] In a typical diode, a p-type anode layer is formed on the front side relative to the n-type drift layer, and an n-type cathode layer is formed on the back side. Current flows between the anode and cathode layers when the diode is turned on. In contrast, in an RFC-type diode, the n-layer that becomes the cathode layer on the back side is broken, and a p-layer is inserted in between. During reverse recovery, holes are injected from the p-layer into the drift layer, thereby suppressing ringing and improving reverse recovery characteristics.

[0004] In the diode described above, a small forward voltage VF and a reverse recovery energy E in the reverse recovery characteristics described above are desirable. REC (Or the reverse recovery charge Qrr) is relatively small. However, in general, VF and E REC Due to the trade-off, it is difficult to reduce both of them. With this in mind, Patent Document 1 describes a further improvement in the structure of such an RFC-type diode.

[0005] Figure 14 This is a simplified cross-sectional view of the diode (semiconductor device 9) described in Patent Document 1. Here, the back side (lower side in the figure) of the n-type semiconductor layer (n-layer 91), which forms the drift region, is the cathode, and the front side (upper side in the figure) is the anode. On the cathode side, a highly concentrated n-type layer (n-type cathode layer 92) is provided as in the conventional configuration, and on the anode side, a p-type anode layer 93, which serves as the anode layer, is provided. Furthermore, a cathode electrode 94 is formed on the back side, and an anode electrode 95 is formed on the front side.

[0006] Here, as described above, on the cathode side, the n-type cathode layer 92 is formed in a segmented manner, and a p-type cathode layer 96 with the opposite conductivity type is disposed between adjacent n-type cathode layers 92. As described above, the presence of the p-type cathode layer 96 suppresses ringing and improves reverse recovery characteristics.

[0007] Furthermore, similarly to the cathode side, the p-type anode layer 93 is configured such that a deeper second p-type anode layer 93B and a shallower first p-type anode layer 93A are alternately formed in the in-plane direction. Here, for the convenience of this application specification, the terms "first" and "second" are used in a manner contrary to those described in Patent Document 1. Regarding the second p-type anode layer 93B, compared to the first p-type anode layer 93A, it has a higher impurity concentration, and it is formed to locally protrude towards the back side.

[0008] In this structure, by setting the ratio of the area (length in the left-right direction in the figure) of the n-type cathode layer 92 and the p-type cathode layer 96 on the cathode side, as well as the ratio of the area, depth, and impurity concentration ratio of the first p-type anode layer 93A and the second p-type anode layer 93B on the anode side, VF and E can be adjusted. REC The relationship between VF and E is thus able to achieve REC Optimization.

[0009] Patent Document 1: Japanese Patent No. 6750668

[0010] In the case where a structure is provided that partially protrudes to the back side from the p-type anode layer 93A, as described above, Figure 14 The region between the end of the deeper portion of the p-type anode layer (the end of the second p-type anode layer 93B) and the n-type cathode layer 92 directly below it, as shown in region X, is prone to breakdown (primary breakdown). In particular, with the expansion of the second p-type anode layer 93B, electrons easily reach the vicinity of the p-type cathode layer 96 on the back side, thereby allowing holes to easily inject from the p-type cathode layer 96 into the drift region (n-layer 91). This large number of holes generates conductivity modulation, resulting in a localized decrease in the resistance of the n-layer 91. A larger current easily flows locally through the n-layer 91, i.e., secondary breakdown easily occurs, thus easily damaging the device. Therefore, an RFC diode that is less prone to such secondary breakdown is desirable. Summary of the Invention

[0011] This disclosure was made in view of such problems, and its purpose is to provide a semiconductor device that solves the aforementioned problems.

[0012] To address the aforementioned issues, this disclosure has the following structure.

[0013] In the semiconductor device disclosed herein, current flows between a first main electrode disposed on the front side of a semiconductor substrate and a second main electrode disposed on the back side of the semiconductor substrate. The semiconductor substrate, on the front side, comprises: a drift region of a first conductivity type; and a front-side semiconductor region of a second conductivity type opposite to the first conductivity type, formed on the front side of the drift region and connected to the first main electrode. On the back side, when viewed from above, a back-side first semiconductor region of the first conductivity type and a back-side second semiconductor region of the second conductivity type, with a higher impurity concentration than the drift region, are alternately formed. The back-side first semiconductor region and the back-side second semiconductor region are connected to the second main electrode. The front-side semiconductor region comprises: a first front-side semiconductor region; and a second front-side semiconductor region, formed grounded to the first front-side semiconductor region and formed deeper than the first front-side semiconductor region. When viewed from above, the back-side first semiconductor region is formed directly below each of the second front-side semiconductor regions, encompassing the second front-side semiconductor regions, and is formed corresponding to each of the second front-side semiconductor regions.

[0014] Alternatively, multiple second front-side semiconductor regions may be arranged in a direction perpendicular to the long side when viewed from above, with the width of the outermost second front-side semiconductor region along said direction being larger than the width of the other second front-side semiconductor regions.

[0015] Alternatively, when viewed from above, each of the second front-side semiconductor regions can be formed as dots.

[0016] Alternatively, when viewed from above, each of the second front-side semiconductor regions includes a portion formed as stripes in the same long-side direction.

[0017] Alternatively, the impurity concentration of the second front-side semiconductor region can be set to be higher than that of the first front-side semiconductor region. On the outermost side of the second front-side semiconductor region, a surface electric field reduction layer is locally provided on the front side of the drift region. The surface electric field reduction layer is of the second conductivity type, and the impurity concentration of the surface electric field reduction layer is lower than that of the first front-side semiconductor region.

[0018] Alternatively, the reduced surface electric field layer may be formed shallower than the second front-side semiconductor region and deeper than the first front-side semiconductor region.

[0019] Alternatively, when viewed from above, the second semiconductor region on the back side is not formed on the outside compared to the second semiconductor region on the front side, which is the outermost side.

[0020] Alternatively, when viewed from above, the minimum width of the second front-side semiconductor region on the front side is in the range of 5μm to 60μm, and the area of ​​the first back-side semiconductor region on the back side accounts for 30% to 70% of the total area of ​​the first back-side semiconductor region and the second back-side semiconductor region.

[0021] Alternatively, the combination of the second front-side semiconductor region and the corresponding rear-side first semiconductor region may be periodically arranged when viewed from above.

[0022] Because this disclosure is configured as described above, an RFC diode that is less prone to secondary breakdown can be obtained. Attached Figure Description

[0023] Figure 1 This diagram schematically illustrates the first and second breakdown states of a diode.

[0024] Figure 2 This is a cross-sectional view (of 1) showing the structure of a semiconductor device according to an embodiment of the present disclosure.

[0025] Figure 3 The result is the result of calculation of the distribution of current density flowing during a single breakdown of the semiconductor device according to the embodiments of this disclosure.

[0026] Figure 4 The result is the result of calculating the dependence of the primary breakdown voltage BV1(a) and secondary breakdown voltage BV2(b) in the semiconductor device according to the embodiments of the present disclosure on the protrusion amount D of the second front side semiconductor region.

[0027] Figure 5 The result is a calculation of the dependence of the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b) in the semiconductor device according to the embodiments of the present disclosure on the width W of the second front-side semiconductor region.

[0028] Figure 6 The result is a calculation of the dependence of the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b) in the semiconductor device according to the embodiments of the present disclosure on the spacing P of the second front-side semiconductor region.

[0029] Figure 7 The result is a calculation of the dependence of the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b) in the semiconductor device according to the embodiments of the present disclosure on the width WN of the first semiconductor region on the back side.

[0030] Figure 8The results are from investigating the relationship between forward voltage VF and reverse recovery charge Qrr by changing the back n-type ratio in an embodiment of the semiconductor device of this disclosure.

[0031] Figure 9 This is a diagram illustrating an example of a planar structure of a semiconductor device according to an embodiment of the present disclosure.

[0032] Figure 10 This is a diagram illustrating another example of a planar structure of a semiconductor device according to an embodiment of the present disclosure.

[0033] Figure 11 This is a cross-sectional view (of 2) showing the structure of a semiconductor device according to an embodiment of the present disclosure.

[0034] Figure 12 This is a cross-sectional view (of 3) showing the structure of a semiconductor device according to an embodiment of the present disclosure.

[0035] Figure 13 This is a diagram illustrating a variation of another example of the planar structure of a semiconductor device according to an embodiment of the present disclosure.

[0036] Figure 14 This is a cross-sectional view showing the structure of an example of a conventional RFC diode.

[0037] Label Explanation

[0038] 1, 9: Semiconductor devices;

[0039] 11, 91: n layers (drift region);

[0040] 12, 92: n-type cathode layer (first semiconductor region on the back side);

[0041] 12A: Terminal-side n-type cathode layer (n-type cathode layer);

[0042] 13, 96: p-type cathode layer (second semiconductor region on the back side);

[0043] 14: Field cutoff layer;

[0044] 15. 93A: First p-type anode layer (first front-side semiconductor region: front-side semiconductor region);

[0045] 16. 93B: Second p-type anode layer (second front-side semiconductor region: front-side semiconductor region);

[0046] 16A: Terminal-side p-type anode layer;

[0047] 17: Terminal n-type layer;

[0048] 18: Reduce the surface electric field layer (reduce the surface electric field region);

[0049] 21, 94: Cathode electrode (second main electrode);

[0050] 22, 95: Anode electrode (first main electrode);

[0051] 23: Interlayer insulation layer;

[0052] 24: Terminal electrode;

[0053] 93: p-type anode layer;

[0054] R1: Active region;

[0055] R2: Terminal area. Detailed Implementation

[0056] The semiconductor device according to embodiments of the present disclosure will be described below. Furthermore, in the following drawings, the same or similar parts are labeled with the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of lengths of various parts, etc., differ from reality. Therefore, specific dimensions should be determined with reference to the following description. Additionally, the drawings also include parts with different dimensional relationships and ratios. Furthermore, the embodiments shown below exemplify a device for embodying the technical concept of the present disclosure; the technical concept of the present disclosure does not limit the shape, structure, arrangement, etc., of the constituent components to the following content. Various modifications can be made to the embodiments of the present invention in the claims. Furthermore, in this disclosure, the terms "upper" and "lower," etc., specifying upper and lower, are used for ease of description; even when disposed on a side surface, as long as it is substantially the same as the constituent elements of the present disclosure, it also falls within the scope of the present disclosure. In addition, "upper" includes not only the case formed in contact with the object but also the case formed with other layers in between. Furthermore, in this disclosure, "connection" is not limited to direct connection. Even when connecting by placing certain components such as resistors between them, as long as it is substantially the same as the constituent elements of this disclosure, it falls within the scope of this disclosure.

[0057] Figure 1 This is a schematic diagram illustrating the breakdown characteristics (current-voltage characteristics under reverse bias) of the semiconductor device (diode) that is in question here. Figure 1In this diagram, the reverse bias current is expressed on a logarithmic scale. Here, the phenomenon where the current increases sharply from a state of low reverse current to the primary breakdown voltage BV1 is called primary breakdown. When the voltage becomes further higher than BV1, at the secondary breakdown voltage BV2, conductivity modulation occurs due to the large number of holes injected into the drift region, resulting in negative resistance. Consequently, a large current flows, leading to component failure. BV1 is, for example, above 500V, and BV2 is even higher; secondary breakdown is caused by the current flowing due to primary breakdown. Because a large current flows particularly during secondary breakdown, it is especially prone to causing damage to the semiconductor device itself or its connected circuitry.

[0058] In this semiconductor device, the current density of the current flowing during a first breakdown is set to be small, and the subsequent second breakdown is set to be difficult to occur (BV2 increases). Therefore, in this semiconductor device, damage during a second breakdown is difficult to occur.

[0059] Typically, in the semiconductor substrate constituting such a semiconductor device (RFC diode or power semiconductor element), an active region that functions as an active element (diode) and a termination region (on the outer periphery) formed in the active region to ensure voltage withstand capability are provided. Figure 14 The structure of the active region is shown only in the illustration; however, the configuration of the semiconductor device comprising both regions is described in relation to embodiments of the present disclosure.

[0060] Figure 2 This is a cross-sectional view showing the structure of the semiconductor device 1. Here, the active region R1 is shown on the left side of the figure, and the termination region R2 is shown on the right side. The center of the semiconductor substrate is located at... Figure 2 To the left. In fact, the terminal region R2 is formed to surround the active region R1 when viewed from above, therefore Figure 1 The terminal region R2 is also formed to the left of the active region R1 in a structure that is symmetrical to it. Their specific planar structures will be described later.

[0061] In the active region R1, Figure 2 In the same structure as the semiconductor device 9 described above, the back side (lower side in the figure) of the n-type semiconductor layer (n-layer 11), which forms the drift region, is used as the cathode, and the front side (upper side in the figure) is used as the anode. On the cathode side, an n-type cathode layer (back side first semiconductor region) 12 and a p-type cathode layer (back side second semiconductor region) 13, which are high-concentration n-type layers, are alternately arranged in the horizontal direction. They are formed with a thin n-type field stop layer 14 sandwiched between them and the n-layer 11. The impurity concentration of the field stop layer 14 is set to be higher than the impurity concentration of the n-layer 11 and lower than the impurity concentration of the n-type cathode layer 12.

[0062] Furthermore, a p-type anode region (front-side semiconductor region) is formed on the entire front side of the active region R1. A shallowly formed first p-type anode layer (first front-side semiconductor region) 15 and a deeper formed second p-type anode layer (second front-side semiconductor region) 16 are provided in the anode region. In addition, a cathode electrode (second main electrode) 21 is provided on the back side and an anode electrode (first main electrode) 22 is provided on the front side. Therefore, during the operation of the semiconductor device 1, a current with rectification characteristics flows between the anode electrode 22 and the cathode electrode 21, similar to a conventional diode. In particular, the improved reverse recovery characteristics due to the presence of the p-type cathode layer 13 are also the same as those described in Patent Document 1.

[0063] exist Figure 2 In the diagram, only three second p-type anode layers 16 and a terminal-side p-type anode layer 16A (described later) are shown on the front side. However, in the active region R1, more second p-type anode layers 16 are periodically arranged in the horizontal direction of the paper, and are also formed outside the area shown on the left. Each second p-type anode layer 16 is actually formed to extend in the vertical direction of the paper, as described later, and is arranged in the horizontal direction of the paper (the direction perpendicular to the extension direction). Hereinafter, only the structure of the region in the active region R1 where the second p-type anode layers 16 are arranged will be described first; the structures of the terminal-side p-type anode layer 16A and the terminal region R2 will be described later. It is further preferred that the spacing of the second p-type anode layers 16 is equal.

[0064] On the back side, the n-type cathode layer 12 and p-type cathode layer 13 are formed as a group, corresponding to the structure on the front side described above. In this case, the n-type cathode layer 12 is positioned directly below the second p-type anode layer 16, and its width is set to be wider than that of the second p-type anode layer 16, so that the second p-type anode layer 16 is contained within the n-type cathode layer 12 when viewed from above. Therefore, the p-type cathode layer 13 is not positioned directly below the second p-type anode layer 16. Furthermore, the impurity concentration of the n-type cathode layer 12 is higher than that of the p-type cathode layer 13, and the impurity concentration of the p-type cathode layer 13 is higher than that of the second p-type anode layer 16.

[0065] According to this structure, even if the primary breakdown voltage BV1 is the same, the current density flowing during the primary breakdown can be reduced, making it difficult for subsequent secondary breakdowns to occur. This will be explained below.

[0066] exist Figure 14In the structure described above, the current path during a single breakdown becomes the bottom end of the second p-type anode layer 93B, allowing electrons to easily reach the vicinity of the p-type cathode layer 96 on the back side. Consequently, holes can easily be injected from the p-type cathode layer 96 into the drift region (n-layer 91). In contrast, in... Figure 2 In this structure, the current path can be set to cover the entire surface from the second p-type anode layer 16 to the corresponding n-type cathode layer 12 directly below it. Therefore, electrons have difficulty reaching the p-type cathode layer 13. Figure 14 Compared to the previous structure, this structure makes secondary breakdown less likely to occur. Moreover, by combining multiple second p-type anode layers 16 with the n-type cathode layer 12 directly below them, the breakdown points can be dispersed, making secondary breakdown even more difficult to occur.

[0067] Figure 3 This is a simulation result of the current density distribution in the drift region (n-layer 11) during a single breakdown in this structure, with shades representing the magnitude of the current density in the semiconductor substrate. As shown here, during a single breakdown, the current does not... Figure 14 The current does not flow in region X, but rather in a large region from directly below the locally deepening second p-type anode layer 16 to the n-type cathode layer 12 below it. Furthermore, multiple second p-type anode layers 16 are provided, and an n-type cathode layer 12 is provided directly below each second p-type anode layer 16, with its width set wider than the second p-type anode layer 16, so that the second p-type anode layer 16 is contained within the n-type cathode layer 12 when viewed from above. This disperses the local current path, further reducing the current density in each current path. Moreover, it suppresses damage caused by local current concentration. Here, the horizontal spacing of the second p-type anode layers 16 (the arrangement direction of the second p-type anode layers 16) is preferably equal to the spacing of the n-type cathode layers 12. Furthermore, the central axis of the second p-type anode layer 16 is aligned with the central axis of the n-type cathode layer 12 directly below it. This makes it difficult for electrons to reach the p-type cathode layer 13, making secondary breakdown less likely.

[0068] The simulation results regarding this point are explained. Figure 4 The results are calculated by simulating the relationship between the protrusion D from the bottom of the first p-type anode layer 15 to the second p-type anode layer 16 and the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b), assuming the drift region (n-layer 11) is silicon with a resistivity of 23 Ω·cm and its thickness (the interval from the second p-type anode layer 16 to the n-type cathode layer 12, etc.) is 50 μm. Figure 2 The width W of the second p-type anode layer 16 is 5 μm, and its impurity concentration is 9 × 10⁻⁶. 16 cm -3The first p-type anode layer 15 has a depth of 4.22 μm and an impurity concentration of 1.08 × 10⁻⁶. 16 cm -3 The periodic spacing P between the second p-type anode layer 16 and the n-type cathode layer 12 is 100 μm, the width WN of the n-type cathode layer 12 is 50 μm, its depth is 0.55 μm, and its impurity concentration is 2.5 × 10⁻⁶. 19 cm -3 The width of the p-type cathode layer 13 is the difference between the aforementioned periodic spacing P and the aforementioned WN, its depth is 0.45 μm, and its impurity concentration is 1 × 10⁻⁶. 18 cm -3 The field stop layer 14 has a thickness of 1.25 μm and an impurity concentration of 9 × 10⁻⁶. 15 cm -3 In subsequent calculations, except for parameters that are set as variable or whose values ​​are explicitly stated, the same applies as described above.

[0069] exist Figure 4 In this context, D=0 corresponds to the case where the second p-type anode layer 16 is not present. According to... Figure 4 As a result of (a), by increasing the protrusion D of the second p-type anode layer 16, the primary breakdown voltage BV1 decreases. This is because by increasing the protrusion D of the second p-type anode layer 16, the distance between the second p-type anode layer 16 and the n-type cathode layer 12 becomes shorter, and the current path in the n-layer 11 becomes shorter. On the other hand, the secondary breakdown voltage BV2 increases when the protrusion D increases, meaning that secondary breakdown is less likely to occur. During primary breakdown, if the second p-type anode layer 16 is not provided, an electric field concentration occurs directly below the first p-type anode layer 15. If a p-type cathode layer 13 is provided directly below the first p-type anode layer 15, electrons can easily reach the p-type cathode layer 13, making secondary breakdown more likely. On the other hand, if the protrusion D increases, the current is concentrated directly below the second p-type anode layer 16, so electrons can easily flow into the n-type cathode layer 12 directly below the second p-type anode layer 16 in large quantities. Therefore, electrons have difficulty reaching the p-type cathode layer 13, thereby making secondary breakdown less likely to occur. To improve the primary breakdown voltage BV1, increasing the resistivity of the silicon substrate (reducing the impurity concentration of the n-layer 11) is effective, thereby simultaneously improving both the primary breakdown voltage BV1 and the secondary breakdown voltage BV2.

[0070] according to Figure 4As a result of (a) and (b), in order to reduce the decrease in the primary breakdown voltage BV1 and increase the secondary breakdown voltage BV2, the protrusion amount D is preferably in the range of 1 μm to 5 μm. On the other hand, regarding the depth of the first p-type anode layer 15, it is appropriately set to a degree that can ensure the protrusion amount D of the second p-type anode layer 16 and ensure the characteristics such as the forward voltage of the diode. In order to ensure the aforementioned range of protrusion amount D while maintaining these characteristics, the ratio of (protrusion amount D) to (depth of the first p-type anode layer 15) is preferably in the range of 0.2 to 1.0.

[0071] in addition, Figure 5 It is a change Figure 2 The width W of the second p-type anode layer 16 in the middle is used to calculate the results of the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b). Here, Figure 2 The protrusion D of the second p-type anode layer 16 is 2 μm, and the width WN of the n-type cathode layer 12 is 50 μm.

[0072] according to Figure 5 The result of (a) shows no significant dependence on the width W in the primary breakdown voltage BV1. This indicates that primary breakdown occurs independently of the width W of the second p-type anode layer 16 at both ends of the second p-type anode layer 16. On the other hand, as Figure 5 As shown in (b), when the width W becomes 60 μm, the secondary breakdown voltage BV2 decreases. This is because when the width W increases, primary breakdown occurs at both ends of the second p-type anode layer 16, thus electrons can easily reach the p-type cathode layer 13, making secondary breakdown more likely.

[0073] according to Figure 5 As a result of (b), the width W of the second p-type anode layer 16 is preferably small. However, if the width W is too small, the current density will be high even if the current path occupies the entire width W of the second p-type anode layer 16. Furthermore, a certain width D is also required to ensure the protrusion D of the second p-type anode layer 16. Therefore, the lower limit of the width D is preferably about 5 μm. Figure 5 As a result of (b), the width D is preferably in the range of 5μm to 60μm, and particularly preferably in the range of 5μm to 40μm.

[0074] By providing multiple combinations of the aforementioned second p-type anode layer 16 and n-type cathode layer 12, the current density in each current path can be reduced, thereby increasing the secondary breakdown voltage BV2. Therefore, reducing the aforementioned spacing P is effective. Figure 6 It is Figure 2The results of calculating the dependence of the primary breakdown voltage BV1(a) and the secondary breakdown voltage BV2(b) on the aforementioned spacing P are given under the following conditions: the width of the active region R1 in the horizontal direction is set to constant; the width W of the second p-type anode layer 16 is set to 5 μm; the protrusion amount D is set to 7 μm; and the width WN of the n-type cathode layer 12 is set to 50 μm.

[0075] according to Figure 6 In (a), within a spacing P of 100 μm to 300 μm, the primary breakdown voltage BV1 remains constant. This is because, as described above, the primary breakdown mechanism occurs at both ends of the second p-type anode layer 16. On the other hand, when the spacing P increases, the secondary breakdown voltage BV2 decreases. This is because if the spacing P is narrower, the local current paths can be more dispersed, and the current flowing directly below the second p-type anode layer 16 is less, thus making secondary breakdown less likely to occur. Therefore, from the viewpoint of increasing the secondary breakdown voltage BV2, it is preferable to decrease the spacing P, but if the spacing P decreases, it is difficult to make the n-type cathode layer 12 larger than the second p-type anode layer 16. In addition, it will affect the ratio of the n-type cathode layer 12 to the p-type cathode layer 13, and the injection efficiency of holes from the p-type cathode layer 13 to the n-layer 11 during reverse recovery will decrease, thus deteriorating the reverse recovery characteristics.

[0076] Next, the width W and protrusion D of the second p-type anode layer 16 were kept constant as described above, and the dependence of the primary breakdown voltage BV1 and the secondary breakdown voltage BV2 on the width WN of the n-type cathode layer 12 was investigated. Figure 7 These are the calculation results of BV1(a) and BV2(b) under this condition.

[0077] like Figure 7 As shown in (a), in this case, no dependence on the width WN is observed in the single breakdown voltage BV1. On the other hand, as Figure 7 As shown in (b), the larger the width WN of the n-type cathode layer 12, the higher the secondary breakdown voltage BV2. This is because, by setting W < WN, the current during primary breakdown flows to the entire n-type cathode layer 12, and by increasing the width WN of the n-type cathode layer 12, the density of this current decreases. Furthermore, because electrons have difficulty reaching the p-type cathode layer 13, secondary breakdown is unlikely to occur. Therefore, a larger width WN is preferable, but when the width WN is 70 μm or more, the secondary breakdown voltage BV2 will not increase further. On the other hand, increasing the width WN requires either further increasing the aforementioned spacing P or narrowing the p-type cathode layer 13. Therefore, it is preferable that the width WN is less than 70 μm, and correspondingly, the spacing P is reduced based on a p-type cathode layer 13 with a certain or greater width.

[0078] In addition, Figure 2In the structure, during forward orientation, the n-type cathode layer 12 becomes the dominant current path on the back side. Therefore, to reduce the forward resistance (reduce the forward voltage VF), the ratio of the n-type cathode layer 12 on the back side (back-side n-type ratio) in the structure of the group (one cycle) of the n-type cathode layer 12 and its adjacent p-type cathode layer 13 is set as the width WN of the n-type cathode layer 12 / the spacing P of the cycle (WN < P). The larger this back-side n-type ratio, the smaller the forward voltage VF. On the other hand, as mentioned above, the p-type cathode layer 13 is provided to improve the reverse recovery characteristics; therefore, when the back-side n-type ratio is large, the reverse recovery characteristics deteriorate. Thus, there is a trade-off between the forward voltage VF and the reverse recovery characteristics.

[0079] Figure 8 This is the result of measuring the relationship between Qrr (reverse recovery charge: the amount of charge required until the reverse recovery current disappears during reverse recovery operation) and the forward voltage VF, using a sample as a reverse recovery characteristic, with the back-side n-type ratio varying within the range of 10% to 70%. According to this result, there is a trade-off between VF and Qrr as described above; if the back-side n-type ratio is small, Qrr decreases while VF increases. However, compared to the case where the back-side n-type ratio is 30% or higher, when the back-side n-type ratio is 20% or lower, the reduction in Qrr is smaller, while the increase in VF is significant. Furthermore, when it exceeds 70%, almost no improvement in reverse recovery characteristics is obtained. Therefore, there is no advantage to having a back-side n-type ratio less than 20%, and the back-side n-type ratio is preferably set within the range of 30% to 70%.

[0080] The above is about Figure 2 The structure in the active region R1 is described. Next, the structure of the terminal region R2, the structure of the terminal region R2 side in the active region R1, and... Figure 2 The planar structure of the semiconductor device 1 will be described. As described above, in this semiconductor device 1, in order to improve the secondary breakdown voltage BV2, it is preferable that a breakdown occurs once between the second p-type anode layer 16 and the n-type cathode layer 12 directly below it, and in each of these combinations. Therefore, it is preferable that no primary breakdown (secondary breakdown) occurs in the terminal region R2.

[0081] exist Figure 2 At the outermost periphery (right end), a high-concentration n-type terminal n-type layer 17 is formed, which is set to the terminal potential. In addition, the first p-type anode layer 15 extends toward the terminal side (right side in the figure), and a p-type reduced surface electric field layer (reduced surface electric field region) 18 with a lower impurity concentration than the first p-type anode layer 15 is formed between the first p-type anode layer 15 and the terminal n-type layer 17.

[0082] Furthermore, on the outermost side of the active region R1 (right side in the figure), a terminal-side p-type anode layer 16A with the same depth and impurity concentration as the second p-type anode layer 16 described above is formed. Directly below the terminal-side p-type anode layer 16A is the n-type cathode layer 12. Therefore, the terminal-side p-type anode layer 16A functions in the same way as the second p-type anode layer 16 in the active region R1, or the terminal-side p-type anode layer 16A can be one of multiple second p-type anode layers 16.

[0083] However, in this structure, a primary breakdown is prone to occur directly below the terminal p-type anode layer 16A at the outermost end of the active region R1. Therefore, in order to reduce the current density at this part during breakdown, Figure 2 The width of the terminal-side p-type anode layer 16A in the horizontal direction is wider than that of the second p-type anode layer 16. Furthermore, the width of the n-type cathode layer 12 (terminal-side n-type cathode layer 12A) directly below the terminal-side p-type anode layer 16A is wider than the width of the n-type cathode layer 12 located further inward (on the left side of the figure). For example, as... Figure 2 As shown, alternatively, a p-type cathode layer 13 may exist only inside the p-type anode layer 16A directly below it on the terminal side, while an n-type cathode layer 12A may be located directly below and outside the p-type anode layer 16A on the terminal side. Primary breakdown is prone to occur on the terminal side in the active region R1, but by making the width of the p-type anode layer 16A on the terminal side wider than the width of the second p-type anode layer 16, primary breakdown can occur over a larger area of ​​the p-type anode layer 16A on the terminal side.

[0084] exist Figure 2 In this process, an interlayer insulating layer 23 is formed on top of the surface electric field reducing layer 18, and a terminal electrode 24, which is insulated from the anode electrode 22 by having the interlayer insulating layer 23 sandwiched between them, is connected to the terminal n-type layer 17. Furthermore, as described above, in Figure 2 The cross-sectional structure is shown, but as will be described later, the terminal-side n-type cathode layer 12A, the terminal-side p-type anode layer 16A, the surface electric field reduction layer 18, and the terminal n-type layer 17 are actually formed as a ring surrounding the active region R1 when viewed from above. The terminal electrode 24 and the interlayer insulating layer 23 can also be formed as a ring, but their planar shapes can be appropriately set as long as the potential of each electrode can be properly controlled.

[0085] The potential of the terminal electrode 24 is, for example, equal to that of the cathode electrode 21. Through the above structure, the potential distribution on the terminal side of the semiconductor substrate is controlled to appropriately perform the aforementioned operation in the active region R1. At this time, the breakdown voltage in the terminal region R2 is mainly determined by the reduced surface electric field layer 18. Therefore, although in Figure 2The description is simplified, but the length of the reduced surface electric field layer 18 in the horizontal direction in the figure is actually set to be sufficiently long so that the withstand voltage between the anode electrode 22 and the terminal electrode 24 is higher than that between the anode electrode 22 and the cathode electrode 21. In addition, to improve this withstand voltage, it is more preferable to provide a field plate structure as described in Japanese Patent No. 3275964 on the front side of the reduced surface electric field layer 18 (in the interlayer insulating layer 23), but its description is omitted here.

[0086] When a surface electric field reduction layer 18 is provided, the surface electric field reduction layer 18 or Figure 2 A breakdown also occurs between the left end (active region R1 side) and the back side, thus a secondary breakdown may occur in this part. Therefore, to prevent breakdown in the terminal region R2, the second p-type anode layer 16 and the terminal-side p-type anode layer 16A are preferably formed deeper than the surface electric field reduction layer 18. That is, it is set to be: [...and...] Figure 2 Compared to the first p-type anode layer 15 and the terminal n-type layer 17 in the terminal region R2, and the surface electric field reduction layer 18 and the n-type cathode layer 12 directly below it, each second p-type anode layer 16 in the active region R1 and the n-type cathode layer 12 directly below it undergo a single breakdown at a lower voltage.

[0087] Figure 9 It is shown Figure 2 A diagram showing an example of the planar structure of semiconductor device 1. Figure 9 In the middle, as viewed from above Figure 2 The top view shows the planar shapes (solid lines) of the second p-type anode layer 16 on the front side and the p-type anode layer 16A on the terminal side, and the planar shapes (dashed lines) of the n-type cathode layer 12 and the p-type cathode layer 13 on the back side. The planar structure of the active region R1 is mainly shown here, and the area outside the active region R1 shown corresponds to the aforementioned terminal region R2. Here, only 13 dot-shaped second p-type anode layers 16 are provided, but in reality, more second p-type anode layers 16 are arranged. Furthermore, the terminal-side p-type anode layers 16A surround the arrangement of the second p-type anode layers 16 in a ring shape. Figure 9 The first p-type anode layer 15 is not described in the text, but as Figure 2 As shown, in the active region R1, the first p-type anode layer 15 is formed over the entire surface. Figure 9 Each of the second p-type anode layers 16 is connected to the first p-type anode layer 15 (and anode electrode 22) on the front side, and their potentials become a common anode potential.

[0088] exist Figure 9In the back side, the dotted n-type cathode layer 12 corresponds to each of the second p-type anode layers 16, and is formed to be wider than the second p-type anode layer 16 in a way that includes the second p-type anode layer 16 when viewed from above. Thus, multiple combinations of the aforementioned second p-type anode layer 16 and the n-type cathode layer 12 directly below it are arranged to improve the secondary breakdown voltage BV2. Furthermore, the width of the terminal-side p-type anode layer 16A is formed to be larger than the diameter of the second p-type anode layer 16. Additionally, in Figure 9 In the active region R1, multiple n-type cathode layers 12 are formed, and p-type cathode layers 13 are formed between the multiple n-type cathode layers 12.

[0089] On the other hand, Figure 9 In this arrangement, outside the second p-type anode layer 16, the n-type cathode layer 12 is uniformly formed, encompassing the region directly below the terminal-side p-type anode layer 16A. Therefore, the p-type cathode layer 13 on the back side is only disposed between the separately disposed n-type cathode layers 12 within the active region R1. Furthermore, Figure 2 The reduced surface electric field layer 18 and the terminal n-type layer 17 are formed in a ring shape surrounding the terminal p-type anode layer 16A on the outer side of the terminal side.

[0090] In this structure, the reverse recovery characteristics (reducing Qrr) are improved by arranging the p-type cathode layer 13 as described above, and the forward voltage VF can be reduced by increasing the area of ​​the n-type cathode layer 12. At this time, as mentioned above, the secondary withstand voltage BV2 can also be improved. Figure 2 In the structure, as described above, the number of second p-type anode layers 16 differs, but is similar to... Figure 9 The right half of the cross-section in the AA direction corresponds to the cross-section in the diagram. Figure 2 The terminal n-type layer 17 and the surface electric field reduction layer 18, etc., in Figure 9 The appropriate terrain on the outside of the structure forms a ring.

[0091] exist Figure 9 In the structure, each second p-type anode layer 16 is formed as a dot, but as a structure to further reduce the current density by expanding the current path during a single breakdown, there is a structure in which each second p-type anode layer 16 is set as a stripe (a long strip in one direction). Figure 10 This is a planar diagram illustrating an example of the structure. Here, the pattern of the n-type cathode layer 12, corresponding to the rectangular shape of the second p-type anode layer 16, includes the pattern of the second p-type anode layer 16 and is a larger rectangular shape.

[0092] and Figure 9 Similarly, Figure 2 sectional view and Figure 10 The right half of the cross-section in the BB direction corresponds to this. Figure 10 The cross-sectional view corresponding to the lower half of the figure is shown in the CC direction (the direction of the long side of the second p-type anode layer 16 where the second p-type anode layer 16 exists). Figure 11 A cross-sectional view of the section in the DD direction (the arrangement direction of the second p-type anode layer 16 at the location where the second p-type anode layer 16 is not formed on the front side but the p-type cathode layer 13 is formed on the back side) corresponding to the right half of the figure is shown. Figure 12 .

[0093] also, Figure 9 , Figure 10 The planar shape of the terminal-side p-type anode layer 16A in the middle Figure 10 The shapes of the p-type cathode layer 13 and n-type cathode layer 12 are simplified to rectangular shapes. In this case, primary breakdown is particularly prone to occur at the corners of the rectangular shape, so it is actually particularly preferable to properly design these corners as R-shapes.

[0094] Figure 13 It shows Figure 10 A planar structure, a variation of the structure. Figure 10 In the active region R1, multiple second p-type anode layers 16 are formed independently and in parallel, with the vertical direction as the long side in the figure. Figure 13 In the structure, they become a structure in which they are connected to the terminal p-type anode layer 16A on the outer side (top and bottom in the figure). Figure 13 In this structure, a p-type cathode layer 13 is provided only on the back side of the region surrounded by the second p-type anode layer 16 and the terminal-side p-type anode layer 16A; the remaining region is designated as an n-type cathode layer 12 (12A). In this structure, the n-type cathode layer 12, corresponding to the second p-type anode layer 16, is also formed to be wider than the second p-type anode layer 16. Figure 13 In the case of this structure, there is no end in the long side direction of the n-type cathode layer 12, thus suppressing the occurrence of breakdown caused by this end, making it easier for breakdown to occur on the terminal side of the p-type anode layer 16A. In this way, a structure in which each of the second p-type anode layers 16 is connected at its end can also be used, in which case they can be connected using the terminal side p-type anode layer 16A. The shape of the n-type cathode layer 12 can be appropriately set accordingly.

[0095] Furthermore, as described above, it is particularly preferred to provide a field plate structure on the upper side of the reduced surface electric field layer 18, thereby ensuring withstand voltage without expanding the terminal region R2. The structure used to implement this preferred solution is appropriately configured as described in Japanese Patent No. 3275964.

[0096] Furthermore, in the above example, the terminal-side p-type anode layer 16A, the surface electric field reduction layer 18, and the terminal n-type layer 17 are formed in a ring shape on the outer periphery of the semiconductor substrate. However, depending on the structure of the active region of the semiconductor device, their shape at the end side of the semiconductor substrate is appropriately set, for example, according to which part is limited by the withstand voltage. Therefore, they are provided at a position closer to the end side than the active region, but their shape does not need to be ring-shaped. It is also possible to provide a trench that does not penetrate the terminal-side p-type anode layer 16A and the second p-type anode layer 16 from the upper surface of the terminal-side p-type anode layer 16A and the second p-type anode layer 16, and to bury the anode electrode 22 in the trench. In addition, the above semiconductor device is described using an RFC diode as an example, but the present invention can also be applied to the diode section of an RC-IGBT.

[0097] Furthermore, other layers can be added or removed appropriately in the semiconductor substrate. Also, in the example above, the same structure can obviously be applied even if the p-type and n-type phases in the semiconductor are completely reversed.

Claims

1. A semiconductor device, wherein current flows between a first main electrode disposed on the front side of a semiconductor substrate and a second main electrode disposed on the back side of the semiconductor substrate, characterized in that, The semiconductor substrate has the following on the front side: The drift region of the first conductivity type; and A semiconductor region of a second conductivity type, opposite to the first conductivity type, is formed on the front side of the drift region and is connected to the first main electrode. On the back side, when viewed from above, a first semiconductor region of the first conductivity type and a second semiconductor region of the second conductivity type, with a higher impurity concentration than the drift region, are alternately formed. The first and second semiconductor regions on the back side are connected to the second main electrode. The front-side semiconductor region includes: First front-side semiconductor region; as well as The second front-side semiconductor region is formed to ground with the first front-side semiconductor region and is formed deeper than the first front-side semiconductor region. When viewed from above, the rear-side first semiconductor region is formed more extensive than the second front-side semiconductor region in a manner that includes the second front-side semiconductor region directly below each of the second front-side semiconductor regions, and is formed corresponding to each of the second front-side semiconductor regions.

2. The semiconductor device according to claim 1, characterized in that, Multiple second front-side semiconductor regions are arranged in a direction perpendicular to the long side when viewed from above. The width of the outermost second front-side semiconductor region along the one direction is formed to be larger than the width of the other second front-side semiconductor regions.

3. The semiconductor device according to claim 1 or 2, characterized in that, When viewed from above, each of the second front-side semiconductor regions is formed as dots.

4. The semiconductor device according to claim 1 or 2, characterized in that, When viewed from above, each of the second front-side semiconductor regions includes a portion formed as stripes in the same long-side direction.

5. The semiconductor device according to claim 1 or 2, characterized in that, The impurity concentration of the second front-side semiconductor region is set to be higher than that of the first front-side semiconductor region. Outside the outermost second front-side semiconductor region, a surface electric field reduction layer is locally disposed on the front side of the drift region. The surface electric field reduction layer is of the second conductivity type, and the impurity concentration of the surface electric field reduction layer is lower than that of the first front-side semiconductor region.

6. The semiconductor device according to claim 5, characterized in that, The reduced surface electric field layer is formed shallower than the second front-side semiconductor region and deeper than the first front-side semiconductor region.

7. The semiconductor device according to claim 1 or 2, characterized in that, When viewed from above, the second semiconductor region on the back side is not formed on the outside compared to the second semiconductor region on the front side, which is the outermost side.

8. The semiconductor device according to claim 1 or 2, characterized in that, When viewed from above, The minimum width of the second front-side semiconductor region on the front side is in the range of 5μm to 60μm. The area of ​​the back-side first semiconductor region relative to the sum of the areas of the back-side first semiconductor region and the back-side second semiconductor region is in the range of 30% to 70%.

9. The semiconductor device according to claim 1 or 2, characterized in that, The combination of the second front-side semiconductor region and the corresponding rear-side first semiconductor region is periodically arranged when viewed from above.

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