Semiconductor device and method for driving semiconductor device

Abstract

The present invention reduces a recovery loss ocurring during recovery of a diode in an RC-IGBT. A semiconductor device 100 has an IGBT and a diode in a same chip. The IGBT has an emitter, a collector, a first trench 3A, and a gate provided inside the first trench 3A. The diode has an anode electrically connected to the emitter, a cathode electrically connected to the collector, a second trench 3B penetrating the anode and reaching the cathode, an in-trench insulating film 4B provided inside the second trench 3B, and a diode gate provided inside the second trench 3B and facing the anode and the cathode with the in-trench insulating film 4B interposed therebetween. The diode gate can apply voltage independently of the gate of the IGBT, and negative voltage is applied to the anode at least in a period T4 in which a reverse current flows during recovery of the diode.

Description

Semiconductor device and method for driving the same

[0001] The present invention relates to a semiconductor device and a method for driving the semiconductor device.

[0002] RC-IGBTs (RC: Reverse-Conducting IGBTs), which incorporate an IGBT (Insulated Gate Bipolar Transistor) and a diode within the same chip, have the advantage of being able to share the termination area between the IGBT and the diode, thereby reducing the chip size. Furthermore, because the IGBT and the diode operate at different times, heat generated by losses in either the IGBT or the diode area is distributed to the other, allowing heat to be dissipated throughout the chip, reducing thermal resistance.

[0003] An example of prior art related to RC-IGBTs is Patent Document 1. FIG. 1 of Patent Document 1 describes a structure in which a trench (3) is formed in the diode region (22) as in the IGBT region (21), and a dummy electrode (6) is provided inside the trench (3) in the diode region (22). Paragraph 0025 of Patent Document 1 also describes that, although the dummy electrode (6) is supplied with, for example, an emitter potential (E), it is not limited to this, and may be supplied with another potential such as a gate potential (G).

[0004] Japanese Patent Application Laid-Open No. 2023-172272

[0005] In an RC-IGBT, the anode potential (A) is the same as the emitter potential (E). As in Patent Document 1, in an RC-IGBT, a trench (3) is also formed in the diode region (22), and when the emitter potential (E) or gate potential (G) is applied to the dummy electrode (6) inside the trench (3) in the diode region (22), the potential of the dummy electrode (6) becomes the same as the anode potential (A) when the diode operates, whether during conduction or recovery of the diode, and therefore the dummy electrode (6) does not affect the operation of the diode.

[0006] Furthermore, if the concentration of holes injected into the diode region of the RC-IGBT before the diode recovery is high, the reverse current increases during recovery, resulting in a problem of increased recovery loss.

[0007] Furthermore, with RC-IGBTs, since the IGBT and diode are fabricated on the same chip, simultaneous optimization of the IGBT and diode is difficult.

[0008] The problem to be solved by the present invention is to provide a semiconductor device and a method for driving the semiconductor device that can reduce recovery loss that occurs during diode recovery in an RC-IGBT.

[0009] In order to solve the above-mentioned problems, the semiconductor device of the present invention is a semiconductor device having an IGBT and a diode on the same chip, wherein the IGBT has an emitter, a collector, a first trench, and a gate provided inside the first trench, and the diode has an anode electrically connected to the emitter, a cathode electrically connected to the collector, a second trench that passes through the anode and reaches the cathode, an intra-trench insulating film provided inside the second trench, and a diode gate that is provided inside the second trench and faces the anode and the cathode via the intra-trench insulating film, and a voltage can be applied to the diode gate independently of the gate of the IGBT, and a negative voltage is applied to the anode at least during a period in which a reverse current flows during recovery of the diode.

[0010] Furthermore, a method for driving a semiconductor device of the present invention is a method for driving the above-mentioned semiconductor device, characterized in that a negative voltage is applied to the diode gate with respect to the anode at least during a period in which a reverse current flows during recovery of the diode.

[0011] According to the present invention, in an RC-IGBT, recovery loss that occurs during diode recovery can be reduced.

[0012] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments and is not to be limited to the disclosed exemplary embodiments.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing and embodiment, the same or similar components are designated by the same reference numerals, and redundant explanations will be omitted.

[0014] In this embodiment, an RC-IGBT having an n-type IGBT will be described as an example. The impurity concentrations of the semiconductor layers increase in the order of n-<n<n+, and p-<p<p+. Note that the impurity concentrations of the semiconductor layers in this embodiment are merely examples and can be changed as appropriate within the range in which the intended operation of the embodiment can be achieved.

[0015] FIG. 1 is a cross-sectional view of a semiconductor device according to an embodiment of the present invention.

[0016] The semiconductor device 100 of this embodiment is an RC-IGBT, and has an IGBT region 21 and a diode region 22 in the same chip (on the same semiconductor substrate).

[0017] The IGBT formed in the IGBT region 21 has an emitter (emitter layer 7), a collector (collector layer 11), a first trench 3A, and a gate (gate electrode 5) provided inside the first trench 3A.

[0018] Specifically, the IGBT in the IGBT region 21 has an n- type drift layer 1, a p-type body layer 2 provided closer to the surface than the drift layer 1, an n+ type emitter layer 7 provided on the surface side of the body layer 2, a first trench 3A penetrating the body layer 2 to reach the drift layer 1, a gate insulating film 4A provided inside the first trench 3A, a gate electrode 5 provided inside the first trench 3A and facing the body layer 2, the emitter layer 7, and the drift layer 1 via the gate insulating film 4A, and a p-type collector layer 11 provided on the back surface side than the drift layer 1. The IGBT in the IGBT region 21 also desirably has an n- type buffer layer 10 between the drift layer 1 and the collector layer 11, the n- type buffer layer 10 having a higher impurity concentration than the drift layer 1.

[0019] The diode formed in the diode region 22 has an anode (anode layer 12) electrically connected to the emitter, a cathode (drift layer 1, buffer layer 10, cathode layer 13) electrically connected to the collector, a second trench 3B that penetrates the anode and reaches the cathode, an intra-trench insulating film 4B provided inside the second trench 3B, and a diode gate (diode gate electrode 6) that is provided inside the second trench 3B and faces the anode and cathode via the intra-trench insulating film 4B.

[0020] Specifically, the diode in the diode region 22 has an n- type drift layer 1 formed in common with the IGBT region 21, a p- type anode layer 12 provided closer to the front surface than the drift layer 1, a second trench 3B penetrating the anode layer 12 to reach the drift layer 1, an intra-trench insulating film 4B provided inside the second trench 3B, a diode gate electrode 6 provided in the second trench 3B and facing the anode layer 12 and the drift layer 1 via the intra-trench insulating film 4B, and an n+ type cathode layer 13 provided closer to the back surface than the drift layer 1. In addition, the diode in the diode region 22 desirably has an n- type buffer layer 10 formed in common with the IGBT region 21 between the drift layer 1 and the cathode layer 13.

[0021] The semiconductor device 100 also includes an interlayer insulating film 9 , a front surface electrode 14 , and a back surface electrode 15 .

[0022] The surface electrode 14 is formed on the surface side of the semiconductor device 100, commonly to the IGBT region 21 and the diode region 22, and functions as an emitter electrode 14A in the IGBT region 21 and as an anode electrode 14B in the diode region 22. The emitter electrode 14A is electrically connected to the emitter layer 7 and the body layer 2 via a contact hole and a p+ type contact layer 8. The anode electrode 14B is electrically connected to the anode layer 12 via a contact hole and a p+ type contact layer 8. This electrically connects the emitter of the IGBT and the anode of the diode. Therefore, the surface electrode 14 has an emitter potential E and an anode potential A.

[0023] The back electrode 15 is formed on the back surface side of the semiconductor device 100, commonly to the IGBT region 21 and the diode region 22, and functions as a collector electrode 15A in the IGBT region 21 and as a cathode electrode 15B in the diode region 22. The collector electrode 15A is electrically connected to the collector layer 11. The cathode electrode 15B is electrically connected to the cathode layer 13. This electrically connects the collector of the IGBT and the cathode of the diode. Therefore, the back electrode 15 is at both collector potential and cathode potential.

[0024] The interlayer insulating film 9 is provided between the various semiconductor layers, the gate electrode 5 , the diode gate electrode 6 and the surface electrode 14 .

[0025] In this embodiment, the diode region 22 does not have the emitter layer 7 that was present in the IGBT region 21. Also, the p-type collector layer 11 in the IGBT region 21 is replaced with an n+ type cathode layer 13 in the diode region 22. Other than this, the structures are almost the same, which has the advantage that most of the manufacturing processes for the IGBT and diode can be shared. Note that the above-described structures of the IGBT and diode are merely examples and are not limiting.

[0026] Next, the operation of the semiconductor device 100 of this embodiment will be described.

[0027] A gate potential G is applied to the gate electrode 5 of the IGBT from a drive circuit (not shown), thereby controlling the on / off of the IGBT, which is a switching element.

[0028] A voltage can be applied to the diode gate electrode 6 of the diode independently of the gate electrode 5 of the IGBT, and a diode gate potential DG is applied to it from a drive circuit (not shown). Here, a negative voltage relative to the anode is applied to the diode gate electrode 6 at least during the period when a reverse current flows during diode recovery, thereby reducing recovery loss that occurs during diode recovery. Furthermore, when the diode is conductive, it is desirable to apply a positive voltage relative to the anode to the diode gate electrode 6. The reasons for this will be explained below.

[0029] FIG. 2 is a cross-sectional view illustrating the operation of the semiconductor device of the embodiment when the diode is conductive.

[0030] When the diode is conductive, the IGBT is controlled to be off. If the emitter potential E, which is the reference potential of the IGBT, is set to, for example, 0 V, then a gate potential G of, for example, −15 V or 0 V is applied to the gate electrode 5.

[0031] When the diode is conductive, the anode potential A is higher than the cathode potential, resulting in a forward bias state. Therefore, holes 31 are injected from the anode layer 12, which is the anode, to the drift layer 1, which is the cathode, and a forward current flows from the anode to the cathode of the diode.

[0032] Here, if the concentration of holes 31 injected when the diode is conductive is high, there is a problem that the reverse current increases during recovery, resulting in an increase in recovery loss.

[0033] Therefore, in this embodiment, when the diode is conductive, a positive voltage with respect to the anode potential A, for example, a potential of +15 V with respect to the anode potential A, is applied to the diode gate electrode 6 as the diode gate potential DG. As a result, a depletion layer 32 is formed in the anode layer 12 around the second trench 3B, and an n-type accumulation layer 33 is formed in the drift layer 1 around the second trench 3B. The depletion layer 32 effectively narrows the width of the anode layer 12, thereby reducing the injection of holes 31 from the anode layer 12. Furthermore, electrons are accumulated in the n-type accumulation layer 33, increasing the electron concentration. Therefore, the n-type accumulation layer 33 acts as a barrier, reducing the injection of holes 31 from the anode layer 12. Furthermore, the electrons accumulated in the n-type accumulation layer 33 increase the electron concentration near the boundary between the anode layer 12 and the drift layer 1. As a result, annihilation of holes 31 and electrons is more likely to occur near this boundary, and the number of holes 31 remaining in the drift layer 1 at the start of the recovery operation is reduced. As a result, the reverse current that flows during recovery can be reduced, and recovery loss can be reduced.

[0034] FIG. 3 is a cross-sectional view illustrating the operation of the semiconductor device of the embodiment during diode recovery.

[0035] Even during the recovery of the diode, the IGBT is controlled to be off.

[0036] During recovery of the diode, the cathode potential is in a reverse bias state higher than the anode potential A. At this time, holes 31 remaining after being injected into the drift layer 1 are discharged via the anode layer 12, and a reverse current flows from the cathode to the anode.

[0037] In this embodiment, during diode recovery, at least during the period in which a reverse current flows, a negative voltage with respect to the anode potential A, for example, a potential of −15 V with respect to the anode potential A, is applied to the diode gate electrode 6 as the diode gate potential DG. As a result, a p-type accumulation layer 34 is formed in the anode layer 12 and drift layer 1 around the second trench 3B. Holes 31 are accumulated in the p-type accumulation layer 34, and the concentration of holes 31 is high. Therefore, the resistance in that region is low, and the holes 31 that were injected into the drift layer 1 and remain are efficiently discharged at high speed. As a result, the period in which a reverse current flows is shortened, and recovery loss can be reduced.

[0038] 4 is a timing chart for explaining a method for driving a semiconductor device according to the embodiment, in which the vertical axis represents voltage or current and the horizontal axis represents time.

[0039] Here, an example will be described in which the semiconductor device 100 of this embodiment is applied to each of the upper arm and the lower arm of a power conversion device. The power conversion device also has a drive circuit (not shown) that drives the semiconductor device 100.

[0040] Assuming that the arm in question is the upper arm, the emitter potential E is, for example, 0 V, and the anode potential A is also 0 V, when the diode in the arm in question operates, a gate potential G of, for example, −15 V is applied to the gate electrode 5 of the IGBT in the arm in question, and the IGBT in the arm in question is controlled to be off.

[0041] In the period before time t1, the paired arm gate potential G' applied to the gate electrode 5 of the IGBT in the lower arm, which is the paired arm, is, for example, -15 V, and the IGBT in the paired arm is controlled to be off. At this time, a reflux current flows in the forward direction through the diode in the paired arm, as shown by the current Id in FIG. 4, and the diode is conducting. During this period, a diode gate potential DG of, for example, +15 V is applied to the diode gate electrode 6 of the diode in the paired arm, reducing the injection of holes 31 as described in FIG. 2. This reduces the reverse current that flows during recovery, and reduces recovery loss.

[0042] At time t1, when the gate potential G' of the arm changes from -15 V to, for example, +15 V, the IGBT of the arm turns on at time t2, after the switching delay time has elapsed, and the recovery operation of the diode of the arm begins. The recovery operation of the diode of the arm occurs during period T3, from time t2 to time t5. During period T3, the current Id decreases from time t2 to time t4, and during period T4, from time t4 to time t5, the direction of the current Id reverses and a reverse current flows. After time t5, when the recovery operation of the diode ends, the current Id becomes zero.

[0043] The diode gate potential DG is applied with, for example, −15 V during a period T2 from time t3 to time t6 so as to include at least the period T4 during which the reverse current flows. This shortens the period during which the reverse current flows as described with reference to FIG. 3, thereby reducing the recovery loss.

[0044] It is desirable that the diode gate potential DG be switched from a positive voltage to a negative voltage with respect to the anode at time t3, which is after time t2 when the diode starts recovery and before time t4 when the reverse current flows. If the switching is too early, the effect of reducing the injection of holes 31 will be insufficient, as described in FIG. 2, and the reverse current flowing during recovery will not be sufficiently reduced. On the other hand, if the switching is too late, the switching will overlap with the period T4 when the reverse current flows, shortening the period during which the effect described in FIG. 3 can be obtained. For example, this can be achieved by controlling a drive circuit (not shown) to change the diode gate potential DG at a timing when a predetermined period T1 has elapsed since time t1 when the arm gate potential G' is changed.

[0045] Furthermore, it is desirable that the diode gate potential DG be switched from a negative voltage to a positive voltage with respect to the anode at time t6, which is after the period T4 during which the reverse current flows. If the voltage is switched too early, it will overlap with the period T4 during which the reverse current flows, shortening the period during which the effect described in FIG. 3 can be obtained. For example, this can be achieved by controlling a drive circuit (not shown) to change the diode gate potential DG at a timing when a predetermined period T2 has elapsed since the time t3 at which the diode gate potential DG was changed.

[0046] According to this embodiment, in the RC-IGBT, the recovery loss that occurs during the recovery of the diode can be reduced.

[0047] Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible within the scope of the technical concept of the present invention. In addition, some or all of the configurations described in the embodiments may be combined and applied.

[0048] 1: Drift layer 2: Body layer 3A: First trench 3B: Second trench 4A: Gate insulating film 4B: In-trench insulating film 5: Gate electrode 6: Diode gate electrode 7: Emitter layer 8: Contact layer 9: Interlayer insulating film 10: Buffer layer 11: Collector layer 12: Anode layer 13: Cathode layer 14: Front electrode 14A: Emitter electrode 14B: Anode electrode 15: Back electrode 15A: Collector electrode 15B: Cathode electrode 21: IGBT region 22: Diode region 31: Hole 32: Depletion layer 33: N-type accumulation layer 34: P-type accumulation layer 100: Semiconductor device G: Gate potential G': Arm gate potential DG: Diode gate potential E: Emitter potential A: Anode potential Id: Current

Claims

1. A semiconductor device having an IGBT and a diode on the same chip, wherein the IGBT has an emitter, a collector, a first trench, and a gate provided inside the first trench, and the diode has an anode electrically connected to the emitter, a cathode electrically connected to the collector, a second trench that passes through the anode and reaches the cathode, an intra-trench insulating film provided inside the second trench, and a diode gate that is provided inside the second trench and faces the anode and the cathode via the intra-trench insulating film, and a voltage can be applied to the diode gate independently of the gate of the IGBT, and a negative voltage is applied to the anode at least during a period when a reverse current flows during recovery of the diode.

2. A semiconductor device according to claim 1, wherein a positive voltage is applied to the diode gate relative to the anode when the diode is conductive.

3. A semiconductor device according to claim 1, wherein the voltage applied to the diode gate is switched from a positive voltage to a negative voltage with respect to the anode after the diode starts recovery and before the reverse current flows.

4. A semiconductor device according to claim 1, wherein the voltage applied to the diode gate is switched from a negative voltage to a positive voltage with respect to the anode at a timing after the period in which the reverse current flows.

5. A method for driving a semiconductor device having an IGBT and a diode on the same chip, wherein the IGBT has an emitter, a collector, a first trench, and a gate provided inside the first trench, and the diode has an anode electrically connected to the emitter, a cathode electrically connected to the collector, a second trench that passes through the anode and reaches the cathode, an intra-trench insulating film provided inside the second trench, and a diode gate that is provided inside the second trench and faces the anode and the cathode via the intra-trench insulating film, and a voltage can be applied to the diode gate independently of the gate of the IGBT, and a negative voltage is applied to the anode at least during a period when a reverse current flows during recovery of the diode.

6. A method for driving a semiconductor device according to claim 5, wherein a positive voltage is applied to the diode gate relative to the anode when the diode is conductive.

7. A method for driving a semiconductor device according to claim 5, wherein the voltage applied to the diode gate is switched from a positive voltage to a negative voltage with respect to the anode after the diode starts recovery and before the reverse current flows.

8. A method for driving a semiconductor device according to claim 5, wherein the voltage applied to the diode gate is switched from a negative voltage to a positive voltage with respect to the anode at a timing after the period in which the reverse current flows.

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