JP2008258262A - Igbt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an IGBT of which the turn-on voltage is low and the breakdown voltage is high. <P>SOLUTION: The IGBT is provided with a first conductive collector region; a second conductive drift region stacked on the collector region; a first conductive body region that is isolated from the collector region by the drift region; a second conductive emitter region that is isolated from the drift region by the body region; and a gate electrode that is opposite to a body region separating the emitter region and the drift region, with an insulation film in between. The drift region is provided with a first low-concentration region that is low in impurity concentration and is in contact with the body region; a high-concentration region that is high in impurity concentration, is in contact with the first low-concentration region and is isolated from the body region by the first low-concentration region and is spread as a layer in the direction of the plane of the semiconductor substrate; and a second low-concentration area that is low impurity concentration and is in contact with the high-concentration region, and isolates the high-concentration region from the collector region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an IGBT.

  A collector region of the first conductivity type, a drift region of the second conductivity type stacked on the collector region, a body region of the first conductivity type separated from the collector region by the drift region, and a drift region by the body region There is known an IGBT including an emitter region of a second conductivity type separated from the gate electrode, and a gate electrode facing a body region in a range where the emitter region and the drift region are separated through an insulating film. When an on voltage is applied to the gate electrode of the IGBT, a channel is formed in the body region. As a result, the second carriers (majority carriers of the second conductivity type semiconductor) flow from the emitter electrode into the drift region through the emitter region and the body region. The second carriers flowing into the drift region pass through the collector region and flow to the collector electrode. When the second carriers flow into the drift region, the first carriers (majority carriers of the first conductivity type semiconductor) flow through the collector region from the collector electrode and flow into the drift region accordingly. When the first carrier and the second carrier flow into the drift region, the conductivity modulation phenomenon is activated in the drift region, and the resistance of the drift region is reduced. The first carriers flowing into the drift region pass through the body region and flow to the emitter electrode. As a result, the IGBT is turned on.

Patent Document 1 discloses a technique for further reducing the ON voltage of the IGBT by further reducing the resistance of the drift region by increasing the amount of holes accumulated in the drift region at the time of ON. In the IGBT of Patent Document 1, the drift region is composed of the following three layers.
A buffer region having a high impurity concentration is provided in a range in contact with the collector region. A barrier region having a high impurity concentration is also provided in a region in contact with the body region. A base region having a low impurity concentration is provided between the buffer region and the barrier region.
In this IGBT, when turned on, holes flow from the collector electrode to the base region through the collector region and the buffer region. The holes flowing into the base region try to flow to the emitter electrode through the barrier region and the body region. However, the interface between the base region and the barrier region serves as a barrier, and holes are prevented from flowing into the barrier region. Therefore, more holes are accumulated in the base region. As the number of holes in the base region increases, the conductivity modulation phenomenon in the base region becomes active and the resistance decreases. Therefore, the IGBT of Patent Document 1 has a low on-voltage.

JP 2003-273359 A

  In the IGBT of Patent Document 1, a barrier region having a relatively high impurity concentration is in contact with the body region. Therefore, when the IGBT is turned off, the depletion layer hardly extends from the interface between the drift region and the body region to the drift region side. For this reason, the IGBT of Patent Document 1 has a problem that the breakdown voltage is low.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an IGBT having a low on-voltage and a high breakdown voltage.

  The IGBT of the present invention includes a first conductivity type collector region, a second conductivity type drift region stacked on the collector region, and a first conductivity type body region separated from the collector region by the drift region. An emitter region of a second conductivity type separated from the drift region by the body region, and a gate electrode facing the body region in a range separating the emitter region and the drift region via an insulating film Yes. The drift region of the IGBT of the present invention includes a first low concentration region, a high concentration region, and a second low concentration region. The first low concentration region is in contact with the body region and has a low impurity concentration. The high concentration region is in contact with the first low concentration region, is separated from the body region by the first low concentration region, spreads in layers in a direction parallel to the surface of the semiconductor substrate, and has a high impurity concentration. The second low concentration region is in contact with the high concentration region, separates the high concentration region from the collector region, and has a low impurity concentration.

The phenomenon that occurs in the IGBT will be described next. For convenience of explanation, a case where the collector region is p-type and the emitter region is n-type will be described first.
When the IGBT is turned on, holes flow from the collector electrode through the collector region and flow into the second low concentration region. The holes flowing into the second low concentration region try to flow to the body region through the high concentration region and the first low concentration region. However, the interface between the second low-concentration region having a low impurity concentration and the high-concentration region having a high impurity concentration serves as a barrier, so that holes can be prevented from flowing into the high-concentration region. Therefore, more holes are accumulated in the second low concentration region, and the conductivity modulation phenomenon in the second low concentration region is activated and the resistance is lowered. Therefore, the on-voltage of the IGBT is low.
Further, when the IGBT is turned off, a depletion layer is formed at the interface between the body region and the first low concentration region. Since the first low-concentration region in contact with the body region has a low impurity concentration, the depletion layer can sufficiently extend from the interface into the first low-concentration region. Therefore, it is possible to suppress the depletion layer from becoming thinner. That is, this IGBT has a sufficient breakdown voltage.
Even when the collector region is n-type and the emitter region is p-type, a phenomenon in which the conductivity type of carriers is reversed occurs. Also in this case, the conductivity modulation phenomenon in the second low concentration region is activated and the resistance is lowered. Even in this IGBT, the on-voltage is low.

In the IGBT described above, the body region is formed in the island region, the high concentration region spreads in layers in a direction parallel to the surface of the semiconductor substrate, and the high concentration region is formed in a predetermined range below the body region. Preferably not.
According to such a configuration, when the IGBT is turned off, the first carriers accumulated in the second low concentration region pass through the predetermined range where the high concentration region is not formed and flow into the body region. Can do. Therefore, the turn-off speed of the IGBT can be improved.

In the IGBT of the above type, an emitter electrode is formed on the upper surface of the body region and the emitter region, and a body contact region having a higher impurity concentration than the body region outside the range is formed in the body region in contact with the emitter electrode. It is preferable that a predetermined range in which a high concentration region is not formed below the body contact region is secured.
According to such a configuration, the turn-off speed of the IGBT can be further improved. Further, the first carrier does not flow through the emitter region, and the occurrence of the phenomenon that the parasitic thyristor is turned on can be prevented.

In the IGBT described above, the high concentration region is preferably formed over the entire range where the channel region and the drift region overlap when the IGBT is turned on when the semiconductor substrate is viewed in plan. The high concentration region only needs to cover the entire range, and may extend to a range beyond that.
In the drift region, the range overlapping with the channel region is a region where the most second carriers flow. In this IGBT, since the high concentration region is formed in the entire range where the channel region and the drift region overlap, the first carriers are accumulated in the second low concentration region in the range. That is, the resistance of the range in which the second carrier flows most in the second low concentration region decreases. Therefore, even if the range where the high concentration region is not formed is formed, the on-voltage of the IGBT can be sufficiently lowered.

(First embodiment)
The IGBT according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of the IGBT 10 of the first embodiment. As illustrated, the IGBT 10 includes a silicon substrate 12, a collector electrode 20, an emitter electrode 40, and a gate electrode 44 covered with an insulating film 42. The collector electrode 20 is formed on substantially the entire lower surface 12 b of the silicon substrate 12. The gate electrode 44 is formed on the upper surface 12 a of the silicon substrate 12 and faces the silicon substrate 12 with the insulating film 42 interposed therebetween. The emitter electrode 40 is formed on the substantially entire surface of the upper surface 12 a of the silicon substrate 12 so as to cover the gate electrode 44. The gate electrode 44 and the emitter electrode 40 are insulated by an insulating film 42.

  In a region facing the lower surface 12b of the silicon substrate 12, a p-type collector layer 22 is formed. An n-type drift layer 30 is formed on the collector layer 22. The drift layer 30 includes a first drift layer 24 in contact with the collector layer 22, a second drift layer 26 formed on the upper side of the first drift layer 24, and a third layer formed on the upper side of the second drift layer 26. The drift layer 28 is used. The n-type impurity concentrations of the first drift layer 24 and the third drift layer 28 are substantially equal. The second drift layer 26 has a higher n-type impurity concentration than the first drift layer 24 and the third drift layer 28. In the region facing the upper surface 12a of the silicon substrate 12, an n-type emitter region 36 and a p-type body region 32 are selectively formed. The body region 32 is formed in the island region. The emitter region 36 is formed in contact with the insulating film 42 and the emitter electrode 40. The body region 32 is formed so as to cover the emitter region 36. The emitter region 36 is separated from the drift layer 30 by the body region 32. The body region 32 is formed in contact with the insulating film 42 and the emitter electrode 40. A range of the body region 32 that faces the gate electrode 44 through the insulating film 42 is a channel formation region 33 in which a channel is formed when an on voltage is applied to the gate electrode 44. A body contact region 34 having a higher p-type impurity concentration than the other part of the body region 32 is formed in a portion of the body region 32 that is in contact with the emitter electrode 40.

FIG. 2 shows the distribution of the n-type impurity concentration N in the drift layer 30 in the section taken along the line II-II in FIG. As shown in the figure, in the first drift layer 24 and the third drift layer 28, the n-type impurity is present at a substantially constant concentration of about 1 × 10 ¹³ / cm ² . In the second drift layer 26, the n-type impurity concentration is locally high. As shown in the drawing, the n-type impurity concentration is 1 × 10 ¹⁵ / cm ² or more in the second drift layer 26.

When a forward voltage is applied between the collector electrode 20 and the emitter electrode 40 of the IGBT 10 and an on-voltage is applied to the gate electrode 44, the IGBT 10 is turned on. That is, a channel is formed in the channel formation region 33 in the body region 32. Then, electrons flow from the emitter electrode 40 through the channel region 33 in the emitter region 36 and the body region 32 into the drift layer 30. The electrons flowing into the drift layer 30 pass through the drift layer 30 and the collector layer 22 and flow to the collector electrode 20.
When electrons flow into the drift layer 30, holes flow from the collector electrode 20 through the collector layer 22 and flow into the first drift layer 24. The holes that have flowed into the first drift layer 24 tend to flow into the second drift layer 26. However, the interface between the first drift layer 24 and the second drift layer 26 serves as a barrier to prevent holes from flowing into the second drift layer 26. Therefore, a relatively small amount of holes flow into the second drift layer 26, and the concentration of holes in the first drift layer 24 increases. Then, the conductivity modulation phenomenon is activated in the first drift layer 24 and the resistance of the first drift layer 24 becomes very small. Therefore, electrons can flow in the first drift layer 24 with almost no loss.
A relatively small amount of holes flowing into the second drift layer 26 flows from the body contact region 34 to the emitter electrode 40 through the third drift layer 28 and the body region 32.

  When the voltage applied to the gate electrode 44 is turned off, the channel formed in the channel formation region 33 disappears and the IGBT 10 is turned off. When the IGBT 10 is turned off, a voltage is applied to the interface between the body region 32 and the third drift layer 28, so that a depletion layer spreads in the vicinity of the interface. Since the n-type impurity concentration of the third drift layer 28 in contact with the body region 32 is low, the depletion layer can sufficiently spread in the third drift layer 28. That is, the thickness of the depletion layer does not become extremely thin. Therefore, the IGBT 10 has a sufficient breakdown voltage.

  As described above, in the IGBT 10, the n-type impurity concentration of the second drift layer 26 is higher than that of the first drift layer 24. Therefore, the holes that have flowed into the first drift layer 24 are unlikely to flow into the second drift layer 26, and the resistance of the first drift layer 24 can be further reduced. That is, the on-voltage of the IGBT 10 is reduced. A third drift layer 28 having an n-type impurity concentration lower than that of the second drift layer 26 is formed between the second drift layer 26 and the body region 32. Therefore, when the IGBT 10 is turned off, a depletion layer extends from the interface between the body region 32 and the third drift layer 28 into the third drift layer 28, and the depletion layer does not become thin. Therefore, the breakdown voltage when the IGBT 10 is off is high.

The n-type impurity concentration of the second drift layer 26 is preferably 1 × 10 ¹⁵ / cm ² or more, and the n-type impurity concentration of the first drift layer 24 is 1 × 10 ¹³ / cm ² or less. It is preferable. When the n-type impurity is distributed at such a concentration, the concentration of holes in the first drift layer 24 can be sufficiently increased when the IGBT 10 is turned on.

The n-type impurity concentration of the third drift layer 28 is preferably 1 × 10 ¹³ / cm ² or less. When the third drift layer 28 is formed in this way, the depletion layer can sufficiently spread in the third drift layer 28.

  In the IGBT 10 of the first embodiment, the second drift layer 26 is formed at substantially the same depth. However, as shown in FIG. 3, the depth at which the second drift layer 26 is formed is the silicon substrate. It may be changed depending on the position of the 12 plane directions. Further, as shown in FIG. 4, the thickness of the second drift layer 26 may change depending on the position of the silicon substrate 12 in the planar direction. Even when the second drift layer 26 is thus formed, the on-voltage of the IGBT 10 can be reduced.

  In the IGBT 10 of the first embodiment, the first drift layer 24 is in contact with the collector layer 22. However, the drift layer 30 may include a buffer layer formed between the first drift layer 24 and the collector layer 22 and having a high n-type impurity concentration.

(Second embodiment)
Next, the IGBT of the second embodiment will be described. In the second embodiment, an IGBT in which the on-voltage is reduced, the breakdown voltage is improved, and the turn-off speed is increased will be described.

  FIG. 5 shows a schematic configuration of the IGBT 100 of the second embodiment. As shown in FIG. 5, the IGBT 100 of the second embodiment is configured in the same manner as the IGBT 10 of the first embodiment except for the drift layer 30.

  As shown in FIG. 5, in the IGBT 100, the second drift layer 26 is not formed in the range C <b> 1 below the body contact region 34. That is, in the range C1, the first drift layer 24 and the third drift layer 28 are in direct contact with each other, and the high concentration region 26 that prevents the holes from flowing into the body contact region 34 is not formed. In other ranges, the second drift layer 26 is formed, and the concentration distribution of the n-type impurity in the drift layer 30 is a distribution shown in FIG.

  When a forward voltage is applied between the collector electrode 20 and the emitter electrode 40 of the IGBT 10 and an on-voltage is applied to the gate electrode 44, electrons pass from the emitter electrode 40 through the emitter region 36 and the channel formation region 33 of the body region 32. It flows into the drift layer 30. The electrons flowing into the drift layer 30 pass through the drift layer 30 and the collector layer 22 and flow to the collector electrode 20.

  When electrons flow into the drift layer 30, holes flow from the collector electrode 20 through the collector layer 22 and flow into the first drift layer 24. The holes flowing into the first drift layer 24 tend to flow toward the third drift layer 28 side. At this time, in the range where the second drift layer 26 is formed (that is, the range excluding the range C1), the interface between the first drift layer 24 and the second drift layer 26 serves as a barrier, and the holes become the third drift layer 28. The flow to the side is suppressed. Therefore, the concentration of holes in the first drift layer 24 below the second drift layer 26 is increased. Therefore, the conductivity modulation phenomenon is activated in the first drift layer 24 in that range, and the resistance is lowered. In the drift layer 30, the lower part of the channel formation region 33 is a range where most electrons flow. Since the second drift layer 26 is formed below the channel formation region 33, the resistance of the first drift layer 24 below the channel formation region 33 is low. Therefore, electrons can flow in the first drift layer 24 with almost no loss.

  As described above, the second drift layer 26 is not formed in the range C <b> 1 below the body contact region 34. Accordingly, holes can easily flow from the first drift layer 24 to the third drift layer 28 in the range C1. Therefore, in the first drift layer 24 below the range C1, the hole concentration is not so high and the resistance is relatively high. However, since not many electrons flow through the first drift layer 24 below the range C1, there is almost no problem even if the resistance is high.

  When the voltage applied to the gate electrode 44 is turned off, the channel formed in the channel formation region 33 disappears. Then, electrons in the silicon substrate 12 are discharged to the collector electrode 20 and holes are discharged to the emitter electrode 40.

  Holes in the first drift layer 24 are unlikely to flow into the second drift layer 26. However, in the IGBT 100, the second drift layer 26 is not formed in the range C1 below the body contact region 34. Therefore, holes in the first drift layer 24 can flow into the third drift layer 28 through the range C1. The holes flowing into the third drift layer 28 pass through the body region 32 and flow from the body contact region 34 to the emitter electrode 40. That is, when the IGBT 100 is turned off, the holes in the first drift layer 24 are quickly discharged to the emitter electrode 40. Particularly, since the range C1 is formed below the body contact region 34 (that is, the position closest to the body contact region 34), the holes in the first drift layer 24 are discharged to the emitter electrode 40 at a higher speed. Therefore, the IGBT 100 can be turned off at high speed.

As described above, in the IGBT 100 of the second embodiment, the second drift layer 26 is not formed in the range C1 below the body contact region 34. Therefore, the IGBT 100 can be turned off at high speed.
In the IGBT 100, the second drift layer 26 is formed below the channel formation region 33. Therefore, when the IGBT 100 is turned on, the resistance in a range where many electrons of the first drift layer 24 flow is lowered. Thereby, the on-voltage of the IGBT 100 is reduced.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

The schematic sectional drawing of IGBT10 of 1st Example. 3 is a graph showing the concentration distribution of n-type impurities in the thickness direction of the drift layer 30. The schematic sectional drawing of IGBT10 of a modification. The schematic sectional drawing of IGBT10 of a modification. The schematic sectional drawing of IGBT100 of 2nd Example.

Explanation of symbols

10: IGBT
12: Silicon substrate 20: Collector electrode 22: Collector layer 24: First drift layer 26: Second drift layer 28: Third drift layer 30: Drift layer 32: Body region 33: Channel formation region 34: Body contact region 36: Emitter region 40: Emitter electrode 42: Insulating film 44: Gate electrode 100: IGBT

Claims (4)

An IGBT,
A collector region of a first conductivity type;
A drift region of a second conductivity type stacked on the collector region;
A body region of a first conductivity type separated from the collector region by a drift region;
An emitter region of a second conductivity type separated from the drift region by a body region;
A gate electrode facing the body region in a range separating the emitter region and the drift region through an insulating film;
With
The drift region is
A first low concentration region in contact with the body region and having a low impurity concentration;
A high-concentration region in contact with the first low-concentration region, separated from the body region by the first low-concentration region, spreading in layers in a direction parallel to the surface of the semiconductor substrate, and having a high impurity concentration;
A second low concentration region that is in contact with the high concentration region, separates the high concentration region from the collector region, and has a low impurity concentration;
IGBT characterized by having. The body region is formed in an island region,
2. The IGBT according to claim 1, wherein the high-concentration region extends in layers in a direction parallel to the surface of the semiconductor substrate and is not formed within a predetermined range below the body region. Emitter electrodes are formed on the upper surfaces of the body region and the emitter region,
A body contact region having a higher impurity concentration than the body region outside the range is formed in the body region in contact with the emitter electrode.
The IGBT according to claim 2, wherein a predetermined range in which the high concentration region is not formed is formed in a lower portion of the body contact region.   The high-concentration region is formed at least over the entire range where the region where the channel is formed and the drift region overlap when the IGBT is turned on when the semiconductor substrate is viewed in plan. IGBT.

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