JP2002076017A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reverse-blocking semiconductor device which displays a good reverse-recovery property when it acts as a diode keeping a favorable turnoff property for a reverse-blocking IGBT. SOLUTION: P-type base layer 3 is formed on a surface of high-relative- resistance n-type base layer 2, p-type collector layer 1 is formed on the back side of the base layer 2, n-type emitter layer 4 is formed on the surface part of the p-type base layer 3, an gate-insulating film 5 is formed on a region of the p-type base film 3 between two of the n-type emitter layer 4 and on the n-type emitter layer 2, a gate electrode 6 is formed on the gate-insulating film 5, and life time killer is localized at the vicinity of the junction of the p-type collector 1 and n-type base layer 2, by He radiation or proton radiation capable of localizing the life time killer into the desired depth. By the localization of life time killer, a reverse-recovery peak current (Irp) when a diode is active can be reduced and the property of reverse-blocking semiconductor becomes a soft-recovery type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor device such as a reverse blocking IGBT which is a power switching element.

[0002]

2. Description of the Related Art At present, bipolar transistors (hereinafter referred to as BJTs) are generally used as switching semiconductor elements.
ipolar Junction Transisto
r), MOS type field effect transistor (hereinafter, MOSF)
ET) and an insulated gate bipolar transistor (hereinafter, referred to as IGBT) are used depending on the application.

The BJT has a small on-resistance due to conductivity modulation in a saturated state, but has a long turn-off time due to the presence of excess carriers due to the accumulation effect of minority carriers at the switching speed, especially at the time of turn-off. Used in relatively low frequency range. Further, since the element is a current-driven element, a loss generated in the drive circuit increases.

On the other hand, since the MOSFET is a voltage-driven element, the loss generated in the drive circuit is small,
The switching speed is high because minority carriers do not accumulate. However, since conductivity modulation due to the injection of minority carriers does not occur, there is a problem that the on-resistance increases. The IGBT is a voltage-driven element, similar to a MOSFET, so that the loss generated in the drive circuit is small. Similarly to the BJT, the IGBT has a conductivity modulation based on the injection of minority carriers. Can be small.

However, at the time of turn-off, in addition to the effect of accumulating minority carriers, minority carriers are re-injected from the back surface due to majority carriers swept out by the expansion of the depletion layer, so that the turn-off time is delayed. Therefore, generally, in a switching circuit, BJT or IGBT is used.
Has a small steady-state loss, but is often used at a relatively low frequency because of a large switching loss.
On the other hand, MOSFETs, on the other hand, have a large steady-state loss but a small switching loss, and thus are often used at relatively high frequencies.

Since the MOSFET has only one pn junction where the withstand voltage characteristic is obtained due to its structure, the withstand voltage characteristic shows only the forward withstand voltage. On the other hand, the BJT and the IGBT have two pn junctions. However, in the BJT, the concentration of the emitter layer is increased in order to increase the injection of carriers from the emitter layer. For this reason, the breakdown voltage of the PN junction between the base and the emitter is small, and it is impossible to obtain the same breakdown voltage characteristics in both forward and reverse directions.

On the other hand, since the IGBT obtains a breakdown voltage characteristic by expanding a depletion layer in the first conductive type base layer, the first conductive type base layer and the second conductive type base layer on the front surface side and the second conductive type base layer on the back surface side. At the respective PN junctions of the one conductivity type base layer and the second conductivity type collector layer, substantially the same breakdown voltage can be secured.
Therefore, it is possible in principle for the IGBT to obtain both forward and reverse breakdown voltage characteristics. However, since a normal IGBT employs a planar-type peripheral withstand voltage structure and is formed only on the surface side where the emitter layer is located, it has only a forward withstand voltage characteristic.

On the other hand, FIG.
Reverse blocking IGBT disclosed in Japanese Patent No. 07469
By forming the P layer 57 on the N base layer 51 on the side wall of the device, reverse blocking breakdown voltage characteristics can be obtained. In the figure, reference numeral 52 denotes a P base layer, 53 denotes an N emitter layer,
4 is a gate insulating film, 55 is a gate electrode, 56 is a P collector layer, 58 is an emitter electrode, 59 is a collector electrode, 60
Is a metal film.

Further, a bidirectional IGBT can be obtained by connecting the reverse blocking IGBT in an anti-parallel manner. The use of this bidirectional IGBT enables control of not only DC current but also AC current.

[0010]

Next, this two-way I
A case in which the GBT is used in a circuit for directly converting AC to AC will be described. The arm of the direct conversion circuit is formed of a bidirectional IGBT, and one reverse blocking IGBT constituting the bidirectional IGBT has an operation mode as a freewheeling diode.

Since the reverse blocking IGBT has a reverse blocking capability, it can be operated as a diode having a reverse blocking withstand voltage by keeping the gate always on.
However, in the direct conversion circuit, the reverse blocking IGBT is used.
Is required to reduce the reverse recovery current. However, the above publication does not disclose operating the reverse blocking IGBT as a diode, and thus does not disclose a method of reducing the reverse recovery current when operating the diode as a diode.

An object of the present invention is to provide a reverse-blocking semiconductor device which exhibits good reverse recovery characteristics when operated as a diode while maintaining good turn-off characteristics of the reverse-blocking IGBT.

[0013]

In order to achieve the above object, a first conductivity type base layer, a second conductivity type base layer selectively formed on the surface of the first conductivity type base layer, A first conductivity type source layer selectively formed on the surface of the second conductivity type base layer; and the second conductivity type base layer sandwiched between the first conductivity type base layer and the first conductivity type source layer. A gate electrode formed thereon via a gate insulating film, a first main electrode formed in contact with the first conductive type source layer and the second conductive type base layer, and a first conductive type base layer. In a semiconductor device having a second conductivity type collector layer formed on the back surface and a second main electrode formed on the collector layer and having a reverse blocking breakdown voltage equivalent to a forward blocking breakdown voltage, a first conductivity type base layer is provided. A lifetime killer near the junction between the collector layer and the second conductivity type collector layer And it formed.

The peak position of the distribution of the lifetime killer is a reverse bias voltage applied to a PN junction formed by the first conductivity type base layer and the second conductivity type base layer, and the depletion layer does not reach the depletion layer. It is good to be inside the first conductivity type base layer. The peak of the lifetime killer distribution is
The distance between the peak position and the PN junction position is in the first conductivity type base layer and is 0 μm to 40 μm.
It is good.

[0015] It is effective that the lifetime killer is introduced by ion irradiation, and this ion is a helium ion or a hydrogen ion. A second conductive type first semiconductor layer formed on the outer peripheral surface of the first conductive type base layer so as to surround the side surface of the second conductive type base layer; Contacting the first semiconductor layer;
It is preferable to have a withstand voltage structure including a second conductive type second semiconductor layer in contact with the conductive type collector layer. It is effective to have a bevel structure.

As described above, by making the lifetime killer localized near the junction between the first conductivity type base layer and the second conductivity type collector layer on the back side, a reverse blocking IGBT is provided.
Can be reduced, and the reverse recovery current can be reduced when operated as a diode.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In all of the following embodiments, the first conductivity type is N-type and the second conductivity type is P-type, but this may be reversed. FIG. 1 is a sectional view of a main part of a semiconductor device according to a first embodiment of the present invention. Here, the semiconductor device is a reverse blocking IGBT.

A P base layer 3 is formed on the surface of an N base layer 2 having a high specific resistance, and a P collector layer 1 is formed on the back side. An N emitter layer 4 is formed on the surface of the P base layer 3 in the active region. A gate insulating film 5 is formed on the P base layer 3 and the N base layer 2 in a region sandwiched between the two N emitter layers 4, and a gate electrode 6 is formed on the gate insulating film 5. Each layer formed from the surface and the emitter side surface on which the gate electrode 6 is formed are covered with an interlayer insulating film 7, a contact hole is formed in the interlayer insulating film 7, and an emitter electrode 8 contacting the P base layer 3 and the N emitter layer 4 is formed. The collector electrode 9 is formed on the P collector layer 1 on the back surface. Next, a P layer 11 is formed on the side wall of the N base layer 2 so as to be in contact with the outer peripheral portion of the breakdown voltage structure 16 and the P collector layer 1.

Before forming the collector electrode 9, lifetime control is performed. This lifetime control does not use a uniform lifetime killer for the whole device such as electron beam irradiation as in the conventional technology, but instead allows a lifetime killer to exist locally at an arbitrary depth.
e irradiation, proton irradiation, etc., the P collector layer 1 and N
It is localized near the junction with the base layer 2.

As described above, by localizing the lifetime killer near the junction, the lifetime killer works effectively even when the depletion layer is expanded at the time of turn-off, so that a high-speed turn-off characteristic is obtained. The reverse recovery characteristic of the PN diode composed of the P collector layer 1 and the N base layer 2 is as follows.
Since the carrier concentration near the junction in the N base layer 2 becomes small, the reverse recovery peak current (Irp) is small and good characteristics of soft recovery are exhibited. FIG. 2 shows the turn-off waveform, FIG.
Shows a reverse recovery waveform when the diode is operated. Here, A is a product of the present invention, and B is a conventional product.

Further, by providing the P layer 11 on the side wall, when the PN junction between the N base layer 2 and the P collector layer 1 is in a reverse bias state (reverse blocking state), the depletion layer becomes the N base layer 2. The inside spreads upward and P
It extends laterally from the layer 11 toward the inside of the device. The depletion layer that spreads in the lateral direction spreads in the opposite direction using a planar breakdown voltage structure formed on the surface, so that a reverse blocking breakdown voltage of the element can be obtained.

FIG. 4 is a waveform diagram showing the breakdown voltage characteristics of the device according to the present invention. Not only forward blocking voltage (forward voltage),
Since there is a reverse blocking withstand voltage (reverse withstand voltage), this reverse blocking type IGB
By always turning on the gate of T, it is possible to operate as a PN diode having a reverse blocking withstand voltage, composed of the P collector layer 1 and the N base layer 2. FIG. 5 is a model diagram of a bidirectional IGBT in which the products of the present invention are connected in anti-parallel. When connected in this way, the withstand voltage characteristic shows the withstand voltage waveform shown in FIG. 4 and is a bidirectional switching element capable of performing forward and reverse switching operations.
For example, when the main terminal T1 is grounded and a positive voltage is applied to the main terminal T2, when a positive voltage is applied to the gate terminal G1, the left element (the first reverse blocking IGBT 41) is turned on to move in the positive direction. Current flows through Conversely, the main terminal T
2 is grounded and a positive voltage is applied to the main terminal T1, a positive voltage is applied to the gate terminal G2 to turn on the element on the right (the second reverse blocking IGBT 42), and a current flows in the reverse direction. Flows. That is, a bidirectional switching operation can be performed.

Of course, the bidirectional IGBT has characteristics equivalent to the turn-off characteristics of the reverse blocking IGBTs 41 and 42 and the reverse recovery characteristics during the operation of the diode. FIG. 6 is a sectional view showing a main part of a semiconductor device according to a second embodiment of the present invention. Here, the semiconductor device is a reverse blocking IGBT.

A region where the lifetime killer is localized is a region where the depletion layer 32 is not depleted when the PN junction 31 between the N base layer 2 and the P base layer 3 is reverse biased (during forward breakdown voltage). (The region where no portion exists) within the N base layer 2. This element can be expected to have the same effects as those described in the first embodiment. FIG. 7 is a sectional view showing a main part of a semiconductor device according to a third embodiment of the present invention. Here, the semiconductor device is a reverse blocking IGBT.

When the peak position L of the distribution when the lifetime killer is localized is defined as the distance from the PN junction 31 to the peak of the density distribution of the lifetime killer (the peak 33 of the distribution), the peak position L Is set to 40 μm or less. Further, the width X (range of 10% of the peak value) of the distribution of the lifetime killer is 20 μm. This element is the first
The same effect as the effect described in the embodiment can be expected.

FIG. 8 shows the peak position L dependence of the reverse recovery peak current Irp during the diode operation. Peak position L
Is set to 40 μm or less, Irp is smaller than that in a case where uniform lifetime killer (dotted level) distribution is obtained, and a favorable reverse recovery characteristic of a soft recovery waveform is exhibited. 8, when the peak position L is brought closer to the PN junction 31, even better reverse recovery characteristics are exhibited. When the peak position L is set to 20 μm or less, Irp is 1/1 of the case of a uniform lifetime killer distribution. It is reduced to about 2.

FIG. 9 is a sectional view showing a main part of a semiconductor device according to a fourth embodiment of the present invention. Here, the semiconductor device is a reverse blocking IGBT. The position where the lifetime killer is localized is the same as in the first to third embodiments, except that the bevel structure 21 is applied as a structure for obtaining a reverse breakdown voltage. is there.

FIG. 10 is a sectional view showing a main part of a semiconductor device according to a fifth embodiment of the present invention. Here, the semiconductor device is a reverse blocking IGBT electrode. The position at which the lifetime killer is localized is the same as in the first to third embodiments, except that a bevel structure 22 different from that of FIG. 9 is applied as a structure for obtaining a reverse breakdown voltage. . Then, as a method of forming the bevel structure 22, a groove 23 reaching the P collector layer 1 from the surface is formed outside the surface planar breakdown voltage structure.

[0029]

According to the present invention, by introducing a lifetime killer locally into the base layer on the collector layer side, a good reverse recovery characteristic can be exhibited during diode operation while maintaining good switching characteristics. A semiconductor device of a reverse blocking type is obtained. Further, by connecting the reverse blocking type semiconductor device in anti-parallel, a bidirectional switching element having good characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a semiconductor device according to a first embodiment of the present invention;

FIG. 2 is a turn-off waveform diagram of a product of the present invention and a conventional product.

FIG. 3 is a reverse recovery waveform diagram of a product of the present invention and a conventional product.

FIG. 4 is a waveform chart of breakdown voltage characteristics of the element according to the present invention.

FIG. 5 is a model diagram of a bidirectional IGBT in which products of the present invention are connected in anti-parallel.

FIG. 6 is a sectional view of a main part of a semiconductor device according to a second embodiment of the present invention;

FIG. 7 is a sectional view of a main part of a semiconductor device according to a third embodiment of the present invention;

FIG. 8 is a view showing the peak position L dependence of the reverse recovery peak current Irp during the diode operation.

FIG. 9 is a sectional view of a main part of a semiconductor device according to a fourth embodiment of the present invention;

FIG. 10 is a sectional view of a main part of a semiconductor device according to a fifth embodiment of the present invention;

FIG. 11 is a sectional view of a main part of a conventional reverse blocking IGBT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 P collector layer 2 N base layer 3 P base layer 4 N emitter layer 5 Gate insulating film 6 Gate electrode 7 Interlayer insulating film 8 Emitter electrode 9 Collector electrode 11, 12, 13 P layer 14 Metal film 15 Insulating film 16 Breakdown voltage structure 17 Active region 20 Lifetime killer 21, 22 Bevel structure 31 PN junction 32 Depletion layer 33 Distribution peak 41 First reverse blocking IGBT 42 Second reverse blocking IGBT G Gate terminal E Emitter terminal C Collector terminal T1, T2 Main terminal G1 , G2 Gate terminal L Peak position X Distribution width

Claims (7)

[Claims] A first conductive type base layer; a second conductive type base layer selectively formed on a surface of the first conductive type base layer; and a second conductive type base layer selectively formed on a surface of the second conductive type base layer. A first conductive type source layer formed, and a gate electrode formed on the second conductive type base layer sandwiched between the first conductive type base layer and the first conductive type source layer via a gate insulating film A first main electrode formed in contact with the first conductive type source layer and the second conductive type base layer, a second conductive type collector layer formed on the back surface of the first conductive type base layer, A semiconductor device comprising a second main electrode formed on the collector layer and having a reverse blocking breakdown voltage equivalent to a forward blocking breakdown voltage, wherein a semiconductor device has a lifetime near the junction between the first conductivity type base layer and the second conductivity type collector layer. A semiconductor device characterized by localizing a time killer. 2. A depletion layer reaches a peak position of a distribution of the lifetime killer by a reverse bias voltage applied to a PN junction formed by the first conductivity type base layer and the second conductivity type base layer. The semiconductor device according to claim 1, wherein the first conductive type base layer is not provided. 3. A peak of the lifetime killer distribution is present in the first conductivity type base layer, and a distance between a position of the peak and a position of the PN junction is 0 μm to 40 μm.
The semiconductor device according to claim 2, wherein the thickness is μm. 4. The semiconductor device according to claim 1, wherein said lifetime killer is introduced by ion irradiation. 5. The semiconductor device according to claim 4, wherein said ions are helium ions or hydrogen ions. 6. A first semiconductor of a second conductivity type formed on the outer peripheral surface of the first conductivity type base layer so as to surround the side surface of the second conductivity type base layer in order to obtain the reverse blocking withstand voltage. 6. A breakdown voltage structure comprising a layer and a second conductivity type second semiconductor layer in contact with the first semiconductor layer and in contact with the second conductivity type collector layer. 13. The semiconductor device according to claim 1. 7. The semiconductor device according to claim 1, wherein the semiconductor device has a bevel structure to obtain the reverse blocking withstand voltage.