BACKGROUND OF THE INVENTION

The present invention relates to a lateral insulated gate bipolar transistor, and more particularly to improvement on a latch-up prevention ability of the lateral insulated gate bipolar transistor.

In the recent years, an insulated gate bipolar transistor (hereinafter referred to as IGBT) is high­lighted as a semiconductor device capable of controlling a relatively large current at a high speed. In order to integrate the IGBT together with another device, it is desirable that an emitter (cathode), a gate (control electrode) and a collector (anode) are placed in the same plane. An example of an IGBT structure satisfying this requirement is a lateral IGBT disclosed by JP-A-­59-132667. The disclosed structure is shown in Fig. 11. In an n⁻ layer 20 are independently provided a player 50 having an impurity concentration higher than that of the n⁻ layer 20 and a p⁺ layer 70 having an impurity higher than that of the p layer 50. In the p layer 50 is provided an n⁺ layer 60 having an impurity concentration higher than the p layer 50. The p layer 50 and the n⁺ layer 60 are electrically short-circuited by an emitter electrode 2. A collector electrode 3 is provided on a surface of the p⁺ layer 70 in ohmic contact with the p⁺ layer 70. An insulating film 10 is provided stretching over the surfaces of the n⁺ layer 60, the p layer 50 and the n⁻ layer 20 and a gate electrode 1 is provided on the insulating film 10. The n⁺ layer 60 and the insulating film 10 are provided opposite to the p⁺ layer 70 and the n⁺ layer 60 exists between the p⁺ layer 70 and a region where the p layer 50 and the emitted electrode 2 are in ohmic contact with each other. In this transistor, when a positive potential is applied to the gate electrode 1, the conductivity of a surface portion of the p layer 50 under the insulating film 10 is inverted into an n type so that a channel is formed. Electrons ⊖ flowing out of the n⁺ layer 60 pass through the channel and the n⁻ layer 20 and reach the p⁺ layer 70 from which positive holes ⊕ are injected. Thereby, the n⁻ layer 20 having a high resistance is conductivity-modulated to exhibit a low resistance, thereby providing a merit that an on-resistance lower than that of a MOSFET having the same forward blocking characteristic can be realized.

In the above-mentioned conventional lateral IGBT, the n⁺ layer 60 exists between the p⁺ layer 70 and the region where the p layer 50 and the emitter electrode 2 are in ohmic contact with each other. In this case, the positive holes ⊕ injected from the p⁺ layer 70 concentrically flow through the p layer 50 under the n⁺ layer 60 and reach the emitter electrode. Therefore, a potential drop is produced due to a resistance component R of the p layer 50 in a lateral direction. As a result, there is a problem that a pn junction formed by the n⁺ layer 60 and the p layer 50 is forward-biased by the potential drop to cause the injection of electrons from the n⁺ layer 60 into the p layer 50 so that there occurs a so-called latch-up phenomenon in which a parasitic thyristor formed by the n⁺ layer 60, the p layer 50, the n⁻ layer 20 and the p⁺ layer 70 is turned on, thereby making it impossible to control a current by the gate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved lateral IGBT which has an improved latch-up prevention ability.

The above object is realized in such a manner that a portion where an emitter electrode electrically contacts a semiconductor region adjacent to a semiconduc­tor region serving as an emitter is provided nearer to a semiconductor region serving as a collector than the semiconductor region serving as the emitter.

In the present invention, carriers injected from the semiconductor region serving as the collector can arrive at the emitter electrode without passing below the semiconductor region serving as the emitter. There­fore, the latch-up prevention ability can be improved, thereby making it possible to control a large current.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figs. 1A and 1B are a longitudinal cross section and a plan view showing a first embodiment of the present invention;
• Fig. 2 is a longitudinal cross section showing a second embodiment of the present invention;
• Fig. 3 is a perspective view showing a third embodiment of the present invention;
• Figs. 4A and 4B are a longitudinal cross section and a plan view showing a fourth embodiment of the present invention;
• Figs. 5 to 8 are longitudinal cross sections showing fifth to eighth embodiments of the present inven­tion;
• Figs. 9A and 9B are a schematic plan view and a circuit diagram of a power converting device in which the present invention is used;
• Fig. 10 shows current waveforms for explaining the operation of the device shown in Figs. 9A and 9B; and
• Fig. 11 is a longitudinal cross section of the conventional lateral IGBT.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be explained by virtue of the accompanying drawings which show embodi­ments thereof.

Figs. 1A and 1B are a longitudinal cross section and a plan view showing a first embodiment of the present invention. On the side of one surface of an n⁻ layer 20, a p layer 50 and a p⁺ layer 70 extending from the surface of the n⁻ layer 20 thereinto are provided apart from each other. In the p layer 50 is provided an n⁺ layer 60 which extends from a surface of the p layer 50 thereinto. An insulating film 10 is provided stretching over the surfaces of the n⁺ layer 60, the p layer 50 and the n⁻ layer 20 and a gate electrode 1 is provided on the insulating film 10. The p layer 50 and the n⁺ layer 60 are provided in ohmic contact with an emitter electrode 2 at a position nearer to the p⁺ layer 70 than the gate electrode 1. A region where the p layer 50 and the emitter electrode 2 are in ohmic contact with each other is positioned nearer to the p⁺ layer 70 than the n⁺ layer 60. A collector electrode 3 is provided in ohmic contact with a surface of the p⁺ layer 70. The p layer 50, the n⁺ layer 60 and the p⁺ layer 70 are juxtaposed, in the one surface of the n⁻ layer 20, with their stripe shapes the longitudinal directions of which are parallel to each other. Necessarily, the emitter electrode 2, the gate electrode 1 and the collector electrode 3 are provided along the p layer 50, the n⁺ layer 60 and the p⁺ layer 70, respectively.

Next, explanation will be made of the opera­tion of the lateral IGBT having the above-mentioned construction. When a positive potential is applied to the gate electrode 1 in a state in which a voltage bringing the collector electrode 3 into a positive potential and the emitter electrode 2 into a negative potential is applied between the collector electrode 3 and the emitter electrode 2, a channel is produced in a surface of the p layer 50 under the insulating film 10 so that electrons ⊖ are flown out of the n⁺ layer 60 through the channel and reach the p⁺ layer 70 through the n⁻ layer 20. In Fig. 1A, the flow of electrons ⊖ is indicated by dotted line. A pn junction between the p⁺ layer 70 and the n⁻ layer 20 is forward-biased by the electrons ⊖ reaching the p⁺ layer 70 so that positive holes ⊕ are injected from the p⁺ layer 70 into the n⁻ layer 20. The positive holes ⊕ pass through the n⁻ layer 20 and the p layer 50 and reach the emitter electrode 2. In Fig. 1A, the flow of positive holes ⊕ is indicated by one-dotted chain line. Since the region where the emitter electrode 2 and the p layer 50 are in ohmic contact with each other is positioned nearer to the p⁺ layer 70 than the n⁺ layer 60, the positive holes ⊕ can arrive at the emitter electrode 2 without passing under the n⁺ layer 60, thereby providing a merit that the latch-up prevention ability is improved and hence it is possible to control a large current. In the present embodiment, it is preferable that the impurity concentrations of the p⁺ layer 70, the n⁻ layer 20, the p layer 50 and the n⁺ layer 60 are equal to 1 x 10¹⁸ to 1 x 10²⁰ atoms/cm³, 1 x 10¹³ to 5 x 10¹⁵ atoms/cm³, 1 x 10¹⁵ to 5 x 10¹⁸ atoms/cm³ and equal to or higher than 1 x 10¹⁹ atoms/cm³, respectively.

Fig. 1A shows the minimum unit of the lateral IGBT for explaining the basic concept of the present invention. An actual product has a structure which a multiplicity of such minimum units are provided in parallel.

Fig. 2 is a longitudinal cross section showing a second embodiment of the present invention. In Fig. 2, the same reference numerals as those in Fig. 1A designate the same portions as those in Fig. 1A. An n⁺ buried layer 61 is provided in an n⁻ layer 20 below a p layer 50 and apart from the p layer 50. In the present embodiment, since electrons ⊖ flow through the n⁺ buried layer 61 having a low resistance, the resistance of a region through which the electrons ⊖ flow is reduced, thereby providing a merit that an ON resistance is lowered as compared with that in the first embodiment. The present embodiment has such a plane structure as shown in Fig. 1B.

Fig. 3 is a perspective view showing a third embodiment of the present invention. In Fig. 3, the same reference numerals as those in Fig. 1A designate the same portions as those in Fig. 1A. An insulating film 10 is provided stretching over a p layer 50 and an n⁻ layer 20 at a side near to a collector electrode 3 and stretching over the n⁻ layer 20, the p layer 50 and a p⁺ layer 60 at a side away from the collector electrode 3. Each of the p layer 50 and a p⁺ layer 70 is formed in a surface of the n⁻ layer 20 and with a shape elongat­ed in one direction and the n⁺ layer 60 is constructed by a plurality of regions which are provided in parallel along a longitudinal direction of the p⁺ layer 70. Therefore, the collector electrode 3 is formed along a longitudinal direction of the p⁺ layer 70, an emitter electrode 2 is divided into a plurality of portions and a gate electrode 1 is formed so as to enclose each emitter electrode 2. In the present embodiment, electrons ⊖ flowing out of the n⁺ layer 60 pass through a channel produced in the vicinity of the p layer under the insulating film 10 and flow into the n⁻ layer 20 from a portion under the insulating film 10 opposing the p⁺ layer 70. Therefore, the electrons and positive holes take the same path in the n⁻ layer 20 and hence the conductivity is sufficiently modulated, thereby providing a merit that an on resistance lower than that in the first embodiment is exhibited.

Figs. 4A and 4B are a longitudinal cross section and a plan view showing a fourth embodiment of the present invention. A p⁺ layer 70 and a p layer 50 elongated in one direction are independently provided in an n⁻ layer 20. An n⁺ layer 63, an n⁺ layer 60 and an n⁺ layer 62 are provided in the p layer 50 and along a longitudinal direction of the p layer 50. The n⁺ layer 60 is positioned between the n⁺ layers 62 and 63 and are divided into a plurality of regions along the longitudinal direction of the p layer 50. An emitter electrode 2 includes a plurality of portions which are in ohmic contact with the n⁺ layer 60 and the p layer 50 positioned on the side near to the p⁺ layer 70 than n⁺ layer 60. A collector electrode 3 is provided on a surface of the p⁺ layer 70 along a longitudinal direction and in ohmic contact with the p⁺ layer 70. A gate electrode 1 is formed on the n⁺ layer 63, the p layer 50 and the n⁻ layer 20 through an insulating film 10 on a side near the collector electrode 3 so as to stretch over the layers 63, 50 and 20 and is formed on the n⁺ layer 60, the p layer 50 and the n⁺ layer 62 through the insulating film 10 on a side away from the collector electrode 3 as to stretch over the layers 60, 50 and 62. Portions of the gate electrode 1 near to and away from the collector electrode 3 are integral with each other. The n⁺ layer 62 and the n⁺ layer 63 are connected by an n⁺ layer 4 but may be connected by a conductor in place of the n⁺ layer 4. Each of opposite ends of the p layer 50 in the longitudinal direction thereof has a predetermined curvature for the purpose of mitigating the concentration of an electric field and the gate electrode 1 is provided through the insulating film 10 on the periphery of the p layer 50 and the n⁻ layer 20 adjacent thereto. The p layer 50, the n⁺ layer 60, the n⁺ layer 62 and the n⁺ layer 63 have a symmetrical structure with respect to line A-A (see Fig. 4B). In this case, two rows for each of the n⁺ layer 60 and the emitter electrode 2 are provided in a longitudinal direction. Preferably, the two rows are positionally shifted from each other in the longitudinal direction. An actual device has a structure in which the p⁺ layers 70 and the p layer 50 are alternately arranged so that the p⁺ layers 70 are positioned at opposite outsides.

The operation of the present embodiment is as follows. When a positive potential is applied to the gate electrode 1 in a state in which a voltage bringing the collector electrode 3 into a positive potential is applied between the collector electrode 3 and the emitter electrode 2, a channel is formed in a surface of the p layer 50 lying below the insulating film 10. With the formation of this channel, electrons ⊖ from the n⁺ layer 60 flow into the n⁺ layer 62 through the channel. The electrons ⊖ arriving at the n⁺ layer 62 reach the n⁺ layer 63 through the n⁺ layer 4 and pass through the channel formed in the p layer 50 below a portion of the gate electrode 1 near to the collector electrode 3 to flow into the n⁻ layer 20, thereby arriving at the p⁺ layer 70. The flow of electrons ⊖ is indicated by dotted line in Fig. 4A. On the other hand, positive holes ⊕ from the p⁺ layer 70 take a route in which they pass through the n⁻ layer 20 to enter into the p layer 50 and reach the emitter electrode 3, as indicated by one-dotted chain line in Fig. 4A. Thus, in the present embodiment, since the flow paths of the electrons ⊖ and the positive holes ⊕ coincide with each other, a sufficient conductivity modulation is made, thereby realizing a lateral IGBT which has an on-resistance lower than that in the first embodiment. Also, a distance along which the electrons flow through the channel is shortened as compared with the third embodiment. Namely, the sum of the length of the channel between the n⁺ layer 60 and the n⁺ layer 62 and the length of the channel between the n⁺ layer 63 and the n⁻ layer 20 in the present embodiment is shorter than the length of the channel in the third embodiment extending from the n⁺ layer 60 to the n⁻ layer 20 and hence the flow distance of electrons ⊖ is short, there­by providing an advantage of low on-resistance.

Fig. 5 is a longitudinal cross section showing a fifth embodiment of the present invention. The present embodiment has a structure in which an n⁻ layer 20 is formed on a p⁻ layer 30 and is surrounded by a p⁺ layer 71. An electrode 5 is provided on a surface of the p⁺ layer 71 in ohmic contact with the p⁺ layer 71. The lowest potential is applied to the electrode 5 so that the p⁺ layer 71 and the p⁻ layer 30 are reverse-biased relative to the n⁻ layer 20. Therefore, the present embodiment has a merit that the lateral IGBT formed on the same p⁻ layer 30 is electrically isolated from the other elements or devices. Such formation of a lateral IGBT in the pn-isolated substrate is applicable to all the other embodiments excepting an embodiment which will be explained in conjunction with Fig. 6.

Fig. 6 is a longitudinal cross section showing a sixth embodiment of the present invention. In the present embodiment, an n⁻ layer 20 is a monocrystalline region which is island-wise formed through an insulating film (or dielectric film) 11 in a supporting substrate 80. In the fifth embodiment, positive holes injected from the p⁺ layer 70 may flow as a leakage current into the electrode 5 applied with the lowest potential, thereby resulting in a loss. In the present embodiment, on the other hand, all of positive holes flow into an emitter electrode 2, thereby providing a merit that any leakage current can be prevented. In the present embodiment, an n region 21 having an impurity concentra­tion higher than the n⁻ layer 20 is formed in a portion of the n⁻ layer 20 adjacent to the p⁺ layer 70 and an n⁺ layer 22 is formed in a portion of the n⁻ layer 20 adjacent to the insulating film 11. Also, a p layer 50 has a p⁺ region 51 adjacent to an n⁺ layer 60.

Such formation of a lateral IGBT in the monocrystalline island of the dielectric-isolated substrate is applicable to all the other embodiments excepting the embodiment shown in Fig. 5.

Fig. 7 is a longitudinal cross section showing a seventh embodiment of the present invention. Two p layers 50 and two p⁺ layers 70 are respectively provided symmetrically with respect to an insulating film 10 and a gate electrode 1. In the second to sixth embodi­ments, in the case where a high voltage is applied between the collector electrode 3 and the emitter electrode 2, a location applied with the strongest electric field and caused to avalanche breakdown is a region under the insulating film 10. This tendency is remarkable in the third and fourth embodiments since the insulating film 10 exists on the collector electrode 3 side. In this case, there is a danger that the insulating film 10 is broken so that the gate electrode 1 and the emitter electrode 2 are short-circuited. In the present embodiment, on the other hand, the p layers 50 are provided on opposite sides of the insulating film 10 in a direction of thickness thereof. Therefore, in the case where a high voltage is applied, the p layers 50 are pinched off under the insulating film 10 by a depletion layer and hence an avalanche breakdown region is the interior of the semiconductor (or n⁻ layer 20) away from the insulating film 10. As a result, no breakdown occur under the insulating film 10, thereby providing a merit that a reliability is increased as compared with the second to sixth embodiments.

In the present embodiment, an emitter electrode 2 is provided on the n⁻ layer 20 through an insulating film 11 to extend toward a collector electrode 3. A portion of the emitter electrode 2 on the insulating film 11 serves as a field plate which properly expands an depletion layer to mitigate an electric field. In the first to sixth embodiments, the gate electrode 1 on the insulating film 10 serves as a field plate. There­fore, when a potential of the gate electrode 1 is changed in order to control the IGBT, the degree of expansion of a depletion layer changes so that a breakdown voltage correspondingly changes. Especially, in Figs. 3, 4 and 5, when a large potential which is negative relative to the emitter electrode 2 is applied to the gate electrode 1, a punch-through phenomenon that a depletion layer reaches the p⁺ layer 70 occurs, thereby lowering a break­down voltage. However, in the present embodiment, since the field plate is formed by the emitter electrode 2, there is provided a merit that a breakdown voltage is stably determined by only a voltage between the collector electrode 3 and the emitter electrode 2 without depending on a control voltage applied to the gate electrode 1.

In the present embodiment, it is preferable that the p⁺ layer 70, the p layer 50 and an n⁺ layer 60 are formed with their shapes elongated in a direction parpendicular to the drawing sheet plane. In that case, a predetermined number of units one of which is shown by one-dotted line A₀-A₀ may be provided in accordance with a current capacity.

Fig. 8 is a longitudinal cross section showing an eighth embodiment of the present invention. A plurality of p layers 50 are provided in parallel in an n⁻ layer 20 surrounded by a p⁺ layer 72. The outermost p layer 50 has one n⁺ layer 60 therein and the inter­mediate p layer 50 has two n⁺ layers 60 therein. An insulating film 10 is provided stretching over a portion of the n⁻ layer 20 which is positioned between the p layers 50 and the p layers 50 and the n⁺ layers 60 which are positioned on opposite sides of that portion of the n⁻ layer 20. A gate electrode 1 is provided on the insulating film 10. An emitter electrode 2 is provided in ohmic contact with the p layer 50 and the n⁺ layer 60. The p layer 50, n⁺ layer 60, gate electrode 1, emitter electrode 2 and p⁺ layer 72 positioned in the outermost periphery and the collector electrode 3 constructs a lateral IGBT A₁ while the p layers 50, n⁺ layers 60, gate electrodes 1, emitter electrodes 2 and p⁺ layers 72 positioned in the intermediate portion and the collector electrode 3 construct a plurality of vertical IGBT's A₂.

In the present embodiment, in an area A₂, positive holes ⊕ are injected from only the p⁺ layer 72 lying in the bottom part. In an area A₁, on the other hand, positive holes ⊕ are injected not only from the p⁺ layer 72 lying in the bottom part but also from the p⁺ layer 72 lying in the side part. Therefore, the positive holes are concentrated in the area A₁. However, in the area A₁, since a region where the emitter electrode 2 is in ohmic contact with the p layer 50 is provided nearer to the p⁺ layer 72 than the n⁺ layer 60, the positive holes arrive at the emitter electrode 2 without passing under the n⁺ layer 60, thereby providing a merit that the latch-up prevention ability is improved.

Figs. 9A and 9B are a schematic plan view and a circuit diagram of an example of a power converting device to which lateral IGBT's according to the present invention are applied, more particularly, an inverter in which a current is controlled by turning on/off four lateral IGBT's. In the figures, reference numerals 80a, 80b, 80c and 80d designate lateral IGBT's formed in an island-like area of a dielectric-isolated substrate 300, numerals 90a, 90b, 90c and 90d diodes formed in another island-like area of the dielectric-isolated substrate 300, symbol T_AC an AC terminal, symbol T_DC DC terminals, symbols G_a, G_b, G_c and G_d gate terminals, numeral 100 a load, and numeral 200 a DC power source. Such a device may involve an operation in which the IGBT 80a is turned on when a current is flowing through the diode 90b. Namely, when the IGBT 80a is turned off in order to control a current in a state in which the IGBT's 80a and 80d are in ON state so that a current I₁ is flown, a current I₂ flows through the IGBT 80d and the diode 90b. At this time, if the IGBT 80a is turned on again, a power source voltage is applied across the diode 90b so that excess carriers having been stored in the diode 90d are swept out, thereby causing a current I₃ to flow transiently. This transient state is schematically shown in Fig. 10. When the IGBT 80a is turned on at instant of time t = t₁, the current I₂ having flown through the diode 90b is decreased and at instant of time t = t₂ the current I₃ having a direction reverse to that of the current I₂ start to flow through the diode 90b. At this time, a current of I₁ + I₃ flows through the IGBT 80a until instant of time t = t₃ when the current I₃ becomes zero. Thus, an excessive current flows through the IGBT 80a during a period of time from t₂ to t₃. Therefore, in the conventional lateral IGBT, latch-up occurs, thereby making it impossible to control a current. However, in the power converting device in which the lateral IGBT's according to the present invention are used, no impossibility of control is encountered since the latch-up prevention ability is improved.

In the foregoing, typical examples of the present invention have been disclosed. However, it should be noted that the present invention is not limited to the disclosed embodiments and various changes or modifications are possible.

In a lateral insulated gate bipolar transistor according to the present invention, since a region where a semiconductor layer having the same conductivity type as a collector layer contacts an emitter electrode is provided nearer to the collector layer than an emitter layer, the latch-up prevention ability is improved, thereby making it possible to control a large current.