Insulated gate bipolar transistor decreasing the gate resistance

The present invention relates to an insulated gate transistor, and more particularly, to an insulated gate transistor which is superior in preventing the latch-up phenomenon or current concentration of the transistor.

Currently, and insulated gate bipolar transistor (hereinafter abbreviated as IGBT) having a fast operation and a low on-resistance is used as a power switching device. The IGBT has a structure, wherein: a p-type base region extending from a main surface to its inner portion and a n-type emitter region extending from the base region to its inner portion are formed on one side of a main surface of a n-type semiconductor substrate, which operates as a drift region; a p-type collector region is formed on another side of the main surface of the semiconductor substrate separate from the base region; emitter electrodes are provided on the emitter region and the base region; and a collector electrode is provided on the collector region. The IGBT has the following feature. When a voltage, which makes the collector electrode have a positive potential relative to the emitter electrode, is applied to the collector electrode, and a positive voltage is applied to the gate electrode, electrons in the emitter region reach the collector region through channels and a drift region. The electrons, which reach the collector region, enhance injection of positive holes from the collector region. Accordingly, the drift region having a high resistance is conductivity-modulated to be a low resistance region, and an on-resistance lower than a MOSFET, the collector region of which is changed to a n-type drain region having no function to inject positive holes, is realized with approximately the same structure as a MOSFET.

When an IC is realized by combining the IGBT with other circuit elements, a lateral structure, wherein the emitter electrode, the collector electrode, and the gate electrode are provided on a same surface of the semiconductor substrate, is desirable in order to facilitate connection among the electrodes. An example of this structure is disclosed, for instance, in JP-A-5-29614 (1993).

On the other hand, in the IGBT, the conventional current which can be passed through a unit composed of a pair of collector-emitter electrodes is restricted. Therefore, a desired current capacity is realized by integrating a large number of unit IGBTS in the semiconductor substrate.

The IGBT disclosed in JP-A-5-29614 (1993) has a structure wherein the emitter region, the base region, and the collector region have a comb shape, respectively, and respective teeth portions of the emitter region and the base region are engaged with the collector region. Gate electrodes are provided on the base region, a drift region in the vicinity of the base region, and the emitter region via an insulating film. The emitter electrode and the collector electrode are provided on each of the emitter region and the base region, respectively. Both the emitter electrode and the collector electrode have a comb shape, and teeth portions of the emitter electrode and the collector electrode are engaged with each other.

Conventionally, polycrystalline silicon is used as the material of the gate electrode. However, in lateral IGBT having a conventional structure, a non-uniformity of the gate resistance is created due to the longitudinal resistance of the gate electrode, and the turn-off action is delayed at the portion having a large gate resistance in a turn-off operation.

Most of the load of the inverter device generally comprises an inductive loads. Therefore, at that time, a current concentration is generated at the portion where the turn-off action is delayed, in addition to the effect of maintaining the flow of the large current due to an inductance. As a result, a latch-up phenomenon is caused at that portion. Accordingly, there has been a problem in that the current which is controllable by the IGBT is restricted to a lower level than a designed value.

In order to decrease the delay of the operation time in the element, technology to decrease the resistance of the gate electrode has been disclosed in JP-A-10-173176 (1998) and other publications. However, the technology relates to the structure of a vertical IGBT, and any idea to integrate an IGBT and a driving circuit for composing an integrated circuit has not been considered.

One of the objects of the present invention is to provide an insulated gate transistor having an improved latch-up preventing performance by decreasing the resistance of the gate electrode.

The feature of the insulated gate transistor for achieving the above object by the present invention is in providing a metallic wiring layer on the emitter electrode via an insulating layer; providing plural regions insulated from a first main electrode in the first main electrode; and connecting the metallic wiring layer electrically with the gate electrode through the plural regions insulated from the first main electrode.

FIG. 1 is a schematic partial plan view of a lateral insulated gate bipolar transistor representing an embodiment of the present invention;

FIG. 2 is a cross sectional view taken along the line A-A′ of FIG. 1;

FIG. 3 is a cross sectional view taken along the line B-B′ of FIG. 1;

FIG. 4 is a schematic partial plan view of a lateral insulated gate bipolar transistor representing another embodiment of the present invention; and

FIG. 5 is a schematic cross sectional view of a vertical insulated gate bipolar transistor according to another embodiment of the present invention.

Hereinafter, details of an embodiment of the present invention will be explained with reference to FIG. 1, FIG. 2 and FIG. 3 .

FIG. 1 is a schematic partial plan view of a lateral insulated gate bipolar transistor representing an embodiment of the present invention, and FIG. 2 is a cross sectional view taken along the line A-A′ of FIG. 1 . In accordance with FIG. 2, a semiconductor substrate 1 comprises a n conductivity type drift region 3 (first semiconductor region) having a main surface plane 2 ; a p conductivity type base region 4 (second semiconductor region) and a p conductivity type collector region 5 (third semiconductor region), each of which extends from the main surface plane 2 into the drift region 3 , and are provided separately from each other, containing a higher impurity concentration than the drift region 3 ; and a n conductivity type emitter region 6 (fourth semiconductor region), which extends from the main surface plane 2 into the base region 4 , containing a higher impurity concentration than the base region 4 . Each of the base region 4 and the collector region 5 has a stripe structure, and these regions are aligned in a longitudinal direction and are disposed alternately in a direction perpendicular to the longitudinal direction, as indicated in FIG. 1 . The emitter region 6 has a stripe shape, and two emitter regions are arranged in the base region 4 in a longitudinal direction extending along the longitudinal direction of the base region 4 . The emitter electrode 7 (first main electrode), shown as a solid line in FIG. 1, has a comb shape with each of the teeth portion 7 a extending along the base region 4 on the main surface plane 2 , and being connected electrically to the emitter region 6 and the base region 4 . The collector electrode 8 (second main electrode) has a comb shape (expressed by a solid line in FIG. 1 ), with each of the teeth portion 8 a extending along the collector region 5 on the main surface plane 2 , and being connected electrically to the collector region 5 . The polycrystalline silicone gate electrode 9 , 9 a (control electrode) having a stripe structure is arranged above the base region 4 , and the drift region 3 and the emitter region 6 , each of which is disposed at adjacent sides of the base region 4 , respectively, on the main surface plane 2 via the gate insulating film 10 and extends in a longitudinal direction along the longitudinal direction of the base region 4 . The gate electrode 9 is connected electrically to the adjacent gate electrode 9 a at three portions, i.e. at both ends and at the middle of its longitudinal direction, using polycrystalline silicone. A first insulating film provided on a part of the base region, the gate electrode, and the drift region, as indicated in FIG. 2 . Each of the teeth portions 7 a of the emitter electrode 7 and the teeth portions 8 a of the collector electrode 8 extend on the first insulating film 11 so as to reach the drift region 3 . A second insulating film 12 is formed above the collector electrode 8 , the emitter electrode 7 , and the first insulating film 11 . The gate line 13 having a comb shape is formed on the second insulating film 12 along the emitter electrode 7 with, for instance, aluminum-silicone. The gate line 13 is connected electrically to the polycrystalline silicone at the connecting portions 9 b of the gate electrode 9 , 9 a provided at three portions (both ends and a middle portion of the gate electrode in the longitudinal direction). FIG. 3 indicate a cross sectional view taken along the line B-B′ in FIG. 1, showing details of the contacting of the teeth portion 13 a of the gate line 13 with the connecting portion 9 b of the gate electrode 9 , 9 a . The connecting portion 9 b of the gate electrode 9 , 9 a is brought in contact with the gate line 13 , by cutting off a part of the emitter electrode 7 , the first insulating film 11 , and the second insulating film 12 , via an aluminum-silicone layer 14 .

In accordance with the structure of the present invention, the resistance of the gate electrode in the longitudinal direction can be decreased by providing plural connecting portions 9 b of the gate electrode 9 , 9 a in contact with the gate line 13 along the longitudinal direction of the gate electrode 9 , in order to pass the gate current at turn-off to the aluminum-silicone line via the nearest connecting point. When plural unit IGBTS are connected in parallel, the gate electrodes of the adjacent unit IGBTS can be readily connected by the gate line 13 , and the gate resistance of the whole IGBT can be uniform. As a result, the operating time at the time of turn off in the unit IGBT and the operating time of the whole IGBT can be uniform. Therefore, current concentration can be prevented, and consequently, the latch-up preventing performance can be improved.

In accordance with the present embodiment, the decrease of the gate resistance can be achieved on the main surface plane of the transistor. Therefore, an IC can be readily formed, because the IGBT and a driving circuit for driving it can be connected to each of the dielectric substrate SOI substrate, or respective elements separated by a PN-junction on the same surface plane.

FIG. 4 is a schematic plan view of the lateral insulated gate bipolar transistor according to another embodiment of the present invention. In accordance with FIG. 4, the connection points with the gate line are provided at three points, i.e. both ends and the middle point, of respective gate electrodes 9 and 9 a , for decreasing the resistance in the longitudinal direction of the gate electrodes 9 and 9 a . The important point for decreasing the gate resistance in the longitudinal direction is to provide plural connecting points on the polycrystalline silicone gate electrode in the longitudinal direction, and to electrically connect each of the connecting points with a low resistance line such as an aluminum-silicone line.

FIG. 5 is a schematic plan view of a vertical insulated gate bipolar transistor of the present invention. The collector region 5 extends to a portion of the drift region 3 directly under the base and emitter region 4 , 6 from the main surface 2 . The operation of the respective regions and electrodes are the same as the operation of the lateral insulated gate bipolar transistor indicated in FIG. 2 . The same advantages as the lateral insulated gate bipolar transistor can be obtained with the vertical insulated gate bipolar transistor.

In accordance with the present invention, not only the gate resistance of the lateral insulated gate bipolar transistor, but also the gate resistance of the vertical insulated gate bipolar transistor can be decreased. Accordingly, the operating time at the turn-off operation can be made uniform in the element, and latch-up preventing performance can be improved.

The present invention can be applied to both lateral and vertical insulated gate transistors, such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In the insulated gate transistor, the collector regions 5 in FIG. 2 and FIG. 5 are of n conductivity type, which is opposite to the conductivity type of the insulated gate bipolar transistors. In accordance with the present invention, the gate resistance is decreased, and the turn-off operation is made uniform in the element, Therefore, the current concentration or current crowding is prevented. Additionally, the present invention is also applicable to an insulated gate transistor in which the p and n conductivity types of the foregoing embodiments is changed to n and p conductivity types, namely to opposite conductivity types, respectively. In this case, the gate resistance is also reduced.