JP3963751B2 - Thyristor - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a thyristor, and more particularly to a thyristor used for a surge protection element for protecting an electronic circuit system from an abnormal voltage or current.
[0002]
[Prior art]
Thyristors are widely used in the communication industry and the like as surge protection elements that protect electronic circuits from abnormal voltages and currents generated in communication lines such as telephone lines.
[0003]
FIG. 2 is a cross-sectional view showing a thyristor according to the prior art. In FIG. 2, 1 is a semiconductor substrate conductive region, 2 is a first N-type conductive region, 3 is a second N-type conductive region, 4 is a first P-type conductive region, 10 is a first electrode, 11 is a second electrode, and 21 and 22. , 23 and 24 are insulators, 40 is a first hole-shaped conductive region, 90 is a boundary surface between the first N-type conductive region 2 and the semiconductor substrate conductive region 1, and 100 is a semiconductor substrate. FIG. 3 is a graph showing the forward characteristics of the thyristor shown in FIG.
[0004]
The semiconductor substrate 100 has a P-type conductivity type. The first N-type conductive region 2 and the second N-type conductive region 3 have an N-type conductivity type formed by impurity diffusion inside the semiconductor substrate 100. The first P-type conductive region 4 has a P-type conductivity type formed by impurity diffusion inside the semiconductor substrate 100. The first electrode 10 and the second electrode 11 are electrodes formed on both main surfaces of the semiconductor substrate 100. Here, the first electrode 10 is electrically connected to both the first P-type conductive region 4 and the first hole-shaped conductive region 40. The second electrode 11 is electrically connected to the second N-type conductive region 3. The first hole-shaped conductive region 40 and the first N-type conductive region 2 are electrically connected.
[0005]
In the thyristor shown in FIG. 2, the side of the surface of the semiconductor substrate 100 where the first N-type conductive region 2 is provided (hereinafter referred to as the upper surface side. Other thyristors described below are also the first N-type of the semiconductor substrate 100. The side of the surface provided with the conductive region 2 is referred to as the upper surface side) is referred to as the side of the surface provided with the second N-type conductive region 3 (hereinafter referred to as the lower surface side. Other thyristors described hereinafter are also semiconductors. The application direction of a voltage having a positive potential with respect to the surface of the substrate 100 on which the second N-type conductive region 3 is provided is the lower surface side. The direction is also referred to as the forward direction). Conversely, the voltage application direction in which the upper surface side is a negative potential with respect to the lower surface side is the reverse direction (this direction is also the reverse direction for the voltage application directions of other thyristors described below). To do.
[0006]
FIG. 3 is a graph showing electrical characteristics in the forward direction of the thyristor shown in FIG. As shown in FIG. 3, in the forward direction, a PNP transistor having a first P-type conductive region 4 as an emitter, a first N-type conductive region 2 as a base, and a semiconductor substrate conductive region 1 as a collector, and a second N-type conductive region 3 Electrons and holes are exchanged between the NPN transistor having the emitter, the semiconductor substrate conductive region 1 as a base, and the first N-type conductive region 2 as a collector, and an ignition operation for shifting from an off state to an on state is performed. .
[0007]
That is, when the forward voltage applied between the first electrode 10 and the second electrode 11 reaches the breakover voltage Vb in FIG. 3 in the thyristor of FIG. A current flows due to the through. That is, the exchange of electrons and holes is actively performed in the boundary surface 90 between the first N-type conductive region 2 and the semiconductor substrate conductive region 1 in the reverse bias state and in the vicinity of the boundary surface 90. Since the base of the PNP transistor and the collector of the NPN transistor are the common first N-type conductive region 2, the thyristor is ignited and transitions to the on state. Needless to say, the depletion layer expands to the maximum when the breakover voltage is reached.
[0008]
Since it is a well-known fact that the thyristor having the PNPN structure is ignited to shift from the off state to the on state, a detailed description of the internal operation is omitted here, but the structure shown in FIG. Then, since the first hole-shaped conductive region 40 is in the center and the first electrode 10 is not directly electrically connected to the first N-type conductive region 2, when the ignition operation is started by an avalanche breakdown, the trigger of the ignition is performed. Current flows from the periphery of the first N-type conductive region 2 toward the first hole-shaped conductive region 40 near the center.
[0009]
As described above, the thyristor that performs the ignition operation as described above suppresses the surge voltage by the breakover voltage Vb, but the response to other electrical surges such as a lightning induced surge is much faster than other surges. Because it is very fast compared to protective elements such as lightning arresters and metal oxide varistors, it is mostly used in places where lightning-induced surges are easily picked up, such as electronic devices in communication networks that require high reliability. Is in a situation.
[0010]
In addition, since it is made of a semiconductor substrate, it has a great maintenance advantage that it can maintain reliability over a long period without being consumed by a surge current.
[0011]
However, even in a thyristor having such an advantage, as its communication speed increases, its electrostatic capacity cannot be ignored. That is, there has been a demand to reduce the capacitance that leads to the deterioration of the quality of communication lines as much as possible. In order to meet this requirement, the capacitance described above is mainly caused by a depletion layer generated at the boundary surface 90 between the first N-type conductive region 2 and the semiconductor substrate conductive region 1, and therefore, simply, the depletion layer has an electric field. It may be as wide as possible with respect to the direction or the entire thyristor may be reduced to reduce the capacitance.
[0012]
However, the expansion of the depletion layer described above cannot be simply realized due to the disadvantage that the breakover voltage becomes high.
[0013]
Further, if the entire thyristor is made small, there is a disadvantage that the conduction area is reduced accordingly and the surge withstand capability is also reduced. Therefore, various devices have been made to increase the surge withstand capability as much as possible, but this has limitations.
[0014]
[Problems to be solved by the invention]
An object of the present invention is to further improve the thyristor having a conventional structure, and to reduce the capacitance without largely changing the breakover voltage.
[0015]
[Means for Solving the Problems]
As a means for solving the above-described problems, the present invention provides a first conductive material of a second conductivity type opposite to the semiconductor substrate formed by being exposed on one surface of the first conductive type semiconductor substrate. A region, a second conductive region of a first conductivity type that is exposed in the one surface and formed in the first conductive region, and the other of the semiconductor substrate facing away from the one surface A third conductive region of the second conductivity type formed by being exposed on the surface, and a second conductive type of the second conductivity type formed by being exposed to the one surface and penetrating through the second conductive region. 4 conductive regions, a fifth conductive region of the first conductivity type that is exposed on the one surface and is formed in the vicinity of the edge of the first conductive region, the second conductive region, In a thyristor comprising electrodes formed so as to be in contact with both of the fourth conductive regions And it shall be characterized in that in the vicinity of the electrode and partially overlap or the electrode when the fifth conductive region saw the semiconductor substrate in plan view.
[0016]
In the configuration described above, the portion where the breakover voltage does not form the first conductive region (first N-type conductive region 2 in FIG. 2) and the conductive region of the semiconductor substrate as compared with the thyristor structure shown in FIG. In order to reduce the capacitance, it is difficult to determine the boundary surface (the semiconductor substrate conductive region 1 in FIG. 2) and its vicinity (boundary surface 90 in FIG. 2), and the electric field is increased by increasing the resistivity of the semiconductor substrate conductive region. The depletion layer can be expanded with respect to the direction. In the configuration described above, the breakover voltage is determined in the first conductive type fifth conductive region.
[0017]
Therefore, compared with the conventional structure shown in FIG. 2, the depletion layer can be expanded perpendicular to the electric field direction while the breakover voltage is maintained at the conventional level, and the conduction area can be made almost constant. Become. Therefore, the capacitance can be reduced without sacrificing other characteristics so much.
[0018]
In the above configuration, the present invention may include a plurality of the fourth conductive regions. Also in this configuration, the breakover voltage is mainly determined by the newly added fifth conductive region of the first conductivity type. Therefore, the capacitance can be reduced without sacrificing other characteristics so much.
[0019]
Further, according to the present invention, in the above configuration, the sixth conductive region of the first conductivity type may be formed so as to be exposed on the other surface and to penetrate the third conductive region. In this case, the reverse direction is the same as the forward characteristic of the diode.
[0020]
Furthermore, in the above configuration, the present invention may include a plurality of the sixth conductive regions.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a thyristor according to a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a thyristor according to a first embodiment of the present invention. In FIG. 1, 1 is a semiconductor substrate conductive region, 2 is a first N-type conductive region, 3 is a second N-type conductive region, 4 is a first P-type conductive region, 10 is a first electrode, 11 is a second electrode, and 21 and 22. 23, 24 are insulators, 30 is a second P-type conductive region, 40 is a first hole-shaped conductive region, 90 is a boundary surface between the first N-type conductive region 2 and the semiconductor substrate conductive region 1, and 100 is a semiconductor substrate.
[0022]
The semiconductor substrate 100 is formed in a cylindrical shape and has a P-type conductivity type. A first N-type conductive region 2 and a second N-type conductive region 3 are formed on the semiconductor substrate 100. Further, the first P-type conductive region 4 is formed in the first N-type conductive region 2, and the first hole-shaped conductive region 40 is formed in the first P-type conductive region 4. Here, the first N-type conductive region 2 and the first hole-shaped conductive region 40 are electrically connected, and the first N-type conductive region 2 is electrically connected to the first electrode 10 through the first hole-shaped conductive region 40. . Furthermore, the semiconductor substrate 100 is disposed so that the end of the first electrode and the vicinity of the end overlap the second P-type conductive region 30 when viewed in plan. The second P-type conductive region is disposed near the outer periphery of the first N-type conductive region 2. The second P-type conductive region 30 is formed in a ring shape near the edge of the semiconductor substrate 100. The first P-type conductive region 4 and the second P-type conductive region 30 are formed by high-temperature diffusion after introducing P-type impurities from the outside using an appropriate mask.
[0023]
The first N-type conductive region 2 and the second N-type conductive region 3 are formed by high-temperature diffusion after introducing N-type impurities from the upper surface side and the lower surface side, respectively. There is a manufacturing advantage that it may be. The first hole-shaped conductive region 40 may be formed with a mask having a pattern corresponding to the first hole-shaped conductive region 40 when forming the first P-type conductive region 4, and this method is actually used from the viewpoint of manufacturing cost. It is preferable to form. Of course, a separate mask may be used if necessary. For example, in order to reduce the resistance value of the first hole-shaped conductive region 40, high-temperature diffusion may be performed after introducing an N-type impurity separately. Other conductive regions may be formed by a plurality of diffusions as required, but is usually once.
[0024]
After all the N-type and P-type impurity diffusion steps are completed, insulators 22, 23, 24, and 25 such as silicon oxide films are stacked and formed by etching for the first electrode 10 and the second electrode 11. Open the window. At this time, it arrange | positions so that the edge part of the 1st electrode 10 and the edge part vicinity may overlap with a 2nd P-type electroconductive area | region seeing the semiconductor substrate 100 planarly.
[0025]
The insulators 21, 22, 23, and 24 are usually formed of a nitride film, an oxide film, or the like. If there is no problem in characteristics, it is possible to use gas or vacuum, but it is preferable to form a multilayer structure composed of a plurality of insulators. Since there are insulators 21, 22, 23, and 24 between the first electrode 10 and the second P-type conductive region, an appropriate combination of materials is considered in consideration of the dielectric constant of the insulator in designing the breakover voltage. The insulator may be optimized. In that case, the thickness of the insulator is naturally also related. The second P-type conductive region 30 is preferably formed in a ring shape, but it is possible to make a cut at one or a plurality of locations of the ring. Also, a large number of independent small island regions may be arranged in a ring shape. Furthermore, the shape of the semiconductor substrate 100 is not limited to a cylindrical shape, and may be another shape such as a rectangular tube shape.
[0026]
Subsequently, the feature point of the operation of the thyristor according to the first embodiment of the present invention will be described. As shown in FIG. 1, the thyristor according to the first embodiment of the present invention is formed so as to be ignited in the forward direction. That is, in the structure shown in FIG. 1, when a voltage is applied in the forward direction, the portion where the electric field is highest in the semiconductor substrate is the end of the first electrode 10 when the semiconductor substrate 100 is viewed in plan. This is the surface of the semiconductor substrate just below and its vicinity. That is, the position where the electric field is highest is in the second P-type conductive region.
[0027]
Therefore, the breakover voltage of the thyristor according to the first embodiment of the present invention changes mainly depending on the arrangement of the second P-type conductive region and the distribution of conductivity, and the conductivity of the semiconductor substrate conductive region 1 is changed. It becomes almost unrelated to the rate. This means that the design for the breakover voltage and the design for reducing the capacitance can be performed independently.
[0028]
In the thyristor structure according to the prior art shown in FIG. 2, as described above, when a voltage is applied in the forward direction, the junction formed by the first N-type conductive region 2 and the semiconductor substrate conductive region 1 is reverse-biased. Since the capacitance has been determined, the breakover voltage increases when the resistivity of the semiconductor substrate conductive region 1 is increased to reduce the capacitance. However, in the present invention, since the maximum electric field region in the semiconductor substrate 100 is located away from the junction formed by the first N-type conductive region 2 and the semiconductor substrate conductive region 1, the resistivity of the semiconductor substrate conductive region 1 is increased. Even so, the breakover voltage can be kept equivalent to that of the thyristor according to the prior art.
[0029]
Therefore, in the thyristor according to the first embodiment of the present invention, the greater the resistivity of the semiconductor substrate conductive region 1, the easier the depletion layer expands in the electric field direction when a forward voltage is applied, As a result, the capacitance can be reduced. If the channel current becomes a problem as the resistivity of the semiconductor substrate conductive region 1 is increased, a separate channel is provided at the end of the semiconductor substrate 100 and in the vicinity thereof, as is often practiced in high voltage semiconductor devices. A stopper may be arranged.
[0030]
That is, according to the thyristor structure of the first embodiment of the present invention, the capacitance can be reduced without greatly changing the breakover voltage.
[0031]
A thyristor according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a cross-sectional view showing a thyristor according to the second embodiment of the present invention. In FIG. 4, 1 is a semiconductor substrate conductive region, 2 is a first N-type conductive region, 3 is a second N-type conductive region, 4 is a first P-type conductive region, 10 is a first electrode, 11 is a second electrode, and 21 and 22. , 23 and 24 are insulators, 30 is a second P-type conductive region, 40, 41 and 42 are first hole-shaped conductive regions, 90 is a boundary surface between the first N-type conductive region 2 and the semiconductor substrate conductive region 1, and 100 is a semiconductor. It is a substrate.
[0032]
As shown in FIG. 4, the thyristor according to the second embodiment of the present invention has a plurality of first hole-shaped conductive regions, and the basic operation is different from that of the thyristor according to the first embodiment. Absent. Here, the thickness of the insulator was set to about 0.6 μm as two layers of an oxide film and a nitride film. The electrode material has good adhesion to those insulating films.
[0033]
Therefore, in the structure according to the second embodiment of the present invention, the capacitance can be reduced without greatly changing the breakover voltage.
[0034]
In addition, a thyristor according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a sectional view showing a thyristor according to a third embodiment of the present invention. In FIG. 5, 1 is a semiconductor substrate conductive region, 2 is a first N-type conductive region, 3 is a second N-type conductive region, 4 is a first P-type conductive region, 10 is a first electrode, 11 is a second electrode, and 21 and 22. 23, 24 are insulators, 30 is a second P-type conductive region, 40, 41, 42 are first hole-shaped conductive regions, 50, 51, 52 are second hole-shaped conductive regions, and 90 is a first N-type conductive region 2. , 100 is a semiconductor substrate.
[0035]
The thyristor according to the third embodiment of the present invention is a so-called reverse conducting thyristor whose reverse characteristic is the forward direction of the diode. The number of the second hole-shaped conductive regions 50, 51, 52 is not limited to three, and may be one or more. Further, the number may be the same as or different from the number of the first hole-shaped conductive regions. The position at which the breakover voltage is determined when the forward voltage is applied is the same as that of the thyristor according to the first and second embodiments of the present invention, and the capacitance is changed without greatly changing the breakover voltage. It can be made smaller.
[0036]
【The invention's effect】
Thus, according to the present invention, unlike the thyristor according to the conventional structure, the maximum electric field region is in or near the fifth conductive region, and the resistivity of the semiconductor substrate can be determined regardless of the breakover voltage. I can do it. Accordingly, the resistivity of the semiconductor substrate can be increased to expand the depletion layer in the direction of the electric field, and the capacitance can be reduced. Therefore, it becomes easier to realize a thyristor having a smaller electrostatic capacity at the same breakover voltage than the thyristor according to the prior art.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a thyristor according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a thyristor according to the prior art.
3 is a graph showing electrical characteristics in the forward direction of the thyristor shown in FIG. 2;
FIG. 4 is a cross-sectional view showing a thyristor according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a thyristor according to a third embodiment of the present invention.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate conductive region 2 1st N type conductive region 3 2nd N type conductive region 4 1st P type conductive region 10 1st electrode 11 2nd electrode 21 Insulator 22 Insulator 23 Insulator 24 Insulator 30 2nd P type conductive region 40 First hole conductive region 41 First hole conductive region 42 First hole conductive region 50 Second hole conductive region 51 Second hole conductive region 52 Second hole conductive region 90 First N-type conductive region 2 and semiconductor Boundary surface 100 of substrate conductive region 1 Semiconductor substrate

Claims (4)

A first conductive region of a second conductivity type opposite to the semiconductor substrate formed by being exposed on one surface of the first conductivity type semiconductor substrate;
A second conductive region of a first conductivity type that is exposed on the one surface and formed in the first conductive region;
A third conductive region of the second conductivity type formed by being exposed on the other surface of the semiconductor substrate facing away from the one surface;
A fourth conductive region of a second conductivity type formed to be exposed on the one surface and penetrate the second conductive region;
A fifth conductive region of a first conductivity type that is exposed on the one surface and formed in the vicinity of an edge of the first conductive region;
In a thyristor comprising an electrode formed so as to be in contact with both the second conductive region and the fourth conductive region,
The thyristor, wherein the fifth conductive region partially overlaps with or is in the vicinity of the electrode when the semiconductor substrate is viewed in plan. The thyristor according to claim 1, wherein a plurality of the fourth conductive regions are formed. 3. The thyristor according to claim 1, wherein a sixth conductive region of the first conductivity type is formed so as to be exposed on the other surface and to penetrate the third conductive region. . The thyristor according to claim 3, wherein a plurality of the sixth conductive regions are formed.

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