JPH0478186B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a surge absorption element for protecting an electric circuit system from abnormal voltages caused by various surge factors such as lightning and switching surges. This invention relates to a surge absorbing element using.

<Prior art> A surge absorbing element is a surge absorbing element that, when a high voltage higher than a specified voltage value called "breakdown voltage" is applied, it absorbs electricity by forming an equivalent low-impedance current line within itself in the subsequent process. , which absorbs the large current associated with the high voltage and clamps the voltage across the element below a certain voltage value to prevent the abnormal voltage from affecting the electrical circuit system to be protected. The operating mechanism of most of the devices used for this purpose was based on the avalanche yield principle.

That is, the avalanche breakdown voltage when a reverse bias is applied to a diode structure using a pn junction or a diode connection structure of a transistor is used to define the breakdown voltage as a surge absorbing element.

<Problems to be Solved by the Invention> As mentioned above, in the conventional surge absorbing element based on the avalanche breakdown principle, the avalanche breakdown voltage itself is the "breakdown voltage" used to describe the characteristics of the surge absorbing element. ” will be directly defined.

However, on the other hand, the avalanche breakdown voltage in such conventional elements depends on the impurity concentration of one of the semiconductor regions forming the high resistivity side of the two regions forming the pn junction, and therefore generally of the semiconductor substrate.
It is almost uniquely defined.

Therefore, in such conventional avalanche breakdown type surge absorbing elements, as long as semiconductor substrates with the same impurity concentration are used, it is impossible or extremely difficult to change the breakdown voltage arbitrarily, and it is difficult to obtain products with different breakdown voltages. Therefore, semiconductor substrates with different impurity concentrations must be used accordingly.

Not only is this extremely irrational in itself, but changing the breakdown voltage also changes other electrical characteristics other than the breakdown voltage, such as junction capacitance and series resistance. In other words, junction capacitance, series resistance, etc. cannot be designed independently of breakdown voltage.

Conversely, in these conventional devices, the impurity concentration of different lots varies from the beginning, even if it is within the allowable tolerance range for each lot. In the case where the board has been supplied, and even if it was known in advance, there is no way to easily correct it, and the result is a surge absorption problem after the product is completed. This is honestly reflected as variations or variations between lots in the breakdown voltage of the device.

Furthermore, in this type of conventional avalanche breakdown type surge absorbing element, there are often limitations in the actual physical structure.

This is because, in this type of surge absorbing element, when the second semiconductor region is formed buried by impurity diffusion into the first semiconductor region, avalanche breakdown is generally likely to occur from the electric field concentration portions at both ends of the junction.
If this were to happen, it would be extremely difficult to flow current uniformly over the entire area of the junction when clamping the input voltage after breakdown.

In addition to these drawbacks, the conventional device described above also has the drawback that the voltage across the device (clamp voltage) does not become very low when the input voltage is clamped after breakdown. In the case of avalanche yield type, rather,
The clamp voltage becomes higher than the breakdown voltage at which avalanche breakdown begins.

Therefore, after breakdown, the power consumed within the device is the product of this clamp voltage and the absorption current, which is quite high in absolute value, resulting in a large amount of heat generation in the device. This, in turn, means that, from a heat capacity standpoint, there are significant limitations on the absorption current that can be tolerated by the device.

This last drawback can be solved by reducing the clamping voltage during surge absorption to a sufficiently low voltage compared to the breakdown voltage, but this type of surge absorption element is Since the clamp voltage of the element used is low enough and is inserted in parallel with the load, if it is lower than the power supply voltage of the power supply section, it will be turned on once due to a surge, even if Even if the cause of the surge disappears, this element remains turned on, and the power supply energy continues to be wasted. This phenomenon is especially called the "follow-on effect."

Therefore, this type of surge absorbing element
Holding current to maintain the on state (1
If h can be set higher than the current value supplied from a device such as a power supply, the element will automatically reset without causing a follow-on phenomenon after the surge factor disappears.

The present invention has been made in view of the conventional circumstances and various shortcomings as described above, and it is possible to improve designability to a considerable extent regardless of the impurity concentration, resistivity, or thickness of the semiconductor substrate used. It is a configuration in which an arbitrary breakdown voltage can be obtained, and therefore other electrical characteristics such as junction capacitance and series resistance can be designed independently regardless of the breakdown voltage, and furthermore, the holding current can be controlled. By disclosing
In short, the purpose is to provide a surge absorbing element that can absorb large currents while effectively suppressing follow-current phenomena by setting a holding current value higher than the normal current value supplied from a power source, etc. be.

<Means for solving the problems> In order to achieve the above object, in the present invention,
In place of the conventional avalanche breakdown type, a punch-through phenomenon is introduced as a new operating principle, and a punch-through type surge absorption element having the following configuration is provided.

1 a first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; a first semiconductor region formed on one surface side of the first semiconductor region; a second semiconductor region having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; contacting the second semiconductor region from the side opposite to the first semiconductor region; a third region that defines an effective thickness of the second semiconductor region by defining a separation distance between the second semiconductor region and the first semiconductor region; a fourth region formed laterally apart from the region and forming an injection junction with the first semiconductor region; the second semiconductor region and the fourth region on the one surface side of the first semiconductor region; and at least a portion of at least a portion from below the second semiconductor region to below the fourth region on the back side opposite to the one surface of the first semiconductor region. a recombination region; and when a depletion layer generated by reverse bias to the pn junction diode reaches the third region, a surge current is generated due to punch-through between the first semiconductor region and the third region. A surge absorption element characterized by: controlling a holding current in the recombination region while absorbing the surge absorption current.

2 a first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; a first semiconductor region formed on one surface side of the first semiconductor region; a second semiconductor region having a conductivity type opposite to the conductivity type and forming a first pn junction diode with the first semiconductor region; and the second semiconductor region from the opposite side from the first semiconductor region. a third region that defines the effective thickness of the second semiconductor region by contacting with the first semiconductor region; The first pn is formed horizontally apart from the second semiconductor region, is of a conductivity type opposite to the first conductivity type, and has a conductivity type opposite to the first semiconductor region.
a fourth semiconductor region forming a second pn junction diode in a direction opposite to that of the junction diode; contacting the fourth semiconductor region from the side opposite to the first semiconductor region; a fifth region defining an effective thickness of the fourth semiconductor region by a distance between the second semiconductor region and the fourth semiconductor region on the one surface side of the first semiconductor region; a carrier provided on one or both of a portion between the two semiconductor regions, and at least a portion of at least a portion from below the second semiconductor region to below the fourth semiconductor region on the back side opposite to the one surface of the first semiconductor region; a recombination region; when a depletion layer generated by reverse biasing one of the first and second two pn junction diodes reaches either the corresponding third region or fifth region; controlling a holding current in the recombination region while absorbing a surge current by punch-through generated between the first semiconductor region and the third region or the first semiconductor region and the fifth region; surge absorption element.

(Function) In the surge absorption element of the first invention, when a reverse bias is applied to the pn junction diode constituted by the first semiconductor region and the second semiconductor region, a depletion layer is generated at the junction. extends toward the first semiconductor region and at the same time extends toward the third region.

When this depletion layer continues to grow in accordance with the magnitude of the applied voltage and eventually reaches the third region, punch-through occurs between the first semiconductor region and the third region, and a surge occurs through this current path. Current begins to be absorbed. This punch-through operation starting voltage is shown as the breakdown voltage in FIG.

However, since this absorbed current flows along a path from the fourth region to the first semiconductor region, as mentioned in the abstract, the fourth region can inject minority carriers into the first semiconductor region. As long as it is made of a material that forms a junction (for example, a semiconductor or silicide of a conductivity type opposite to that of the first semiconductor region, or even a metal capable of injecting electrons if the first semiconductor region is p-type). , minority carriers are injected from the fourth region into the first semiconductor region, so even if the second semiconductor region and the third region are electrically short-circuited via the external terminal,
As a result of the minority carriers flowing into the second semiconductor region, a voltage drop occurs in the second semiconductor region,
Carrier injection occurs from the third region to the second semiconductor region.

While this carrier injection process is repeated, when a current larger than the value shown as the breakover current in FIG. 2 flows, the voltage across the device increases through the positive feedback phenomenon. In other words, the clamp voltage becomes an extremely low voltage. Therefore, the surge absorbing element of the present invention can absorb large currents while suppressing heat generation of the element.

Note that a voltage exhibiting a breakover current can be called a breakover voltage, and this breakover voltage is generally higher than the breakdown voltage as shown in FIG. 2.

Therefore, if we follow the voltage history across the device from its initial operation to voltage clamping, we can see that with the application of a surge, if it is above the breakdown voltage, punch-through operation will begin, and the absorbed current will break over. The voltage across the device increases somewhat until the current reaches the current, but once the breakover current is exceeded, the breakover voltage shifts to an extremely low clamp voltage.

The value of the breakover current is determined by the resistance of the second semiconductor region, the shape of the third region with respect to the first semiconductor region, the shape of the fourth region with respect to the first semiconductor region, and further, as described below. When the first semiconductor region is directly connected to an external terminal, it can be determined depending on the resistance of the first semiconductor region and the shape of the vicinity of the fourth region.

On the other hand, considering the breakdown voltage that starts the punch-through operation, in the surge absorbing element of the present invention, to what extent should the height position of the third semiconductor region that is in contact with the second semiconductor region on the opposite side with respect to the first semiconductor region be determined? In other words, depending on how much the effective thickness of the intermediate second semiconductor region is set, the punch-through voltage between the first and third regions, that is, the breakdown voltage can be arbitrarily changed and controlled. Become something.

For example, if the effective thickness of the intermediate second semiconductor region is set thick, a larger reverse bias will be required for the generated depletion layer to extend to the third region, assuming other conditions are the same. This ultimately increases the breakdown voltage at which the device breaks down, and conversely, if the effective thickness of the intermediate second semiconductor region is set thin, the generated depletion layer can easily become the third semiconductor region even at a relatively low applied voltage. This means that the breakdown voltage has been set low.

Of course, such breakdown voltage can also be controlled by the impurity concentration of the intermediate second semiconductor region, but
In any case, in view of the above, in accordance with the present invention, it is possible to use an appropriate commercially available semiconductor substrate wafer as the first semiconductor region as it is, or to use the same type of semiconductor substrate as the starting material. It can be seen that a surge absorbing element with a desired breakdown voltage can be obtained.

Furthermore, by appropriately controlling the effective thickness of the second semiconductor region and its impurity concentration, it becomes possible to design the junction capacitance and series resistance independently for any breakdown voltage.

Furthermore, with respect to the semiconductor substrate itself or a first semiconductor region formed separately on the semiconductor substrate,
The method of sequentially forming the second semiconductor region and the third region may be based on existing epitaxial growth technology, ion implantation, selective diffusion, etc. Since the effective thickness and impurity concentration of the second semiconductor region can be extremely well controlled even with current technology, the surge absorbing element produced by the present invention will ultimately have extremely high precision. It can be done.

On the other hand, from a structural point of view, the effective thickness of the second semiconductor region can be set thin regardless of the thickness of the first region. No pre-processing,
It is also possible to use the device in its thick form as is (which is also more common), so it does not require an increase in the number of steps and does not cause a decrease in physical strength. It is also possible to form a plurality of them, which has the effect of facilitating integration.

In addition, in the structure of the present invention, a part of the first semiconductor region between the second semiconductor region and the fourth region on one surface side of the first semiconductor region, and a part of the first semiconductor region that is opposite to the one surface of the first semiconductor region Since a carrier recombination region is provided in one or both of at least a portion (the entire portion if necessary) from below the second semiconductor region to below the fourth region on the back side, the reference numeral in FIG. The value of the holding current, denoted h, can also be controlled.

That is, while the current injected from the fourth region is small, the minority carriers that try to pass through or near the area where these carrier recombination regions are provided are recombined with the majority carriers in the carrier recombination region. However, as the current increases, the recombination speed cannot keep up with the supply speed of minority carriers, and minority carriers begin to pass through the recombination region or its vicinity, and as a result, the device eventually turns on. Since this mechanism occurs, in some cases, more current must flow than in the case where there is no carrier recombination region, and the holding current can be controlled.

In practice, such carrier recombination regions are formed as regions with many crystal defects by abrading, etc., by shot bonding, or by thermal diffusion of heavy metals such as iron or gold. However, the value of the holding current controlled by this will depend on the area and depth of the carrier recombination region to be formed, and if the recombination region is formed using crystal defects or heavy metals, the value of the holding current will depend on the recombination region. Depending on factors such as the concentration of bonding centers, a desired value can be determined with a considerable degree of design freedom.

In this way, the ability to control the holding current h means that there is no surge factor and the holding current value can be set lower than the minimum current value supplied from other devices under normal operating conditions. This means that the following current phenomenon described above can be effectively prevented, and after the surge factor disappears,
It also becomes possible to automatically reset the device.

Further, as is clear from the above principle, the second semiconductor region and the third region may be placed at the same potential at the external terminal, and therefore, the external terminal may be drawn out from the same drawing terminal. However, on the contrary, it may be possible to draw out signals independently from each dedicated terminal and apply an appropriate bias between these two terminals.In this way, even after the device is completed or when the device is in actual operation, By changing and adjusting the bias voltage, the punch-through voltage, that is, the breakdown voltage as a surge absorbing element can be made variable.

Note that, as is clear from the above, the breakover voltage naturally changes as the breakdown voltage changes.

In contrast to the first invention, the second invention is capable of absorbing bipolar surge currents.

That is, if the fourth region is limited to semiconductors and is considered to be a region equivalent to the second semiconductor region in the first invention, and similarly the fifth region is considered to be a region equivalent to the third region in the first invention, then As described above, the punch-through phenomenon that may occur in the first pn junction diode of the second invention, which corresponds to the pn junction diode of the first invention, constituted by the first semiconductor region and the second semiconductor region is due to the reverse polarity. A similar phenomenon occurs as a result of reverse biasing of the second pn junction diode constituted by the first semiconductor region and the fourth semiconductor region with respect to the surge current.

In other words, when punch-through occurs in the second pn junction diode between the first semiconductor region and the fourth semiconductor region, the second semiconductor region is not a semiconductor in the description of the first invention. It performs the function of the fourth area when configured.

For this reason, the explanations regarding the second semiconductor region can be applied to the fourth semiconductor region, and the explanations regarding the third region can be applied as is to the fifth region, and the same applies to other considerations. Become.

Therefore, if the clamp voltage is low enough,
The advantages that the surge absorbing element of the first invention had, such as good ability to arbitrarily design breakdown voltage and holding current, can be exhibited in the surge absorbing element of the second invention in exactly the same way.

In addition, in this second invention, the carrier recombination region for setting and controlling the holding current value is determined depending on the physical or geometrical arrangement relationship, such as whether it is close to the second semiconductor region or the fourth semiconductor region. , it is also possible to intentionally make the holding current value different for each polarity.

(Examples) Some of the illustrated embodiments of the present invention will be described in detail below. Of course, there are individual embodiments for the first invention and the second invention, but as already mentioned, the two are extremely closely related and can be referred to from each other.

The surge absorbing element 10 shown in FIG. 1 is one of the basic embodiments according to the first invention, and uses the semiconductor substrate as it is as the first semiconductor region 1 of the first conductivity type, and uses the semiconductor substrate as it is as the first semiconductor region 1 of the first conductivity type. , a second semiconductor region 2 and a third region 3 are sequentially formed on one surface by double diffusion technology, while a fourth region 4 is formed laterally apart from the second semiconductor region 2. be.

Hereinafter, for convenience, the side where these regions 2, 3, and 4 are located will be referred to as the front surface of the semiconductor substrate 1, and the surface opposite thereto will be referred to as the back surface.

In the relationship between the regions as described above, in this embodiment, the first semiconductor region 1 is an n-type semiconductor, so
The second semiconductor region 2 is made p-type and the fourth region 4 is also made a p-type semiconductor region by a diffusion technique of an appropriate impurity such as boron.

On the other hand, since the third region 3 forms one end of the main current line when punch-through occurs, it is preferable that the third region 3 has high conductivity. It is formed as ^{a +} type region by double diffusion of impurities into the second semiconductor region 2. In practice, this can be obtained by high concentration phosphorous diffusion or the like.

Furthermore, as shown by the solid line in the figure, the carrier recombination region 1R is at least a portion from below the second semiconductor region 2 to below the fourth semiconductor region 4 (in the case shown) on the back side of the semiconductor substrate 1. is formed in a portion extending over a portion of each of the lower regions 2 and 4), or in the case of a second semiconductor region on the front surface side of the semiconductor substrate 1, as shown by the imaginary line in the figure. 2 and the fourth semiconductor region 4.

However, in some cases, this carrier recombination region 1R may be provided on both the front and back surfaces of the substrate, and especially when provided on the back surface of the substrate, it may be provided on the entire surface of the substrate for convenience of manufacturing. .

Further, this carrier recombination region 1R can be obtained as a region in which crystal defects are intentionally increased by abrading or the like, or as a region in which a shot junction is formed. It can be obtained as a region selectively diffused into one semiconductor region 1.

In such a configuration, the second, third, and fourth regions 2, 3, and 4 are eventually attached with respective lead-out terminals to complete the device.
The lead-out terminal 2t of the second semiconductor region 2 and the lead-out terminal 3t of the third region 3 are line lines indicated by imaginary lines in the figure.
As shown by Ls, it may be short-circuited at the manufacturing stage, or it may be pulled out separately and short-circuited by the user, or an appropriate bias source may be inserted as described later.

In the case of short-circuiting, the line Ls should actually be formed of a metal layer or the like that is deposited in series on the exposed surface of the second semiconductor region 2 and the exposed surface of the third region 3 and is in contact with the ohmic. I can do it.

First, explanation will be given assuming that both terminals 2t and 3t are thus short-circuited by the line Ls, and a surge voltage is applied between them and the lead terminal 4t of the fourth semiconductor region 4.

In such a surge absorbing element 10, as already explained in the operation section, when a reverse bias is applied to the pn junction between the first semiconductor region 1 and the second semiconductor region 2, the depletion caused by the reverse bias is applied. The layer is applied not only to the side of the first semiconductor region 1 but also to the third region 3.
It also grows towards the side.

Therefore, if a surge voltage is applied between the terminals 2t, 3t and the terminal 4t and is considerably large in the phase of applying reverse bias to the pn junction, the upper end of the depletion layer It is possible that three regions are reached.

This state is the start of a punch-through state between the first semiconductor region 1 and the third region 3, and is the start of a low impedance state in which a large current can flow or a breakdown state as the present surge absorbing element. This starting point is shown in FIG. 2 as the breakdown voltage on the voltage axis.

When such a breakdown start state is realized, the terminal 2
A surge current begins to flow between t, 3t and terminal 4t,
Holes are injected into the first semiconductor region 1 from the fourth semiconductor region 4, collected in the second semiconductor region 2, and become an external current (device current) via the external terminal 2t.

Therefore, the product of the resistance of the second semiconductor region 2 sandwiched between the third region 3 and the first semiconductor region 1 and the above current is the forward voltage of the pn junction diode composed of regions 2 and 3. When they become equal, electrons are injected from the third region 3 into the second semiconductor region 2, which causes an increase in current, and holes are again injected from the fourth semiconductor region 4, a positive feedback phenomenon. occurs.

The current value at which such a positive feedback phenomenon begins to occur is the breakover current mentioned above, and the voltage across the element at this time (external terminals 4t, 3
t voltage) becomes the breakover voltage.

As mentioned above, this breakover voltage is somewhat larger than the breakdown voltage, but
Once positive feedback begins to occur, the voltage across the device transitions to a significantly lower value. This value is shown as the clamp voltage in Figure 2, but it is approximately equal to the product of the absorbed current and the series resistance of each part plus one forward voltage of the p-n junction. It's equal.

As understood from this mechanism,
The surge absorbing element 10 of the present invention maintains a high breakdown voltage when no surge is applied, suppresses the current flowing within the element to the minimum limit, and prevents unnecessary power consumption by the element. Once a surge is applied above the breakdown voltage, it will soon exhibit an extremely low clamping voltage, absorbing a large current and reliably protecting the subsequent circuit system.

The breakdown voltage in the present surge absorbing element 10 is determined not only by the resistivity or impurity concentration of the first semiconductor region 1 but also by the distance between the first semiconductor region 1 and the third region 3 in the second semiconductor region. Since the punch-through voltage can be controlled depending on the effective thickness Dt of 2 and/or the impurity concentration, it can be arbitrarily set within a fairly wide design range. In fact, according to experiments conducted by the present applicant, it has been confirmed that this design width covers an extremely wide range from several volts to several hundred volts.

In the case of the embodiment shown in FIG. 1, as described above, the second semiconductor region 2 and the third region 3 are formed on the semiconductor substrate 1 by the double diffusion technique. In this case, the second semiconductor region 2
After the formation of the second semiconductor region 2, the effective thickness Dt of
Diffusion depth of impurities for forming the third region from the surface
By controlling Dd, it can be directly controlled. That is, in the case of the double diffusion technique, changing or changing the height position of the third region 3 with respect to the first semiconductor region directly changes the effective thickness Dt of the second semiconductor region 2.

On the other hand, when the second semiconductor region 2 and the third region 3 are formed by epitaxial growth technology,
The effective thickness Dt of the second semiconductor region 2 is generally defined by the growth film thickness itself, which is determined based on the various conditions in the epitaxy.
Even in that case, the existence of the third region 3 still actually defines the effective thickness Dt regarding punch-through.

Whether by diffusion technology or epitaxy, the effective thickness Dt of the second semiconductor region 2 can be controlled by
Since it is possible to control with extremely high accuracy even with existing techniques, the surge absorbing element according to the present invention can ultimately set its breakdown voltage with extremely high accuracy.

Similarly, the impurity concentration in the second semiconductor region 2, which is another factor that determines the punch-through voltage and, ultimately, the breakdown voltage of this device, can also be adjusted and controlled with extremely high precision using existing technology. can.

In other words, in the case of the device of the present invention, when designing the breakdown voltage, the second semiconductor region 2
This means that it has two variables, the effective thickness Dt and the impurity concentration, which each have good design properties and are independent of each other.

Therefore, if you use only one of these variables,
By using both and arranging them appropriately,
It can be seen that not only can the breakdown voltage be set over a very wide range, but also that other electrical properties such as junction capacitance and series resistance can be designed independently of the breakdown voltage.

Of course, the fourth semiconductor region 4 can also be formed with good controllability using conventional techniques such as impurity diffusion and epitaxy.
As already mentioned, in the case of the first invention, it is sufficient that the fourth region 4 is formed of a material that forms an injection junction capable of injecting minority carriers into the first semiconductor region 1. It is not limited to being a semiconductor of the opposite conductivity type to the first semiconductor region 1 as in the embodiment, but it may be made of silicide, or if the first semiconductor region 1 is p-type, it may be a semiconductor that can be injected with electrons. It may also be made of metal.

In addition to these, the carrier recombination region 1R provided in the present invention can control the holding current h shown in FIG. 2 for the following reasons.

As also shown in FIG. 1, the minority carriers injected from the fourth semiconductor region 4 according to the above-described operation move into the semiconductor substrate as indicated by arrows f1, f2a, and f2b, respectively. It is possible to take various routes, among which arrow f1
The few carriers who moved in accordance with the
The minority carriers that reach the semiconductor region 2 but move along the arrow f2a are captured by the majority carriers there and disappear if the above-mentioned carrier recombination region 1R is provided on the front surface side of the semiconductor substrate 1. Resulting in.

Similarly, if the carrier recombination region 1R is provided on the back side of the semiconductor substrate 1, the minority carriers moving along the arrow f2b are also captured by the majority carriers and disappear there.

However, when the amount of minority carriers supplied to these carrier recombination regions increases, the force of the supply speed becomes higher than the recombination speed, and the carriers pass through the carrier recombination region and its vicinity directly and are transferred to the second semiconductor. A carrier begins to develop into region 2, thus eventually turning the device on.

Therefore, in other words, the holding current value h shows a higher value when there is a carrier recombination region 1R as in this embodiment than when there is no carrier recombination region 1R.

The value of this holding current value h can be controlled by the area, depth, etc. of the carrier recombination region 1R, and especially when the carrier recombination region 1R is formed by crystal defects or thermal diffusion of heavy metals, It can also be controlled by the concentration of recombination centers.

By the way, as is clear from the explanation through the first embodiment above, in the surge absorbing element of the present invention, in principle, the current of the surge current after punch-through occurs between the first and third regions. The distribution will be relatively uniform. However, if further uniformity is to be ensured, a configuration as shown in FIG. 3 may be adopted.

That is, in the second embodiment shown in the third figure, a plurality of third regions 3 are formed for the second semiconductor region 2 of the opposite conductivity type formed on the surface of the semiconductor substrate or the first semiconductor region 1. Divided third area elements 31, 32, 33, ..., 3n (n in the case shown)
=5), each area element 31
~3n are designed to be electrically connected to the outside from a common lead terminal 3t.

With such a structure, the electric field concentration effect seen in conventional avalanche breakdown devices can be avoided, and a uniform current distribution can be obtained. Therefore, the current capacity can also be increased approximately in proportion to the element area.

The other considerations described in the first embodiment can be similarly adopted in the third embodiment. The carrier recombination region 1R is naturally provided on both or one of the front and back surfaces of the substrate, and exhibits exactly the same effect as described above. Regarding these points, the same applies to other embodiments related to the second invention below. In addition, the two terminals 2t, 3
t can not only be short-circuited due to the operating principle as described above, but also has the effect of avoiding transient phenomena when used in a short-circuited manner.

In the surge absorbing element configured as in the present invention, the breakdown voltage that should be originally determined by the punch-through phenomenon is different between the first semiconductor region 1 and the second semiconductor region 2.
As the avalanche breakdown voltage approaches the avalanche breakdown voltage, controllability may deteriorate.

When there is such a risk, in order to prevent or suppress the avalanche breakdown that begins to occur at the junction of the end portions of the second semiconductor region 2 at an early stage, as shown in FIG. 4 as an embodiment of the second invention to be described later. Then, a guard ring region 2G of the same conductivity type as the second semiconductor region is formed so as to surround the second semiconductor region 2, or a guard ring region 2G of the same conductivity type as the second semiconductor region is formed, or similarly as shown in FIG. In order to It is preferable to extend it further beyond the junction with the semiconductor region.

In this way, the concentration of the electric field at the edge of the second semiconductor region is alleviated and the avalanche breakdown voltage is effectively increased, thereby reducing the breakdown voltage that can only be achieved by punch-through, in accordance with the idea of the present invention. Designability can be expanded and improved.

Next, an embodiment of the second invention shown in FIGS. 4 and 5 will be described.

Also in the embodiment shown in FIGS. 4 and 5,
First semiconductor region 1, second semiconductor region 2, third region 3, third region elements 31, 32, 33, ..., 3n
The same configuration, shape, and arrangement relationship as in the embodiment according to the first invention shown in FIGS. 1 and 3 can be applied. Rather, in this embodiment of the second invention, in addition to the configuration of the surge absorption element shown in FIG. 3, third region elements 31, 32, 33, . . . are provided in the fourth semiconductor region 4. ,3n
Fifth region elements 51, 52, 5 substantially similar to
It can be considered that 3,...,5n are added.

Therefore, in the surge absorbing elements shown in FIGS. 4 and 5, the diode that causes punch-through is connected to the first semiconductor region 1 and the second semiconductor region depending on the polarity of the surge voltage applied between the terminals 3t and 5t. It may be a first diode composed of the semiconductor region 2, or a second diode composed of the first semiconductor region 1 and the fourth semiconductor region 4,
Regardless of which of the diodes the punch-through phenomenon occurs in, the operating mechanism has already been established in the first semiconductor region 1 and the second semiconductor region 2 of the first invention.
This is exactly the same as explained regarding the diode composed of.

In other words, the surge absorbing element as an embodiment according to the second invention can exhibit an absorbing function for bipolar surge voltages or surge currents. Of course, the ability to determine the breakdown voltage and holding current value h with good design efficiency with respect to surge voltage is exactly the same as in the surge absorbing element described in connection with the first invention.

Therefore, the carrier recombination region 1R is
The same function as in the first embodiment is shown for bipolar surges, but the arrangement position is the second semiconductor region 2.
It is also possible to intentionally make the holding current value h for each polarity different depending on whether it is close to the fourth semiconductor region 4 or the fourth semiconductor region 4 .

The difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. The only difference is in the means used to prevent or suppress it at different stages.

In other words, in the embodiment shown in FIG. 4, as mentioned briefly above, the second semiconductor region 2 and the fourth semiconductor region 4 are surrounded by the same conductivity type as the second and fourth semiconductor regions. Guard ring regions 2G and 4G are formed, and in the embodiment shown in the fifth figure, the surfaces of the second semiconductor region 2 and the third semiconductor region 3, and the surfaces of the fourth semiconductor region 4 and the fifth region 5 are formed. The end edges 6a, 7a of the ohmic electrodes 6, 7 formed in series on the surface are further extended beyond the joining end with the first semiconductor region 1 via the insulating film 8. .

Of course, in the embodiments shown in the fourth and fifth figures, the third and fifth regions 3 and 5 are each composed of a plurality of region element groups 31 to 3n and 51 to 5n for the regions, but Most basically, these third area 3 and fifth area 5 are each formed as a single undivided area, as represented by the third area 3 shown in FIG. 1 of the first invention. You can leave it there.

In the case of the surge absorbing element of the present invention as shown in each of the embodiments described above, in principle, additional treatments such as end face polishing, which are required in conventional avalanche yielding type devices, are not required after the device is completed. Therefore, a plurality of the configurations of each of the above-mentioned embodiments can be simultaneously manufactured in one semiconductor substrate 1.

However, when there is no need to integrate a large number of semiconductors, as another means for increasing the avalanche breakdown voltage mentioned above, as shown in FIG. The portion corresponding to the joint end may be etched or cut with a slope perpendicular to the surface or at an angle.
The fact that even the side surfaces of the fourth region 4 are treated in the same way can be seen as simply a result of the above-mentioned processing, but on the contrary, the same p-type layer is automatically etched by the above-mentioned etching process. It is also shown that the second and fourth regions can be formed separately.

Further, although the case shown in FIG. 6 concerns the surge absorbing element corresponding to the first invention of the present invention, the same idea can be applied to the surge absorbing element corresponding to the second invention. However, when such a simple method is used, a suitable protective film (not shown) is usually required on the cut-off surface.

Next, a somewhat special usage of the surge absorbing element of the present invention will be explained by referring to the first illustrated embodiment of the first invention. If they are pulled out individually, as shown in Figure 7A,
Appropriate bias source Vb between these terminals 2t and 3t
By inserting , it is also possible to control the punch-through voltage from the outside.

As a model of surge voltage, terminal 3 for the third region
t and the terminal 4t of the fourth semiconductor region 4. As shown in FIG. When the high voltage Vr corresponding to the surge voltage is applied, the state changes from the state shown by the solid line when the voltage is not applied to the state shown by the imaginary line in the figure. However, in the illustrated case, in order to observe the bias effect as described below, the high voltage source potential corresponding to the surge voltage is shown in a state that has not yet reached the level of causing punch-through.

In this state, depending on the polarity and magnitude of the bias potential supplied from the bias source Vb,
Regarding the second region 2 and the third region 3, the band structure changes as shown by the arrow "" in the case of reverse bias and as shown by the arrow "ⓓ" in the case of forward bias. Therefore, it can be seen that the punch-through voltage of the surge absorbing element can be controlled externally by the bias potential and its polarity.

Of course, such a bias configuration can be applied to both the diodes on the second semiconductor region side and the fourth semiconductor region side in common or independently in the surge absorbing element of the second invention shown in FIGS. 4 and 5. can.

Finally, as an example, the effects of the present invention will be confirmed by comparing actual devices.

First, a surge absorbing element conforming to the configuration of the second invention was created through the steps described below.

Resistivity 5Ω-cm, conductivity type n-type, 111 planes,
A 300 μm thick silicon wafer is placed in the first semiconductor region 1.
The starting material is first coated with 6000Å of SiO ₂ on its surface.
A film was formed.

Next, the second semiconductor region 2 and the fourth semiconductor region 4
In order to define the planar shape of the silicon oxide film, a photo-etching process is applied to the silicon oxide film on the surface according to a predetermined pattern to open impurity diffusion windows, and boron is diffused through each diffusion window to determine its depth. Then, p-type regions 2 and 4 having a thickness of 2.5 μm were formed.

In this pattern, the second and fourth regions 2 and 4, each having a width of 200 μm, are alternately repeated at intervals of 70 μm.

After newly forming a silicon oxide film on the wafer surface, in order to define the planar shapes of the plurality of third region elements 31 to 3n and fifth region elements 51 to 5n,
The silicon oxide film was photo-etched in accordance with a predetermined pattern to form impurity diffusion windows for a plurality of third region elements and fifth region elements.

Phosphorus is diffused at a high concentration from this diffusion window, and the fifth region element 5 has a depth of 1.2 μm, similar to the third region 3 consisting of a set of n ⁺ type third region elements 31 to 3n.
A fifth region 5 consisting of a set of 1 to 5n was formed.
Therefore, at the same time, the finally completed second semiconductor region 2 and fourth semiconductor region 4 were formed and defined, and their effective thickness Dt was set to 1.3 μm.

After this, an inventive device A in which alumina powder was sprayed onto the backside of the wafer and ablated to form a carrier recombination region, and a comparative device B without ablation and therefore without a carrier recombination region were prepared.

Thereafter, in order to adopt an ohmic contact common to the second and third regions and a common ohmic contact to the fourth and fifth regions in both the device A of the present invention and the comparative device B, photo etching and metal thin film were applied. Through vapor deposition and etching steps, electrodes 6, 7 and terminals 2t, 3t; 4t, 5t were formed. Electrodes or terminals 1t on the semiconductor substrate side were also formed at the same time in the metal thin film deposition process.

Under such a configuration, as a third comparison surge absorbing element C in a different sense, a surge absorbing element C is used to absorb surges between the terminals 2t, 3t (or 4t, 5t) on the front side of the board and the terminal 1t on the back side of the board. When a model was constructed to absorb the surge, its breakdown voltage was 120V, and the surge absorption current was up to 300A/ ^cm2 .

On the other hand, surge absorbing element A according to the idea of the present invention
With the above configuration, the terminals 2t, 3t and 4t,
5t, which absorbs bipolar surges, the breakdown voltage was almost the same as 121V, but the breakover current density was 4A/ ^cm2 ,
The surge absorption current density was able to reach a maximum of 5000A/cm ² .

Looking at this characteristic example, the effect of the fourth semiconductor region on the set of second and third regions provided by the present invention and the effect of the second semiconductor region on the set of fourth and fifth regions are extremely large. It turns out that it is.

Also, under the same conditions as above, when forming the n ⁺ type third and fifth regions 3 and 5, which will substantially define the effective thickness of the second and fourth semiconductor regions 2 and 4, By changing the diffusion time of , the breakdown voltage could be varied from 30V to 170V.
Of course, this variation range is not the maximum variation range, and it has been confirmed that if other conditions are also taken into account, an extremely wide variation range from several volts to several hundred volts can be obtained.

Furthermore, when comparing device A having a carrier recombination region according to the present invention and device B not having a carrier recombination region with respect to the holding current h, in the device A according to the present invention,
While 0.3A was obtained, comparative element B
It was only getting 40mA. This clearly shows that the carrier recombination region incorporated according to the present invention greatly controls the holding current.

It was also verified that the breakdown mechanism in this device can be reliably controlled solely by the punch-through phenomenon, without relying on tunneling or avalanche breakdown.

Of course, from the characteristic example taken for the second invention, even in the surge absorbing element according to the first invention without the fifth semiconductor region in the fourth semiconductor region, the surge absorption polarity is unipolar. Just by becoming
It is almost self-evident that the characteristics tend to be similar in terms of holding current and the like.

In addition, if the breakover current is further increased and a "small surge" occurs, such as a simple transient noise with a large time differential value of voltage but an extremely short duration, this will occur below the DC breakdown voltage. In order to prevent the response from occurring, the contact area of the second semiconductor region and/or the fourth semiconductor region with the metal thin film must be increased, or in particular, in the case of the device according to the first invention, as shown in FIG. To,
The fourth semiconductor region 4 is formed by a plurality of region elements 41, 42,
. . , 4n, and the first semiconductor region portions 11, ₁₂ , . One semiconductor region portion 11,1
2, . . . , 1n _-1 are provided with common ohmic contact electrodes to form a terminal 1t, and a common line is similarly formed for the fourth semiconductor region element group 41, 42, . . . , 4n to form a terminal 4t. It's good to pull it out and use it.

In any case, the breakover current can also be arbitrarily designed within a considerable range.

<Effects of the Invention> According to the present invention, various superior effects can be obtained as compared to existing avalanche breakdown type elements, as listed below.

Semiconductor substrates or semiconductor wafers are the most expensive and least flexible components of this type of device, but according to the present invention, surges with different breakdown voltages can be removed even from a starting wafer with the same material constant. An absorption element can be obtained.

Since the set of the second semiconductor region and the third region and the set of the fourth semiconductor region and the fifth region can be formed only from the same side with respect to the first semiconductor region, the breakdown voltage can be changed and determined. Control to achieve a desired breakdown voltage is extremely simple and can be performed with high precision.

Other electrical properties, such as junction capacitance and series resistance, can be designed independently of the breakdown voltage, and therefore, for example, other electrical properties can be made substantially the same even at different breakdown voltages. .

It is also easy to integrate multiple elements within a common semiconductor substrate.

It has a design principle that reduces the terminal voltage (clamp voltage) even more than the breakdown voltage in the large current region, so it can absorb even extremely large surge currents and has an extremely high ability to protect the circuit system.

Even though the clamp voltage can be greatly reduced as described above, the holding current can be set to a large value due to the presence of the carrier recombination region, so the device is automatically reset after the surge disappears, reducing the follow-on effect. It can be avoided.

In addition to the above effects, if the second invention is used,
Can absorb surge currents of both polarities.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a first embodiment according to the first invention of the present invention, FIG. 2 is an operational characteristic diagram of the first illustrated embodiment, and FIG. 3 is a schematic configuration diagram of a second embodiment according to the first invention. , FIG. 4 and FIG. 5 are schematic configuration diagrams of each embodiment according to the second invention of the present invention, FIG. 6 is an explanatory diagram of an example for eliminating the influence of avalanche breakdown voltage in the surge absorbing element of the present invention, and FIG. The figure is an explanatory diagram of an example of a special usage of the surge absorbing element of the present invention, and FIG. 8 is a schematic configuration diagram of still another modified example of the surge absorbing element according to the first invention. In the figure, 1 is a first semiconductor region or a semiconductor substrate,
1R is a carrier recombination region, 2 is a second semiconductor region, 3 is a third region, 31 to 3n are third region elements,
4 is a fourth semiconductor region, 41 to 4n are fourth semiconductor region elements, 5 is a fifth region, 51 to 5n are fifth region elements, 2G and 4G are guard rings, and 10 is the surge absorbing element of the present invention as a whole. , is.

Claims (1)

[Claims] 1. A first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; on one surface side of the first semiconductor region; a second semiconductor region that is formed and has a conductivity type opposite to the first semiconductor region and forms a pn junction diode with the first semiconductor region; a third region that defines the effective thickness of the second semiconductor region by making contact with the first semiconductor region; and a third region that defines the effective thickness of the second semiconductor region by contacting the first semiconductor region; a fourth region formed laterally apart from the second semiconductor region and forming an injection junction with the first semiconductor region; a fourth region on the one surface side of the first semiconductor region; a portion between the semiconductor region and the fourth region; and at least a portion of the back surface of the first semiconductor region opposite to the one surface from below the second semiconductor region to below the fourth region, or a carrier recombination region provided on both; and a region between the first semiconductor region and the third region that is formed when a depletion layer generated by reverse bias to the pn junction diode reaches the third region; A surge absorption element characterized by: controlling a holding current in the recombination region while absorbing a surge current by punch-through. 2 a first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; a first semiconductor region formed on one surface side of the first semiconductor region; a second semiconductor region having a conductivity type opposite to the conductivity type and forming a first pn junction diode with the first semiconductor region; and the second semiconductor region from the opposite side from the first semiconductor region. a third region that defines an effective thickness of the second semiconductor region by contacting the first semiconductor region with a distance between the third region and the first semiconductor region; It is formed horizontally apart from the second semiconductor region, is of a conductivity type opposite to the first conductivity type, and has a direction opposite to the first pn junction diode between the first semiconductor region and the second semiconductor region. A fourth semiconductor region forming a second pn junction diode; and a fourth semiconductor region that contacts the fourth semiconductor region from the opposite side to the first semiconductor region to reduce the separation distance between the fourth semiconductor region and the first semiconductor region. a fifth region that defines the effective thickness of the fourth semiconductor region; a portion between the second semiconductor region and the fourth semiconductor region on the one surface side of the first semiconductor region; a carrier recombination region provided on one or both of at least a portion from below the second semiconductor region to below the fourth semiconductor region on the back surface side opposite to the one surface of the one semiconductor region; The first semiconductor region formed when the depletion layer generated by reverse biasing one of the first and second two pn junction diodes reaches either the corresponding third region or fifth region; A surge absorption element characterized by: controlling a holding current in the recombination region while absorbing the surge current by punch-through between the third region or the first semiconductor region and the fifth region.