JPS6265383A - Surge absorbing element - Google Patents

Abstract

PURPOSE:To make the control of breakdown voltage and clamp voltage considerably simple and highly accurate by absorbing a surge current by punch-through between a first semiconductor region and a third region and specifying a clamp voltage by a breakdown voltage of a rectifying junction between a fourth and a fifth regions. CONSTITUTION:When a reverse bias is applied to a p-n junction between a first semiconductor region 1 and a second semiconductor region 2, a produced depletion layer reaches a third region 3 and a punch-through state starts. When the product of an element current and a resistance of the second semiconductor region 3 sandwiched with the third region 3 and the first region 1 becomes equal to a forward voltage of the p-n junction diode composed of the regions 2 and 3, positive feedback phenomenon occurs. Accordingly, a clamp voltage as an element becomes the seem of a breakdown voltage in a rectifying junction of the fourth and fifth semiconductor regions 4 and 5 and a low voltage between the third and fourth regions and if an impurity concentration of the fourth semiconductor region 4 is properly determined, it can be determined arbitralily.

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, and in particular 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 absorption element that utilizes the phenomenon.

<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 pn junction diode structure or a transistor diode connection structure is used to define the breakdown voltage as a surge absorbing element.

<Problems to be solved by the invention> In the conventional surge absorption element based on the avalanche yield principle,
As mentioned above, the avalanche breakdown voltage itself directly defines the "breakdown voltage" used when evaluating the characteristics of a surge absorbing element.

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 circular region forming the pn junction, and thus generally of the semiconductor substrate. It becomes fixed.

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 in itself extremely unreasonable, but changing the breakdown voltage will also change the junction capacitance, direct resistance, etc.
Other electrical characteristics besides breakdown voltage will also change. In other words, junction capacitance, series resistance, etc. cannot be designed independently of breakdown voltage.

Conversely, in such conventional devices, even if each loft is within the allowable tolerance range, the impurity concentration varies from the beginning between different lofts. In the case where the board has been supplied, and even if this was known in advance, there is no easy way to correct this, and the result is that the surge absorbing element after it is completed as a product. It is honestly reflected as loft-to-loft variations or variations in breakdown voltage.

The same can be said of the clamp voltage that occurs when the device is turned on due to a surge exceeding the breakdown voltage or even a voltage called breakover voltage. Conventionally,
There was no way to freely design this clamp voltage.

Furthermore, in this type of conventional avalanche breakdown type surge absorption element,
This often creates constraints in the actual physical structure.

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

In addition to these drawbacks, the above-mentioned conventional device also has the drawback that the above-mentioned clamp voltage does not become very low in absolute value when the input voltage is clamped after breakdown. In the case of avalanche breakdown, the clamp voltage is rather 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, which is quite high in absolute value, and the absorbed current, resulting in a large amount of heat generation in the device. From this point of view, this means that this creates a significant limitation on the absorption current that can be tolerated by the device.

However, this does not necessarily mean that it is better to lower this clamp voltage as much as possible.

This is because this type of surge absorption element is inserted in parallel to the load between the power supply part of the circuit system to be protected and the load, so the clamp voltage of the element used is sufficiently low, If the voltage is lower than the power supply voltage of the device, since it has been turned on six times due to a surge, even if the surge factor disappears afterwards, this device will maintain the turned-on state, wasting power energy. This is because it continues to be consumed (this is called the follow-on phenomenon).

Therefore, although it is a matter of balance with the aforementioned design, it is most desirable to set the clamp voltage to a value as close as possible to the power supply voltage of the circuit system to which it is applied, although it is higher than that. This is because while heat generation can be suppressed to the minimum limit, once the surge factor disappears, it will automatically reset without causing a follow-on phenomenon.

The present invention has been made in view of the above-mentioned conventional circumstances, and it is possible to conduct a conductive substrate of any width with good design ease, regardless of the impurity concentration, resistivity, or thickness of the conductive substrate used. The breakdown voltage and clamp voltage can be obtained, and other electrical characteristics such as junction capacitance and series resistance can be designed independently, regardless of the breakdown voltage or clamp voltage. It is an object of the present invention to provide a surge absorbing element that can absorb a large current while reducing the voltage sufficiently to the lower limit that does not cause the following current phenomenon compared to the breakdown voltage.

<Means for Solving the Problems> In order to achieve the above object, in the present invention, a punch-through phenomenon is introduced as a new operating principle in place of the conventional avalanche yielding type with respect to the yielding mechanism at the initial stage of operation.
Regarding the regulation of the clamp voltage after breakdown, the following surge absorption element is provided as a surge absorption element with a novel configuration that can utilize avalanche breakdown, Zener breakdown, or punch-through phenomenon.

l) a first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; one of the upper and lower surfaces of the first semiconductor region; a second semiconductor region formed on the side and having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; from the side opposite to the first semiconductor region; A third region that contacts the first semiconductor region and defines the effective thickness of the second semiconductor region by determining the separation distance between the first semiconductor region and the first semiconductor region. - It is formed on the other surface side opposite to the one surface of the above-mentioned upper and lower surfaces of the first semiconductor region, or a fourth region formed spaced apart and forming an injection junction with the first semiconductor region; a fifth region forming a rectifying junction therebetween; the first semiconductor region and the third region formed when a depletion layer generated by reverse bias of the pn junction diode reaches the corresponding third region; 2. A surge absorbing element that absorbs a surge current by punch-through between the fourth region and the fifth region, and has a clamp voltage defined by a breakdown voltage of the rectifying junction between the fourth region and the fifth region.

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 second semiconductor region formed on the surface side and having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; a side opposite to the first semiconductor region; a third region that defines an effective thickness of the second semiconductor region by contacting the second semiconductor region with respect to the first semiconductor region; It is formed on the other surface side opposite to the one surface of the upper and lower surfaces, or it is formed on the one surface side laterally spaced apart from the second semiconductor region, and the first semiconductor region a fourth region forming an injection junction with the semiconductor region; and a fifth region forming a rectifying junction with the fourth region by contacting the fourth region from a side opposite to the first semiconductor region; a sixth region further forming a rectifying junction from the side opposite to the fourth region with respect to the fifth region;
A surge current is absorbed by the punch-through between the first semiconductor region and the third region, which occurs when the depletion layer produced by the reverse bias of the junction diode reaches the corresponding third region, and the fifth region A surge absorption element characterized in that a clamp voltage is defined by punch-through through the surge absorption element.

3) a first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate; one of the upper and lower surfaces of the first semiconductor region; a second semiconductor region formed on the side and having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; from the side opposite to the first semiconductor region; a third region that is in contact with the second semiconductor region and defines an effective thickness of the second semiconductor region by determining a distance between the third region and the first semiconductor region; It is formed on the other surface side facing the one surface among both surfaces, or is formed on the one surface side laterally spaced apart from the semiconductor region of the upper foot temperature two,
a fourth region forming an injection junction with the first semiconductor region; an auxiliary region forming a rectifying junction from the side opposite to the second semiconductor region with respect to the third region;
When the depletion layer generated by reverse bias to the junction diode reaches the third region, the punch-through between the first semiconductor region and the fifth region absorbs the surge current, and the third region and the fifth region absorb the surge current. A surge absorbing element characterized in that a clamp voltage is defined by a breakdown voltage of the rectifying junction between the auxiliary region and the rectifying junction.

<Function> Firstly, to describe the function common to all of the above-mentioned first to third inventions, the surge absorbing element of the present invention includes a first semiconductor region and a second semiconductor region. As a reverse bias is applied to the pn junction diode, the depletion layer generated at the junction extends not only toward the first semiconductor region but also 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, even if the fifth region etc. in the first and second inventions are formed protruding from the fourth region, this absorbed current mainly flows through the path from the fourth region to the first semiconductor region. As mentioned in the summary, the fourth region is made of a material that forms an injection junction capable of injecting minority carriers into the first semiconductor region (for example, a semiconductor of a conductivity type opposite to that of the first semiconductor region, silicide, Furthermore, as long as the first semiconductor region is made of a p-type metal (such as a metal capable of injecting electrons), injection of minority carriers from the third region into the first semiconductor region occurs, and therefore the external Even if the second semiconductor region and the third region are electrically short-circuited through the terminal, a voltage drop occurs in the second semiconductor region as a result of the minority carriers flowing into the second semiconductor region, and a voltage drop occurs in the second semiconductor region. Carrier injection occurs into the second semiconductor region.

While this carrier injection process is repeated, eventually a current larger than the value shown as the breakover current in Figure 4 flows, and through a positive feedback phenomenon, the fourth region The voltage between the three regions is extremely low under clamped conditions.

However, in the first invention, the voltage across the element, that is, the clamp voltage as an element characteristic, is the avalanche breakdown voltage or Zener breakdown voltage between the fourth region and the fifth region, and in the second invention, the clamp voltage is the voltage between the fourth region and the fifth region. The punch-through voltage through the region, and in the third invention, the avalanche or Zener breakdown voltage between the third region and the auxiliary region are added to the extremely low voltage between the third and fourth regions, respectively. Become.

This clamp voltage can be achieved with good design efficiency even with existing technology by controlling the impurity concentration and/or thickness of each region related to the avalanche breakdown voltage, Zener breakdown voltage, or punch-through voltage. It can be set arbitrarily within a certain design range.

Therefore, while the surge absorbing element of the present invention can absorb large currents while suppressing the heat generation of the element, the clamp voltage can be designed arbitrarily, and therefore the power supply of the circuit system to which the present surge absorbing element is applied. It becomes possible and easy to automatically reset the lamp voltage by setting the optimum lamp voltage to prevent the following current phenomenon from occurring according to the voltage.

Note that the voltage that exhibits a breakover current is
This breakover voltage, which can be called an overvoltage, is generally higher than the breakdown voltage, as shown in FIG.

Therefore, if we follow the voltage history across the device from its initial operation to voltage clamping, we can see that with surge application,
If the current exceeds the breakdown voltage, punch-through operation will begin, and the voltage across the device will rise somewhat until the absorbed current reaches the breakover current, but once the current exceeds the breakover 1i current, the breakover current will rise. - Move from the overvoltage to the clamp voltage, which can be set arbitrarily as described above.

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, from the above, in the case of the present invention, suitable commercially available It can be seen that a surge absorbing element having any desired breakdown voltage can be obtained even if a semiconductor substrate wafer is used as it is, or even if the same type of semiconductor substrate is used as a starting material.

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, the method of sequentially forming the second semiconductor region and the third region on the semiconductor substrate itself or on the first semiconductor region formed separately on the semiconductor substrate may be performed using existing epitaxial growth technology. , ion implantation, selective diffusion, etc., but in any case, the effective thickness and impurity concentration of the second semiconductor region can be extremely well controlled even with current technology, so in the end, it is impossible to do so by uninvented methods. The generated surge absorbing element can have extremely high accuracy, if necessary.

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. It can also be used as is without pre-processing (which is also more common), so it does not require an increase in the number of steps or decrease in physical strength, and can be used as a single semiconductor substrate. It is also possible to form a plurality of elements of the present invention within the device, which has the effect of facilitating integration.

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,
Therefore, it is possible to draw out to the outside from the same drawing terminal, but conversely, it is also possible to draw out from each dedicated terminal independently and apply an appropriate bias between these two terminals. Then, even after the device is completed or even when the device is in an unstable state, by changing and adjusting the bias voltage, the punch-through voltage, that is, the breakdown voltage as a surge absorbing device can be made variable.

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

<Examples> Some of the illustrated embodiments of the present invention will be described in detail below. Of course, there are individual embodiments of the first invention, second invention, and third invention, but as already mentioned, they are all very closely related and can be referred to each other, and especially Considerations and modifications other than how to define the clamp voltage are mutually applicable.

The surge absorbing elements shown in FIGS. 1A, 1B, and 1C are basic embodiments of the first invention, and the embodiment shown in FIG. The embodiment shown in the figure is an embodiment corresponding to the third invention.

In either case, the semiconductor substrate is used as it is as the first semiconductor region l of the first conductivity type, and the third and fourth regions 3 and 4 are
In addition to the semiconductor region, the fifth region 5 of the first and second inventions and the auxiliary region 7 of the third invention are also made of semiconductor material.

In the embodiment shown in FIG. 1(A) and the embodiments shown in FIGS. 2 and 3, double diffusion technology is generally applied to one of the upper and lower surfaces of the first semiconductor region l. A fourth semiconductor region 4 is formed on the other surface of the first semiconductor region l, that is, on the back surface side, with respect to the second semiconductor region 2 and the third semiconductor region 3 that are formed, but as shown in FIG. 1(B) , (C), on the same surface on which the second semiconductor region 2 is provided, except that the second semiconductor region 2
A fourth semiconductor region 4 is formed using a diffusion technique and spaced apart from each other in the lateral direction.

In these embodiments, the first semiconductor region 1 was selected to be a t-n type semiconductor in relation to the cross-sectional structure, and therefore the second semiconductor region 2 was made to be a p-type semiconductor by a diffusion technique of an appropriate impurity such as boron. At the same time, the fourth semiconductor region 4 is also p
type semiconductor region.

Therefore, of course, in the embodiments of the first and second inventions shown in FIGS. The conductivity type of the semiconductor region 5 is selected to be n type, and the third
In the embodiment of the third invention shown in the figure, the conductivity type of the auxiliary region 7 forming a rectifying junction with the third region 3 is selected to be p-type.

In the case of the embodiments shown in FIGS. 1CB) and 1C, it is preferable that a high concentration impurity layer 1b, which will be described later, be provided on the back side of the first semiconductor region 1; Since it is not directly involved in the basic configuration or principle operation of the present invention, it may be assumed that this is not present at the beginning in the following description.

The third region 3 related to the first and second inventions and the auxiliary region 7 related to the third invention form one end of the main current line when punch-through occurs, and therefore preferably have high conductivity. In each of these embodiments, high impurity concentration, ie, p+ type and n+ type regions, are formed by double diffusion of impurities.

Each region 2; 3 or 7; 5 or 6 is completed as an element by attaching an ohmic lead-out terminal, but the lead-out terminal 2t of the second semiconductor region 2 and the third region related to the first invention and the second invention are As shown by the virtual line line Ls in each corresponding figure, the lead terminal 3t of No. 3 may be short-circuited at the manufacturing stage, or may be pulled out separately and short-circuited by the user. , or an appropriate bias source may be inserted as described below.On the other hand, the second region 2 and the third region 3 related to the third invention are as shown in FIG. Generally, it is connected externally by a line or an electrode Lc.

In the above case, when short-circuiting the terminals 2t and 3,
In reality, the line Lm can 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 to make ohmic contact with them.

First, both the terminals 2t and 3t are short-circuited by the lines Ls and Lc in this way, and between the two terminals as a surge absorbing element, that is, in the embodiments of the first and second inventions, the terminals 2t and 3t are short-circuited by the lines Ls and Lc. The description will be made assuming that a surge voltage is applied between the lead terminal 5t of the fifth semiconductor region 5 and between the auxiliary region terminal 7t and the fourth region terminal 4t in the embodiment related to the third invention.

In such a surge absorbing element lO, as already explained in the section of operation, when a reverse bias is applied to the pn junction between the first semiconductor region l and the second semiconductor region 2,
The resulting depletion layer extends not only toward the first semiconductor region 1 side but also toward the third region 3 side.

Therefore, if a surge voltage is applied between the terminals 2t, 3t and the terminal 5 or between the terminal 4t and the terminal 7, and the surge voltage is considerably large in the phase of applying reverse bias to the pn junction, the It may happen that the upper end of the depletion layer reaches the third region 3.

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. 4 as the breakdown voltage on the voltage axis.

When such a breakdown start state is realized, the terminal 2t.

A surge current flows between the terminal 3t and the terminal 5 or between the terminal 4t and the terminal 7, and holes are injected from the fourth semiconductor region 4 into the first semiconductor region l, and are collected in the second semiconductor region 2. It becomes an external current (element current) via an external terminal.

Therefore, the product of the resistance of the second semiconductor region 2 sandwiched between the third region 3 and the first semiconductor region l and the above-mentioned current is
3, electrons are injected from the third region 3 into the second semiconductor region 2, which causes an increase in current, and the current flows again into the fourth semiconductor region 3. A positive feedback phenomenon occurs in which holes are injected from 4.

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 (between external terminals 3t and 5 is
, ? is the breakover voltage.

As already mentioned, this breakover voltage will be somewhat larger than the breakdown voltage, but once positive feedback begins to occur, the voltage between the third region 3 and the fourth region 4 will decrease. Transition to a significantly lower value. Specifically, this value is approximately equal to C, which is the product of the absorbed current and the series resistance of each part plus one forward voltage of the pn junction.

However, the clamp voltage for the element shown in FIG. 4 is defined as follows depending on the embodiment of each invention.

First, in the embodiments shown in the first figures related to the first invention, the breakdown voltage at the rectifying junction between the fourth semiconductor region 4 and the fifth semiconductor region 5 is added to the extremely low voltage between the third and fourth regions. It becomes what it is.

Therefore, by appropriately setting the impurity concentration of the fourth semiconductor region 4, the clamp voltage of this element can be set arbitrarily.

In the embodiment related to the second invention shown in FIG.
By providing the sixth region (in this case, a p-type semiconductor region) 6 made of a material capable of forming a rectifying junction with respect to the fifth semiconductor region 5, the punch-through voltage of the fifth region can be increased from that of the third and fourth regions. This is in addition to the extremely low voltage between regions.

Therefore, by controlling the impurity concentration and thickness of the fifth region 5, any desired clamp voltage can be obtained with good controllability over a considerably wide design range.

In the third embodiment of the third invention, the avalanche or Zener breakdown voltage between the auxiliary region 7 formed in the third region 3 and the third region is the same as that between the third and fourth regions. Therefore, by controlling the impurity concentration of the third semiconductor region, the clamp voltage of the element can be set arbitrarily.

Note that in the embodiment shown in FIG. 1(C) according to the first invention, as can be seen when compared with the embodiment shown in FIG. 1(B), the fifth semiconductor region 5 in contact with the fourth semiconductor region 4 This is done so that the breakdown current flows uniformly across the junction surface. It is for the same reason that the sides of regions 4 to 6 are shaped like a mesa in the embodiment of the second invention shown in FIG.

As understood from the above 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 has a significant effect on the surge absorbing element 10 of the present invention. While preventing the power from being dissipated, once a surge is applied above the breakdown voltage, it will soon reach the specified clamp voltage you set, absorbing the large current and ensuring the subsequent circuit system. In addition to protection, by appropriately setting the clamp voltage, it is possible to prevent the following current phenomenon, and it is possible to prevent the power supply voltage of the circuit system from continuing to turn on uselessly even after the surge factor has disappeared.

The breakdown voltage in the present surge absorbing element lO that operates in this manner 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 l and the third region 3. Since the punch-through voltage can be controlled depending on the effective thickness Dt of the second semiconductor region 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 ports.

In each of the above embodiments, as described above, the semiconductor substrate l
In contrast, the second semiconductor region 2 and third region 3 are created using double diffusion technology, but in such a case,
The effective thickness Dt of the second semiconductor region 2 is directly controlled by controlling the diffusion depth Dd of the impurity for forming the third region from the surface after the first semiconductor region 2 is formed. Become. In other words, when using double diffusion technology,
The height position of the third region 3 relative to the first semiconductor region can be changed or changed directly by setting the effective thickness 01 of the second semiconductor region 2.
will change.

On the other hand, when the second semiconductor region 2 and the third region 3 are formed by epitaxial growth technology, the effective thickness 01 of the second semiconductor region 2 is the growth film thickness itself determined based on the conditions in the epitaxy. In this case, the existence of the third region 3 still actually defines the effective thickness Dt regarding bunch-through.

Whether using diffusion technology or epitaxy, the effective thickness Dt of the second semiconductor region 2 can be controlled with extremely high precision even with existing technology.
The surge absorbing element according to the present invention allows its breakdown voltage to be set with extremely high accuracy.

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

The above also shows that in the case of the device of the present invention, two variables, the effective thickness Dt and the impurity concentration of the second semiconductor region 2, each of which has good designability and are independent from each other, are used to design the breakdown voltage. It means doing. Therefore, by using only one or both of these variables and arranging them appropriately, it is not only possible to set the breakdown voltage over an extremely wide range, but also to control other electrical characteristics such as junction capacitance and series resistance. It can be seen that it can also be designed independently of the breakdown voltage.

Of course, the fourth semiconductor region 4 related to the regulation of the clamp voltage
, the fifth semiconductor region 5, and K the sixth region 6 and the auxiliary region 7.
Also, the sixth region of the second invention, the auxiliary region of the third invention, etc., which are formed with good controllability by using conventional techniques such as impurity diffusion and epitaxy, are not limited to being made of semiconductor, and are not limited to the first semiconductor region. Depending on the conductivity type, it can be made of silicide or, in some cases, metal.

Furthermore, as I mentioned earlier, Figure 1 (B) and Figure 1 (C)
), an n+ or p+ type high concentration impurity region layer 1b is formed on the back side of the semiconductor substrate or the first semiconductor region 1, regardless of the conductivity type of the region 1. It is desirable that the carrier be kept as it is because the carrier can be transported efficiently.

That is, when an n-type semiconductor is selected for the first semiconductor region l as shown in the figure, the conductivity type of the high concentration impurity region layer 1b is set to n.
If the medium size is selected, a kind of built-in electric field is generated between the high concentration impurity region layer 1b and the first semiconductor region l, and as shown in FIG.
As represented by arrow fl in the figure in B), the holes injected from the fourth semiconductor region 4 are repelled near the high concentration impurity region layer tb and escape to the back side of the first semiconductor region. Things will disappear.

In addition, when a p medium type high concentration impurity region layer 1b is formed on the back side of the first semiconductor region mi of the same nJJl, as schematically shown by arrows f2a and f2b in FIG. As holes fill up in the P+ type high concentration impurity region 1b, its potential increases, and eventually the high concentration impurity region layer 1b! Holes are emitted from b, or are bounced back as shown by arrow f2c, thereby preventing the holes from permeating to the back side of the first semiconductor region.

Such a so-called lateral arrangement can also be adopted for the embodiments shown in FIGS. 2 and 3, and therefore, in such a case, the high concentration impurity region 1
b can also be formed on the back side of the first semiconductor region.

As is clear from the above explanation through each of the embodiments of the first, second, and third embodiments of the present invention, in the surge absorbing element of the present invention, in principle, punching occurs between the first and third regions. The current distribution of the surge current after the through occurs becomes relatively uniform.

However, if further uniformity is to be ensured, a configuration as shown in FIG. 5, which is representative as a modified example of the first illustrated embodiment according to the first invention, can also be adopted.

That is, in the embodiment shown in the fifth figure, a plurality of third regions 3 are formed for the second semiconductor region 2 of the opposite conductivity type formed on one surface side of the semiconductor substrate or the first semiconductor region l. Divided third area elements 31 , 32 , 33 ,
.

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 area of the C element.

In the case of this embodiment, the fifth region is formed to protrude laterally from the fourth region, which prevents avalanche or Zener breakdown in this region and maintains uniformity of the breakdown current. Therefore, as in FIG. 1(C) above, there is a meaning in excluding corner joints.

The other considerations described in the first embodiment can be similarly applied to the embodiment shown in FIG. 1, and the embodiment shown in FIGS. When the fourth and fifth regions 4 and 5 are arranged on the same surface side of the first semiconductor region 1 as the second and third region 2.3 sides, This may be similarly adopted for the high concentration impurity region layer tb if necessary.Note that the two terminals 2t and 3t can not only be short-circuited due to the operating principle as described above, but also be short-circuited. This also has the effect of avoiding transient phenomena.

Conversely, the idea of the embodiment shown in FIG.
It can also be applied as is to the embodiments shown in rI4 and FIG.

In the surge absorbing element configured as in the present invention, when the breakdown voltage, which should originally be defined by the punch-through phenomenon, becomes close to the avalanche breakdown voltage of the first semiconductor region 1 and the second semiconductor region 2, controllability deteriorates. If there is such a risk, a sixth As shown in the figure, a guard ring region 2G of the same conductivity type as the second semiconductor region is formed to surround the second semiconductor region 2, or as shown in FIG. Region 2 and third semiconductor region 3
It is preferable that the end edge portion Mat of 6 is further extended through the insulating film 8 to the ohmic electrode formed in series on the surface of the second semiconductor region beyond the junction with the first semiconductor region at the end of the second semiconductor region. .

In this way, the concentration of the electric field at the end of the second semiconductor region is alleviated and the avalanche breakdown voltage is effectively increased, thereby making it possible to design the breakdown voltage only by punch-through, in accordance with the idea of the present invention. can be expanded and improved.

In the embodiment shown in FIG.
t is also extended beyond the junction end with the fourth semiconductor region 4 via the insulating film 9.

Of course, the ideas of the embodiments shown in Figures 6 and 7 can also be applied to the second and third inventions, and in Figures 6 and 7, the third area 3 is a plurality of area element groups for each area. 31 to 3n, but as represented by the third region 3 shown in FIG. 1, these third regions 3 are most basically each treated as a single region. It may be formed.

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

However, when there is no need to accumulate a large number of
As another means for increasing the avalanche breakdown voltage mentioned above, as shown in FIG. 8, the first and second semiconductor regions 1.
The portion corresponding to the joint end between the two may be etched or cut with a slope perpendicular to the surface or at an angle.

Such processing may also be effective regarding the relationship between the fourth region 4 and the fifth region 5. However, when such a simple method is used, it is possible to apply appropriate protection to the cut surface. I
(not shown).

In addition, in order to increase the uniformity of the current flowing through the junction that defines the clamp voltage, the fourth region 4 may be constructed from a set of a plurality of region elements 41, 42, , , 14n, as shown in FIG. Again, this divisional configuration can be similarly applied to each of the embodiments of the second and third inventions.

Here, as a representative example shown in FIG. 1(A),
To explain a somewhat special usage of the surge absorbing element of the present invention, the second semiconductor region 2 and the third region 3 are connected to different terminals 2.
If you draw it individually from t and 3t, the first
As shown in Figure 0 (A), these terminals 2t, 3
By inserting an appropriate bias source vb between , it is also possible to control the punch-through voltage from the outside.

As a model of the surge voltage, a high voltage source V connected between the third region terminal 3t and the terminal 5t of the fifth semiconductor region 5 is used.
Considering r, the energy band structure of this surge absorbing element changes from the state shown by the solid line when no surge voltage is applied, to the high voltage corresponding to the surge voltage, as shown in Figure 1θ (B). When the voltage Vr is applied, the state changes to the state shown by the virtual 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, when the second region 2 and the third region 3 are reverse biased, a forward bias is applied as shown by the arrow "neck". In each case, the band structure changes as shown by the arrow "1". Therefore, depending on the bias potential and its polarity, it is possible to know at a moment's notice whether the strike through lightning FFI+outside #R≠) as a surge absorbing element is accurate.

Each embodiment of the present invention has been described in detail above, and finally, as an example, the effects of the present invention will be confirmed by comparing actual devices.

First, a surge absorbing element of the present invention shown in FIG. 5 without the second and fourth semiconductor regions 4 and the fifth region 5 was prepared for comparison using the steps described below.

Resistivity 5Ω-C■, conductivity type n-type, (111) plane, 300
A silicon wafer of a certain thickness was used as the starting material for the first semiconductor region 1, and 6000 SiO2 films were first formed on its front and back surfaces.

Among them, only the SiO2 film on the back surface was removed and high concentration phosphorus was diffused to three depths.

Next, in order to define the planar shape of the second semiconductor region 2, a photo-etching process was applied to the silicon oxide film on the surface according to a predetermined pattern to open an impurity diffusion window.

Boron is diffused through this diffusion window, and its depth is 2.5
A p-type bond castle spanning 1ffl was formed.

After a new silicon oxide film is formed on the wafer surface, the silicon oxide film is photo-etched in accordance with a predetermined pattern in order to define the planar shape of the plurality of third region elements 31 to 3n. Impurity diffusion windows for three third region elements were formed.

Phosphorus is diffused in high concentration through this diffusion window, and its depth is 1.2
A fifth region 3 consisting of a set of n0-type third region elements 31 to 3n was formed. Therefore, at the same time, the second semiconductor region 2 is formed, and its effective thickness at is 1.3.
It was considered an obstacle.

After that, electrodes or terminals 2t, 3t are formed through photo-etching, metal thin film deposition, and etching processes to form a common ohmic contact in the second and third regions.
was formed. Electrodes or terminals on the semiconductor substrate side were also formed at the same time in the metal thin film deposition process.

The breakdown voltage of a comparison surge absorbing element produced by such a process was 120V, and the surge absorption current could reach a maximum of 300A/cm2.

On the other hand, as a surge absorbing element according to the idea of the present invention, the manufacturing process up to the third region is the same as that of the comparative surge absorbing element, but a fourth semiconductor region is formed on the back side of the n-type semiconductor substrate. In the surge absorbing element in which the p-type medium region is formed by impurity diffusion, the n-type medium region as the fifth semiconductor region 5 is formed by impurity diffusion, and the electrodes or terminals 5t are formed by metal thin film deposition, the breakdown voltage is as follows. The voltage was approximately the same as 121V, but the breakover current was 4A/c2 and the surge absorption current was up to 500QA/c2.

Further, the variation width of the clamp voltage could be controlled to any value from 5 to 50V.

Looking at this characteristic example, it can be seen that the S values of the fourth semiconductor region 4 and the fifth region 5 provided according to the present invention are extremely large.

Also, under the same conditions as above, the breakdown voltage was It was possible to vary the voltage between 30V and 170V. Of course, this variation range is not the maximum variation range, and it has been confirmed that if other conditions are taken into account, an extremely wide range of variation from several volts to several hundred ports can be obtained.

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

For example, in the device shown in the third figure, the fourth region 4 in the figure is modified to consist of a stack of the second and third regions 2.3 and the auxiliary region 7, but the impurity concentration of the fifth region is lower than that of the auxiliary region. By controlling the concentration to such a level that the breakdown voltage for defining the clamp voltage can be defined, the effects of the present invention can be exhibited against bipolar surge currents.

<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 most inflexible components of this type of device, but according to the present invention, even starting wafers with the same material constant can have different breakdown voltages. A surge absorbing element can be obtained.

■The set of the second semiconductor region and the third region, the set of the fourth semiconductor region and the fifth region, or the set of the second semiconductor region, the third region, and the auxiliary region are the same for the first semiconductor region. Since it can be formed only from the surface side, it is extremely easy to change the breakdown voltage and/or clamp voltage and control to obtain the predetermined breakdown voltage and clamp voltage, and high accuracy is required.

■ Other electrical characteristics, such as junction capacitance and series resistance, can be designed independently of the breakdown voltage and clamp voltage. Therefore, for example, even with different breakdown voltages and clamp voltages, other electrical characteristics are almost the same. It is also possible to do this.

(2) It is also easy to integrate multiple elements on a common semiconductor substrate.

■Since the design principle is such that the clamp voltage is reduced even more than the breakdown voltage in the large current region, it can absorb even extremely large surge currents and has an extremely high ability to protect circuit systems.

■Even though the clamp voltage is greatly reduced, if necessary, set the value so that it does not become an extremely low value, or so that it corresponds to the power supply voltage of the circuit system to which this surge absorbing element is applied. Therefore, it is also possible to prevent a follow-on phenomenon in which conduction continues even after the surge factor has disappeared.

[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 a schematic configuration diagram of an embodiment of a surge absorbing element according to the second invention, and FIG. 3 is according to the third invention. A schematic configuration diagram of one embodiment, FIG. 4 is an operational characteristic diagram of the device of the present invention, FIG. 5 is a schematic configuration diagram of a modified example according to the first invention, FIGS. 6 and 7,
8 and 9 are schematic configuration diagrams of further modified examples of the embodiment of the present invention, and FIG. 51110 is an explanatory diagram of an example of a special usage of the surge absorbing element of the present invention. In the figure, l is a first semiconductor region or a semiconductor substrate, 2 is a second semiconductor region, 3 is a third region, 31 to 3n are third region elements, 4 is a fourth region, 4l-4n are fourth region elements, 5 is a fifth region, 6 is a sixth region, 7 is an auxiliary region, and 10 is the entire surge absorbing element of the present invention.

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; both upper and lower surfaces of the first semiconductor region; a second semiconductor region formed on one surface side, having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; a third region that defines an effective thickness of the second semiconductor region by determining a separation distance from the first semiconductor region by contacting the second semiconductor region from a side opposite to the third region; Formed on the other surface facing the one surface of the upper and lower surfaces of one semiconductor region, or formed laterally apart from the second semiconductor region on the one surface side. a fourth region forming an injection junction with the first semiconductor region; and a fourth region forming a rectifying junction with the fourth region by contacting the fourth region from a side opposite to the first semiconductor region; a fifth region to be formed; and a punch-through between the first semiconductor region and the third region that occurs when a depletion layer generated by reverse bias of the pn junction diode reaches the corresponding third region. What is claimed is: 1. A surge absorbing element that absorbs surge currents and has a clamp voltage defined by a breakdown voltage of the rectifying junction between the fourth region and the fifth region. 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; one of the upper and lower surfaces of the first semiconductor region; a second semiconductor region formed on the side and having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; from the side opposite to the first semiconductor region; a third region that is in contact with the second semiconductor region and defines an effective thickness of the second semiconductor region by determining a distance between the third region and the first semiconductor region; The first semiconductor is formed on the other surface facing the one surface among both surfaces, or is formed on the one surface side so as to be laterally spaced apart from the second semiconductor region. a fourth region forming an injection junction with the first semiconductor region; a fifth region forming a rectifying junction with the fourth region by contacting the fourth region from a side opposite to the first semiconductor region; a sixth region forming a rectifying junction from the side opposite to the fourth region; and the pn
A surge current is absorbed by the punch-through between the first semiconductor region and the third region, which occurs when the depletion layer produced by the reverse bias of the junction diode reaches the corresponding third region, and the fifth region A surge absorption element characterized in that a clamp voltage is defined by punch-through through the surge absorption element. 3) A first semiconductor region of a first conductivity type formed as the semiconductor substrate itself or separately formed with respect to the semiconductor substrate: one surface of both upper and lower surfaces of the first semiconductor region; a second semiconductor region formed on the side and having a conductivity type opposite to the first semiconductor region and forming a pn junction diode with the first semiconductor region; from the side opposite to the first semiconductor region; a third region that is in contact with the second semiconductor region and defines an effective thickness of the second semiconductor region by determining a distance between the third region and the first semiconductor region; The first semiconductor is formed on the other surface facing the one surface among both surfaces, or is formed on the one surface side so as to be laterally spaced apart from the second semiconductor region. a fourth region forming an injection junction with the pn region; an auxiliary region forming a rectifying junction from the side opposite to the second semiconductor region with respect to the third region;
A surge current is absorbed by the punch-through between the first semiconductor region and the third region that occurs when the depletion layer generated by reverse bias to the junction diode reaches the third region, and the surge current is absorbed by the third region and the third region. A surge absorbing element characterized in that a clamp voltage is defined by a breakdown voltage of the rectifying junction between the auxiliary region and the rectifying junction.