JP2001144191A - Electrostatic protective element, electrostatic protective circuit, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce the triggering voltage of an electrostatic protective element using a simple configuration. SOLUTION: A MOS element is used mainly as a triggering element, and a charge generated by static electricity is injected to a base electrode B of a parasitic bipolar transistor 11 by at tunnel current Im of the MOS element as a support, thus rapidly increasing the base potential of the parasitic bipolar transistor 11. Also, to surely inject a tunnel current Im to the base electrode B of the parasitic bipolar transistor 11, a low-resistance layer is provided in a semiconductor substrate, and the alignment of the parasitic bipolar transistor 11 and the trigger element are devised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device used to prevent destruction due to static electricity.

[0002]

2. Description of the Related Art In general, semiconductor devices are easily damaged by static electricity. For this reason, various protection elements and protection devices including these protection elements are provided between input / output pads connected to the outside and internal circuits. The circuit is built in. In particular, the gate insulating film of MOS devices is easily damaged by static electricity.
In a MOS circuit, if excessive charge exceeding the operating voltage of the semiconductor device is generated due to electrostatic discharge of the input / output pad, the excess charge is immediately discharged to the ground before reaching the gate insulating film breakdown voltage of the internal CMOS circuit. There is a need to. When a negative electrostatic discharge is applied to the input / output pad of the CMOS circuit, the static electricity can be easily released due to the forward characteristics of the n + p diode.However, when a positive electrostatic discharge is applied, n + Since protection is difficult with a p-diode, a parasitic bipolar transistor or a parasitic thyristor has conventionally been used as an effective electrostatic protection element.

A conventional electrostatic protection circuit using a parasitic bipolar transistor is realized by a structure in which a gate electrode G is grounded as shown in FIG. 1A, and a conventional electrostatic protection circuit using a parasitic thyristor is This is realized by a lateral thyristor 2 as shown in FIG. These protection circuits have high versatility because the manufacturing process of the nMOSFET of the internal CMOS circuit can be used.

A conventional electrostatic protection circuit including a MOS field-effect transistor shown in FIG. 1A is a circuit in which a substrate resistance Rsub of a p-type semiconductor substrate 12 is connected to a base electrode B of an npn-type parasitic bipolar transistor 11. Are equivalent.
FIG. 7A shows a circuit diagram of the equivalent circuit, and FIG. 1B shows the current-voltage characteristics. The electrostatic protection principle of the electrostatic protection circuit using the parasitic bipolar transistor will be disclosed below.

When an excessive negative voltage due to electrostatic discharge is applied to the input / output pad, the n + layer on the electrode D side and the p +
Static electricity is discharged to the ground by the forward characteristic of the n + p junction formed with the die semiconductor substrate 12. That is, FIG.
As shown in (2), when the voltage exceeds the offset voltage Vos, a forward current If flows to discharge the static electricity to the ground.

When an excessive positive voltage due to electrostatic discharge is applied to the input / output pad, the static electricity is discharged to the ground by a snapback characteristic with respect to a reverse voltage.
That is, as shown in FIG. 1B, as the applied voltage increases, the reverse current Ir of the n + p junction gradually increases,
The reverse current Ir flows into the substrate resistance Rsub, and the potential of the base electrode B rises due to the voltage drop (15). When the first trigger potential (Vt1, It1) is reached near the breakdown of the n + p junction of the npn-type parasitic bipolar transistor 11, the npn-type parasitic bipolar transistor 11 is turned on by an increase in the potential of the base electrode B, and the electrode is turned on. A large current flows from D to the electrode S to discharge static electricity to the ground (1
6) When the applied voltage further increases, the current also increases (17). However, the npn-type parasitic bipolar transistor 11 breaks down again (Vt2, It2), and follows the decrease in voltage and the increase in current (18). Irreversibly changes due to high heat, leading to destruction (19).

The lateral thyristor 2 shown in FIG.
Lateral pnp parasitic bipolar transistor and vertical n
This is equivalent to a circuit in which the pn-type parasitic bipolar transistor 21 and the resistance Rnw of the n-well region and the substrate resistance Rsub of the p-type semiconductor substrate 22 are connected. FIG. 7 is a circuit diagram of the equivalent circuit.
FIG. 2 (b) shows the current-voltage characteristics thereof. The principle of electrostatic protection of the electrostatic protection circuit using a parasitic thyristor is substantially the same as the principle of electrostatic protection of the electrostatic protection circuit using a parasitic bipolar transistor.

When an excessive negative voltage due to electrostatic discharge is applied to the input / output pad, the n + layer on the electrode C side and the p +
Static electricity is discharged to the ground by the forward characteristic of the n + p junction formed with the die semiconductor substrate 22. That is, FIG.
As shown in (2), when the voltage exceeds the offset voltage Vos, a forward current flows to discharge static electricity to the ground.

When an excessive positive voltage due to electrostatic discharge is applied to the input / output pad, the static electricity is discharged to the ground by a snapback characteristic with respect to a reverse voltage.
That is, as shown in FIG. 2B, as the applied voltage increases, the reverse current of the n + p junction gradually increases, the reverse current flows into the substrate resistance Rsub, and the potential of the base electrode B is reduced by the voltage drop. Rises (15 '). Vertical
When the first trigger potential (Vt1, It1) is reached in the vicinity of the breakdown of the n + p junction of the npn-type parasitic bipolar transistor 21, the vertical npn-type parasitic bipolar transistor 21 is turned on by the rise in the potential of the base electrode B. At the same time, the horizontal thyristor 2 is turned on by the positive feedback action of the two transistors in the vertical and horizontal directions, and a large current flows from the electrode A to the electrode K to discharge static electricity to the ground (16 '). When the applied voltage further increases, the current also increases (17 ').
The npn-type parasitic bipolar transistor 21 breaks down again (V
t2, It2), following a drop in voltage and an increase in current (1
8 '), the device undergoes irreversible changes due to high heat and leads to destruction (19').

[0010]

By the way, recent advances in technology have led to more and more miniaturization of devices due to the miniaturization of semiconductor devices, but have also produced soft devices that break down at low voltage. Recently, in ultra-miniaturized CMOS devices, the gate insulating film of a MOS element has been thinned to about 4 nm, and the gate insulating film breakdown voltage has been reduced to about 7 volts. In the future, miniaturization of semiconductor devices,
There is no doubt that device miniaturization will be advanced. Therefore, when a conventional electrostatic protection circuit is used for a miniaturized device, an accident may occur that the device is destroyed by static electricity before the electrostatic protection circuit operates (triggers). To cope with this, an electrostatic protection element or an electrostatic protection circuit having a low operating voltage (trigger voltage) corresponding to a low breakdown voltage of a miniaturized device must be developed and produced. However, even with successful development and production, the devices are becoming smaller and the same will be repeated many times in the future.

An object of the present invention is to provide an electrostatic protection element and an electrostatic protection circuit which can effectively deal with the above problems. That is, first, to efficiently lower the trigger voltage of the electrostatic protection element, specifically, within a range not lower than the operating voltage of the internal circuit, but at a low voltage equal to or lower than the breakdown voltage of the internal circuit. It is an object to provide an electrostatic protection element and an electrostatic protection circuit that operate. Secondly, there is provided an economical electrostatic protection element and an electrostatic protection circuit which can use the existing electrostatic protection element manufacturing method or the electrostatic protection element manufactured by the method without any change. The purpose is to: Third, it is an object of the present invention to provide an electrostatic protection element and an electrostatic protection circuit which are not damaged by the rise of the applied voltage.

[0012]

According to a first aspect of the present invention, there is provided a parasitic bipolar transistor and a trigger element for injecting a charge generated by static electricity into a base region of the parasitic bipolar transistor. It is an electrostatic protection element characterized by comprising:

Therefore, according to the electrostatic protection element of the first aspect of the present invention, since the trigger element for injecting the charge generated by static electricity into the base electrode of the parasitic bipolar transistor is provided, the operating voltage (trigger voltage) of the parasitic bipolar transistor is provided. ) Is reduced.

[0014] The second invention of the present application for solving the above problems is as follows.
In the electrostatic protection element according to the first aspect of the present invention, the trigger element has an insulating film, and charges generated by static electricity pass through the insulating film by a tunnel effect and are injected into a base region of the parasitic bipolar transistor. It is characterized by.

Therefore, according to the electrostatic protection element of the second invention of the present application, the charge is cut off by the insulating film at the time of low voltage by the trigger element, and is passed by the tunnel effect at the time of high voltage to flow to the base electrode of the parasitic bipolar transistor. Therefore, there is an advantage that in a normal state in which no electrostatic discharge occurs, no useless current is caused to flow to the ground, and only in a dangerous state in which the electrostatic discharge occurs, an excessive charge caused by static electricity is caused to flow to the ground.

[0016] The third invention of the present application for solving the above problems is as follows.
A capacitive element characterized in that a gate electrode is provided on a semiconductor substrate via a gate insulating film, and an element isolation layer is formed on the semiconductor substrate around the gate electrode.

Therefore, according to the capacitive element of the third invention of the present application, the rise of the voltage Vox applied to the gate insulating film before the gate insulating film is broken is suppressed, so that the gate insulating film is prevented from being broken. There is an advantage that can be. The principle will be described with reference to FIGS. Since the trench as the element isolation layer is provided, the minority carriers gathering in the inversion layer 41 on the surface of the semiconductor substrate become insufficient, and it is necessary to extend the depletion layer 42 to make up for this. Therefore, in order to extend the depletion layer, even if the voltage applied to the gate electrode increases beyond a certain value, the increase in the voltage is applied to the increase from the voltage Vs1 to Vs2 applied to the semiconductor substrate, and the voltage applied to the gate insulating film is increased. This is because it is not used for increasing the applied voltage Vox. At this time, the voltage Vox applied to the gate insulating film is saturated, and the tunnel current passing through the gate insulating film depending on the voltage Vox is also saturated. In order to increase the tendency that the minority carriers gathering in the inversion layer 41 become insufficient, it is preferable that the trench as the element isolation layer is filled with an insulator such as SiO2. A semiconductor region having the opposite polarity to the semiconductor substrate may be provided instead of the trench.

[0018] The fourth invention of the present application for solving the above-mentioned problems is as follows.
The capacitive element according to the third aspect of the present invention is characterized in that a low-resistance layer is formed in a semiconductor substrate.

Therefore, according to the capacitive element of the fourth aspect of the present invention, the rise in the voltage applied to the gate insulating film before the gate insulating film is broken is suppressed, so that the gate insulating film can be prevented from being broken. The advantage is that the tunnel current that has passed through the gate insulating film can be induced along the low-resistance layer, making it possible to adjust the tunnel current, such as concentrating it at one point or diffusing it to a certain area. is there.

[0020] The fifth invention of the present application for solving the above problems is as follows.
The capacitive element according to the third invention or the fourth invention of the present application is characterized in that a diode is connected in parallel to the gate electrode.

Therefore, according to the capacitive element of the fifth aspect of the present invention, since the diodes are connected in parallel, the rise in the voltage applied to the gate electrode rises and falls with the breakdown voltage of the connected diode. In addition, there is an advantage that after the breakdown of the diode, the reverse current of the diode and the tunnel current are added and flow to the semiconductor substrate.

[0022] The sixth invention of the present application for solving the above problems is as follows.
In the electrostatic protection device of the first invention or the second invention of the present application, one or more of the capacitive elements of the third invention of the present application, the fourth invention of the present application, and the fifth invention of the present application are provided. It is characterized in that a capacitive element is used as a trigger element.

Therefore, according to the electrostatic protection element of the sixth aspect of the present invention, the parasitic bipolar transistor is triggered by the injection of the trigger current of one or more trigger elements. There is an advantage that the operating voltage (trigger voltage) of the parasitic bipolar transistor can be correspondingly reduced. A seventh aspect of the present invention for solving the above-mentioned problems is a MIS field-effect transistor, one or more capacitive elements among the capacitive elements according to the third to fifth aspects of the present invention, and the capacitive element. A contact element formed at a position outside the element isolation layer, and a resistor element having one end connected to the ground is connected at the other end to the contact layer and the gate electrode of the MIS field effect transistor. An electrostatic protection circuit characterized in that: Therefore, according to the electrostatic protection circuit of the seventh aspect of the present invention, the electric charge generated by the electrostatic discharge causes the gate of one or more of the capacitive elements of the third to fifth aspects of the present invention. It is applied to the electrodes and flows as a tunnel current through the insulating film into the semiconductor substrate. Further, the charge flowing into the semiconductor substrate can be collected by the contact layer, the collected charge can flow to the resistance element, and a voltage can be applied to the gate electrode by a voltage drop of the resistance element. Therefore,
As the voltage rises due to electrostatic discharge, the potential of the gate electrode of the MIS field-effect transistor increases, and when a voltage equal to or higher than the threshold voltage of the MIS field-effect transistor is applied to the gate electrode, the drain current becomes a parasitic bipolar transistor. There is an advantage that the parasitic bipolar transistor flows into the base region of the transistor and can be operated at a low voltage. As a result that the parasitic bipolar transistor can be operated at a low voltage, there is an advantage that the operating voltage of the electrostatic protection circuit can be reduced and an internal circuit having a low withstand voltage can be effectively protected from static electricity. Further, according to the electrostatic protection circuit of the seventh aspect of the present invention, since the tunnel current is derived from the wiring, there is an advantage that the parasitic bipolar transistor and the capacitor need not be close to each other.

[0024] The eighth invention of the present application for solving the above problems is as follows.
In the electrostatic protection circuit according to the seventh aspect of the present invention, the voltage applied to the gate electrode due to the voltage drop of the resistance element is equal to M
The IS field-effect transistor is characterized in that it has a clamp element for keeping the breakdown voltage of the gate insulating film below the withstand voltage. Therefore, according to the electrostatic protection circuit of the eighth aspect of the present invention, since the clamp element for maintaining the voltage applied to the gate electrode due to the voltage drop of the resistance element to be equal to or less than the withstand voltage of the gate insulating film is provided, excessive static electricity causes There is an advantage that even if a large tunnel current occurs, the gate insulating film can be effectively protected from dielectric breakdown. A ninth invention of the present application which solves the above-mentioned problem is the one of one or more of the electrostatic protection elements of the first invention of the present application, the second invention of the present application, and the sixth invention of the present application. This is an electrostatic protection circuit applied.

Therefore, the electrostatic protection circuit according to the ninth invention of the present application is provided with the electrostatic protection elements of the first invention of the present application, the second invention of the present application, and the sixth invention of the present application. Is quickly discharged to the ground.

According to a tenth invention of the present application which solves the above-mentioned problem, in the electrostatic protection circuit according to the ninth invention of the present application, the parasitic bipolar transistor and the trigger element are arranged so that their mutually adjacent areas increase. It is characterized by that.

The closer the parasitic bipolar transistor and the trigger element are, the easier it is to inject the trigger current into the base electrode of the parasitic bipolar transistor. Therefore, according to the electrostatic protection circuit of the tenth aspect of the present invention, since the adjacent area between the parasitic bipolar transistor and the trigger element is arranged to be increased, the trigger current is reliably injected into the base electrode of the parasitic bipolar transistor. There is an advantage that unnecessary current is not passed.

The eleventh invention of the present application which solves the above-mentioned problem is a semiconductor device incorporating the electrostatic protection circuit of any one of the seventh to tenth inventions of the present application.

Therefore, in the semiconductor device according to the eleventh aspect of the present invention, the internal circuit is protected by the electrostatic protection circuit according to any one of the seventh to tenth aspects of the present invention. Has the advantage of being strong.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electrostatic protection element, an electrostatic protection circuit and a semiconductor device according to an embodiment of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 3A is a cross-sectional view showing a capacitive element (Embodiment 1) according to an embodiment of the present invention, and FIG. 3B is a diagram showing a current-voltage characteristic with respect to a reverse voltage. Show. As shown in FIG. 3A, the capacitive element according to the first embodiment has a silicon oxide insulating film 32 on a p-type semiconductor substrate 34 and a gate electrode 31 thereon.
A trench 33 was formed in the p-type semiconductor substrate 34 around the periphery of the gate electrode 31 and the trench 33 was filled with a silicon oxide insulator. Furthermore, a parasitic n + p diode is formed by burying an n + layer at a position adjacent to the gate electrode 31 of the p-type semiconductor substrate 34, and the n + electrode and the gate electrode 31 are connected by a conductive wire.

The current-voltage characteristic of the capacitive element according to the first embodiment having such a configuration with respect to the reverse voltage is represented by a solid line graph 3a shown in FIG. 3B. Applied voltage is 4
The current hardly flows due to the action of the insulating film and the diode until the voltage becomes about volts, and the current value rises due to the tunnel current Im from about 4 volts. Thereafter, the tunnel current Im is saturated by the action of the trench described above, but the diode breaks down near the applied voltage of 10 volts, and the current value increases again due to the reverse current Ir. That is, the added amount Im + Ir of the tunnel current Im and the reverse current Ir flows to the substrate resistance Rsub of the p-type semiconductor substrate 34.

Regardless of the capacitance element of the first embodiment, in the case where charges can always be supplied from the diffusion layer to the inversion layer, such as when the potential of the diffusion layer provided adjacent to the gate electrode is fixed. As shown by a broken line 3b in the graph of FIG. 3B, the potential rises, and the MOS element causes insulation film breakdown before the diode breaks down (3c). The capacitance element of the first embodiment is effectively prevented by providing an element isolation layer. However, if only the element isolation layer is provided, the voltage changes parallel to the horizontal axis as indicated by a broken line 3f, and only the voltage applied to the p-type semiconductor substrate 34 continues to increase while the current is saturated, and the heat is irreversible due to high heat. Change leads to destruction (3 g). The capacitance element according to the first embodiment uses a diode as a MOS.
Since it is connected in parallel with the element, when the breakdown voltage is equal to or higher than the breakdown voltage of the diode, the rise of the voltage is limited according to the characteristic of the diode indicated by the broken line 3d, and the reverse current Ir is reduced by p.
It flows to the substrate low resistance Rsub of the type semiconductor substrate 34. That is, since the MOS element and the diode are connected in parallel in the capacitive element of the first embodiment, the solid line graph 3a of FIG. 3B showing the current-voltage characteristics is indicated by the broken lines 3f and 3d.
Is added in the current direction, thereby preventing the breakdown 3c of the insulating film of the MOS device, the breakdown 3g of the semiconductor substrate 34 of the MOS device, and the breakdown 3e of the diode.

Embodiment 2 Next, an electrostatic protection element and an electrostatic protection circuit (Embodiment 2) according to another embodiment of the present invention will be described with reference to FIG. FIG. 5A shows the configuration, and FIG. 5B shows the current-voltage characteristics with respect to the reverse voltage. The electrostatic protection element and the electrostatic protection circuit according to the second embodiment are provided on a p-type semiconductor substrate 51 of an nMOSFET 1 which is a conventional electrostatic protection element.
Is formed at a position adjacent to the nMOSFET 1, and is connected between the input / output pad and the internal CMOS circuit and to the ground. The n + electrode of the parasitic n + p diode of the capacitive element 3 is an nMOSFET
This is shared with the electrode D formed on the n + 1 layer. The circuit diagram is shown in FIG.

In the case of the conventional electrostatic protection circuit composed only of the nMOSFET 1, the parasitic bipolar transistor 11 is triggered only by the reverse current Ir. However, the electrostatic protection circuit of the second embodiment uses the tunnel current Im as the trigger current. Since the trigger voltage Vt1 is used, the trigger voltage Vt1 can be reduced 53.

Here, an example in which the electrostatic protection element and the electrostatic protection circuit of the second embodiment are utilized as effective electrostatic breakdown protection means will be described with numerical values. Conventionally, the normal operating voltage of the internal CMOS circuit is 3.3 V, the thickness of the gate insulating film is 8 nm, the breakdown voltage is 10 V, and the parasitic bipolar transistor 11
Is necessary to turn on the base potential, that is,
In the case where the potential difference between the substrate resistances Rsub is 0.8 V and the nMOSFET 1 serving as the electrostatic protection element is set so that the trigger potential Vt1 = 9 V and the base potential of the parasitic bipolar transistor 11 can be set to 0.8 V, the gate insulating film is now used. 4nm film thickness
And change it to As the thickness of the gate insulating film becomes 4 nm, the gate insulating film breakdown voltage drops to 7 V, and in the conventional nMOSFET 1, the conventional gate insulating film is broken before the electrostatic protection circuit is triggered.

Therefore, an electrostatic protection element and an electrostatic protection circuit according to the second embodiment were manufactured. At that time, nMOSFET1 is the internal CMO
Using the same production line as the nMOSFET used for the S circuit,
The capacitive element 3 could also be manufactured by the conventional manufacturing process.
Therefore, the internal CMOS circuit, nMOSFET 1 and capacitor 3
The thickness of each of the gate insulating films was 4 nm. As a result of applying the electrostatic protection element and the electrostatic protection circuit of the second embodiment to a semiconductor device, when the applied voltage exceeds the normal operating voltage of 3.3 V of the internal CMOS circuit due to electrostatic discharge and becomes 4 V, the capacitance element 3 Started flowing a tunnel current to the base electrode B of the parasitic bipolar transistor.
When the voltage reaches V, the potential difference between the substrate resistances Rsub becomes 0.8 V, the parasitic bipolar transistor 11 is turned on, and the excess charge generated by the static electricity is quickly discharged to the ground, and the gate insulating film of the internal CMOS circuit is damaged. Could be prevented.

Third Embodiment Next, an electrostatic protection element and an electrostatic protection circuit (third embodiment) according to another embodiment of the present invention will be described with reference to FIG. FIG. 6A shows a configuration diagram thereof, and FIG. 6B shows a current-voltage characteristic with respect to the reverse voltage. In the electrostatic protection element and the electrostatic protection circuit according to the third embodiment, the capacitance element 3 according to the first embodiment is formed on the p-type semiconductor substrate 61 of the lateral thyristor 2 which is a conventional electrostatic protection element. The circuit diagram is shown in FIG.

In the case of the conventional electrostatic protection circuit composed only of the lateral thyristor 2, the parasitic bipolar transistor 21 is triggered only by the reverse current Ir. However, the electrostatic protection circuit of the third embodiment reduces the tunnel current Im. Since the trigger voltage is used for the trigger current, a lower voltage 63 of the trigger voltage Vt1 can be obtained.

Embodiment 4 Next, an electrostatic protection element and an electrostatic protection circuit (Embodiment 4) according to another embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 8, the electrostatic protection element and the electrostatic protection circuit of the fourth embodiment are different from the electrostatic protection element and the electrostatic protection circuit of the second embodiment to the ground without passing through the substrate resistance Rsub. In order to reduce the tunnel current 52 that flows, a high-concentration low-resistance layer 81 is formed in a p-type semiconductor substrate 51. The low resistance layer 81 is formed in a range where the tunnel current Im is guided to the base electrode B of the parasitic bipolar transistor 11. In other words, it is formed below the silicon oxide insulating film 32 and in a range from a spot outside a region surrounded by the trench 33 where a depletion layer is generated at the time of application to the base electrode B of the parasitic bipolar transistor 11 and immediately before the spot. It is. At this time, it is preferable that the low resistance layer 81 is not formed in a region where a depletion layer is generated at the time of application. Further, it is preferable that the low resistance layer 81 is not formed in the region of the substrate resistance Rsub. This is because the resistance value of the substrate resistance Rsub decreases, the voltage of the base electrode B hardly increases, and the trigger voltage Vt1 of the electrostatic protection circuit increases.

Low resistance layer 81 as a constituent element of the fourth embodiment
Is similarly applicable to the electrostatic protection element and the electrostatic protection circuit of the third embodiment, and reduces the tunnel current 62 flowing to the ground without passing through the substrate resistance Rsub.

Embodiment 5 Next, an electrostatic protection element and an electrostatic protection circuit (Embodiment 5) according to another embodiment of the present invention will be described with reference to FIG. As shown in FIG. 9, the electrostatic protection circuit according to the fifth embodiment includes:
An embodiment of the electrostatic protection circuit according to the eighth aspect of the present invention, wherein the parasitic bipolar transistor and the trigger element are arranged so that their adjacent areas increase. Trigger elements are arranged in a grid pattern and alternately.

In the electrostatic protection circuit according to the fifth embodiment,
Since the parasitic bipolar transistors are arranged on four sides of one trigger element, unnecessary tunnel current that does not flow into the base electrode B of the parasitic bipolar transistor is reduced. Conversely, since the trigger elements are arranged on four sides of one parasitic bipolar transistor, the trigger current flows into the base electrode B of the parasitic bipolar transistor, the trigger current flowing through the substrate resistance Rsub is increased, and the trigger voltage Vt1 of the electrostatic protection circuit is increased.
To reduce the voltage efficiently.

When the low resistance layer 81 is provided, a resistance layer branched toward the base electrodes B of four parasitic bipolar transistors adjacent to one trigger element is formed.

Embodiment 6 Next, an electrostatic protection element and an electrostatic protection circuit (Embodiment 6) according to another embodiment of the present invention will be described with reference to FIG. FIG. 10A is a configuration diagram, FIG. 10B is a current-voltage characteristic with respect to the reverse voltage, and FIG. 11A is a circuit diagram thereof. Parasitic bipolar transistor 11
In order to operate at a low voltage, it is necessary to raise its base potential quickly. For this purpose, one means is to increase the current Isub flowing into the substrate from the electrode D of the nMOSFET 11. Embodiment 6 As shown in FIG.
The electrostatic protection element and the electrostatic protection circuit according to the second embodiment are different from the electrostatic protection element and the electrostatic protection circuit according to the second embodiment in that a P + diffusion layer 6 serving as a substrate contact is formed near the outside of the trench 33. It is an element, and is an electrostatic protection circuit in which the P + diffusion layer 6 is connected to the gate electrode G by wiring, and then connected to the ground via the resistor R. That is, when static electricity is applied, a tunnel current flowing through the insulating film 2 of the capacitive element 3
Im is a P + diffusion layer 6 that becomes a substrate contact, and nMOS
A circuit is formed that flows to the ground via the gate electrode G of the FET 1 and the resistor R. Also in this case, the electrode S is directly dropped to the ground. That is, the resistance R
Is not connected between the electrode S and the ground as shown in FIGS. If a resistor R is connected between the electrode S and the ground, a large current flows from the electrode D to the electrode S, and the resistance becomes a resistance when discharging static electricity to the ground, and the charge generated by the static electricity cannot be discharged quickly. is there.

In the second and third embodiments, the base potential is increased by flowing the tunnel current Im to the substrate resistance Rsub. However, in the sixth embodiment, when static electricity is applied, the tunnel current Im flowing through the insulating film is transferred from the P + diffusion layer 6 serving as the substrate contact to the gate electrode G of the parasitic bipolar transistor 1, and
By flowing to the ground via the resistor R, the nMOS
This is to raise the potential of the gate electrode G of the FET 1 to trigger the parasitic bipolar transistor 11 at a low voltage.

FIG. 12 shows the gate voltage Vg of the MOSFET and the substrate current.
The current-voltage characteristics of Isub are shown. It is understood that when a voltage equal to or higher than the threshold voltage of the MOSFET is applied to the gate electrode G, the substrate current Isub sharply increases. Therefore, nMOSFET1
The potential of the gate electrode G is increased, and nM is applied to the gate electrode G.
When a voltage higher than the threshold voltage of the OSFET 1 is applied, the substrate current Isub sharply increases. Therefore, the base potential of the parasitic bipolar transistor 11 rises, and the parasitic bipolar transistor 11 is triggered at a low voltage. With such a mechanism, as shown by an arrow 93 in FIG. 10B, a lowering of the trigger voltage Vt1 of the electrostatic protection element can be obtained.

In the case of the electrostatic protection circuit according to the sixth embodiment, the voltage Vg corresponding to the voltage drop (= tunnel current Im × resistance R)
Is applied to the gate electrode G of the nMOSFET 1 and the gate voltage V
When g becomes equal to or higher than the threshold voltage of the nMOSFET 1, the substrate current Isub flowing through the substrate rapidly increases, the base electrode B of the parasitic bipolar transistor 11 rises due to a voltage drop, and the parasitic bipolar transistor 11 is triggered. Suppose nMOSF
When the threshold voltage of ET1 is 0.5V, the gate voltage
It is preferable to optimize the tunnel current Im and the resistance R such that Vg = Im × R is about 1 to 2 V.

In the case of the conventional electrostatic protection circuit composed only of nMOSFETs, the parasitic bipolar transistor 11 is triggered by Ir of only the reverse current. However, according to the electrostatic protection circuit of the sixth embodiment, as shown in FIG. 10B, by applying a voltage to the gate electrode G, it flows into the base electrode B of the parasitic bipolar transistor 11, and the substrate resistance Rsub. The substrate current Isub flowing can be increased, and the trigger voltage Vt1 of the electrostatic protection circuit can be reduced.

Seventh Embodiment Next, an electrostatic protection circuit (seventh embodiment) according to another embodiment of the present invention will be described with reference to FIG. FIG. 13 shows a configuration diagram thereof, and FIG. 11B shows a circuit diagram thereof. In the electrostatic protection circuit according to the sixth embodiment, the voltage Vg (= tunnel current Im × resistance R) corresponding to the voltage drop in the resistance R is nM
It is applied to the gate electrode G of OSFET1. However, at this time, if the ESD electrostatic pulse is large and the tunnel current Im flows too much, the gate voltage Vg increases, and there is a possibility that the gate insulating film 7 of the nMOSFET 1 may be broken down.
Therefore, it is effective to connect a protection circuit 5 that clamps the gate voltage Vg of the nMOSFET 1 to a level lower than the withstand voltage of the gate insulating film. As shown in FIG. 13, the electrostatic protection element and the electrostatic protection circuit according to the seventh embodiment are different from the electrostatic protection element and the electrostatic protection circuit according to the sixth embodiment in that the protection circuit 5 is connected to the gate electrode G.
And an electrostatic protection circuit connected between the ground and the ground. Also in the electrostatic protection circuit of the seventh embodiment, the voltage Vg (= tunnel current) corresponding to the voltage drop is similar to the electrostatic protection circuit of the sixth embodiment.
Im × resistance R) is applied to the gate electrode G of the nMOSFET 1, but when the gate voltage Vg becomes larger than necessary,
The protection circuit 5 operates, and clamps the gate voltage Vg to be equal to or lower than the withstand voltage of the gate insulating film 7. The protection circuit 5 may be a generally used clamp element. here,
The example is shown in which the gate electrode G of the nMOSFET 1 is connected to the ground. Generally, since the gate insulating film of the MOSFET in the input / output circuit is thicker than the gate insulating film in the internal circuit,
The clamp voltage of the protection circuit 5 used here may be smaller than the withstand voltage of the gate insulating film of the MOSFET of the input / output circuit.

As described above, according to the electrostatic protection circuit of the seventh embodiment, the ESD electrostatic pulse is large and the tunnel current I
Even when m flows excessively, dielectric breakdown of the gate insulating film 7 of the nMOSFET 1 can be prevented.

[0053]

According to the electrostatic protection element, the electrostatic protection circuit and the semiconductor device of the present invention, first, the trigger voltage of the electrostatic protection element can be efficiently reduced. Secondly, there is provided an economical electrostatic protection element and an electrostatic protection circuit which can use the existing electrostatic protection element manufacturing method or the electrostatic protection element manufactured by the method without any change. I was able to. Third, it was possible to provide an electrostatic protection element and an electrostatic protection circuit which are not damaged by the rise of the applied voltage. Fourth, by ensuring that the tunnel current flows as a trigger current into the base electrode or substrate resistance of the parasitic bipolar transistor,
Further, it is possible to provide an electrostatic protection element and an electrostatic protection circuit in which the trigger voltage is efficiently reduced. Fifth, by providing a wide variety of electrostatic protection elements and devising arrangements thereof, the number of ways of assembling the electrostatic protection circuit has expanded and the level of trigger voltage reduction has been infinite. It was made possible to select.

[Brief description of the drawings]

FIG. 1 is a configuration diagram (a) of a conventional electrostatic protection circuit and a current-voltage characteristic graph thereof.

FIG. 2 is a configuration diagram (a) of another conventional electrostatic protection circuit and a current-voltage characteristic graph thereof.

FIGS. 3A and 3B are a configuration diagram showing a capacitive element according to the first embodiment of the present invention and a current-voltage characteristic graph thereof; FIGS.

FIGS. 4A and 4B are band diagrams (a) and (b) showing characteristics of a capacitive element according to a third aspect of the present invention.

5A is a configuration diagram showing an electrostatic protection element and an electrostatic protection circuit according to a second embodiment of the present invention, and FIG. 5B is a current-voltage characteristic graph thereof.

6A is a configuration diagram showing an electrostatic protection element and an electrostatic protection circuit according to a third embodiment of the present invention, and FIG. 6B is a current-voltage characteristic graph thereof.

7A is a circuit diagram showing an equivalent circuit of a conventional electrostatic protection circuit, FIG. 7B is a circuit diagram showing an equivalent circuit of another conventional electrostatic protection circuit, and FIG. Circuit diagram (c) showing an equivalent circuit of the electrostatic protection circuit and Embodiment 3 of the present invention
FIG. 3D is a circuit diagram illustrating an equivalent circuit of the electrostatic protection circuit of FIG. Reference numeral 71 denotes a MOS element.

FIG. 8 is a configuration diagram illustrating an electrostatic protection element and an electrostatic protection circuit according to a fourth embodiment of the present invention.

FIG. 9 is an element array diagram showing an electrostatic protection circuit according to a fifth embodiment of the present invention.

10A is a configuration diagram showing an electrostatic protection element and an electrostatic protection circuit according to a sixth embodiment of the present invention, and FIG. 10B is a current-voltage characteristic graph thereof.

11A is a circuit diagram showing an equivalent circuit of the electrostatic protection circuit according to the sixth embodiment of the present invention, and FIG. 11B is a circuit diagram showing an equivalent circuit of the electrostatic protection circuit according to the seventh embodiment.

FIG. 12 is a graph showing current-voltage characteristics of a MOSFET gate voltage Vg and a substrate current Isub.

FIG. 13 is a configuration diagram illustrating an electrostatic protection element and an electrostatic protection circuit according to a seventh embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 nMOSFET 2 lateral thyristor 11, 21 npn-type parasitic bipolar transistor Rsub substrate resistance Rnw Resistance in n-well region 12, 22, 34, 51, 61 p-type semiconductor substrate 3 capacitance element 31 of the present invention 31 gate electrode 32 silicon Oxide insulating film 33 Reverse current of trench Ir n + p junction Im tunnel current If forward current of n + p junction 41 Inversion layer 42 Depletion layer 5 Protection circuit such as clamp element 81 Low resistance layer

Continued on front page F term (reference) 5F038 AC03 AC14 BH01 BH02 BH03 BH04 BH05 BH06 BH07 BH13 EZ04 EZ20 5F040 DA00 DA23 DA24 DB01 DB06 DB09 DB10 EB17 5F048 AA02 AB06 AB07 AC10 CC01 CC05 CC06 CC08 CC15 CC16

Claims (11)

[Claims] 1. An electrostatic protection element comprising: a parasitic bipolar transistor; and a trigger element for injecting a charge generated by static electricity into a base region of the parasitic bipolar transistor. 2. The device according to claim 1, wherein the trigger element has an insulating film, and charges generated by static electricity pass through the insulating film by a tunnel effect and are injected into a base region of the parasitic bipolar transistor. 3. The electrostatic protection element according to claim 1. 3. A capacitor comprising a gate electrode provided on a semiconductor substrate via a gate insulating film, and an element isolation layer formed on the semiconductor substrate around the gate electrode. 4. The capacitive element according to claim 3, wherein a low resistance layer is formed in the semiconductor substrate. 5. The capacitive element according to claim 3, wherein a diode is connected to the gate electrode in parallel. 6. The electrostatic protection according to claim 1, wherein one or more of the capacitive elements according to claim 3 is used as the trigger element. element. 7. A MIS field-effect transistor, one or more of the capacitive elements according to claim 3, and a contact formed at a position outside an element isolation layer of the capacitive element. A resistance element having one end connected to the ground by wiring, and the other end connected by wiring to the contact layer and the gate electrode of the MIS field-effect transistor. 8. The semiconductor device according to claim 7, further comprising a clamp element for holding a voltage applied to the gate electrode by a voltage drop of the resistance element to be equal to or less than a withstand voltage of a gate insulating film of the MIS field-effect transistor. An electrostatic protection circuit as described. 9. An electrostatic protection circuit to which one or two or more of the electrostatic protection elements according to claim 1, 2 and 6 are applied. 10. The electrostatic protection circuit according to claim 9, wherein the parasitic bipolar transistor and the trigger element are arranged so that their adjacent areas increase. 11. A semiconductor device incorporating the electrostatic protection circuit according to any one of claims 7 to 10.