JPS61190973A - Electrostatic breakdown preventive element - Google Patents

Abstract

PURPOSE:To operate the titled element positively at high speed with a comparatively small layout area while inhibiting the increase of input capacitance at a minimum by forming two bipolar-transistor sections sharing a collector region into the same semiconductor island. CONSTITUTION:When high-voltage pulses +Vp having plus polarity are applied to an external input terminal Pin, a thyristor by two bipolar-transistors Q1 and Q2 is shaped equivalently. When the high-voltage pulses +Vp exceeds a predetermined threshold (+ several hundred V), a potential difference is generated between a base and an emitter in Q2 because currents +Ic flow through base pinch resistors R1, R2, thus generating a positive feedback between Q1 and Q2, then triggering the thyristor. Accordingly, high-voltage pulses +Vp is clamped, thus protecting an internal circuit 10 from a breakdown.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to electrostatic breakdown prevention element technology and technology that is particularly effective when applied to microfabricated semiconductor integrated circuit devices, such as C-MOS type or The present invention relates to a technique effective for use in high-speed Schottky semiconductor integrated circuit devices.

[Background technology]

For example, microfabricated C-MOS type or high-speed key type semiconductor integrated circuit devices require so-called electrostatic damage prevention elements to protect their internal circuits from high voltage pulses such as static electricity. It's coming.

Regarding this electrostatic damage prevention element, for example, "Integrated Circuit Engineering (2)" published by Corona Publishing Co., Ltd., co-authored by Hisayoshi Yanai and Minoru Nagata, 147
．． It is described on page 148.

However, this type of electrostatic damage prevention element is generally large in size, and in miniaturized semiconductor integrated circuit devices, the electrostatic damage prevention element occupies an unreasonably large amount of the limited layout area. Furthermore, the inventors have found that there is a problem in that the electrostatic breakdown prevention element causes disadvantages such as, for example, significantly increasing input capacitance.

[Purpose of the invention]

An object of the present invention is to provide an electrostatic breakdown prevention element technology that can operate reliably and at high speed with a relatively small layout area, and can minimize an increase in input capacitance.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief description of typical inventions disclosed in this application is as follows.

In other words, by forming two bipolar transistor sections that share the same semiconductor island pressure collector region, it is possible to operate reliably and at high speed with a relatively small layout area, and to minimize the increase in input capacitance. It achieves the purpose of making it possible to hold down.

[Embodiments] Hereinafter, typical embodiments of the present invention will be described with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows an embodiment of the electrostatic damage prevention element according to the present invention, and FIG. 2 shows a planar layout of the electrostatic damage prevention element shown in FIG.

The electrostatic damage prevention device shown in FIGS. 1 and 2 is connected to an external input terminal pin Pin and an internal circuit 1 of a semiconductor integrated circuit device.
0 protects the internal circuit 10 from high voltage pulses caused by static electricity or the like. First, the semiconductor integrated enclosure device in which this electrostatic damage prevention element is formed includes:
A semiconductor substrate is used in which a p-type semiconductor substrate I, which is a second conductivity type, and an n-type silicon epitaxial layer 2, which is a first conductivity type, are formed. An n+ type buried layer 3 is formed between the p- type semiconductor substrate 1 and the n- type silicon epitaxial layer 11i20. The electrostatic breakdown prevention element consists of an island of the same p-type semiconductor, that is, an n-type semiconductor surrounded by isolation regions (not shown).
Two islands of p-type base diffusion layers 4a and 4b are formed within the island of - type silicon epitaxial layer 2, and furthermore, two islands of p-type base diffusion layers 4a and 4b are formed within the island of each p-type base diffusion #4a and 4b, respectively. form an island. Then, the island of one p-type base diffusion layer 4a and the island of the n+ type emitter diffusion layer 5a formed in this p-type base diffusion layer 4a are commonly connected to each other to connect the external input terminal pin Pin and the internal circuit 10. and the other p-type base diffusion layer 4
b island and n+ formed in this p-type base diffusion layer 4b.
It is constructed by commonly connecting the islands of the type emitter diffusion layer 5b and connecting them to a constant potential (ground potential GND).

Here, the internal circuit 10 has a minimum dimension of 1 to 3 μm, for example.
Circuits using highly miniaturized MOS or bipolar elements such as these are formed at high density.

Also, 7a, 7b, 8a, 8b, 9a, 9M! Although electrodes are shown, electrodes 9a and 9b are not connected to anything and are open. 6 indicates an oxide film on the surface.

Note that VCC indicates a power supply potential.

As described above, an electrostatic breakdown prevention element having the functions and effects described below is formed as if by two bipolar transistors sharing a transistor region in the same semiconductor.

3 and 4 show equivalent circuits of the electrostatic breakdown prevention device shown in FIGS. 1 and 2. FIG.

First, when a high voltage pulse +Vp of positive polarity is applied to the external input terminal pin Pin K, a thyristor is equivalently formed by two bipolar transistors Q1 and Q2 as shown at 5 in FIG. Then, when the high voltage pulse +Vp exceeds the required threshold (+several hundred V),
+Ic caused by this high voltage pulse +VpK flows through the pace pinch resistor R1°R2, resulting in a Km level difference between the pace emitter of Q2, which causes positive feedback between Ql and Q2, triggering the thyristor. Ru. As a result, the high voltage pulse +Vp applied to the external input terminal pin Pin is clamped, and the internal circuit 10 is protected from destruction. After this, when Vp drops to a sufficiently safe voltage, the potential difference between the base and emitter of Q1 and Q2 decreases, and the positive feedback state of Ql and Q2 is released, which causes the external input terminal pin Pin and the internal circuit 10 to It becomes substantially separated from the electrostatic breakdown prevention element.

Note that R3 is the n- type silicon epitaxial tank 2 and the n+
The resistance due to the mold buried layer 3 is shown.

Next, when a negative polarity high voltage pulse -Vp is applied to the external input terminal pin Pin, 5K is applied as shown in FIG.
, a thyristor is formed isometrically by two bipolar transistors Q1 and Q3. In this case as well, this high voltage pulse -Vp is set to a predetermined threshold °C/value (-several hundred ■)
When the voltage exceeds -Ic caused by this high voltage pulse -Vp, it flows through the base pinch resistors R2 and R1, creating a potential difference between the base and emitter of Q3, which causes positive feedback between Ql and Q3, resulting in the above-mentioned Thyristor is triggered. As a result, the high voltage pulse -Vp applied to the external input terminal pin Pin is clamped, and the internal circuit 10 is protected from destruction. After that, as in the case above, when Vp drops to a safe voltage, the potential difference between the base and emitter of Q3 drops and the positive feedback state of Ql and Q3 is released, which causes the external input terminal pin Pin and the internal The circuit 10 becomes substantially disconnected from the electrostatic discharge protection device.

As described above, the internal circuit 10 is reliably protected from high voltage pulses of both positive and negative polarities +Vpe -Vp by using a configuration similar to that of forming two bipolar transistor sections sharing a collector region within the same semiconductor island. It is now possible to protect it. In this way, since the structure is essentially just forming two piebaler e transistor parts, K is very suitable for microfabrication. Accordingly, an increase in the input capacitance parasitic to the external input terminal pin Pin can also be suppressed to a minimum. Furthermore, two bipolar transistors Ql, Q2 or QteQ
A sufficiently high operating speed can be obtained by the mutual positive feedback operation of 3.

Further, in the embodiment shown in FIGS. 1 and 2, open electrodes 9a and 9b, which are not connected to anything, are connected to portions of the n+ type emitter diffusion layers 5a and 5b that face each other on the inside.
This averages the current distribution between the p-type base diffusion layers 4a and 4b, greatly increasing the allowable current capacity of Ql formed in the lateral direction, and absorbing the energy of high voltage pulses. It is now possible to obtain a large capacity.

FIG. 5 shows another embodiment of the invention.

In the embodiment shown in the same figure, two of the above-mentioned electrostatic damage prevention elements are used.
The constant potential source for one of the electrostatic breakdown prevention elements 20 is constant potential ■. . At the same time, the constant potential source of the other electrostatic breakdown prevention element 30 is determined to be the ground potential GND. From this K, protection characteristics with better symmetry can be obtained against high voltage pulses of either positive or negative polarity. [Effects] (11 Sharing the collector region within the same semiconductor island
A structure similar to that of forming two bipolar transistor sections has the effect that the internal circuit can be reliably protected from high voltage pulses caused by static electricity.

(2) Furthermore, since the structure is essentially just forming two bipolar transistor sections, it is very convenient for microfabrication.

(3) Furthermore, miniaturization has the effect of minimizing the increase in input capacitance parasitic to external input terminal pins.

(4) Furthermore, since the operation is performed by the mutual positive feedback operation of the two bipolar transistors, it is possible to obtain the effect that a sufficiently high operation speed can be obtained.

Although the invention made by the present inventor has been specifically explained above based on examples, it is understood that this invention is not limited to the above-mentioned examples and can be modified in various ways without departing from the gist thereof. Not even.

[Application field]

As mentioned above, the input protection a! Although the description has been made regarding the case where the present invention is applied to a luminous technique, the present invention is not limited thereto, and can also be applied to, for example, a protection technique on the output side.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing one embodiment of the electrostatic breakdown prevention element according to the present invention, Figure 2 is a diagram showing the planar layout of Figure 1, and Figure 3 is when a positive high voltage pulse is applied. 4 is an equivalent circuit diagram when a negative high voltage pulse is applied. FIG. 5 is an equivalent circuit diagram showing another embodiment of this invention. Pin...external input terminal Pin, 10...internal circuit,
4a, 4b-p type base diffusion layer, 5a, 5b-n+ type emitter diffusion layer, +v p, -V p... high voltage pulse due to static electricity, etc., 1... p- base semiconductor substrate 1.2
...nW silicon epitaxial 152.3...
n+ type buried layer 3, Ql, Q2. Q3... Bipolar transistor that makes up Cyrisk.

Claims (1)

[Claims] 1. An electrostatic breakdown prevention element interposed between an external terminal pin and an internal circuit of a semiconductor integrated circuit device, which comprises two islands of a second conductivity type within an island of a first conductivity type semiconductor. Furthermore, an island of the first conductivity type is formed within each island of the second conductivity type, and one island of the second conductivity type and a first conductivity type island formed within this island are formed.
The islands of the second conductivity type are commonly connected to each other and connected in parallel between the external terminal pin and the internal circuit, and the other island of the second conductivity type and the island of the first conductivity type formed within this island are connected in common to each other. An electrostatic breakdown prevention element characterized by being connected to a constant potential. 2. The electrostatic breakdown prevention element according to claim 1, wherein the constant potential is a ground potential or a power supply potential.