JP2015029103A - Esd protection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ESD protection element having improved ESD resistance.SOLUTION: An ESD protection element is provided with: a bipolar transistor including a collector diffusion layer 7, which is connected to a first terminal Pad, and an emitter terminal E1i; and a current control resistor R1i that is provided on each of a plurality of current paths from a second terminal GND to the collector diffusion layer 7 through an emitter diffusion layer 4.

Description

  The present invention relates to an ESD protection element for protecting an internal circuit from electrostatic discharge (ESD), and more particularly to an ESD protection element using a bipolar transistor.

  In recent years, there has been a demand for improvement in reliability of semiconductor integrated circuits (ICs) used in various fields. For example, high reliability is particularly required for an IC used for a product that affects human life when a failure occurs, such as a driver circuit for an in-vehicle car navigation system or a medical liquid crystal monitor. In order to realize such high reliability of the product, it is necessary to make it strong against external overvoltage (electrostatic discharge). That is, an IC having a high ESD tolerance is demanded.

  In order to enhance ESD tolerance of LSI (Large Scale Integration), a protection element (ESD protection element) against ESD is provided between the internal circuit of the LSI chip and the outside (input / output pad). The ESD protection element changes the path of surge current generated by electrostatic discharge (ESD) and prevents the internal circuit of the LSI from being destroyed.

  Generally, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), bipolar transistors, and thyristors are used as ESD protection elements. For example, ESD protection elements using NPN bipolar transistors include “ESD Protection Connections in Advanced High-Voltage Technologies for Automotive” (see Non-Patent Document 1), IEEE JOURNAL OF SOLITUL SILID-STOLIRS. 40, NO. 8, P.I. 1751 AUGUST 2005 (see Non-Patent Document 2).

“ESD Protection Connections in Advanced High-Voltage Technologies for Automotive”, EOS / ESD SYMPOSIUM 2006, P.A. 54 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 40, NO. 8, P.I. 1751 AUGUST 2005

  With reference to FIGS. 1 to 3, a conventional ESD protection device using a bipolar transistor will be described. FIG. 1 is a cross-sectional view taken along the line A-A ′ of FIG. FIG. 2 is a plan view showing a structure of a conventional ESD protection element. FIG. 3 is a diagram showing an equivalent circuit of an ESD protection element according to the prior art.

Referring to FIG. 1, ESD protection device according to the prior art, P-type substrate 101 in the Z-axis direction lower (P-sub), N-type buried layer 102 (NBL) is formed, N in the Z-axis direction upper ^- A collector region 103 and an N-type lead region 105 are formed. A P ⁻ base region 104 that functions as a base region is formed in an upper layer in the Z-axis direction of the N ⁻ collector region 103. On the P ⁻ base region 104, a high concentration P type diffusion layer 87 (hereinafter referred to as P ⁺ base diffusion layer 87) and a contact 84 functioning as a base terminal B20, and a high concentration N type diffusion layer functioning as an emitter terminal E10. 88 (hereinafter referred to as an N ⁺ emitter diffusion layer 88) and a contact 85 are provided. On the N-type extraction region 105, a high-concentration N-type diffusion layer 89 (hereinafter referred to as N ⁺ collector diffusion layer 89) and a contact 86 functioning as the collector terminal C10 are provided. The P ⁺ base diffusion layer 87, the N ⁺ emitter diffusion layer 88, and the N ⁺ collector diffusion layer 89 are separated by the element isolation region 106.

Referring to FIG. 2, P ⁺ base diffusion layer 87 is connected to grounded metal wiring 81 through a plurality of contacts 84 provided in the base width W direction (Y-axis direction). The N ⁺ emitter diffusion layer 88 is connected to the grounded metal wiring 81 through a plurality of contacts 85 provided in the base width W direction (Y-axis direction). Similarly, the N ⁺ collector diffusion layer 89 is connected to a pad (Pad) via a plurality of contacts 86 and metal wirings 82 provided in the base width W direction (Y-axis direction). The pad is connected to an internal circuit (not shown).

Referring to FIGS. 1 to 3, in P-type well 104 functioning as a base, a region immediately below N ⁺ emitter diffusion layer 88 is defined as base region B10. Initially, when a high voltage due to ESD is applied to the pad, breakdown occurs at the junction between the base region B10 and the collector terminal C10, and holes generated near the junction flow to the base terminal B20 and are generated near the junction. Electrons flow to the collector terminal C10. At this time, the voltage drop due to the parasitic resistance R _B between the base region B10 and the base terminal B20, the voltage of the base region B10 (base potential) increases. When the base potential rises, the diode formed between the emitter terminal E10 and the base region B10 is turned on, and a surge current due to ESD starts to flow between the collector terminal C10 and the emitter terminal E10. Thereby, it is possible to prevent a surge current due to ESD from flowing to the internal circuit.

  When an ESD surge current flows from the collector terminal C10 of the bipolar transistor to the emitter terminal E10, it exists in a depletion layer that occurs in the junction breakdown region (near the junction region between the collector and the base, or near the collector buried layer and the base boundary). Heat is generated by the electric field generated and current caused by electrons flowing from the emitter terminal E10 into the depletion layer, and the temperature of the current path rises. On the other hand, since a plurality of contacts 85 and 86 are arranged in the base width W direction (Y-axis direction shown in FIG. 2), there are a plurality of current paths between the collector and the emitter. The current amounts of the plurality of current paths are not uniform and vary in the base width W direction (Y-axis direction). That is, a region where a surge current flowing between the collector and the emitter is large and a region where the surge current is small appear. In a region where the amount of current is large, the temperature is higher than that in a region where the amount of current is small, so that carriers increase and resistance decreases, and a larger current flows. For example, referring to FIG. 2, a surge current larger than that in other regions flows in a region where the amount of current and the temperature rise locally. As described above, when the current is locally concentrated, the region easily breaks down and causes a reduction in the ESD resistance of the entire ESD protection device.

  As described above, the ESD protection element according to the prior art has a reduced ESD tolerance because the element breakdown occurs due to current concentration (thermal runaway) caused by current density fluctuation in the base width W direction (Y-axis direction). .

  [Means for Solving the Problems] will be described below by using the numbers and symbols used in [Mode for Carrying Out the Invention] in parentheses. The numbers and symbols are added to clarify the correspondence between the description of [Claims] and the description of [Mode for Carrying Out the Invention]. [Claims] It should not be used for the interpretation of the technical scope of the invention described in.

  The ESD (Electrostatic Discharge) protection element according to the present invention is an ESD protection element using a bipolar transistor. The bipolar transistor includes a collector diffusion layer (7) connected to the first terminal (Pad) and an emitter terminal, and a collector diffusion layer (from the second terminal (GND) through the emitter diffusion layer (4)). 7) and a current control resistor (11) provided on each of the plurality of current paths.

  In this way, the current path between the emitter diffusion layer (4) and the second terminal to which the ESD surge is applied is separated, and the current control resistor (11) is disposed on each path. As a result, current concentration caused by fluctuations in the current density of the surge current flowing into the emitter diffusion layer (4) is suppressed, and the ESD tolerance that has been reduced in the prior art is improved.

  According to the ESD protection element of the present invention, the ESD tolerance can be improved.

FIG. 1 is a cross-sectional view taken along the line A-A ′ of FIG. FIG. 2 is a plan view showing a structure of a conventional ESD protection element. FIG. 3 is a diagram showing an equivalent circuit of an ESD protection element according to the prior art. FIG. 4 is a plan view showing the structure of the ESD protection element according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view taken along the line B-B ′ in FIG. 4 showing the structure of the ESD protection element according to the first embodiment of the present invention. FIG. 6 is a diagram showing an equivalent circuit in the first embodiment of the ESD protection element according to the present invention. FIG. 7 is a plan view showing the structure of the ESD protection element according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view taken along the line C-C ′ in FIG. 7 showing the structure of the ESD protection element according to the second embodiment of the present invention. FIG. 9 is a diagram showing an equivalent circuit in the second embodiment of the ESD protection element according to the present invention. FIG. 10 is a plan view showing the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 11 is a cross-sectional view taken along the line D-D ′ in FIG. 10 showing the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 12 is a diagram showing an equivalent circuit in the third embodiment of the ESD protection element according to the present invention. FIG. 13 is a plan view showing a modification of the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 14 is a cross-sectional view taken along line E-E ′ in FIG. 13 showing a modification of the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 15 is a plan view showing the structure of the ESD protection element according to the fourth embodiment of the present invention. 16 is a cross-sectional view taken along the line H-H ′ in FIG. 15 showing the structure of the ESD protection element according to the fourth embodiment of the present invention. FIG. 17 is a diagram showing an equivalent circuit in the fourth to seventh embodiments of the ESD protection element according to the present invention. FIG. 18 is a plan view showing the structure of the ESD protection element according to the fifth embodiment of the present invention. FIG. 19 is a cross-sectional view taken along the line I-I ′ in FIG. 18 showing the structure of the ESD protection element according to the fifth embodiment of the present invention. FIG. 20 is a plan view showing the structure of the ESD protection element according to the sixth embodiment of the present invention. 21 is a cross-sectional view taken along the line J-J ′ in FIG. 20 showing the structure of the ESD protection element according to the sixth embodiment of the present invention. FIG. 22 is a plan view showing the structure of the ESD protection element according to the seventh embodiment of the present invention. FIG. 23 is a plan view showing a modification of the seventh embodiment of the ESD protection element according to the present invention. FIG. 24 is a plan view showing a modified example of the configuration of the ESD protection element according to the fourth embodiment of the present invention. FIG. 25 is a cross-sectional view showing the structure of the ESD protection element according to the eighth embodiment of the present invention. FIG. 26 is a cross-sectional view showing the structure of the ESD protection element according to the ninth embodiment of the present invention. FIG. 27 is a plan view showing the structure of a modified example of the third embodiment of the ESD protection element according to the present invention. FIG. 28 is a plan view showing the structure of a variation of the ESD protection element shown in FIG. 29 is a cross-sectional view taken along the line I-I ′ in FIG. 28. FIG. 30 is a plan view showing a structure in another modification of the third embodiment.

  Hereinafter, an embodiment of an ESD protection element according to the present invention will be described with reference to the accompanying drawings. In the present embodiment, an ESD protection element using a bipolar transistor for preventing ESD damage to an internal circuit (not shown) will be described.

1. First Embodiment With reference to FIGS. 4 to 6, the configuration and operation of an ESD protection element according to a first embodiment of the present invention will be described. FIG. 4 is a plan view showing the structure of the ESD protection element according to the first embodiment of the present invention. 5 is a cross-sectional view taken along the line BB ′ in FIG. 4 showing the structure of the ESD protection element according to the first embodiment of the present invention. FIG. 6 is a diagram showing an equivalent circuit in the first embodiment of the ESD protection element according to the present invention.

Referring to FIG. 4, the ESD protection element in the first embodiment functions as a high-concentration P-type diffusion layer 1 (hereinafter referred to as P ⁺ base diffusion layer 1) that functions as a base of a bipolar transistor, and as an emitter. High concentration N type diffusion layer 4 (hereinafter referred to as N ⁺ emitter diffusion layer 4) and N ⁺ diffusion layer 7 (hereinafter referred to as N ⁺ collector diffusion layer 7) functioning as a collector.

The P ⁺ base diffusion layer 1 is connected to a common metal wiring 3 through a plurality of contacts 2 provided along the base width W direction (Y-axis direction). The metal wiring 3 is connected to a power supply (GND) via a resistor R2. Thereby, the plurality of contacts 2 function as the base terminal B1 grounded via the common resistor R2.

The N ⁺ emitter diffusion layer 4 is connected to a plurality of metal wirings 6 via a plurality of contacts 5 provided along the base width W direction (Y-axis direction). The plurality of metal wirings 6 are connected to one end of a plurality of current control resistors 11 (R11 to R1n) via a plurality of contacts 10. The other ends of the plurality of current control resistors 11 (R11 to R1n) are connected to a common metal wiring 13 through a plurality of contacts 12. The metal wiring 13 is connected to a power source (GND). Thus, the plurality of contacts 5 function as emitter terminals E11 to E1n that are grounded via different current control resistors 11 (R11 to R1n). The current control resistor 11 is preferably made of, for example, polysilicon or a diffusion layer.

The N ⁺ collector diffusion layer 7 is connected to a pad (Pad) via a plurality of contacts 8 and a metal wiring 9 provided along the base width W direction (Y-axis direction). The pad is connected to an internal circuit (not shown). Thereby, the plurality of contacts 8 function as collector terminals C1 commonly connected to the pads.

Each of the P ⁺ base diffusion layer 1 and the N ⁺ emitter diffusion layer 4 in the first embodiment is continuously formed in the base width W direction (Y-axis direction).

FIG. 5 is a view showing a cross-sectional structure taken along the line BB ′ of the ESD element shown in FIG. However, in FIG. 5, the structure of the wiring layer is omitted. Referring to FIG. 5, in the ESD protection element in the first embodiment, a P-type substrate 201 (P-sub) and an N-type buried layer 202 are formed in order from the lower layer in the Z-axis direction, and the N-type buried layer 202 is formed. N-type extraction regions 205 and 206 and an N ⁻ collector region 203 are formed thereon. The N ⁻ collector region 203 is formed between the N-type extraction region 205 and the N-type extraction region 206, and a P ⁻ base region 204 that functions as a base region is formed in an upper layer in the Z-axis direction.

On the P ⁻ base region 204, a P ⁺ base diffusion layer 1 and a contact 2 functioning as a base terminal B1, and a high-concentration N-type diffusion layer 4 functioning as an emitter terminal E1i (hereinafter referred to as N ⁺ emitter diffusion layer 4). And a contact 5 are provided. On the N-type lead region 205, a high-concentration N-type diffusion layer 7 (hereinafter referred to as N ⁺ collector diffusion layer 7) and a contact 8 functioning as the collector terminal C1 are provided. Further, a high concentration N-type diffusion layer 207 is provided on the N-type extraction region 206. The N ⁺ diffusion layer 207, the P ⁺ base diffusion layer 1, the N ⁺ emitter diffusion layer 4, and the N ⁺ collector diffusion layer 7 are separated by an element isolation region 208 (for example, an oxide insulating film).

The base terminal B1 is connected to the resistor R2 through the common metal wiring 3 together with other base terminals B1 (P ⁺ base diffusion layer 1 and contact 2) provided on the same P ⁺ base diffusion layer 1. Similarly, the collector terminal C1 is connected to the pad via the common metal wiring 9 together with other collector terminals C1 (N ⁺ collector diffusion layer 7 and contact 8) provided on the same N-type lead region 205. . On the other hand, the emitter terminal E1i is connected to a metal wiring 6 and a current control resistor 11 which are different from other emitter terminals (N ⁺ emitter diffusion layer 4 and contact 5) provided on the same P ⁺ base diffusion layer 1.

When a high voltage is applied to the pad (Pad) and the junction between the P ⁻ base region 204 and the N ⁻ collector region 203 breaks down, the hole current generated by the breakdown is reduced to the base immediately below the emitter terminal E1i. It flows into the region (base region B2i) and flows out to the power source (GND) via the contact 2. At this time, the resistance component (resistance Rbi) of the base region (P ⁻ base region 204) extending from the base region B2i to the P ⁺ base diffusion layer 1 (base terminal B1i) raises the base potential (voltage of the base region B2i). Acts as a resistance.

  FIG. 6 is an equivalent circuit of this embodiment. In the equivalent circuit of FIG. 6, the ESD protection element is described as being composed of a plurality of bipolar transistors in order to appropriately explain the operation of this embodiment. Referring to FIG. 6, the ESD protection element in the first embodiment is composed of a plurality of NPN bipolar transformers having emitter terminals E11 to E1n, base regions B21 to B2n, and collector terminals C11 to C1n. .

Referring to FIGS. 4 and 6, emitter terminals E11 to E1n are arranged on a common N ⁺ emitter diffusion layer region and are connected by a diffusion layer resistance. Therefore, resistors RLe1 to RLen are formed by the N ⁺ emitter diffusion layer 4 between the emitter terminals E11 to E1n. Similarly, resistors RLb1 to RLbn are formed by the P ⁻ base region 204 between the base regions B21 to B2n which are regions immediately below the emitter terminals E11 to E1n. The collector terminals C11 to C1n are connected by a common N-type buried layer 202 and N-type lead-out regions 205 and 206. Therefore, resistors RLC1 to RLCn are formed by the N-type buried layer 202 and the N-type lead regions 205 and 206 between the collector terminals C11 to C1n. Further, resistors Rb1 to Rbn are formed by the P ⁻ base region 204 between the base regions B21 to B2n and the nearest base terminals B11 to B1n, respectively.

  As described above, the plurality of transistors are separated from each other by the resistors RLC1 to RLCn, the resistors RLb1 to RLbn, and the resistors RLe1 to RLen. Thereby, current paths of surge currents flowing through the plurality of transistors are separated from each other. Further, current adjustment resistors R11 to R1n are connected to the emitter terminals E11 to E1n, respectively. From the above, since the current (surge current) due to electrons flowing from the power supply (GND) flows in a distributed manner in the current adjustment resistors R11 to R1n, current concentration on the specific emitter terminal E1i can be avoided.

  Next, the operation of the ESD protection element in the first embodiment will be described.

Initially, when a high voltage pulse due to ESD is applied to the pad, the potentials of the N ⁺ collector diffusion layer 7 and the N-type extraction region 205 rapidly increase. At this time, the junction between the P ⁻ base region 204 and the N ⁻ collector region 203 breaks down, and the hole current generated by the breakdown is supplied from the collector terminals C11 to C1n through the base terminals B11 to B1n and the resistor R2. Here, it flows to GND). Then, the voltage (base potential) of the base regions B21 to B2n increases due to the voltage drop due to the resistor R2 and the resistors Rb1 to Rbn. When the base potential rises, the diode formed between the N ⁺ emitter diffusion layer 4 and the P ⁻ base region 204 is turned on, and electrons are emitted from the emitter terminals E1i to E1n, the collector terminals C11 to C1n, and the current control resistor 11. By flowing between the power supply (GND) and the pad (Pad) via (R1i to R1n), a current (surge current) due to ESD starts to flow. Thereby, it is possible to prevent a surge current due to ESD from flowing to the internal circuit.

When an ESD surge current flows from the collector terminals C11 to C1n of the bipolar transistor to the emitter terminal E1i, it exists in a depletion layer generated in the junction breakdown region (near the boundary between the P ^- base region 204 and the collector-side N ^- collector region 203). Generated and the electron current flowing from the emitter terminal E1i into the depletion layer generates heat, and the temperature of the current path (especially the depletion layer region having a high electric field) rises. On the other hand, since the contacts 5 and 8 are arranged in the base width W direction (Y-axis direction) as in the conventional case, there are a plurality of current paths between the collector and the emitter. In general, there is no guarantee that the current amount of each of the plurality of current paths is uniform, and there is variation in the base width W direction (Y-axis direction).

  In the present invention, the current path from the contact 5 forming the emitter terminals E11 to E1n to the power supply (GND) is separated by the plurality of metal wirings 6, and the current control resistor 11 exists on each path. For this reason, local increase (concentration) of the current flowing from the emitter to the collector terminals C11 to C1n can be suppressed. In the present invention, the current between the emitter terminals E11 to E1n and the collector terminals C11 to C1n is suppressed by the voltage drop caused by the current control resistor 11 (R11 to R1n). The amount is also suppressed. For example, when the surge current from the collector terminals C11 to C1n to the emitter terminal E1i is concentrated, the amount of current between the emitter terminal E1i and the collector terminals C11 to C1n increases locally, but the voltage drop due to the current control resistor R1i Therefore, the amount of current is suppressed. Accordingly, the current flowing from the collector terminals C11 to C1n flows to the collector terminals C11 to C1n via another emitter terminal different from the emitter terminal E1i where the current concentration should have occurred without the current control resistor R1i. Start. As a result, the amount of current flowing between the collector terminals C11 to C1n and the emitters E11 to E1n is made uniform.

  As described above, in the present invention, the current paths between each of the plurality of emitter terminals E11 to E1n and the power supply (GND) are separated, and the current control resistor R11 is disposed on each path. Thereby, the current concentration resulting from the fluctuation of the current density in the base width W direction (Y-axis direction) is suppressed, and the ESD tolerance that has been reduced in the prior art can be improved.

2. Second Embodiment Although the base terminal of the ESD protection element in the first embodiment is grounded via the resistor R2 provided outside, the base terminal of the ESD protection element in the second embodiment Are grounded via current control resistors R11 to R1n. Below, the ESD protection element in 2nd Embodiment is demonstrated about a structure and operation | movement different from 1st Embodiment.

  With reference to FIGS. 7 to 9, the configuration and operation of the ESD protection element according to the second embodiment of the present invention will be described. FIG. 7 is a plan view showing the structure of the ESD protection element according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view taken along the line C-C ′ in FIG. 7 showing the structure of the ESD protection element according to the second embodiment of the present invention. However, in FIG. 8, the structure of the wiring layer is omitted. FIG. 9 is a diagram showing an equivalent circuit in the second embodiment of the ESD protection element according to the present invention.

Referring to FIG. 7, P ⁺ base diffusion layer 1 is connected to a plurality of metal wirings 15 through a plurality of contacts 14 provided along the base width W direction (Y-axis direction). The plurality of metal wirings 15 are connected to one ends of the plurality of current control resistors 11 (R11 to R1n) through the plurality of contacts 10. The other ends of the plurality of current control resistors 11 (R11 to R1n) are connected to a common metal wiring 13 through a plurality of contacts 12. The metal wiring 13 is connected to a power source (GND). Thus, the plurality of contacts 14 function as base terminals B11 to B1n that are grounded via different current control resistors 11 (R11 to R1n).

The N ⁺ emitter diffusion layer 4 is connected to a plurality of metal wirings 15 via a plurality of contacts 5 provided along the base width W direction (Y-axis direction). Thus, the plurality of contacts 5 function as emitter terminals E11 to E1n that are grounded via different current control resistors 11 (R11 to R1n).

Each of the P ⁺ base diffusion layer 1 and the N ⁺ emitter diffusion layer 4 in the second embodiment is formed continuously in the base width W direction (Y-axis direction) as in the first embodiment. .

FIG. 8 is a diagram showing a cross-sectional structure taken along the line CC ′ of the ESD element shown in FIG. Referring to FIG. 8, the ESD protection element according to the second embodiment functions as P ⁺ base diffusion layer 1 and contact 14 functioning as base terminal B1i and as emitter terminal E1i on P ⁻ base region 204. An N ⁺ emitter diffusion layer 4 and a contact 5 are provided. The base terminal B1i and the emitter terminal E1i are connected to a power source (GND) through a common metal wiring 15 and a current control resistor 11 (R1i). Other structures are the same as those in the first embodiment.

  As described above, in the ESD element in the second embodiment, the resistor R2 shown in the first embodiment is not used as a resistor for raising the base potential. In the second embodiment, since a resistance element (resistor R2) for performing a bipolar operation is not required, the circuit area can be reduced. In addition, since the wiring connecting the emitter terminals E11 to E1n and the current control resistors R11 to R1n is also used as a wiring for grounding the base, the circuit area can be further reduced.

  With the configuration as described above, the ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG. Referring to FIG. 9, in the second embodiment, base terminals B11 to B1n and emitter terminals E11 to 1n are connected to a power supply (GND) via common current adjustment resistors R11 to R1n, respectively. For example, the base terminal B11 and the emitter terminal E11 are grounded via the current adjustment resistor R11. Since other circuit configurations are the same as those of the first embodiment, description thereof will be omitted.

  Next, the operation of the ESD protection element in the second embodiment will be described.

Initially, when a high voltage pulse due to ESD is applied to the pad, the potentials of the N ⁺ collector diffusion layer 7 and the N-type extraction region 205 rapidly increase. At this time, the junction between the P ⁻ base region 204 and the N ⁻ collector region 203 breaks down, and the hole current generated by the breakdown flows into the P ⁻ base region 204, and the base terminals B 1 i to B 1 n and the current control resistor 11 ( R1i to R1n) flow to the power source (here, GND). And the voltage (base potential) of base terminal B2i-B2n rises by the voltage drop by resistance Rb1-Rbn. When the base potential rises, the diode formed between the N ⁺ emitter diffusion layer 4 and the P ⁻ base region 204 is turned on, and surge currents caused by ESD cause emitter terminals E11 to E1n, collector terminals C11 to C1n, and current. It starts to flow between the power supply (GND) and the pad (Pad) via the control resistor 11 (R1i). Thereby, it is possible to prevent a surge current due to ESD from flowing to the internal circuit.

  Since a plurality of base terminals B11 to B1n and collector terminals C11 to C1n are arranged in the base width W direction (Y-axis direction), there are a plurality of regions that can serve as a current path between the collector and the base. On the other hand, breakdown may occur locally due to process variations and three-dimensional layout effects. For this reason, junction breakdown due to ESD occurs locally or in a wide area. Comparing the amount of current generated in the breakdown when the breakdown occurs locally and in the wide area, the current when the breakdown occurs is more than the amount of current when the breakdown occurs locally Become more. For this reason, when there is a common resistor R2 in addition to the resistors Rb1 to Rbn in the current path between the base terminals B11 to B1n and the power supply (GND) as in the first embodiment, a breakdown occurrence region As a result, the amount of current flowing through the resistor R2 varies, and as a result, the amount of increase in the base potential varies depending on how breakdown occurs. In this case, if the breakdown generation region is small, the amount of increase in the base voltage is small. Therefore, unless the resistance R2 is increased, the ESD protection element cannot reliably perform the bipolar operation.

  In the second embodiment, even if breakdown occurs locally, the base current caused by the breakdown is caused by the resistors Rb1 to Rbn in the vicinity of the region where the breakdown occurs and the base resistance in the vicinity via the metal wiring 15. The current control resistor 11 connected. For this reason, when the current density of the base current is the same, the increase in the potential of the base is the same regardless of whether the breakdown range is wide or narrow. Therefore, in the ESD protection element according to the second embodiment, the bipolar operation is stably performed regardless of the size and position of the breakdown generation region. Therefore, the size of the current control resistor 11 used to raise the base potential is large. There is no need to increase the size.

When the resistance value for raising the base potential to perform a bipolar operation (the resistance value between the base regions B21 to B2n to the power supply (GND)) is increased, noise resistance may be reduced with respect to the base. Here, with reference to FIG. 5, a mechanism in which an operation failure due to noise occurs will be described. Since there is a parasitic junction capacitance (Ccb) between the collector (N-type buried layer 202) and the base (P ^- base region 204), when noise enters the collector, the current due to the noise is the junction capacitance (Ccb). Flows through the base to GND. At this time, the current due to the noise passes through the base resistor Rbi and the resistor R2, and causes a voltage drop to change the potential of the base B2i (base potential). The fluctuation value of the potential at the base B2i at this time is (current due to noise) × (R2 + Rbi), and increases as R2 increases. Further, the time during which the variation of the potential of the base B2i (base potential) at this time is determined by (R2 + Rbi) × Ccb. At this time, if the time for the base potential to become higher than the emitter potential due to noise is longer than the time necessary for the bipolar transistor to operate, the bipolar transistor becomes conductive. In order to avoid such bipolar operation due to noise, the size of the resistor R2 is reduced, and the delay of the voltage transmission time is a desired time determined from the time required for the operation of the bipolar transistor and the noise frequency. Must be smaller.

  In the second embodiment, it is not necessary to arrange the base-GND resistor R2 included in the ESD protection element of the first embodiment (FIGS. 4, 5, and 6). Bipolar operation due to can be avoided. That is, according to the ESD protection element in the second embodiment, not only the ESD tolerance but also the noise tolerance is improved.

3. Third Embodiment With reference to FIGS. 10 to 12, a third embodiment of the ESD protection element according to the present invention will be described. In the ESD protection element according to the first and second embodiments, the P ⁺ base diffusion layer 1 and the N ⁺ emitter diffusion layer 4 are continuously formed in the base width W direction (Y-axis direction). On the other hand, referring to FIG. 10 and FIG. 11, in the ESD protection element in the third embodiment, the P ⁺ base diffusion layer 16 forming the base terminal and the N ⁺ emitter diffusion layer 17 forming the emitter terminal are in contact with each other. Each region in which is formed is divided in the base width W direction (Y-axis direction). Hereinafter, the ESD protection element in the third embodiment will be described with respect to the configuration and operation different from those of the second embodiment.

  FIG. 10 is a plan view showing the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 11 is a cross-sectional view taken along the line D-D ′ in FIG. 10 showing the structure of the ESD protection element according to the third embodiment of the present invention. However, in FIG. 11, the structure of the wiring layer is omitted. FIG. 12 shows an equivalent circuit of the ESD protection element in the third embodiment.

Referring to FIG. 10, the ESD protection element in the third embodiment includes a plurality of P ⁺ base diffusion layers 16 separated by element isolation regions 208 arranged in the base width W direction (Y-axis direction). A plurality of N ⁺ emitter diffusion layers 17 are formed. Specifically, referring to FIG. 11, each of the plurality of N ⁺ emitter diffusion layers 17 is separated by element isolation region 208 and formed on P ⁻ base region 204 corresponding to each of the plurality of contacts 5. The Similarly, each of the plurality of P ⁺ base diffusion layers 16 is separated by the element isolation region 208 and formed on the P ⁻ base region 204 corresponding to each of the plurality of contacts 14. Other structures are the same as those of the second embodiment.

In the ESD protection element in the present embodiment, a plurality of P ⁺ base diffusion layers 16 and a plurality of N ⁺ emitter diffusion layers 17 corresponding to the plurality of contacts 5 and 14 and the metal wiring 15 (current path of surge current) are formed. ing. Since the plurality of P ⁺ base diffusion layers 16 and N ⁺ emitter diffusion layers 17 are separated in the base width W direction (Y-axis direction), the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion from which the surge current is separated are separated. It does not concentrate in one place through the layer 16. When the P ⁺ base diffusion layer and the N ⁺ emitter diffusion layer are not separated in the base width W direction (Y-axis direction) as in the second embodiment, the current flows to the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion. The current may be concentrated at a specific location through the layer 16 and the device may be destroyed. However, in this embodiment, since the region that can be a current path is isolated by the element isolation region 208, local bias in temperature rise and other factors that promote current concentration are suppressed. Concentration of current at a specific location is suppressed.

  With the configuration as described above, the ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG. Referring to FIG. 12, the third embodiment is an equivalent circuit in which resistors RLe1 to RLen formed between emitter terminals E11 to E1n are deleted from the ESD protection circuit shown in FIG. Since other circuit configurations are the same as those of the second embodiment, description thereof will be omitted.

  Since the emitter terminals E11 to E1n are separated from each other, the current path of the current between the emitter terminals is cut off. Further, current control resistors R11 to R1n are connected to the emitter terminals E11 to E1n, respectively. For this reason, the current that flows out to the power supply (GND) flows in a distributed manner in the current adjustment resistors R11 to R1n, thereby avoiding the concentration of surge current. From the above, in the third embodiment, the concentration of current at the breakdown location is reduced as compared with the second embodiment, and the ESD tolerance is further improved.

In the ESD protection element shown in FIGS. 10 and 11, the plurality of P ⁺ base diffusion layers 16 and the plurality of N ⁺ emitter diffusion layers 17 are separated from each other by element isolation regions. As shown, it may be separated by a polysilicon gate 18. A modified example of the configuration of the ESD protection element according to the third embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a plan view showing a modification of the structure of the ESD protection element according to the third embodiment of the present invention. FIG. 14 is a cross-sectional view taken along line EE ′ in FIG. 13 showing a modification of the structure of the ESD protection element according to the third embodiment of the present invention. However, in FIG. 14, the structure of the wiring layer is omitted.

Referring to FIGS. 13 and 14, each of the plurality of N ⁺ emitter diffusion layers 17 is separated by polysilicon gate 18 and formed on P ⁻ base region 204 corresponding to each of the plurality of contacts 5. . Similarly, each of the plurality of P ⁺ base diffusion layers 16 is separated by the polysilicon gate 18 and formed on the P ⁻ base region 204 corresponding to each of the plurality of contacts 14. The polysilicon gate 18 is formed on the oxide insulating film 19 formed on the P ⁻ base region 204 between the N ⁺ emitter diffusion layer 17 (or the P ⁺ diffusion layer 16).

  In the present modification, the region that can be a current path is separated by the polysilicon gate 18, so that the amount of surge current flowing from another region into the current path near the breakdown location is reduced (or eliminated). Therefore, the concentration of current at the breakdown location is reduced as compared with the second embodiment, and the ESD tolerance is further improved.

  In the ESD protection element according to the third embodiment, surge current concentration is avoided by using the current control resistors R11 to R1n provided outside the region where the bipolar transistor is formed. R1n may be provided in a region where a bipolar transistor is formed. For example, by increasing the width of the emitter diffusion layer in the direction along the current path between the emitter and the ground, the resistance component due to the emitter diffusion layer or a silicide film formed on the emitter diffusion layer can be used as the current control resistor R11. . Hereinafter, embodiments in which a current control resistor is provided in a region where a bipolar transistor is formed will be described as fourth to seventh embodiments.

4). Fourth Embodiment With reference to FIGS. 15 to 17, the configuration and operation of an ESD protection element according to a fourth embodiment of the present invention will be described. Below, a different part from 3rd Embodiment is demonstrated. FIG. 15 is a plan view showing the structure of the ESD protection element according to the fourth embodiment of the present invention. 16 is a cross-sectional view taken along the line HH ′ of FIG. 15 showing the structure of the ESD protection element according to the fourth embodiment of the present invention. FIG. 17 is a diagram showing an equivalent circuit in the fourth embodiment of the ESD protection element according to the present invention. However, the silicide film 41 is omitted in FIG. 15, and the structure of the wiring layer is omitted in FIG. In addition, the other embodiments of the present invention can be applied to both cases where there is a silicide or no silicide, but the explanation regarding the silicide is omitted.

Referring to FIGS. 15 and 16, the ESD protection element according to the fourth embodiment has a plurality of N ⁺ emitter diffusions arranged in the base width W direction (Y-axis direction) and separated by element isolation region 208. A layer 31 and a plurality of P ⁺ base diffusion layers 32 are formed. The plurality of N ⁺ emitter diffusion layers 31 and the plurality of P ⁺ base diffusion layers 32 are adjacent to each other in the direction perpendicular to the base width direction (X-axis direction). In the fourth embodiment, a silicide film is formed on the emitter diffusion layer, and resistance components (resistors Re1 to Ren) in the silicide film are used as current control resistors that suppress current concentration of surge currents. Specifically, the silicide film 41 is formed on the N ⁺ emitter diffusion layer 31 and the P ⁺ base diffusion layer 32. A contact 42 is formed on the silicide film 41 on the P ⁺ base diffusion layer 32, and the P ⁺ base diffusion layer 32 is connected to the metal wiring 34 through the contact 42. The metal wiring 34 is connected to a power source (here, GND). Silicide films 43 and 45 are formed on the N ⁺ collector diffusion layer 7 and the N ⁺ diffusion layer 207, respectively. A plurality of contacts 44 are formed in the silicide film 43 on the N ⁺ collector diffusion layer 7, and the N ⁺ collector diffusion layer 7 is connected to the metal wiring 9 (pad) via the contact 44.

Referring to FIG. 16, N ⁺ emitter diffusion layer 31 and P ⁺ base diffusion layer 32 are formed on P ⁻ base region 204 serving as a base region. The N ⁺ emitter diffusion layer 31 is formed between the P ⁺ base diffusion layer 32 and the N ⁺ collector diffusion layer 7 and has a width in a direction perpendicular to the base width direction (Y-axis direction) having a predetermined length. Is set. As a result, an end region (emitter terminal E1i) on the P ⁺ base diffusion layer 32 side (base terminal B1i side) in the N ⁺ emitter diffusion layer 31 and an end portion on the N ⁺ collector diffusion layer 7 side (collector terminal C1i side). The region (emitter region E2i) is separated by a predetermined distance.

Referring to FIG. 16, when a high voltage is applied to the pad (Pad) and the ESD protection element performs a bipolar operation, a current (surge current) flowing between the power supply (GND) and the collector terminal C1i is used as an electron flow. If described, the flow of electrons flows from the contact 42 (emitter terminal E1i) to the collector side (N-type extraction region 205) through the silicide film 41. At this time, the electron flow due to the surge flows from the contact 42 (emitter terminal E1i) into the silicide film 41, and from the end region (emitter region E2i) of the N ⁺ emitter diffusion layer 31 on the collector side (N-type extraction region 205). Flows out. For this reason, the resistance component (resistance Rei) of the silicide film 41 from the contact 42 (emitter terminal E1i) to the vicinity of the emitter region E2i on the collector side functions as a current control resistor for controlling the amount of surge current. Thereby, it is possible to prevent the surge current from concentrating on the emitter terminal E1i.

When a high voltage is applied to the pad (Pad) and the junction between the P ⁻ base region 204 and the N ⁻ collector region 203 breaks down, the hole current flowing into the base region B2i immediately below the emitter region E2i is A current flows out to the power supply (GND) through the contact 42. At this time, the resistance component (resistance Rbi) of the base region (P ⁻ base region 204) extending from the contact 42 (base terminal B1i) to the base region B2i immediately below the emitter region E2i is the voltage (base potential) of the base region B2i. Functions as a resistance to pull up.

The width of the N ⁺ emitter diffusion layer 31 in the direction connecting the base and the collector (the length from the emitter terminal E1i to the emitter region E2i) is such that the current control resistor (Rei) prevents current concentration of the surge current. It is preferable to set to. Further, the width of the N ⁺ emitter diffusion layer 31 is preferably set to such a size that the resistor Rbi can raise the base potential to a potential at which bipolar operation is possible.

  With the configuration as described above, the ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG. Referring to FIG. 17, the ESD protection element in the fourth embodiment is formed with a plurality of NPN bipolar transformers having emitter regions E21 to E2n, base regions B21 to B2n, and collector terminals C11 to C1n.

Referring to FIGS. 15 and 17, emitter terminals E <b> 11 to E <b> 1 n are separated by element isolation region 208. Resistors Re1 to Ren by the silicide film 41 are formed between the emitter regions E21 to E2n and the nearest emitter terminals E11 to E1i, respectively.
On the other hand, resistors RLb1 to RLbn are formed by the P ⁻ base region 204 between the base regions B21 to B2n, which are regions immediately below the emitter terminals E11 to E1n. The collector terminals C11 to C1n are formed on the common N-type buried layer 202 and the N-type lead region 205. Therefore, resistors RLC1 to RLCn are formed by the N-type buried layer 202 and the N-type lead region 205 between the collector terminals C11 to C1n. Further, resistors Rb1 to Rbn are formed by the P ⁻ base region 204 between the base regions B21 to B2n and the nearest base terminals B11 to B1i, respectively.

  As described above, the emitters of the plurality of transistors are separated from each other by the element isolation region. Thereby, current paths of surge currents flowing through the plurality of transistors are separated from each other. Further, resistors Re1 to Ren functioning as current adjustment resistors are connected to the emitter terminals E11 to E1n, respectively. From the above, since the electron current (surge current) flowing from the power supply (GND) flows in a distributed manner to the plurality of resistors Re1 to Ren, current concentration on the specific emitter terminal E1i can be avoided.

Resistors Rb1 to Rbn are formed by the P ^- base region 204 between the base terminals B11 to B1n and the base regions B21 to 21n. When a high voltage is applied to the pad (Pad), the potentials of the base regions B21 to B2n are increased by the resistors Rb1 to Rbn, and the ESD protection element starts a bipolar operation.

As described above, in the ESD protection element according to the present embodiment, the current control resistors (resistors Re1 to Ren) for avoiding current concentration of surge current are formed by the silicide film 41, and the resistor Rb1 for raising the base potential. ~ Rbn is formed by the P ^- base region 204. For this reason, it is not necessary to provide a resistance for current control or a resistance for raising the base potential outside the device, so that the wiring amount and the number of elements of the ESD protection element can be reduced.

5. Fifth Embodiment A modified example (fifth embodiment) of the ESD protection element in the fourth embodiment will be described with reference to FIGS. FIG. 18 is a plan view showing the structure of the ESD protection element according to the fifth embodiment of the present invention. FIG. 19 is a cross-sectional view taken along the line II ′ of FIG. 18 showing the structure of the ESD protection element according to the fifth embodiment of the present invention. Below, a different part from 4th Embodiment is demonstrated. However, the silicide film 41 is omitted in FIG. 18, and the structure of the wiring layer is omitted in FIG.

In the fourth embodiment, a surge current (collector current) flows to the N ⁺ emitter diffusion layer 31 (emitter terminal E1i) via a contact formed in the upper layer of the P ⁺ base diffusion layer 32. On the other hand, in the fifth embodiment, a surge current flows through a contact formed in a region on the N ⁺ emitter diffusion layer 31.

Specifically, the contact 46 is formed in the silicide film 41 on the N ⁺ emitter diffusion layer 31. The silicide film 41 is connected to the metal wiring 35 through the contact 46. The metal wiring 35 is connected to a power source (GND). The contact 46 is preferably provided in the vicinity of the contact 42 on the P ⁺ base diffusion layer 32.

Referring to FIG. 19, when a high voltage is applied to the pad (Pad) and the ESD protection element performs a bipolar operation, the current (surge current) flowing between the power supply (GND) and the collector terminal C1 is the flow of electrons. As described above, the current flows from the contact 46 through the silicide film 41 to the collector side (N-type extraction region 205). At this time, the flow of electrons flows from the contact 46 (emitter terminal E1i) into the silicide film 41, and flows out from the end region (emitter region E2i) of the N ⁺ emitter diffusion layer 31 on the collector side (N-type extraction region 205). Therefore, the resistance component (resistance Rei) of the silicide film 41 from the contact 46 (emitter terminal E1i) to the vicinity of the emitter region E2i on the collector side and the resistance component (not shown in FIG. 17) due to the contact 46 are the amount of collector current. It functions as a current control resistor that controls the current. Thereby, it is possible to prevent the surge current from concentrating on the emitter terminal E1i. Other configurations and operations are the same as those in the fourth embodiment.

In the fifth embodiment, since the resistance component of the contact 46 can be used as a current control resistor, the width of the N ⁺ emitter diffusion layer 31 (the length from the emitter terminal E1i to the emitter region E2i) is set to the fourth embodiment. Can be made smaller. However, it goes without saying that the width of the N ⁺ emitter diffusion layer 31 is set to such a size that the resistor Rei can raise the base potential to a potential at which bipolar operation is possible.

  With the configuration as described above, the ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG.

6). Sixth Embodiment A modified example (sixth embodiment) of an ESD protection element in the fifth embodiment will be described with reference to FIGS. FIG. 20 is a plan view showing the structure of the ESD protection element according to the sixth embodiment of the present invention. FIG. 21 is a cross-sectional view taken along the line JJ ′ in FIG. 20 showing the structure of the ESD protection element according to the sixth embodiment of the present invention. Below, a different part from 5th Embodiment is demonstrated. However, the silicide film 41 is omitted in FIG. 20, and the structure of the wiring layer is omitted in FIG.

In the sixth embodiment, the N ⁻ emitter diffusion layer 31 and the P ⁺ base diffusion layer 32 are formed separately, and the N ⁻ emitter diffusion layer 31, the P ⁺ base diffusion layer 32, and the N ⁺ collector diffusion layer 7 are formed. No silicide film is formed on each upper layer, and contacts 33, 36, and 8 are provided. In the ESD element according to the present embodiment, a surge current flows through the contact 36 formed on the N ⁺ emitter diffusion layer 31.

Specifically, the N ⁻ emitter diffusion layer 31 and the P ⁺ base diffusion layer 32 are separated by an element isolation region 47 (for example, an oxide insulating film). A contact 36 is formed on the N ⁺ emitter diffusion layer 31. N ⁺ emitter diffusion layer 31 is connected to metal interconnection 34 via contact 36. The contact 36 is preferably provided in the vicinity of the contact 33 on the P ⁺ base diffusion layer 32.

Referring to FIG. 21, when a high voltage is applied to the pad (Pad) and the ESD protection element performs a bipolar operation, a current (surge current) flowing between the power supply (GND) and the collector terminal C1i is expressed as an electron flow. If it describes, it will flow from the contact 36 (emitter terminal E1i) to the collector side (N-type extraction region 205) through the N ⁺ emitter diffusion layer 31. At this time, the flow of electrons flows from the contact 36 (emitter terminal E1i) into the N ⁺ emitter diffusion layer 31 and from the end portion (emitter region E2i) of the N ⁺ emitter diffusion layer 31 on the collector side (N-type extraction region 205). It flows out to the collector side. Therefore, the resistance component (resistor Rei) of the N ⁺ emitter diffusion layer 31 from the contact 36 (emitter terminal E1i) to the vicinity of the emitter region E2i on the collector side functions as a current control resistor that controls the amount of collector current. Thereby, it is possible to prevent the surge current from concentrating on the emitter terminal E1i. Other configurations and operations are the same as those of the fifth embodiment.

In the sixth embodiment, the resistance component (not shown in FIG. 17) of the contact 33 can be used as a current control resistor as in the fifth embodiment. Therefore, the width of the N ⁺ emitter diffusion layer 31 (from the emitter terminal E1i). The length to the emitter region E2i) can be made smaller than that in the fourth embodiment. However, it goes without saying that the width of the N ⁺ emitter diffusion layer 31 is set to such a size that the resistor Rei can raise the base potential to a potential at which bipolar operation is possible.

  With the configuration as described above, the ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG.

7). 7th Embodiment FIG. 22: is a top view which shows the structure in 7th Embodiment of the ESD protection element by this invention. As described above, if the emitter diffusion layer is separated in the base width direction (Y-axis direction), concentration of surge current can be prevented. However, the base diffusion layer is not necessarily separated in the base width direction (Y-axis direction).

With reference to FIG. 22, the ESD protection element in 7th Embodiment is demonstrated. In the ESD protection element in the seventh embodiment, the P ⁺ base diffusion layer 32 in the fourth embodiment is formed continuously (without separation) in the base width direction (Y-axis direction). Other configurations are the same as those of the fourth embodiment. Therefore, the N ⁺ emitter diffusion layer 31 is isolated by the element isolation region 208 as in the fourth embodiment. The HH ′ cross section of the ESD protection element in the seventh embodiment is the same as the structure shown in FIG.

FIG. 23 is a plan view showing a modification of the seventh embodiment. In the ESD protection element shown in FIG. 22, the N ⁺ emitter diffusion layer 31 is completely separated in the base width direction (Y-axis direction), but may be partially adjacent. The ESD protection element shown in FIG. 23 includes a comb-shaped N ⁺ emitter diffusion layer in place of the N ⁺ emitter diffusion layer 31 of the ESD protection element shown in FIG. The N ⁺ emitter diffusion layer is partially formed continuously in the base width direction (Y-axis direction) and partially separated.

Specifically, the region near the base terminals B11 to B1i in the N ⁺ emitter diffusion layer of this modification is continuously formed in the base width direction (Y-axis direction), and the region on the contact terminals C11 to C1i side is an element isolation region. Separated by 208. Here, the separated width L (the width in the direction perpendicular to the base width direction (X-axis direction)) is preferably set to a size that can avoid the surge current concentration.

  The ESD protection element shown in FIG. 23 has the same H-H ′ cross section as the structure shown in FIG. 16.

  Even in the configuration as described above, since the emitter terminals E11 to E1i are separated, the path of the surge current is separated, and the resistance component (resistor Re1) by the silicide film 41 is used as the current control resistor. Thereby, concentration of surge current can be prevented. In the seventh embodiment, the case where the resistance component due to the silicide film is a current adjustment resistor has been described as an example. However, by providing a contact on the emitter diffusion layer without providing the silicide film, the resistance component of the diffusion layer can be reduced. The present invention can also be applied when used as a current control resistor (sixth embodiment).

  The ESD protection element in the present embodiment is represented by an equivalent circuit shown in FIG.

  The emitter diffusion layer or base diffusion layer in the fourth to seventh embodiments is separated by the element isolation region 208 in the base width direction (Y-axis direction), but is separated by other methods. Also good. For example, as shown in FIG. 24, in the fourth embodiment, each diffusion layer may be separated by a polysilicon gate 50 instead of the element isolation region. The element isolation method using the polysilicon gate 50 is the same as that in the third embodiment, and the description thereof will be omitted.

  In the following, when not only a positive voltage but also a negative high voltage is applied to the pad, no current flows during normal operation, but when ESD is applied, a surge current flows to the power supply (GND) to protect the internal circuit. This example will be described as eighth and ninth embodiments.

8). Eighth Embodiment With reference to FIG. 25, the configuration and operation of an ESD protection element according to an eighth embodiment of the present invention will be described. FIG. 25 is a cross-sectional view showing the structure of the ESD protection element according to the eighth embodiment of the present invention.

  In the ESD protection element according to the eighth embodiment, the ESD protection element (transistor structure) according to the first embodiment is arranged symmetrically on the power supply (GND) side and the pad side.

With reference to FIG. 25, the structure of the ESD protection element in the eighth embodiment will be described. In the ESD protection element in the eighth embodiment, a P-type substrate 301 (P-sub) and an N-type buried layer 302 are formed in order from the lower layer in the Z-axis direction, and an N-type lead region 305 is formed on the N-type buried layer 302. 316, 326 and N ^- collector regions 313, 323 are formed. The N ⁻ collector region 313 is formed between the N-type extraction region 305 and the N-type extraction region 316, and a P ⁻ base region 314 that functions as a base region is formed in an upper layer in the Z-axis direction. The N ⁻ collector region 323 is formed between the N-type extraction region 305 and the N-type extraction region 326, and a P ⁻ base region 324 that functions as a base region is formed in an upper layer in the Z-axis direction.

On the P ⁻ base region 314, a P ⁺ base diffusion layer 51 and a contact 57 that function as the base terminal B110 in the bipolar operation, and an N ⁺ emitter diffusion layer 52 and a contact 58 that function as the emitter terminal E11i are provided. Yes. An N ⁺ collector diffusion layer 53 that functions as the collector terminal C110 is provided on the N-type lead region 316. Further, an N ⁺ diffusion layer 207 is provided on the N-type extraction region 305. The N ⁺ diffusion layer 207, the P ⁺ base diffusion layer 51, the N ⁺ emitter diffusion layer 52, and the N ⁺ collector diffusion layer 53 are separated by an element isolation region 308 (for example, an oxide insulating film).

On the P ⁻ base region 324, a P ⁺ base diffusion layer 54 and a contact 60 that function as a base terminal B 120 during bipolar operation, and an N ⁺ emitter diffusion layer 55 and a contact 61 that function as an emitter terminal E 12 i are provided. Yes. An N ⁺ collector diffusion layer 56 that functions as a collector terminal C120 is provided on the N-type lead region 326. The N ⁺ diffusion layer 207, the P ⁺ base diffusion layer 54, the N ⁺ emitter diffusion layer 55, and the N ⁺ collector diffusion layer 56 are separated by an element isolation region 308 (for example, an oxide insulating film).

The P ⁺ base diffusion layer 51 is connected to one end of the resistor R210 through the contact 57. The N ⁺ emitter diffusion layer 52 is connected to one end of the current adjustment resistor R11i through the contact 58. The other end of the resistor R210 and the other end of the current control resistor R11i are commonly connected to a power source (GND). On the other hand, the P ⁺ base diffusion layer 54 is connected to one end of the resistor R220 through the contact 60. The N ⁺ emitter diffusion layer 55 is connected to one end of the current adjustment resistor R12i through the contact 61. The other end of the resistor R220 and the other end of the current R12i are commonly connected to a pad (Pad).

  With the configuration described above, the emitter terminal E11i of the transistor connected to the pad (Pad) side is connected to the pad via the current control resistor R11i, and the base terminal B110 is connected to the pad (Pad) via the resistor R210. The

  The emitter terminal E12i of the transistor connected to the power supply (GND) side is grounded via the current control resistor R12i, the base terminal B120 is grounded via the resistor R220, and the collector terminal C120 is connected via the N-type buried layer 302. It is connected to the collector terminal C110 of the pad side transistor.

  Since there are a plurality of the above-described structures as in the first embodiment, the current path of the surge current flowing through the ESD protection element is dispersed.

When a positive voltage is applied to the pad, the diode formed by P ⁻ base region 314 and N ⁻ collector region 313 is forward biased, and the diode formed by P ⁻ base region 324 and N ⁻ collector region 323 is Reverse biased. Here, when a positive voltage higher than the withstand voltage of the diode formed by the P ⁻ base region 324 and the N ⁻ collector region 323 is applied to the pad, current is supplied from the pad to the power supply (GND) via the resistors R210 and R220. Flowing. As a result, the voltage of the base terminal B120 increases due to the voltage drop of the resistor R220, the transistor on the power supply (GND) side operates, and a surge current starts to flow between the pad and the power supply (GND). At this time, the surge current flows from the pad to the power supply (GND) through the N ⁻ collector region 323, the P ⁻ base region 324, the N ⁺ emitter diffusion layer 55, and the current adjustment resistor R12i.

On the other hand, when a negative voltage is applied to the pad, the diode formed by the P ⁻ base region 314 and the N ⁻ collector region 313 is biased in the reverse direction, and formed by the P ⁻ base region 324 and the N ⁻ collector region 323. The diode is forward biased. Here, when a negative voltage equal to or lower than the withstand voltage of the diode formed by the P ⁻ base region 314 and the N ⁻ collector region 313 is applied to the pad, current is supplied from the power supply (GND) to the pad via the resistors R210 and R220. Flowing. As a result, the voltage of the base terminal B110 increases due to the voltage drop of the resistor R210, the pad side transistor operates, and a surge current starts to flow between the pad and the power supply (GND). At this time, the surge current flows from the power supply (GND) to the power supply (GND) through the N ⁻ collector region 313, the P ⁻ base region 314, the N ⁺ emitter diffusion layer 52, and the current adjustment resistor R11i.

  As described above, the surge current (ESD current) that flows through the transistor on the power supply side flows through the plurality of current adjustment resistors R12i, so that current concentration on the elements in the transistor can be avoided. The same applies to the pad-side transistor.

9. Ninth Embodiment With reference to FIG. 26, the configuration and operation of an ESD protection element according to a ninth embodiment of the present invention will be described. FIG. 26 is a cross-sectional view showing the structure of the ESD protection element according to the ninth embodiment of the present invention.

  In the ESD protection element according to the ninth embodiment, the ESD protection element (transistor structure) according to the second embodiment is arranged symmetrically on the power supply (GND) side and the pad side.

With reference to FIG. 26, the structure of the ESD protection element in the ninth embodiment will be described. The P ⁺ base diffusion layer 51 and the contact 57 function as the base terminal B11i and are connected to the current adjustment resistor R11i. The P ⁺ base diffusion layer 54 and the contact 60 function as the base terminal B12i and are connected to the current adjustment resistor R12i. Other structures are the same as those in the eighth embodiment. Since there are a plurality of the above-described structures as in the second embodiment, the current path of the surge current flowing through the ESD protection element is dispersed.

When a positive voltage is applied to the pad, the diode formed by P ⁻ base region 314 and N ⁻ collector region 313 is forward biased, and the diode formed by P ⁻ base region 324 and N ⁻ collector region 323 is Reverse biased. Here, when a positive voltage higher than the withstand voltage of the diode formed by the P ⁻ base region 324 and the N ⁻ collector region 323 is applied to the pad, a current is supplied from the pad through the resistors R11i and R12i to the power supply (GND). Flowing into. As a result, the voltage at the base terminal B120 rises due to the voltage drop of the current adjustment resistor R12i, the transistor on the power supply side operates, and a surge current starts to flow from the pad to the power supply (GND). At this time, the surge current flows from the pad to the power supply (GND) through the N ⁻ collector region 323, the P ⁻ base region 324, the N ⁺ emitter diffusion layer 55, and the current adjustment resistor R12i.

On the other hand, when a negative voltage is applied to the pad, the diode formed by the P ⁻ base region 314 and the N ⁻ collector region 313 is biased in the reverse direction, and formed by the P ⁻ base region 324 and the N ⁻ collector region 323. The diode is forward biased. Here, when a negative voltage equal to or lower than the withstand voltage of the diode formed by the P ⁻ base region 314 and the N ⁻ collector region 313 is applied to the pad, current is supplied from the power supply (GND) to the pad through the resistor R12i and the resistor R11i. Flowing into. As a result, the voltage at the base terminal B110 increases due to the voltage drop of the current adjustment resistor R11i, and the transistor on the pad side operates to start a surge current from the power supply (GND) to the pad.

  As described above, the surge current (ESD current) flowing through the transistor on the power supply side flows through the plurality of current adjustment resistors R12i, so that current concentration on the elements in the transistor can be avoided. The same applies to the pad-side transistor. In this embodiment, even when a high voltage of a high level or a low level is applied, a high voltage is not applied to the transistor in the ESD protection circuit, and element destruction can be avoided.

A modification of the third embodiment will be described with reference to FIG. FIG. 27 is a plan view showing the structure of a modified example of the third embodiment of the ESD protection element according to the present invention. In the ESD protection element shown in FIG. 27, the plurality of P ⁺ base diffusion layers 16 separated from each other in the base width W direction (Y-axis direction) in the ESD protection element in the third embodiment are the same P ⁺ base. The diffusion layer 76 connects. The P ⁺ base diffusion layers 16 and 76 form a comb-shaped P ⁺ base diffusion layer. Other structures are the same as those of the third embodiment.

Specifically, the P ⁺ base diffusion layer 16 in this example diffuses in the region of the width L3 separated by the element isolation region 208 and in the direction perpendicular to the base width direction (X-axis direction) by the P ⁺ base diffusion layer 76. The layer has a region of width L2 formed continuously. Here, the widths L2 and L3 indicate the width in the direction perpendicular to the base width direction (X-axis direction), and the width L2 is preferably smaller than the width L1 of the entire P ⁺ base diffusion layer 16 in the X-axis direction. The width L3 is preferably set to a size that can avoid the surge current concentration. For this reason, the width L3 is preferably larger than the width L2.

Next, a modification of the ESD protection element shown in FIG. 27 will be described with reference to FIGS. FIG. 28 is a plan view showing the structure of a variation of the ESD protection element shown in FIG. 29 is a cross-sectional view taken along the line II ′ of FIG. In the ESD protection element shown in FIG. 27, the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16 are separated from each other in the X-axis direction by the element isolation region 208. In the ESD protection element shown in FIG. These are brought into contact. That is, the ESD protection element of this example shows a batting structure in which the element isolation region 208 between the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16 in the X-axis direction is deleted and the two are heterojunctioned.

When noise enters the collector, the current due to the noise flows into the junction capacitance (Ccb) and flows to the GND through the base. At this time, the current due to the noise passes through the base resistor Rbi and causes a voltage drop to change the potential of the base B2i (base potential). At this time, the fluctuation value of the potential at the base B2i is (current due to noise) × Rbi, and increases as Rbi increases. In addition, the time during which the fluctuation of the potential of the base B2i (base potential) at this time is determined by Rbi × Ccb. If the diode composed of the emitter and the base is not turned on, no current flows through the emitter. At this time, the time required for the bipolar transistor to operate is the time during which the base potential becomes higher than the emitter potential due to noise. When this occurs, the bipolar transistor becomes conductive. In order to avoid such a bipolar operation due to noise, in this example, since the distance between the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16 is shorter than that in the third embodiment, the P ⁻ base region 204 is formed. The current path between the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16 is shortened, and the resistance component Rbi in the P ⁻ base region 204 is reduced. As a result, (current due to noise) × Rbi and Rbi × Ccb are reduced, and the occurrence of bipolar operation due to noise is suppressed.

Thus, by shortening the distance between the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16, it is possible to reduce the risk that the bipolar transistor operates due to noise. In order to obtain such an effect, the N ⁺ emitter diffusion layer 17 and the P ⁺ base diffusion layer 16 do not necessarily have to be joined. For example, in the third embodiment, the above effect can be achieved by reducing the width of the element isolation region 208 between the emitter and the base.

  With reference to FIG. 30, another modification of the third embodiment will be described. FIG. 30 is a plan view showing a structure in another modification of the third embodiment.

Further, in the ESD protection element shown in FIG. 30, a plurality of metal wirings 15 separated from each other in the base width W direction (Y-axis direction) in the ESD protection element in the third embodiment are connected to the N ⁺ emitter diffusion layer. 17 are connected by metal wiring 75. Other structures are the same as those of the third embodiment.

  In the ESD protection element shown in FIG. 30, the metal wiring 75 connected on the emitter in the Y-axis direction functions as a heat capacity that absorbs the heat generated by the ESD pulse current, and thus has an effect of improving the ESD protection performance.

  The embodiment of the present invention has been described in detail above, but the specific configuration is not limited to the above-described embodiment, and changes within a scope not departing from the gist of the present invention are included in the present invention. . The first to ninth embodiments can be combined as long as there is no technical contradiction. For example, the base diffusion layer and the emitter diffusion layer in the first embodiment may be separated as in the third embodiment. The power supply may be set to another potential different from the ground potential. Furthermore, the present invention can also be applied to an ESD protection element using a lateral PNP bipolar transistor or a lateral NPN bipolar transistor.

1, 16, 32, 51: P ⁺ base diffusion layer 2, 5, 8, 10, 12, 14, 33, 36, 42, 44, 46, 57, 58, 60, 61: contact 3, 6, 9, 13, 15, 34, 35: Metal wiring 4, 17, 31, 52: N ⁺ emitter diffusion layer 7, 53, 56: N ⁺ collector diffusion layer 11, R11 to R1n, Re1 to Ren, R11i: Current control resistor 18 50: polysilicon gate 19: oxide insulating film 41, 43: silicide film 201, 301: P-type substrate 202, 302: N-type buried layer 203, 313, 323: N ⁻ collector region 204, 314, 324: P ⁻ Base region 205, 206, 305, 316, 326: N-type extraction region 207: N ⁺ diffusion layer 47, 208, 308: Element isolation region B1, B11 to B1n, B110, B120, B11i, B12i: Base terminals B21-B2n: Base terminals (base region)
C1, C11-C1n, C110, C120: Collector terminals E11-E1n, E2i, E11i, E12i: Emitter terminals E21-E2n: Emitter regions R2, RLb1-RLbn, RLe1-RLen, RLC1-RLCn, Rb1-Rbn, Re1- Ren: Resistance

Claims (3)

In an ESD (Electrostatic Discharge) protection element using a bipolar transistor,
A first terminal;
A collector region connected to the first terminal;
A second terminal;
The base region,
A first emitter diffusion layer provided on a surface of the base region;
A second emitter diffusion layer provided on the surface of the base region;
A first base diffusion layer provided on a surface of the base region;
A second base diffusion layer provided on the surface of the base region,
A first silicide layer is formed on surfaces of the first emitter diffusion layer and the first base diffusion layer,
A first base contact is formed immediately above the first base diffusion layer on the surface of the first silicide layer,
The first base contacts are connected to each other by the second terminal and metal wiring,
A second silicide layer is formed on the surfaces of the second emitter diffusion layer and the second base diffusion layer,
A second base contact is formed immediately above the second base diffusion layer on the surface of the second silicide layer,
The second base contacts are connected to each other by the second terminal and the metal wiring,
The first emitter diffusion layer and the second emitter diffusion layer are separated by an element isolation region on the surface of the base region,
The ESD protection element, wherein the first base diffusion layer and the second base diffusion layer are separated by the element isolation region on the surface of the base region. The ESD protection element according to claim 1,
The bipolar transistor is:
A first bipolar transistor comprising the first emitter diffusion layer and the first base diffusion layer connected to the second terminal via the first silicide layer;
A second bipolar transistor comprising the second emitter diffusion layer and the second base diffusion layer connected to the second terminal via the second silicide layer;
The first bipolar transistor and the second bipolar transistor are connected via the collector region. The ESD protection element according to claim 1 or 2,
The bipolar transistor is a vertical NPN bipolar transistor.

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