A bidirectional low trigger voltage ESD protection device

Abstract

The present invention discloses a bidirectional low trigger voltage ESD protection device, which includes an SOI-type P substrate material, an NWdeep well region, a PW1 well region, and a PW2 well region that are sequentially arranged on the surface of the SOI-type P substrate material from bottom to top. PSD ohmic contact regions and NSD ohmic contact regions are formed in the NWdeep well region, the PW1 well region, the PW2 well region, and the SOI-type P substrate material. The ESD protection device is electrically isolated by two trench regions and is divided into an auxiliary trigger triode NPN4, an SCR unit, and an auxiliary trigger triode NPN3 from left to right in sequence. This structure reduces the trigger voltage of the traditional bidirectional SCR structure from more than 10V to about 4V, and can be adjusted by the size of PW2 and the dose of PW2. Since the two punch-through triodes of the auxiliary trigger unit only play a role in assisting the triggering of the SCR to turn on, and the main current discharge path is the SCR structure, the auxiliary trigger unit does not occupy a large layout area. At the same time, the use of the bidirectional SCR structure can effectively reduce the layout area of the bidirectional low trigger voltage ESD protection device formed by the existing reverse parallel connection.

Description

Technical Field

[0001] The invention belongs to the field of integrated circuit electrostatic discharge (ESD) protection. Background Art

[0002] Electrostatic discharge (ESD) is a common phenomenon in nature. It is essentially the transfer of static charge between objects. This static charge transfer speed is fast, and the transient voltage can reach 1kV or even higher. With the continuous reduction of semiconductor manufacturing process size and the continuous expansion of integrated circuit scale, the impact of electrostatic discharge on integrated circuits is becoming more and more serious, and the resulting product failure and yield reduction problems have also attracted much attention. Therefore, it is crucial to provide effective ESD protection for various products. Among the many electronic products, if effective ESD protection is to be implemented for a class of electronic products with an operating voltage of about 2.5V, ESD protection devices are usually required to have the following characteristics: First, in order to match the low operating voltage of electronic products, ESD protection devices must have a low trigger voltage and a higher maintenance voltage; second, in order to implement effective ESD protection for such electronic products, ESD protection devices must have strong robustness; third, in order not to affect the data transmission of such electronic products, ESD protection devices must have extremely low capacitance.

[0003] Devices commonly used for ESD protection include diodes, GGNMOS (Gate Grounded NMOS), BJT (Triode), SCR (Silicon Controlled Rectifier), etc. Since SCR has the highest robustness and the strongest discharge current capability, SCR is used as the ESD protection device for such low-operating voltage electronic products. For electronic products with an operating voltage of about 2.5V, the breakdown voltage of the ESD protection device usually needs to reach a breakdown voltage of 3.5V or above, but the breakdown voltage cannot be too high. If it is too high, after the ESD event occurs, the breakdown voltage of the electronic product is reached but the breakdown voltage of the protection device is not reached, resulting in the ESD protection device being unable to implement effective protection. However, since the trigger voltage of the SCR depends on the breakdown of the reverse biased PN junction, which is much greater than the required trigger voltage, an auxiliary trigger unit is required to assist the SCR in opening. The auxiliary trigger unit includes: diode string auxiliary trigger, Zener auxiliary trigger, GGNMOS auxiliary trigger, and punch-through transistor auxiliary trigger. At a breakdown voltage of 3.5V, 4 to 5 diodes are required, and bidirectional devices require twice the number of diodes, which will increase the chip area. Zener diodes will cause a lot of leakage, increasing the power consumption of the overall system. The GGNMOS process is not compatible and will increase the device capacitance. Therefore, a through-transistor NPN is used for auxiliary triggering. By adjusting the size of the through-transistor base and emitter, the leakage current can be suppressed and the breakdown voltage can be adjusted.

[0004] Traditional bidirectional SCR structure ESD protection device, its structure diagram Figure 1 Generally adopted Figure 1 , Figure 2 The equivalent circuit diagram of the device is shown in Figure 2. It can be seen from the equivalent circuit diagram that the bidirectional SCR device is composed of two PNP transistors and one NPN transistor. The manufacturing method is: Figure 1 In the figure, the substrate is an N-type substrate 1110, a PW well region 1120 is formed in the N-type substrate 1110, and the process parameters of PW1 and PW2 are exactly the same. A first PSD ohmic contact region 1130 and a first NSD ohmic contact region 1140 are formed in the PW well region 1120. After the injection is completed, a dielectric layer 1150 is deposited, and then holes are etched and metal is deposited to form a metal anode 1101 and a metal cathode 1102. In the above process, the process manufacturing parameters of PW1 and PW2, PSD1 and PSD2, and NSD1NSD2 are exactly the same, just for the convenience of subsequent description of the working mechanism. According to the device structure schematic diagram and the equivalent circuit diagram, it can be seen that the device is symmetrical. Whether the device applies a voltage at the cathode or the anode, the trigger mechanism is the same, so it is sufficient to consider only unidirectional discharge. When the forward ESD current is injected into the metal anode 1101, the PN junction formed by Nsub and PW2 is in a reverse bias state. As the voltage increases, the reverse bias junction undergoes avalanche breakdown. As the current increases, when the voltage drop across PW2 and NSD2 reaches 0.7V, the SCR turns on, and a conductivity modulation effect occurs inside the device, generating a low-resistance path from PSD1 to NSD2. The conduction of this SCR path establishes positive feedback between PNP and NPN2 in the equivalent circuit diagram, discharging the ESD current.

[0005] The equivalent circuit diagram of the existing bidirectional low trigger voltage ESD protection device is as follows: Figure 4 , Figure 5 As shown. Among them, Figure 4 It is a bidirectional ESD protection device assisted by transistor NPN2. Figure 5 It is a bidirectional ESD protection device with diode string auxiliary trigger. One of its bidirectional paths only shows the anti-parallel structure of a unilateral circuit. Therefore, only the working mechanism of one branch is explained. Figure 4, when a high potential is applied to the metal anode 1101, the right branch is in a reverse cutoff state, and the working mode is left conduction. As the voltage at the metal anode 1101 increases, the collector junction of the transistor NPN2 will be punched through, causing the current to increase rapidly. The punch-through current will serve as an auxiliary trigger current for the left SCR. As the current increases, the SCR path is opened, and a conductivity modulation effect occurs inside it. Then the current flows along the low-resistance path of the SCR to the metal cathode 1102. For the bidirectional ESD protection device assisted by a diode string, its working mechanism is exactly the same as the auxiliary trigger mechanism of the transistor NPN2, and the number of diodes determines the size of the trigger voltage. Therefore, when the operating voltage of the external system is about 2.5V, a diode string auxiliary trigger is often not used, because the number of diode strings will increase a lot, resulting in a lot of increase in the layout area.

[0006] like Figure 1 The ESD protection device shown is a typical bidirectional SCR structure, and the trigger voltage is completely determined by the reverse-biased junction breakdown voltage of the N-type substrate and the PW well region. Figure 4 The ESD protection device shown in the figure uses a single-side device in reverse parallel to form a bidirectional device, and uses a through transistor NPN to reduce the overall trigger voltage. Figure 5 The ESD protection device shown in the figure adopts the method of reverse parallel connection of unilateral devices to form a bidirectional device, and uses a diode string to reduce the overall trigger voltage, and its trigger voltage is determined by the number of diode strings. The existing low trigger voltage ESD protection device formed by reverse parallel connection of unilateral devices will double the layout area. In order to solve the problem of increasing the layout area of ​​bidirectional devices, the present invention provides a new technical solution. By introducing a new technical structure, the layout area can be greatly reduced while ensuring the same trigger voltage, which is conducive to saving more costs. Summary of the invention

[0007] The object of the present invention is to provide an ESD protection device with a bidirectional low trigger voltage formed by non-reverse parallel connection, which can effectively save the layout area by realizing a through-transistor NPN triggering bidirectional SCR structure through metal interconnection.

[0008] The technical solution adopted by the present invention is a bidirectional low trigger voltage ESD protection device, including an SOI type P substrate material, an NWdeep well region, a PW1 well region, and a PW2 well region arranged in sequence from bottom to top on the surface of the SOI type P substrate material, and a PSD ohmic contact region and an NSD ohmic contact region are formed in the NWdeep well region, the PW1 well region, the PW2 well region and the SOI type P substrate material. The ESD protection device is electrically isolated by two groove regions and is divided from left to right into an auxiliary trigger transistor NPN4, an SCR unit and an auxiliary trigger transistor NPN3.

[0009] In some embodiments, the SCR unit is composed of the SOI type P substrate material, the NWdeep well region, the PW1 well region, the NSD ohmic contact region, and the PSD ohmic contact region.

[0010] In some embodiments, the auxiliary trigger transistors NPN3 and NPN4 are composed of the SOI type P substrate material, the PW2 well region, and the NSD ohmic contact region.

[0011] In some embodiments, the invention further comprises a first metal electrode and a second metal electrode, wherein the first metal electrode and the second metal electrode form a current loop through an interconnecting metal.

[0012] Beneficial effects:

[0013] The existing bidirectional low trigger voltage ESD protection device is improved, and the bidirectional SCR structure is used as the protection unit of the ESD protection device. The through transistors NPN3 and NPN4 are used as the auxiliary trigger units of the protection unit to realize bidirectional low voltage auxiliary triggering. The trigger voltage of the overall device is the sum of the through voltage of the through transistor and the forward bias voltage of the PNP emitter junction in the bidirectional SCR structure. SOI is used to achieve electrical isolation between the protection unit and the auxiliary trigger unit. This structure reduces the trigger voltage of more than 10V of the traditional bidirectional SCR structure to about 4V, and can be adjusted by the size of PW2 and the dosage of PW2. In addition, since the two through transistors of the auxiliary trigger unit only play the role of auxiliary triggering SCR opening, the main current discharge path is the SCR structure, so the auxiliary trigger unit does not occupy a large layout area. At the same time, the use of a bidirectional SCR structure can effectively reduce the layout area of ​​the existing bidirectional low trigger voltage ESD protection device composed of reverse parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structural cross section of a traditional bidirectional SCR protection device;

[0015] Figure 2 It is the equivalent circuit diagram of the traditional bidirectional SCR protection device;

[0016] Figure 3 Schematic diagram of the volt-ampere characteristic curve of a traditional bidirectional SCR protection device;

[0017] Figure 4 It is the equivalent circuit diagram of the existing low trigger voltage bidirectional ESD protection device;

[0018] Figure 5 is an equivalent circuit diagram of another existing low trigger voltage bidirectional ESD protection device;

[0019] Figure 6It is a schematic diagram of the structural cross-section of the low trigger voltage bidirectional ESD protection device of the present invention;

[0020] Figure 7 It is a concise structural cross-sectional diagram of the low trigger voltage bidirectional ESD protection device of the present invention's patent;

[0021] Figure 8 It is the equivalent circuit diagram of the low trigger voltage bidirectional ESD protection device of the present invention's patent;

[0022] Fig. 9 It is a schematic diagram of the volt-ampere characteristic curves of a traditional bidirectional SCR device and a low trigger voltage bidirectional ESD protection device of the present invention. DETAILED DESCRIPTION

[0023] Aiming at the high trigger voltage of the traditional bidirectional SCR structure protection device and the technical defects of the existing low trigger voltage bidirectional ESD protection device, the present invention designs a non-reverse parallel bidirectional low trigger voltage ESD protection device, and improves the structure of the ESD protection device SCR to make it a bidirectional SCR structure, which can effectively improve the following problems: Figure 1 The conventional bidirectional SCR protection device shown has a high trigger voltage and Figure 4 , Figure 5 The layout area of ​​the bidirectional protection device formed by reverse parallel connection is too large. The trigger voltage is reduced while reducing the layout area of ​​the bidirectional device.

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0025] The present invention embodiment designs a non-reverse parallel bidirectional low trigger voltage ESD protection device, by optimizing the structure of the SCR thyristor unit of the ESD protection device, that is, forming a deep N-well NWdeep well region 120, a PW1 well region 130, and a PW2 well region 140 on the P-type SOI substrate material, and forming an NSD ohmic contact region 150 and a PSD ohmic contact region 160 in the NWdeep well region 120, the PW1 well region 130, the PW2 well region 140 and the SOI-type P substrate material 110. Two NPN and one PNP structures are formed, and when the voltage is applied from the first metal electrode 101 to the second metal electrode 102, the SCR path is from PNP to NPN2. When the voltage is applied from the second metal electrode 102 to the first metal electrode 101, the SCR path is from PNP to NPN1. And the trigger voltage is reduced by penetrating transistors NPN3 and NPN4. Effective improvements such as Figure 1 The conventional bidirectional SCR protection device shown has a high trigger voltage and Figure 4 , Figure 5 The problem of using reverse parallel connection to form a bidirectional protection device with too large a layout area.

[0026] The traditional bidirectional SCR structure ESD protection device, its structural diagram, equivalent circuit diagram and volt-ampere characteristic curve diagram are as follows Figure 1 , 2 , 3. It can be seen from the equivalent circuit diagram that the bidirectional SCR device is composed of two PNP transistors and one NPN transistor. The manufacturing method is: Figure 1 In the figure, the substrate is an N-type substrate 1110, a PW well region 1120 is formed in the N-type substrate 1110, and the process parameters of PW1 and PW2 are exactly the same. A first PSD ohmic contact region 1130 and a first NSD ohmic contact region 1140 are formed in the PW well region 1120. After the injection is completed, a dielectric layer 1150 is deposited, and then holes are etched and metal is deposited to form a metal anode 1101 and a metal cathode 1102. In the above process, the process manufacturing parameters of PW1 and PW2, PSD1 and PSD2, and NSD1NSD2 are exactly the same, just for the convenience of subsequent description of the working mechanism. According to the device structure schematic diagram and the equivalent circuit diagram, it can be seen that the device is symmetrical. Whether the device applies a voltage at the cathode or the anode, the trigger mechanism is the same, so it is sufficient to consider only unidirectional discharge. When the forward ESD current is injected into the metal anode 1101, the PN junction formed by Nsub and PW2 is in a reverse bias state. As the voltage increases, the reverse bias junction undergoes avalanche breakdown. As the current increases, when the voltage drop across PW2 and NSD2 reaches 0.7V, the SCR turns on, and a conductivity modulation effect occurs inside the device, generating a low-resistance path from PSD1 to NSD2. The conduction of this SCR path establishes positive feedback between PNP and NPN2 in the equivalent circuit diagram, discharging the ESD current.

[0027] The equivalent circuit diagram of the existing bidirectional low trigger voltage ESD protection device is as follows: Figure 4 , Figure 5 As shown. Among them, Figure 4 It is a bidirectional ESD protection device assisted by transistor NPN2. Figure 5 It is a bidirectional ESD protection device with diode string auxiliary trigger. One of its bidirectional paths only shows the anti-parallel structure of a unilateral circuit. Therefore, only the working mechanism of one branch is explained. Figure 4, when a high potential is applied to the metal anode 1101, the right branch is in a reverse cutoff state, and the working mode is left conduction. As the voltage at the metal anode 1101 increases, the collector junction of the transistor NPN2 will be punched through, causing the current to increase rapidly. The punch-through current will serve as an auxiliary trigger current for the left SCR. As the current increases, the SCR path is opened, and a conductivity modulation effect occurs inside it. Then the current flows along the low-resistance path of the SCR to the metal cathode 1102. For the bidirectional ESD protection device assisted by a diode string, its working mechanism is exactly the same as the auxiliary trigger mechanism of the transistor NPN2, and the number of diodes determines the size of the trigger voltage. Therefore, when the operating voltage of the external system is about 2.5V, a diode string auxiliary trigger is often not used, because the number of diode strings will increase a lot, resulting in a lot of increase in the layout area.

[0028] like Figure 1 The ESD protection device shown is a typical bidirectional SCR structure, and the trigger voltage is completely determined by the reverse-biased junction breakdown voltage of the N-type substrate and the PW well region. Figure 4 The ESD protection device shown in the figure uses a single-side device in reverse parallel to form a bidirectional device, and uses a through transistor NPN to reduce the overall trigger voltage. Figure 5 The ESD protection device shown in the figure adopts the method of reverse parallel connection of unilateral devices to form a bidirectional device, and uses a diode string to reduce the overall trigger voltage, and its trigger voltage is determined by the number of diode strings. The existing low trigger voltage ESD protection device formed by reverse parallel connection of unilateral devices will double the layout area. In order to solve the problem of increasing the layout area of ​​bidirectional devices, the present invention provides a new technical solution. By introducing a new structure, the layout area can be greatly reduced while ensuring the same trigger voltage, which is conducive to saving more costs.

[0029] The patented bidirectional low trigger voltage ESD protection device adopts Figure 6The structure includes two units: the ESD protection unit adopts the SCR structure and the auxiliary trigger unit adopts NPN3 and NPN4. In order to prevent the parasitic effect between the bidirectional SCR and the punch-through NPN and reduce the parasitic capacitance of the device, the two units are electrically isolated by using SOI with grooves. NWdeep well area 120, PW1 well area 130, PW2 well area 140 are formed in the SOI type P substrate material 110, and NSD ohmic contact area 150 and PSD ohmic contact area 160 are formed in the NWdeep well area 120, PW1 well area 130, PW2 well area 140 and SOI type P substrate material 110. After the impurity injection annealing is completed, the groove area 170 forms electrical isolation between the bidirectional SCR and the punch-through NPN. After the internal process manufacturing of the device is completed, the dielectric layer deposition, etching, and metal interconnection process are carried out. The first metal electrode 101 and the second metal electrode 102 form a current loop through the interconnected metal.

[0030] like Figure 6 The simplified structural diagram of the bidirectional ESD protection device is as follows Figure 7 As shown, the equivalent circuit diagram is as follows Figure 8 As shown, the bidirectional auxiliary trigger function is realized by using the through transistors NPN3 and NPN4. The auxiliary trigger device NPN is added to the traditional bidirectional SCR structure to realize ESD protection for low working voltage. The SCR unit is composed of SOI type P substrate material 110, NWdeep well area 120, PW1 well area 130, NSD ohmic contact area 150, and PSD ohmic contact area 160. The auxiliary trigger transistors NPN3 and NPN4 are composed of SOI type P substrate material 110, PW2 well area 140, and NSD ohmic contact area 150. The electrical isolation of the bidirectional SCR unit and the auxiliary trigger transistors NPN3 and NPN4 is formed by the groove area 170.

[0031] like Figure 6 The volt-ampere characteristic curve of the equivalent circuit diagram of the bidirectional ESD protection device is shown in Fig. 9As shown, according to the device structure schematic diagram and the equivalent circuit diagram, it can be known that the SCR structure of the ESD protection unit is composed of two NPNs and one PNP, realizing a bidirectional trigger structure. Regardless of whether the device applies voltage at the cathode or the anode, the trigger mechanism is the same, so it is sufficient to consider only unidirectional discharge. When the first metal electrode 101 is connected to a high potential and the second metal electrode 102 is connected to a low potential, the current in the bidirectional protection unit SCR enters the SCR through the emitter junction of the PNP, that is, the right PSD. Since the NWdeep well region 120 and the left PW1 are in a reverse biased cutoff state, the current flows along the middle NSD ohmic contact region to the auxiliary trigger unit NPN3 instead of NPN2. In addition, since the breakdown voltage of NPN4 is greater than the breakdown voltage of NPN3, as the voltage increases, the auxiliary trigger transistor NPN3 is preferentially penetrated, and the current begins to increase. The current flows from the transistor NPN3 to the second metal electrode 102 at a low potential. As the voltage continues to increase, the current also continues to increase. When the emitter junction voltage drop of NPN2, that is, the junction voltage drop of the left PW1 well region and NSD, reaches 0.7V, the SCR is triggered to turn on, generating a negative resistance effect, and the volt-ampere characteristic curve shows hysteresis. At this time, the current flows from the first metal electrode 101 through the parasitic transistors PNP and NPN2 in the SCR unit, and finally flows to the second metal electrode 102. When the first metal electrode 101 is connected to a low potential and the second metal electrode 102 is connected to a high potential, the working principle is the same as above. The transistor NPN4 is preferentially triggered to be penetrated, and the current flows from the second metal electrode 102 through the parasitic transistors PNP and NPN1 in the SCR unit, and finally flows to the first metal electrode 101. Figure 1 The protection structure of the ESD protection device shown is an SCR thyristor, which can introduce a stronger conductivity modulation effect compared to a diode structure and a triode structure. The trigger voltage of the SCR thyristor depends on process parameters such as the size of the PW2 of the auxiliary trigger triode NPN and the implantation dose of PW2. In this circuit, the trigger voltage is the sum of the emitter junction of the parasitic triode PNP and the punch-through voltage of the punch-through triode NPN3 or NPN4. Compared with the traditional trigger mechanism of the SCR thyristor, a lower trigger voltage can be obtained.

[0032] The advantage of the present invention is that the existing bidirectional low trigger voltage ESD protection device is improved, the bidirectional SCR structure is used as the protection unit of the ESD protection device, and the through transistors NPN3 and NPN4 are used as the auxiliary trigger units of the protection unit to realize bidirectional low voltage auxiliary triggering. The trigger voltage of the overall device is the sum of the through voltage of the through transistor and the forward bias voltage of the PNP emitter junction in the bidirectional SCR structure. SOI is used to achieve electrical isolation between the protection unit and the auxiliary trigger unit. This structure reduces the trigger voltage of more than 10V of the traditional bidirectional SCR structure to about 4V, and can be adjusted by the size of PW2 and the dosage of PW2. In addition, since the two through transistors of the auxiliary trigger unit only play the role of auxiliary triggering SCR opening, the main current discharge path is the SCR structure, so the auxiliary trigger unit does not occupy a large layout area, and the use of the bidirectional SCR structure can effectively reduce the layout area of ​​the existing bidirectional low trigger voltage ESD protection device composed of reverse parallel.

[0033] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to preferred examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A bidirectional low trigger voltage ESD protection device, characterized in that: It comprises an SOI type P substrate material (110), an NWdeep well region (120), a PW1 well region (130), and a PW2 well region (140) which are sequentially arranged on the surface of the SOI type P substrate material (110) from bottom to top, a PSD ohmic contact region (160) and an NSD ohmic contact region (150) are formed in the NWdeep well region (120), the PW1 well region (130), the PW2 well region (140), and the SOI type P substrate material (110), and the ESD protection device is electrically isolated by two groove regions (170) and is sequentially divided from left to right into an auxiliary trigger transistor NPN4, an SCR unit, and an auxiliary trigger transistor NPN3, thereby forming two NPN structures and one PNP structure; The invention also comprises a first metal electrode (101) and a second metal electrode (102), wherein the first metal electrode (101) and the second metal electrode (102) form a current loop through interconnected metal, and when a voltage is applied from the first metal electrode (101) to the second metal electrode (102), the SCR path is from PNP to NPN2, and when a voltage is applied from the second metal electrode (102) to the first metal electrode (101), the SCR path is from PNP to NPN1.

2. The ESD protection device according to claim 1, characterized in that: The SCR unit is composed of the SOI type P substrate material (110), an NWdeep well region (120), a PW1 well region (130), an NSD ohmic contact region (150), and a PSD ohmic contact region (160).

3. The ESD protection device according to claim 1, characterized in that: The auxiliary trigger transistors NPN3 and NPN4 are composed of the SOI type P substrate material (110), a PW2 well region (140), and an NSD ohmic contact region (150).

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