US20010043449A1 - ESD protection apparatus and method for fabricating the same - Google Patents

ESD protection apparatus and method for fabricating the same Download PDF

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US20010043449A1
US20010043449A1 US09/852,735 US85273501A US2001043449A1 US 20010043449 A1 US20010043449 A1 US 20010043449A1 US 85273501 A US85273501 A US 85273501A US 2001043449 A1 US2001043449 A1 US 2001043449A1
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bipolar transistor
connected
diode
longitudinal bipolar
layer
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US09/852,735
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Mototsugu Okushima
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NEC Electronics Corp
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NEC Corp
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Publication of US20010043449A1 publication Critical patent/US20010043449A1/en
Assigned to NEC ELECTRONICS CORPORATION reassignment NEC ELECTRONICS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NEC CORPORATION
Priority claimed from US11/649,211 external-priority patent/US7629210B2/en
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/02Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
    • H01L27/0203Particular design considerations for integrated circuits
    • H01L27/0248Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection
    • H01L27/0251Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection for MOS devices
    • H01L27/0259Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection for MOS devices using bipolar transistors as protective elements
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/02Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
    • H01L27/0203Particular design considerations for integrated circuits
    • H01L27/0248Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection
    • H01L27/0251Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection for MOS devices
    • H01L27/0255Particular design considerations for integrated circuits for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection for MOS devices using diodes as protective elements
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L2924/00Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001Technical content checked by a classifier
    • H01L2924/0002Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

To make electric current concentration and electric field concentration hardly take place in junction parts even in case of performing miniaturization and to achieve triggering at low voltage. An ESD protection apparatus is installed between an input terminal 6 of a semiconductor integrated circuit chip and a CMOS transistor 100 and includes a trigger element 310 comprising diodes 311, 312 which are broken down by overvoltage applied to the input terminal 6 and an ESD protection element 210 including longitudinal bipolar transistors 211, 212 for discharging the accumulated electric charge of the input terminal 6 by being electrically communicated owing to the breakdown of the diodes 311, 312.

Description

    BACKGROUND OF THE INVENTION
  • 1. Field of the Invention [0001]
  • The present invention relates to an ESD protection apparatus to be installed in a semiconductor integrated circuit chip in order to protect a semiconductor integrated circuit from electrostatic discharge (ESD) and to a method for fabricating the protection apparatus. [0002]
  • 2. Description of the Prior Art [0003]
  • A conventional ESD protection apparatus in the CMOS process generally protects a semiconductor integrated circuit using a MOSFET transverse parasitic bipolar transistor by releasing the electric current in the transverse direction in a silicon substrate. On the other hand, the ESD protection apparatus has been required to be further miniaturized since the number of pins to be mounted on one chip has been increased sharply following the recent acute requirement of development of semiconductor integrated circuits made finer. [0004]
  • BRIEF SUMMARY OF THE INVENTION
  • Object of the Invention [0005]
  • However, as the miniaturization has been proceeding further, the electric current concentration and electric field concentration upon the junction parts has been increased more, so that the ESD protection apparatus has sometimes been broken owing to the heat generation. Therefore, there has been a limit to further improve the capability of the ESD protection apparatus. Further, the gate insulation film of a CMOS transistor has recently been made thinner, so that the gate insulation film sometimes has been broken before the ESD protection apparatus starts operating (reference to FIG. 33). Consequently, it has highly been expected to develop the ESD protection apparatus capable of triggering at a lower voltage. [0006]
  • Hence, the present invention aims to provide an ESD protection apparatus in which electric current concentration and electric field concentration upon the junction parts hardly take place even if miniaturization is advanced and which is capable of triggering at a lower voltage and to provide a method for fabricating such an ESD protection apparatus. [0007]
  • SUMMARY OF THE INVENTION
  • The ESD protection apparatus of the present invention is to be installed between a pad of a semiconductor integrated circuit chip and an inner circuit of the semiconductor integrated circuit chip. The ESD protection apparatus is provided with a trigger element comprising a diode to be broken down by overvoltage applied to the pad and an ESD protection element comprising a longitudinal bipolar transistor for discharging the accumulated electric charge of the pad by being electrically communicated attributed to the breakdown of the diode (claim [0008] 1).
  • As compared with a transverse bipolar transistor, a longitudinal bipolar transistor has a wide junction surface area for the same occupancy surface area, so that even if miniaturization is promoted, the electric current concentration and the electric field concentration hardly take place. On the other hand, a diode is easy to set a desired breakdown voltage by changing the impurity concentration. Consequently, an ESD protection apparatus in which electric current concentration and electric field concentration upon the junction parts hardly take place even if miniaturization is advanced and which is capable of triggering at a lower voltage can be obtained by utilizing the breakdown voltage of a diode for the trigger of a longitudinal bipolar transistor. [0009]
  • A first practical example of an ESD protection apparatus of the present invention is as follows (claim [0010] 3). The pad is an input terminal or an output terminal. The trigger element comprises a first and a second diodes and a first and a second resistors. The ESD protection element comprises NPN type first and second longitudinal bipolar transistors. Regarding the first diode, the cathode is connected with the pad and the anode is connected with the base of the first longitudinal bipolar transistor. Regarding the second diode, the cathode is connected with an electric power source terminal and the anode is connected with the base of the second longitudinal bipolar transistor. The first resistor is connected between the anode of the first diode and the ground terminal. The second resistor is connected between the anode of the second diode and the pad. Regarding the first longitudinal bipolar transistor, the collector is connected with the pad and the emitter is connected with the ground terminal. Regarding the second longitudinal bipolar transistor, the collector is connected with the electric power source terminal and the emitter is connected with the pad. Incidentally, at least either of a first diode, a first resistor and a first longitudinal bipolar transistor or a second diode, a second resistor and a second longitudinal bipolar transistor may be provided (the same is applied also for other claims).
  • A second practical example of an ESD protection apparatus of the present invention is as follows (claim [0011] 5). The pad is an electric power source terminal. The longitudinal bipolar transistor is NPN type. Regarding the diode, the cathode is connected with the pad and the anode is connected with the base of the longitudinal bipolar transistor. A resistor is connected between the anode of the diode and a ground terminal. Regarding the longitudinal bipolar transistor, the collector is connected with the pad and the emitter is connected with the ground terminal.
  • An ESD protection apparatus of the present invention may has the following constitution (claim [0012] 11). The trigger element comprises, as a diode to be broken down by overvoltage applied to the pad, a first longitudinal bipolar transistor whose collector and base work and which discharges the accumulated electric charge of the pad by being electrically communicated attributed to the breakdown of the diode. The ESD protection element comprises a second longitudinal bipolar transistor for discharging the accumulated electric charge of the pad by being electrically communicated attributed to the breakdown of the diode.
  • Practical examples of this case are as follows (claims [0013] 12, 13). The pad is an input terminal or an output terminal. The trigger element comprises an NPN type longitudinal bipolar transistor A and an NPN longitudinal bipolar transistor B working as the first longitudinal bipolar transistor and a first and a second resistors. The ESD protection element comprises an NPN type longitudinal bipolar transistor C and an NPN type longitudinal bipolar transistor D working as the second longitudinal bipolar transistor. Regarding the longitudinal bipolar transistors A, C, the collectors are connected with the pad and the bases are connected with each other and the emitters are connected with a ground terminal. The first resistor is connected between the bases of the longitudinal bipolar transistors A, C and the ground terminal. Regarding the longitudinal bipolar transistors B, D, the collectors are connected with an electric power source terminal and the bases are connected with each other and the emitters are connected with the pad. The second resistor is connected between the bases of the longitudinal bipolar transistors B, D and the pad (claim 12).
  • The pad is an electric power source terminal. The first and second longitudinal bipolar transistors are NPN type and their collectors are connected with the pad and their bases are connected with each other and their emitters are connected with a ground terminal. A resistor is connected between the bases of the first and second longitudinal bipolar transistors and the ground terminal (claim [0014] 13).
  • The conductive types P and N maybe taken as reverse conductive types N and P, respectively (claims [0015] 4, 6, 14 and 15). Even if the P and the N are reversed, the kind of a carrier alone is changed and naturally the same function can be realized. Incidentally, when the longitudinal bipolar transistor is taken as PNP type, the positions of the diode and the resistor are replaced with each other.
  • The diode may comprise a single diode or plural diodes connected in series, the overvoltage may be an forward voltage for the diode and the breakdown may be a substantial breakdown by being electrically communicated (claims [0016] 2 and 7 to 10). The diode forward descending voltage is, compared with the breakdown voltage, hard to depend on high impurity concentration and a low voltage. Consequently, by selecting the number of diodes to be connected in series, a desired substantial breakdown voltage can be accurately set.
  • In the ESD protection apparatus according to claims [0017] 11, 12, 13 and 14 or 15, the collector layers of the above described first longitudinal bipolar transistor and the above described second longitudinal bipolar transistor may be as simultaneously formed (claim 16).
  • In the ESD protection apparatus according to claims [0018] 11, 12, 13 and 14 or 15, the above described first longitudinal bipolar transistor and the above described second longitudinal bipolar transistor may have a common collector layer (claim 17).
  • In the ESD protection apparatus according to claims [0019] 1, 2, 3, 5, 7, 9, 11 and 12 or 13, the longitudinal bipolar transistor or the diode comprises all or some of: a first Ntype well formed on the P type silicon substrate surface; a second Ntype well adjacent to this first Ntype well and formed on the P type silicon substrate surface; a second N+ layer formed on this second Ntype well surface; the Ptype well formed on the first Ntype well surface; the P+ layer and a first N+ layer formed on this Ptype well surface apart from each other; the insulation material installed between these P+ layer and the first N+ layer for preventing the electric connection with the P+ layer and the first N+ layer, wherein the second Ntype well and the Ptype well may be insulated by the insulation material for isolation and the P type silicon substrate and the Ptype well may be insulated by the insulation material for isolation (claim 18). In this case, the conductive type P and N may be taken as the reverse conductive N and P, respectively (claim 19).
  • In the ESD protection apparatus according to claim [0020] 18, the P+ layer and the first and second N+ layers may be formed simultaneously with the P+ layer and the N+ layer of the CMOS transistor constituting the inner circuit (claim 20). The same is also applied for the ESD protection apparatus according to claim 19 (claim 21).
  • In the ESD protection device according to claim [0021] 18, a second Ntype well may be formed simultaneously with the Ntype well of the CMOS transistor constituting the inner circuit (claim 22). The same is also applied for the ESD protection apparatus according to claim 19 (claim 23).
  • In the ESD protection device according to claim [0022] 18 or claim 19, the insulation material maybe a dummy gate or a mere insulation material formed simultaneously formed with the gate electrode and the gate insulation film of the CMOS transistor constituting the inner circuit (claim 24). This dummy electrode or the insulation film may be formed in a ring shape on the silicon substrate surface (claim 25).
  • In the ESD protection apparatus according to claims [0023] 1, 2, 3, 5 and 7 or 9, the diode may comprises: the Ntype well formed on the P type silicon substrate surface; the P+ layer and the N+ layer formed on the Ntype well surface apart from each other; and the insulation material formed in the inside from the above described P type silicon substrate surface between these P+ layer and N+ layer (Claim 26) . In this case, in the ESD protection apparatus according to claims 1, 2, 4, 6 and 8 or 10, the conductive type P and N may be the reverse conductive type N and P, respectively (claim 27).
  • In the ESD protection apparatus according to claims [0024] 1, 2, 3, 5 and 7 or 9, the diode comprises: the Ntype well formed on the P type silicon substrate surface; the Ptype well formed on this Ntype well surface; the P+ layer and the N + layer formed on this Ptype well surface apart from each other; and the insulation material installed on the P type silicon substrate surface between these P+ layer and N+ layer, wherein the P type silicon substrate and the Ptype well may be insulated by the insulation material for isolation (claim 28). In this case, in the ESD protection apparatus according to claims 1, 2, 4, 6 and 8 or 10, the conductive type P and N may be taken as the reverse conductive type N and P, respectively (claim 29).
  • An ESD protection apparatus of the present invention may further have the following constitution (claim [0025] 30). The diode comprises a Ptype well formed on the surface of a silicon substrate, an N+ type layer and a P+ type layer formed on the Ptype well surface at an interval from each other, and a dummy gate electrode formed on the Ptype well via an insulation film and between the N+ type layer and the P+ type layer and connected with a ground terminal. In this case, the electric field between the N+ layer and the dummy gate electrode is intensified, the ESD trigger at a lower voltage. Incidentally, the conductive type P and N may be the reverse conductive type N and P, respectively (claim 31).
  • A method for fabricating an ESD protection apparatus relevant to the present invention is a method for fabricating an ESD protection apparatus according to claim [0026] 1 and comprises the following steps (claim 32). (1) A first step of simultaneously forming an Ntype well of a CMOS transistor composing the inner circuit and an Ntype well for connector connection to be connected with the collector of the longitudinal bipolar transistor on a P type silicon substrate. (2) A second step of simultaneously forming a collector Ntype well to be a collector of the longitudinal bipolar transistor and an Ntype well of the diode on the P type silicon substrate. (3) A third step of simultaneously forming a Ptype layer to be a base in the collector Ntype well of the longitudinal bipolar transistor and a Ptype layer to be an anode in the Ntype well of the diode. (4) A fourth step of simultaneously forming an N+ type layer in the Ptype well of the CMOS transistor, an N+ type layer in the Ntype well for collector connection of the longitudinal bipolar transistor, an N+ type layer to be an emitter in the Ptype layer of the longitudinal bipolar transistor, and an N+ type layer to be a cathode in the Ptype layer of the diode. (5) A fifth step of simultaneously forming a P+ type layer on the Ntype well of the CMOS transistor, a P+ type layer on the Ptype layer of the longitudinal bipolar transistor, and a P+ type layer on the Ptype layer of the diode. In this case, the method for fabricating the ESD protection apparatus according to claim 2 allows the anode and the cathode to be reversed (claim 33).
  • An ESD protection apparatus relevant to the present invention can be fabricated simultaneously in the fabrication process of a CMOS transistor except the steps (2) and (3). Since the steps (2) and (3) comprise ion implantation in the same parts, required is only one sheet of mask to be added in the conventional CMOS transistor fabrication process. [0027]
  • Further, the ESD protection apparatus fabrication method may further comprise a step of forming a dummy gate electrode simultaneously with a gate electrode of the CMOS transistor in the region where the collector N[0028] type well of the longitudinal bipolar transistor and Ntype well of the diode are formed in the second step (2). Incidentally, the dummy gate electrode is to prevent connection between the N+ type layers of the longitudinal bipolar transistor and the diode formed in the step (4) and the P+ type layers of the longitudinal bipolar transistor and the diode formed in the step (5) in the subsequent steps (claim 34). Alternatively, the ESD protection apparatus fabrication method may further comprise a step of forming an insulation layer which prevents connection between the N+ type layers of the longitudinal bipolar transistor and the diode formed in the step (4) and the P+ type layers of the longitudinal bipolar transistor and the diode formed in the step (5) in the subsequent steps (claim 35). In the method for fabricating the ESD protection apparatus relevant to the present invention also, the conductive type P and N may be the reverse type N and P, respectively (claim 36).
  • In other words, as a method for protecting a semiconductor device from electrostatic discharge (ESD) , the present invention provides a structure of an ESD protection apparatus in which a trigger element working at a low voltage and a longitudinal bipolar transistor are formed employing a fabrication method mutually compatible with a conventional CMOSFET fabrication process and which prevents electric current concentration and provides high ESD withstand level by enabling the trigger element to work at a lower voltage at which the gate insulation film of a MOS transistor in the inside is not broken at the time when the electrostatic pulses are applied to the input/output pad or an electric power source pad and making the longitudinal bipolar transistor work by the triggered electric current, and releasing the large quantity of electric charge in the longitudinal direction of the silicon substrate and the present invention provides a method for fabricating an ESD protection apparatus with such a structure.[0029]
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a circuit diagram illustrating a first embodiment of an ESD protection apparatus of the present invention; [0030]
  • FIG. 2 is a plan view of the ESD protection apparatus of FIG. 1; [0031]
  • FIG. 3 is a longitudinal cross-section figure cut along the III-III line in FIG. 2; [0032]
  • FIG. 4 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 2 and FIG. 3; [0033]
  • FIG. 5 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 2 and FIG. 3; [0034]
  • FIG. 6 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 2 and FIG. 3; [0035]
  • FIG. 7 is a graph showing the voltage-ampere characteristic in case of applying electrostatic pulses of ESD to the pad in the ESD protection apparatus of FIG. 1; [0036]
  • FIG. 8 is a graph showing the breakdown current values per unit length in case of using the ESD protection apparatus of FIG. 1 and in case of using a transverse parasitic bipolar transistor, a conventional MOS transistor; [0037]
  • FIG. 9 is a circuit diagram illustrating a second embodiment of an ESD protection apparatus of the present invention; [0038]
  • FIG. 10 is a plan view illustrating a third embodiment of an ESD protection apparatus of the present invention; [0039]
  • FIG. 11 is a longitudinal cross-section figure cut along the XI-XI line in FIG. 10; [0040]
  • FIG. 12 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 10 and FIG. 11; [0041]
  • FIG. 13 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 10 and FIG. 11; [0042]
  • FIG. 14 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 10 and FIG. 11; [0043]
  • FIG. 15 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 10 and FIG. 11; [0044]
  • FIG. 16 is a circuit diagram illustrating a fourth embodiment of an ESD protection apparatus of the present invention; [0045]
  • FIG. 17 is a plane view of the ESD protection apparatus in FIG. 16; [0046]
  • FIG. 18 is a longitudinal cross-section figure cut along the XVIII-XVIII line in FIG. 17; [0047]
  • FIG. 19 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 16; [0048]
  • FIG. 20 is a cross-section figure showing the method for fabricating the ESD protection apparatus of FIG. 16; [0049]
  • FIG. 21 is a plan view illustrating a fifth embodiment of an ESD protection apparatus of the present invention; [0050]
  • FIG. 22 is a longitudinal cross-section figure cut along the XXII-XXII line in FIG. 21; [0051]
  • FIG. 23 is a plan view illustrating a sixth embodiment of an ESD protection apparatus of the present invention; [0052]
  • FIG. 24 is a longitudinal cross-section figure cut along the XXIV-XXIV line in FIG. 23; [0053]
  • FIG. 25 is a cross-section figure illustrating a seventh embodiment of an ESD protection apparatus of the present invention; [0054]
  • FIG. 26 is a circuit diagram showing a eighth embodiment of the ESD protection apparatus relevant to the present invention; [0055]
  • FIG. 27 is a longitudinal cross-sectional view of the ESD protection apparatus of FIG. 26; [0056]
  • FIG. 28 is a graph showing a comparison result of characteristics of a trigger element using the breakdown of an inverse diode and the trigger element multistage-connecting the forward diodes in series; [0057]
  • FIG. 29 is a graph showing an electric current voltage characteristic at the time when electrostatic pulses of the ESD are applied to the pad in the ESD protection apparatus of FIG. 26; [0058]
  • FIG. 30 is a circuit diagram showing a ninth embodiment of the ESD protection apparatus relevant to the present invention; [0059]
  • FIG. 31 is a cross-sectional view of a tenth embodiment of the ESD protection apparatus relevant to the present invention; [0060]
  • FIG. 32A is a cross-sectional view showing a diode comprising a P[0061] + layer/an N well formed in the existing CMOS process in the eighth embodiment;
  • FIG. 32B is a cross-sectional view showing one portion of the longitudinal bipolar transistor in the tenth embodiment; and [0062]
  • FIG. 33 is a graph showing the voltage-ampere characteristic in case of applying electrostatic pulses of ESD of a pad in a conventional technique.[0063]
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • FIG. 1 to FIG. 3 illustrates a first embodiment of an ESD protection apparatus relevant to the present invention and FIG. 1 is a circuit diagram, FIG. 2 is a plan view, and FIG. 3 is a longitudinal cross-section figure along the III-III line in FIG. 2. Hereinafter, description will be given with reference to these figures. The ESD protection apparatus of this embodiment works as an input buffer protection circuit. [0064]
  • The ESD protection apparatus of this embodiment is installed between an input terminal (an input pad) [0065] 6 of a semiconductor integrated circuit chip and a CMOS transistor 100 and comprises a trigger element 310 comprising diodes 311, 312 which are broken down by overvoltage applied to the input terminal 6 and an ESD protection element 210 comprising longitudinal bipolar transistors 211, 212 for discharging the accumulated electric charge of the input terminal 6 by being electrically communicated owing to the breakdown of the diodes 311, 312. Incidentally, FIG. 2 and FIG. 3 show only the longitudinal bipolar transistor 211 as some of ESD protection element 210 and only the diode 311 as some of the trigger element 310.
  • The CMOS transistor [0066] 100 is a CMOS inverter comprising an NMOS transistor 101 and a PMOS transistor 102. Regarding the diode 311, the cathode is connected with the input terminal 6 and the anode is connected with the base of the longitudinal bipolar transistor 211. Regarding the diode 312, the cathode is connected with an electric power terminal 7 and the anode is connected with the base of the longitudinal bipolar transistor 212. A resistor 313 is connected with the anode of the diode 311 and a ground terminal 8. A resistor 314 is connected between the anode of the diode 312 and the input terminal 6. The longitudinal bipolar transistors 211, 212 are both NPN type. Regarding the longitudinal bipolar transistor 211, the collector is connected with the input terminal 6 and the emitter is connected with the ground terminal 8. Regarding the longitudinal bipolar transistor 212, the collector is connected with electric power terminal 7 and the emitter is connected with the input terminal 6. The resistors 313, 314 are made of a singly crystal silicon, a polysilicon, a metal or the like formed in the same semiconductor integrated circuit chip.
  • Since today it has swiftly been promote to make the gate insulation film of a CMOS transistor thinner, it is required for the ESD protection apparatus [0067] 210 works at a lower voltage at which the gate insulation film of the CMOS transistor 100 is broken. In this embodiment, the base potential of the longitudinal bipolar transistors 211, 212 is increased by voltage decreased at the time when the trigger current, which is the breakdown current of the diodes 311, 312, flows in the resistors 313, 314 to turn on longitudinal bipolar transistors 211, 212. Consequently, the large quantity of the electric charge attributed to the static electricity accumulated in the input terminal 6 is released in the longitudinal direction of the silicon substrate. As a result, electric current concentration can be prevented and a high ESD withstand level can be obtained.
  • To form the trigger element [0068] 310 comprising the ESD protection element 210 comprising longitudinal bipolar transistors 211, 212 and the diodes 311, 312 can be carried out by adding only one ion implantation mask in the common fabrication process of a CMOSFET. Hereinafter, the fabrication method will be described with the reference to FIG. 2 and FIG. 3.
  • At first, the ESD protection element [0069] 210 will be described. Simultaneously with the N+ type diffusion layer 1 of the CMOS transistor 100, the collector lead parts 10 and the emitters 11 are formed and simultaneously with the P+ type diffusion layer 2 of the CMOS transistor 100, the base lead parts 12 are formed. The dummy gate electrodes 13 formed simultaneously with the gate electrodes 3 of the CMOS transistor 100 are employed in order to separate the silicide of the emitters 11 and the base lead parts 12. The dummy gate electrodes 13 are not for applying potential but separate the silicide. Opening parts 50 are formed in a resist using an additional mask for ion implantation and ion implantation is carried out to simultaneously form the Pregion bases 16 and the collector N wells 17. The collector N wells 17 formed at that time and the collector lead parts 10 formed separately are connected with each other by the N wells 14 for connection simultaneously formed with the N well 5 of the CMOS transistor 100. Consequently, longitudinal bipolar transistors can be fabricated utilizing the CMOS process. Incidentally, the ion implantation may be carried out either before or after of the formation of the gate electrodes 3.
  • The trigger element [0070] 310 will be described next. The N30 Ptype diode has the same structure as the emitters 11 and bases 16 of the ESD protection element 210 and simultaneously with the N+ type diffusion layer 1 of the CMOS transistor 100, the N+ part 21 is formed and simultaneously with the Ptype diffusion layer 2 of the CMOS transistor 100, the lead parts 22 of the Pparts 26 are formed. Consequently, it is enabled to set a desired trigger voltage and the leakage level in the opposed direction.
  • FIG. 4 to FIG .[0071] 6 are cross-section illustrations illustrating the method for fabricating the ESD protection apparatus of this embodiment. Hereinafter, the method for fabricating the ESD protection apparatus of the present invention will be described in details.
  • At first, as illustrated in FIG. 4, simultaneously with formation of N well [0072] 5 of CMOS transistor 100, collector lead parts 10 and N wells 14 for connection of the ESD protection element 210 are formed. The doping concentration of these regions is about 1017/cm−3 to 1018/cm31 3. Also, simultaneously with formation of the gate electrodes 3 of the CMOS transistor 100, the dummy gate electrodes 13 of the ESD protection element 210 and a dummy gate electrode 23 of the trigger element 310 are formed. That is for preventing the emitters 11 and the base lead parts 12 of the ESD protection element 210 from being connected with the silicide formed later on the diffusion layer. In the same manner, that is for preventing the N+ part 21 and the lead parts 22 of trigger element 310 from being connected with the silicide later.
  • Successively, using opening parts [0073] 50 of a resist with a prescribed shape as a mask as illustrated in FIG. 5, ion implantation in about 1018/cm−3 dose is carried out to form the bases 16 of the ESD protection element 210 and continuously ion implantation in about 1018/cm−3 dose is carried out to form the collector N wells 17. At that time, the Ppart 26 and the N well 27 of the trigger element 310 are simultaneously formed.
  • Successively, as illustrated in FIG. 6, simultaneously with formation of the N[0074] + type diffusion layer 1 of the CMOS transistors 100, the collector lead parts 10, emitters 11, N+ parts 21, and the like are formed.
  • Successively, as illustrated in FIG. 3, simultaneously with the P[0075] type diffusion layer 2 of the CMOS transistors 100, the base lead parts 12 and lead parts 22 are formed. Finally, wirings are formed on these upper layers to form a circuit as illustrated in FIG. 1.
  • Next, the operation of the ESD protection apparatus of this embodiment will be described with the reference to FIG. 1 and FIG. 3. [0076]
  • The following description is of the operation at the time when the electrostatic pulses are applied to the input terminal [0077] 6. At first , when pulses of positive ESD relative to the ground terminal 8 are applied to the input terminal 6, high voltage is applied to the ESD protection element 210, trigger element 310, and the gate insulation film of the CMOS transistors 100. Therefore, it is required to release the electric charge by ESD by operation of the ESD protection element 210 before the gate insulation film of the CMOS transistors 100 is broken down.
  • If the gate insulation film of the CMOS transistors [0078] 100 is 4 nm, the gate insulation film is broken by stress of constant voltage of about 8V. That is, it is required for the ESD protection element 210 to operate at a voltage lower than that. However, in the case where the ESD protection element 210, which comprises longitudinal bipolar transistors, is formed, since the withstand voltage between the collector N wells 17 and the Pregion bases 16 are about as high as 10V, it is insufficient to protect the CMOS transistors 100 whose gate insulation film is thin and fine only by the ESD protection element 210.
  • Hence, it is required to form the trigger element [0079] 310 which operates at a voltage as low as possible and not lower than the electric power source voltage. Since the Ppart 26 of the trigger element 310 is formed by ion implantation, a desired trigger voltage or leakage level in the opposed direction can be set by controlling the dose quantity and it is easy to obtain trigger voltage of about 4 V.
  • FIG. 7 shows the voltage-ampere characteristic in case of electrostatic pulses application to the pad. At first, when the trigger element [0080] 310 works at about 4V, the resultant trigger current and the resistor 313 increase the base potential of the ESD protection element 210 to start the ESD protection element 210. When the ESD protection element 210 starts working, the electric charge applied to the input terminal 6 by the ESD can be released to the ground terminal 8 through the longitudinal bipolar transistor 211. Consequently, if the withstand voltage of the gate insulation film of the inner circuits of the CMOS transistors 100 is 8 V, the electric charge can be released at a lower voltage than that, so that the breakdown of the gate insulation film can be prevented.
  • Further, when pulses of negative ESD are applied to the input terminal [0081] 6 in relation to the ground terminal 8, since the collector N wells 17 and the P substrate 51 of the ESD protection element 210 shown in FIG. 3 are in N+/Pnormal direction, electric charge can smoothly be released.
  • FIG. 8 shows the breakdown electric current values per unit length in case of using the ESD protection apparatus of the present invention and in case of using a transverse parasitic bipolar transistor, which is a conventional MOS transistor. The breakdown electric current of the ESD protection element of this embodiment comprising longitudinal bipolar transistors is higher than that of an ESD protection element comprising transverse bipolar transistors. Also, if the inner gate insulation film is as thin as about 2 nm, the breakdown electric current is sharply lowered in case of the transverse bipolar transistors, the decrease is slight in case of the longitudinal bipolar transistors. [0082]
  • FIG. 9 is a circuit diagram showing a second embodiment of an ESD protection apparatus relevant to the present invention. Hereinafter, description will be given with reference to the figure. The ESD protection apparatus of this embodiment works as an electric power source protection circuit. [0083]
  • The ESD protection apparatus of this embodiment is installed between an electric power terminal (an electric power pad) [0084] 7 of a semiconductor integrated circuit chip and an inner circuit 103 and comprises a trigger element 315 comprising a diode 316 to be broken down by overvoltage applied to the electric power terminal 7 and an ESD protection element 213 comprising a longitudinal bipolar transistor 214 for discharging the accumulated electric charge of the electric power terminal 7 by being electrically communicated owing to the breakdown of the diode 316.
  • Regarding the diode [0085] 316, the cathode is connected with the electric power terminal 7 and the anode is connected with the base of the longitudinal bipolar transistor 214. A resistor 317 is connected between the anode of the diode 316 and a ground terminal 8. Regarding the longitudinal bipolar transistor 214, it is NPN type, and the collector is connected with the electric power terminal 7 and the emitter is connected with the ground terminal 8.
  • The plan view and the cross-section figure are same as FIG. 2 and FIG. 3 except the reference numerals. Consequently, the ESD protection apparatus of this embodiment also performs the same functions and effects. [0086]
  • FIG. 10 to FIG. 15 illustrate a third embodiment of an ESD protection apparatus relevant to the present invention. FIG. 10 shows a plan view, FIG. 11 shows the longitudinal cross-section figure cut along the XI-XI line in FIG. 10, and FIG. 12 to FIG. 15 show the cross-section figures illustrating the fabrication method. Hereinafter, description will be given with reference to these figures. Incidentally, the same reference numerals are assigned to these same as the parts in FIG. 2 and FIG. 6 and their description is omitted. [0087]
  • The ESD protection apparatus of this embodiment is an example in which insulation films [0088] 18, 28 (SiO2 or SiN) covering the diffusion layer as to prevent silicide formation are used for resistor element formation in place of the dummy gate electrodes 13, 23 for silicide separation (in FIG. 2 and FIG. 3).
  • At first, as illustrated in FIG. 12, simultaneously with formation of the N well [0089] 5 of the CMOS transistors 100, the N well 14 for connection with the collector lead parts 10 of the ESD protection element 200 is formed.
  • Successively, as illustrated in FIG. 13, using opening parts [0090] 50 of a resist with a prescribed shape as a mask, ion implantation is carried out to form the bases 16 of the ESD protection element 200 and continuously ion implantation is carried out to form the collector N wells 17. At that time, the Ppart 26 and the N well 27 of the trigger element 300 are simultaneously formed.
  • Successively, as illustrated in FIG. 14, simultaneously with formation of the N[0091] + type diffusion layer 1 of the CMOS transistors 100, the collector lead parts 10, emitters 11, N+ parts 21, and the like are formed.
  • Successively, as illustrated in FIG. 15, simultaneously with the P[0092] + type diffusion layer 2 of the CMOS transistors 100, the base lead parts 12, lead parts 22, and the like are formed.
  • Successively, as illustrated in FIG. 11, the insulation film [0093] 18 in ESD protection element 200 and the insulation film 28 in the trigger element 310 are formed. That is for preventing the connection of the emitters 11 and the base lead parts 12 of ESD protection element 200 with each other by the silicide formed in the diffusion layer thereafter. Simultaneously, that is also for preventing the connection of the N+ part 21 and the lead parts 22 of trigger element 300 with each other by the silicide.
  • Finally, wirings are formed on these upper layers to form a circuit as illustrated in FIG. 1. [0094]
  • FIG. 16 to FIG. 18 illustrate a fourth embodiment of an ESD protection apparatus relevant to the present invention. FIG. 16 shows a circuit diagram, FIG. 17 shows a plan view, and FIG. 18 shows the longitudinal cross-section figure cut along the XVIII-XVIII line in FIG. 17. Hereinafter, description will be given with reference to these figures. In the ESD protection apparatus of this embodiment, the trigger element is also used as a longitudinal bipolar transistor of the ESD protection element. [0095]
  • The ESD protection apparatus of this embodiment is installed between an electric power terminal (an electric power pad) [0096] 7 of a semiconductor integrated circuit chip and an inner circuit 103 and comprises a trigger element 400 comprising a diode 402 to be broken down by overvoltage applied to the electric power terminal 7 and an ESD protection element 200 comprising a longitudinal bipolar transistor 201 for discharging the accumulated electric charge of the electric power terminal 7 by being electrically communicated owing to the breakdown of the diode 402.
  • The diode [0097] 402 is between the collector and the base of the longitudinal bipolar transistor 401. The cathode of the diode 402, which the collector of the longitudinal bipolar transistor 401, is connected with the electric power terminal 7 and the anode of the diode 402, which is the base of the longitudinal bipolar transistor 401, is connected with the base of the longitudinal bipolar transistor 201. A resistor 403 is connected between the anode of the diode 402, which is the base of the longitudinal bipolar transistor 401, and a ground terminal 8. Regarding the longitudinal bipolar transistors 201, 402, they are NPN type, and the collector is connected with the electric power terminal 7 and the emitter is connected with the ground terminal 8.
  • In this embodiment, emitter lead parts [0098] 40 are formed in the trigger element 400 and connected as illustrated in FIG. 16 and FIG. 18. By connecting in such a manner, the longitudinal bipolar transistor 401 is formed in the trigger element 400 and the trigger element 400 can work as an ESD protection element. The base potential of the longitudinal bipolar transistors 201, 401 is increased by the trigger current of the diode 402 composed of the N+ part (the collector) 41 and the Ppart (the base) 46 of the trigger element 400 and the resistor 403 and owing the cooperation, the electric charge attributed to the static electricity accumulated in the electric power terminal 7 can be released by both of them. Incidentally, although the ESD protection apparatus of this embodiment is employed as the electric power pad, it may be also employed as an input pad or an output pad by installing two as same in the first embodiment.
  • FIG. 19 and FIG. 20 are cross-section figures illustrating the method for fabricating the ESD protection apparatus of this embodiment. Hereinafter, detailed description of the method for fabricating the ESD protection apparatus of this embodiment will be given with reference to FIG. 18 to FIG. 20. [0099]
  • At first, simultaneously with formation of N well [0100] 5 of the CMOS transistors 100, N wells 14 for connection for the collector lead parts 10 of the ESD protection element 200 and N wells 44 for emitter connection of the trigger element 400 are formed.
  • Successively, as illustrated in FIG. 19, using opening parts [0101] 50 of a resist with a prescribed shape as a mask, ion implantation is carried out to form the bases 16 of the ESD protection element 200 and continuously ion implantation is carried out to form the collector N wells 17. At that time, the Ppart 46 and the emitter N well 47 of the trigger element 400 are simultaneously formed.
  • Successively, as illustrated in FIG. 20, simultaneously with formation of the N[0102] + type diffusion layer 1 of the CMOS transistors, the collector lead parts 10 and emitters 11 of the ESD protection element 200, as well as the emitter lead parts 40 and collector 41 of the trigger element 400 are formed. Further, simultaneously with formation of the P+ type diffusion layer 2 of the CMOS transistors 100, the base lead parts 12 and lead parts 42 of the Pparts 46 to be base of the trigger element 400 are formed.
  • The insulation film [0103] 18 of the ESD protection element 200 and the insulation film 48 of the trigger element 400 are formed. That is for preventing the emitters 11 and the base lead parts 12 of the ESD protection element 200 from being connected with the silicide formed later on the diffusion layer. In the same manner, that is for preventing the N+ part 41 and the lead parts 42 of trigger element 400 from being connected with the silicide later.
  • Finally, wirings are formed on these upper layers to form a circuit as illustrated in FIG. 16. [0104]
  • FIG. 21 to FIG. 22 illustrate a fifth embodiment of an ESD protection apparatus relevant to the present invention. FIG. 21 shows a plan view and FIG. 22 shows the longitudinal cross-section figure cut along the XXII-XXII line in FIG. 21. Hereinafter, description will be given with reference to these figures. In the ESD protection apparatus of this embodiment, the collector of the ESD protection elements is utilized in common in order to miniaturize the surface area. [0105]
  • The ESD protection apparatus [0106] 230 of this embodiment comprises one collector N well 17′ by making two collector N wells 17 in common in the ESD protection element 200 of the third embodiment illustrated in FIG. 10 and FIG. 11. The surface area is miniaturized by using collector lead parts 10 only in both ends of the collector N well 17′. The method for fabricating the ESD protection apparatus of this embodiment is same as that of the third embodiment illustrated in FIG. 12 to FIG. 15.
  • FIG. 23 to FIG. 24 illustrate a sixth embodiment of an ESD protection apparatus relevant to the present invention. FIG. 23 shows a plan view and FIG. 24 shows the longitudinal cross-section figure cut along the XXIV-XXIV line in FIG. 23. Hereinafter, description will be given with reference to these figures. In the ESD protection apparatus of this embodiment, the ESD protection element and the trigger element are made in common in order to miniaturize the surface area. [0107]
  • The ESD protection elements [0108] 240 and the trigger element 310 of this embodiment are formed by combining two bases 16 and the Ppart 26 of the ESD protection element 200 and the trigger element 300 in the third embodiment illustrated in FIG. 10 and FIG. 11 into one base 16′ and at the same time combining two collector N wells 17 and the N well 27 of the ESD protection element 200 and the trigger element 300 in the third embodiment into one collector N well 19. The surface area is miniaturized by using collector lead parts 10 of the ESD protection elements 240 only in both ends. The method for fabricating the ESD protection apparatus of this embodiment is same as that of the third embodiment illustrated in FIG. 12 to FIG. 15.
  • FIG. 25 illustrates the longitudinal cross-section figure of a seventh embodiment of an ESD protection apparatus relevant to the present invention. Hereinafter, description will be given with reference to the figure. In the ESD protection apparatus of this embodiment, the ESD protection element is made to be a trigger element capable of triggering at lower voltage. [0109]
  • The ESD protection apparatus of this embodiment is same as the first embodiment except that the dummy gate electrode [0110] 23 of the trigger element 310 is fixed in the ground. In case of fixing the dummy gate electrodes 23 of the trigger element 310 in the ground, the electric field is intensified between the N+ part 21 and the dummy gate electrodes 23, so that triggering is caused at a lower voltage.
  • FIG. 26 and FIG. 27 show a eighth embodiment of the ESD protection apparatus relevant to the present invention, FIG. 26 is a circuit diagram and FIG. 27 is a cross-sectional view. Hereinafter, description will be given with reference to these drawings. Parts identical with those in FIGS. 1 and 3 are given the same reference numerals as in FIGS. 1 and 3, and description thereof will be omitted. The ESD protection apparatus of the present embodiment acts as an input buffer protection circuit. [0111]
  • The ESD protection apparatus of the present embodiment is installed between an input terminal (an input pad) [0112] 6 of a semiconductor integrated circuit chip and a CMOS transistor 100 and comprises a trigger element 510 comprising diodes 511, 512 which are broken down by overvoltage applied to the input terminal 6 and an ESD protection element 210 comprising longitudinal bipolar transistors 211, 212 for discharging the accumulated electric charge of the input terminal 6 by being electrically communicated owing to the breakdown of the diodes 511, 512. The diodes 511, 512 are a plurality of diodes connected in series, and the overvoltage is a forward voltage for the diodes 511, 512 and the breakdown is a substantial breakdown by being electrically communicated. Incidentally, the diodes 511, 512 are illustrated in FIG. 26 as four diodes connected in series, but in FIG. 27 simplified and illustrated as two diodes connected in series for convenience's sake.
  • Regarding the diode [0113] 511, a cathode is connected with a base of the longitudinal bipolar transistor 211 and an anode is connected with the input terminal 6. Regarding the diode 512, the cathode is connected with the base of the longitudinal bipolar transistor 212 and the anode is connected with an electric power source terminal 7. A resistor 313 is connected between the cathode of the diode 511 and a ground terminal 8. A resistor 314 is connected between the cathode of the diode 512 and the input terminal 6.
  • The longitudinal bipolar transistor [0114] 211, 212 use the same transistors as those of a first embodiment. The diodes 511, 512 are formed by an N+ diffusion layer 1, a P+ diffusion layer 2 and an N well 5 and the like which are formed at the time of the usual CMOS process.
  • In the first embodiment, for the trigger element, the breakdown of the inverse diode was utilized. In contrast, in the present embodiment, the trigger element [0115] 510 multistage-connected for raising a forward diode equal to or more than an electric power source voltage is employed.
  • Especially, a low voltage operation device having equal to or less than 1.5V has an extremely thin gate insulation film and therefore is broken down by application of equal to or more than 5V. For realizing low voltage trigger capable of preventing the breakdown of the gate insulation film in this voltage range, the present embodiment is effective. In the present embodiment, by changing serial connection stages of the diode corresponding to the electric power source voltage, a desired trigger voltage can be secured. [0116]
  • FIG. 28 is a graph showing a comparison result of the characteristics of the trigger element utilizing the breakdown of the inverse diode and the trigger element multistage-connecting the forward diodes in series. Hereinafter, description will be given with reference to this illustration. [0117]
  • Regarding utilization of the inverse breakdown, when the triggering at a voltage equal to or less than 5V is to be performed, by thickening the concentration of coupling, the lowering of the voltage to a certain degree is possible. However, before the breakdown, a zener leak is increased, thereby causing a drawback which is an increase of an off leak at the usual LSI operation time. For this reason, the lowering of the breakdown voltage to equal to or more than this is difficult. Hence, by using the trigger element for multistage-connecting the forward diodes and supplying the electric current to the base of the longitudinal bipolar transistor, the ESD protection element triggering at much lower voltage can be realized. [0118]
  • FIG. 29 is a graph showing an electric current voltage characteristic when an ESD electrostatic pulse is applied to a pad in the ESD protection apparatus of the present embodiment. Hereinafter, description will be given with reference to this illustration. [0119]
  • If a trigger voltage of one stage portion of the diode is taken as Vf (about 0.6V), the trigger voltage Vf of the diodes of four stages connected in series is Vf×[0120] 4=about 2.4V. When a surge of the ESD is applied to the pad and exceeds 2.4V, the forward series connection diodes are electrically communicated and inject the electric current into the base of the longitudinal bipolar transistor. By this trigger electric current, the longitudinal bipolar transistor which is a protection element of a high driving force starts operation, thereby discharging a charge of the ESD.
  • In recent years, the CMOS device operating at a low voltage of about 1.2V uses an extremely thin gate insulation film having a thickness of about equal to or less than 2.5 nm. The breakdown withstand pressure of this gate insulation film is about 4V to 5V. In such a case, by multistage-connecting the forward diodes in series and setting the triggering voltage in such a manner as to be larger than the electric power voltage of the CMOS inner circuit, no malfunction is caused during actual operation of the LSI and the triggering of the ESD discharge can be performed below the withstand pressure of the gate insulation film. [0121]
  • FIG. 30 is a circuit diagram showing a ninth embodiment of the ESD protection apparatus relevant to the present invention. Hereinafter, description will be given with reference to this illustration. The ESD protection apparatus of the present embodiment acts as an electric power source protection circuit. [0122]
  • The ESD protection apparatus of the present embodiment comprises a trigger element [0123] 515 comprising a diode 516 which is provided between the power source terminal 7 and the inner circuit 103 of the semiconductor integrated circuit and is broken down by overvoltage applied to an electric power source terminal 7, and an ESD protection element 213 comprising the longitudinal bipolar transistor 214 for discharging the accumulated electric charge of the electric power source terminal 7 by being electrically communicated owing to the breakdown of the diode 516. The diode 516 is a plurality of diodes connected in series, and the overvoltage is a forward voltage for the diode 516 and the breakdown is a substantial breakdown by being electrically communicated.
  • Regarding the diode [0124] 516, a cathode is connected with a base of the longitudinal bipolar transistor 214 and an anode is connected with the electric power source terminal 7. A resistor 317 is connected between the cathode of the diode 516 and a ground terminal 8. A longitudinal bipolar transistor 214 is of NPN type, and its collector is connected with the electric power source terminal 7, and its emitter is connected with the ground terminal 8.
  • A cross-sectional view thereof corresponds to FIG. 27. Consequently, the ESD protection apparatus of the present embodiment also performs the same functions and effects as the eighth embodiment. [0125]
  • FIG. 31 is a cross-sectional view showing a tenth embodiment of the ESD protection apparatus relevant to the present invention. Hereinafter, description will be given with reference to the illustration. Incidentally, the circuit diagram of the ESD protection apparatus of the present embodiment is the same as the eighth embodiment (FIG. 26). [0126]
  • In the present embodiment, as a trigger element [0127] 510, the diodes simultaneously formed at the time when the longitudinal bipolar transistor is formed are used by connecting them in series in a forward direction. In the eighth embodiment as shown in FIG. 27, a diode comprising P+ layers 2/an N well 5 is used. In contrast, in the present embodiment, a diode comprising an N+ layer 521/a Player 526 formed at the time when the longitudinal bipolar transistor is formed is used. In a high electric current area at a time such as the ESD charge discharging time, a resistance of a well is dominant and this resistance determines a discharging capacity.
  • Regarding the diode comprising P[0128] + layers 2/an N well 5 as shown in FIG. 27, the electric current flows under a separation region and therefore a resistance is increased. In contrast to this, in the present embodiment, a separation between the P+ layer 522/the N+ layer 521 is performed by a dummy gate 523 at a formation time of the longitudinal bipolar transistor, and since adjustment of the concentration of the Player 526 is possible by additional injection of the longitudinal bipolar transistor, the lowering of the resistance at the high electric current area is possible.
  • In the diode comprising the P[0129] + layers 2/the N well 5 as shown in FIG. 27, since a parasitic longitudinal bipolar transistor comprising the P+ layer/the N well 5/a P substrate 51 is formed, the electric current flowing into the P substrate 51 is generated. For this reason, the electric current to be supplied to the longitudinal bipolar transistor which is a protection element is reduced. However, in the present embodiment, since an N well 527 formed simultaneously with a collector layer 17 of an ESD protection element 210 exists, the diode comprising the N+ layer 521/the Player 526 can prevent the electric current flowing in a longitudinal direction, and therefore the electric current can be supplied to the base of the ESD protection element 210 with high efficiency (refer to FIG. 32). Consequently, according to the present embodiment, since a trigger electric current can be supplied to a base of the longitudinal bipolar transistor with high efficiency, the size of the trigger element can be reduced.
  • Incidentally, the present invention is, needless to mention, not limited to the foregoing first to the tenth embodiments. For example, the P type may be taken as the N type and the N type may be taken as the P type. Consequently, the NPN type may be taken as the PNP type with each N type and P type taken as the inverse conductive type. [0130]
  • In an ESD protection apparatus of the present invention, since the breakdown voltage of a diode is used as a trigger of a longitudinal bipolar transistor, electric current concentration and electric field concentration are hardly caused in junction parts even if miniaturization is promoted and moreover the characteristic of triggering at a low voltage can be obtained. The method for fabricating an ESD protection apparatus of the present invention is make it easy to fabricate an ESD protection apparatus of the present invention by adding only one mask in a common CMOS process. [0131]
  • In other words, the effects of the present invention is as follows. The first effect is that since electric current is released in the longitudinal direction by employing a longitudinal bipolar transistor, electric current concentration is suppressed as compared with the case of releasing the electric current in the transverse direction by using a conventional CMOSFET type parasitic bipolar transistor and consequently the ESD protection element itself is hardly broken. The second effect is that since the electric current to be discharged for the same surface area is high, the surface area required for an ESD protection element can be miniaturized and consequently decrease of the input capacity necessary for high speed operation can be performed. The third effect is that since a longitudinal bipolar transistor and a trigger element can be formed by adding only one ion implantation mask for an ESD protection circuit in a common CMOSFET process, the fabrication method is carried out in a compatible process with the CMOSFET process. The fourth effect is that owing to the trigger element capable of working a low voltage, the breakdown of the gate insulation film in CMOSFET can be prevented. The fifth effect is that an element capable of triggering at a desired voltage can be form. [0132]
  • The invention may be embodied in other specific forms without departing from the spirit or essential characteristic thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims as therefore intended to be embraced therein. [0133]
  • The entire disclosure of Japanese Patent Application No. 2000-141304 (Filed on May 15 [0134] th, 2000) including specification, claims, drawings and summary are incorporated herein by reference in its entirety.

Claims (36)

What is claimed is:
1. An ESD protection apparatus installed between a pad of a semiconductor integrated circuit chip and an inner circuit of said semiconductor integrated circuit chip, comprising:
a trigger element having a diode to be broken down by overvoltage applied to said pad; and
an ESD protection element having a longitudinal bipolar transistor for discharging the accumulated electric charge of said pad by being electrically communicated attributed to the breakdown of said diode.
2. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises a single diode or plural diodes connected in series;
said overvoltage is a forward voltage for the diode; and
said breakdown is a substantial breakdown owing to conduction.
3. The ESD protection apparatus according to
claim 1
, wherein said pad is an input terminal or an output terminal;
said trigger element comprises a first and a second diodes and a first and a second resistors;
said ESD protection element comprises NPN type first and second longitudinal bipolar transistors;
a cathode of said first diode is connected with said pad and an anode of said first diode is connected with a base of said first longitudinal bipolar transistor;
a cathode of said second diode is connected with an electric power source terminal and an anode of said second diode is connected with a base of said second longitudinal bipolar transistor;
said first resistor is connected between the anode of said first diode and a ground terminal;
said second resistor is connected between the anode of said second diode and said pad;
a collector of said first longitudinal bipolar transistor is connected with said pad and an emitter of said first longitudinal bipolar transistor is connected with said ground terminal; and
a collector of said second longitudinal bipolar transistor is connected with said electric power source terminal and an emitter of said second longitudinal bipolar transistor is connected with said pad; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
4. The ESD protection apparatus according to
claim 1
, wherein said pad is an input terminal or an output terminal;
said trigger element comprises first and second diodes and first and second resistors;
said ESD protection element comprises PNP type first and second longitudinal bipolar transistors;
a cathode of said first diode is connected with a base of said first longitudinal bipolar transistor and an anode of said first diode is connected with a ground terminal;
a cathode of said second diode is connected with a base of said second longitudinal bipolar transistor and an anode of said second diode is connected with said pad;
said first resistor is connected between the cathode of said first diode and said pad;
said second resistor is connected between the cathode of said second diode and said electric power source terminal;
a collector of said first longitudinal bipolar transistor is connected with said ground terminal and an emitter of said first longitudinal bipolar transistor is connected with said pad; and
a collector of said second longitudinal bipolar transistor is connected with said pad and an emitter of said second longitudinal bipolar transistor is connected with said electric power source terminal; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
5. The ESD protection apparatus according to
claim 1
, wherein said pad is an electric power source terminal;
said longitudinal bipolar transistor is NPN type;
the cathode of said diode is connected with said pad and the anode of said diode is connected with the base of said longitudinal bipolar transistor;
a resistor is connected between the anode of said diode and a ground terminal; and
the collector of said longitudinal bipolar transistor is connected with said pad and the emitter of said longitudinal bipolar transistor is connected with said ground terminal.
6. The ESD protection apparatus according to
claim 1
, wherein said pad is an electric power terminal;
said longitudinal bipolar transistor is of PNP type;
a cathode of said diode is connected with a base of said longitudinal bipolar transistor and an anode of said diode is connected with a ground terminal;
a resistor is connected between the cathode of said diode and said electric power terminal; and
a collector of said longitudinal bipolar transistor is connected with said ground terminal and an emitter of said longitudinal bipolar transistor is connected with said pad.
7. The ESD protection apparatus according to
claim 2
,
wherein said pad is an input terminal or an output terminal;
said trigger element comprises first and second diodes and first and second resistors;
said ESD protection element comprises NPN type first and second longitudinal bipolar transistors;
an anode of said first diode is connected with said pad and a cathode of said first diode is connected with a base of said first longitudinal bipolar transistor;
an anode of said second diode is connected with an electric power source terminal and a cathode of said second diode is connected with a base of said second longitudinal bipolar transistor;
said first resistor is connected between the cathode of said first diode and the ground terminal;
said second resistor is connected between the cathode of said second diode and said pad;
a collector of said first longitudinal bipolar transistor is connected with said pad and an emitter of said first longitudinal bipolar transistor is connected with said ground terminal; and
a collector of said second longitudinal bipolar transistor is connected with said electric power source terminal and an emitter of said second longitudinal bipolar transistor is connected with said pad; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
8. The ESD protection apparatus according to
claim 2
,
wherein said pad is an input terminal or an output terminal;
said trigger element comprises first and second diodes and first and second resistors;
said ESD protection element comprises PNP type first and second longitudinal bipolar transistors;
an anode of said first diode is connected with a base of said first longitudinal bipolar transistor and a cathode of said first diode is connected with a ground terminal;
an anode of said second diode is connected with a base of said second longitudinal bipolar transistor and a cathode of said second diode is connected with said pad;
said first resistor is connected between the anode of said first diode and said pad;
said second resistor is connected between the anode of said second diode and said electric power source terminal;
the collector of said first longitudinal bipolar transistor is connected with said ground terminal and the emitter of said first longitudinal bipolar transistor is connected with said pad;
the collector of said second longitudinal bipolar transistor is connected with said pad and the emitter of said second longitudinal bipolar transistor is connected with said electric power source terminal; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
9. The ESD protection apparatus according to
claim 2
,
wherein said pad is an electric power source terminal;
said longitudinal bipolar transistor is of NPN type;
an anode of said diode is connected with said pad and a cathode of said diode is connected with a base of said longitudinal bipolar transistor;
a resistor is connected between the cathode of said diode and a ground terminal;
a collector of said longitudinal bipolar transistor is connected with said pad and an emitter of said longitudinal bipolar transistor is connected with said ground terminal; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
10. The ESD protection apparatus according to
claim 2
,
wherein said pad is an electric power source terminal;
said longitudinal bipolar transistor is of PNP type;
an anode of said diode is connected with a base of said longitudinal bipolar transistor and a cathode of said diode is connected with a ground terminal;
a resistor is connected between the anode of said diode and said electric power source terminal;
a collector of said longitudinal bipolar transistor is connected with said ground terminal and an emitter of said longitudinal bipolar transistor is connected with said pad; and
at least either of said first diode, said first resistor and said first longitudinal bipolar transistor or said second diode, said second resistor and said second longitudinal bipolar transistor are provided.
11. An ESD protection apparatus installed between a pad of a semiconductor integrated circuit chip and an inner circuit of said semiconductor integrated circuit chip, comprising:
a trigger element having a first longitudinal bipolar transistor whose collector and base act as a diode to be broken down by overvoltage applied to said pad and which discharges the accumulated electric charge of said pad by being electrically communicated due to the breakdown of the diode; and
an ESD protection element having a second longitudinal bipolar transistor for discharging the accumulated electric charge of said pad by being electrically communicated attributed to the breakdown of the diode.
12. The ESD protection device according to
claim 11
, wherein said pad is an input terminal or an output terminal;
said trigger element comprises an NPN type longitudinal bipolar transistor A and an NPN type longitudinal bipolar transistor B acting as said first longitudinal bipolar transistor, and a first and a second resistors;
said ESD protection element comprises an NPN type longitudinal bipolar transistor C and an NPN type longitudinal bipolar transistor D acting as said second longitudinal bipolar transistor;
collectors of said longitudinal bipolar transistors A, C are connected with said pad, bases thereof are connected with each other and emitters thereof are connected with a ground terminal;
said first resistor is connected between the bases of said longitudinal bipolar transistors A, C and said ground terminal;
collectors of said longitudinal bipolar transistors B, D are connected with an electric power source terminal, bases thereof are connected with each other and emitters thereof are connected with said pads;
said second resistor is connected between the bases of said longitudinal bipolar transistors B, D and said pads; and
at least either of said first resistor and said first longitudinal bipolar transistor or said second resistor and said second longitudinal bipolar transistor are provided.
13. The ESD protection apparatus according to
claim 11
, wherein said pad is an electric power source terminal;
said first and second longitudinal bipolar transistors are NPN type and their collectors are connected with said pad and their bases are connected with each other and their emitters are connected with a ground terminal; and
a resistor is connected between the bases of said first and second longitudinal bipolar transistors and the ground terminal.
14. The ESD protection apparatus according to
claim 11
, wherein said pad is an input terminal or an output terminal;
said trigger element comprises a PNP type longitudinal bipolar transistor A and a PNP type longitudinal bipolar transistor, B acting as said first longitudinal bipolar transistor, and a first and a second resistors;
said ESD protection element comprises a PNP type longitudinal bipolar transistor C and a PNP type longitudinal bipolar transistor D acting as said second longitudinal bipolar transistor;
emitters of said bipolar transistors A, C are connected with said pads, bases thereof are connected with each other and collectors thereof are connected with a ground terminal;
said first resistor is connected between the bases of said longitudinal bipolar transistors A, C and said pads;
emitters of said longitudinal bipolar transistors B, D are connected with an electric power source terminal, bases thereof are connected with each other and collectors thereof are connected with said pads;
said second resistor is connected between the bases of said longitudinal bipolar transistors B, D and said electric power source terminal; and
at least either of said first resistor and said first longitudinal bipolar transistor or said second resistor and said second longitudinal bipolar transistor are provided.
15. The ESD protection apparatus according to
claim 11
, wherein said pad is an electric power source terminal;
said first and second longitudinal bipolar transistors are PNP type, and collectors thereof are connected with a ground terminal, bases thereof are connected with each other and emitters thereof are connected with said pads; and
resistors are connected between the bases of said first and second longitudinal bipolar transistors and said pads.
16. The ESD protection apparatus according to
claim 11
, wherein collector layers of said first longitudinal bipolar transistor and an emitter layers of said second longitudinal bipolar transistor are simultaneously formed.
17. The ESD protection apparatus according to
claim 11
, wherein a collector layer of said first longitudinal bipolar transistor and an emitter layer of said second longitudinal bipolar transistor are a common layer.
18. The ESD protection apparatus according to
claim 1
, wherein said longitudinal bipolar transistor or said diode comprises all or some of: a first Ntype well formed on a P type silicon substrate surface; a second Ntype well adjacent to the first Ntype well and formed on said P type silicon substrate surface; a second N+ layer formed on the second Ntype well surface; a Ptype well formed on said first Ntype well surface; a P+ layer and a first N+ layer formed on the Ptype well surface apart from each other; and an insulation material installed between the P+ layer and the first N+ layer for preventing an electric connection with said P++ layer and the first N+ layer, and
said second Ntype well and said Ptype well are insulated by the insulation material for isolation, and said P type silicon substrate and said Ptype well are insulated by the insulation material for isolation.
19. The ESD protection apparatus according to
claim 1
, wherein said longitudinal bipolar transistor or said diode comprises all or some of: a first Ptype well formed on a N type silicon substrate surface; a second Ptype well adjacent to the first Ptype well and formed on said N type silicon substrate surface; a second P+ layer formed on this second Ptype well surface; a Ntype well formed on said first Ptype well surface; a N+ layer and a first P+ layer formed on the Ntype well surface apart from each other; and an insulation material installed between the N+ layer and the first P+ layer for preventing the electric connection with said P+ layer and first N+ layer, and
said second Ptype well and said Ntype well are insulated by the insulation material for isolation, and said N type silicon substrate and said Ntype well are insulated by the insulation material for isolation.
20. The ESD protection apparatus according to
claim 18
, wherein said P+ layer and said first and second N+ layers are formed simultaneously with the P+ layer and the N+ layers of a CMOS transistor constituting said inner circuit.
21. The ESD protection apparatus according to
claim 19
, wherein said N+ layer and said first and second P+ layers are formed simultaneously with the N+ layers and the P+ layer of the CMOS constituting said inner circuit.
22. The ESD protection apparatus according to the
claim 18
, wherein said second Ntype well is formed simultaneously with the Ntype well of the CMOS transistor constituting said inner circuit.
23. The ESD protection apparatus according to the
claim 19
, wherein said second Ptype well is formed simultaneously with the Ptype well of the CMOS transistor constituting said inner circuit.
24. The ESD protection apparatus according to
claim 18
, wherein said insulation material is a dummy gate electrode or a simple insulation film formed simultaneously with a gate electrode and a gate insulation film of the CMOS transistor constituting said inner circuit.
25. The ESD protection apparatus according to
claim 24
, wherein said dummy gate electrode or said insulation film is formed in a ring shape on said silicon substrate surface.
26. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: an Ntype well formed on a P type silicon substrate surface; a P+ layer and an N+ layer formed on the Ntype well surface apart from each other; and an insulation material formed inside from said P type silicon substrate surface between the P+ layer and N+ layer.
27. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: a Ptype well formed on an N type silicon substrate surface; a P+ layer and an N+ layer formed on the Ptype well surface apart from each other; and an insulation material formed inside from said P type silicon substrate surface between the P+ layer and N+ layer.
28. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: an Ntype well formed on a P type silicon substrate surface; a Ptype well formed on the Ntype well surface; a P+ layer and N+ layer formed on the Ptype well surface apart from each other; and an insulation material installed on said P type silicon substrate surface between the P+ layer and N+ layer for preventing electric connection between said P+ layer and N+ layer, and
said P type silicon substrate and said Ptype well are insulated by the insulation material for isolation.
29. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: a Ptype well formed on an N type silicon substrate surface; an Ntype well formed on the Ptype well surface; a P+ layer and N+ layer formed on the Ntype well surface apart from each other; and an insulation material installed on said N type silicon substrate surface between the Player and N+ layer for preventing electric connection between said P+ layer and N+ layer, and
said N type silicon substrate and said N+ type well are insulated by the insulation material for isolation.
30. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: a Ptype well formed on a silicon substrate surface; N+ layer and the P+ layer formed on the P+ type well surface apart from each other; and a dummy gate electrode installed on said Ptype well between the N+ layer and P+ layer through an insulation film and connected with a ground terminal.
31. The ESD protection apparatus according to
claim 1
,
wherein said diode comprises: a Ntype well formed on a silicon substrate surface; N+ layer and the P+ layer formed on the Ntype well surface apart from each other; and a dummy gate electrode installed on said Ntype well between the N+ layer and P+ layer through an insulation film and connected with a ground terminal.
32. A method for fabricating an ESD protection apparatus according to
claim 1
, comprising:
a first step of simultaneously forming an Ntype well of a CMOS transistor composing said inner circuit and an Ntype well for collector connection to be connected with the collector of said longitudinal bipolar transistor on a P type silicon substrate;
a second step of simultaneously forming a collector Ntype well to be a collector of said longitudinal bipolar transistor and an Ntype well of said diode on said P type silicon substrate;
a third step of simultaneously forming a Ptype layer to be a base in the collector Ntype well of said longitudinal bipolar transistor and a Ptype layer to be an anode in the Ntype well of said diode;
a fourth step of simultaneously forming an N+ type layer in the Ptype well of said CMOS transistor, an N+ type layer in the Ntype well for collector connection of said longitudinal bipolar transistor, an N+ type layer to be an emitter in the Ptype layer of said longitudinal bipolar transistor, and an N+ type layer to be a cathode in the Ptype layer of said diode; and
a fifth step of simultaneously forming a P+ type layer on the Ntype well of said CMOS transistor, a P+ type layer on the Ptype layer of said longitudinal bipolar transistor, and a P+ type layer on the Ptype layer of said diode.
33. A method for fabricating the ESD protection apparatus according to
claim 2
, comprising:
a first step of simultaneously forming an Ntype well of a CMOS transistor constituting said inner circuit and the Ntype well for collector connection to be connected with said longitudinal bipolar transistor on a P type silicon substrate;
a second step of simultaneously forming a collector Ntype well to be a collector of said longitudinal bipolar transistor and the Ntype well of said diode on said P type silicon substrate;
a third step of simultaneously forming a Ptype layer to be a base in the collector Ntype well of said longitudinal bipolar transistor and the Ptype layer to be a cathode in the Ntype well of said diode;
a fourth step of simultaneously forming an N+ layer in the Ptype well of said CMOS transistor, the N+ layer in the Ntype well for collector connection of said longitudinal bipolar transistor, the N+ layer to be an emitter in the Ptype layer of said longitudinal bipolar transistor, and the N+ layer to be an anode in the Ptype layer of said diode; and
a fifth step of simultaneously forming the P+ layer in the Ntype well of said CMOS transistor, the P+ layer in the P+ type layer of said longitudinal bipolar transistor and the Player in the Ptype layer of said diode.
34. The method for fabricating an ESD protection apparatus according to
claim 32
, further comprising a step of forming a dummy gate electrode simultaneously with a gate electrode of said CMOS transistor in the region where the collector Ntype well of said longitudinal bipolar transistor and Ntype well of said diode are formed in said second step, wherein said dummy gate electrode is to prevent connection in the subsequent steps between the N+ type layers of said longitudinal bipolar transistor and said diode formed in said fourth step and the P+ type layers of said longitudinal bipolar transistor and said diode formed in the fifth step.
35. The method for fabricating an ESD protection apparatus according to
claim 32
, further comprising a step of forming an insulation layer which prevents connection in the subsequent steps between the N+ type layers of said longitudinal bipolar transistor and said diode formed in said fourth step and the P+ type layers of said longitudinal bipolar transistor and said diode formed in the fifth step.
36. The method for fabricating an ESD protection apparatus according to
claim 32
, wherein an N replaces said conductive type P and a P replaces said conductive type N.
US09/852,735 2000-05-15 2001-05-11 ESD protection apparatus and method for fabricating the same Abandoned US20010043449A1 (en)

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US20060223258A1 (en) 2006-10-05

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