High Voltage ESD Protection Apparatus
A device comprises a high voltage n well and a high voltage p well over a buried layer, a first low voltage n well over the high voltage n well, wherein a bottom portion of the first low voltage n well is surrounded by the high voltage n well, an N+ region over the first low voltage n well, a second low voltage n well and a low voltage p well over the high voltage p well, a first P+ region over the second low voltage n well and a second P+ region over the low voltage p well.
This application is a continuation of U.S. patent application Ser. No. 16/227,726, filed on Dec. 20, 2018, which is a continuation of U.S. patent application Ser. No. 15/165,832, filed on May 26, 2016, now U.S. Pat. No. 10,163,891 issued on Dec. 25, 2018, which is a divisional of U.S. patent application Ser. No. 13/243,688, filed on Sep. 23, 2011, now U.S. Pat. No. 9,356,012 issued on May 31, 2016, which applications are incorporated herein by reference.
BACKGROUNDElectrostatic discharge (ESD) is a rapid discharge that flows between two objects due to the build-up of static charge. ESD may destroy semiconductor devices because the rapid discharge can produce a relatively large current. In order to reduce the semiconductor failures due to ESD, ESD protection circuits have been developed to provide a current discharge path. When an ESD event occurs, the discharge current is conducted through the discharge path without going through the internal circuits to be protected.
In the semiconductor technology, ESD protection solutions such as NMOS transistors, Silicon-Controlled Rectifiers (SCRs) and RC triggered PMOS transistors are widely used. Each ESD protection device may comprise a detection circuit and an ESD current discharge path. For example, an RC triggered ESD protection circuit may comprise a discharge transistor, a driver and an ESD spike detection circuit. The ESD spike detection circuit may include a resistance element and a capacitance element connected in series to form an RC detection circuit. The node between the resistance element and the capacitance element is coupled to the gate of the discharge transistor via the driver. The time constant formed by the resistance element and the capacitance element is so chosen that the discharge transistor is turned off when the ESD protection device operates in a normal power up mode. On the other hand, the discharge transistor is turned on when an ESD spike occurs at a power bus to which the ESD protection circuit is coupled. The turn-on of the discharge transistor may provide a bypass of the ESD current from the power bus to ground so as to clamp the voltage of the power bus to a level below the maximum rating voltage to which the internal circuit is specified, so that it helps to prevent the large voltage spike from damaging the internal circuits being protected.
Similarly, a PNP transistor can be used as an ESD protection device. More particularly, the emitter of the PNP transistor is coupled to an input/output (I/O) pad of an integrated circuit and the collector of the PNP transistor is coupled to ground. When an ESD event occurs, an external voltage across the I/O pad and ground increases beyond the reverse-bias breakdown voltage of the PNP transistor. As a result, a conductive path is established between the emitter and the collector of the PNP transistor. Such a conductive path allows the large amount of ESD energy to be discharged in a relatively short amount of time. As a consequence, the internal circuit components of the integrated circuit can be protected from being damaged by the ESD event.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTSThe making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention will be described with respect to preferred embodiments in a specific context, an NPN transistor based electrostatic discharge (ESD) protection device. The invention may also be applied, however, to a variety of ESD protection devices.
The ESD protection structure 100 further comprises a first high voltage P well (HVPW) region 122, a high voltage N well (HVNW) region 124 and a second HVPW region 126. As shown in
The first P+ region 102 is formed on the SHP region 112. The first P+ region 102 is separated from the first SHN region 114 by the second isolation region 144. The N+ region 106 is formed on the second SHN region 116. The second P+ region 108 is formed on the second HVPW 126. As shown in
In
The SHP region 112, the first SHN region 114 and the second SHN region 116 are fabricated in a low voltage CMOS process. In accordance with an embodiment, the SHP region 112, the first SHN region 114 and the second SHN region 116 are fabricated in a 5V CMOS process. It should further be noted that while the SHP region 112, the first SHN region 114 and the second SHN region 116 appear to be similar in
In accordance with an embodiment, the first P+ region 102, the second P+ region 108 and the N+ region 106 are highly doped. The first P+ region 102, the second P+ region 108 and the N+ region 106 have a doping density of between about 1020/cm3 and 1021/cm3. In addition, the SHP region 112, the first SHN region 114 and the second SHN region 116 are heavily doped regions. The SHP region 112 has a doping density of between about 1017/cm3 and 1018/cm3. The first SHN region 114 and the second SHN region 116 have a doping density of between about 1017/cm3 and 1018/cm3. Furthermore, in accordance with an embodiment, the first HVPW region 122 has a doping density of about 1017/cm3. Likewise, the HVPW region 124 and the second HVPW region 126 have a doping density of 1017/cm3.
It should be noted that the doping technique used in the previous example is selected purely for demonstration purposes and is not intended to limit the various embodiments to any particular doping technique. One skilled in the art will recognize that alternate embodiment could be employed (such as employing the diffusion technique).
The isolation regions 142, 144, 146 and 148 are used to isolate active regions so as to prevent leakage current from flowing between adjacent active regions. The isolation region (e.g., the first isolation region 142) can be formed by various ways (e.g., thermally grown, deposited) and materials (e.g., silicon oxide, silicon nitride). In accordance with an embodiment, the isolation regions (e.g., the first isolation region 142) may be fabricated by a surface trench isolation (STI) technique.
In accordance with an embodiment, the ESD protection structure 100 may comprise two depletion regions. A first depletion region is formed between the HVNW region 124 and the first HVPW region 122. One skilled in the art will recognize that the first depletion region can provide a breakdown voltage when the first depletion region is reverse biased during an ESD event. The detailed operation of the breakdown voltage of the ESD protection structure 100 will be described below with respect to FIG. 2 and
In
The NPN transistor 220 has an emitter 212, a base 216 and a collector 214. The emitter 212, the base 216 and the collector 214 are formed by the first SHN region 114, the first P+ region 102 and the N+ region 106 respectively. The emitter 212 is electrically coupled to the cathode of the diode 210. The base 216 is either coupled to the emitter 212 or floating. In sum, a simplified circuit diagram 200 depicts that the corresponding circuit of the ESD protection structure 100 is formed by a series connection of the diode 210 and the NPN transistor 220.
However, it should be recognized that while
As known in the art, the NPN transistor 220 has a breakdown voltage. When a large voltage spike is applied between the collector 214 and the emitter 212, the NPN transistor 220 may experience an avalanche breakdown in which a large current is allowed to flow from the collector 214 to the emitter 212. The current path from the collector 214 to the emitter 212 may provide a bypass of the ESD current and clamp the voltage between the collector 214 and the emitter 212 to a level below the maximum rating voltage of the internal circuit, so that it helps to prevent the large voltage spike from damaging the internal circuits being protected. Similarly, the diode 210 has a breakdown voltage (e.g., 10V) when a voltage is applied between the cathode and the anode of the diode 210. In sum, the ESD protection circuit 200 has a breakdown voltage equivalent to the NPN transistor's 220 breakdown voltage plus the diode's 210 breakdown voltage.
The ESD protection circuit 200 is typically placed at an I/O pad and a VSS of a device to be protected (not shown but illustrated in
Furthermore, the diode 210 allows the ESD current to flow from the cathode to the anode when the voltage across the cathode and the anode exceeds the breakdown voltage of the diode 210 (e.g., 10y). In addition, the diode 210 may clamp the voltage between the cathode and the anode to its breakdown voltage (e.g., 10y). The conduction of both the diode 210 and the NPN transistor 220 clamps the voltage between the collector 214 and the anode of the diode 210 to a lower level so that the internal circuits coupled to the collector 214 can be protected.
It should be noted that both the diode 210 and the NPN transistor 220 may turn on nearly simultaneously. However, for convenience the description above uses a slightly earlier turn-on of the NPN transistor 220 as an example to describe the breakdown mechanism. It is understood that the turn-on sequence between the diode 210 and the NPN transistor 220 plays no role in this embodiment. The breakdowns of two series-connected elements (e.g., diode 210 and NPN transistor 220) in the ESD protection circuit 200 may be performed in any arbitrary sequence. However, the specifically discussed example above is preferred.
The curve 304 represents the I-V relationship for the ESD protection circuit 200 during an ESD event. As shown in
It should be noted that in
In
In accordance with an embodiment, the ESD protection structure 800 may comprises two depletion regions. A first depletion region is formed between the N+ region 802 and the HVPW region 822. One skilled in the art will recognize that the first depletion region can provide a breakdown voltage when the first depletion region is reverse biased during an ESD event. In addition, a second depletion region is formed between the p-type metal contact 852 and the SHN region 812. Since the second depletion region is connected in series with the first depletion region, the second depletion region may provide additional breakdown voltage during an ESD event.
It should be noted that in
When an ESD event occurs between the I/O pad 1206 and the VSS pad 1204, the ESD protection circuit 200 conducts the ESD current, and the turn-on of an ESD protection circuit (e.g., the ESD protection circuit 200) clamps the voltage between the I/O pad 1206 and the VSS pad 1204 below the maximum voltage to which the internal circuits 1202 are specified, so that the internal circuits 1202 coupled between the I/O pad 1206 and the VSS pad 1204 are protected. An advantageous feature of the described circuit level ESD protection is the ESD protection circuit provides a bypass for ESD current to flow so that the various circuit components of the internal circuit 1202 are protected.
It should be noted that the ESD protection circuit 200 may be coupled between the VDD pad 1208 and the VSS pad 1204 as indicated by the dashed line in
In
As described above with respect to
Although embodiments of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Claims
1. A semiconductor device comprising:
- a substrate;
- a transistor in the substrate, comprising: a collector comprising an n-type region; a base comprising a first p-type region; and an emitter comprising an N well;
- a first P well in the substrate and under the first p-type region;
- a second P well in the substrate, wherein the first P well and the N well extend into the second P well;
- a first isolation region in the substrate between the n-type region and the first p-type region;
- a second isolation region in the substrate between the n-type region and the N well; and
- a PN junction connected in series with the transistor, wherein the PN junction comprises the N well and a second p-type region over the N well.
2. The semiconductor device of claim 1, wherein the second p-type region is a p-type metal contact.
3. The semiconductor device of claim 2, wherein a lower surface of the p-type metal contact facing the substrate contacts and extends along an upper surface of the N well.
4. The semiconductor device of claim 1, wherein the n-type region, the first p-type region, the N well, the first isolation region, and the second isolation region have a coplanar upper surface.
5. The semiconductor device of claim 4, wherein the first isolation region extends continuously from the first p-type region to the n-type region, and wherein the second isolation region extends continuously from the n-type region to the N well.
6. The semiconductor device of claim 5, wherein the first isolation region and the second isolation region extend deeper into the substrate than the n-type region and the first p-type region, wherein the N well extends deeper into the substrate than the first isolation region and the second isolation region.
7. The semiconductor device of claim 1, wherein the first P well contacts and extends along a lower surface of the first p-type region.
8. The semiconductor device of claim 7, wherein the first P well further contacts and extends along a sidewall of the first isolation region and a first portion of a bottom surface of the first isolation region.
9. The semiconductor device of claim 8, wherein the second P well contacts and extends along a second portion of the bottom surface of the first isolation region.
10. The semiconductor device of claim 1, wherein the N well contacts and extends along a sidewall of the second isolation region and a first portion of a bottom surface of the second isolation region, wherein the second P well contacts and extends along a second portion of the bottom surface of the second isolation region.
11. The semiconductor device of claim 10, wherein the second P well contacts and extends along a lower surface of the n-type region, wherein there is a depletion region at the lower surface of the n-type region.
12. A semiconductor device comprising:
- a substrate;
- a diode having a PN junction, the diode comprising a metal contact and an N well, wherein the N well is in the substrate, and the metal contact is over the N well;
- a transistor in the substrate and connected in series with the diode, wherein the transistor comprises an emitter, a collector, and a base, wherein the collector comprises an n-type region, the base comprises a p-type region, and the emitter comprises the N well;
- a first P well in the substrate and under the p-type region; and
- a second P well in the substrate, wherein the second P well extends along a lower surface of the n-type region, and at least partially surrounds the first P well and the N well.
13. The semiconductor device of claim 12, wherein the metal contact is a p-type metal contact.
14. The semiconductor device of claim 12, wherein the n-type region is in the substrate and laterally between the N well and the p-type region.
15. The semiconductor device of claim 14, further comprises:
- a first isolation region in the substrate and extending continuously from the p-type region to the n-type region; and
- a second isolation region in the substrate and extending continuously from the n-type region to the N well.
16. The semiconductor device of claim 15, wherein the first P well contacts and extends along the p-type region and a first portion of a bottom surface of the first isolation region, wherein the N well contacts and extends along a first portion of a bottom surface of the second isolation region, wherein the second P well contacts and extends along a second portion of the bottom surface of the first isolation region and a second portion of the bottom surface of the second isolation region.
17. A semiconductor device comprising:
- a substrate;
- a transistor in the substrate, the transistor comprising: a base; an emitter; and a collector, wherein the collector is disposed in the substrate laterally between the base and the emitter;
- a first isolation region in the substrate between the base and the collector;
- a second isolation region in the substrate between the emitter and the collector;
- a third isolation region in the substrate, wherein the emitter is between the second isolation region and the third isolation region; and
- a diode connected in series with the transistor, the diode comprising a metal contact forming a PN junction with the emitter of the transistor, wherein the metal contact overlies the emitter and extends continuously from the second isolation region to the third isolation region.
18. The semiconductor device of claim 17, wherein the base is a first doped semiconductor region in the substrate, the collector is a second doped semiconductor region in the substrate, and the emitter is a first well region in the substrate.
19. The semiconductor device of claim 18, further comprising:
- a second well region in the substrate under the first doped semiconductor region; and
- a third well region in the substrate, wherein the first well region and the second well region extend into the third well region, wherein the first well region has a first dopant of a first type, the first type being n-type or p-type, wherein the second well region and the third well region has a second dopant of a second type different from the first type, the second type being p-type or n-type.
20. The semiconductor device of claim 19, wherein the first well region covers a first portion of a lower surface of the second isolation region, and the second well region covers a first portion of a lower surface of the first isolation region, wherein the third well region covers a second portion of the lower surface of the first isolation region and a second portion of the lower surface of the second isolation region.
Type: Application
Filed: Feb 11, 2022
Publication Date: May 26, 2022
Inventors: Yi-Feng Chang (Xinbei), Jam-Wem Lee (Hsinchu)
Application Number: 17/669,953