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Patent Searching and Data


Title:
BIPOLAR SCR
Document Type and Number:
WIPO Patent Application WO/2017/173444
Kind Code:
A1
Abstract:
In described examples, a high-voltage bipolar semiconductor controlled rectifier SCR (100) includes: an emitter region (102) having a first polarity and overlying a base region (104) having a second polarity different from the first polarity; a collector region (106, 108) having the first polarity and lying under the base region (104); an anode region (114, 116, 120) having the second polarity; a first sinker region (118) having the first polarity and contacting the collector region (106, 108), wherein the anode region (114, 116, 120) is between the first sinker region (118) and the base region (104); and a second sinker region (112) having the first polarity and contacting the collector region (106, 108, 110), the second sinker region (112) lying between the anode region (114, 116, 120) and the base region (104), wherein an extension (120) of the anode region (114, 116, 120) extends under a portion of the second sinker region (112).

Inventors:
APPASWAMY ARAVIND C (US)
PHILLIPS STANLEY (US)
Application Number:
US2017/025738
Publication Date:
October 05, 2017
Filing Date:
April 03, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
TEXAS INSTRUMENTS INC (US)
TEXAS INSTRUMENTS JAPAN (JP)
International Classes:
H01L29/06
Foreign References:
US6815732B12004-11-09
US5808342A1998-09-15
US7309905B22007-12-18
US7719026B22010-05-18
EP2442359A12012-04-18
US6770918B22004-08-03
Other References:
See also references of EP 3437135A4
Attorney, Agent or Firm:
DAVIS, Jr., Michael A. et al. (P.O. Box 655474 Mail Station 399, Dallas TX, US)
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Claims:
CLAIMS

What is claimed is:

1. A high-voltage bipolar semiconductor controlled rectifier (SCR) comprising:

an emitter region having a first polarity and overlying a base region having a second polarity different from the first polarity;

a collector region having the first polarity and lying under the base region;

an anode region having the second polarity;

a first sinker region having the first polarity and contacting the collector region, wherein the anode region is between the first sinker region and the base region; and

a second sinker region having the first polarity and contacting the collector region, the second sinker region lying between the anode region and the base region, wherein an extension of the anode region extends under a portion of the second sinker region.

2. The high-voltage bipolar SCR as recited in claim 1 further comprising first metallization that connects the anode region and the first sinker region.

3. The high-voltage bipolar SCR as recited in claim 2 further comprising second metallization that contacts the second sinker region and has a floating voltage.

4. The high-voltage bipolar SCR as recited in claim 2 further comprising second metallization contacting the second sinker region, wherein the second metallization is switchably connected to the first metallization.

5. The high-voltage bipolar SCR as recited in claim 2 further comprising shallow trench isolation that lies between the anode region and each of the first sinker region and the second sinker region.

6. The high-voltage bipolar SCR as recited in claim 2 further comprising deep trench isolation that surrounds the high-voltage bipolar SCR.

7. The high-voltage bipolar SCR as recited in claim 6 wherein the shallow trench isolation separates the SCR from the deep trench isolation.

8. The high-voltage bipolar SCR as recited in claim 7 wherein the shallow trench isolation separates the first sinker, the anode region and the base region from the deep trench isolation and the second sinker region contacts the deep trench isolation.

9. The high-voltage bipolar SCR as recited in claim 6 wherein the shallow trench isolation separates the first sinker and the anode region from the deep trench isolation and the second sinker region extends laterally to encircle a region containing the emitter region and the base region.

10. The high-voltage bipolar SCR as recited in claim 5 wherein the second sinker region extends laterally to encircle a region containing the emitter region and the base region, the anode region extends laterally to encircle the second sinker region and the first sinker region extends laterally to encircle the anode region.

11. The high-voltage bipolar SCR as recited in claim 5 wherein the high-voltage bipolar SCR is repeated multiple times within the deep trench isolation.

12. The high-voltage bipolar SCR as recited in claim 1 wherein the first polarity is n-type and the second polarity is p-type.

13. The high-voltage bipolar SCR as recited in claim 5 wherein the high-voltage bipolar semiconductor controlled rectifier is a silicon controlled rectifier.

14. A high-voltage bipolar semiconductor controlled rectifier (SCR) comprising:

an emitter region having a first polarity and overlying a base region having a second polarity different from the first polarity;

a collector region having the first polarity and lying under the base region;

an epitaxial layer having the first polarity and lying under the collector region;

a buried layer having the first polarity and lying under the epitaxial layer;

an anode region having the second polarity and comprising a source/drain implantation, a deep-well implantation and a buried layer extension implantation, the buried layer extension implantation contacting the epitaxial layer;

a first sinker region having the first polarity and comprising a source/drain implantation, a deep-well implantation and a buried-layer-extension implantation, wherein the anode region is between the first sinker region and the base region; and

a second sinker region having the first polarity and comprising a source/drain implantation and a deep-well implantation, and a buried-layer-extension implantation, wherein the buried-layer-extension implantation of the anode region extends under a portion of the second sinker region.

15. The high-voltage bipolar SCR as recited in claim 14 wherein the source/drain implantation of the first polarity and the source/drain implantation of the second polarity each are doped at a concentration of about 1020/cm3.

16. The high-voltage bipolar SCR as recited in claim 15 wherein the deep-well implantation of the first polarity is doped at a concentration between 5x10 18 /cm 3 and 1019 /cm 3 and the deep-well implantation of the second polarity is doped at a concentration between 1018/cm3 and 1019/cm3.

17. The high-voltage bipolar SCR as recited in claim 16 wherein the buried-layer-extension implantation of the first polarity is doped at a concentration of 1018/cm3 or greater and the buried-layer-extension implantation of the second polarity is doped at a concentration between 1018/cm3 and 1019/cm3.

18. The high-voltage bipolar SCR as recited in claim 17 wherein the buried layer implantation of the first polarity is doped at a concentration of about 1019/cm3, the epitaxial layer implantation of the second polarity is doped at a concentration between 5xl015/cm3 and 1017/cm3, and the collector region is doped at a concentration of 1015/cm3.

19. The high-voltage bipolar SCR as recited in claim 18 wherein the emitter is doped at a concentration between 5x10 19 /cm 3 and 1020 /cm 3 and the base region is doped at a concentration of between 5xl017/cm3 and 1019/cm3.

20. The high-voltage bipolar SCR as recited in claim 19 wherein the first polarity is n-type and the second polarity is p-type.

Description:
BIPOLAR SCR

[0001] This relates generally to integrated circuit designs, and more particularly to implementing a bipolar-based semiconductor controlled rectifier for an electrostatic discharge protection circuit.

BACKGROUND

[0002] Integrated circuits are susceptible to damage from electrostatic discharge from common environmental sources and can be destroyed when subjected to voltages higher than their intended voltage supply. Electrostatic discharge (ESD) protection circuits are used to discharge current from ESD events harmlessly, with silicon controlled rectifiers (SCR) providing an effective solution in a small area. However, issues remain in the design of SCRs for high- voltage pins. A solution is lacking with regard to a low-leakage, low-capacitance bipolar based SCR for high voltage pins. Non-SCR based solutions are inefficient, while existing SCR designs suffer from high leakage due to punch-through issues.

SUMMARY

[0003] In described examples of a high-voltage bipolar semiconductor controlled rectifier (SCR), the SCR includes: an emitter region having a first polarity and overlying a base region having a second polarity different from the first polarity; a collector region having the first polarity and lying under the base region; an anode region having the second polarity; a first sinker region having the first polarity and contacting the collector region, wherein the anode region is between the first sinker region and the base region; and a second sinker region having the first polarity and contacting the collector region, the second sinker region lying between the anode region and the base region, wherein an extension of the anode region extends under a portion of the second sinker region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 depicts a cross-sectional view of an SCR according to an embodiment.

[0005] FIG. 2 depicts a current-voltage diagram of the SCR of FIG. 1.

[0006] FIG. 3 depicts a cross-sectional view of an SCR according to an embodiment. [0007] FIG. 4 depicts a cross-sectional view of an SCR according to an embodiment.

[0008] FIG. 5 depicts a plan view of the SCR of FIG. 1 according to an embodiment.

[0009] FIG. 6 depicts a plan view of the SCR of FIG. 1 according to an embodiment.

[0010] FIG. 7 depicts a plan view of the SCR of FIG. 1 according to an embodiment.

[0011] FIG. 8 depicts a plan view of the SCR of FIG. 1 according to an embodiment.

[0012] FIG. 9 depicts an example embodiment of a conventional bipolar SCR.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0013] In the drawings, like references indicate similar elements. Different references to "an" or "one" embodiment in this description are not necessarily to the same embodiment, and such references may mean at least one. Further, if a particular feature, structure or characteristic is described in connection with an embodiment, then such feature, structure or characteristic in connection with other embodiments, irrespective of whether explicitly described.

[0014] Described examples include an SCR that contains a blocking junction to prevent punch through. The blocking junction is constructed by modifying the collector sinker region and introducing anode junctions under the modified sinker to enable SCR action. The modified sinker can be used to change the trigger/holding current of the SCR, and the construction allows for independent modification of the trigger current while maintaining the immunity to PNP injection from the substrate.

[0015] FIG. 9 shows a cross-sectional view of a conventional SCR 900. SCR 900 is built on a bipolar transistor, i.e., the NPN transistor formed by n-type region N-Emitter 902, which is formed over p-type region P-Base 904 and an underlying n-type collector formed by Region 906, n-type buried layer extension (NBLX) 908 and n-type buried layer (NBL) 910. The collector is contacted by n-type Sinker 918, which is formed by three different implantations, referred to herein as n-type source/drain (NSD), n-type deep well (DEEPN) and NBLX. The cross-hatched areas represent Shallow Trench Isolation 920 or other dielectric layers. Because this example is an NPN transistor, a heavily doped p-type layer (p-type source/drain (PSD) 914) is inserted into the NPN transistor to create a PNPN structure that acts as an SCR. SCR 900 works well at voltages in the range of 3-5 volts, but when higher voltages are used, multiple issues arise. One issue is punch-through; for example, whenever a reverse bias is applied from P-Base 904 to Region 906, the field can potentially go all the way to the anode, PSD 914, as shown by the arrows in FIG. 9. This situation shorts out one of the internal bipolar transistors, giving a very leaky SCR at a very low voltage, so that SCR 900 can't hold high voltages at low current. Other issues can also arise, such as parasitic MOS transistors or charges on the shallow trench isolation that can cause a short, but basically, at a very low voltage, PSD 914, the anode for SCR 900, is soft-shorted to P-Base 904, which is part of the cathode, causing a high amount of leakage.

[0016] One way to avoid the leakage shown in FIG. 9 is to place PSD 914 on the outside of N-Sinker Region 918. However, in this configuration, the gain on the P P portion of the SCR becomes very low, which does not allow proper SCR action.

[0017] FIG. 1 shows a cross sectional diagram of a first embodiment of a semiconductor controlled rectifier (SCR) 100 having an increased immunity to the shorting effects described hereinabove. Here and in the following description, SCR refers to a semiconductor controlled rectifier rather than a silicon controlled rectifier, which is a special case of a semiconductor controlled rectifier. Generally, reference to a semiconductor region as "heavily doped" means having a concentration of 10 18 /cm 3 or greater. Likewise, "lightly doped" means a semiconductor region having a concentration of less than 10 18 /cm 3 . In both cases, the doped regions may be formed by ion implantation or other known methods. Furthermore, the drawing figures are not to scale. In the following description, the term "electrically connected" means an ohmic current path exists between two or more cited elements and does not preclude the existence of resistors, parasitic elements or other circuit elements within the current path.

[0018] SCR 100 includes a p-type substrate (not specifically shown) and an n-type collector region that includes heavily doped n-type buried layer ( BL) 110, lightly-doped n-type epitaxial layer (NEPI) 108 and lightly doped Region 106. N-type buried layer (NBL) 110 is again contacted by n-type Sinker 118, which receives highly-doped implants NSD, DEEPN and NBLX. Heavily doped p-type region P-Base 104 overlies N-type Region 106 and heavily doped n-type region N-Emitter 102 overlies P-Base 104.

[0019] Heavily-doped p-type region PSD 114 is now isolated from n-type Region 106 by a secondary heavily doped n-type Sinker 112, which is placed between PSD 1 14 and P-Base 104 and receives implants NSD and DEEPN (but not the NBLX implant). Sinker 112 acts as a blocking junction for the leakage in the SCR of FIG. 9. Heavily doped p-type region PSD 114 is thus blocked from leakage by Sinker 112. To enable SCR action, two heavily-doped p-type regions, i.e., p-type deep well (DEEPP) 116 and p-type buried layer extension (PBLX) 120 provide an anode junction that extends partially under Sinker 112 to contact epitaxial layer NEPI 108. The presence of modified Sinker 112 and anode junction PBLX 120 relocates the current for SCR events deeper in the device. Leakage between P-Base 104 and PBLX 120 is possible in the current configuration, but such leakage would occur at a higher voltage than the rated voltage of the inherent transistor, so this is not a great concern. Sinker Region 118 serves two purposes: it allows the SCR to be isolated from the substrate without needing deep trench isolation; and by having different resistance in series with Sinker 118 versus Sinker 112, the trigger voltage of the SCR is decoupled from the propensity of the SCR to inject current into the substrate.

[0020] In an example embodiment, usual doping for each implant or layer in FIG. 1 can be as follows: N-Emitter is doped at between 5x10 19 /cm 3 and 1020 /cm 3 ; P-Base at between 5x1017 /cm 3 and 10 19 /cm 3 ; EPI at between 5xl0 15 /cm 3 and 10 17 /cm 3 ; BL at about 10 19 /cm 3 ; NSD at about 10 20 /cm 3 ; DEEPN at between 5xl0 18 /cm 3 and 10 19 /cm 3 ; BLX at about 10 18 /cm 3 or greater; PSD at about 10 20 /cm 3 ; DEEPP at between 10 18 /cm 3 and 10 19 /cm 3 ; PBLX at between 10 18 /cm 3 and 10 19 /cm 3 ; and Region 106 at about 10 15 /cm 3 . However, the DEEPN implant used in Sinker 112 does not need to be as heavily doped as noted to serve as a blocking junction; an implant in the range between 10 16 /cm 3 and 10 18 /cm 3 would also work.

[0021] SCRs are usually connected as shown in FIG. 1, where a metallization layer forms Connector 122 that connects Sinker 118 (which forms the base of an inherent PNP transistor) to PSD 114 (which forms the anode of the SCR). Sinker 118 and PSD 114 can be connected directly, as illustrated, or through a resistor (not specifically shown). The resistor or lack thereof determines how much the inherent PNP transistor turns on. Connection 124 to Sinker 112 is generally left floating to cause any current to come from the p-type regions. When SCR 100 is turned on, i.e., during an ESD event, current flows from PSD Region 114 through NEPI 108 and N-type Region 106 to P-Base 104 and then to N-Emitter 102. The described SCR may provide one or more of the following benefits: the SCR is isolated; the design can allow independent control of trigger current and the amount of PNP injection from the substrate (as will be described hereinbelow); the production of the SCR does not require the use of any additional masks; leakage issues are avoided; and the base bipolar on which he SCR is built is maintained, allowing for the same breakdown voltage.

[0022] FIG. 2 depicts a current-voltage diagram 200 of the SCR of FIG. 1, with the horizontal axis showing the voltage and the vertical axis identifying the current across the SCR. A 100 nanosecond Transmission Line Pulse (TLP) is provided to SCR 100 and the I-V characteristics are measured. As shown, the voltage rises to approximately 6-7 volts with very little current, then snaps back as the SCR is triggered. At that point, the SCR goes into action and takes large amounts of current away from the protected circuits.

[0023] The SCR of FIG. 1 can also be implemented with the dopant types being reversed, i.e., with n-type dopants interchanged with p-type dopants and vice versa, as shown in FIG. 3. SCR 300 includes an n-type substrate (not specifically shown) and a p-type collector region that includes heavily doped buried layer PBL 310, lightly-doped epitaxial layer PEPI 308 and lightly doped Region 306. Buried layer PBL 310 is contacted by p-type Sinker 318, which receives highly-doped implants PSD, DEEPP and PBLX. Heavily doped n-type region N-Base 304 overlies p-type Region 306 and heavily doped p-type region P-Emitter 302 overlies N-Base 304.

[0024] Heavily-doped n-type region NSD 314 is now isolated from p-type Region 306 by secondary heavily doped p-type Sinker 312, which is placed between NSD 314 and N-Base 304 and receives implants PSD and DEEPP (but not the PBLX implant). Sinker 312 acts as a blocking junction for the leakage in the SCR of FIG. 9. Heavily doped N-type region NSD 314 is thus blocked from leakage by Sinker 312. To enable SCR action, heavily-doped n-type regions DEEPN 316 and NBLX 320 provide an anode junction that extends partially under Sinker 312 to contact epitaxial layer PEPI 308. The presence of modified Sinker 312 and anode junction NBLX 320 relocates the current for SCR events deeper in the device. As described hereinabove, leakage is possible between N-Base 304 and NBLX 320 in the current configuration, but such leakage would occur at a higher voltage than the rated voltage of the inherent transistor.

[0025] A variation on the connections in the described embodiment is shown as SCR 400 in FIG. 4. In FIG. 1, Connector 124 was left floating. However, in this embodiment, Connector 424 is switchably connected to Connector 422, e.g., through a MOSFET (not specifically shown). As shown in FIG. 2, an embodiment of SCR 100 has a trigger voltage of about 6-7 volts. However, if this SCR is used in a system having a normal operating voltage, such as 15 volts, the SCR will trigger at an undesirably low voltage. The described switch between Connections 422 and 424 provides a way to modify the holding or trigger current, allowing SCR 400 to be used in higher-voltage situations. In normal operation, when the anode PSD 414 and extensions DEEPP 116 and PBLX 120, inject carriers that reach P-Base 104, NEPI 108 injects additional carriers. However, if the switch between Terminals 422 and 424 is closed, some of the carriers are "stolen" by Sinker 112 and do not contribute to the SCR action. Accordingly, when the switch is closed, the trigger voltage shown in FIG. 2 can be stretched nearer to 30 volts, for example. The switch is designed to be closed during normal operation of the circuit, but to open during ESD events. Although the doping of FIG. 4 is shown as corresponding to the doping of FIG. 1, the switchable connection between Terminals 422 and 424 can also be used with the doping profile of FIG. 3 or with any of the embodiments described herein.

[0026] FIGS. 5-8 disclose plan views of the embodiment of FIG. 1, giving different ways in which the layout of this device can be implemented. These plan views are equally applicable to the embodiment of FIG. 3 in which the polarity of the dopants is reversed, and with or without the switchable connection to the secondary sinker. FIG. 5 discloses a basic implementation, while each of FIGS. 6-8 provide ways in which punch-though can be improved near the edge of Deep Trench Isolation.

[0027] As shown in SCR 500, N-Emitter 102 and P-Base 104 are shown extending laterally in this drawing, with P-Base 104 extending beyond N-Emitter 102 in all four directions. Sinker 112, PSD 114 and Sinker 118 are laterally isolated from P-Base 104 and from each other by Shallow Trench Isolation 530, which laterally surrounds the entire SCR. PBLX 120, which provides the new anode junction, is shown as dotted lines. Also, Deep Trench Isolation 532, which is not shown in FIG. 1, isolates SCR 500 from the rest of the chip.

[0028] FIG. 6 discloses SCR 600, in which Sinker 112 is extended at each end so that Sinker 112 touches Deep Trench Isolation 532 to provide improved punch-through near the deep trench isolation. Other elements of the SCR are unchanged. FIG. 7 discloses SCR 700, in which the two segments of Sinker 112 are joined at each end to form Ring 734. Ring 734 laterally surrounds P-Base 104. Another modification is shown in FIG. 8, which discloses SCR 800 in which each of Sinker 112, PSD 114, and Sinker 118 is laterally extended at their ends to form respective Rings 834, 836, and 838 respectively. In this configuration, the deep trench is not needed to isolate the SCR from the substrate.

[0029] Other modifications to the circuit are also possible. Although a single Emitter "finger" 102 is shown overlying P-Base 104, multiple Emitter fingers 102 can be placed within P-Base 104; the same can be true when the dopant type is reversed, as in FIG. 3. In one embodiment, the entire SCR structure can be repeated multiple times within the deep trench isolation.

[0030] Reference to an element in the singular does not mean "one and only one" unless explicitly so stated, but instead means "one or more."

[0031] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.