Lateral high voltage SCR with integrated negative strike diode

An SCR with a first semiconductor region and plural concentric semiconductor regions, each surrounding the first semiconductor region. The SCR also includes, surrounded by at least one concentric semiconductor region in the plurality of concentric semiconductor regions, an electrically non-contacted region of a semiconductor type and positioned to modulate a snapback voltage of the silicon controlled rectifier and an electrically-contacted region of the semiconductor type and positioned to provide a diodic response between the at least one concentric semiconductor region in the plurality of concentric semiconductor regions and the electrically-contacted region.

BACKGROUND

The example embodiments relate to a silicon controlled rectifier (SCR), as may be used in electrostatic discharge (ESD) protection.

ESD is the sudden flow of electricity between two objects as electrical charge transfers from one of the objects to the other. For integrated circuit (IC) durability and longevity, ESD protection is sometimes included and applied to an IC circuit or IC node(s). Such protections are more common and necessary as ICs are downscaled, dopant concentrations are increased, and ICs are implemented in locations where nearby structures provide potential ESD pulse sources. ESD protection redirects current away from the IC in the event of an ESD pulse (strike), preventing damage that otherwise could occur were the strike received by an IC signal path. When an ESD strike is not occurring, ideally the ESD protection circuit does not affect IC operation.

One approach to ESD protection is an SCR with an anode connected to an electrical pad that is to be ESD protected. The SCR requires various attributes in such an ESD application. For example, the SCR is off under nominal conditions at the pad, but the SCR needs a robust snapback response to a positive ESD strike at the pad (and also at the SCR anode). The snapback is to occur when the pad voltage reaches a positive trigger level, typically much higher than the pad nominal voltage. When the trigger voltage is reached or exceeded, the desired SCR response is for the SCR to conduct, the voltage across it to drop quickly (snaps back) to a much lower holding voltage, and at the same time current through the SCR is to significantly increase, to shunt that ESD pulse current. Certain SCR devices also include a negative strike diode to provide a diodic response to a negative ESD strike at the pad. Accordingly, when the pad voltage reaches a negative trigger level, the desired response is for the SCR to conduct the current with a response resembling that of a diode, with a negative current shunted from the SCR anode to its cathode.

While the above concepts have been implemented with varying degrees of success, certain drawbacks may occur. For example, area efficiency is often a key design consideration. However, certain area-reducing geometries may compromise performance. To the contrary, alternative approaches to avoid such performance compromise may propose a separate negative strike diode. Such an approach, however, is not ideal as it requires large (and possibly parallel) diodes, increasing concerns of leakage, capacitance, and area.

This document provides example embodiments that may improve on certain of the above concepts, as detailed below.

SUMMARY

In one example embodiment, there is an SCR, comprising a first semiconductor region and a plurality of concentric semiconductor regions, wherein each concentric semiconductor region in the plurality of concentric semiconductor regions surrounds the first semiconductor region. The SCR also includes, surrounded by at least one concentric semiconductor region in the plurality of concentric semiconductor regions, an electrically non-contacted region of a semiconductor type and positioned to modulate a snapback voltage of the silicon controlled rectifier and an electrically-contacted region of the semiconductor type and positioned to provide a diodic response between the at least one concentric semiconductor region in the plurality of concentric semiconductor regions and the electrically-contacted region.

Other aspects and embodiments are also disclosed and claimed.

DETAILED DESCRIPTION

FIG.1illustrates an electrical diagram of an ESD protection system100. The ESD protection system100includes a first node102that is ESD protected. As an example, the first node102is connected to an IC104, where the first node102may by example be an input and/or output (“input/output”) pad of the IC104. As another example, the first node102may represent an internal conductive point of the IC104, or an external conductive point of the IC104, including a pin. The IC104may be any type of circuit, for which it is expected that the first node102may experience ESD events, such as in a relatively high voltage device or environment. As further detailed later, the ESD protection system100endeavors to shunt energy to protect the IC104during an ESD strike, where the ESD strike may, in terms of polarity, be either a positive or negative strike at the first node102.

The first node102is also connected to an anode106of an SCR108, where the SCR108provides ESD protection to the first node102(and, by extension, to the IC104).FIG.1illustrates the SCR108electrically, where later discussion and illustrations detail an example embodiment in which the SCR108is implemented as a lateral semiconductor device. Electrically, the SCR108includes a PNP bipolar junction transistor (BJT)110and an NPN BJT112. As shown later, structurally the PNP and NPN BJTs110and112may share some common p-type and n-type regions, which the shared regions embody portions of theFIG.1electrical connectivity. Also regarding that connectivity, in addition to the anode106, the SCR108includes a cathode114(which may or may not connect to the device substrate), which is connected to a second node116of the IC104, where the second node116may be connected to a low potential, such as ground. The anode106is provided by the PNP BJT110emitter, and the cathode114is provided by the NPN BJT112emitter. The collector of the PNP BJT110is connected to the base of the NPN BJT112, and the collector of the NPN BJT112is connected to the base of the PNP BJT110. The preceding connections are generally accomplished through the structural relationship of semiconductor regions, while an additional level of contact, such as through metal, can include two additional contact connections shown inFIG.1by dashed lines and that provide interconnects between semiconductor regions. Specifically, a first contact connection118is an electrical contact that provides the anode106and couples to both the PNP BJT110emitter and the NPN BJT112collector (and to the PNP BJT110base). And, a second contact connection120is an electrical contact that provides the cathode114and couples to both the NPN BJT112emitter and the PNP BJT110collector (and to the NPN BJT112base). Lastly, while not explicitly labeled inFIG.1, the NPN BJT112base-to-PNP BJT110collector connection is also sometimes referred to as a gate of the SCR108, where the gate in some implementations is floating and in others can be connected to a voltage bias.

FIG.2illustrates a first cross-sectional view of theFIG.1SCR108in a semiconductor implementation, and along the line2-2in the plan view ofFIG.3, whereFIG.3is further explained later. Portions of the SCR108are formed generally in layers relative to a p type layer200, such as a p type substrate (e.g., a p type substrate and a small layer of lightly doped p type epitaxial (epi) layer atop it). N type portions are formed in the p type layer200, for example as shown by an n type buried layer202, above which is an n type epi layer204. The n type buried layer202may be formed by implanting and diffusing (e.g., by heat) relatively heavily concentrated n type dopants. The n type epi layer204may be formed by growing the n type epi layer204with appropriate (e.g., relatively lightly concentrated) n type dopants. Toward the outside edges of the illustrated layout, trench regions206and208are formed, for example by first forming a trench through the various layers down to the p type layer200, second forming sidewall oxides (not separately shown) along each trench region206and208, third filling the remaining void, between the sidewall oxides, with doped polysilicon to provide a deep electrical contact down to the p type layer200, and fourth providing a highly doped p+ contact on top of the doped polysilicon, so that electrical contact, such as in a metal layer, can be made to the highly doped p+ contact, Accordingly, the highly doped p+ contact provides an electrical conductive path through the doped polysilicon and to the p type layer200.

Additional portions of the SCR108are formed relative to the above-described layers and an upper edge210of the n epi layer204. A first p well212and a second p well214are formed within the n type epi layer204, for example by implanting and diffusing relatively lightly concentrated p type dopants. Within the first p well212, a first p+ region216and a first n+ region218are formed, for example by ion implantation. Similarly, within the second p well214, a second p+ region220and a second n+ region222are formed, for example by ion implantation. Centrally shown inFIG.2and adjacent the upper edge210, a third n+ region224is formed. Outwardly from the third n+ region224, a third p+ region226and a fourth p+ region228are formed within the n type epi layer204, or in an alternative embodiment a respective p well may be formed first in those areas with each of the third p+ region226and the fourth p+ region228then formed in a respective one of those p wells, akin to each of the first p+ region216and second p+ region220being formed in a respective p well212and214. Outwardly from third p+ region226, a fourth n+ region230is formed, and similarly and outwardly from the fourth p+ region228, a fifth n+ region232is formed. Lastly, various isolation regions234(e.g., silicon dioxide) are shown along the upper edge210, as may be formed by various processes, including local isolation of silicon (LOCOS).

FIG.2also includes theFIG.1anode106and the cathode114, as well as the related first and second contact connections118and120, now further described. As introduction, certain combinations of regions and areas inFIG.2provide the structural equivalent to theFIG.1schematic of the PNP BJT110and the NPN BJT112; to assist the reader, the schematic of each of those two BJTs is superimposed inFIG.2, respectively, in large dashed lines. Accordingly, and for the approximate left half ofFIG.2, the PNP BJT110is provided by: (i) the third p+ region226as its emitter; (ii) a path through the n type epi layer204as its base; and (iii) the combination of a path through the first p well212and the first p+ region216as its collector. Also in that approximate left half ofFIG.2, the NPN BJT112is provided by: (i) the first n+ region218as its emitter; (ii) a path through the first p well212as its base; and (iii) the combination of a path through the n epi layer204and the third n+ region224as its collector. For reference, the following Table1summarizes each BJT base, collector, or emitter, and its corresponding structural counterpart(s) in the approximate left half ofFIG.2:

TABLE 1BJT componentStructural counterpart(s)PNP BJT 110 emitterthird p + region 226PNP BJT 110 basen type epi layer 204PNP BJT 110 collectorfirst p well 212 and first p + region 216NPN BJT 112 emitterfirst n + region 218NPN BJT 112 basefirst p well 212NPN BJT 112 collectorn epi layer 204 and third n + region 224
Given the preceding, each of the first and second contact connections118and120may be formed in a contact (e.g., metal) layer. Accordingly, the anode106is connected by the first contact connection118to the PNP BJT110emitter (the third p+ region226) and to the NPN BJT112collector (the third n+ region224, which is electrically conductive to the n epi layer204). And, the cathode114is connected by the second contact connection120to the PNP BJT110collector (the first p+ region216, which is electrically conductive to the first p well212) and the NPN BJT112emitter (the first n+ region218).

TheFIG.2cross-sectional view illustration is symmetric (or at least approximately symmetric) about an imaginary vertical line down its middle, due to a ring like top view architecture of the SCR108as further discussed later. Accordingly, the preceding discussion relating to the approximate left half ofFIG.2introduces like observations with respect to the right half ofFIG.2, that is, the structure to the right also may represent theFIG.1PNP BJT110and the NPN BJT112. The following Table2thus summarizes each BJT base, collector, or emitter, and its corresponding structural counterpart(s) in the approximate right half ofFIG.2:

TABLE 2BJT componentStructural counterpart(s)PNP BJT 110 emitterfourth p + region 228PNP BJT 110 basen type epi layer 204PNP BJT 110 collectorsecond p well 214 and second p + region 220NPN BJT 112 emittersecond n + region 222NPN BJT 112 basesecond p well 214NPN BJT 112 collectorn epi layer 204 and third n + region 224
From the preceding, and from theFIG.2illustration of alone, one skilled in the art may anticipate, as a first approximation, symmetric operation about the vertical center of the SCR108, in terms of charge application and resultant circuit behavior. However, at least two other SCR108aspects are now introduced, with further details demonstrated inFIGS.3and4. First, the SCR108includes the fourth n+ region230and the fifth n+ region232, which inFIG.2are electrically non-contacted in the physical sense that there is no structural metal layer applying a potential to those regions—however, for reasons detailed later, note that each of the fourth n+ region230and the fifth n+ region232is coupled, resistively through the n epi layer204, to the anode potential applied to the third n+ region224, which may further impact the SCR108operation. Second, the SCR108is symmetric in theFIG.2dimension, but is asymmetric in another dimension, which also impacts the SCR108operation and, as shown below, does so favorably in producing respectively different SCR responses, relative to either a positive or negative polarity ESD strike.

FIG.3illustrates a plan view of the SCR108, which is simplified by either not illustrating or labeling certain regions (e.g., theFIG.2isolation regions234and the trench regions206and208). The plan view illustrates that the SCR108is generally concentric in that several of its features, but not all, fully surround a common center CTR. For example, theFIG.3left outermost boundary illustrates the outermost border of the first p well212, and symmetrically about the CTR, theFIG.3right outermost boundary illustrates the outermost border of the second p well214. Further, theFIG.3plan view reveals that these two p wells212and214are actually a same p type semiconductor region that forms a first p type continuous region that surrounds the CTR within the SCR108; for reference sake, where such a continuous region exists, it also may be referred to herein by including both numbers fromFIG.2, separated by a forward slash (e.g., first p type continuous well region212/214). As another example, to the interior of the first p type continuous well region212/214, theFIG.3left side illustrates the first p+ region216, and symmetrically about the CTR, theFIG.3right side illustrates the second p+ region220. Here again, these two p+ regions216and220are actually within a same and first p+ type continuous region216/220that surrounds the CTR within the SCR108. Accordingly, portions along the first p+ type continuous region216/220may provide theFIG.2PNP BJT110collector. Closer to the CTR than the first p+ type continuous216/220region is a first n+ type continuous region218/222, surrounding the CTR and including the first n+ region218and the second n+ region222. Accordingly, portions along the first n+ type continuous218/222region may provide theFIG.2NPN BJT110emitter. As still another example, and closest to the CTR, a second p+ type continuous region226/228concentrically surrounds the CTR, and it includes theFIG.2third p+ region226and theFIG.2fourth p+ region228. Given the various concentric regions, the SCR108may be considered a ring link architecture.

FIG.3also illustrates a first interior n+ region230/232, which is surrounded by some of the other continuous regions (e.g., the first p type continuous well region212/214; the first p+ type continuous216/220region; the first n+ type continuous region218/222) and includes theFIG.2fourth n+ region230and the fifth n+ region232, which recall are electrically non-contacted. The first interior n+ region230/232, however, is not continuous around the entirety of the CTR, but instead, forms a U-shape in theFIG.3plan perspective, having terminal ends302and304. Beyond the terminal ends302and304and, also surrounded by the same continuous regions that surround the first interior n+ region230/232, the SCR108also includes a second interior n+ region306. In an example embodiment, the second interior n+ region306is formed from a same dopant type and concentration as the first interior n+ region230/232. Also in an example embodiment, the second interior n+ region306is generally rectangular from a plan perspective. Still further in an example embodiment, the second interior n+ region306is spaced a same minimum distance, D1, from the second p+ type continuous region226/228, as is first interior n+ region230/232. Note that distance D1, as with other distances described herein, is stated to be a minimum distance, to describe a measure of the closest distance between the identified structures. Accordingly, the distance D1is measured between respective points where the first interior n+ region230/232is closest to the second p+ type continuous region226/228, and similarly where the second interior n+ region306is closest to the second p+ type continuous region226/228. Also with respect to the first interior n+ region230/232, if the first interior n+ region230/232were continuous to surround the entirety of the second p+ type continuous region226/228, then the geometry could include that of the second interior n+ region306. Instead, however, the discontinuity created by the terminal ends302and304cause an electrical isolation between the first interior n+ region230/232and the second interior n+ region306, so that each may be electrically configured in a different manner, as further detailed below.

FIG.4illustrates a cross-sectional view of theFIG.1SCR108along the line4-4in the plan view ofFIG.3, which is orthogonal with respect to theFIG.2view. Items illustrated to the left inFIG.4appear generally the same as inFIG.2, although theFIG.3reference numbers are also used inFIG.4, whereFIG.3introduced that someFIG.2regions are from continuous regions introduced inFIG.3. TheFIG.4view traverses some of those continuous regions, so the continuous region reference is shown inFIG.4. For example, to the left inFIG.4and regarding the PNP BJT110, its collector is formed by the first p+ type continuous region216/220and the first p type continuous well region212/214, and its emitter is formed by the second p+ type continuous region226/228. As another example to the left inFIG.4and regarding the NPN BJT112, its emitter is formed by the first n+ type continuous region218/222, and its base is formed by the first p type continuous well region212/214.

FIG.4illustrates additional aspects of the independent first interior n+ region230/232and the second interior n+ region306, introduced above in connection withFIG.3. Recall in plan view those two regions generally align in a concentric geometry relative to other surrounding regions, but they are physically isolated from one another.FIG.4further illustrates that electrically the two regions are also distinctive. Particularly, as noted above from theFIG.2discussion, the fourth n+ region230and the fifth n+ region232are electrically non-contacted, and as shown inFIG.3, those regions are in the same first interior n+ region230/232. InFIG.4, however, the anode106is connected as it was inFIG.2, but in addition it is further connected to the second interior n+ region306. InFIG.4, therefore, to the left side of the centrally-located third n+ region224, there is a first interior n+ region230/232that is electrically non-contacted (hereafter, the electrically non-contacted first interior n+ region230/232), while to the right side of the centrally-located third n+ region224, there is a second interior n+ region306that is electrically-contacted (hereafter, the electrically-contacted second interior n+ region306). Accordingly, if a signal is applied to the anode106, including a possible ESD strike, that signal is coupled as described earlier to the PNP BJT110emitter (via the second p+ type continuous region226/228) and to the NPN BJT112collector (via the third n+ region224), and as shown inFIG.4, it is also coupled to the electrically-contacted second interior n+ region306. Thus, while portions of the electrically non-contacted first interior n+ region230/232and the electrically-contacted second interior n+ region306are symmetrically positioned relative to the centrally-located third n+ region224, the two electrically differ, one electrically non-contacted and one the electrically-contacted by the anode106. The operational effects from this difference are described later.

FIG.4also illustrates a geometric asymmetry relative to the electrically non-contacted first interior n+ region230/232and the electrically-contacted second interior n+region306. First, in a symmetric manner, a same distance D1is shown outwardly and to the right and left relative to the centrally-located third n+ region224; in the left, D1is between the outer boundary of the second p+ type continuous region226/228and the inner boundary of the electrically non-contacted first interior n+ region230/232, and to the right D1is between the outer boundary of the second p+ type continuous region226/228and the inner boundary of the electrically-contacted second interior n+ region306. Accordingly, each of the inner boundary of the electrically non-contacted first interior n+ region230/232and the inner boundary of the electrically-contacted second interior n+ region306is generally symmetrically spaced about theFIG.3CTR. Second, in an asymmetric manner, the next spatial relationship shown outwardly from the inner boundary of the electrically non-contacted first interior n+ region230/232and the inner boundary of the electrically-contacted second interior n+ region306is not a same dimension. Specifically, to the left and outward from the electrically non-contacted first interior n+ region230/232, a minimum distance D2occurs to the adjacent positioned first p type continuous well region212/214; in contrast, to the right and outward from the electrically-contacted second interior n+ region306, a minimum distance D3, which is larger than D2(e.g., by a factor of two to three), occurs to the adjacent positioned first p type continuous well region212/214. Accordingly, the electrically non-contacted first interior n+ region230/232is a closer distance (D2) to its adjacent first p type continuous well region212/214than is the distance (D3) between the electrically-contacted second interior n+ region306and its adjacent first p type continuous well region212/214. As described below, these differing distances facilitate favorable SCR108operational attributes. Also in this regard, recall that within the first p type continuous well region212/214there is a more inwardly located first n+ type continuous region218/222. Accordingly, a similar spatial difference arises on theFIG.4left and right side with respect to the illustrated portions of that first n+ type continuous region218/222. Particularly, the electrically non-contacted first interior n+ region230/232is a closer minimum distance D4to its adjacent portion of the first n+ type continuous region218/222than is a minimum distance D5between the electrically-contacted second interior n+ region306and its adjacent first n+ type continuous region218/222. Indeed, these relative spatial differences, combined with a possible potential from the anode106to the electrically-contacted second interior n+ region306, create different electrical conductive paths to the left and right ofFIG.4. In this regard and for illustrative purposes, a schematic of a diode402is superimposed to the right inFIG.4, with its anode provided by the combination of the illustrated portion of the first p+ type continuous region216/220and the adjacent first p type continuous well region212/214, and with its cathode provided by a portion of the n type epi layer204and the electrically-contacted second interior n+ region306. The diode402operation is discussed later.

The electrical operation of the SCR108, as depicted inFIGS.2through4, is now described. From the prior discussion and theFIG.3plan view, in general the SCR operates in a first manner in theFIG.3horizontal direction (across theFIG.2cross-section) and in a second manner in theFIG.3vertical direction (across theFIG.4cross-section). The different operations are influenced, in this example embodiment, by differing geometries in those two, generally orthogonal, directions. Particularly, a first set of continuous and concentric regions provide a first aspect of these operations, while a second set of regions, including the physically and electrically differing electrically non-contacted first interior n+ region230/232and electrically-contacted second interior n+ region306, provide a second and differing aspect of these operations.

FIG.5illustrates a response curve500to a positive ESD strike on the SCR108anode106. The response curve500illustrates voltage along its horizontal axis and current along its vertical axis. Prior to the positive ESD strike, the SCR108remains in a non-conductive state and presents a very high resistance, both of which are favorable attributes in an ESD protective system, such as in theFIG.1ESD protection system100. When the positive ESD strike occurs, voltage quickly rises at the anode106, and a trigger voltage Vtr is reached, which in the illustrated example is approximately 70V. In response, the SCR108resistance quickly drops, the SCR108begins to conduct far greater current, and the anode voltage quickly decreases, sometimes referred to as snapback, to a voltage less than 10V.

TheFIG.5response curve500also can be understood in connection with theFIG.2cross-sectional view. With the connected relationship of the PNP BJT110and the NPN BJT112, a turning on of one BJT turns on the other. In theFIG.5example of a positive ESD strike, the positive charges couples through the third n+ region224and increases the potential of the n type epi layer204. The increased n type epi layer204potential will reach the avalanche breakdown level of the junction between that n type epi layer204and, to the left inFIG.2, the first p well212and, to the right inFIG.2, to the second p well214. The breakdown level is the SCR108trigger voltage, and that trigger voltage also can be reduced, as is sometimes favorably desired, by either the electrically non-contacted fourth n+ region230to the left inFIG.2or the electrically non-contacted fifth n+ region232to the right inFIG.2, as each reduces the resistance in a portion of the charge path between the n epi layer204and either the first p well212or the second p well214, respectively, thereby modulating (adjusting, in this case reducing) the breakdown voltage. At breakdown, current flows through the junction, thereby providing base current to, and turning on, the NPN BJT112. Once the NPN BJT112is on to conduct sufficient current, that current turns on the PNP BJT110. With both BJT110and112conducting, a large current can pass through the SCR108asFIG.5shows with the rise to approximately 3.7A, which inFIG.1thereby shunts the positive ESD strike charge to the IC102second node116. As the charge dissipates, the current flow reduces to a level insufficient to keep the BJTs110and112on, at which point the SCR108returns to an off state.

FIG.6illustrates a response curve600to a negative ESD strike on the SCR108anode106. The response curve600illustrates voltage along its horizontal axis and current along its vertical axis. Prior to the negative ESD strike, again the SCR108remains in a non-conductive state and presents a very high resistance. When the negative ESD strike occurs, note that were theFIG.2cross-section to be representative of all cross-sections across the SCR108, then it would be possible that the SCR108would operate again in a snapback manner, with opposite polarity of that shown inFIG.5. Such a response to a negative surge, however, is not desirable, as the high trigger voltage can result in damage to a protected circuit (e.g., theFIG.1IC104). Indeed, note that in the positive direction (FIG.5), the internal junctions of the IC104may tolerate some initial rise in the anode signal as those junctions also are likely to have a relatively high breakdown voltage, whereas in the negative direction, those internal junctions are likely to be diodic, thereby less robust to a high negative spike and, as a result, requiring a diodic protective response by the SCR108. Accordingly, and for reasons detailed below, for a negative strike the SCR108provides the response curve600. In the response curve600, as voltage magnitude increases in the negative direction, current magnitude also increases in the negative direction, and at least a portion of the response curve600is approximately linear. Such a response is akin to the operation of a diode, and such diodic response is favorable in theFIG.1ESD protection system100as the current resulting from the ESD negative strike begins to shunt with near linearity to the rise in magnitude of voltage.

TheFIG.6response curve600also can be understood in connection with theFIG.4cross-sectional view. To the left ofFIG.4, the structure is the same as it is inFIG.2, with the possible conduction of both the PNP BJT110and NPN BJT112. As noted above, however, the operation of only those BJTs in response to a negative strike could create an undesirable snapback type response, including accumulating too large a voltage at the anode106(and theFIG.1first node102) before discharging current. However, to the right ofFIG.4, recall the illustration of the diode402. Particularly, because the anode106is connected to the electrically-contacted second interior n+ region306, when a negative ESD strike occurs at the anode106, the negative charge coupled to the electrically-contacted second interior n+ region306creates a lower resistance conductive path through the regions represented by the diode402, those being, from right to left inFIG.4: (i) the first p+ type continuous region216/220; (ii) the first p type continuous well region212/214; (iii) the n type epi layer204; and (iv) the electrically contacted second interior n+ region306. Accordingly, in one aspect, the diode402facilitates theFIG.6response curve600. In addition, the increased spatial relationship to the right ofFIG.4, as shown by D3and D5, relative to the shorter corresponding distances to the left ofFIG.4, as shown by D2and D4, further facilitates the response curve600. Particularly, because the anode106applies a bias to the electrically-contacted second interior n+ region306during the negative ESD strike, ifFIG.4were equally dimensioned on its right as it is on its left, then the bias could create a parasitic NPN transistor, including the right side first n+ type continuous region218/222, the right side first p type continuous well region212/214, and the electrically-contacted second interior n+ region306; so, in contrast to the left side NPN BJT112which has its collector at the (centrally located) third n+ region224, a right side parasitic NPN could occur with a collector at the electrically-contacted second interior n+ region306, creating undesirable operation. With the relative increased dimension of D3or D5, however, the possibility of a right side parasitic NPN transistor is reduced, while the possibility of the desired operation of the diode402is increased. Indeed, these factors thereby combine to produce a favorable snapback response curve500inFIG.5and a favorable diode response curve600inFIG.6.

Certain of the above concepts may be summarized by returning toFIG.3. Generally, the vertically-illustrated “legs” of the U-shaped configuration of the electrically non-contacted first interior n+ region230/232provides theFIG.2cross-section, when taken across those legs, as they are symmetrically spaced relative to the other continuous regions of the first p+ type continuous216/220region, the first n+ type continuous region218/222, the second p+ type continuous region226/228, and about the third n+ region224is formed. In those locations, the SCR108operation provides theFIG.5response curve500, in response to a positive ESD strike, and with the trigger voltage modulated by the electrical state of the electrically non-contacted first interior n+ region230/232. Also generally,FIG.3in the vertical direction provides theFIG.4cross-section, when taken from one side of the CTR across the n+ region between the vertically-illustrated legs of the U-shaped configuration of the first interior n+ region230/232, and to the other side through the electrically-contacted second interior n+ region306. In those locations, the SCR108operation provides theFIG.6response curve600, in response to a negative ESD strike. Accordingly, the combination of orientations across the partially concentric SCR108structure, and/or the selective anode connection to the electrically-contacted second interior n+ region306in combination with the electrically non-contacted first interior n+ region230/232, provides a favorable response to both positive and negative ESD strikes.

FIG.7illustrates a first alternative SCR700, in a plan view that includes many of the same aspects as theFIG.3SCR108, and like numbers are used for like items in both figures. As to a difference, however, in theFIG.7SCR700, instead of the U-shaped electrically non-contacted first interior n+ region230/232, the SCR includes an electrically non-contacted third interior n+ region702that is shaped generally the same as (but not necessarily equally dimensioned), and parallel to, the electrically-contacted second interior n+ region306, and the electrically non-contacted third interior n+ region702is on the opposite side of the third n+ region224, as compared to the electrically-contacted second interior n+ region306. In the SCR700, the electrically non-contacted third interior n+ region702can be influenced by anode potential through a resistive path, while again the electrically-contacted second interior n+ region306is physically connected to the SCR anode106. Accordingly, a vertical cross section across the approximate center ofFIG.7provides the same structure as shown inFIG.4, albeit with the electrically non-contacted third interior n+ region702replacing theFIG.4illustration of the electrically non-contacted first interior n+region230/232(and for reference, the line4-4is again shown inFIG.7). Returning then toFIG.4, but in the context of theFIG.7SCR700, the structure generally to the left ofFIG.4supports theFIG.5snapback response curve500, while the structure generally to the right ofFIG.4supports theFIG.6diodic response curve600. Additionally, theFIG.7SCR700may reduce field and current crowding that can occur at corners, inasmuch as both of the electrically-contacted second interior n+ region306and the electrically non-contacted third interior n+ region702are rectangular and parallel with respect to one another.

FIG.8illustrates a plan view, andFIG.9illustrates a cross-sectional view across the vertical dashed line9-9inFIG.8, of a second alternative SCR800. The SCR800includes many of the same aspects as theFIG.3SCR108, and like numbers are used for like items in both figures. The SCR800includes, however, as shown along the horizontal top of inFIG.8, an enlarged p+ region902in the continuous p well212/214. As shown in theFIG.9cross-sectional view, the enlarged p+ region is the only heavy doped region within that area of the continuous p well212/214, while in contrast the comparableFIG.4cross-sectional view includes two heavy doped regions, namely, the first p+ type continuous region216/220and the first n+ type continuous region218/222in the continuous p well212/214. Accordingly, inFIGS.8and9, the first n+ type continuous region218/222is non-concentric in the sense that it terminates at ends804and806, rather than fully surround the third n+ region224. Further, with this structure of excluding the first n+ type continuous region218/222along the top ofFIG.8, thenFIG.9includes a schematic of a diode904superimposed to the right, with its anode provided by the combination of the illustrated portion of the enlarged p+ type region902and the adjacent first p type continuous well region212/214, and with its cathode provided by a portion of the n type epi layer204and the electrically-contacted second interior n+ region306. By comparingFIG.9toFIG.4, note that theFIG.4diode402has an n+ type continuous region218/222proximate the diode402and within the same p well continuous region212/214as the diode402, while theFIG.9diode904has no such proximate n+ region. InFIG.4, the possible parasitic effects (e.g., creating a parasitic NPN conductive path) of the proximate n+ type continuous region218/222are reduced by enlarging the distance D5between that region and the electrically-contacted second interior n+ region306. In contrast, inFIG.9, there is no such comparable parasitic effect because there is no proximate n+ region; further, with the absence of that n+ region, a minimum distance D6between a portion of the diode902anode provided by the first p type continuous well region212/214is smaller than theFIG.4distance D3between analogous regions, thereby reducing the overall size of the SCR900, as compared to the SCR108.

FIG.10illustrates a cross-sectional view of a third alternative SCR1000. The SCR1000includes the same items as theFIG.2SCR108, with the exception that instead of the earlier-describedFIG.2trench regions206and208, in the same relative vicinity the SCR1000includes p type junction isolation regions1002and1004. Additionally, instead of theFIG.2n type buried layer202, which spanned the entire distance between the trench regions206and208, the SCRO1000includes an n type buried layer1006which may not span the entire distance between the p type junction isolation regions1002and1004. Each of the p type junction isolation regions1002and1004is formed from the upper edge210of the n epi layer204down to contact the p type layer200. Further, from a plan perspective (not separately shown), the p type junction isolation regions1002and1004form a continuous p type junction isolation region1002/1004that surrounds portions of the SCR1000within that continuous region. Accordingly, the surrounding portion isolates the SCR1000, including its n type epi layer204, for example relative to other components that also may be formed in connection with the same p type layer200, with that layer serving as a common substrate for such components.

TheFIG.10SCR1000may be modified to form other alternative embodiments. For example,FIG.10illustrates a distance D7between the innermost edge of each of the p type junction isolation regions1002and1004and its proximate respective first p well212or second p well214. In different embodiments, the distance D7may be shortened or lengthened. For example, D7may be shortened to an extent such that a diffusion tail from a p type junction isolation region1002or1004intersects the respective one of the proximate first p well212or second p well214. In this manner, the dopant profile from the intersecting portion of the p type junction isolation region1002or1004may affect the gain of the NPN BJT112. As another example, a separate step of forming the first p well212and second p well214can be eliminated, and instead the formation of the p type junction isolation regions1002and1004can be modified to cause the lateral diffusion of each to be sufficiently inward and under the first p+ type continuous region216/220and the first n+ type continuous region218/222, thereby providing both the SCR isolation and a p type area so as to facilitate the NPN BJT112, PNP110, and diode402structures described above.

FIG.11illustrates a cross-sectional view of a fourth alternative SCR1100. The SCR1100includes the same items as theFIG.2SCR108, with an exception that instead of the earlier-described n type epi layer204, the SCR1100includes a p type epi layer1102. Additionally, an n well1104is formed within a central location of the p type epi layer1102, and then the third n+ region224and the second p+ type continuous region226/228are formed within the n well1104. In an example embodiment, the n well1104is formed to a depth to contact the n type buried layer202. Accordingly, theFIG.11andFIG.2alternatives illustrate the flexibility of example embodiments contemplated in connection with either p type or n type epi layers, where the choice of either may in some instances be controlled by other components formed on the same IC as the SCR, but existing outside the surrounding layers of the SCR. In either case, an SCR with benefits as illustrated also may be implemented.

The illustrated example embodiments provide an SCR, for example for use in ESD protection. These embodiments may provide various benefits over prior ESD devices. For example, the various configurations provide benefit of a generally concentric layout that incorporates a negative strike diode. Such configurations can reduce overall area that otherwise might be required by some prior art devices, for example those that include large parallel ESD diodes. As another benefit, eliminating separate negative strike diodes also eliminates potential leakage and capacitance concerns. As still another benefit, various inventive aspects can be implemented in a variety of configurations. Several configurations have been presented, and the inventive scope may include still others as contemplated or may be determined by one skilled in the art from the teachings of this document. For instance, aspects of the described configurations may be selected and combined; for example, theFIG.7parallel electrically non-contacted third interior n+ region702and electrically-contacted second interior n+ region306may be implemented with theFIG.9enlarged p+ region902and/or eliminated first n+ type continuous region218/222in that well. Accordingly, additional modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the following claims.