Diode triggered silicon controlled rectifier

The present disclosure relates to semiconductor structures and, more particularly, to diode triggered silicon controlled rectifiers and methods of manufacture.

A Silicon Controlled Rectifier (SCR) is a semiconductor or integrated circuit (IC) that allows the control of current using a small current. A diode triggered SCR is a very useful ESD protection device due to trigger voltage tunability; however, diode triggered SCRs cannot be used for mid or high voltage electrostatic discharge (ESD) protection. This is due to the fact that the trigger voltage tunability does not scale with a number of trigger diodes.

For example, diode triggered SCRs are known to exhibit the Darlington effect which reduces the amount of current in each subsequent diode. In essence, the voltage dropped by each additional diode is reduced. Also, the leakage of the SCR is increased. Accordingly, there is a diminishing gain achieved with of additional diodes, which is caused by the Darlington effect.

In an aspect of the disclosure, a structure comprises: a diode string comprising a first type of diodes; and a second type of diode in bulk technology in series with the diode string of the first type of diodes.

In an aspect of the disclosure, a structure comprises: multiple P+ and N+ regions forming a diode string without Darlington effect; and a single diode or string of diodes in bulk technology electrically connected to the diode string.

In an aspect of the disclosure, a structure comprises: a diode string comprising, in series, alternating P+ regions and N+ regions in semiconductor on insulator material; and a single diode or string of diodes in a bulk wafer electrically connected to a last N+ region of the diode string.

The present disclosure is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present disclosure.

FIG. 1 shows stringed diodes and respective fabrication processes in accordance with aspects of the present disclosure.

FIG. 2 shows the stringed diodes of FIG. 1 with a diode triggered silicon controlled rectifier (SCR) and respective fabrication processes in accordance with aspects of the present disclosure.

FIG. 3 shows the stringed diodes with a diode triggered silicon controlled rectifier (SCR) of FIG. 2 and respective fabrication processes in accordance with aspects of the present disclosure.

FIG. 4 shows a schematic diagram of a diode triggered silicon controlled rectifier (SCR) in accordance with aspects of the present disclosure.

The present disclosure relates to semiconductor structures and, more particularly, to diode triggered silicon controlled rectifiers (SCR) and methods of manufacture. More specifically, the present disclosure provides a diode triggered SCR with hybrid diodes. In embodiments, the hybrid diodes include diodes formed on both semiconductor on insulator (SOI) technologies (i.e., SOI diodes) and bulk substrate technologies (i.e., bulk diodes). Advantageously, the present disclosure provides a solution for mid-voltage low capacitance low leakage ESD protection.

In more specific embodiments, the diode triggered SCRs include a combination of trigger diodes in bulk and SOI technologies. The diode triggered SCRs are capable of maintaining trigger voltage tunability and scaling with any number of trigger diodes, thus offering an ESD protection solution for both mid or high voltage range. This is due to the fact that the diode triggered SCRs are able to mitigate the Darlington effect observed in known diode triggered SCRs. For example, the SOI diodes are capable of eliminating the Darlington effect as they are strictly two (2) terminal diodes. By avoiding the Darlington effect, the SOI diodes will exhibit lower leakage and higher voltage trigger (Vtrigger). On the other hand, the bulk diodes inject electrons into the substrate to facilitate triggering. In addition, the last diode of the diode string is a bulk diode and, hence, does not form a bulk diode string.

The diode triggered SCRs of the present disclosure can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form structures with dimensions in the micrometer and nanometer scale. The methodologies, i.e., technologies, employed to manufacture the diode triggered SCRs of the present disclosure have been adopted from integrated circuit (IC) technology. For example, the structures are built on wafers and are realized in films of material patterned by photolithographic processes on the top of a wafer. In particular, the fabrication of the diode triggered SCRs use three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.

FIG. 1 shows stringed diodes and respective fabrication processes in accordance with aspects of the present disclosure. In particular, the structure 10 includes SOI technology 12 and bulk technology 14 . The SOI technology 12 includes two (2) terminal diodes 25 a , 25 b ; whereas, the bulk technology includes a transistor 27 in a bulk wafer which acts as a diode. It should be understood by those of skill in the art that although two diodes 25 a , 25 b are shown in SOI technology, additional diodes are also contemplated herein. Although a single transistor 27 is shown, the use of additional transistors is contemplated herein.

In embodiments, the SOI technology 12 includes a substrate 12 a , e.g., wafer, in addition to an insulator layer 12 b and a semiconductor material 12 c . The substrate 12 a can be a p-type substrate, the insulator layer 12 b can be a buried oxide material and the semiconductor material 12 c can be any suitable semiconductor material. For example, the semiconductor material 12 c may be composed of any suitable material including, but not limited to, Si, SiGe, SiGeC, SiC, GaAs, InAs, InP, and other III/V or II/VI compound semiconductors.

In further embodiments, the bulk technology 14 can be formed from the SOI technology 12 . Specifically, the bulk technology 14 can be formed by etching or removing the insulator layer 12 b and the semiconductor material 12 c from the SOI technology 12 , leaving the p-type substrate 12 a . The insulator layer 12 b and the semiconductor material 12 c can be removed by conventional lithography and etching processes, e.g., reactive ion etching (RIE), using selective chemistries as should be understood by those of skill in the art.

Prior to forming the bulk technology 14 , a plurality of shallow trench isolation regions 16 a , 16 b are formed using conventional lithography, etching and deposition processes. For example, a resist formed over the semiconductor material 12 c is exposed to energy (light) to form a pattern (opening). An etching process with a selective chemistry, e.g., RIE, will be used to form one or more trenches in the insulator material 12 b and substrate 12 a , through the openings of the resist. Following the resist removal by a conventional oxygen ashing process or other known stripants, insulator material, e.g., oxide, can be deposited within the trenches by any conventional deposition processes, e.g., chemical vapor deposition (CVD) processes. Any residual material on the surface of the semiconductor material 12 c can be removed by conventional chemical mechanical polishing (CMP) processes.

In embodiments, at least one shallow trench isolation region 16 a will be formed between the SOI technology 12 and the bulk technology 14 ; whereas, at least one shallow trench isolation region 16 b will be formed between a P+ region 18 a and a N+ region 18 b of the bulk technology 14 . In embodiments, the shallow trench isolation region 16 b will extend into a N-well 20 of the bulk technology 14 , which can extend into the substrate 12 a of the SOI technology 12 . The P+ region 18 a , N+ region 18 b and the N-well 20 can be formed by conventional ion implantation processes known to those of skill in the art such that no further explanation is required for a complete understanding of the present disclosure. In embodiments, the P+ region 18 a , N-well 20 and the p-type substrate 12 a will form a PNP transistor 27 (which acts as a very low leakage diode) in the bulk technology 14 . The PNP transistor 27 (e.g., diode 27 ) is a last diode of the diode string and, hence, does not form a bulk diode string. Accordingly, the diode 27 is capable of dropping a large voltage without the Darlington effect due to it receiving a large current.

Still referring to FIG. 1 , by using conventional ion implantation processes known to those of skill in the art, a N-well 22 is formed in the semiconductor material 12 c . Thereafter, alternating P+ regions 24 a and N+ regions 24 b are formed in the semiconductor material 12 c , with a P+ region 24 a and N+ region 24 b of adjacent diodes 25 a , 25 b contacting one another. In this way, the adjacent diodes 25 a , 25 b are strictly two (2) terminal diodes in series, which can eliminate the Darlington effect. The shallow trench isolation region 16 a separates the diodes 25 a , 25 b from the diode 27 . A ground pad 26 electrically contacts the N+ region 18 b and an I/O pad 28 electrically contacts the P+ region 24 a′.

A silicide block layer 30 is formed over each of the diodes 25 a , 25 b , i.e., over the N-well 20 and contacting the respective P+ and N+ regions 24 a , 24 b . In embodiments, the silicide block layer 30 can be formed by conventional silicide processes. As should be understood by those of skill in the art, the silicide process begins with deposition of a thin transition metal layer, e.g., nickel, cobalt or titanium, over the diodes 25 a , 25 b . After deposition and patterning processes, the structure is heated allowing the transition metal to react with exposed silicon (or other semiconductor material as described herein) in the active regions of the semiconductor device (e.g., diodes 25 a , 25 b ) forming a low-resistance transition metal silicide. Following the reaction, any remaining transition metal can be removed by chemical etching, leaving silicide contacts in the active regions of the device. The N+ region of the SOI diode 25 b is electrically connected to the P+ region of the bulk diode 27 . A dielectric layer 32 (e.g., oxide) can then be deposited over the diodes 25 a , 25 b , 27 , with wiring connections between the pads, diodes, etc., embedded within the dielectric layer 32 . It should be noted that, although the diodes 25 a and 25 b are shown bounded by silicide block, they could also be bounded with the FET gate material or any other available insulator.

FIG. 2 shows the stringed diodes of FIG. 1 with a diode triggered silicon controlled rectifier (SCR) and respective fabrication processes. More specifically, the structure 10 a of FIG. 2 show the stringed diodes 25 a , 25 b , 27 of FIG. 1 represented at reference numeral 100 and a SCR represented at reference numeral 110 . As should be understood by one of skill in the art, the stringed diodes 25 a , 25 b and 27 will help trigger the SCR 110 .

In embodiments, the SCR 110 is formed in bulk technology and includes a P-well 50 and a N-well 52 formed using conventional ion implantation processes as already described herein. Alternating P+ regions 54 a and N+ regions 54 b are formed in the respective P-well 50 and N-well 52 , separated by shallow trench isolation regions 16 c . In embodiments, the alternating P+ regions 54 a and N+ regions 54 b formed in the respective P-well 50 and N-well 52 form a PNP transistor 55 a and NPN transistor 55 b , respectively. A shallow trench isolation region 16 d separates the SCR 110 from the stringed diodes 100 of FIG. 1 .

The bulk technology, shallow trench isolation regions, the P+ regions (anodes), and the N+ regions (cathodes) are formed in the manner already described herein. In this embodiment, the ground pad 26 is connected to the P+ region 54 a ′ and N+ region 54 b ′ of the P-well 50 , in addition to the N+ region 18 b . Also, in this embodiment, the I/O pad 28 is connected to the P+ region (anode) 54 a in the N-well 52 . The SCR 110 and the stringed diode 25 a are connected through the respective N+ region 54 b of the SCR 110 and P+ region 24 a of the diode 25 a.

In operation using the structure 10 a of FIG. 2 , an ESD event on the I/O pad 28 will pass current through the P+ region 54 a , N-well 52 and N+ region 54 b to the stringed diodes 25 a , 25 b , 27 . The current will pass through the bulk diode 27 and N+ region 18 b to the ground pad 26 . The current will then trigger the SCR 110 . Once the SCR is triggered, most of the current from the P+ region (anode) 54 a can flow backwards into the N+ region (cathode) 54 b ′ of the P-well 50 .

FIG. 3 shows stringed diodes with a diode triggered SCR 110 of FIG. 2 and respective fabrication processes. More specifically, the structure 10 b of FIG. 3 includes a string of diodes 25 a , 25 b that are fabricated from doped gate material as represented by reference numerals 62 a , 62 b . That is, in this embodiment, the alternating P+ regions 24 a and N+ regions 24 b shown in FIG. 1 are replaced with doped gate material 62 a , 62 b . The doped gate material can be a P-doped poly material 62 a and N-doped poly material 62 b , separated by a N-well region 22 . The P-doped poly material 62 a and the N-doped poly material 62 b can be formed on a gate dielectric material (also represented by reference numerals 62 a , 62 b ). In embodiments, the gate dielectric material can be a high-k dielectric material such as hafnium oxide; although other dielectric materials are also contemplated herein. In addition, instead of using SOI technology, in this embodiment the doped gate material 62 a , 62 b is formed over a shallow isolation structure 60 formed in the N-well 20 of the bulk technology. In embodiments, the P-doped poly material 62 a and a N-doped poly material 62 b can be deposited and patterned using conventional deposition, lithography and patterning processes.

FIG. 4 shows a schematic diagram of a diode triggered silicon controlled rectifier in accordance with aspects of the present disclosure. As shown in FIG. 4 , the stringed diodes 25 a , 25 b , 27 are provided in series. The arrow represents the forward bias and drive current of the diodes 25 a , 25 b , 27 . By using the diodes 25 a , 25 b in SOI technology, it is possible to avoid bipolar gain and hence the Darlington effect. Particularly, unlike conventional structures, there will be no leakage of the diodes 25 a , 25 b to ground, and hence there will be no diminishing gains by using additional diodes (which causes the Darlington effect). Also, by maintaining a fraction of the diodes in bulk allows for the injection of carriers into substrate which facilitates triggering.

The method(s) as described above is used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.