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Title:
FINFET TECHNOLOGY USING DEEP ISOLATION
Document Type and Number:
WIPO Patent Application WO/2019/173033
Kind Code:
A1
Abstract:
FinFET transistors (102), (104), P-N junctions (150) and methods (400) for forming the same are described herein. In one example, a FinFET transistor (102, 104) is described that includes a channel region (214) wrapped by a metal gate (208), the channel region (214) connecting source and drain regions (210), (212). A first oxide isolation layer (112) is disposed on a first side of the fin (202) and a second oxide isolation layer (114) is disposed on a second side of the fin (202), where the second side is opposite of the first side. The second oxide isolation layer (114) has a thickness (284) greater than a thickness (280) of the first oxide isolation layer (112).

Inventors:
KARP, James (2100 Logic Drive, San Jose, CA, 95124, US)
HART, Michael, J. (2100 Logic Drive, San Jose, CA, 95124, US)
Application Number:
US2019/018067
Publication Date:
September 12, 2019
Filing Date:
February 14, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
XILINX, INC. (2100 Logic Drive, San Jose, CA, 95124, US)
International Classes:
H01L21/8238; H01L21/762; H01L27/092
Foreign References:
US20080029821A12008-02-07
US20150060959A12015-03-05
US20150311201A12015-10-29
US4683488A1987-07-28
Other References:
None
Attorney, Agent or Firm:
PARANDOOSH, David A et al. (Xilinx, Inc.2100 Logic Driv, San Jose CA, 95124, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A P-N junction comprising:

a first P-type FinFET transistor;

a first N-type FinFET transistor disposed adjacent the first P-type FinFET transistor; and

a first oxide isolation layer laterally separating the first N-type FinFET transistor from the adjacent the first P-type FinFET transistor, the first oxide isolation layer having a thickness of greater than 150nm.

2. The P-N junction of claim 1 , wherein the first P-type FinFET transistor comprises:

a second oxide isolation layer disposed on a side of the first P-type FinFET transistor opposite the first oxide isolation layer, the second oxide isolation layer having a thickness of less than half of a thickness of the first oxide isolation layer.

3. The P-N junction of claim 2, wherein the thickness of the first oxide isolation layer is at least three times the thickness of the second oxide isolation layer.

4. The P-N junction of claims 1 -3, wherein the bhrh · bRhR product gain of the P-N junction is less than 1.

5. The P-N junction of claim 1 further comprising:

a second P-type FinFET transistor disposed adjacent the first P-type FinFET transistor; and

a second oxide isolation layer laterally separating the first P-type FinFET transistor from the adjacent second P-type FinFET transistor, the second oxide isolation layer having a thickness of less than half a thickness of the first oxide isolation layer.

6. The P-N junction of claim 5, wherein the thickness of the second oxide isolation layer is less than 80nm and the thickness of the first oxide isolation layer is greater than 200nm.

7. The P-N junction of claim 5, wherein a width of the first oxide isolation layer defined between the first P-type FinFET transistor and the adjacent second N-type FinFET transistor is greater than a width of the second oxide isolation layer defined between the first P-type FinFET transistor and the adjacent second P-type FinFET transistor.

8. The P-N junction of claim 1 further comprising:

a second N-type FinFET transistor disposed adjacent the first N-type FinFET transistor; and

a second oxide isolation layer laterally separating the first N-type FinFET transistor from the adjacent second N-type FinFET transistor, the second oxide isolation layer having a thickness less than the thickness of the first oxide isolation layer.

9. The P-N junction of claim 8, wherein the thickness of the second oxide isolation layer is less than 80nm and the thickness of the first oxide isolation layer is greater than 200nm.

10. The P-N junction of claim 8, wherein a width of the first oxide isolation layer is greater than a width of the second oxide isolation layer.

11. The P-N junction of claim 1 further comprising:

a second FinFET transistor disposed adjacent one of the first P-type FinFET transistor and first N-type FinFET transistor, the second FinFET transistor being of the same type as a closer of the first P-type FinFET transistor and first N-type FinFET transistor; and a second oxide isolation layer laterally separating the second FinFET transistor from the adjacent one of the first P-type FinFET transistor and first N-type FinFET transistor, the second oxide isolation layer having a thickness substantially equal to the thickness of the first oxide isolation layer.

12. A method for forming a P-N junction, the method comprising:

etching a semiconductor substrate to form a plurality of high aspect ratio fins, the plurality of high aspect ratio fins including a first high aspect ratio fin and a second high aspect ratio fin separated by a first high aspect ratio trench;

filling the first high aspect ratio trench with an oxide material;

removing a portion of the oxide material filling the first high aspect ratio trench; and

stopping the removal of the oxide material filling the first high aspect ratio trench to form a first oxide isolation layer having a thickness of at least 150nm.

13. The method of claim 12, wherein etching the semiconductor substrate to form the plurality of high aspect ratio fins further comprises:

forming the first high aspect ratio fin in a p-doped region of the semiconductor substrate; and

forming the second high aspect ratio fin in an n-doped region of the

semiconductor substrate, the first and second high aspect ratio fins separated by the first high aspect ratio trench.

14. The method of claim 13 further comprising:

forming a third high aspect ratio fin of the plurality of high aspect ratio fins in a p-doped region of the semiconductor substrate adjacent the first high aspect ratio fin; and

forming a second oxide isolation layer having a thickness less than 100nm between the first and third high aspect ratio fins.

15. The method of claim 13 further comprising:

filling a second first high aspect ratio trench etched in the semiconductor substrate with an oxide material;

removing a portion of the oxide material filling the second high aspect ratio trench; and

stopping the removal of the oxide material filling the second high aspect ratio trench to form a second oxide isolation layer having a thickness less than half of the thickness of the first oxide isolation layer.

Description:
FINFET TECHNOLOGY USING DEEP ISOLATION

TECHNICAL FIELD

Embodiments of the present invention generally relate to FinFET transistors, P-N junctions and methods for forming the same. More particularly, embodiments of the present invention relate to FinFET transistors and P-N junctions having deep oxide isolation layers.

BACKGROUND

FinFET transistors have begun to replace traditional planar transistors in next generation electronic devices due to the ability to enhance the control of current flowing between source and drain regions of the transistors at smaller nanometer nodes. Devices, such as memory structures, also benefit from the use of FinFET transistors because FinFET transistors have lower power and provide increased transistor density while enabling improved device

performance.

Memory structures that use FinFET transistors remain susceptible to single event latch-ups (SEL), just like planar transistors. Latch-up i n CMOS technologies is caused by the triggering of a parasitic p-n-p-n SCR (silicon controlled rectifier) structure. S E L is caused by transient currents originating from charges generated along the track of an incident charged particle. Neutrons are the primary cause of SEL in terrestrial applications. Conventional S E L m itigation techniques for planar transistor aim to decouple or weaken elements of the parasitic SCR structure. S uch techniques are typically associated with an area penalty that can be tolerated for a given application . U ntil recently both CM OS and underlying S E L device physics have scaled together in planar transistors, thus al lowi ng predictable S E L results for a given design flow. However, this has changed with the recent introduction of Fin FET technology as it has been observed that the failure rate associated with SEL events in FinFET transistors is generally higher than that of planar transistors.

Thus, there is a need for an improved FinFET transistor. SUMMARY

FinFET transistors, P-N junctions and methods for forming the same are described herein. In one example, a FinFET transistor is described that includes a fin having channel region wrapped by a metal gate, the channel region connecting a source region and a drain region of the fin. A first oxide isolation layer is disposed on a first side of the fin and a second oxide isolation layer is disposed on a second side of the fin, where the second side is opposite of the first side. The second oxide isolation layer has a thickness greater than a thickness of the first oxide isolation layer.

In another example, a P-N junction is described. The P-N junction includes a first P-type FinFET transistor, a first N-type FinFET transistor and first oxide isolation layer. The first N-type FinFET transistor is disposed adjacent the first P-type FinFET transistor. The first oxide isolation layer lateral separates the first N-type FinFET transistor from the adjacent the first P-type FinFET transistor. The first oxide isolation layer has a thickness of at least 150 nm.

In still another example, a P-N junction is described that includes a first P- type FinFET transistor, a first N-type FinFET transistor and first oxide isolation layer. The first N-type FinFET transistor is disposed adjacent the first P-type FinFET transistor. The first oxide isolation layer lateral separates the first N-type FinFET transistor from the adjacent the first P-type FinFET transistor. The -N junction has a b hrh · b RhR product gain of less than 1.

In yet another example, a method for forming a P-N junction is described that includes etching a semiconductor substrate to form a plurality of high aspect ratio fins, the plurality of high aspect ratio fins including a first high aspect ratio fin and a second high aspect ratio fin separated by a first high aspect ratio trench, filling the first high aspect ratio trench with an oxide material, removing a portion of the oxide material filling the first high aspect ratio trench, and stopping the removal of the oxide material filling the first high aspect ratio trench to form an oxide isolation layer having a thickness of at least 150nm. BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

Figure 1 is a schematic sectional view of an electronic device having a P- N junction that includes FinFET transistors.

Figure 2 is an isometric view of a portion of the electronic device of Figure 1 illustrating a P-type FinFET transistor disposed adjacent an N-type FinFET transistor.

Figures 3A-3H are sectional views of a film stack during different stages of a sequence for forming the electronic device of Figure 1 having adjacent P- type and N-type FinFET transistors.

Figure 4 is a block diagram of a method for forming an electronic device having adjacent P-type and N-type FinFET transistors.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

It is contemplated that elements of one embodiment may be beneficially incorporated in other embodiments.

DETAILED DESCRIPTION

The FinFET technology has significantly improved CMOS performance and has enabled Moore’s Law scaling down to advanced nodes of 7 nm and beyond. The manufacturing of FinFET transistors required a significant change in the geometry of the shallow trench isolation (STI). The purpose of the STI is to electrically isolate adjacent transistors. Advanced planar CMOS transistors have STI depths in the range of about 200 to about 250 nm. For FinFET technologies, the exposed silicon fin is formed by etching-back the STI, which results in an STI depth of between about 70 to about 80 nm. FinFET designs can expect even further STI depth reduction with continued CMOS scaling. From planar to FinFET d e s i g n s , the approximately 3 times reduction in t h e STI depth has significantly reduced the minimum substrate path between source/drain of adjacent pMOS and nMOS transistors. This does not deteriorate p/nMOS isolation during normal CMOS operation, when all p-n junctions are under reverse bias. However, the reduced substrate path between adjacent junctions has been found to allow triggering of parasitic SCR latch-up, when junctions of both pMOS and nMOS transistors can be forward biased during an SEL transient.

As discussed above, conventional FinFET transistors are susceptible to SEL events due to the reduced substrate path between adjacent junctions. Conventional FinFET transistors are particularly more susceptible to SEL events due to high energy particle strikes than conventional planar transistors. High energy particles include neutrons, thermal neutrons, alpha particles and the like. In particular, the inventors have observed that 10 times less energy is needed to cause an SEL event due to high energy particle strikes on conventional FinFET transistors as compared to conventional planar transistors. The inventors have discovered a strong dependence between oxide isolation thickness between N- type and P-type FinFET transistors and the probability of high energy particle strike SEL events. Thus, the disclosure herein describes techniques for improving the resistance of electronic devices employing FinFET transistors to SEL events by selectively increasing oxide isolation thickness almost 2-3 times that of conventional FinFET transistors. Moreover, while the oxide isolation thicknesses between N-type and P-type FinFET transistors are increased, shallower oxide isolation thicknesses between same types of FinFET transistors may be maintained. Thus, electronic devices with robust resistance to SEL events may be realized with a minimal increase in fabrication costs. Moreover, the novel FinFET transistors described herein are at up to 10 times less susceptible to SEL events than traditional FinFET transistors, desirably approaching and even equaling that of planar transistors.

Figure 1 is a schematic diagram of one example of an electronic device 100 having a P-N junction 150 defined between an N-type FinFET transistor 102 and an adjacent P-type FinFET transistor 104. In the example of Figure 1 , the electronic device 100 is configured as a CMOS device. However, the FinFET transistors 102, 104 may be configured for use in other types of devices that include both N-type and P-type FinFET transistors 102, 104.

The N-type and P-type FinFET transistors 102, 104 are formed on a semiconductor substrate 106. The FinFET transistors 102, 104 may be formed by additive or subtractive techniques, including techniques currently known or developed in the future.

The substrate 106 may be a silicon substrate or a substrate comprised of another suitable material. The substrate 106 includes a P-well 152 and an N- well 154. In the example depicted in Figure 1 , the N-well 154 is illustrated as formed on the P-well 152. However, the P-well 152 may alternatively be formed on the N-well 154, or the P-well 152 may be laterally spaced from the N-well 154, for example in a twin-tub configuration. The P-well 152 and the N-well 154 may be formed using ion implantation, diffusion or other suitable technique. In one example, the P-well 152 is doped with phosphorus, while the N-well 154 is doped with boron.

In the example depicted in Figure 1 , there are at least two N-type FinFET transistors 102 formed on the P-well 152. There are also at least two P-type FinFET transistors 104 formed on the N-well 154. One of the N-type FinFET transistors 102 is disposed adjacent to one of the P-type FinFET transistors 104. An oxide isolation layer 1 12 is disposed in trench 108 formed between each adjacent FinFET transistors of the same type. For example, the oxide isolation layer 1 12 is disposed between each pair of adjacent N-type FinFET transistors 102. The oxide isolation layer 1 12 is also disposed between each adjacent pair of P-type FinFET transistors 104. An oxide isolation layer 1 14 is disposed in a trench 1 10 formed between adjacent FinFET transistors of different types. For example, the oxide isolation layer 1 14 is disposed between the N-type FinFET transistor 102 that is adjacent to the P-type FinFET transistor 104. The depth of a portion of the trench 1 10 containing oxide material is at least double the depth of a portion of the trench 108 containing oxide material, thus making the thickness of the oxide isolation layer 1 14 is at least double the thickness of the oxide isolation layer 1 12. The deeper trench 1 10 and thicker oxide isolation layer 1 14 provides excellent resistance against SEL events across the P-N junction 150 as further discussed below. Additional details of the P-N junction 150 are illustrated in the isometric view of a portion of the electronic device 100 of Figure 1 depicted in Figure 2. As shown in Figure 2, the N-type FinFET transistor 102 includes a high aspect ratio fin 202 and a metal gate 208, both of which extend upwards from the substrate 106. The fin 202 may be formed by additive or subtractive techniques. In one example, the fin 202 may be formed may be formed from silicon, silicon germanium, germanium or lll-V material. The fin 202 may be optionally covered with thin oxide capping layer 206.

The oxide isolation layer 1 12 is formed on the substrate 106 between the fins 202 of the N-type FinFET transistors 102. In one example, the oxide isolation layer 1 12 is formed in the trench 108 defined between the fins 202. The oxide isolation layer 1 12 is formed from one or more of silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), low-k dielectric, or other suitable material. Similarly, the oxide isolation layer 1 14 is formed on the substrate 106, such as in the trench 1 10 defined between the fin 202 of the N- type FinFET transistor 102 and a high aspect ratio fin 252 of the P-the FinFET transistor 104. The oxide isolation layer 1 14 may be comprised of the same materials suitable for use as the oxide isolation layer 1 12.

The metal gate 208 generally has a fin-shape that is perpendicular to a plane of the substrate 106 and is also perpendicular to a plane of the fin 202.

The metal gate 208 surrounds a portion of the fin 202, separates a source region 212 of the fin 202 from a drain region 210 of the fin 202. The source and drain regions 212, 210 are generally aligned in a common plane extending

perpendicular to a plane of the substrate 106. The source and drain regions 212, 210 also are oriented perpendicular to a plane of the metal gate 208.

The metal gate 208 wraps around a channel region 214 defined between the source and drain regions 212, 210. The channel region 214 is formed from the same material as the regions 212, 210 as the channel region 214 is an integral part of the fin 202. When the metal gate 208 is energized, current flows through the channel region 214 from the source region 212 to the drain region 210.

The metal gate 208 is formed from a gate electrode disposed over a gate dielectric material. The gate dielectric material separates the gate electrode from the channel region 214. The gate electrode may be polysilicon, Ta, TiN, TiAIN, TiSiN, TaN, TaAIN, TaSiN, W, WN, Re, Ir, Ru, Mo, Al, Cu, CO, Ni, WN/RU0 2, ZrSi2, MoSi2, TaSi2, NiSi2, or other suitable material.

The gate dielectric material may be a high-K oxide, such as a hafnium based material. Examples of hafnium based materials that are suitable for use as the gate dielectric material include HfO x , HfSiO x , HfSiON, HfZrO, HfLaO, HfTaO, HfTiO and the like. Alternatively, the gate dielectric material may LaO, AIO, ZrO, Zr02, ZrSi02, LaSiO, AlSiO, TiO, Ta 2 0 5 , Ta 2 0 3 , Y2O3, STO, BTO, BaZrO, or other suitable material. In one example, the metal gate 208 is formed from a polysilicon gate electrode disposed over an HfO x gate dielectric material.

The metal gate 208 may also include additional layers, such as capping layers and interfacial layers. For example, a capping layer may be disposed between the gate dielectric material and the metal gate material. The capping layer may be lanthanum oxide, LaSiO, manganese oxide, aluminum oxide, or other suitable material. The capping layer may have a thickness ranging from about 3 to about 10 angstroms. In another example, an interfacial layer may be disposed between the gate dielectric material and the channel region 214. The interfacial layer may have a thickness ranging from about 3 to about 10 angstroms. The interfacial layer may be an oxide, such as silicon oxide or silicon oxynitride. Alternatively, the interfacial layer may be silicon nitride or other suitable material.

The P-type FinFET transistor 104 includes the fin 252 and a metal gate 258, both of which extend upwards from the substrate 106. As with the fin 202, the fin 252 may be formed by additive or subtractive techniques. In one example, the fin 252 may be formed may be formed from silicon, silicon germanium, germanium or lll-V material. The fin 252 may be optionally covered with thin oxide capping layer 256.

The metal gate 258 generally has a fin-shape that is perpendicular to a plane of the substrate 106 and is also perpendicular to a plane of the fin 252.

The metal gate 258 surrounds a portion of the fin 252, separates a source region 262 of the fin 252 from a drain region 260 of the fin 252. The source and drain regions 262, 260 are generally aligned in a common plane extending

perpendicular to a plane of the substrate 106. The source and drain regions 262, 260 also are oriented perpendicular to a plane of the metal gate 258. The metal gate 258 wraps around a channel region 264 defined between the source and drain regions 262, 260. The channel region 264 is formed from the same material as the regions 262, 260 as the channel region 264 is an integral part of the fin 252. When the metal gate 258 is energized, current flows through the channel region 264 from the source region 262 to the drain region 260.

The metal gate 258 is formed from a gate electrode disposed over a gate dielectric material. The gate dielectric material separates the gate electrode from the channel region 264. The metal gate 258 is constructed similar to as described above with reference to the metal gate 208, and may also include additional layers, such as capping layers and interfacial layers as described above with reference to the metal gate 208.

The N-type FinFET transistors 102 are separated by a pitch or distance 282. In one example, the distance 282 is about 42nm. The N-type FinFET transistor 102 is separated from the P-type FinFET transistor 104 by a distance 286. The distance 286 is generally larger than the distance 282 to accommodate fabrication of the deeper oxide isolation layer 1 14. For example, the oxide isolation layer 1 14 has a thickness 284 that is greater than a thickness 280 of the oxide isolation layer 1 12. In one example, the thickness 284 is at least about twice the thickness 280 of the oxide isolation layer 1 12. In another example, the thickness 284 is at least three times the thickness 280 of the oxide isolation layer 1 12. It is contemplated that the distance 286 defining the width of the trench 1 10 and oxide isolation layer 1 12 may be tapered or stepped such that the a width at a bottom of the trench 1 10 is much less than the width at the portion of the trench 1 10 at which the oxide isolation layer 1 12 is exposed opposite the substrate 106. For example, the width at the bottom of the trench 1 10 may be about the same as the distance 282.

In the example depicted in Figure 2, the thickness 280 of the oxide isolation layer 1 12 is less than about 100 nm, such as between 70-80 nm. In contrast, the thickness 284 of the oxide isolation layer 1 14 is greater than 150 nm, such as between 200-250 nm. Stated in another manner, the thickness 284 of the oxide isolation layer 1 14 is at least twice the thickness 280 of the oxide isolation layer 1 12. In one example, the thickness 284 of the oxide isolation layer 1 14 is at least 2.5 times the thickness 280 of the oxide isolation layer 1 12. In yet another example, the thickness 284 of the oxide isolation layer 1 14 is at least 3 times the thickness 280 of the oxide isolation layer 1 12. The deep thickness 284 of the oxide isolation layer 1 14 assist preventing charged particles from traveling between the wells 152, 154, thus increasing the resistance to SEL events. In one example, the SEL resistance due to the thickness 284 of the oxide isolation layer 1 14 across the P-N junction 150 is about 10 times greater than that of a conventional FinFET designs.

It should be appreciated that the thickness of the oxide isolation layer 1 14 selected to improve the resistance to SEL events may be different depending on the technology node and critical dimensions of the FinFET comprising the P-N junction 150, and expected energy levels of the particles present in the environment for which the device was designed for use. For example, terrestrial applications encounter particles having much lower energy levels than applications that are designed to be utilized in hardened or non-terrestrial applications. The thickness 284 of the oxide isolation layer 1 14 described above has proven suitable for terrestrial applications for FinFET manufactured utilizing the 16 nm technology node. Non-terrestrial applications, such as aerospace or other applications requiring hardening against higher energy particles (relative to normally encountered terrestrial particle), at the same technology node would generally have a thicker oxide isolation layer 1 14.

The improved the resistance to SEL events achieved utilizing the techniques disclosed herein may also be characterized as reducing the product gain of b hrh · b RhR of the parasitic SCR compared to conventional designs using FinFET technology. Generally, b hrh and b rhr are the gains of the two transistors in the feedback loop of the parasitic SCR. Maintaining the b hrh · b RhR product gain to less than 1 will prevent latch-up. The beta gains for the parasitic bipolars are strong functions of the distance in the SCR current path. Since deeper STI increases this distance it reduces the b h h · b RhR product gain. The bipolar transistor beta gains also depend on the currents in the bipolar transistors of the parasitic SCR. The higher the currents the higher the b hrh · b RhR product gain. Since said currents are proportional to the deposited charge from an ion strike, the thickness 284 of the oxide isolation layer 1 14 may be selected such that the b hRh · b rhr product gain is less than a predefined design and radiation

environment threshold, such as less than 1 for common terrestrial radiation environments. Higher energy ion strikes encountered in space radiation environments will deposit significantly more charges and cause higher currents in the parasitic bipolar transistors. This in turn will raise the b hr h · b R h R product gain above 1 and the same thickness 284 may not be sufficient to prevent SEL in such space radiation environments. A higher thickness 284 may be required to prevent SEL in such high energy radiation environments.

Figures 3A-3H are sectional views of a film stack during different stages of a sequence for forming the electronic device 100 of Figure 1 having adjacent N-type and P-type FinFET transistors 102, 104. Figure 4 is a block diagram of a method 400 for forming an electronic device, such as the electronic device 100 having adjacent N-type and P-type FinFET transistors 102, 104 such as by the sequence illustrated in Figures 3A-3H. It is contemplated that the method 400 may be utilized to form other electronic devices having P-N junctions 150.

The method 400 begins at operation 402 by patterning a first mask layer 300 on a substrate, such as the substrate 106, such as illustrated in Figure 3A. The N-well and P-well are not illustrated in Figures 3A-3H to avoid cluttering the figures. The first mask layer 300 includes a plurality of openings 302 through which exposed regions 304 of the substrate 106 are exposed for etching and trench formation. The first mask layer 300 may be a photoresist mask, a hard mask or combination thereof.

At operation 404, the exposed regions 304 of the substrate 106 are etched to form trenches 108, as illustrated in Figure 3B. The trenches 108 formed in the substrate 106 are fabricated by dry (e.g., plasma) etching. Suitable etchants include halogens and halogen containing compounds such as Cl 2 , CF 4 , SF 6 , NF 3 , and CCI2F2 among others. Wet etching or other suitable technique may alternatively be utilized. Suitable wet etchants include nitric acid (HNO 3 ) and hydrofluoric acid (HF), potassium hydroxide (KOH), ethylenediamine

pyrocatechol (EDP) and tetramethylammonium hydroxide (TMAH), among others.

The material of the substrate 106 remaining between the trenches 108 form the fins 202, 252. The distance 282 between fins 202 is less than the distance 286 between a pair of adjacent fins 202, 252. The distance 282 may be at least half the distance 286, such as at least a quarter of the distance 286. The larger distance 286 between the pair of adjacent fins 202, 252 allows the trench 1 10 to be much deeper than the trenches 108, thereby facilitating a thicker oxide isolation layer 1 14 to be disposed in the trench 1 10 relative to the oxide isolation layer 1 12 disposed in the trench 108, as further illustrated in later operations of the method 400 described below.

At operation 406, the first mask layer 300 is removed, as illustrated in Figure 3C. In one example the first mask layer 300 is removed by an ashing process, such as by exposure to an oxygen containing plasma, or other suitable method.

At operation 408, a second mask layer 320 is disposed on the fins 202, 252 and trenches 108. The second mask layer 320 is patterned to form an opening 322 through which the substrate 106 may be etched, such as illustrated in Figure 3D. The second mask layer 320 may be fabricated and patterned from materials and techniques such as described with reference to the first mask layer 300.

At operation 410, the substrate 106 is etched through the opening 322 in the second mask layer 320 to form the trench 1 10. As illustrated in Figure 3E, the trench 1 10 is deeper than the trench 108. Although not to scale, the trench 1 10 is at least two times deeper than the trench 108, and even as much as 2.5 or more times deeper than the trench 108. Additionally, the trench 1 10 is at least about two times wider than the trench 108, such as at least 3 to 4 times deeper than the trench 108. The wider trench 1 10 facilitates forming a deeper trench 1 10, such that more oxide isolation layer may be utilized for improved upset resistance from high energy particle strikes. After etching, the second mask layer 320 is removed, for example, by ashing in the presence of an oxygen containing plasma or other suitable method.

At operation 412, the trenches 108, 1 10 are filled with oxide material to form the oxide isolation layers 1 12 and oxide isolation layer 1 14, as illustrated in Figure 3F. The oxide isolation layers 1 12, 1 14 may be deposited utilizing spin- on, chemical vapor deposition, atomic layer deposition or other suitable technique. A top surface of the oxide isolation layers 1 12, 1 14 may be made coplanar with the top surface of the fins 202, 252, for example, using an etch back or chemical mechanical polishing or other suitable planarization technique.

Once the trenches 108, 1 10 are filled with oxide material, a third mask layer 330 is deposited and patterned on the oxide material to form openings 332. The third mask layer 330 may be fabricated and patterned from materials and techniques such as described with reference to the first mask layer 300. At operation 414, a portion of the oxide material forming the oxide isolation layers 1 12 and oxide isolation layer 1 14 is etched through openings 332 in the third mask layer 330 to set the thickness 280 of the oxide material filling the trenches 108 and the thickness 284 of the oxide material filling the trench 1 10, as illustrated in Figure 3G.

At operation 416, the third mask layer 330 is removed. The third mask layer 330 may be removed by ashing in the presence of an oxygen containing plasma, or other suitable method. After operation 416, the metal gates 208, 258 are formed over the fins 202, 252 to form the transistors 102, 104 as illustrated in Figures 1 and 2.

Thus, the FinFET transistors 102, 104 and particularly the P-N junction 150 described herein have greater SEL resistance as compared to conventional FinFET transistors and conventional P-N junctions. As the FinFET transistors 102, 104 comprising the P-N junction 150 have a reduced probability of SEL events due to high energy particle strikes as compared to conventional FinFET transistors, the electronic device 100, such as CMOS or other electronic devices, are more robust compared to conventional electronic devices. The increased thickness of the oxide isolation layer 1 14 disposed between the N-type FinFET transistor 102 and the P-type FinFET transistor 104 allows most of the charge from impacting particles to be dissipated in the substrate before diffusing around the large area due to the relatively thicker material comprising of the oxide isolation layer 1 14 disposed in the deeper trench 1 10 (as compared to trenches 108), thus adding an extra protection again multi-bit upsets and minimizing the occurrence of uncorrectable events in electronic devices 100 in which P-N junction 150 is utilized. Advantageously, the FinFET transistors 102, 104 comprising the P-N junction 150 are up to 10 times less susceptible to SEL events than traditional FinFET transistors, desirably approaching and even equaling that of planar FinFET transistors.

In one example, FinFET transistors, P-N junctions and methods for forming the same are described herein. Such a FinFET transistor may include: a metal gate; a fin comprising: a source region; a drain region; and a channel region wrapped by the metal gate, the channel region connecting the source and drain regions; a first oxide isolation layer disposed on a first side of the source fin; and a second oxide isolation layer disposed on a second side of the source fin, the second side opposite of the first side, the second oxide isolation layer having a thickness greater than a thickness of the first oxide isolation layer.

In some such FinFET transistor, the thickness of the second oxide isolation layer may be at least twice the thickness of the first oxide isolation layer.

In some such FinFET transistor, the thickness of the second oxide isolation layer may be between 200nm and 250nm.

In another example, a P-N junction is described. Such a P-N junction may include: a first P-type FinFET transistor; a first N-type FinFET transistor disposed adjacent the first P-type FinFET transistor; and a first oxide isolation layer laterally separating the first N-type FinFET transistor from the adjacent the first P-type FinFET transistor, the first oxide isolation layer having a thickness of greater than 150nm.

In some such P-N junction, the first P-type FinFET transistor may include: a second oxide isolation layer disposed on a side of the first P-type FinFET transistor opposite the first oxide isolation layer, the second oxide isolation layer having a thickness of less than half of a thickness of the first oxide isolation layer.

In some such P-N junction, the thickness of the first oxide isolation layer may be at least three times the thickness of the second oxide isolation layer.

In some such P-N junction, the b hrh · b RhR product gain of the P-N junction may be less than 1.

Some such P-N junction may further include: a second P-type FinFET transistor disposed adjacent the first P-type FinFET transistor; and a second oxide isolation layer laterally separating the first P-type FinFET transistor from the adjacent second P-type FinFET transistor, the second oxide isolation layer having a thickness of less than half a thickness of the first oxide isolation layer.

In some such P-N junction, the thickness of the second oxide isolation layer is less than 80nm and the thickness of the first oxide isolation layer may be greater than 200nm. In some such P-N junction, a width of the first oxide isolation layer defined between the first P-type FinFET transistor and the adjacent second N-type FinFET transistor may be greater than a width of the second oxide isolation layer defined between the first P-type FinFET transistor and the adjacent second P- type FinFET transistor.

Some such P-N junction may further include: a second N-type FinFET transistor disposed adjacent the first N-type FinFET transistor; and a second oxide isolation layer laterally separating the first N-type FinFET transistor from the adjacent second N-type FinFET transistor, the second oxide isolation layer having a thickness less than the thickness of the first oxide isolation layer.

In some such P-N junction, the thickness of the second oxide isolation layer may be less than 80nm and the thickness of the first oxide isolation layer may be greater than 200nm.

In some such P-N junction, a width of the first oxide isolation layer may be greater than a width of the second oxide isolation layer.

Some such P-N junction may further include: a second FinFET transistor disposed adjacent one of the first P-type FinFET transistor and first N-type FinFET transistor, the second FinFET transistor being of the same type as a closer of the first P-type FinFET transistor and first N-type FinFET transistor; and a second oxide isolation layer laterally separating the second FinFET transistor from the adjacent one of the first P-type FinFET transistor and first N-type FinFET transistor, the second oxide isolation layer having a thickness

substantially equal to the thickness of the first oxide isolation layer.

In yet another example, a method for forming a P-N junction is described. Such a method for forming a P-N junction may include: etching a semiconductor substrate to form a plurality of high aspect ratio fins, the plurality of high aspect ratio fins including a first high aspect ratio fin and a second high aspect ratio fin separated by a first high aspect ratio trench; filling the first high aspect ratio trench with an oxide material; removing a portion of the oxide material filling the first high aspect ratio trench; and stopping the removal of the oxide material filling the first high aspect ratio trench to form a first oxide isolation layer having a thickness of at least 150nm.

In some such method, etching the semiconductor substrate to form the plurality of high aspect ratio fins may further include: forming the first high aspect ratio fin in a p-doped region of the semiconductor substrate; and forming the second high aspect ratio fin in an n-doped region of the semiconductor substrate, the first and second high aspect ratio fins separated by the first high aspect ratio trench.

Some such method may further include: forming a third high aspect ratio fin of the plurality of high aspect ratio fins in a p-doped region of the

semiconductor substrate adjacent the first high aspect ratio fin; and forming a second oxide isolation layer having a thickness less than 100nm between the first and third high aspect ratio fins.

In some such method, filling the first high aspect ratio trench with the oxide material may include: filling the first high aspect ratio trench with at least one material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), and a low-k dielectric.

In some such method, the first high aspect ratio fin may be formed from silicon, silicon germanium, germanium or lll-V material.

Some such method may further include: filling a second first high aspect ratio trench etched in the semiconductor substrate with an oxide material;

removing a portion of the oxide material filling the second high aspect ratio trench; and stopping the removal of the oxide material filling the second high aspect ratio trench to form a second oxide isolation layer having a thickness less than half of the thickness of the first oxide isolation layer.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.