# Patent

## Title
E-fuse with hybrid metallization

## Abstract

An e-fuse structure including a fuse link having a first region made of a first conductor and a second region made of a second conductor. The first conductor and the second conductor are in the same wiring level. The first conductor has a higher electrical resistance than the second conductor. The first conductor has a higher resistance to electromigration than the second conductor. The first region and the second region have a common width. The length of the first region is longer than the length of the second region.

## Background
CROSS REFERENCE
The present application is a continuation-in-part of and claims priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 13/890,642, titled HIGH PERFORMANCE REFRACTORY METAL/COPPER INTERCONNECTS TO ELIMINATE ELECTROMIGRATION filed on May 9, 2013, which is herein incorporated by reference in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to metallization structures for integrated circuits on a semiconductor chip. In particular, the invention relates to a programmable electrical fuse with hybrid metallization including a high conductivity interconnect portion abutting a refractory metal interconnect portion.
2. Description of Related Art
A fuse is an electrical structure that is normally conducting that with the application of a suitable electrical current is “blown” to form an open in the circuit. Programming refers to applying a current to intentionally blow a fuse and create an open circuit. In integrated circuitry memory devices, fuses can be used for activating redundancy in memory chips and for programming functions and codes in logic chips. Specifically, dynamic random access memory (DRAM) and static random access memory (SRAM) may employ fuses for such purposes.
Electrical fuses (e-fuses) can also be used to prevent decreased chip yield caused by random defects generated in the manufacturing process. Moreover, e-fuses provide for future customization of a standardized chip design. For example, e-fuses may provide for a variety of voltage options, packaging pin out options, or any other options desired by the manufacturer to be employed prior to the final processing. These customization possibilities make it easier to use one basic design for several different end products and help increase chip yield.
Some e-fuses take advantage of electromigration effects to blow and create the open circuit. For example, electromigration can be defined as the transport of material caused by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. In e-fuses that take advantage of electromigration effect, such transport of material caused by the gradual movement of ions can produce voids which cause the e-fuse to blow and create the open circuit or an increase in resistance above a pre-set target.
However, in a typical e-fuse, electromigration may cause unpredictable voids; thus, potentially creating the open circuit in undesirable locations. Furthermore, typical e-fuse programming may require high programming currents and long programming times. Such programming currents and times may result in unpredictable void formation which may negatively affect other circuits adjacent to the e-fuse. Therefore, it may be desirable to program an e-fuse with lower programming currents and shorter programming times. In addition, predictable and repeatable void formation may also be preferred.
BRIEF SUMMARY OF THE INVENTION
According to one embodiment of the present invention, an e-fuse structure is provided. The e-fuse structure may include a fuse link including a first region made of a first conductor and a second region made of a second conductor. The first conductor and the second conductor are in the same wiring level. The first conductor has a higher electrical resistance than the second conductor. The first conductor has a higher resistance to electromigration than the second conductor. The first region and the second region have a common width. The length of the first region is longer than the length of the second region.
According to another embodiment, a method of forming an e-fuse structure is provided. The method may include forming a first opening in a dielectric layer, forming a first liner in the first opening, filling the first opening with a first conductor, and polishing the first conductor and first liner to be co-planar with the dielectric layer. The method may further include forming a second opening in the dielectric layer adjacent to the first opening, the first opening being longer than the second opening, and the second opening partially overlapping the first opening, forming a second liner in the second opening, where the first and second opening have a common width, and where the first opening is longer than the second opening, filling the second opening with a second conductor, where the first conductor has a higher electrical resistance than the second conductor, and where the first conductor has a higher resistance to electromigration than the second conductor, and polishing the second conductor and the second liner to be co-planar with the dielectric layer, the first conductor, and the first liner.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow chart 100 of the steps of forming a hybrid interconnects structure according to one embodiment of the present invention;
FIG. 2 illustrates, in cross section, forming a first opening in a dielectric according to an embodiment of the present invention;
FIG. 3 illustrates, in cross section, lining, filling and planarizing the first liner and first conductor in the dielectric to form the first interconnect according to an embodiment of the present invention;
FIG. 4 illustrates, in cross section, forming a second opening in the dielectric according to an embodiment;
FIG. 5 is a top down illustration of first conductor and second interconnect opening according to an embodiment of the present invention;
FIG. 6 illustrates, in cross section, lining, filling and planarizing the second liner and second conductor in the dielectric to form the second interconnect according to an embodiment of the present invention;
FIG. 7 is a top down illustration of first conductor and second conductor according to an embodiment of the present invention; and
FIG. 8 illustrates, in cross section, structure having three levels of interconnects according to an embodiment of the present invention.
FIG. 9 illustrates, in cross section, the formation of an e-fuse having hybrid metallization according to an embodiment of the present invention.
FIG. 10 is a top down view of FIG. 9 according to an embodiment of the present invention.
FIG. 11 is a top down view of FIG. 9 according to an alternate embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
The basic principle of the invention includes methods of making a hybrid interconnect structures. The methods result in structures which have a first interconnect (including a first line and first via), a second interconnect (including a second line and a second via), preferably in the same level and co-planar. The first interconnect is made of a first conductor material and the second interconnect is made of a second conductor material. The first line and the second line have different widths and may have different heights and aspect ratios. The first and second lines may directly contact each other.
FIG. 1 is a flow chart 100 of the steps of forming a hybrid interconnects structure according to a preferred embodiment. Step 110 is forming a first opening in a dielectric; step 120 is lining and filling the first opening with a first liner and first conductor; step 130 is planarizing the first liner and first conductor; step 140 forming a second opening in the dielectric; step 150 is lining and filling the second opening with a second liner and second conductor; step 160 is planarizing the second liner and second conductor. Each of the steps, and the resulting structures, will be discussed in detail below.
FIG. 2 is a cross section illustration of forming a first opening in a dielectric according to an embodiment. A dielectric layer 200 is over substrate 210. Using standard lithography and reactive ion etching (herein “RIE”) techniques a first interconnect opening 220 including a first via opening 224 and first line opening 222 is formed in the dielectric 200. The substrate 210, in most cases, is a preceding interconnection level of the device. However, the substrate can also be a contact level of a device or any prior surface which requires interconnects above it. The dielectric 200 can be any dielectric layer or more likely a combination of dielectric layers. In a preferred embodiment, the dielectric layer is a low dielectric constant material above a dielectric cap layer which may also function as an etch stop. By way of example and not limitation, the dielectric cap layer may include silicon and nitrogen containing materials or silicon and carbon containing materials or combinations thereof; for example silicon nitride (Si3N4), silicon carbide (SiC), silicon carbon nitride (SiCN) or hydrogenated silicon carbide (SiCH). Low dielectric constant materials are those with dielectric constant less than 4 and preferably less than 3.6. By way of example and not limitation, low dielectric constant materials include silicon-carbon-oxygen containing materials such as hydrogenated silicon carbon oxide (SiCOH), porous dielectric materials such as porous SiCOH, or organic materials. In yet another embodiment, the dielectric layer 200 includes a silicon and oxygen containing material having a dielectric constant around 4. FIG. 2 also illustrates a preferred, but not required, embodiment having a hardmask 202 above the dielectric 200. The hardmask 202 can include a single layer or multiple layers. In a preferred embodiment, hardmask 202 can act as a polish stop and/or an etch stop. In a preferred embodiment, the hardmask includes a silicon dioxide film, preferably from a TEOS precursor. The first via opening 224 and first line opening 222 can be formed in a via first or a via last process.
FIG. 3 is a cross section illustration after depositing and planarizing the first liner 230 and first conductor 232 in the dielectric 200 to form the first interconnect 240. In a preferred embodiment, chemical mechanical polishing is the planarization method, in such a case, hardmask 202 can act as a polish stop. The first interconnect 240 includes a first line 242 portion (former first line opening 222) and a first via 244 portion (former first via opening 224). The first liner 230 lines the former first line opening 222 and first via opening 224 and is in contact with dielectric 200. The first liner 230 can comprise one or more layers. The first liner 230 should perform at least one of the following functions: promote adhesion of the dielectric 200 and first conductor 232, and should prevent diffusion from the first conductor 232 to the dielectric 200 or vice versa. Thus, the identity of the first liner 230 can vary with the identity of the first conductor 232.
In a preferred embodiment, the first conductor 232 may include a refractory metal. Refractory metals include tungsten, niobium, molybdenum, tantalum or rhenium. The following elements are also sometimes considered refractory metals: titanium, vanadium, chromium, hafnium, ruthenium, zirconium, osmium, rhodium and iridium. Alternatively, first conductor 232 could be manganese nitride or cobalt. First conductor 232 may be an alloy of one of the previously mentioned materials. In a preferred embodiment, the first conductor 232 includes tungsten and the first liner 230 includes titanium and/or titanium nitride layer(s).
FIG. 4 is a cross section illustration of forming a second opening in the dielectric prior to second metallization according to an embodiment. The second interconnect opening 250 includes a second via opening 254 and second line opening 252 formed in the dielectric 200. The second via opening 254 and second line opening 252 can be formed in a via first or a via last process. The embodiment shown in FIG. 4 was made in a via last process. In a via last process line hardmask 302 is formed over the entire substrate and opened in areas where the second line opening 252 in the dielectric 200 will be. The line hardmask 302 can include one or more dielectric or conducting films or combinations thereof. By way of example and not limitation, line hardmask may include silicon dioxide, silicon nitride, tantalum, tantalum nitride, titanium, titanium carbide, or titanium nitride. As seen in FIG. 4, sometimes the opening in the line hardmask 302 overlaps with the first line 242 portion, such that a region of first line portion 242 adjacent second line opening 252 is not covered by the line hardmask 302. In such a situation, while not illustrated in FIG. 4, a top corner of the first line portion 242 adjacent second interconnection opening 250 (and in particular, adjacent to second line opening 252) can be faceted as result of the second line opening etch. Thus, a portion of first liner 230 may be missing or reduced in this region. In addition, a portion of first conductor 232 may be missing or reduced in the faceted region.
FIG. 5 is a top down view of FIG. 4. The dotted line on the left represents first line portion 242 under the line hardmask 302. The dotted line on the right represents second via opening 254 of the second opening 250. Note that the embodiment illustrated in FIG. 5 has a second line opening 252 wider than first line portion 242.
FIG. 6 is a cross section illustration after lining, filling and planarizing the second liner 260 and second conductor 262 in the second opening of dielectric 200 to form the second interconnect 270. The second interconnect 270 includes a second line 272 portion (former second line opening 252) and a second via 274 portion (former second via opening 254). The second liner 260 lines the former second line opening 252 and second via opening 254 and is in contact with dielectric 200, substrate 210, and first liner 230. The second liner 260 can comprise one or more layers. The second liner 260 should perform at least one of the following functions: promote adhesion of the dielectric 200 and second conductor 262, and should prevent diffusion from the second conductor 262 to the dielectric 200 or vice versa. Thus, the identity of the second liner 260 can vary with the identity of the second conductor 262. In a preferred embodiment, the second liner includes a tantalum nitride layer and a tantalum layer. Other liner materials in lieu or in addition to preferred materials include but are not limited to manganese containing layers, aluminum containing layers, ruthenium containing layers or cobalt containing layers. The second conductor 262 is a low resistivity metal or metal alloy in comparison to the first conductor 232. In a preferred embodiment, the second conductor includes copper or copper doped with another metal, for example, but not limitation, manganese, aluminum, cobalt or ruthenium.
Referring to FIG. 6, during planarization of the second interconnect 270, the first interconnect 240 is at least partially covered by line hardmask 302 in a preferred embodiment, or by the second liner 260 in embodiments not using a line hardmask 302. Thus, galvanic exposure of the first interconnect 240 is minimized. Optionally, to further minimize galvanic corrosion of the first interconnect 240, the second liner 260 may be removed by a dry etch, for example RIE, rather than a polish in a slurry. Thus, in some embodiments, second liner 260 may be removed in a non-aqueous environment to avoid the possibility of galvanic corrosion. In a preferred embodiment, the planarization process removes most or all of hardmask 202, thus FIG. 6 illustrates a preferred embodiment in which the interconnects are co-planar with dielectric layer 200, rather than co-planar with any remaining hardmask 202.
Still referring to FIG. 6, as mentioned earlier with respect to FIG. 4, a top corner of first line portion 242 adjacent the second line 272 may be faceted. While the faceting is not shown in FIG. 6, it will be appreciated, that the faceting may result in second liner 260 being in contact with not only first liner 230, but also in contact with a first conductor 232.
Again referring to FIG. 6, a preferred embodiment is shown in which the height (H1) of the first line 242 is greater than the height (H2) of the second line 272. It is also contemplated that the first and second lines, 242 and 272 respectively, have the same height. In either of these embodiments (equal heights or varying heights), the lines are substantially co-planar. Note, that in another embodiment contemplated wherein the first line and second line are on different levels (Mx and Mx+1, respectively, for example), the first and second lines will not be co-planar with each other, but will be co-planar with other metal lines in their respective levels.
Being able to independently control the heights of the first 242 and second 272 lines is a source of a distinct advantage of the present invention: the ability to tune resistance and any associated voltage drop. With respect to resistance, the first line 242 is narrower than the second line 272, and the first line is preferably made of tungsten, a higher resistivity material than copper (the conductor of the second line 272). Accordingly, if the lines had the same height, the first line 242 would have higher resistance than the second line 272, and, resistive circuit delay may be introduced. However, because the height (H1) of the first line 242 is independent of the height (H2) of the second line 272, the first height (H1) can be larger and thus the resistance of the first line 242 reduced. Thus, any signal delay caused by using a high resistivity material in a narrow line is mitigated. Voltage drop is also affected by the choice of materials, line widths and line heights in an analogous manner.
Referring to FIG. 7, a preferred embodiment is shown in which the width (W1) of the first line 242 is less than the width (W2) of the second line 272. Thus, the first line 242 and second line 272 can have independent aspect ratios even though they exist in the same dielectric 200 (i.e. are in the same metal level). Furthermore, when the lines have different and independent aspect ratios, the first and second vias (244 and 274, respectively) will also have different aspect ratios which are independent of each other despite being in the same metal level.
Generally speaking, narrow lines which are candidates for the refractory metal first conductor material 232 are lines having a width of equal to or less than about 40 nm, 35 nm, 30 nm, 25 nm, 20 nm, 15 nm, 10 nm, and 5 nm and widths there between. In one embodiment, line widths which are candidates for the refractory metal first conductor 232 are lines that are less than three times the minimum lithographic width for that node, whereas low resistivity second conductors 262 are lines that are greater than or equal to three times the minimum line width for that node. In another embodiment, line widths which are candidates for the refractory metal first conductor 232 are lines that are less than two times the minimum lithographic width for that node, whereas low resistivity second conductors 262 are lines that are greater than or equal to two times the minimum line width for that node. In a preferred embodiment, line widths which are candidates for the refractory metal first conductor 232 are lines that are equal to the minimum lithographic width for that technology node, whereas low resistivity second conductors 262 are lines that are greater than or equal to three times the minimum line width for that node. Table 1 below is an example of expected minimum line widths at each node.







TABLE 1







Line widths by node












Technology
Minimum
3x




node (nm)
width line (nm)
width line (nm)
Pitch (nm)
















22
40
120
80



14
32
96
64



10
22
66
44



7
16
48
32



5
11
33
22










Referring again to FIG. 7, the second line 272 is aligned such that a portion of second line 272 wraps around an end of first line 242. Thus, in this embodiment, second liner 260 and first liner 230 contact each other on three sides of first line 242. The overlap is possible because first conductor/liner 232/230 is able to withstand the reactive ion etching used to create second opening 250. It is also possible that the overlay of first and second lines, 242 and 272 respectively, results in the two lines abutting each other rather than partial wrapping shown in FIG. 7. In either case, a line can be drawn (s1 to s2) that traces the materials where the two lines meet. Starting at point s1 in FIG. 7 and moving to point s2 the first material encountered is first conductor 232, followed by first liner 230, second liner 260 and second conductor 262. Thus, in a preferred embodiment, the materials from s1 to s2 are a refractory metal such as tungsten as first conductor 232, titanium nitride followed by titanium layers as first liner 230, tantalum nitride followed by tantalum as second liner 260 and copper or a copper alloy as a low resistivity second conductor 262. It should be noted that the second conductor 262 may be capped with a metallic layer, for example if the second conductor is copper or a copper alloy it may be capped with CoWP, CuMn, CuAl or other metallic caps which preferably inhibit electromigration flow.
Referring back to FIG. 6, the first line 242 and second line 272 occupy the same level in a back end of line structure (i.e. they are both Mx lines where x=1, 2, 3 . . . ), and this is the preferred embodiment: narrow lines of one material (refractory) and wide lines of the same level with another (lower resistivity) material. However, it is also contemplated that narrow lines and wide lines at different levels have different conductor materials. For example, lower level lines are typically narrower than higher level lines, accordingly, a lower level may have substantially all refractory metal lines, while an upper level line has a mix of refractory and low resistivity metal lines (which may or may not contact each other within the same line level), while still an uppermost level line may be all low resistivity line.
Referring to FIG. 8, the via and line depletion advantage of the present invention will be discussed. FIG. 8 illustrates the hybrid metallization of FIG. 6 wherein the substrate 210 includes a lower level dielectric 214 and conductors 212 and 212′ (Mx−1 line level). One of the lower level conductors 212 is in contact with the first via 244. FIG. 8 also includes an upper level interconnect 280 (Mx+1 level) in contact with the first line 242. The upper level interconnect 280 is embedded in a dielectric layer 200′ similar to that described in conjunction with dielectric layer 200. In a first scenario, a current (i1) flows from the lower level conductor 212 through the interconnect 240 and into upper level interconnect 280; accordingly, the electrons flow in the opposite direction, namely from upper level interconnect 280 through interconnect 240 to lower level conductor 212. If the first interconnect 240 was small and made of copper, line depletion would expect to take place, meaning material would move out of the line 242 of the first interconnect 240 in response to the high current density and a void would form near the line 242 under the via of the upper level interconnect 280 causing an open or increasing the resistance to create a high resistance line. Similarly, if the current came from the opposite direction (i2), meaning from the upper level interconnect 280 above (accordingly, electrons moving from lower interconnect 212 through first interconnect 240 and into upper level interconnect 280), via depletion would be expected. In via depletion mode, material would move out of the via 244 of the first interconnect 240 in response to the high current density and a void would form near the via 244 causing an open or increasing the resistance to create a high resistance via. However, because the present invention uses a refractory metal in both the line 242 and the via 244 of the interconnect 240, the interconnect 240 is protected from both line depletion and via depletion.
In an alternative embodiment, the advantages of the hybrid metallization scheme described above may be exploited to produce an electronic fuse (e-fuse) having improved characteristics, for example, lower programming currents and shorter programming times.
The basic principle of the alternative embodiment includes methods of making a hybrid e-fuse structure. The methods result in structures which include a fuse region having a first region and a second region. The fuse regions being made up of a first conductor and a second conductor, preferably in the same level and co-planar with one another. The first and second conductors having a similar width and a similar height, but different lengths. Preferably, the first region is longer than the second region. The first and second conductor are in direct contact and may each be in electrical contact with one or more nearby interconnect structures.
The e-fuse is a structure that may be programmed in accordance with the application of a suitable electrical current. For example, an electrical current may be provided through the e-fuse to eventually cause the resistance of the e-fuse to exceed a predetermined threshold. A suitable electrical current depends on the e-fuse design and may range from about 10 mA to about 25 mA, and ranges there between. Alternatively, programming may occur at a threshold current density. For example, a typical current density of 1000 MA/cm2 may be required to program the e-fuse. Additionally, a circuit is considered to be programmed, and open, when the e-fuse resistance increases more than an order of magnitude over the initial pre-programmed resistance of the e-fuse.
During programming of the e-fuse, one or more voids may form in unexpected locations due to non-optimized processing. Location of the voids may be uncontrollable and may affect the yield and reliability of the e-fuse. The voids may be due in part to the electromigration of conductive interconnect material within the e-fuse.
Ideally only the targeted e-fuse will be programmed while maintaining the integrity of all surrounding circuits. One embodiment by which to fabricate an e-fuse having two different conductive materials, or hybrid metallization, is described in detail below by referring to the accompanying drawings FIGS. 9-11. In the present embodiment, an e-fuse fabricated in a single metallization level may include a fuse link having at least two different conductive materials
Referring now to FIG. 9, a structure 400 is shown. The structure 400 may include a substrate 402, an Mx level 404, and an Mx+1 level 406. The substrate 402 may be substantially similar to the substrate 210 described above. The Mx level 404 may include a first Mx metal 408, a second Mx metal 410, an Mx dielectric layer 412, and an Mx cap 414. The Mx level 404 may represent any interconnect level in the structure 400. In one embodiment, the Mx level 404 may represent a metallization level directly above a contact level or an active device level. The Mx+1 level 406 may include a first Mx+1 metal 416, a first Mx+1 via 418, a second Mx+1 metal 420, a second Mx+1 via 422, a fuse link 424, an Mx+1 dielectric layer 426, and an Mx+1 cap 428. It should be noted that while only two interconnect levels are shown, in some embodiments the structure 400 may have multiple interconnect levels either above, below, or above and below the Mx level 404 and the Mx+1 level 406.
The Mx dielectric layer 412 may be substantially similar to the dielectric layer 200 described above. In one embodiment, the Mx dielectric layer 412 may include any suitable dielectric material, for example, silicon oxide (SiO2), silicon nitride (Si3N4), hydrogenated silicon carbon oxide (SiCOH), silicon based low k dielectrics, or porous dielectrics. Known suitable deposition techniques, such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or physical vapor deposition may be used to form the Mx dielectric layer 412. The Mx dielectric layer 412 may have a typical thickness ranging from about 100 nm to about 450 nm and ranges there between, although a thickness less than 100 nm and greater than 450 nm may be acceptable.
The first and second Mx metals 408, 410 may be formed using any known technique, and may include any suitable conductive interconnect material, for example, copper. Both the first and second Mx metals 408, 410 may include a typical line or wire found in a typical semiconductor circuit. The first and second Mx metals 408, 410 may be substantially similar structures and may be fabricated using, for example, a typical single damascene technique in which a conductive interconnect material may be deposited in a trench formed in the Mx dielectric layer 412.
In one embodiment, the first and second Mx metals 408, 410 may include various barrier liners (not shown). One barrier liner may include, for example, tantalum nitride (TaN), followed by an additional layer including tantalum (Ta). One barrier liner may include, for example, titanium (Ti), followed by an additional layer including titanium nitride (TiN). Other barrier liners may include cobalt (Co) or ruthenium (Ru) either alone or in combination with any other suitable liner. The conductive interconnect material may include, for example, copper (Cu), aluminum (Al), or tungsten (W). The conductive interconnect material may be formed using a filling technique such as electroplating, electroless plating, chemical vapor deposition, physical vapor deposition or a combination of methods. The conductive interconnect material may alternatively include a dopant, such as, for example, manganese (Mn), magnesium (Mg), copper (Cu), aluminum (Al) or other known dopants. A seed layer (not shown) may optionally be deposited using any suitable deposition technique, for example chemical vapor deposition or physical vapor deposition, prior to filling the trench. The seed layer may also include similar dopants as the conductive interconnect material.
With continued reference to FIG. 9, the Mx cap 414 may be deposited over the structure 400. The Mx cap 414 may electrically insulate the Mx level 404 from additional interconnect levels that may be subsequently formed above the Mx level 404, for example the Mx+1 level 406. The Mx cap 414 may be used to improve interconnect reliability and prevent copper from diffusing into an Mx+1 dielectric that may be subsequently formed above. The Mx cap 414 may be deposited using typical deposition techniques, for example, chemical vapor deposition. The Mx cap 414 may include any suitable dielectric material, for example, silicon nitride (Si3N4), silicon carbide (SiC), silicon carbon nitride (SiCN), hydrogenated silicon carbide (SiCH), or other known capping materials. The Mx cap 414 may have a thickness ranging from about 15 nm to about 55 nm and ranges there between, although a thickness less than 15 nm and greater than 55 nm may be acceptable.
Next, the Mx+1 level 406 may be formed above the Mx level 404. First, the Mx+1 dielectric 426 may be deposited. The Mx+1 dielectric 426 may be substantially similar in all respects to the Mx dielectric layer 412 described above.
The fuse link 424 may be formed in accordance with the techniques described above with reference to FIGS. 1-7. In the present embodiment, the fuse link 424 may have a first region 430 and a second region 432. It should be noted that the first region 430 may correspond with the first interconnect 240 (FIG. 6), and the second region 432 may correspond with the second interconnect 270 (FIG. 6). More specifically, the first region 430 may be substantially similar to the first interconnect 240 (FIG. 6), and the second region 432 may be substantially similar to the second interconnect 270 (FIG. 6).
A first trench may be formed in the Mx+1 dielectric 426. The first trench may then be filled with a refractory metal to form the first region 430 of the fuse link 424. Any refractory metal, such as, for example, tungsten, niobium, molybdenum, tantalum or rhenium may be used. In one embodiment, tungsten may be deposited in the first trench using any known disposition technique.
In one embodiment, the first region 430 of the fuse link 424 may include various barrier liners (not shown) similar to the barrier liners described above with reference to the first and second Mx metals 408, 410. Furthermore, a seed layer (not shown) may optionally be deposited, as described above, prior to filling the first trench with the refractory metal. A chemical mechanical polishing technique may be applied to ensure complete removal of excess conductive interconnect material prior to forming the second region 432 of the fuse link 424 or any surrounding interconnect structures.
Next, a second trench may be formed in the Mx+1 dielectric 426 adjacent to the first region 430 of the fuse link 424. The second trench may at least partially overlap the first region 430 of the fuse link 424. One or more dual damascene openings may be formed in the Mx+1 dielectric 426 adjacent to the fuse link 424. In one embodiment, one dual damascene opening may be formed adjacent to the first region 430 of the fuse link 424, and another dual damascene opening may be formed adjacent to the second trench opening, or the second region 432 of the fuse link 424.
Either of the dual damascene openings may include a trench opening and a via opening. The dual damascene openings may be formed using any suitable masking and etching technique known in the art, including either a trench first technique or a via first technique. In one embodiment, a dry etching technique using a fluorine based etchant, such as, for example CxFy, may be used. The trench openings may be any size and shape suitable for the formation of any BEOL interconnect structure so desired.
More specifically, the via openings may extend vertically from a bottom of the trench openings to a top of either the first Mx metal 408 or the second Mx metal 410. In one embodiment, one dual damascene opening may be formed above the first Mx metal 408 and another dual damascene opening may be formed above the second Mx metal 410, as illustrated in the figures. The first and second Mx metal 406, 408 may preferably be exposed by the formation of the dual damascene openings, more specifically, by the formation of the via openings.
Both the second trench opening and the dual damascene openings may then be filled with a conductive interconnect material, or conductor, to form the second region 432 of the fuse link 424 and to form the first Mx+1 metal 416, the first Mx+1 via 418, the second Mx+1 metal 420, and the second Mx+1 via 422. The conductive interconnect material may be substantially similar to that described above with reference to the first and second Mx metals 408, 410. In one embodiment, the conductive interconnect material of the second region 432 of the fuse link 424, the first Mx+1 metal 416, the first Mx+1 via 418, the second Mx+1 metal 420, and the second Mx+1 via 422 may be copper.
In one embodiment, the second region 432 of the fuse link 424, the first Mx+1 metal 416, the first Mx+1 via 418, the second Mx+1 metal 420, and the second Mx+1 via 422 may include various barrier liners (not shown) similar to the barrier liners described above with reference to the first and second Mx metals 408, 410. Furthermore, a seed layer (not shown) may optionally be deposited, as described above, prior to filling the trench openings and via openings with the conductive interconnect material. After filling the first Mx+1 metal 416, the first Mx+1 via 418, the second Mx+1 metal 420, and the second Mx+1 via 422 with the conductive interconnect material the Mx+1 cap 428 may be deposited on top of the structure 400. A chemical mechanical polishing technique may be applied to ensure complete removal of excess conductive interconnect material prior to depositing the Mx+1 cap 428. The Mx+1 cap 428 may be substantially similar to the Mx cap 414 described above.
Vias, generally, may be used to form electrical connections between the metallization of two interconnect levels. The via 418 may extend vertically from the first Mx metal 408 to the first Mx+1 metal 416, and the via 422 may extend vertically from the second Mx metal 410 to the second Mx+1 metal 420.
Generally, the first Mx+1 via 418 and the second Mx+1 via 422 may have a width or diameter of a typical via opening formed in the BEOL. In one embodiment, the first Mx+1 via 418 and the second Mx+1 via 422 may have an aspect ratio of about 4:1 or more, and a diameter or width ranging from about 10 nm to about 100 nm and ranges there between, although a via diameter less than 10 nm and greater than 100 nm may be acceptable.
Referring now to FIG. 10, and with continued reference to FIG. 9, alternative embodiments will now be described. FIG. 10 is a top view of FIG. 9. Both the first region 430 and the second region 432 of the fuse link 424 may preferably have the same width, but different lengths (I1,I2). The total length of the fuse link 424 may be equal to the length (I1) of the first region 430 plus the length (I2) of the second region 432. In one embodiment, the total length of the fuse link 424 may range from about 0.5 μm to about 5.0 μm. The length (I1) of the first region 430 of the fuse link 424 may range from about 70% to about 80% of the total length (I1+I2) of the fuse link 424.
The first region 430 and the second region 432, of the fuse link 424, may have a width (w1) equal to that of a typical interconnect structure. In one embodiment, the first region 430 and the second region 432, of the fuse link 424, may have a width (w1) ranging from about 5 nm to about 40 nm. Furthermore, the width (w1) of the first and second regions 430, 432 of the fuse link 424 may be less than a width (w2) of the first Mx+1 metal 416 or a width (w3) of the second Mx+1 metal 420. Additionally, the first region 430 and the second region 432, of the fuse link 424, may have a height (h) or vertical thickness equal to that of a typical interconnect structure. In one embodiment, the first region 430 and the second region 432, of the fuse link 424, may have a height (h) ranging from about 25 nm to about 100 nm.
With continued reference to FIGS. 9 and 10, a final e-fuse structure is shown according to one embodiment. Therefore, the first Mx+1 metal 416, the second Mx+1 metal 420, and the fuse link 424 may together form the final e-fuse structure. The first and second Mx+1 metals 416, 420 may include any active interconnect structure in the BEOL. In the present embodiment, electrical connection to the e-fuse is provided by the first Mx+1 via 418 and the second Mx+1 via 422. The e-fuse structure as depicted in the figures may effectively lower the require programming current and shorten the programming time, thereby increasing programming reliability and efficiency.
In the present embodiment, the fuse link 424 may be fabricated with two different conductive materials, one having better electromigration characteristics than the other. Therefore, the e-fuse, and more specifically the fuse link 424, may be fabricated specifically to exploit the different electromigration behavior between the first region 430 and the second region 432.
In one embodiment, the first region 430 may be made from a refractory metal, such as, for example, tungsten, and the first Mx+1 metal 416, the first Mx+1 via 418, the second Mx+1 metal 420, the second Mx+1 via 422, and the second region 432 may be made from copper. Generally, refractory metals have a high electromigration tolerance, and thus a high resistance to the effects of electromigration. In any case, refractory metals, in general, may have more resistance to the effects of electromigration than copper.
Referring now to FIG. 11, a final e-fuse structure is shown according to another embodiment. FIG. 11 is a top view of the structure 400 of FIG. 9 according to an alternative embodiment. The present embodiment, unlike the embodiment described above and illustrated in FIGS. 9 and 10, illustrates an asymmetric e-fuse design. The asymmetric e-fuse structure of the present embodiment may include the first Mx+1 metal 416, the second Mx+1 metal 420, and the fuse link 424. The asymmetric e-fuse structure of the present embodiment contemplates using two different metal shapes on either end of the fuse link 424, as illustrated in the figure. For example, the first Mx+1 metal 416 and the second Mx+1 metal 420 have different shapes. In the present embodiment, the first Mx+1 metal 416 may have a shape of a typical interconnect structure, but the second Mx+1 metal 420 may have a different shape designed to have smaller grains and therefore more grain boundaries. For example a finger shape 434, as illustrated, may be used to achieve smaller grains, and more grain boundaries due in part to the narrow finger configuration (e.g. 436). More grain boundaries in the narrow finger regions 436 may enhance the effects of electromigration. As such, the finger regions 436 of the second Mx+1 metal 420 may induce or encourage the electromigration of copper from the second region 432 of the fuse link 424 into the second Mx+1 metal 420. It should be noted that any suitable shape that may increase the number of grain boundaries is contemplated, and may be used to enhance the effects of electromigration.
The embodiments disclosed herein have the capability to improve the failure mechanism of the e-fuse structure by lowering the programming current and reducing the programming times. In turn, lowering the programming current and reducing the programming time effectively improves the reliability and efficiency of the e-fuse structure.
While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims including single damascene lines. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

## Claims

1. An e-fuse structure comprising:
a fuse link having a first region made of a first conductor and a first liner, and a second region made of a second conductor and a second liner, the first conductor and the second conductor are separated by both the first liner and the second liner such that a distance between the first conductor and the second conductor is approximately equal to a wall thickness of the first liner plus a wall thickness of the second liner,
wherein the first conductor and the second conductor are in the same wiring level,
wherein the first conductor has a higher electrical resistance than the second conductor,
wherein the first conductor has a higher resistance to electromigration than the second conductor,
wherein the second conductor is a metal alloy,
wherein the first region and the second region have a common width, and
wherein the length of the first region is longer than the length of the second region.

2. The structure of claim 1, wherein the total length of the fuse link is equal to the length of the first region plus the length of the second region, and wherein the total length of the fuse link ranges from about 0.5 um to about 5.0 um, and the width of the first and second regions ranges from about 5 nm to about 40 nm.

3. The structure of claim 1, wherein the length of the first region ranges from about 70% to about 80% of the total length of the fuse link.

4. The structure of claim 1, wherein the first conductor comprises a refractory metal.

5. The structure of claim 1, wherein the first conductor comprises tungsten.

6. The structure of claim 1, wherein the first liner includes titanium, titanium nitride, or combinations thereof, and wherein the second liner includes tantalum, tantalum nitride, ruthenium, cobalt, or combinations thereof.

7. The structure of claim 1, wherein the second conductor comprises copper.

8. The structure of claim 1, further comprising:
a void located in the second conductor adjacent to an interface between the first and second conductors, such that the electrical resistance between the first and second conductors is more than an order of magnitude over the initial pre-programmed resistance of the e-fuse before void formation.

9. The structure of claim 1, further comprising:
a third conductor in electrical contact with the first conductor; and
a fourth conductor in electrical contact with the second conductor,
wherein the first and second conductors have a width less than either the third conductor or the fourth conductor.

10. The structure of claim 9, wherein the third and fourth conductors comprise copper, and wherein the fourth conductor comprises a higher number of grain boundaries than the third conductor.

11. A method of forming an e-fuse structure comprising:
forming a first interconnect opening in a dielectric layer, the first interconnect opening comprising a first via opening and a first trench opening;
forming a first liner in the first interconnect opening;
filling the first interconnect opening with a first conductor;
polishing the first conductor and first liner to be co-planar with the dielectric layer;
forming a second interconnect opening in the dielectric layer while protecting at least a portion of the first conductor and at least a portion of the first liner with a line hardmask such that at least a vertical portion of the first liner is exposed by forming the second interconnect opening, the second interconnect opening comprising a second via opening and a second trench opening, the first trench opening being longer than the second trench opening;
forming a second liner in the second interconnect opening, a vertical portion of the second liner is in direct contact with the vertical portion of the first liner, wherein the first and second trench openings have a common width;
filling the second interconnect opening with a second conductor, wherein the first conductor has a higher electrical resistance than the second conductor, and wherein the first conductor has a higher resistance to electromigration than the second conductor; and
polishing the second conductor and the second liner to be co-planar with the dielectric layer, the first conductor, and the first liner.

12. The method of claim 11, wherein the total length of the first trench opening plus the second trench opening ranges from about 0.5 um to about 5.0 um, and the width of the first and second trench openings ranges from about 5 nm to about 40 nm.

13. The method of claim 11, wherein the length of the first trench opening ranges from about 70% to about 80% of the total length of the first trench opening plus the second trench opening.

14. The method of claim 11, wherein filling the first interconnect opening with the first conductor comprises:
depositing a refractory metal.

15. The method of claim 11, wherein filling the first interconnect opening with the first conductor comprises:
depositing tungsten.

16. The method of claim 11, wherein forming the first liner in the first interconnect opening comprises:
depositing titanium, titanium nitride, or combinations thereof.

17. The method of claim 11, wherein forming the second liner in the second interconnect opening comprises:
depositing tantalum, tantalum nitride, ruthenium, cobalt, or combinations thereof.

18. The method of claim 11, wherein filling the second interconnect opening with the second conductor comprises:
depositing copper.

19. The method of claim 11, further comprising:
applying a programming current to the e-fuse causing a void to form in the second conductor, such that the electrical resistance between the first and second conductors is more than an order of magnitude over the initial pre-programmed resistance of the e-fuse before void formation.