Self-aligned top via formation at the edge of interconnects

Abstract

Techniques for forming self-aligned top vias at interconnect end portions are provided. In one embodiment, a method for forming a self-aligned via at an interconnect end portion includes: patterning (even / odd) metal interconnects using a (first / second) hard mask; cutting the hard mask and the even or odd selected metal interconnects using a cut mask with windows that expose the hard mask overlying the cut regions of the selected metal interconnects; enlarging the windows to expose the hard mask on either side of the cut regions; selectively etching the hard mask using the enlarged windows to form T-shaped cavities within the cut regions; filling the T-shaped cavities with a gap-fill dielectric; removing the hard mask; and recessing the metal interconnects such that the gap-fill dielectric overhangs portions of the selected metal interconnects forming a self-aligned via at the end of the metal interconnects. A structure is also provided.

Description

[Technical Field]

[0001] The present invention relates to top via formation, and in particular to techniques for self-aligned top via formation at the edge of a wiring line. [Background technology]

[0002] In semiconductor device metallization processes, vias are often formed above the metal lines. However, alignment problems can arise with such top-via methods, especially when the vias are formed above the edges of the metal lines.

[0003] One of the challenges in the top-via approach is to form the via at the line edge without any variation in the via critical dimension (CD). Controlling the via CD, however, is difficult if alignment with the metal line is performed using lithography. That is, limited overlay shift causes the via to move away from or be cut off by the line edge, resulting in a reduction in the via CD. Overlay shift can occur due to misalignment between patterns during the lithography process.

[0004] Therefore, improved techniques for top-via formation would be desirable. Summary of the Invention

[0005] The present invention provides techniques for forming self-aligned top vias at the edge of a wiring line. In one aspect of the invention, a method for forming a self-aligned top via at the edge of a wiring line is provided. The method includes the steps of: patterning metal lines, including alternating even and odd metal lines, using a hard mask, including a first hard mask for patterning the even metal lines and a second hard mask for patterning the odd metal lines; cutting the hard mask and the selected metal lines using a cut mask having windows that expose the hard mask overlying cut areas of the selected metal lines; enlarging the windows in the cut mask to expose the hard mask on either side of the cut areas of the selected metal lines; selectively etching the hard mask using the enlarged windows in the cut mask to form T-shaped cavities in the cut areas of the selected metal lines; filling the T-shaped cavities with a gap-fill dielectric; removing the hard mask; and recessing the metal lines selectively relative to the gap-fill dielectric, whereby the recessing causes the gap-fill dielectric to overhang portions of the selected metal lines forming self-aligned vias at the ends of the metal lines.

[0006] In another aspect of the present invention, another method for forming a self-aligned via at a wiring end is provided, the method including the steps of: patterning metal wiring including alternating even and odd metal wiring using hard masks, including a first hard mask for patterning the even metal wiring and a second hard mask for patterning the odd metal wiring; cutting the first hard mask and selected ones of the even metal wiring using a first cut mask having windows exposing the first hard mask overlying the cut region of the selected even metal wiring; enlarging the windows in the first cut mask to expose the first hard mask on either side of the cut region of the selected even metal wiring; selectively etching the first hard mask using the enlarged windows in the first cut mask to form a first T-shaped cavity within the cut region of the selected even metal wiring; and cutting the second hard mask having windows exposing the second hard mask overlying the cut region of the selected odd metal wiring. cutting a selected one of the second hard mask and the odd metal lines using a mask; enlarging a window in the second cut mask to expose the second hard mask on either side of the cut area of ​​the selected odd metal line; selectively etching the second hard mask using the enlarged window in the second cut mask to form a second T-shaped cavity in the cut area of ​​the selected odd metal line; filling the first T-shaped cavity and the second T-shaped cavity with a gap-fill dielectric; removing the first hard mask and the second hard mask; and recessing the metal lines selectively relative to the gap-fill dielectric, whereby the recessing causes the gap-fill dielectric to overhang portions of the selected even metal line and the selected odd metal line forming self-aligned vias at the ends of the metal lines.

[0007] In yet another aspect of the present invention, there is provided yet another method for forming a self-aligned via at a line end, the method comprising: patterning metal lines including alternating even and odd metal lines using hard masks, including a first hard mask for patterning the even metal lines and a second hard mask for patterning the odd metal lines; cutting the first hard mask and selected ones of the even metal lines using a first cut mask having windows exposing the first hard mask overlying the cut areas of the selected even metal lines; enlarging the windows in the first cut mask to expose the first hard mask on either side of the cut areas of the selected even metal lines; selectively etching the first hard mask using the enlarged windows in the first cut mask to form a first T-shaped cavity within the cut areas of the selected even metal lines; and cutting the second hard mask and selected ones of the odd metal lines using a second cut mask having windows exposing the second hard mask overlying the cut areas of the selected odd metal lines. enlarging the window of the second cut mask to expose the second hard mask on either side of the cut area of ​​the selected odd metal lines; selectively etching the second hard mask using the enlarged window of the second cut mask to form a second T-shaped cavity in the cut area of ​​the selected odd metal lines; cutting the first hard mask using a mask having a window exposing the first hard mask covering a non-wiring end of one of the even metal lines to form a gap in the first hard mask; cutting the second hard mask using another mask having a window exposing the second hard mask covering a non-wiring end of one of the odd metal lines to form a gap in the second hard mask; filling the first T-shaped cavity, the second T-shaped cavity, the gap in the first hard mask, and the gap in the second hard mask with a gap-fill dielectric; and removing the first hard mask and the second hard mask;recessing the metal lines selectively relative to the gapfill dielectric, whereby the recessing gapfill dielectric overhangs portions of the even metal lines forming self-aligned vias at the ends of the even and odd metal lines, and where the step of recessing the metal lines selectively relative to the gapfill dielectric in the gaps of the first hard mask and the gapfill dielectric in the gaps of the second hard mask forms non-end vias;

[0008] In yet another aspect of the invention, a structure is provided that includes: metal lines; a cut in a selected one of the metal lines; vias aligned to the line ends of the selected metal lines on either side of the cut; and a gap-fill dielectric between the line ends.

[0009] A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a top-down view illustrating a first hard mask for patterning the even metal lines and a second hard mask for patterning the odd metal lines, as well as a dielectric material deposited over / surrounding the (even / odd) metal lines and the first and second hard masks, according to an embodiment of the invention. [Figure 2] 2A-2C are cross-sectional views (AA') illustrating a first hard mask covering one of the even metal lines according to an embodiment of the present invention. [Figure 3] FIG. 10 is a cross-sectional view (B-B') illustrating a second hard mask covering one of the odd metal lines, according to an embodiment of the present invention. [Figure 4]FIG. 1C is a top-down view illustrating a (first) cut mask formed over the first and second hard masks having a window exposing the first hard mask over a cut region of a selected one of the even metal lines to be cut, according to an embodiment of the present invention. [Figure 5] FIG. 10 is a cross-sectional view (A-A') illustrating a first cut mask being used to pattern / cut the first hard mask covering the select even metal lines, according to an embodiment of the present invention. [Figure 6] 10A-B' are cross-sectional views illustrating that even when a window in a first cut mask encroaches on an adjacent odd metal line, cutting of the odd metal line does not occur due to the use of different first and second hard masks, according to an embodiment of the present invention. [Figure 7] 1A-1B are cross-sectional views (AA') illustrating patterns transferred from a first hard mask to selected even metal lines and cutting the even metal lines, according to an embodiment of the present invention. [Figure 8] FIG. 10 is a top-down view illustrating lateral etching of the first cut mask being performed to enlarge the window, according to an embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view (A-A') illustrating the first cut mask after the window has been enlarged / widened by lateral etching and the first cut mask being used to selectively etch portions of the first hard mask covering select (even) metal lines on either side of the cut area exposed by the enlarged / widened window to form a (first) "T-shaped" cavity, according to an embodiment of the present invention. [Figure 10] FIG. 10B is a cross-sectional view (B-B') illustrating that the use of different first / second hard mask materials and selective etching prevents any etching of the second hard mask, even when the now enlarged window in the first cut mask encroaches on the second hard mask covering the adjacent odd metal lines, in accordance with an embodiment of the present invention. [Figure 11]FIG. 1C is a top-down view illustrating a (second) cut mask formed over the first and second hard masks having a window exposing the second hard mask over a cut region of a selected one of the odd metal lines to be cut, according to an embodiment of the present invention. [Figure 12] FIG. 10 is a cross-sectional view (A-A') illustrating that even when a window in the second cut mask encroaches on an adjacent even metal line, cutting of the even metal line does not occur due to the use of different first and second hard masks, according to an embodiment of the present invention. [Figure 13] 10A-B′ are cross-sectional views illustrating a second cut mask being used to pattern / cut the second hard mask covering the selected odd metal lines, and the pattern being transferred from the second hard mask to the selected odd metal lines, cutting the odd metal lines, according to an embodiment of the present invention. [Figure 14] FIG. 10 is a cross-sectional view (A-A') illustrating that following lateral etching of the first cut mask to enlarge the window, the use of different first / second hard mask materials and selective etching prevents any etching of the first hard mask, even when the now enlarged window in the second cut mask encroaches on the first hard mask covering the adjacent even metal lines, according to an embodiment of the present invention. [Figure 15] FIG. 10B is a cross-sectional view (B-B') illustrating the second cut mask after the window has been enlarged / widened by lateral etching and the second cut mask being used to selectively etch portions of the second hard mask covering select (odd) metal lines on either side of the cut area exposed by the enlarged / widened window to form a (second) "T-shaped" cavity, according to an embodiment of the present invention. [Figure 16]FIG. 1C is a top-down view illustrating a (third) cut mask formed over the first and second hard masks having a window exposing the first hard mask covering one of the even metal lines, and the third cut mask being used to pattern the first hard mask covering a select even metal line to form a gap in the first hard mask, according to an embodiment of the present invention. [Figure 17] 10 is a cross-sectional view (A-A') illustrating that a (third) cut mask fills the first T-shaped cavity within the cut area of ​​the selected even metal wiring, according to an embodiment of the present invention. [Figure 18] FIG. 1C is a top-down view illustrating a (fourth) cut mask formed over the first and second hard masks having a window exposing the second hard mask covering one of the odd metal lines, and the fourth cut mask being used to pattern the second hard mask covering a select odd metal line to form a gap in the first hard mask, according to an embodiment of the present invention. [Figure 19] FIG. 10 is a cross-sectional view (A-A') illustrating a (fourth) cut mask filling the second T-shaped cavity within the cut area of ​​the selected odd metal wiring, according to an embodiment of the present invention. [Figure 20] FIG. 10 is a top-down view illustrating the first / second T-shaped cavities in the cut areas of the selective even / odd metal lines and the gap-fill dielectric being deposited into / filling the (non-line end) gaps in the first / second hard masks, according to an embodiment of the present invention. [Figure 21] 1A-1B are cross-sectional views (AA') illustrating a gap-fill dielectric filling a first T-shaped cavity in a cut area of ​​a selective even metal line according to an embodiment of the present invention. [Figure 22] 10 is a cross-sectional view (B-B') illustrating the gap-fill dielectric filling the second T-shaped cavity in the cut area of ​​the selected odd metal wiring according to an embodiment of the present invention. [Figure 23]FIG. 10 is a cross-sectional view (A-A') illustrating the removal of the first hard mask selectively to the gap-fill dielectric and recessing the even metal lines, thereby not recessing the gap-fill dielectric-covered portions of the even metal lines at the line ends and forming vias that are self-aligned to the (even) line ends, in accordance with an embodiment of the present invention. [Figure 24] FIG. 10B is a cross-sectional view (B-B') illustrating the second hard mask being removed selectively to the gap-fill dielectric and the odd metal lines being recessed, thereby not recessing the gap-fill dielectric-covered portions of the odd metal lines at the line ends and forming vias that are self-aligned to the (odd) line ends, in accordance with an embodiment of the present invention. [Figure 25] 10A-10C are cross-sectional views (A-A') illustrating the gap-fill dielectric being polished back, thereby exposing the tops of the vias at the even wiring ends, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Provided herein is a technique for forming self-aligned top vias at the line edge that utilizes cut lithography to first define the line cut, then widen the cut area mask opening and transfer the pattern to an underlying metal line hard mask layer. The widened opening is then subsequently filled with a dielectric to form a mask for the self-aligned top via at the line edge. As described in detail below, this technique places vias on both sides of the line cut area (i.e., at the line edge). Advantageously, there is no via critical dimension (CD) variation that would otherwise result from lithographically aligning the via to the previously formed line cut. Furthermore, using this process, the via CD at the line edge is controlled by the amount of lateral etching of the hard mask.

[0012] An exemplary method for forming self-aligned vias at interconnect ends will now be described with reference to FIGS. 1-25. As shown in FIG. 1 (top-down view), the process begins with patterning even metal interconnects using a first hard mask 102 and odd metal interconnects using a second hard mask 104. The terms "even" and "odd" are used herein to refer to alternating metal interconnects. The designation of which metal interconnects are even and which are odd is arbitrary. However, if a given metal interconnect is even, then the next adjacent metal interconnect is odd, or vice versa. The terms "first" and "second" are also sometimes used herein to refer to even and odd metal interconnects, respectively.

[0013] Note that the following description illustrates forming self-aligned vias at even / odd metal wiring ends, as well as non-end vias above even / odd metal wiring ends. However, it should be understood that the present technique may be implemented to form any of these end vias and / or non-end vias for even / odd metal wiring, alone or in combination, and in any order. For example, one may simply choose to implement the technique to form end vias above even and / or odd wiring ends and / or to form non-end vias for even and / or odd metal wiring.

[0014] This approach requires different hard masks (formed from different materials) for the even and odd metal lines. As will become apparent from the following discussion, this dual hard mask configuration enables selective cutting of the odd metal lines relative to the even metal lines, and vice versa. According to an exemplary embodiment, the first hard mask 102 is formed from a material such as titanium (Ti), tantalum (Ta), titanium oxide (TiOx), titanium nitride (TiN), or tantalum nitride (TaN), or a combination thereof, and the second hard mask 104 is formed from a material such as silicon nitride (SiN), silicon carbonitride (SiCN), hydrogen-containing silicon carbonitride (SiCNH), or silicon carbide (SiC), or a combination thereof. The first and second hard masks 102 and 104 can be patterned using a patterning technique, such as lithography followed by an etching process. Suitable etching processes include, but are not limited to, directional (anisotropic) etching processes, such as reactive ion etching (RIE). Alternatively, the first and second hard masks 102 and 104 may be formed by any other suitable technique, including, but not limited to, sidewall image transfer (SIT), self-aligned double patterning (SADP), self-aligned quadruple patterning (SAQP), and other self-aligned multiple patterning (SAMP).

[0015] A directional (anisotropic) etching process, such as RIE, can be utilized to form the even and odd metal lines using the first and second hard masks 102 and 104, respectively. That is, the first and second hard masks 102 and 104 are formed on a metal layer (not explicitly shown in the figures), which is then patterned into individual even and odd metal lines. Suitable metals for the metal layer / metal lines include, but are not limited to, tungsten (W), cobalt (Co), or ruthenium (Ru), or combinations thereof.

[0016] A dielectric material 106 is then deposited over / surrounding the (even / odd) metal interconnects and the first and second hard masks 102 and 104, followed by a polishing process such as chemical-mechanical polishing (CMP) to remove excess dielectric. Suitable dielectric materials 106 include, but are not limited to, oxide materials such as silicon dioxide (SiOx) and / or organosilicate glass (SiCOH) and / or ultra-low-k interlayer dielectric (ULK-IDL) materials, e.g., with a dielectric constant k of less than 2.7. By comparison, silicon dioxide (SiO2) has a dielectric constant k value of 3.9. Suitable ultra-low-k dielectric materials include, but are not limited to, porous organosilicate glass (pSiCOH).

[0017] Figure 2 is a cross-sectional view (along line A-A' - see Figure 1) illustrating the first hard mask 102 overlying the even metal wiring 202. Figure 3 is a cross-sectional view (along line B-B' - see Figure 1) illustrating the second hard mask 104 overlying the odd metal wiring 302.

[0018] Cutting of the even metal lines 202 is then performed. To do so, a (first) cut mask 402 is formed over the first and second hard masks 102 and 104. See FIG. 4 (top-down view). A window 404 (exposing the cut area) is present in the cut mask 402 over one of the first hard masks 102 (covering a selected one of the even metal lines 202 to be cut). According to an exemplary embodiment, the cut mask 402 is formed from a multilayer lithography stack including, but not limited to, a photoresist disposed over an antireflective coating layer (ARC) and an organic planarization layer (OPL). Ideally, the window 404 opens only the first hard mask 102 over the selected even metal lines 202 to be cut (i.e., the desired cut area). However, as illustrated in FIG. 6 and described below, the use of different hard masks for the even and odd metal lines widens the process window because a different / second hard mask 104 exists over and protects the adjacent odd metal lines.

[0019] FIG. 5 is a cross-sectional view (along line A-A') illustrating the cut mask 402 being used to pattern / cut the first hard mask 102 over the selected even metal lines 202 to be cut. As shown in FIG. 6 (cross-sectional view along line B-B'), even when the window 404 encroaches on the adjacent odd metal lines 302, the odd metal lines 302 are protected by the second hard mask 104 (i.e., a different hard mask material—see above). In this way, cutting of the odd metal lines 302 does not occur. By way of example only, a plasma etching process using a chlorine-containing plasma can be used to selectively etch the hard mask 102.

[0020] 7 is a cross-sectional view (along line A-A') illustrating the pattern being transferred from the first hard mask 102 to the selected even metal lines 202, cutting the even metal lines 202. A directional (anisotropic) etching process, such as RIE, can be used to cut the metal lines.

[0021] As shown in FIG. 8 (top-down view), a lateral etch (see arrows 802) of the cut mask 402 is then performed to enlarge the window 404. This enlarging / widening of the window 404 defines the width of the via, which will now be located on either side of the interconnect cut area (i.e., at the ends of the selected even metal lines 202 being cut) based on the lateral etch. According to an exemplary embodiment, this lateral etching of the cut mask 402 is performed using oxygen plasma etching. Care must be taken to widen / widen the window 404 sufficiently to expose a portion of the first hard mask 102 covering the selected (even) metal lines on either side of the cut area, without widening the window 404 too much, which would expose the first hard mask 102 covering another, different, even metal line 202.

[0022] FIG. 9 is a cross-sectional view (along line A-A′) illustrating the cut mask 402 after the window 404 has been enlarged / widened by lateral etching. As explained above, enlarging the window 404 exposes portions of the first hard mask 102 covering the selected (even) metal lines on either side of the cut area. Next, as shown in FIG. 9 , the cut mask 402 is used to selectively etch those portions of the first hard mask 102 covering the selected (even) metal lines on either side of the cut area exposed by the enlarged / widened window 404. As mentioned above, a plasma etching process using a chlorine-containing plasma can be used to selectively etch the hard mask 102. As shown in FIG. 9 , the etched first hard mask 102 covering the cut area of ​​the selected even metal lines forms a (first) “T-shaped” cavity 902.

[0023] 10 (cross-sectional view (along line B-B')), the use of different first / second hard mask materials and selective etching prevents any etching of the second hard mask 104, even though the now enlarged window 404 encroaches on the adjacent second hard mask 104 / odd metal lines 302. After the first hard mask 102 covering the selected (even) metal lines on either side of the cut area is etched through the enlarged window 404, the cut mask 402 is removed.

[0024] The same general process is then used to cut a selected one of the odd metal lines 302. That is, as shown in FIG. 11 (top-down view), a (second) cut mask 1102 is formed over the first and second hard masks 102 and 104. A window 1104 (exposing the cut area) is present in the cut mask 1102 (covering the selected one of the odd metal lines 302 to be cut) that covers one of the second hard masks 104. According to an exemplary embodiment, the cut mask 1102 is formed from a multilayer lithography stack, such as a photoresist / ARC / OPL stack. Ideally, the window 1104 opens only the second hard mask 104 that covers the selected odd metal line 302 to be cut (i.e., the desired cut area). However, the use of different hard masks for the even and odd metal lines expands the process window because the different / first hard mask 102 exists over and protects the adjacent even metal line. That is, as shown in FIG. 12 (cross-sectional view (along line A-A')), even if the window 1104 encroaches on an adjacent even metal line 202, that even metal line 202 is protected by the first hard mask 102 (i.e., a different hard mask material - see above). In this way, no cutting of that even metal line 202 occurs. By way of example only, a plasma etching process using a fluorocarbon plasma can be used to selectively etch the hard mask 104. Furthermore, as shown in FIG. 12, the cut mask 1102 fills the T-shaped cavity 902 in the cut area of ​​the selected even metal line.

[0025] FIG. 13 is a cross-sectional view (along line B-B') illustrating the cut mask 1102 being used to pattern / cut the second hard mask 104 covering the selected odd metal lines 302 and the pattern transferred from the second hard mask 104 to the selected odd metal lines 302, cutting the odd metal lines 302. A directional (anisotropic) etching process, such as RIE, can be used for metal line cutting. The individual hard mask and metal line patterning steps combined in FIG. 13 are depicted in FIGS. 5 and 7 (in the case of patterning the selective even metal lines) and described above.

[0026] A lateral etch of the cut mask 1102 is then performed to widen the window 1104 above the second hard mask 104 and the selective odd metal lines 302. As shown in the cross-sectional view (along line A-A') of Figure 14, the use of different first / second hard mask materials and the selective etch prevent any etching of the first hard mask 102, even if the now enlarged window 1104 (see arrow 1402) encroaches on the adjacent first hard mask 102 / even metal lines 202.

[0027] As explained above, widening this window 1104 defines the width of the vias now located on either side of the line cut area (i.e., at the ends of the selected odd metal lines 302 being cut) based on a lateral etch. According to an exemplary embodiment, this lateral etching of the cut mask 1102 is performed using an oxygen plasma etch. Care must be taken to widen / extend the window 1104 sufficiently to expose a portion of the second hard mask 104 covering the selected (odd) metal lines on either side of the cut area, without widening the window 1104 too much, which would expose the second hard mask 104 covering another, different odd metal line 302.

[0028] FIG. 15 is a cross-sectional view (along line B-B′) illustrating the cut mask 1102 after the window 1104 has been enlarged / widened by lateral etching. As explained above, enlarging the window 1104 exposes portions of the second hard mask 104 covering the selected (odd) metal lines on either side of the cut area. Next, as shown in FIG. 15 , the cut mask 1102 is used to selectively etch those portions of the second hard mask 104 covering the selected (odd) metal lines on either side of the cut area exposed by the enlarged / widened window 1104. As mentioned above, a plasma etching process using a fluorocarbon plasma can be used to selectively etch the hard mask 104. As shown in FIG. 15 , the etched second hard mask 104 covering the cut area of ​​the selected odd metal lines forms a (second) “T-shaped” cavity 1502. After the second hard mask 104 covering the selected (odd) metal lines on either side of the cut area is etched through the enlarged windows 1104, the cut mask 1102 is removed.

[0029] Non-end vias, i.e., top vias that are not above the ends of the metal lines, can also be patterned in the first and second hard masks 102 / 104, respectively, covering the even and odd metal lines 202 / 302. For example, as shown in FIG. 16 (top-down view), a (third) via mask 1602 is formed over the first and second hard masks 102 and 104. A window 1604 (defining the via area) is present in the via mask 1602 over one of the first hard masks 102 that covers a selected one of the even metal lines 202. According to an exemplary embodiment, the via mask 1602 is formed from a multilayer lithography stack, such as a photoresist / ARC / OPL stack. As shown in the cross-sectional view (along line A-A') of FIG. 17, the via mask 1602 fills the T-shaped cavity 902 in the cut area of ​​the selected even metal line. In the same manner, via mask 1602 fills T-shaped cavities 1502 in the cut areas of selected odd metal lines (not explicitly shown in the figure).

[0030] 16 , the via mask 1602 is then used to pattern the first hard mask 102 overlying the selected even metal lines 202, forming gaps 1606 in the first hard mask 102. As provided above, a plasma etching process using a chlorine-containing plasma can be used to selectively etch the hard mask 102. After the non-end vias are etched into the first hard mask 102 overlying the selected (even) metal lines, the via mask 1602 is removed.

[0031] The same process is applied to form non-end vias in the second hard mask 104 covering the selected odd metal lines. For example, as shown in FIG. 18 (top-down view), a (fourth) via mask 1802 is formed over the first and second hard masks 102 and 104. A window 1804 (defining the via area) is present in the via mask 1802 over one of the second hard masks 104 covering a selected one of the odd metal lines 302. According to an exemplary embodiment, the via mask 1802 is formed from a multilayer lithography stack, such as a photoresist / ARC / OPL stack. As shown in FIG. 19 (cross-sectional view along line B-B'), the via mask 1802 fills the T-shaped cavity 1502 in the cut area of ​​the selected odd metal line. In the same manner, via mask 1802 fills T-shaped cavities 902 in the via regions of select even metal lines (not explicitly shown in the figure).

[0032] 18 , the via mask 1802 is then used to pattern the second hard mask 104 overlying the selected odd metal lines 302, forming gaps 1806 in the second hard mask 104. As provided above, a plasma etching process using a fluorocarbon plasma can be used to selectively etch the hard mask 104. After the non-end vias are etched into the second hard mask 104 overlying the selected (odd) metal lines, the via mask 1802 is removed.

[0033] A gapfill dielectric is then deposited and filled into the (line-end) T-shaped cavities 902 / 1502 in the cut areas of the selective even / odd metal lines and into the (non-line-end) gaps 1606 / 1806 in the first / second hard masks 102 / 104, followed by a polishing process such as CMP to remove excess dielectric. Suitable gapfill dielectric materials include, but are not limited to, silicon dioxide (SiOx) and / or spin-on glass (SoG). That is, as shown in FIG. 20 (top-down view), the gapfill dielectric 2002 now fills the T-shaped cavities 902 / 1502 in the cut areas of the selective even / odd metal lines and into the (non-line-end) gaps 1606 / 1806 in the first / second hard masks 102 / 104.

[0034] 21 is a cross-sectional view (along line A-A') illustrating the gap-filling dielectric 2002 filling the T-shaped cavity 902 in the cut area of ​​the selected even metal wiring. FIG. 22 is a cross-sectional view (along line B-B') illustrating the gap-filling dielectric 2002 filling the T-shaped cavity 1502 in the cut area of ​​the selected odd metal wiring. Optionally, the overhang on one side of the T-shaped gap-filling dielectric 2002 can be removed, for example, using an additional mask (not shown), to avoid forming vias on both sides of the cut in both the odd and even wiring. This allows for the formation of self-aligned vias on only one side of the cut.

[0035] The first / second hard mask 102 / 104 is then removed using a metal line etch selective to the hard mask and gapfill dielectric 2002. That is, FIG. 23 is a cross-sectional view (along line A-A') illustrating the first hard mask 102 being selectively removed relative to the gapfill dielectric 2002 and the recessed even metal lines 202. Due to the configuration of the T-shaped cavity 902, the gapfill dielectric 2002 overhangs / covers the portions of the even metal lines 202 at the line ends. As a result, this covered portion of the even metal lines 202 at the line ends is not recessed, forming vias 2302 self-aligned to the (even) line ends. This process also forms non-line-end vias (not shown). As described above, a plasma etching process using a chlorine-containing plasma can be used to selectively etch the hard mask 102. Metal-selective RIE can be utilized to recess the even metal lines 202 selectively relative to the gapfill dielectric 2002.

[0036] FIG. 24 is a cross-sectional view (along line B-B′) illustrating the second hard mask 104 being selectively removed relative to the gapfill dielectric 2002 and the recessed odd metal lines 302. Due to the T-shaped cavity 1502, the gapfill dielectric 2002 overhangs / covers the portions of the odd metal lines 302 at the line ends. As a result, this covered portion of the odd metal lines 302 at the line ends is not recessed, forming vias 2402 self-aligned to the (odd) line ends. This process also forms non-line-end vias (not shown). As mentioned above, a plasma etching process using a fluorocarbon plasma can be used to selectively etch the hard mask 104. Metal-selective RIE can be used to recess the odd metal lines 302 selectively relative to the gapfill dielectric 2002.

[0037] All of the processes described above can damage the dielectric material 106. Thus, according to an exemplary embodiment, this damaged dielectric material 106 is removed and replaced with new dielectric material (now given the reference numeral 106′). In that case, the dielectric material 106′ not only fills the spaces between the wires, but also fills the spaces between all the top vias along the wires (wire end vias 2302, 2402 and other non-wire end vias).

[0038] Finally, a process such as CMP is then utilized to polish the surface of dielectric material 106' and gap-fill dielectric 2002 down to vias 2302 / 2402, thereby exposing the tops of vias 2302 / 2402 at the even / odd wiring ends. For example, Figure 25 is a cross-sectional view (along line A-A') showing gap-fill dielectric 2002 being polished down to via 2302, thereby exposing the tops of vias 2302 at the even wiring ends. The same configuration would exist for via 2402 at the odd wiring ends.

[0039] The resulting structure includes a cut in at least one selected one (i.e., even and / or odd) of the metal lines, as shown, for example, in Figure 25. Vias (e.g., via 2302 in Figure 25) are perfectly aligned with the line ends of the selected metal lines on either side of the cut. For example, as shown in Figure 25, the sidewalls of each of vias 2302 are flush with the line ends of the selected metal lines. Gap-fill dielectric 2002 is present between the line ends.

[0040] Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to these precise embodiments, and that various other changes and modifications can be made by those skilled in the art without departing from the scope of the invention.

Claims

1. 1. A method for forming a self-aligned via at an edge of a wiring, comprising: patterning metal wiring comprising alternating even and odd metal wiring using hard masks, the hard mask including a first hard mask for patterning even metal wiring and a second hard mask for patterning odd metal wiring; cutting the hard mask and the even or odd selected metal lines using a cut mask having windows that expose the hard mask overlying cut areas of the selected metal lines; enlarging the window in the cut mask to expose the hard mask on at least one side of the cut area of ​​the selected metal line; selectively etching the hard mask using the enlarged window in the cut mask to form a T-shaped cavity in the cut area of ​​the selected metal line; filling the T-shaped cavity with a gap-fill dielectric; removing the hard mask; recessing the metal line selectively relative to the gap-fill dielectric, whereby portions of the selected metal line overhanging the gap-fill dielectric form the self-aligned via at an end of the metal line; A method comprising:

2. depositing a dielectric layer covering the even metal lines, the odd metal lines, and the hard mask after the recessing step; The method of claim 1 further comprising:

3. cutting the hard mask using a mask having a window exposing the hard mask covering a non-interconnect end of one of the metal interconnects to form a gap in the hard mask; filling the gap in the hard mask with the gap-fill dielectric, the recessing selectively recessing the metal line relative to the gap-fill dielectric in the gap to form a non-line end via; 3. The method of claim 1 or 2, further comprising:

4. 4. The method of claim 1, further comprising removing an overhang of the gap-fill dielectric such that the recessing step forms a self-aligned via only at one end of the selected metal line.

5. The step of cutting the selected metal wiring includes: patterning the hard mask over the selected metal interconnects using the cut mask; transferring a pattern from the hard mask to the selected metal lines to cut the selected metal lines; 5. The method of claim 1, comprising:

6. 6. The method of claim 1, wherein the step of enlarging the window in the cut mask comprises using lateral etching.

7. The method of any of claims 1 to 6, further comprising the step of polishing the gap-fill dielectric after the recessing step.

8. cutting the first hard mask and the selected even metal wiring using a first cut mask having an window exposing the first hard mask covering a cut region of a selected even metal wiring of the even metal wiring; enlarging the window in the first cut mask to expose the first hard mask on at least one side of the cut area of ​​the selected even metal interconnect; Selectively etching the first hard mask using the enlarged window of the first cut mask to form a first T-shaped cavity in the cut area of ​​the selected even metal wiring; cutting the second hard mask and the selected odd metal wiring using a second cut mask having an window exposing the second hard mask covering a cut region of a selected odd metal wiring of a selected one of the odd metal wirings; enlarging the window in the second cut mask to expose the second hard mask on either side of the cut area of ​​the selected odd metal line; Selectively etching the second hard mask using the enlarged window of the second cut mask to form a second T-shaped cavity in the cut area of ​​the selected odd metal wiring; filling the first T-shaped cavity and the second T-shaped cavity with a gap-fill dielectric; removing the first hard mask and the second hard mask; recessing the metal lines selectively relative to the gap-fill dielectric, the recessing causing the gap-fill dielectric to overhang portions of the selected even metal lines and the selected odd metal lines forming the self-aligned via at an end of the metal lines; The method of claim 1 , comprising:

9. cutting the first hard mask using a mask having a window exposing the first hard mask covering a non-wire end of one of the even metal wires to form a gap in the first hard mask; filling the gap in the first hard mask with the gap-fill dielectric, the recessing selectively recessing the metal line relative to the gap-fill dielectric in the gap in the first hard mask to form a non-end via; The method of claim 8 further comprising:

10. cutting the second hard mask using another mask having a window exposing the second hard mask covering a non-wiring end of one of the odd metal wirings to form a gap in the second hard mask; filling the gap in the second hard mask with the gap-fill dielectric, the recessing selectively recessing the metal line relative to the gap-fill dielectric in the gap of the second hard mask to form another non-end via; 10. The method of claim 9, further comprising:

11. cutting the first hard mask using a mask having a window exposing the first hard mask covering a non-wire end of one of the even metal wires to form a gap in the first hard mask; cutting the second hard mask using another mask having a window exposing the second hard mask covering a non-wiring end of one of the odd metal wirings to form a gap in the second hard mask; filling the first T-shaped cavity, the second T-shaped cavity, the gap in the first hard mask, and the gap in the second hard mask with a gap-fill dielectric; removing the first hard mask and the second hard mask; recessing the metal lines selectively relative to the gap-fill dielectric, whereby portions of the selected metal lines overhanging the gap-fill dielectric form the self-aligned vias at the ends of the even and odd metal lines, and whereby the metal lines are recessed selectively relative to the gap-fill dielectric in the gaps of the first hard mask and the gap-fill dielectric in the gaps of the second hard mask to form non-end vias; The method of claim 10, comprising:

12. 12. The method of claim 1, wherein the first hard mask and the second hard mask comprise different materials.

13. 13. The method of claim 1, wherein the first hard mask comprises a material selected from the group consisting of titanium (Ti), tantalum (Ta), titanium oxide (TiOx), titanium nitride (TiN), tantalum nitride (TaN), and combinations thereof.

14. 14. The method of claim 1, wherein the second hard mask comprises a material selected from the group consisting of silicon nitride (SiN), silicon carbonitride (SiCN), hydrogen-containing silicon carbonitride (SiCNH), silicon carbide (SiC), and combinations thereof.

15. 15. The method of claim 1, wherein the even and odd metal wiring comprises a metal selected from the group consisting of tungsten (W), cobalt (Co), ruthenium (Ru), and combinations thereof.

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