DETAILED DESCRIPTION OF THE INVENTION
[0028] FIG. 1 is a partial cross-sectional view of an interconnect structure 100 constructed in accordance with the present invention for use with a multilevel interconnect. Structure 100 , the fabrication of which is described below, includes a first layer 110 having a first intermetal dielectric layer 111 and a metal portion 112 ; an etched protective layer 120 ; an etched second intermetal dielectric layer 130 ; a via 170 ; and a trench 190 . Structure 100 can accommodate the deposition of an inlaid multilevel interconnect metal. As is evident from FIG. 1 , structure 100 is characterized by the absence of any undesirable “ear” (i.e., structural formation of resist residue) on the etched IMD layer 130 at the trench/via edge.
[0029] FIGS. 2 A-J illustrate a first embodiment of the method of fabricating the structure 100 depicted in FIG. 1 . FIGS. 3 A-C are a flow diagram of the fabrication sequence corresponding to FIGS. 2 A-J. The method includes first assembling a dual hardmask structure to be etched. As depicted in FIG. 2A, a first layer 110 comprising a first intermetal dielectric layer 111 and a metal portion 112 is formed (step 1010 ). The metal of metal portion 112 may be Cu or any other metal typically employed as a multilevel interconnect. A first protective layer 120 is deposited (step 1020 ) upon the first layer 110 . The first protective layer 120 typically comprises a material selected from the group consisting of silicon nitrides, silicon carbo-nitrides, and silicon carbides.
[0030] A second intermetal dielectric layer 130 is deposited (step 1030 ) upon the first protective layer 120 . A second protective layer 135 is deposited (step 1035 ) upon the second intermetal dielectric layer 130 . The second protective layer 135 typically comprises a material selected from the group consisting of silicon oxides, silicon nitrides, silicon carbo-nitrides, silicon carbides, and titanium nitrides. In another embodiment, the second protective layer 135 can be a dielectric antireflective coating. The second protective layer 135 serves to protect the underlying second intermetal dielectric layer 130 from possible contamination associated with exposure to the subsequently-deposited photoresist (described below).
[0031] A layer of amorphous carbon as a first hardmask layer 140 capable of being etched by a second etch process (described below) is deposited (step 1040 ) upon the second protective layer 135 . A second hardmask layer 150 capable of being etched by a first etch process (described below) is deposited (step 1050 ) upon the amorphous carbon layer 140 . Then, in the final step of assembling the layered structure prior to etching, a first layer of photoresist 160 is deposited (step 1060 ) upon the second hardmask layer 150 and patterned with an opening 161 through which etching will occur.
[0032] The amorphous carbon layer 140 , which can be deposited as a PECVD film, has a very slow etch rate for the etch chemistry associated with the material of the second hardmask layer 150 (i.e., the etch selectivity can be as high as 100:1). Furthermore, amorphous carbon can be easily etched with an etch chemistry (described below) that does not etch the second hardmask layer 150 . This unique property of amorphous carbon makes it possible to use, for example, a stack of the amorphous carbon layer 140 and the second hardmask layer 150 as a dual hardmask in the present dual damascene process.
[0033] The second hardmask layer 150 typically comprises a material selected from the group consisting of silicon oxides, silicon nitrides, silicon carbo-nitrides, silicon carbides, and titanium nitrides. In another embodiment, the layer of material 150 can be a dielectric antireflective coating.
[0034] Next, in the first etching step, a first portion of a via 170 is formed by etching ( FIG. 2 B)(step 1070 ) the second hardmask layer 150 using a first etch process. The first etch process, which etches the second hardmask layer 150 , typically employs a plasma containing C x F y H z . An oxide, for example, can be easily etched by a plasma having C x F y H z (e.g., CF 4 ), but is not etched at all by any of the etchants (described below) that may be used to etch the amorphous carbon layer 140 .
[0035] In the next via-patterning step, a second portion of the via 170 is formed by etching ( FIG. 2 C)(step 1080 ) the amorphous carbon layer 140 using a second etch process. During step 1080 , for the following two reasons, the first layer of photoresist 160 is completely consumed. First, the photoresist layer 160 is etched by the same etchant as is the amorphous carbon layer 140 . The photoresist layer 160 etches faster than amorphous carbon layer 140 because the amorphous carbon is harder than photoresist. Secondly, because a dual hardmask is employed, and because a second layer of photoresist 180 ( FIG. 2D ) is employed for subsequent etching steps (described below), the photoresist layer 160 can be a relatively thin layer, having a thickness chosen to provide the optimal photo-imaging performance. The photoresist layer 160 typically has a thickness of from 1000 to 6000 Å.
[0036] The second etch process, which etches the amorphous carbon layer 140 , typically employs an etchant selected from the group consisting of O 2 plasma, N 2 and O 2 plasma, N 2 O plasma, NO plasma, H 2 plasma, and NH 3 plasma. For example, with O 2 plasma, or a plasma of N 2 and O 2 , the layer of material 140 can be easily etched and results in the release of CO 2 . With H 2 plasma or NH 3 plasma, the amorphous carbon layer 140 can be easily etched and results in the release of CH 4 .
[0037] Next, before trench patterning is begun, a second layer of photoresist 180 is deposited ( FIG. 2 D)(step 1090 ) on the etched second hardmask layer 150 and patterned with an opening 181 through which etching will occur. A first portion of a trench 190 is then formed by etching ( FIG. 2 E)(step 1100 ) the etched second hardmask layer 150 through opening 181 using the first etch process. The amorphous carbon layer 140 is an excellent etch stop because amorphous carbon layer 140 is not selectively etched with the etched second hardmask layer 150 .
[0038] In addition, because of the presence of second protective layer 135 , the second intermetal dielectric layer 130 is advantageously never exposed to the photoresist 180 , thus avoiding any potential poisoning of the layer 130 . This feature of the present invention, therefore, minimizes the potential for poisoning that can arise with conventional processes in which the via is fully opened to the level of the intermetal dielectric layer before the second layer of photoresist is applied, thereby exposing the intermetal dielectric layer to direct contact with the photoresist.
[0039] A third portion of the via 170 is then formed by etching ( FIG. 2 F)(step 1110 ) the second protective layer 135 and the second intermetal dielectric layer 130 using the first etch process. In this step, the etched amorphous carbon layer 140 is used as a hardmask to effect the via etch through the second protective layer 135 and the second intermetal dielectric layer 130 , and some of the photoresist 180 is consumed. The via etch can be a full via etch stop on the protective layer 120 as shown in FIG. 2 F, or a partial etch. The second protective layer 135 and the second intermetal dielectric layer 130 are etched with the first etch process, typically by a plasma containing C x F y H z (e.g., CF 4 ).
[0040] A second portion of the trench 190 is formed by etching ( FIG. 2 G)(step 1120 ) the etched amorphous carbon layer 140 using the second etch process. In this step, the etched second hardmask layer 150 serves as the hardmask, and trench patterning is effected through the etched amorphous carbon layer 140 as the photoresist 180 is completely consumed.
[0041] In the next step, trench etching of the etched second protective layer 135 and the etched second intermetal dielectric layer 130 is effected using the first etch process, with the etched amorphous carbon layer 140 serving as the hardmask. Thus, a third portion of the trench 190 is formed by etching ( FIG. 2 H)(step 1130 ) the etched second protective layer 135 and the etched second intermetal dielectric layer 130 and thereby removing all of the etched second hardmask layer 150 .
[0042] The etched amorphous carbon layer 140 is then removed by etching ( FIG. 21 )(step 1140 ) using the second etch process without in any way damaging the etched second intermetal dielectric layer 130 . This step of etching to remove the amorphous carbon layer 140 typically employs the above-described etchant selected from the group consisting of O 2 plasma, N 2 and O 2 plasma, N 2 O plasma, NO plasma, H 2 plasma, and NH 3 plasma. Alternatively, the etching to remove the amorphous carbon layer 140 may employ a hot non-plasma etchant selected from the group consisting of O 2 , O 3 , N 2 O, NO, H 2 , and NH 3 . Without plasma, however, the etch is isotropic, and the gaseous etchant must be employed at an elevated temperature. Other non-plasma etchants may be employed to remove the amorphous carbon layer 140 , such as compounds of the formula C x F y H z , but with these etchants the etch rate is much slower than that attainable with either the above-described plasma etchants (i.e., O 2 plasma, N 2 and O 2 plasma, N 2 O plasma, NO plasma, H 2 plasma, and NH 3 plasma) or hot non-plasma etchants (i.e., O 2 , O 3 , N 2 O, NO, H 2 , and NH 3 ).
[0043] The etched second protective layer 135 and a portion of the first protective layer 120 that is disposed above the metal portion 112 are then removed by etching ( FIG. 2 J)(step 1150 ) using the first etch process so as to complete the formation of the via 170 . The resultant structure 100 is thus ready for deposition of the inlaid interconnect metal.
[0044] The etch chemistry of the photoresist layers 160 and 180 is similar to the etch chemistry of the amorphous carbon layer 140 , but the photoresist etches faster because amorphous carbon is harder than photoresist. As indicated above, in conventional dual damascene processes, the photoresist is optimized not for imaging performance, but rather, for its etch resistance. That is, because the photoresist must be etch resistant (i.e., relatively thick) in a conventional process, the imaging qualities of the photoresist may be compromised for the benefit of etch performance. An advantage of the present invention is that because the amorphous carbon layer 140 and the second hardmask layer 150 are used as the dual hardmask, the photoresist can be made thinner and thus optimized for the best imaging performance.
[0045] FIGS. 4 A-I illustrate a second embodiment of the method of fabricating the structure 100 depicted in FIG. 1 . FIGS. 5 A-C are a flow diagram of the fabrication sequence corresponding to FIGS. 4 A-I. As with the first method embodiment, the method includes first assembling a dual hardmask structure to be etched. In this second embodiment of the method, the first five steps of assembling the layered structure (steps 2010 , 2020 , 2030 , 2040 , and 2050 ) are identical to the first five steps described above (steps 1010 , 1020 , 1030 , 1040 , and 1050 ) for the first embodiment of the method of fabrication.
[0046] As depicted in FIG. 4A, a first layer 210 comprising a first intermetal dielectric layer 211 and a metal portion 212 is formed (step 2010 ). The metal of metal portion 212 may be Cu or any other metal typically employed as a multilevel interconnect. A first protective layer 220 is deposited (step 2020 ) upon the first layer 210 . The first protective layer 220 typically comprises a material selected from the group consisting of silicon nitrides, silicon carbo-nitrides, and silicon carbides.
[0047] A second intermetal dielectric layer 230 is deposited (step 2030 ) upon the first protective layer 220 . A second protective layer 235 is deposited (step 2035 ) upon the second intermetal dielectric layer 230 . The second protective layer 235 typically comprises a material selected from the group consisting of silicon oxides, silicon nitrides, silicon carbo-nitrides, silicon carbides, and titanium nitrides. In another embodiment, the second protective layer 235 can be a dielectric antireflective coating. The second protective layer 235 serves to protect the underlying second intermetal dielectric layer 230 from possible contamination associated with exposure to the subsequently-deposited photoresist (described below).
[0048] A layer of amorphous carbon as a first hardmask layer 240 capable of being etched by a second etch process (described below) is deposited (step 2040 ) upon the second protective layer 230 . A second hardmask layer 250 capable of being etched by a first etch process (described below) is deposited (step 2050 ) upon the amorphous carbon layer 240 . Then, in the final step of assembling the layered structure prior to etching, a first layer of photoresist 260 is deposited (step 2060 ) upon the second hardmask layer 250 and patterned with an opening 261 through which etching will occur. Because a dual hardmask is employed, and because a second layer of photoresist 280 is employed for subsequent etching steps (described below), the photoresist layer 260 can be a relatively thin layer, having a thickness chosen to provide the optimal photo-imaging performance. The photoresist layer 260 typically has a thickness of from 1000 to 6000 Å.
[0049] The amorphous carbon layer 240 , which can be deposited as a PECVD film, has a very slow etch rate for the etch chemistry associated with the material of the second hardmask layer 250 (i.e., the etch selectivity can be as high as 100:1). Furthermore, amorphous carbon can be easily etched with an etch chemistry that does not etch the second hardmask layer 250 . This unique property of amorphous carbon makes it possible to use, for example, a stack of the amorphous carbon layer 240 and the second hardmask layer 250 as a dual hardmask in the present dual damascene process.
[0050] The second hardmask layer 250 typically comprises a material selected from the group consisting of silicon oxides, silicon nitrides, silicon carbo-nitrides, silicon carbides, and titanium nitrides. In another embodiment, the layer of material 250 can be a dielectric antireflective coating.
[0051] Next, in the first etching step, a first portion of a trench 270 is formed by etching ( FIG. 4 B)(step 2070 ) the second hardmask layer 250 using a first etch process. The amorphous carbon layer 240 is an excellent etch stop because amorphous carbon layer 240 is not selectively etched with the second hardmask layer 250 .
[0052] The first etch process, which etches the second hardmask layer 250 , typically employs a plasma containing C x F y H z . An oxide, for example, can be easily etched by a plasma containing C x F y H z , (e.g., CF 4 ), but is not etched at all by any of the etchants (described below) that may be used to etch the amorphous carbon layer 240 .
[0053] A second layer of photoresist 280 is then deposited ( FIG. 4 C)(step 2080 ) upon the etched second hardmask layer 250 and on a portion of the amorphous carbon layer 240 and patterned with an opening 281 through which etching will occur. A first portion of a via 290 is formed by etching.( FIG. 4 D)(step 2090 ) the amorphous carbon layer 240 using a second etch process. Because of the presence of second protective layer 235 , the second intermetal dielectric layer 230 is advantageously never exposed to the photoresist 280 , thus avoiding any potential poisoning reaction with the layer 230 .
[0054] The second etch process, which etches the amorphous carbon layer 240 , typically employs an etchant selected from the group consisting of O 2 plasma, N 2 and O 2 plasma, H 2 plasma, and NH 3 plasma. For example, with O 2 plasma, or a plasma of N 2 and O 2 , the layer of material 240 can be easily etched and results in the release of CO 2 . With H 2 plasma or NH 3 plasma, the amorphous carbon layer 240 can be easily etched and results in the release of CH 4 .
[0055] A second portion of the via 290 is then formed by etching ( FIG. 4 E)(step 2100 ) the second protective layer 235 and the second intermetal dielectric layer 230 using the first etch process. A second portion of the trench 270 is formed by etching ( FIG. 4 F)(step 2110 ) the etched amorphous carbon layer 240 using the second etch process. In this step, the second layer of photoresist 280 is removed, and the etched second hardmask layer 250 serves as the hardmask.
[0056] A third portion of the trench 270 is formed by etching ( FIG. 4 G)(step 2120 ) the etched second protective layer 235 and the etched second intermetal dielectric layer 230 using the first etch process and thereby removing all of the etched second hardmask layer 250 . In this step, the etched amorphous carbon layer 240 serves as the hardmask.
[0057] The etched amorphous carbon layer 240 is then removed by etching ( FIG. 4 H)(step 2130 ) using the second etch process. This step of etching to remove the amorphous carbon layer 240 typically employs the above-described etchant selected from the group consisting of O 2 plasma, N 2 and O 2 plasma, N 2 O plasma, NO plasma, H 2 plasma, and NH 3 plasma. Alternatively, the etching to remove the amorphous carbon layer 240 may employ a hot non-plasma etchant selected from the group consisting of O 2 , O 3 , N 2 O, NO, H 2 , and NH 3 . Without plasma, however, the etch is isotropic, and the gaseous etchant must be employed at an elevated temperature. Other non-plasma etchants may be employed to remove the amorphous carbon layer 240 , such as compounds of the formula C x F y H z , but with these etchants the etch rate is much slower than that attainable with either the above-described plasma etchants (i.e., O 2 plasma, N 2 and O 2 plasma, N 2 O plasma, NO plasma, H 2 plasma, and NH 3 plasma) or hot non-plasma etchants (i.e., O 2 , O 3 , N 2 O, NO, H 2 , and NH 3 ).
[0058] The etched second protective layer 235 and a portion of the first protective layer 220 that is disposed above the metal portion 212 are then removed by etching ( FIG. 41 )(step 2140 ) using the first etch process so as to complete the formation of the via 290 . The resultant structure 100 is thus ready for deposition of the inlaid interconnect metal.
[0059] The etch chemistry of the photoresist layers 260 and 280 is similar to that of the etch chemistry of the amorphous carbon layer 240 , but the photoresist etches faster because amorphous carbon is harder than photoresist. As indicated above, in conventional dual damascene processes, the photoresist is optimized not for imaging performance, but rather, for its etch resistance. That is, because the photoresist must be etch resistant (i.e., relatively thick) in a conventional process, the imaging qualities of the photoresist may be compromised for the benefit of etch performance. An advantage of the present invention is that because the amorphous carbon layer 240 and the second hardmask layer 250 are used as the dual hardmask, the photoresist can be made thinner and thus optimized for the best imaging performance.
[0060] The present invention is also directed to a structure 101 depicted in FIG. 2A ( 201 depicted in FIG. 4A ) for use in fabricating a dual damascene opening according to the above-described first and second embodiments of the method of fabrication. As depicted in FIG. 2A ( FIG. 4A ), structure 101 ( 201 ) comprises a first layer 110 ( 210 ) comprising a first intermetal dielectric layer 111 ( 211 ) and a metal portion 112 ( 212 ). A first protective layer 120 ( 220 ) is disposed on the first layer 110 ( 210 ), and a second intermetal dielectric layer 130 ( 230 ) is disposed on the first protective layer 120 ( 220 ). A second protective layer 135 ( 235 ) is disposed on the second intermetal dielectric layer 130 ( 230 ). A layer of amorphous carbon as a first hardmask layer 140 ( 240 ) capable of being etched by a second etch process is disposed on the second protective layer 135 ( 235 ), and a second hardmask layer 150 ( 250 ) capable of being etched by a first etch process is disposed on the amorphous carbon layer 140 ( 240 ). A layer of photoresist 160 ( 260 ) is disposed on the second hardmask layer 150 ( 250 ) and has an opening 161 ( 261 ) through which etching will occur.
[0061] The present invention, therefore, provides a method and structure having several advantages over conventional dual damascene processes and structures. By virtue of the features described herein, such as the selective etch chemistry employed with the dual hardmask, the present method affords flexibility unattainable with conventional dual damascene processes. First, by virtue of the protective layers, the via, after being opened, is never in contact with the photoresist. This eliminates the “ear” formation problem at the trench/via edge which results from the presence of photoresist residue on the IMD layer.
[0062] Secondly, this processing sequence eliminates the potential “poisoning” of the IMD layer which can result from the interaction between the photoresist and the IMD layer during application of the photoresist.
[0063] Thirdly, the photolithographic imaging for both the trench and the via are completed before the IMD etch, so, if necessary, it is easy to rework any patterning misalignments to ensure that both the trench and the via are etched correctly.
[0064] Fourthly, the conventional requirement that the photoresist be etch resistant is not a constraint with the present method. That is, because the amorphous carbon layer and the second hardmask layer are used as the dual hardmask, the photoresist can be made thinner and thus optimized for the best imaging performance. Finally, because each of the hardmask layers is ultimately removed in the fabrication sequence, they do not impact the final IMD structure.
[0065] Although the invention has been described and illustrated as being suitable for use in semiconductor fabrication applications, the invention is not limited to these embodiments. Rather, the invention could be employed in any service in which the flexibility and benefits associated with the above-described features would be desirable.
[0066] Accordingly, the above description and accompanying drawings are only illustrative of exemplary embodiments that can achieve the features and advantages of the present invention. It is not intended that the invention be limited to the embodiments shown and described in detail herein. The invention is limited only by the scope of the following claims.