Abstract:
A stack that includes, from bottom to top, a nitrogen-containing dielectric layer, an interconnect level dielectric material layer, and a hard mask layer is formed on a substrate. The hard mask layer and the interconnect level dielectric material layer are patterned by an etch. Employing the patterned hard mask layer as an etch mask, the nitrogen-containing dielectric layer is patterned by a break-through anisotropic etch, which employs a fluorohydrocarbon-containing plasma to break through the nitrogen-containing dielectric layer. Fluorohydrocarbon gases used to generate the fluorohydrocarbon-containing plasma generate a carbon-rich polymer residue, which interact with the nitrogen-containing dielectric layer to form volatile compounds. Plasma energy can be decreased below 100 eV to reduce damage to physically exposed surfaces of the interconnect level dielectric material layer.

Description:
RELATED APPLICATION 
     This application is a divisional of U.S. Ser. No. 13/281,732, filed Oct. 26, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to semiconductor processing methods, and particularly to methods for anisotropically etching a nitrogen-containing dielectric layer at low energy, and structures for effecting the same. 
     “Trench-first” BEOL applications suffer issues due to residue formation with exposed metal surfaces, metallic hard-mask retention, and damage to low-k materials such as organosilicate glass throughout the pattern transfer process. Residual fluorine is usually linked to residue formation as well as low-k damage. However, residual fluorine is needed to provide sufficient etch rate for the material of a cap layer during the final stage of the pattern transfer process. 
     Increasing hard mask retention through process optimization is challenging. Thus, there is a lower limit on the initial thickness of the hard mask that can be employed for adequate lithography process window. 
     Deposition of removable sidewall polymer deposition to impede damage to the low-k materials has been extensively attempted. The removable sidewall polymer deposit fills the periphery of an opening formed during an anisotropic etch process. The removable sidewall polymer deposit is removed, by a wet etch or a dry etch, during subsequent etching processing steps once the bottom of the trench is reached at the end of the anisotropic etch process. The requirement for removal of the sidewall polymer deposition severely limits the etching process window for the anisotropic etch, and effective increases the minimum dimension of a via hole that can be formed by the anisotropic etch. 
     Thus, an anisotropic etch process is desired that does not fill a periphery of a via hole with a polymer and provide protection to the low-k materials at the same time. 
     BRIEF SUMMARY 
     A stack that includes, from bottom to top, a nitrogen-containing dielectric layer, an interconnect level dielectric material layer, and a hard mask layer is formed on a substrate. The hard mask layer and the interconnect level dielectric material layer are patterned by an etch. Employing the patterned hard mask layer as an etch mask, the nitrogen-containing dielectric layer is patterned by a break-through anisotropic etch, which employs a fluorohydrocarbon-containing plasma to break through the nitrogen-containing dielectric layer. Fluorohydrocarbon gases used to generate the fluorohydrocarbon-containing plasma generate a carbon-rich polymer residue, which interact with the nitrogen-containing dielectric layer to form volatile compounds. Plasma energy can be decreased below 100 eV to reduce damage to physically exposed surfaces of the interconnect level dielectric material layer. 
     According to an aspect of the present disclosure, a method of forming a metal interconnect structure is provided. The method includes: forming a stack including, from bottom to top, a substrate, a nitrogen-containing dielectric layer, an interconnect level dielectric material layer, and a hard mask layer; forming an opening within the hard mask layer and the low-k dielectric material layer; and anisotropically etching a physically exposed portion of the nitrogen-containing dielectric layer underneath the opening employing a fluorohydrocarbon-containing plasma. A volatile compound is formed on, and evaporates from, a surface of the nitrogen-containing dielectric layer. The volatile compound includes nitrogen derived from the nitrogen-containing dielectric layer and a carbon-rich polymer including carbon and fluorine and having a ratio of carbon to fluorine that is greater than 1. 
     According to another aspect of the present disclosure, a structure is provided, which includes: a stack including, from bottom to top, a substrate, a nitrogen-containing dielectric layer, an interconnect level dielectric material layer, and a hard mask layer; an opening present within the hard mask layer and the low-k dielectric material layer and extending downward into at least an upper portion of the nitrogen-containing dielectric layer; and a volatile compound located on a surface of the nitrogen-containing dielectric layer within in the opening. The volatile compound includes nitrogen and a carbon-rich polymer including carbon and fluorine and having a ratio of carbon to fluorine that is greater than 1. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view of a first exemplary structure after formation of a stack including a substrate, a nitrogen-containing dielectric layer, an interconnect level dielectric layer, a dielectric cap layer, and a metallic hard mask layer according to a first embodiment of the present disclosure. 
         FIG. 2  is a vertical cross-sectional view of the first exemplary structure after application and lithographic patterning of a photoresist, and transfer of the pattern in the photoresist into the metallic hard mask layer and the dielectric cap layer according to the first embodiment of the present disclosure. 
         FIG. 3  is a vertical cross-sectional view of the first exemplary structure after removal of the photoresist, and transfer of the pattern in the metallic hard mask layer into the interconnect level dielectric layer according to the first embodiment of the present disclosure. 
         FIG. 4  is a vertical cross-sectional view of the first exemplary structure during an anisotropic etch of the nitrogen-containing dielectric layer according to the first embodiment of the present disclosure. 
         FIG. 5  is a vertical cross-sectional view of the first exemplary structure after the anisotropic etch according to the first embodiment of the present disclosure. 
         FIG. 6  is a vertical cross-sectional view of the first exemplary structure after removal of a polymer and deposition of a conductive material layer in a cavity within the stack of the nitrogen-containing dielectric layer, the interconnect level dielectric layer, the dielectric cap layer, and the metallic hard mask layer according to the first embodiment of the present disclosure. 
         FIG. 7  is a vertical cross-sectional view of the first exemplary structure after planarization of the deposited conductive material and removal of the metallic hard mask layer according to the first embodiment of the present disclosure. 
         FIG. 8  is a vertical cross-sectional view of the first exemplary structure after forming an overlying interconnect level structure according to the first embodiment of the present disclosure. 
         FIG. 9  is a vertical cross-sectional view of a second exemplary structure after formation of a via cavity according to a second embodiment of the present disclosure. 
         FIG. 10  is a vertical cross-sectional view of the second exemplary structure after applying and lithographically patterning a photoresist according to the second embodiment of the present disclosure. 
         FIG. 11  is a vertical cross-sectional view of the second exemplary structure after transfer of the pattern in the photoresist into a metallic hard mask layer, a dielectric cap layer, and an upper portion of the interconnect level dielectric layer to form a line cavity according to the second embodiment of the present disclosure. 
         FIG. 12  is a vertical cross-sectional view of the second exemplary structure during an anisotropic etch of the nitrogen-containing dielectric layer according to the second embodiment of the present disclosure. 
         FIG. 13  is a vertical cross-sectional view of the second exemplary structure after the anisotropic etch of the nitrogen-containing dielectric layer according to the second embodiment of the present disclosure. 
         FIG. 14  is a vertical cross-sectional view of the second exemplary structure after removal of a polymer and deposition of a conductive material in a line and via cavity within the stack of the nitrogen-containing dielectric layer, the interconnect level dielectric layer, the dielectric cap layer, and the metallic hard mask layer according to the second embodiment of the present disclosure. 
         FIG. 15  is a vertical cross-sectional view of the second exemplary structure after planarization of the deposited conductive material and removal of the metallic hard mask layer according to the second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As stated above, the present disclosure relates to methods for anisotropically etching a nitrogen-containing dielectric layer at low energy, and structures for effecting the same, which are now described in detail with accompanying figures. Throughout the drawings, the same reference numerals or letters are used to designate like or equivalent elements. The drawings are not necessarily drawn to scale. 
     Referring to  FIG. 1 , a first exemplary structure according to a first embodiment of the present disclosure includes a vertical material stack. The vertical material stack includes a substrate  10 , an optional underling metal interconnect level structure  200 , a nitrogen-containing dielectric layer  28 , an interconnect level dielectric layer  30 , a dielectric cap layer  32 , and a metallic hard mask layer  36 . 
     The substrate  10  can include a semiconductor material, an insulator material, a conductive material, or a combination thereof. The semiconductor material can be an elemental semiconductor material such as silicon, germanium, carbon, or an alloy thereof, a III-V compound semiconductor material, a II-VI compound semiconductor material, or any combination or stack thereof. The semiconductor material can be doped with electrical dopants such as B, Ga, In, P, As, and Sb. Multiple semiconductor materials can be present in the substrate. The insulator material can be doped or undoped silicon oxide, doped derivatives of silicon oxide, silicon nitride, silicon oxynitride, a dielectric metal oxide having a dielectric constant greater than 3.9, or a combination or stack thereof. Multiple insulator materials can be present in the substrate  10 . The conductive material can include a metallic material such as Cu, W, Ti, Ta, Al, WN, TiN, TaN, WC, TiC, TiC, or alloys thereof. The substrate  10  can include at least one semiconductor device (not shown) such as a field effect transistor, a junction transistor, a diode, a thyristor, a capacitor, an inductor, or any other semiconductor device or optical device known in the art. Further, the substrate  10  can include a contact-level dielectric material layer and contact via structures embedded therein. 
     If present, the optional underling metal interconnect level structure  200  includes at least one conductive structure  24  and at least one underlying dielectric layer in each line level and in each via level. The optional underlying metal interconnect level structure  200  can include one or more line levels and/or one or more via levels. Each line level includes at least one conductive line structure providing a lateral conductive path. Each via level includes at least one conductive via structure providing a vertical conductive path. The at least one conductive structure  24  includes the at least one conductive line structure in the one or more line levels, and the at least one conductive via structure in the one or more via levels. 
     The at least one underlying dielectric layer in a line level or in a via level can include doped or undoped silicon oxide (i.e., doped silicate glass or undoped silicate glass), silicon nitride, organosilicate glass that includes Si, C, O, H, and optionally N, a dielectric metal oxide, or a combination thereof. For example, an underlying dielectric layer can include a stack, from bottom to top, of an underlying silicon nitride layer  18 , an underlying interconnect level dielectric layer  20  including a porous or non-porous organosilicate glass, and a dielectric cap layer  22  including silicon nitride or a nitrogen-doped organosilicate glass. 
     The nitrogen-containing dielectric layer  28  includes a dielectric material that contains nitrogen. Exemplary dielectric materials that contain nitrogen that can be employed for the nitrogen-containing dielectric layer  28  include, but are not limited to, silicon nitride, silicon oxynitride, a dielectric material having a dielectric constant less than 3.9 and including nitrogen, a dielectric metal oxynitride, or a combination thereof. The thickness of the nitrogen-containing dielectric layer  28  can be from 1 nm to 30 nm, although lesser and greater thicknesses can also be employed. 
     Silicon nitride that can be employed for the nitrogen-containing dielectric layer  28  can be a stoichiometric silicon nitride having the atomic ratio of 3:4 between silicon and nitrogen, or can be a non-stoichiometric silicon nitride. The silicon nitride in the nitrogen-containing dielectric layer  28  can be formed, for example, by chemical vapor deposition (CVD), and may, or may not, be treated with ultraviolet radiation and/or with thermal treatment. 
     Silicon oxynitride that can be employed for the nitrogen-containing dielectric layer  28  has a composition of SiO x N y , in which x is a positive number greater than 0 and less than 2, and y is a positive number greater than 0 and less than 4/3. The silicon oxynitride in the nitrogen-containing dielectric layer  28  can be formed, for example, by deposition of a silicon oxynitride by chemical vapor deposition, by deposition of silicon nitride followed by thermal oxidation or plasma oxidation, or by deposition of silicon oxide followed by thermal nitridation or plasma nitridation. 
     Dielectric materials having a dielectric constant less than 3.9 are referred to as low dielectric constant (low-k) dielectric materials. Nitrogen-containing low-k dielectric materials that can be employed for the nitrogen-containing dielectric layer  28  include, but are not limited to, a nitrogen-containing organosilicate glass. The nitrogen-containing organosilicate glass includes Si, C, O, H, and N. An exemplary nitrogen-containing organosilicate glass is NBLoK™ that is commercially available from Applied Materials, Inc. The nitrogen-containing low-k dielectric material that is employed for the nitrogen-containing dielectric layer  28  can be deposited, for example, by chemical vapor deposition. 
     Dielectric metal oxynitrides that can be employed for the nitrogen-containing dielectric layer  28  include, but are not limited to, HfO x N y , ZrO x N y , La 2 O x N y , Al 2 O x N y , TiO x N y , SrTiO x N y , LaAlO x N y , Y 2 O x N y , and an alloy thereof. Each value of x is independently from 0.5 to 3 and each value of y is independently from 0 to 2. 
     The interconnect level dielectric layer  30  includes a dielectric material such as silicon oxide, silicon nitride, or a low-k dielectric material such as organosilicate glass including at least Si, C, O, and H, and optionally N. The silicon oxide includes spin-on-oxide (SOG), undoped silicon oxide (undoped silicate glass), and doped silicon oxide (i.e., doped silicate glass) such as fluorosilicate glass (FSG), phosphosilicate glass (PSG), borosilicate glass (BSG), and borophosphosilicate glass (BPSG). The interconnect level dielectric layer  30  can be deposited, for example, by plasma enhanced chemical vapor deposition (PECVD) or spin coating. The thickness of the interconnect level dielectric layer  30  can be from 30 nm to 600 nm, although lesser and greater thicknesses can also be employed. 
     In one embodiment, the interconnect level dielectric layer  30  includes a porous or non-porous organosilicate glass having a dielectric constant less than 2.8 and including Si, C, O, and H. The porous or non-porous organosilicate glass can be deposited, for example, by plasma enhanced chemical vapor deposition (PECVD). 
     The dielectric cap layer  32  includes a non-porous dielectric material such as silicon oxide, silicon nitride, silicon oxynitride, a dielectric metal oxide, or a combination thereof. The dielectric cap layer  32  can be formed, for example, by plasma enhanced chemical vapor deposition (PECVD). The thickness of the dielectric cap layer  32  can be from 5 nm to 300 nm, although lesser and greater thicknesses can also be employed. 
     The metallic hard mask layer  36  includes a metallic material such as WN, TiN, TaN, WC, TiC, TiC, or stacks or alloys thereof. The metallic dielectric cap layer  36  can be formed, for example, by physical vapor deposition (PVD) or chemical vapor deposition (CVD). The thickness of the metallic hard mask layer  36  can be from 5 nm to 300 nm, although lesser and greater thicknesses can also be employed. 
     Referring to  FIG. 2 , a photoresist  37  is formed either directly on the top surface of the metallic hard mask layer  36 . The photoresist  37  may be formed, for example, by spin coating. The photoresist  37  can be a deep ultraviolet (DUV) photoresist, a mid-ultraviolet (MUV) photoresist, an extreme ultraviolet (EUV) photoresist, or an electron beam (e-beam) photoresist. The material of the photoresist  37  reacts to illumination by light in a wavelength range or electron irradiation, and is chemically changed, for example, by cross-linking. The thickness of the photoresist  37  can be from 30 nm to 600 nm, and typically from 60 nm to 300 nm, although lesser and greater thicknesses can also be employed. 
     The photoresist  37  is lithographically exposed, and is subsequently developed. An opening having a first width w 1  is formed within the photoresist  37  after the lithographic exposure and development. A top surface of the metallic hard mask layer  36  is physically exposed at the bottom of the opening in the photoresist  37 . The pattern in the photoresist  37  includes, for example, an opening  39  having a first width w 1 , which is determined by the lithographic exposure conditions. 
     The pattern in the photoresist  37  is transferred into the metallic hard mask layer  36  and the dielectric cap layer  32  by at least one etch. The at least one etch can include an anisotropic etch such as a reactive ion etch, or an isotropic etch such as a wet etch. 
     In one embodiment, the pattern in the photoresist  37  is transferred into the metallic hard mask layer  36  by a first anisotropic etch that etches the metallic material of the metallic hard mask layer  36  employing the photoresist  37  as an etch mask. The pattern in the metallic hard mask layer  36  is then transferred into the dielectric hard mask layer  32  employing a second anisotropic etch that etches the dielectric material of the dielectric hard mask layer  32 . 
     The photoresist  37  is subsequently removed, for example, by ashing. 
     Referring to  FIG. 3 , an anisotropic etch is performed to transfer the pattern in the metallic hard mask layer  36  into the interconnect level dielectric layer  30 . An opening, which is herein referred to as a cavity  31 , having a second width w 2  and extending from the top surface of the metallic hard mask layer  36  to the bottom of the interconnect level dielectric layer  30 , is formed by the anisotropic etch. 
     The anisotropic etch can employ a plasma of etchants. The species for the etchants can be selected based on the composition of the dielectric material in the interconnect level dielectric layer  30  and the selectivity of the anisotropic etch to the metallic material of the metallic hard mask layer  36 , i.e., the ratio of the thickness of removed dielectric material(s) of the interconnect level dielectric layer  30  to the thickness of the removed metallic material(s) of the metallic hard mask layer  36 . In one embodiment, a selectivity greater than 10 can be achieved if the interconnect level dielectric layer  30  includes an organosilicate glass, and the metallic hard mask layer  36  includes a metallic nitride such as TaN, TiN, and/or WN and/or a metallic carbide such as TaC, TiC, and/or WC. 
     Referring to  FIG. 4 , the first exemplary structure is placed into a process chamber configured for a plasma etch, i.e., a reactive ion etch. An anisotropic etch employing a fluorohydrocarbon-containing plasma is performed on the first exemplary structure. The pattern in the metallic hard mask layer  36  is transferred into an upper portion of the nitrogen-containing dielectric layer  28  during the initial phase of the anisotropic etch. 
     The composition of the gas supplied into the process chamber includes one or more fluorohydrocarbon gas (hereafter referred to as “the fluorohydrocarbon gas”) having a composition of C x H y F z , wherein x is an integer selected from 3, 4, 5, and 6, y and z are positive integers, and y is greater than z. For example, the fluorohydrocarbon gas include one or more of C 3 H 5 F 3 , C 3 H 6 F 2 , C 3 H 7 F, C 3 H 4 F 2 , C 3 H 5 F, C 3 H 3 F, C 4 H 6 F 4 , C 4 H 7 F 3 , C 4 H 8 F 2 , C 4 H 9 F, C 4 H 5 F 3 , C 4 H 6 F 2 , C 4 H 7 F, C 4 H 4 F 2 , C 4 H 5 F, C 5 H 7 F 5 , C 5 H 8 F 4 , C 5 H 9 F 3 , C 5 H 10 F 2 , C 5 H 11 F, C 5 H 6 F 4 , C 5 H 7 F 3 , C 5 H 8 F 2 , C 5 H 9 F, C 5 H 5 F 3 , C 5 H 6 F 2 , C 5 H 7 F, C 6 H 8 F 6 , C 6 H 9 F 5 , C 6 H 10 F 4 , C 6 H 11 F 3 , C 6 H 12 F 2 , C 6 H 13 F, C 6 H 7 F 5 , C 6 H 8 F 4 , C 6 H 9 F 3 , C 6 H 10 F 2 , C 6 H 11 F, C 6 H 6 F 4 , C 6 H 7 F 3 , C 6 H 8 F 2 , and C 6 H 9 F. Correspondingly, the fluorohydrocarbon-containing plasma includes ions of C x H y F z . Optionally, the composition of the gas supplied into the process chamber can include O 2 , N 2 , Ar, CO, and/or CO 2 . In other words, the fluorohydrocarbon-containing plasma optionally includes a plasma of oxygen. 
     Non-limiting specific examples of C x H y F z , wherein x is an integer selected from 3, 4, 5, and 6, y and z are positive integers, and y is greater than z, include alkanes, alkenes, and alkynes. 
     In one embodiment, the fluorohydrocarbon gas can include one or more alkane fluorohydrocarbon gas having the formula of C x H y F z , wherein x is an integer selected from 3, 4, and 5, y and z are positive integers, and y is greater than z. The one or more alkane fluorohydrocarbon gas can include, but are not limited to: saturated liner fluorohydrocarbons shown by C 3 H 7 F such as 1-fluoropropane, 2-fluoropropane; saturated liner fluorohydrocarbons shown by C 3 H 6 F 2  such as 1,1-difluoropropane, 2,2-difluoropropane, 1,2-difluoropropane, 1,3-difluoropropane; saturated liner fluorohydrocarbons shown by C 3 H 5 F 3  such as 1,1,1-trifluoropropane, 1,1,2-trifluoropropane, 1,1,3-trifluoropropane, 1,2,2-trifluoropropane; saturated cyclic fluorohydrocarbon shown by C 3 H 5 F such as fluorocyclopropane; saturated cyclic fluorohydrocarbon shown by C 3 H 4 F 2  such as 1,2-difluorocycloproapne; saturated liner fluorohydrocarbons shown by C 4 H 9 F such as 1-fluorobutane, 2-fluorobutane; saturated liner fluorohydrocarbons shown by C 4 H 8 F 2  such as 1-fluoro-2-methylpropane, 1,1-difluorobutane, 2,2-difluorobutane, 1,2-difluorobutane, 1,3-difluorobutane, 1,4-difluorobutane, 2,3-difluorobutane, 1,1-difluoro-2-methylpropane, 1,2-difluoro-2-methylpropane, 1,3-difluoro-2-methylpropane; saturated liner fluorohydrocarbons shown by C 4 H 7 F 3  such as 1,1,1-trifluorobutane, 1,1,1-trifluoro-2-methylpropane, 1,1,2-trifluorobutane, 1,1,3-trifluorobutane, 1,1,4-trifluorobutane, 2,2,3-trifluorobutane, 2,2,4-trifluorobutane, 1,1,2-trifluoro-2-methylpropane; saturated liner fluorohydrocarbons shown by C 4 H 6 F 4  such as 1,1,1,2-tetrafluorobutane, 1,1,1,3-tetrafluorobutane, 1,1,1,4-tetrafluorobutane, 1,1,2,2-tetrafluorobutane, 1,1,2,3-tetrafluorobutane, 1,1,2,4-tetrafluorobutane, 1,1,3,3-tetrafluroobutane, 1,1,3,4-tetrafluorobutane, 1,1,4,4-tetrafluorobutane, 2,2,3,3-tetrafluorobutane, 2,2,3,4-tetrafluorobutane, 1,2,3,4-tetrafluorobutane, 1,1,1,2-tetrafluoro-2-methylpropane, 1,1,1,3-tetrafluoro-2-methylpropane, 1,1,2,3-tetrafluoro-2-methylpropane, 1,1,3,3-tetrafluoro-2-methylpropane; saturated cyclic fluorohydrocarbon shown by C 4 H 7 F such as fluorocyclobutane; saturated cyclic fluorohydrocarbons shown by C4H6F2 such as 1,1-difluorocyclobutane, 1,2-difluorocyclobutane, 1,3-difluorocyclobutane; saturated cyclic fluorohydrocarbon shown by C 4 H 5 F 3  such as 1,1,2-trifluorocyclobutane, 1,1,3-triflurocyclobutane; saturated liner fluorohydrocarbons shown by C 5 H 11 F such as 1-fluoropentane, 2-fluoropentane, 3-fluoropentane, 1-fluoro-2-methylbutane, 1-fluoro-3-methylbutane, 2-fluoro-3-methylbutane, 1-fluoro-2,2-dimethylpropane; saturated liner fluorohydrocarbons shown by C 5 H 10 F 2  such as 1,1-difluoropenatne, 2,2-difluoropentane, 3,3-difluoropentane, 1,2-difluoropentane, 1,3-difluoropentane, 1,4-difluoropentane, 1,5-difluoropentane, 1,1-difluoro-2-methylbutane, 1,1-difluoro-3-methylbutane, 1,2-difluoro-2-methylbutane, 1,2-difluoro-3-methylbutane, 1,3-difluoro-2-methylbutane, 1,3-difluoro-3-methylbutane, 1,4-difluoro-2-methylbutane, 2,2-difluoro-3-methylbutane, 2,3-difluoro-2-methylbutane, 1,1-difluoro-2,2-dimethylpropane, 1,3-difluoro-2,2-dimethylproapne, 1-fluoro-2-fluoromethylbutane; saturated liner fluorohydrocarbons shown by C 5 H 9 F 3  such as 1,1,1-trifluoropentane, 1,1,2-trifluoropentane, 1,1,3-trifluoropentane, 1,1,4-trifluoropentane, 1,1,1-trifluoro-2-methylbutane, 1,1,2-trifluoro2,3-dimethylpropane; saturated cyclic fluorohydrocarbons shown by C 5 H 9 F such as fluorocyclopentane, 1-fluoro-2-methylcyclobutane, 1-fluoro-3-methylcyclobutane, (fluoromethyl)-cyclobutane; saturated cyclic fluorohydrocarbons shown by C 5 H 8 F 2  such as 1,2-difluorocyclopentane, 1,3-difluorocyclopentane, 1,1-difluoro-2-methylcyclobutane, 1,1-difluoro-3-methylcyclobutane; saturated cyclic fluorohydrocarbons shown by C 5 H 7 F 3  such as 1,1,2-trifluorocyclopentane, 1,2,3,trifluorocyclopentane. 
     Additionally or alternatively, the fluorohydrocarbon gas can include one or more alkene fluorohydrocarbon gas having the formula of C x H y F z , wherein x is an integer selected from 3, 4, and 5, y and z are positive integers, and y is greater than z. The one or more alkene fluorohydrocarbon gas can include, but are not limited to: unsaturated liner fluorohydrocarbons shown by C 3 H 5 F such as 3-fluoropropene, 1-fluoropropene, 2-fluoropropene; unsaturated liner fluorohydrocarbons shown by C 3 H 4 F 2  such as 1,1-difluoropropene, 3,3-difluoropropene; unsaturated cyclic fluorohydrocarbons shown by C3H 3 F such as 3-fluorocyclopropene, 1-fluorocyclopropene; unsaturated liner fluorohydrocarbons shown by C 4 H 7 F such as 1-fluorobutene, 2-fluorobutene, 3-fluorobutene, 4-fluorobutene, 1-fluoro-2-butene, 2-fluoro-2-butene, 1-fluoro-2-methylpropene, 3-fluoro-2-methylpropene, 2-(fluoromethyl)-propene; unsaturated liner fluorohydrocarbons shown by C 4 H 6 F 2  such as 1,1-difluoro-2-methylpropene, 3,3-difluoro-2-methylpropene, 2-(fluoromethyl)-fluoropropene, 3,3-difluorobutene, 4,4-difluorobutene, 1,2-difluorobutene, 1,1-difluoro-2-butene, 1,4-difluoro-2-butene; unsaturated liner fluorohydrocarbons shown by C 4 H 5 F 3  such as 4,4,4-trifluorobutene, 3,3,4-trifluorobutene, 1,1,1-trifluoro-2-butene, 1,1,4-trifluoro-2-butene; unsaturated cyclic fluorohydrocarbons shown by C 4 H 5 F such as 1-fluorocyclobutene, 3-fluorocyclobutene; unsaturated cyclic fluorohydrocarbons shown by C 4 H 4 F 2  such as 3,3-difluorocyclobutene, 3,4-difluorocyclobutene; unsaturated liner fluorohydrocarbons shown by C 5 H 9 F such as 1-fluoropentene, 2-fluoropenten, 3-fluoropenten, 4-fluoropentene, 5-fluoropenten, 1-fluoro-2-pentene, 2-fluoro-2-pentene, 3-fluoro-2-pentene, 4-fluoro-2-pentene, 5-fluoro-2-pentene, 1-fluoro-2-methylbutene, 1-fluoro-3-methylbutene, 3-fluoro-2-methylbutene, 3-fluoro-3-methylbutene, 4-fluoro-2-methylbutene, 4-fluoro-3-methylbutene, 1-fluoro-2-methyl-2-butene, 1-fluoro-3-methyl-2-butene, 2-fluoro-3-methyl-2-butene, 2-(fluoromethyl)-butene; unsaturated liner fluorohydrocarbons shown by C 5 H 8 F 2  such as 3,3-difluoropentene, 4,4-difluoropentene, 5,5-difluoropentene, 1,2-difluoropentene, 3,4-difluoropentene, 3,5-difluoropentene, 4,5-difluoropentene; unsaturated cyclic fluorohydrocarbons shown by C 5 H 7 F such as 1-fluorocyclopentene, 3-fluorocylopentene, 4-fluorocyclopentene; unsaturated cyclic fluorohydrocarbons shown by C 5 H 6 F 2  such as 3,3-difluorocyclopentene, 4,4-difluorocyclopentene, 1,3-difluorocyclopentene, 1,4-difluorocyclopentene, 3,5-difluorocyclopentene. 
     Additionally or alternatively, the fluorohydrocarbon gas can include one or more alkyne fluorohydrocarbon gas having the formula of C x H y F z , wherein x is an integer selected from 3, 4, and 5, y and z are positive integers, and y is greater than z. The one or more alkyne fluorohydrocarbon gas can include, but are not limited to: unsaturated liner fluorohydrocarbon shown by C 3 H 3 F such as 3-fluoropropyne; unsaturated liner fluorohydrocarbon shown by C 3 H 2 F 2  such as 3,3-difluoropropyne; unsaturated liner fluorohydrocarbons shown by C 4 H 5 F such as 3-fluorobutyne, 4-fluorobutyne, 1-fluoro-2-butyne; unsaturated liner fluorohydrocarbons shown by C 4 H 4 F 2  such as 3,3-difluorobutyne, 4,4-difluorobutyne, 3,4-difluorobutyne, 1,4-difluoro-2-butyne; unsaturated liner fluorohydrocarbons shown by C 5 H 7 F such as 3-fluoropentyne, 4-fluoropentyne, 5-fluoropentyne, 1-fluoro-2-pentyne, 4-fluoro-2-pentyne, 5-fluoro-2-pentyne, 3-(fluoromethyl)-butyne; unsaturated liner fluorohydrocarbons shown by C 5 H 6 F 2  such as 3,3-difluoropentyne, 4,4-difluoropentyne, 5,5-difluoropentyne, 3,4-difluoropentyne, 4,5-difluoropentyne, 1,1-difluoro-2-pentyne, 4,4-difluor-2-pentyne, 5,5-difluoro-2-pentyne, 4,5-difluoro-2-pentyne, 3-(difluoromethyl)-butyne, 3-(fluoromethyl)-4-fluorobutyne. 
     The fluorohydrocarbon-containing plasma generates a fluorohydrocarbon-containing polymer during the anisotropic etch. The fluorohydrocarbon-containing polymer is deposited on the recessed surface of the nitrogen-containing dielectric layer  28  to form a first fluorohydrocarbon-containing polymer portion  29 , and on the top surface of the metallic hard mask layer  36  to form a second fluorohydrocarbon-containing polymer portion  23 . The fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  includes carbon, hydrogen, and fluorine. The atomic concentration of carbon in the fluorohydrocarbon-containing polymer is greater than the atomic concentration of fluorine in the fluorohydrocarbon-containing polymer. 
     The atomic concentration of carbon is greater than the atomic concentration of fluorine in the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23 . In other words, the atomic ratio of carbon to fluorine is greater than 1 in the fluorohydrocarbon-containing polymer. Thus, the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  is a “carbon-rich” polymer. As used herein, a fluorohydrocarbon-containing polymer is “carbon-rich” if the atomic concentration of carbon is greater than the atomic concentration of fluorine. 
     The fluorohydrocarbon-containing polymer includes hydrogen at an atomic concentration that is at least one half of the atomic concentration of carbon in the carbon-rich fluorohydrocarbon-containing polymer  33 . In one embodiment, the atomic ratio of hydrogen to carbon in the fluorohydrocarbon-containing polymer is between 0.5 and 3.0. 
     The fluorohydrocarbon-containing polymer is a carbon-based polymer, i.e., more than 10% of all bonds therein are bonded to at least one carbon atom. In one embodiment, the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  includes carbon at an atomic concentration between 30% and 40%, hydrogen at an atomic concentration between 40 and 50%, fluorine at an atomic concentration between 5.0% and 10.0%, and oxygen at an atomic concentration less than 5%. 
     The physically exposed portion of the nitrogen-containing dielectric layer  28  is anisotropically etched underneath the cavity  31  by the fluorohydrocarbon-containing plasma. An opening, i.e., the cavity  31 , is present within the metallic hard mask layer  36 , the dielectric cap layer  32 , and the interconnect level dielectric layer  30  and extends downward into at least the upper portion of the nitrogen-containing dielectric layer  28 . The fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  reacts with nitrogen atoms in the nitrogen-containing dielectric layer  22  to form a nitrogen-containing volatile compound. As used herein, a compound is “volatile” if it evaporates in vacuum at 297.3 K. The nitrogen-containing volatile compound is formed on, volatilizes at, and evaporates from, the recessed surface of the nitrogen-containing dielectric layer  28 . The nitrogen-containing volatile compound includes nitrogen derived from the nitrogen-containing dielectric layer and the carbon-rich fluorohydrocarbon-containing polymer of the first fluorohydrocarbon-containing polymer portion  29 , which includes carbon and fluorine and has an atomic ratio of carbon to fluorine that is greater than 1. 
     The nitrogen-containing volatile compound has a general formula of C i H j F k N l , wherein i, j, k, and l are integers. The value for i can be from 1 to 6, the value for j can be from 0 to 8, the value for k can be from 0 to 6, and the value for 1 can be from 0 to 4, although lesser and greater values can be employed for each of i, j, k, and l. The nitrogen-containing volatile compound volatilizes, and is removed from, the recessed surface of the nitrogen-containing dielectric layer  22 . In contrast, the fluorohydrocarbon-containing polymer in the second fluorohydrocarbon-containing polymer portion  23  does not react with the underlying metallic material of the metallic hard mask layer  36 . The second fluorohydrocarbon-containing polymer portion  23  includes the same carbon-rich fluorohydrocarbon-containing polymer as the first fluorohydrocarbon-containing polymer portion  29 , and does not include nitrogen. 
     Thus, the average thickness of the first fluorohydrocarbon-containing polymer portion  29  saturates at a steady-state thickness, which is herein referred to as a first thickness. The first thickness is typically from 0.2 nm to 1.0 nm, although lesser and greater thicknesses can also be employed depending on the composition and energy of the fluorohydrocarbon-containing plasma. Because the fluorohydrocarbon-containing polymer in the second fluorohydrocarbon-containing polymer portion  23  does not react with the underlying metallic material of the metallic hard mask layer  36 , the average thickness of the second fluorohydrocarbon-containing polymer portion  23  tends to continually increase with the progression of the anisotropic etch, or saturates at a thickness that is greater than the first thickness. The saturation value for the second thickness can be from 1 nm to 3 nm, although the saturation value can be lesser or greater depending on the composition and energy of the fluorohydrocarbon-containing plasma. The second thickness is greater than the first thickness throughout the duration of the anisotropic etch. 
     The quantity of the fluorohydrocarbon-containing polymer generated in this anisotropic etch tends to be profuse relative to conventional plasma processes employing ions of CF 4  or CHF 3  having comparable kinetic energy for the plasma because the source gases have a high atomic percentage of carbon and a high atomic percentage of hydrogen relative to CF 4  or CHF 3  employed in conventional anisotropic etch processes. For example, the quantity of the fluorohydrocarbon-containing polymer generated in this anisotropic etch is at least twice as much as, and in some embodiments ten or more times as much as, the amount of polymer generated in conventional plasma processes employing ions of CF 4  or CHF 3  having comparable kinetic energy. Thus, the energy of the fluorohydrocarbon-containing plasma of the present disclosure can be significantly lowered relative to the energy employed for conventional anisotropic etch processes. Specifically, while conventional plasma requires minimum ion energy of 200 eV, the ions in the fluorohydrocarbon-containing plasma of the present disclosure can have an energy less than 200 eV. The ions in the fluorohydrocarbon-containing plasma of the present disclosure can have an average kinetic energy between 10 eV and 1 keV. In one embodiment, the ions in the fluorohydrocarbon-containing plasma of the present disclosure can have an average kinetic energy in a range from 10 eV to 100 eV. 
     Due to the high carbon content and the high hydrogen content in the source gas(es) of the fluorohydrocarbon-containing plasma relative to the carbon content and the hydrogen content of conventional plasmas of CF 4  or CHF 3 , the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  has different properties than polymers deposited in a plasma etch process employing CF 4  or CHF 3 . For example, the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  has a refractive index in a range from 1.8 to 2.2, while polymers deposited in a plasma etch process employing CF 4  or CHF 3  have a refractive index in a range from 1.4-1.7. Further, the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  has a density in a range from 1.5 g/cm 3  to 1.8 g/cm 3 , while polymers deposited in a plasma etch process employing CF 4  or CHF 3  have a density greater than 1.7 g/cm 3  to 2.0 g/cm 3 . In one embodiment, the fluorohydrocarbon-containing polymer in the first fluorohydrocarbon-containing polymer portion  29  and the second fluorohydrocarbon-containing polymer portion  23  has a density in a range from 1.5 g/cm 3  to 1.7 g/cm 3 . 
     In one embodiment, the interconnect level dielectric layer  30  includes a low-k dielectric material such as organosilicate glass, and the fluorohydrocarbon-containing plasma causes a structural damage to the physically exposed surfaces of the low-k dielectric material. Specifically, the chemical bonds among the molecules of the low-k dielectric material are partially damaged, and fluorine can be incorporated into the low-k dielectric material during the anisotropic etch to convert a vertical surface portion of the interconnect level dielectric layer  30  laterally surrounding the cavity  31  into a fluorine-containing damaged low-k material portion  33 . The thickness t of the fluorine-containing damaged low-k material portion  33  can be from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. Due to the carbon-rich nature of the polymer, the thickness of the fluorine-containing damaged low-k material portion  33  is less than a thickness of a damaged low-k material portion formed in an anisotropic etch process employing a comparable CF 4  and/or CHF 3  plasmas. 
     Referring to  FIG. 5 , the transfer of the pattern in metallic hard mask layer  36  proceeds to the bottom surface of the nitrogen-containing dielectric layer  28  as the anisotropic etch continues until a top surface of the substrate  10  or a top surface of the optional underlying metal interconnect level structure  200  is exposed. The substrate  10  or the optional underlying metal interconnect level structure  200  can be employed as an etch stop layer for the anisotropic etch. For example, the change in the composition of the ions in the fluorohydrocarbon-containing plasma that accompanies physical exposure of the top surface of the substrate  10  or the optional underlying metal interconnect level structure  200  can be detected by optical means, and employed as a signal that triggers an immediate termination, or a delayed termination (after an overetch), of the anisotropic etch. 
     The cavity  31  may be a line trench that defines the spatial extent of a conductive line structure to be subsequently formed, or may be a via hole that defines the spatial extent of a conductive via structure to be subsequently formed. A plurality of cavities  31  can be formed in the stack of the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 . 
     Referring to  FIG. 6 , any remaining polymer at the end of the anisotropic etch is removed, for example, by a wet clean. A conductive material layer  34 L is deposited in the cavity  31  within the stack of the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 , for example, by electroplating, electroless plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), or a combination thereof. The conductive material layer  34 L includes at least one metallic material such as Cu, Al, W, TiN, TaN, WN, TiC, TaC, WC, and combinations thereof. The deposited conductive material of the conductive material layer  34 L completely fills the cavity  31  within the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 . 
     Referring to  FIG. 7 , the excess conductive material above the top surface of the dielectric cap layer  32  and the metallic hard mask layer  36  are removed, for example, by chemical mechanical planarization (CMP). The dielectric cap layer  32  can be employed as a stopping layer for the planarization process. The remaining portion of the conductive material layer  34 L after planarization constitutes a metal interconnect structure  34 , which can be a conductive line or a conductive via depending the lateral extent of the conductive material layer  34 L and the topological features of the conductive material layer  34 L with respect to the underlying at least one conductive structure  24  in the optional underling metal interconnect level structure  200 , if present, and with respect to overlying conductive structures that may be optionally formed. 
     Referring to  FIG. 8 , an overlying interconnect level structure  500  can be optionally formed. The overlying interconnect level structure  500  can include, for example, an overlying nitrogen-containing dielectric layer  38 , an overlying interconnect level dielectric layer  50 , an overlying dielectric layer  52 , and an overlying metal interconnect structure  54 . The overlying interconnect level structure  500  can be formed, for example, employing the same methods as in the processing steps of  FIGS. 2-7 . 
     Referring to  FIG. 9 , a second exemplary structure according to a second embodiment of the present disclosure can be derived from the first exemplary structure of  FIG. 1 , and by modifying the processing steps of  FIG. 2  such that the cavity  31  does not extend to the top surface of the nitrogen-including dielectric layer  28  at the end of the pattern transfer from the photoresist  37  to the upper portion of the interconnect level dielectric layer  30 . The cavity  31  as formed within the second exemplary structure is herein referred to as a via cavity  31 ′. Thus, there is a finite distance between the bottom surface of the via cavity  31 ′ and the top surface of the nitrogen-containing dielectric layer  28  after removal of the photoresist  37  at the processing step corresponding to the processing step of  FIG. 3 . The vertical distance between the topmost surface of the interconnect level dielectric layer  30  and the bottom surface of the via cavity  31 ′ can be from 15% to 85% of the vertical distance between the topmost surface of the interconnect level dielectric layer  30  and the bottommost surface of the interconnect level dielectric layer  30 . The width of the via cavity  31 ′ at the end of the etch is herein referred to as a via width wv. The pattern of the via cavity  31 ′ can be selected to define an area of a conductive via structure to be subsequently formed. 
     Referring to  FIG. 10 , another photoresist  47  is applied over the second exemplary structure, and is lithographically patterned to form an opening  49  in the photoresist  47 . The opening  49  overlies the cavity  31 , and the area of the opening  49  may include the entirety of the area of the cavity  31 . The width of the opening  49  is herein referred to as a line width wl. The pattern of the opening  49  can be selected to define an area of a conductive line structure to be subsequently formed. 
     Referring to  FIG. 11 , an anisotropic etch is performed to transfer the pattern in the metallic hard mask layer  36  into an upper portion of the interconnect level dielectric layer  30  to form a line cavity  41 . At the same time, the anisotropic etch also recesses the bottom surface of the via cavity  31 ′. A dual damascene integrated cavity including the line cavity  41  and the via cavity  31 ′ is formed within the material stack of the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 . A planar bottom surface of the line cavity  41  can be located at a level between the bottommost surface of the interconnect level dielectric layer  30  and the topmost surface of the interconnect level dielectric layer  30 . 
     The anisotropic etch can employ a plasma of etchants as in the first embodiment. The species for the etchants can be selected based on the composition of the dielectric material in the interconnect level dielectric layer  30  and the selectivity of the anisotropic etch to the metallic material of the metallic hard mask layer  36 . In one embodiment, a selectivity greater than 10 can be achieved if the interconnect level dielectric layer  30  includes an organosilicate glass, and the metallic hard mask layer  36  includes a metallic nitride such as TaN, TiN, and/or WN and/or a metallic carbide such as TaC, TiC, and/or WC. 
     Referring to  FIG. 12 , the second exemplary structure is placed into a process chamber configured for a plasma etch. An anisotropic etch employing a fluorohydrocarbon-containing plasma is performed on the second exemplary structure. The pattern in the via cavity  31 ′ is transferred into an upper portion of the nitrogen-containing dielectric layer  28  during the initial phase of the anisotropic etch. 
     The same fluorohydrocarbon-containing plasma can be employed as in the first embodiment. Thus, a first fluorohydrocarbon-containing polymer portion  29  is formed on a recessed surface of the nitrogen-containing dielectric layer  28 , and a second fluorohydrocarbon-containing polymer portion  23  is formed on the top surface of the metallic hard mask layer  36 . The composition and physical properties of the first fluorohydrocarbon-containing polymer portion  29  and second fluorohydrocarbon-containing polymer portion  23  are the same as in the first embodiment. Thus, the same nitrogen-containing volatile compound is formed in the second fluorohydrocarbon-containing polymer portion  23  by the reaction of the nitrogen atoms from the nitrogen-containing dielectric layer  28  and the carbon-rich fluorohydrocarbon-containing polymer present within the first fluorohydrocarbon-containing polymer portion  29 . 
     In one embodiment, the interconnect level dielectric layer  30  includes a low-k dielectric material such as organosilicate glass, and the fluorohydrocarbon-containing plasma causes a structural damage to the physically exposed surfaces of the low-k dielectric material. Thus, fluorine can be incorporated into the low-k dielectric material of the interconnect level dielectric layer  30  during the anisotropic etch to convert a vertical surface portion of the interconnect level dielectric layer  30  around the line cavity  41  to form an upper vertical fluorine-containing damaged low-k material portion  43 , a horizontal surface portion of the interconnect level dielectric layer  30  at the bottom of the line cavity  41  to form a horizontal fluorine-containing damaged low-k material portion  35 , and a vertical surface portion of the interconnect level dielectric layer  30  around the via cavity  31 ′ to form a lower vertical fluorine-containing damaged low-k material portion  33 ′, respectively. The thickness t of the various fluorine-containing damaged low-k material portions ( 43 ,  35 ,  33 ′) can be from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. Because of the carbon rich nature of the CHF ion and the lower energy, the thickness of the horizontal fluorine-containing damaged low-k material portion  35  is lesser than a thickness of damaged low-k material regions formed in an anisotropic etch process employing a comparable CF 4  and/or CHF 3  plasmas. 
     Referring to  FIG. 13 , the transfer of the pattern in the via cavity  31 ′ into the nitrogen-containing dielectric layer  28  proceeds to the bottom surface of the nitrogen-containing dielectric layer  28  as the anisotropic etch continues until a top surface of the substrate  10  or a top surface of the optional underlying metal interconnect level structure  200  is exposed. The substrate  10  or the optional underlying metal interconnect level structure  200  can be employed as an etch stop layer for the anisotropic etch. For example, the change in the composition of the ions in the fluorohydrocarbon-containing plasma that accompanies physical exposure of the top surface of the substrate  10  or the optional underlying metal interconnect level structure  200  can be detected by optical means, and employed as a signal that triggers an immediate termination, or a delayed termination (after an overetch), of the anisotropic etch. A plurality of dual damascene integrated cavities ( 41 ,  31 ′) can be formed in the stack of the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 . 
     Referring to  FIG. 14 , any remaining polymer at the end of the anisotropic etch is removed, for example, by a wet clean. A conductive material layer  34 L is deposited in the cavity  31  within the stack of the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 , for example, by electroplating, electroless plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), or a combination thereof. The conductive material layer  34 L includes at least one metallic material such as Cu, Al, W, TiN, TaN, WN, TiC, TaC, WC, and combinations thereof. The deposited conductive material of the conductive material layer  34 L completely fills the dual damascene integrated cavity ( 41 ,  31 ′) within the nitrogen-containing dielectric layer  28 , the interconnect level dielectric layer  30 , the dielectric cap layer  32 , and the metallic hard mask layer  36 . 
     Referring to  FIG. 15 , the excess conductive material above the top surface of the dielectric cap layer  32  and the metallic hard mask layer  36  are removed, for example, by chemical mechanical planarization (CMP). The dielectric cap layer  32  can be employed as a stopping layer for the planarization process. The remaining portion of the conductive material layer  34 L after planarization constitutes a metal interconnect structure  34 , which is an integrated line and via structure. 
     While the disclosure has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the disclosure is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the disclosure and the following claims.