Abstract:
Novel methods of double patterning a photosensitive resin composition are provided. The methods involve applying the photosensitive composition to a substrate and thermally crosslinking the composition. The crosslinked layer can be used to provide reflection control. Upon exposure to light, the crosslinked polymer (or oligomer or monomer) in the compositions will decrosslink, rendering the light-exposed portions soluble in typical photoresist developing solutions (e.g., alkaline developers). Advantageously, the crosslinked portions of the composition remain insoluble in the solvent used to form the photosensitive composition. As a result, the coating, lithographic, and or developing steps can be repeated multiple times in varying order, depending upon the particular process, without destroying earlier-formed patterns.

Description:
RELATED APPLICATIONS 
     This application claims the priority benefit of a provisional application entitled ANTI-REFLECTIVE IMAGING LAYER FOR MULTIPLE PATTERNING PROCESS, Ser. No. 60/822,823, filed Aug. 18, 2006, incorporated by reference herein 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with novel, double patterning methods that utilize a thermally crosslinkable, photosensitive composition. 
     2. Description of the Prior Art 
     Trends toward improving the photolithography process include the use of high numerical aperture (NA) tools and/or immersion fluids. Using imaging tools with high NA capabilities (&gt;1.0) by themselves or in combination with immersion provides a method to achieve higher resolution of patterns with smaller critical dimension and higher density. These advances are possible because of the larger amount of light that can be transferred to the imaging layer. However, these options are quite costly and require new tool sets. 
     Multi-patterning techniques, have been used to attempt to achieve high-density lithography. However, these are lacking in that photoresist patterns are destroyed by repeated photoresist applications. 
     There is a need for improved methods to allow higher-density patterning utilizing presently available equipment. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes these problems by broadly providing a method of forming a microelectronic structure. The method comprises applying a photosensitive composition to the surface of a substrate to form an imaging layer adjacent the substrate surface. The components (e.g., polymers, oligomers, compounds) in the imaging layer are then crosslinked, and the layer is exposed to light to yield light-exposed portions in said layer that have been chemically modified as a result of this light exposure. The imaging layer is contacted with a developer, preferably an aqueous alkaline developer, so as to remove the light-exposed portions from the substrate and form a patterned imaging layer. 
     A second photosensitive composition is then added to form a second imaging layer on the patterned imaging layer. This is accomplished without first heating the patterned imaging layer, which would have been essential in prior art processes. That second imaging layer can then be patterned and developed, and this coating/patterning/developing process can be repeated multiple times if desired. After the process has been repeated sufficiently to form the desired pattern in the imaging layer, that pattern can be transferred to the substrate. 
     In another embodiment, the crosslinked imaging layer is exposed to light to yield the light-exposed portions in said layer. Then, the layer is subjected to one or more additional light-exposure steps, with each step yielding more light-exposed portions in the imaging layer. After the desired exposures have occurred, a single development step can be carried out to remove all light-exposed portions, yielding a patterned imaging layer that can ultimately be transferred to the substrate. Alternatively, a development step can be carried out after each light exposure step in order to remove the light-exposed portions prior to the next light exposure step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing illustrating a process according to the invention 
         FIG. 2  is a schematic drawing illustrating a second embodiment of the inventive process; and 
         FIG. 3  is a schematic drawing illustrating a third embodiment of the inventive process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Inventive Method 
       FIG. 1  illustrates one embodiment of the inventive process. A substrate  10  having an upper surface  12  is provided. Any conventional microelectronic substrate can be utilized, including substrates comprising one or more of the following: silicon, aluminum, tungsten, tungsten silicide, gallium arsenide, germanium, tantalum, tantalum nitride, SiGe, and mixtures of the foregoing. 
     As shown in step (a), a thermally crosslinkable and photochemically decrosslinkable composition is applied to the surface  12  to form an imaging layer  14  having an upper surface  16 . The composition can be applied by any known application method, with one preferred method being spin-coating the composition at speeds of from about 750 rpm to about 3,500 rpm (preferably from about 1,000 rpm to about 2,500 rpm) for a time period of from about 10 seconds to about 120 seconds (preferably from about 20 seconds to about 60 seconds). 
     The layer  14  is then baked so as to induce thermal crosslinking of the layer  14 . Preferred baking conditions involve temperatures of at least about 100° C., preferably from about 100° C. to about 250° C., and more preferably from about 120° C. to about 200° C., and for time periods of from about 10 seconds to about 90 seconds. The thickness of the crosslinked imaging layer  14  will typically be from about 10 nm to about 150 nm, and preferably from about 30 nm to about 80 nm. 
     The crosslinked layer  14  will be sufficiently crosslinked that it will be substantially insoluble in typical photoresist solvents (including the solvent that was present in the photosensitive composition used to form layer  14 ). Thus, when subjected to a stripping test, the crosslinked layers  14  will have a percent stripping of less than about 5%, preferably less than about 1%, and even more preferably about 0%. The stripping test involves first determining the thickness (by taking the average of measurements at five different locations) of the cured layer. This is the initial average film thickness. Next, a solvent (e.g., ethyl lactate, PGME, PGMEA) is puddled onto the cured film for about 10 seconds, followed by spin drying at about 2,000-3,500 rpm for about 20-30 seconds to remove the solvent. The thickness is measured again at five different points on the wafer using ellipsometry, and the average of these measurements is determined. This is the average final film thickness. 
     The amount of stripping is the difference between the initial and final average film thicknesses. The percent stripping is: 
     
       
         
           
             
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     In the embodiment of  FIG. 1 , the best use of layer  14  would typically be simply as an imaging layer. In these instances, the k value (imaginary component of the complex index of refraction) is preferably from about 0 to about 0.5. 
     At step (b), a mask  18  is positioned above the surface  16  of imaging layer  14 , and light  20  is directed at the mask  18 . The mask  18  has open areas  22  designed to permit light to pass by the mask  18  and contact surface  16  of imaging layer  14 . The remaining solid portions  24  of mask  18  are designed to prevent light from contacting surface  16  of imaging layer  14  in certain areas. Those skilled in the art will readily understand that the arrangement of open areas  22  and solid portions  24  is designed based upon the desired pattern to be formed in imaging layer  14  and ultimately in the substrate surface  12 . The present inventive process can be used with UV light of most wavelengths, but wavelengths of 157 nm, 193 nm, 248 nm, and 365 nm are most preferred. 
     Upon being exposed to light, the portions  26  of the imaging layer  14  that are exposed to light undergo a photochemical reaction so that the layer  14  is photochemically decrosslinked. More specifically, an acid is generated from the PAG upon exposure to light, and this acid “decrosslinks” the polymer, oligomer, or compound in the layer. That is, the acid catalyzes the breaking of the bond that was formed between the polymer, oligomer, or compound and the crosslinker upon thermal crosslinking. After light exposure the imaging layer  14  is preferably subjected to a post-exposure bake (as used herein, post-exposure bakes are carried out at a temperature of less than about 150° C., preferably less than about 140° C., and more preferably from about 90° C. to about 140° C. for a time period of from about 30 seconds to about 90 seconds). 
     Advantageously, the light-exposed portion  26 , which was made developer soluble with the above steps, is contacted with a developer as shown in step (c). The developer removes the portions  26  of imaging layer  14  to leave behind openings  28 . Openings  28  can be holes, trenches, spaces, etc., and will ultimately be transferred to the substrate  10 . “Developer soluble” as used herein means the portions  26  that have been exposed to light can be substantially removed with conventional aqueous developers such as tetramethyl ammonium hydroxide and KOH developers. At least about 95%, preferably at least about 99%, and even more preferably 100% of the portions will be removed by a base developer such as tetramethyl ammonium hydroxide and/or KOH developers. 
     The inventive process is particular advantageous in that it is a double-patterning process. That is, the stack  30  that has been coated, subjected to lithography, and developed, can now be coated, subjected to lithography, and developed again to create further patterns, Referring to step (d), a thermally crosslinkable and photochemically decrosslinkable composition is applied to form a second imaging layer  32  having an upper surface  34 . Because the imaging layer  14  was crosslinked, this second coating step is possible while still maintaining the previously-formed pattern intact. Furthermore, this layer remains intact without requiring an additional heating (hardening) step to be carried out on the imaging layer  14 . So, in this embodiment and in all embodiments of this application, the only heating steps occur during thermal crosslinking and during any post-exposure bakes. 
     The composition application would be similar to that described above with respect to step (a). Furthermore, one would typically use the same thermally crosslinkable and photochemically decrosslinkable composition used in the earlier step (a), but this is not required, and different compositions (e.g., a conventional photoresist for the second photosensitive composition) could be used if desired. The same baking conditions would be followed as described in step (a), and the thickness “T” of the second imaging layer  32  on top of the highest remaining portion of imaging layer  14  would also be the same as described above with step (a). 
     In step (e), a mask  36  having the desired pattern formed therein is positioned over surface  34  of second imaging layer  32 , and light exposure is repeated as described in step (b) above. Exposed portions  38  are formed in second imaging layer  32 , and the stack  40  is preferably subjected to a post-exposure bake followed by contact with a developer (step (f)). This results in the removal of exposed portions  38  to leave behind openings  42 . Again, these openings  42  can be holes, trenches, or spaces. The raised portions  44  remaining on substrate surface  12  are typically referred to as lines or raised features. This pattern of holes, trenches, spaces, lines, and raised features will ultimately be transferred to the substrate  10 . 
     The above coating, baking, light exposure, optional post-exposure baking, and developing steps can be repeated as many more times as desired and as is feasible for the particular pattern  46  to be formed in substrate surface  12 . The stack  48 , which comprises substrate  10  and pattern  46  on substrate surface  12 , is then subjected to an etching process (e.g., plasma etch), whereby the pattern  46  is transferred to the substrate  10 , so that substrate  10  now includes the openings  42  and portions  44  formed therein. It will be appreciated that it is not necessary to perform any etching steps prior to this point in the process. That is, steps (a)-(f) are carried out without any etching occurring. Half pitch dimensions of less than about 50 nm can be achieved with this method. The patterned substrate is then subjected to further fabrication steps (e.g., metallization). 
       FIG. 2  illustrates a second embodiment of the inventive process. Like numbering is used for all embodiments to designate similar materials. The same process conditions (e.g., spin speeds, temperatures, time periods, wavelengths) as well as compositions, substrates, developers, and masks used as in  FIG. 1  would be used in this embodiment. 
     In the embodiment of  FIG. 2 , a photoresist  45  having an upper surface  47  is applied (e.g., via spin-coating) to the upper surface  16  of imaging layer  12  after thermal crosslinking of imaging layer  12 . During exposure step (b), the light also chemically alters portion  27  of resist  45  to make it more soluble in typical developers. After this exposure step (b) (and the optional post-exposure bake), the stack is not developed but is instead immediately subjected to a second exposure step (c), where another mask  36  is utilized to create the second pattern in imaging layer  26  and photoresist  45 . This could be followed with more exposure steps with other masks, if desired. Once the desired number of exposure steps has been carried out, the imaging layer  14  and photoresist  45  are developed (step (d)) to yield patterned layer  46 . Conventional etching, metallization, etc., can then be carried out to complete the device manufacture. 
     In the embodiment of  FIG. 3 , a photoresist  45  is also utilized as was the case in  FIG. 2 . After exposure step (b), the stack is developed (step (c)) similar to the embodiment of  FIG. 1 . However, rather than being subjected to a second coating step as was done in the embodiment of  FIG. 1 , imaging layer  14  and the photoresist  45  are subjected to a second exposure step (d) with a second mask  36  to expose other portions of layer  14  and resist  45  to light. After this exposure, the imaging layer  14  and resist  45  are subjected to a second developing step (e) to further pattern the layers. This exposure-develop sequence can be repeated as many times as desired, after which the stack  48  is etched to transfer the pattern to the substrate  10 , followed by subsequent processing such as metallization. 
     In the embodiments of  FIGS. 2 and 3 , it will again be appreciated that it is not necessary to perform any etching steps prior to this point in the process. That is, steps (a)-(d) of  FIG. 2  and steps (a)-(e) of  FIG. 3  are carried out without any etching occurring. Furthermore, the process can be repeated with multiple photoresist layers (of the same or different chemical composition) as desired for the particular process. 
     In the embodiments of  FIGS. 2 and 3 , the layer  14  would typically be functioning as a bottom anti-reflective coating. In these instances, the crosslinked layers will be formulated to provide superior light absorbance. The n value of the crosslinked layer  14  would be at least about 1.3, and preferably from about 1.4 to about 2.0, while the k value will be least about 0.1, and preferably from about 0.2 to about 0.5, at the wavelength of use (e.g., 157 nm, 193 nm, 248 nm, 365 nm). The OD of the cured layers will be at least about 5/μm, preferably from about 5-15/μm, and even more preferably from about 10-15 μm, at the wavelength of use (e.g., 157 nm, 193 nm, 248 nm, 365 nm). 
     When being used as a bottom anti-reflective coating, it is preferred that the compositions be applied in quantities such that the thickness of the layer  14  after curing or crosslinking will be within about 20% of the first maximum thickness of the composition. The first maximum thickness of a composition is defined as: 
                 First   ⁢           ⁢   Maximum   ⁢           ⁢   Thickness     =     λ     2   ⁢   n         ,         
where λ is the wavelength of use, and n is the real component of the refractive index of the composition. Even more preferably, the thickness of the crosslinked layer  14  is within about 15%, even more preferably within about 10%, and even more preferably within about 5% of the first maximum thickness of the composition. The use of the photosensitive composition at these thicknesses results in improved properties, including the ability to print structures with critical dimension control and to provide adequate coverage for reflection control over topography.
 
     Compositions for Use in the Invention Method 
     As mentioned above, the composition used for the present process should be thermally crosslinkable and photosensitive (i.e., photochemically decrosslinkable). The preferred compositions will comprise a crosslinkable polymer, oligomer, and/or monomer dissolved or dispersed in a solvent system along with a photoacid generator (PAG) a crosslinker (referred to interchangeably with crosslinking agent). 
     Suitable polymers include those selected from the group consisting of aliphatic polymers, acrylates, methacrylates, polyesters, polycarbonates, novolaks, polyamic acids, polysulfonyl esters, polycarbonate-sulfones (i.e., polymers which include recurring monomers having both an —SO 2  group and a —CO 3  group), and mixtures thereof. Suitable solvent systems, crosslinkers, PAGs, and ingredient quantities include any of those discussed below. 
     One suitable composition is disclosed in U.S. patent application Ser. No. 11/683,309, incorporated by reference here. This type of composition comprises a compound selected from the group consisting of polymers, oligomers, and mixtures thereof dissolved or dispersed in a solvent system. The compound is preferably present in the composition at a level of from about 0.5-10% by weight, preferably from about 0.5-5% by weight, and more preferably from about 1-4% by weight, based upon the total weight of all ingredients in the composition taken as 100% by weight. 
     If the compound is a polymer, it is preferred that the average molecular weight be from about 1,000-100,000 Daltons, and more preferably from about 1,000-25,000 Daltons. Preferred polymers include those selected from the group consisting of aliphatic polymers, acrylates, methacrylates, polyesters, polycarbonates, novolaks, polyamic acids, and mixtures thereof. 
     If the compound is an oligomer, it is preferred that the molecular weight be from about 500-3,000 Daltons, and more preferably from about 500-1,500 Daltons. Preferred oligomers include substituted and unsubstituted acrylates, methacrylates, novolaks, isocyanurates, glycidyl ethers, and mixtures thereof. 
     Regardless of whether the compound is an oligomer or polymer, and regardless of the structure of the polymer backbone or oligomer core, it is preferred that the compound comprise an acid functional group. The acid group is preferably present in the compound at a level of at least about 5% by weight, preferably from about 5-90% by weight, and even more preferably from about 5-50% by weight, based upon the total weight of the compound taken as 100% by weight. Preferred acid groups are groups other than phenolics, such as carboxylic acids (—COOH). 
     Unlike prior art compositions, the acid group is preferably not protected by a protective group. That is, at least about 95%, preferably at least about 98%, and preferably about 100% of the acid groups are free of protective groups. A protective group is a group that prevents the acid from being reactive. 
     Because protective groups are not necessary with the present invention, it is also preferred that the compound is not acid-sensitive. An acid-sensitive polymer or oligomer is one that contains protective groups that are removed, decomposed, or otherwise converted in the presence of an acid. 
     In another embodiment, a combination of protected acid groups and unprotected acid groups could be utilized. In these embodiments, the molar ratio of protected acid groups to unprotected acid groups is from about 1:3 to about 3:1, and more preferably from about 1:2 to about 1:1. 
     In embodiments where the composition is being used as a bottom anti-reflective coating, the composition comprises a chromophore (light attenuating compound or moiety). The chromophore can be bonded with the compound (either to a functional group on the compound or directly to the polymer backbone or oligomer core), or the chromophore can simply be physically mixed in the composition. The chromophore should be present in the composition at a level of from about 5-50% by weight, and preferably from about 20-40% by weight, based upon the total weight of the compound taken as 100% by weight. The chromophore is selected based upon the wavelength at which the compositions will be processed. For example, at wavelengths of 248 nm, preferred chromophores include naphthalenes (e.g., naphthoic acid methacrylate, 3,7-dihydroxynaphthoic acid), heterocyclic chromophores, carbazoles, anthracenes (e.g., 9-anthracene methyl metacrylate, 9-anthracenecarboxylic acid), and functional moieties of the foregoing. At wavelengths of 193 nm, preferred chromophores include substituted and unsubstituted phenyls, heterocyclic chromophores (e.g., furan rings, thiophene rings), and functional moieties of the foregoing. The preferred inventive compositions will also include a crosslinker. 
     Preferred crosslinkers are vinyl ether crosslinkers. It is preferred that the vinyl ether crosslinkers be multi-functional, and more preferably tri- and tetra-functional. 
     Preferred vinyl ether crosslinkers have the formula
 
R—(X—O—CH═CH 2 ) n ,
 
where R is selected from the group consisting of aryls (preferably C 6 -C 12 ) and alkyls (preferably C 1 -C 18 , and more preferably C 1 -C 10 ), each X is individually selected from the group consisting of: alkyls (preferably C 1 -C 18 , and more preferably C 1 -C 10 ); alkoxys (preferably C 1 -C 18 , and more preferably C 1 -C 10 ); carboxys; and combinations of two or more of the foregoing, and n is 2-6. The most preferred vinyl ether crosslinkers include those selected from the group consisting of ethylene glycol vinyl ether, trimethylolpropane trivinyl ether, 1,4-cyclohexane dimethanol divinyl ether, and mixtures thereof. Another preferred vinyl ether crosslinker has a formula selected from the group consisting of
 
     
       
                 
         
             
             
         
      
     
     The preferred compositions also contain a catalyst. The preferred catalyst is an acid generator, and particularly a PAG (both ionic and/or non-ionic). Any PAG that produces an acid in the presence of light is suitable. Preferred PAGs include onium salts (e.g., triphenyl sulfonium perfluorosulfonates such as triphenyl sulfonium nonaflate and triphenyl sulfonium triflate), oxime-sulfonates (e.g., those sold under the name CGI® by CIBA), and triazines (e.g., TAZ108® available from Midori Kagaku Company). 
     The compositions preferably comprise from about 0.1-10% by weight of catalyst, and more preferably from about 1-5% by weight of catalyst, based upon the total weight of the polymer and oligomer solids in the composition taken as 100% by weight. 
     Although a thermal acid generator (“TAG”) can be included in the inventive compositions, in a preferred embodiment the composition is essentially free of TAGs. That is, any TAGs are present at very low levels of less than about 0.05% by weight, and preferably about 0% by weight, based upon the total weight of the composition taken as 100% by weight. 
     It will be appreciated that a number of other optional ingredients can be included in the compositions as well. Typical optional ingredients include surfactants, amine bases, and adhesion promoters. 
     The compositions of this embodiment are formed by simply dispersing or dissolving the polymers, oligomers, or mixtures thereof in a suitable solvent system, preferably at ambient conditions and for a sufficient amount of time to form a substantially homogeneous dispersion. The other ingredients (e.g., crosslinker, PAG) are preferably dispersed or dissolved in the solvent system along with the compound. 
     Preferred solvent systems of this embodiment include a solvent selected from the group consisting of propylene glycol methyl ether acetate (PGMEA), propylene glycol methyl ether (PGME), propylene glycol n-propyl ether (PnP), ethyl lactate (EL), and mixtures thereof. Preferably, the solvent system has a boiling point of from about 50-250° C., and more preferably from about 100-175° C. The solvent system should be utilized at a level of from about 80-99% by weight, and preferably from about 95-99% by weight, based upon the total weight of the composition taken as 100% by weight. 
     Another composition suitable for use in the present inventive methods is described in U.S. Pat. No. 7,108,958, incorporated by reference herein. The compositions in this embodiment include polymers selected from the group consisting of polycarbonates, polysulfonyl esters, and polycarbonate-sulfones. 
     In embodiments where the polymer is a polycarbonate, preferred polycarbonates comprise recurring monomers having the formula 
                                
where each of R 1  and R 2  is individually selected from the group consisting of functional moieties of diols, including aliphatic (preferably C 1 -C 12 ) diols, aromatic (preferably C 4 -C 12 ) diols, and heterocyclic diols). Preferred diols include those selected from the group consisting of bisphenols.
 
     In one embodiment, at least one of R 1  and R 2  is selected from the group consisting of functional moieties of the bisphenols (and preferably bisphenol P and/or bisphenol Z). In this embodiment, it is preferred that the other of R 1  and R 2  has the formula 
                                
where R 5  is an alkyl group (substituted or unsubstituted, preferably C 1 -C 12 , and more preferably C 1 -C 6 ), and Ar is an aryl group (substituted or unsubstituted, preferably at least C 4 , more preferably C 4 -C 12 , and even more preferably C 6 -C 10 ).
 
     In another embodiment, when one of R 1  or R 2  is a moiety of bisphenol A, the other of R 1  and R 2  is a group other than 
     
       
                 
         
             
             
         
      
     
     Particularly preferred R 1  and R 2  groups include those having a structure selected from the group consisting of 
     
       
                 
         
             
             
         
      
     
     As used herein, the term “functional moiety” is intended to refer to moieties of compounds whose respective structures have been altered so that they may bond with other compounds. For example, the structure 
                                
would be considered a functional moiety of bisphenol A, with the hydrogen atoms from each of the —OH groups originally present in the compound having been removed so that the oxygen atoms can bond with another compound or moiety.
 
     In embodiments where the polymer is a polysulfonyl ester, the polymer preferably has the formula 
                                
where X 1  is selected from the group consisting of functional moieties of diols and dioximes. Preferred diols include aliphatic (preferably C 1 -C 12 ) diols, aromatic (preferably C 4 -C 12 ) diols, and heterocyclic diols. Particularly preferred diols include those selected from the group consisting of the bisphenols. Preferred dioximes include aliphatic (preferably C 1 -C 12 ) dioximes, aromatic (preferably C 4 -C 12 ) dioximes, and heterocyclic dioximes. Particularly preferred dioximes include those derived from the condensation of an aliphatic diamine (NH 2 -carbon chain-NH 2 ) and substituted or unsubstituted hydroxybenzaldehydes and hydroxyacetyl benzenes. One particularly preferred example is 1,4-diacetyl benzene dioxime.
 
     In a preferred embodiments X 1  has the formula —O—Z—O— where Z is selected from the group consisting of substituted and unsubstituted aryls (preferably at least C 4 , more preferably C 4 -C 12 , and even more preferably C 6 -C 10 ), substituted and unsubstituted alkyls (preferably C 1 -C 12 , and more preferably C 1 -C 6 ), and combinations thereof. Particularly preferred X 1  groups have a structure selected from the group consisting of 
     
       
                 
         
             
             
         
      
     
     In formula (II), X 2  is selected from the group consisting of substituted and unsubstituted aryls (preferably at least C 4 , more preferably C 4 -C 12 , and even more preferably C 6 -C 10 ) and substituted and unsubstituted alkyls (preferably C 1 -C 12 , and more preferably C 1 -C 6 ). Particularly preferred X 2  groups include those selected from the group consisting of phenyls, naphthyls, furyls, thionyls, and anthranyls. It is preferred that at least one of X 1  and X 2  includes an aromatic portion or other light absorbing group. 
     In embodiments where the polymer is a polycarbonate sulfone, a preferred structure for this polymer is 
                                
where each of R 3  and R 4  is individually selected from the group consisting of substituted and unsubstituted aryls (preferably at least C 4 , more preferably C 4 -C 12 , and even more preferably C 6 -C 10 ), and alkyls (preferably C 1 -C 12 , and more preferably C 1 -C 6 ).
 
     At least one of R 3  and R 4  will include an —SO 2  group, and it is preferred that at least one of R 3  and R 4  includes an aromatic portion or other light absorbing group. Particularly preferred R 3  and R 4  groups include those selected from the group consisting of 
     
       
                 
         
             
             
         
      
     
     Preferably, the polymer has an average molecular weight of from about 1,000-100,000 Daltons, more preferably from about 2,000-50,000 Daltons, and even more preferably from about 2,000-20,000 Daltons. 
     The compositions of this embodiment are formed by simply dispersing or dissolving the polymer(s) in a suitable solvent system, preferably at ambient conditions and for a sufficient amount of time to form a substantially homogeneous dispersion. Preferred compositions comprise from about 1-20% by weight polymer, and preferably from about 2-10% by weight polymer, based upon the total weight of the composition taken as 100% by weight. 
     The solvent systems of this embodiment can include any solvent suitable for use in the microelectronic manufacturing environment. Preferred solvent systems include a solvent selected from the group consisting of propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, propylene glycol, n-propyl ether (PnP), cyclohexanone, γ-butyrolactone, and mixtures thereof. The solvent should be present in the composition at a level of from about 80-98% by weight, based upon the total weight of the composition taken as 100% by weight. Preferably, the solvent system has a boiling point of from about 100-160° C. 
     Any additional ingredients are also preferably dispersed in the solvent system along with the polymer. Examples of suitable additional ingredients include crosslinking agents, catalysts (e.g., PAGs), and surfactants. Preferred crosslinking agents include aminoplasts (e.g., POWDERLINK® 1174, Cymel® products), multifunctional epoxy resins (e.g., MY720, CY179MA, DENACOL), anhydrides, and mixtures thereof. When used, the crosslinking agent is present in the composition at a level of from about 10-50% by weight, and preferably from about 15-30% by weight, based upon the total weight of the solids in the composition taken as 100% by weight. 
     Suitable PAGs include both ionic and nonionic PAGs. Examples of particularly preferred PAGs include sulfonic acid-type PAGs such as those sold under the names CGI 261, CGI 1397, and CGI 1311 (CIBA Specialty Chemicals). When used, the PAG should be present in the composition at a level of from about 0.05-10% by weight, and preferably from about 2-8% by weight, based upon the total weight of the solids in the composition taken as 100% by weight. 
     EXAMPLES 
     The following examples set forth preferred methods in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention. 
     Example 1 
     Coating Formulation Made with Non-Light Absorbing Polymer 
     1. Preparation of Polymer A 
     In this procedure, 9.00 grams of cyclohexyl acrylate (obtained from Polysciences, Warrington, Pa.) and 5.01 grams of methacrylic acid (obtained from Aldrich, Milwaukee, Wis.) were added to a 250-ml, two-neck flask equipped with a stir bar, addition funnel with a nitrogen inlet, and condenser with a nitrogen outlet. These reagents were dissolved by adding 50.00 grams of PGME (obtained from Harcross, St. Louis, Mo.) and stirring under a nitrogen atmosphere. In a separate container, 3.00 grams of dicumyl peroxide (obtained from Acros, N.J.) were dissolved in 36.15 grams of PGME, and this solution was transferred to the addition funnel. The flask was immersed in an oil bath and heated until the solution started to reflux. Upon reflux, the dicumyl peroxide solution was added to the monomer solution. The resulting solution was refluxed for 24 hours. A very light yellow solution was obtained. The solution was cooled to room temperature and transferred to a Nalgene bottle for storage. Molecular weight analysis by gel permeation chromatography using tetrahydrofuran (obtained from Fisher, Fairlawn, N.J.) as the solvent gave a weight-averaged molecular weight of 17,600 Daltons. The optical properties of Polymer A are given in Table 1. 
                                         TABLE I               n at   k at   n at                   193 nm   193 nm   633 nm   Thickness (Å)   Cauchy A   Cauchy B                   1.6857   0.052   1.5   1410   1.4879   0.0049777                    
2. Preparation of Chromophore A
 
     To synthesize Chromophore A, 10.77 grams of tris(2,3-epoxypropyl) isocyanurate (obtained from Aldrich, Milwaukee, Wis.), 19.23 grams of 3,7-dihydroxy-2-naphthoic acid (obtained from Aldrich, Milwaukee, Wis., 0.32 gram of tetrabutylphosphonium bromide (obtained from Aldrich, Milwaukee, Wis.), and 70.0 grams of PGME were added to a 250-ml, two-neck flask with stir bar, nitrogen inlet, and condenser. The flask was heated to 100° C. in an oil bath for 24 hours with stirring and nitrogen flow. After cooling, the chromophore was precipitated in approximately 500 ml of water, rinsed once with 100 ml of water, and dried in vacuum oven at 50° C. overnight. 
     3. Preparation of Vinyl Either Crosslinker 
     In this procedure, 25.15 g of tetramethylene glycol monovinyl ether, 22.91 g triethylamine, and 250 ml THF were added to a 500-ml, 2-necked flask equipped with a stir bar, addition funnel, condenser, and nitrogen inlet and outlet. The solution was stirred under a low flow of nitrogen and immersed in an ice water bath. 
     Next, 20.00 g of 1,3,5-benzenetricarbonyl trichloride were dissolved in 50 ml THF in a closed Erlenmeyer flask. This solution was transferred to the addition funnel. The contents of the addition funnel were added dropwise (over approximately 15 minutes) to the stirring solution of tetramethylene glycol monovinyl ether, triethylamine, and THF. A white precipitate formed upon contact. After addition was completed, the flask was removed from the ice water bath and stirred for approximately 2 hours at room temperature (about 20° C.). The flask was then immersed in an oil bath, and the slurry was heated and kept at reflux for 3 hours. The flask was removed from the heat and allowed to cool to room temperature. 
     The slurry was then suction filtered to give a yellow solution. The yellow solution was concentrated using a rotavap to remove the THF. The yellow oil was dissolved using 100 ml of diethylether. This solution was washed and extracted twice with 25-ml portions of aqueous, 12.5% tetramethylammonium hydroxide. This was followed with two washing and extraction steps with 50 ml of deionized water. The ether layer was allowed to settle out and collected. The ether layer was dried by mixing with 5.0 g of activated basic alumina. The mixture was stirred for 1 hour and gravity filtered. The clear yellow liquid was concentrated in a rotavap to give a yellow viscous oil. 
     The vinyl ether crosslinker, 1,3,5-benzenetricarboxylic acid, tris[4-(ethenyloxy)butyl]ester, had the following structure: 
                                
4. Preparation of Coating Formulation 1
 
     A bottom anti-reflective coating formulation, Formulation 1, containing 1.4364 grams of Polymer A (14% solids in PGME), 0.6033 gram of Chromophore A, 39.5923 grams of PGME, 9.9058 grams of PGMEA (obtained from Harcross, St. Louis, Mo.), 0.4737 gram of vinyl ether crosslinker prepared above, 0.0232 gram of TPS-OH (obtained from Midori Kagaku, Japan), and 0.0523 gram BBI-106 (obtained from Midori Kagaku, Japan) was prepared and filtered through a 0.1-micron endpoint filter. The above formulation was spin-coated at 1,500 rpm onto a silicon substrate and then baked at 165° C. The optical constants at 193 nm were measured using a variable angle spectroscopic ellipsometer (VASE) and were determined to be n=1.557 and k=0.216. The film was rinsed with ethyl lactate (“EL,” obtained from Harcross, St. Louis, Mo.) to test the film&#39;s resistance to the resist solvent, exposed to light from a mercury-xenon lamp, post-exposure baked at 130° C. for 90 seconds, and immersed in developer (MF-319, obtained from Rohm &amp; Haas, MA) for 60 seconds. Table II below shows that bottom anti-reflective coating Formulation 1 had good solvent resistance, and that it can only be removed by an alkaline developer after exposure. 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Bottom Anti-Reflective Coating Formulation 1 Film Properties. 
               
             
          
           
               
                   
                   
                   
                 Thickness after 
                   
                 Thickness after 
                   
               
               
                 Initial 
                 Thickness 
                   
                 Exposure, PEB 
                 % 
                 Development 
               
               
                 Thickness 
                 after 20 s 
                 % EL 
                 and Development 
                 change, 
                 (Å) (no 
                 % change, 
               
               
                 (Å) 
                 EL rinse (Å) 
                 strip 
                 (Å) 
                 exposed 
                 exposure) 
                 unexposed 
               
               
                   
               
               
                 758 
                 773 
                 1.6 
                 0 
                 100 
                 770 
                 0.39 
               
               
                   
               
             
          
         
       
     
     Example 2 
     Coating Formulation Made with Light-Absorbing Polymer 
     1. Preparation of Polymer B 
     In this procedure, 21.29 grains of styrene (obtained from Aldrich, St. Louis, Mo.), 26.17 grams of t-butyl methacrylate (obtained from Aldrich, Milwaukee, Wis.), 25.22 grams of methacrylic acid, and 491.84 grains of PGME were combined in a 1,000 ml, three-neck flask equipped with a magnetic stir bar, thermometer, addition funnel with nitrogen inlet, and condenser. A solution of 1.81 grams of 2,2′-azobis(2-methylpropionitrile) (“AIBN,” obtained from Aldrich, Milwaukee, W), and 164.32 grams of PGME were added to the addition funnel. The flask was heated to 100° C. in an oil bath with stirring and nitrogen flow. After the contents of the flask reached 100° C., the AIBN solution was added to the reaction. Upon complete addition, the reaction was kept at 100° C. for 24 hours. After cooling, the polymer was precipitated in approximately 4 liters of hexanes, rinsed two times with 200 ml of hexanes, and dried in a vacuum oven at 50° C. overnight. 
     2. Preparation of Coating Formulation 2 
     To make the coating Formulation 2, 0.1006 gram of Polymer B, 0.302 gram of Chromophore A, 35.5438 grams of PGME, 8.8929 grains of PGMEA, 0.4737 grain of vinyl ether crosslinker prepared above, 0.0309 grain of triethanolamine quencher (obtained from Aldrich, Milwaukee, Wis.) in 10% PGME solution, and 0.0523 gram BBI-106 were combined and filtered through 0.1-micron endpoint filter. The formulation was spin-coated at 1,500 rpm onto a silicon substrate and then baked at 160° C. The optical constants at 193 nm were measured using a VASE and were determined to be n=1.536 and k=0.272. The film was rinsed with EL to test the film&#39;s resistance to the resist solvent, exposed to light from a mercury-xenon lamp, post-exposure baked at 130° C. for 90 seconds, and immersed in developer (MF-319) for 60 seconds. Table III below shows that the bottom anti-reflective coating had good solvent resistance, and that it could only be removed by an alkaline developer after exposure. 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 Bottom Anti-reflective Coating Formulation 2 Film Properties. 
               
             
          
           
               
                   
                 Thickness 
                   
                 Thickness After 
                   
                 Thickness After 
                   
               
               
                 Initial 
                 After 20-s 
                   
                 Exposure, PEB, 
                 % 
                 Development 
               
               
                 Thickness 
                 EL Rinse 
                 % EL 
                 and Development 
                 Change, 
                 (unexposed) 
                 % Change, 
               
               
                 (Å) 
                 (Å) 
                 Strip 
                 (Å) 
                 Exposed 
                 (Å) 
                 Unexposed 
               
               
                   
               
               
                 592 
                 599 
                 1.18 
                 0 
                 100 
                 602 
                 0.50 
               
               
                   
               
             
          
         
       
     
     Example 3 
     Multi-Patterning Process Using Bottom Anti-Reflective Coating 
     To make bottom anti-reflective coating Formulation 3, 11.226 grams of Polymer B, 739.3 grams of PGME, 185.0 grams of PGMEA, 3.306 grams of a vinyl ether crosslinker prepared above, 0.859 grains of triethanolamine quencher in 10% PGME solution, and 0.330 grams of a mixture of 50% triphenyl sulfonium perfluoro butanesulfonate and 50% tris-(4-tert-butylphenyl)sulfonium perfluoro butanesulfonate (obtained from Aldrich, Milwaukee, Wis.) were combined and filtered through 0.1-micron endpoint filter. To test the multiple patterning process, the formulation was spin-coated at 1500 rpm onto a silicon substrate and then baked at 160° C. A 1-inch circular mask was placed over the film and then exposed using a mercury-xenon lamp, post-exposure baked at 130° C. for 90 seconds, immersed in developer (MF-319) for 60 seconds, rinsed with deionized water, and spin dried. The process left a circle printed on the substrate with a thickness of 54 nm. The exposed areas had no film remaining. This wafer was coated once again and processed two more times as described above. The resulting wafer had 3 circles printed on different locations on the substrate. This example demonstrates that all features printed before the last exposure remain on the substrate even after multiple exposures, bakes, developments, and rinses. 
     Example 4 
     Multiple-Patterning Process Using Bottom Anti-Reflective Coating 
     Using Formulation 3 described above, a double-patterning scheme as shown in  FIG. 2  was demonstrated. The formulation was spin-coated at 1,500 rpm for 60 seconds onto a silicon substrate and then baked at 160° C. for 60 seconds. A photoresist (AR1682J, obtained from JSR Corp.) was spin-coated at 3,200 rpm for 60 seconds on top of the bottom anti-reflective coating. The resist and bottom anti-reflective films were then baked at 110° C. for 60 seconds. A test (contact) mask was placed on top of the wafer, and the films exposed under a mercury-xenon lamp for 5 seconds (at 20 mJ/sec using a 254-nm dose meter). The mask was then turned approximately 90 degrees from its previous orientation, and the films were exposed for another 5 seconds. The wafer was post-exposure baked at 110° C. for 60 seconds and then immersed in a developer (MF-319) for 60 seconds. The wafer was rinsed with deionized water and spin-dried. Overlapping images were observed, showing the imageability of both resist and bottom anti-reflective films. 
     Example 5 
     Multiple-Patterning Process Using Bottom Anti-Reflective Coating 
     Using Formulation 3 described above, a double-patterning scheme as shown in  FIG. 3  was demonstrated. The formulation was spin-coated at 1,500 rpm for 60 seconds onto a silicon substrate and then baked at 160° C. for 60 seconds. A photoresist (AR1682J) was spin-coated at 3,200 rpm for 60 seconds on top of the bottom anti-reflective coating. The resist and bottom anti-reflective coating films were then baked at 110° C. for 60 seconds. A test (contact) mask was placed on top of the wafer, and the films exposed under a mercury-xenon lamp for 5 seconds (at 20 mJ/sec using a 254 nm dose meter). The wafer was post-expose baked at 110° C. for 60 seconds then immersed in developer (PD523, obtained from Moses Lake Industries) for 60 seconds. The wafer was rinsed with deionized water and spin-dried. A second coat of photoresist was applied (AR1682J, 3200 rpm, 60 sec.). The resist and bottom anti-reflective films were then baked again at 110° C. for 60 seconds. The mask was then turned approximately 90 degrees from its previous orientation, and then the films were exposed for another 5 seconds. The wafer was post-expose baked at 110° C. for 60 seconds and then immersed in developer for 60 seconds. The wafer was rinsed with deionized water and spin-dried. Overlapping images were observed, showing the imageability of both resist and anti-reflective films.