Patent Publication Number: US-2003228474-A1

Title: Photoresist compositions

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to new photoresist compositions that are suitable for short wavelength imaging, including sub-300 nm and sub-200 nm such as 248 nm, 193 nm and 157 nm. Photoresists of the invention can exhibit significant adhesion to SiON and other inorganic surface layers. Preferred photoresists of the invention are characterized by comprising a polymer, particularly a copolymer that has one or more pendant adhesion-promoting groups that can enhance adhesion to an underlying surface, including an underlying SiON layer.  
       [0003] 2. Background  
       [0004] Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.  
       [0005] A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble.  
       [0006] While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-quarter micron and even sub-tenth micron features.  
       [0007] Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of below 300 nm such as 248 nm, or even 200 nm or less such as 193 nm. Quite recently, F 2  excimer laser imaging, i.e. radiation having a wavelength of about 157 nm, has been considered as a route to manufacture of even smaller features. See, generally, Kunz, et al., SPIE Proceedings (Advances in Resist Technology), vol. 3678, pages 13-23 (1999).  
       [0008] Silicon oxynitride (SiON) layers and other inorganics such as Si 3 N 4  coatings have been employed in semiconductor device manufacture, for example as an etch stop layer and an inorganic antireflective layer. See, for instance, U.S. Pat. Nos. 6,124,217; 6,153,504; and 6,245,682.  
       [0009] It would be desirable to have new photoresist compositions that could be imaged at short wavelengths such as sub-300 nm and sub-200 nm. It would be particularly desirable to have such photoresists that would provide good resolution on SiON and other inorganic substrate layers.  
       SUMMARY OF THE INVENTION  
       [0010] Novel photoresist compositions are provided that comprise an adhesion-promoting polymer component and one or more photoacid generator compounds. Preferred resists of the invention are useful for short-wavelength imaging, including sub-300 nm and sub-200 nm wavelengths such as 248 nm, 193 nm and 157 nm.  
       [0011] The adhesion-promoting polymer preferably comprises a copolymer that contains one or more pendant groups (“adhesion-promoting groups”) that can impart enhanced adhesion of a coating layer of a photoresist containing the polymer to an underlying substrate, including a SiON layer.  
       [0012] We have found that organic antireflective materials may have limited applications at extremely short imaging wavelengths such as sub-170 nm, particularly 157 nm. At such short wavelengths, the antireflective layer is optimally quite thin (e.g. ≦30 nm layer thickness). Current organic antireflective compositions have not provided sufficient absorbance at such layer thicknesses. Hence, inorganic antireflective materials such as SiON and Si 3 N 4  appear to have greater potential as an antireflective layer for sub-170 nm imaging such as 157 nm.  
       [0013] We also have found that prior photoresists can adhere relatively poorly to such inorganic surface coatings, resulting in reduced resolution of a patterned image.  
       [0014] We have now found that photoresists of the invention can adhere will to such inorganic surface layers, including SiON layers. See, for instance, the comparative data set forth in Example 2, which follows.  
       [0015] The term adhesion-promoting group or moiety refers to herein a moiety that is incorporated into a resist polymer and provides a discernable increase in adhesion of the resist to a SiON surface layer. A discernable increase in adhesion is indicated by resist to a SiON surface layer. A discernable increase in adhesion is indicated by enhanced resolution relative to a control resist (same resist processed in same manner, but resist resin has not been modified to include the candidate adhesion-promoting groups). Such enhanced resolution is determined by visual inspection of scanning electron micrographs (SEMs) of the resist with candidate adhesion-promoting moieties (test resist) and the control resist. See, for instance, the clearly discernable difference between the SEMs of FIGS. 1A and 1B. Thus, suitable adhesion-promoting moieties for any given resist system can be readily identified empirically. Preferred adhesion-promoting moieties and polymers are disclosed in detail herein.  
       [0016] Preferred adhesion-promoting polymer groups contain one or more electron-withdrawing atoms and/or moieties, such as halogen (preferably F); fluoroalkyl including fluoro(C 1-6 alkyl) and perfluoroalkyl such as perfluoro(C 1-6 alkyl) especially perfluoro(C 1-3 alkyl) e.g. —CF 3 , —CF 2 CF 3  and the like; nitro; alkanoyl including C 1-6 alkonyl including formyl and acetyl; hydroxy and hydroxyalkyl (alcohol) such as hydroxy(C 1-6 alkyl) including hydroxymethyl (HOCH 2 —), hydroxyethyl (HOCH 2 CH 2 — and CH 3 CH(OH)—) and the like; etc.  
       [0017] Adhesion-promoting groups may comprise multiple moieties that are electron-withdrawing. For instance, an adhesion-promoting group may comprise an ester group that has fluoro or fluoroalkyl substitution. That is, an adhesion-promoting group may comprise an ester group, e.g. a group of the formula —C(═O)OR, that has further electron-withdrawing substitution, e.g. where R is fluoroalkyl.  
       [0018] Without being bound by any theory, it is believed that moieties that have significant solubilizing effects in aqueous alkaline developer solutions will be less preferred as an adhesion-promoting group. For such reasons, a carboxy or carboxylate group (e.g. —COOH) and amides may be less preferred.  
       [0019] Also, preferred adhesion-promoting groups include those that can exhibit significant hydrogen-bonding properties to various polar moieties of a SiON surface layer. Thus, preferred are adhesion-promoting groups that comprise alcohol (i.e. hydroxyalkyl), fluoroalkyl and other moieties having similar H-bonding characteristics.  
       [0020] Particularly for sub-200 nm imaging, and even more particularly for sub 170 nm imaging such as 157 nm imaging, preferred adhesion-promoting groups will not contain moieties that are significantly absorbing of exposure radiation, e.g. conjugated systems, or for 157 nm imaging, extended alkyl chains such as an alkyl chain having more than about 8 consecutive carbon atoms.  
       [0021] Generally preferred adhesion-promoting polymer groups do not contain phenyl or other aromatic moiety. Particularly preferred adhesion-promoting groups also are substantially inert to typical lithographic (photoresist) processing, i.e. the groups do not undergo a deblocking or covalent bond-breaking reaction during typical lithographic processing of a photoresist containing the polymer, e.g. a pre-exposure soft-bake of up to about 165° C. for 1-2 minutes, exposure to activating radiation, post-exposure bake of up to about 110-130° C. for 1-2 minutes, and alkaline aqueous development.  
       [0022] A photoresist composition of the invention may comprise a single resin, or a blend of multiple, distinct resins. Generally preferred are resists that contain a single resin. That single resin preferably contains both photoacid-labile groups (e.g. photoacid-labile ester or acetal groups) and adhesion-promoting groups.  
       [0023] Alternatively, although less preferred, a resist composition of the invention may comprise a plurality of distinct resins, e.g. where a first resin comprises photoacid-labile groups but is free or at least essentially free (e.g. less than about 5, 4, 3, 2 or 1 mole percent based on total polymer units) of adhesion-promoting groups, and a second resin that comprises adhesion-promoting groups but is free or at least essentially free (e.g. less than about 5, 4, 3, 2 or 1 mole percent based on total polymer units) of photoacid-labile groups.  
       [0024] A resin that comprises adhesion-promoting units suitably will have a weight average molecular weight in excess of about 500 daltons, more preferably a weight average molecular weight of at least about 1,000, 2,000, 3,000, 4,000 or 5,000 daltons. Higher molecular weight materials also will be suitable, e.g. a resin having a weight average molecular weight of about 8,000, 10,000, 15,000 or 20,000 daltons. Resins having weight average molecular weights in excess of about 50,000, 100,000 or 150,000 will be less preferred for at least some applications.  
       [0025] As indicated above, preferred resins that contain adhesion-promoting groups are copolymers, i.e. contain two or more distinct repeat units. Particularly preferred adhesion-promoting copolymers are terpolymers (three distinct repeat units), tetrapolymers (four distinct repeat units) and pentapolymers (five distinct repeat units). As used herein, the term “copolymer” is inclusive of polymers having two distinct repeat units as well as higher order polymers, i.e. polymers that have more than two distinct repeat units such as terpolymers, tetrapolymers, pentapolymers, etc.  
       [0026] The repeat units of a polymer used in a resist of the invention may suitably vary depending on the exposure wavelength used for imaging the resist. More particularly, for resist to be imaged at wavelengths greater than 200 nm, the resin may suitably contain aromatic units, particularly optionally substituted phenyl units, preferably phenolic units such as provided by polymerization of a vinylphenol. For resists to be imaged with radiation having a wavelength of less than 200 nm such as 193 nm or 157 nm, the resin suitably may be substantially, essentially or completely free of any phenyl or other aromatic units. A resin that is substantially free of aromatic units has less than about 5 mole percent aromatic units based on total resin units, preferably less than about 4, 3, 2, 1 or 0.5 mole percent aromatic units based on total resin units.  
       [0027] In addition to adhesion-promoting groups, preferred resin units include fluorine-containing moieties, such as may be provided by polymerization of an unsaturated fluorinated monomer particularly tetrafluoroethylene, or a monomer containing a fluorinated alcohol particularly where the hydroxy is bound to a secondary or tertiary carbon e.g. hexafluoro-iso-propanol (—C(OH)(CF 3 ) 2 ).  
       [0028] Additional preferred units of an adhesion-promoting polymer include alicyclic groups, e.g. repeat units that contain a fused alicyclic ring together with repeat units that comprise pendant alicyclic groups.  
       [0029] Unless otherwise indicated, an alicyclic group as referred to herein is inclusive of a group having all carbon ring members as well as group having one or more hetero atoms (e.g. O, S, N or Si, particularly O or S) ring members. A carbon alicyclic group contains all carbon atoms such as e.g. adamantyl, norbornyl, fencyl, pinnanyl, and the like. A heteroalicyclic group contains at least one hetero atom (e.g. O, S, N or Si, particularly O or S) ring member. Alicyclic groups are understood not to be aromatic.  
       [0030] The invention also includes substrates coated by a photoresist as disclosed herein, including substrates having an inorganic surface coating such as a SiON or Si 3 N 4  coating.  
       [0031] Methods for forming relief images also are provided, including methods for forming a highly resolved relief image such as a pattern of lines (dense or isolated) where each line has vertical or essentially vertical sidewalls and a line width of about 0.40 microns or less, or even about 0.25, 0.20, 0.15, or 0.10 microns or less. In such methods, preferably a coating layer of a resist of the invention is imaged with short-wavelength radiation, particularly sub-300 or sub-200 nm radiation, especially 248 nm, 193 nm, and 157 nm radiation, and higher energy radiation such as radiation having a wavelength of less than 100 nm, EUV, electron beam, ion beam or x-ray imaging.  
       [0032] The invention further comprises articles of manufacture comprising substrates such as a microelectronic wafer having coated thereon the photoresists and relief images of the invention. Methods for producing such articles of manufacture also are providing, which generally comprise use of a photoresist of the invention.  
       [0033] Other aspects of the invention are disclosed infra. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0034]FIG. 1 (which includes FIGS. 1A and 1B) shows scanning electron micrographs (SEMs) of lithographic results of Example 2 which follows. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0035] As discussed above, we now provide new photoresist compositions that comprise one or more photoacid generator compounds and a resin that adhesion-promoting groups that can provide enhanced adhesion to an underlying surface, particularly inorganic coating layers such as those containing SiON and Si 3 N 4 .  
     [0036] We have discovered that through resist polymer modification adhesion to inorganic surfaces, including SiON and Si 3 N 4  surfaces, can be dramatically improved. The modified polymer is preferably the photoreactive resin (deblocking) of a chemically-amplified positive resist. The polymer is modified to include one or more adhesion-promoting moieties or groups.  
     [0037] As discussed above, the adhesion-promoting groups are preferably pendant to the resin backbone, and the resin is preferably a copolymer, with terpolymers, tetrapolymers and pentapolymers being especially suitable. Particularly preferred are adhesion-promoting resins that have fluorine substitution.  
     [0038] Adhesion-promoting resins that have acrylate content also are preferred, including where adhesion-promoting groups(s) are present in polymerized acrylate repeat units. Unless otherwise indicated, references herein to an acrylate are inclusive of substituted acrylates such as methacrylates.  
     [0039] Preferred fluorine-containing units of polymers used in resists of the invention are suitably derived from at least one ethylenically unsaturated compound. Preferably, such a fluorine substituent is separated from the unsaturated carbons by at least one saturated carbon in order to not unduly inhibit the polymerization reaction. Such fluorinated units may be provided by e.g. polymerization of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, trifluoroetbylene, vinylidene fluoride, vinyl fluoride, and the like  
     [0040] Exemplary preferred fluorinated unsaturated compounds for synthesis of polymers utilized in resists of the invention include the following of Formulae (A), (B), (C) and (D):  
                 
 
     [0041] wherein in Formulae (D), X is a linker, preferably —CH 2 —, —CH 2 OCH 2 —, or —OCH 2 —; and n is 0 or 1.  
     [0042] Additional preferred monomers for use in a polymer of a resist of the invention may comprise a group of the following formula:  
                 
 
     [0043] wherein X is a linker, preferably —CH 2 —, —CH 2 OCH 2 —, or —OCH 2 — 
     [0044] Y is hydrogen, a chemical bond linking the oxygen and group Z, (—CH 2 —)p where p is 1 or 2, —CH 2 O—, or CHRO— where R is C 1-16 alkyl, preferably C 1-4 alkyl; and  
     [0045] Z is alkyl preferably having 1 to about 18 carbons and including tri(C 1-6 )alkylmethyl; tetrahydropyranyl; or tetrahydrofuranyl;  
     [0046] and preferably X is —OCH 2 —; preferably Y is a bond or —CH 2 O—; and preferably Z is t-butyl, methyl, tetrahydropyranyl, or tetrahydrofuranyl.  
     [0047] Resins used in resists of the invention, including adhesion-promoting polymers, also may contain additional units.  
     [0048] Particularly preferred adhesion-promoting polymers used in resists of the invention include those that comprise a structure corresponding to the following Formula I:  
                 
 
     [0049] wherein Q represents an optionally substituted carbon alicyclic ring fused to the polymer backbone (i.e. two Q ring members being adjacent carbons of the polymer backbone), the alicyclic ring suitably having 5 to about 18 carbon atoms and is suitably a single ring (e.g. cyclopentyl, cyclohexyl or cycloheptyl), or more preferably Q is polycyclic e.g. and contain 2 or 3 bridged, fused or otherwise linked rings, and preferred substituents of a substituted Q group include photoacid-labile moieties such as a photoacid-labile ester, or a dissolution-enhancing groups such as —OCH 2 C(OH)(CH 3 ) 2 ;  
     [0050] X is a group containing one or more fluorine atoms, particularly as may be provided by polymerization of a fluorinated unsaturated compound, preferably a fluorinated unsaturated compound such as a compound that has at least one fluorine atom covalently attached to ethylenically unsaturated atom, e.g. tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, and the like;  
     [0051] Y comprises an adhesion-promoting moiety as discussed above, e.g. a haloalkyl, hydroxyalkyl, etc. as may be provided e.g. by polymerization of suitable monomers such as ethylhydroxy acrylate, trifluoroethyl acrylate, and the like;  
     [0052] preferably the polymer comprises photoacid-labile groups, and such groups may be a moiety of the above Q, X and Y groups;  
     [0053] p, r and s are mole fractions of the depicted units based on total units in the polymer, and p, r and s are each greater than zero.  
     [0054] Particularly preferred adhesion-promoting polymers for use in a resist of the invention has a separate repeat unit that has a photoacid-labile group, such as polymers that comprise a structure corresponding to the following Formula II:  
                 
 
     [0055] wherein Q, X, Y, p, r and s are the same as defined in Formula I above;  
     [0056] Z is a group that comprises a photoacid-labile group such as a photoacid-labile ester or acetal group, such as may be provided by polymerization of t-butyl acrylate, t-butyl methacrylate, and the like; and  
     [0057] t is the mole fraction of the depicted photoacid-labile unit based on total units in the polymer, and t is greater than zero.  
     [0058] In polymers of Formula II, suitably units Y that contain adhesion-promoting groups need not contain photoacid-labile group substitution.  
     [0059] Generally preferred adhesion-promoting polymers will contains at least about 2 or 3 mole percent adhesion-promoting units based on total units of the polymer, more preferably at least about 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25 or 30 mole percent adhesion-promoting units based on total units of the polymer. Suitably an adhesion-promoting polymer is present in a photoresist composition in an amount of at least about 2, 3 or 4 weight percent based on total solids of the resist composition (all component except solvent), more preferably at least about 5, 6, 7, 8, 10, 12 or 15 weight percent based on total solids of the compositions.  
     [0060] As discussed above, at least one resist component will comprise photoacid-labile units. It is generally preferred that the resin that comprises adhesion-promoting groups also contains photoacid-labile groups, although a separate resin may be employed that contains photoacid-labile groups as discussed above, even if such a multiple resin system is less preferred. Preferred photoacid-labile groups of a resin used in a resist of the invention include photoacid-labile acyclic esters such as a tert-butyl ester, or an ester containing a tertiary alicyclic group. Such photoacid-labile esters may be directly pendant from the resin backbone or other polymer unit such as a carbon alicyclic, heteroalicyclic or other polymer unit (e.g. where the photoacid-labile group is of the formula —C(═O)OR, where R is tert-butyl or other non-cyclic alkyl group, or a tertiary alicyclic group and is directly linked to the polymer backbone or unit), or the ester moieties may be spaced from the polymer backbone or other polymer unit, e.g. by an optionally alkylene linkage (e.g. —(CH 2 ) 1-4 C(═O)OR, where R is tert-butyl or other non-cyclic alkyl group, or a tertiary alicyclic group). Such photoacid-labile groups also suitably may contain fluorine substitution at available positions.  
     [0061] Preferred photoacid-labile tertiary alicyclic hydrocarbon ester moieties are polycyclic groups such adamantyl, ethylfencyl or a tricyclodecanyl moiety. References herein to a “tertiary alicyclic ester group” or other similar term indicate that a tertiary alicyclic ring carbon is covalently linked to the ester oxygen, i.e.—C(═O)O—TR′ where T is a tertiary ring carbon of alicyclic group R′. In at least many cases, preferably a tertiary ring carbon of the alicyclic moiety will be covalently linked to the ester oxygen. However, the tertiary carbon linked to the ester oxygen also can be exocyclic to the alicyclic ring, typically where the alicyclic ring is one of the substituents of the exocyclic tertiary carbon. Typically, the tertiary carbon linked to the ester oxygen will be substituted by the alicyclic ring itself, and/or one, two or three alkyl groups preferably having 1 to about 5 or 6 carbon atoms. The alicyclic group also preferably will not contain aromatic substitution. The alicyclic groups may be suitably monocyclic, or polycyclic, particularly bicyclic or tricyclic groups.  
     [0062] Preferred alicyclic moieties (e.g. group TR′ of —C(═O)O—TR′) of photoacid labile ester groups of polymers of the invention have rather large volume. It has been found that such bulky alicyclic groups can provide enhanced resolution when used in copolymers of the invention.  
     [0063] More particularly, preferred alicyclic groups of photoacid-labile ester groups will have a molecular volume of at least about 125 or about 130 Å 3 , more preferably a molecular volume of at least about 135, 140, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200 Å 3 . Alicyclic groups larger than about 220 or 250 Å 3  may be less preferred, in at least some applications. References herein to molecular volumes designate volumetric size as determined by standard computer modeling, which provides optimized chemical bond lengths and angles. A preferred computer program for determining molecular volume as referred to herein is Alchemy 2000, available from Tripos. For a further discussion of computer-based determination of molecular size, see T Omote et al,  Polymers for Advanced Technologies, volume  4, pp. 277-287.  
     [0064] Particularly preferred tertiary alicyclic groups of photoacid-labile units include the following, where the wavy line depicts a bond to the carboxyl oxygen of the ester group, and R is suitably optionally substituted alkyl, particularly C 1-6 alkyl such as methyl, ethyl, etc.  
                 
 
     [0065] As also indicated above, polymers for use in positive resists of the invention may contain photoacid-labile groups that do not contain an alicyclic moiety. For example, polymers of the invention may contain photoacid-labile ester units, such as a photoacid-labile, alkyl ester. Generally, the carboxyl oxygen (i.e. the carboxyl oxygen as underlined as follows: —C(═O) O ) of the photoacid-labile ester will be covalently linked to the tertiary carbon. Branched photoacid-labile esters are generally preferred such as t-butyl and —C(CH 3 ) 2 CH(CH 3 ) 2 .  
     [0066] In this regard, polymers used in resists of the invention may contain distinct photoacid-labile groups, i.e. the polymer may contain two or more ester groups that have distinct ester moiety substitutions e.g. one ester may have an alicyclic moiety and another ester may have an acyclic moiety such as t-butyl, or the polymer may contain both ester and other functional groups that are photoacid-labile such as acetals, ketals and/or ethers.  
     [0067] Suitable polymers for use in the resists of the invention also are disclosed in e.g. U.S. Pat. Nos. 6,306,554; 6,300,035; and 6,165,674, all assigned to the Shipley Company. Those described polymers would be modified in accordance with the invention by incorporating an adhesion-promoting repeat unit in the described polymers. The polymers disclosed in U.S. Pat. Nos. 6,306,554 and 6,165,674 would be preferred for sub-200 nm imaging, and the polymers described in U.S. Pat. No. 6,300,035 would be preferred for imaging at longer wavelengths such as 248 nm.  
     [0068] As discussed, various resin moieties may be optionally substituted, including groups of Formulae I and II. A “substituted” substituent may be substituted at one or more available positions, typically 1, 2, or 3 positions by one or more suitable groups such as e.g. halogen (particularly F); cyano; C 1-6  alkyl; C 1-6  alkoxy; C 1-6  alkylthio; C 1-6  alkylsulfonyl; C 2-6  alkenyl; C 2-6  alkynyl; hydroxyl; nitro; alkanoyl such as a C 1-6  alkanoyl e.g. acyl and the like; etc.  
     [0069] Polymers of the invention can be prepared by a variety of methods. One suitable method is an addition reaction which may include free radical polymerization, e.g., by reaction of selected monomers to provide the various units as discussed above in the presence of a radical initiator under an inert atmosphere (e.g., N 2  or argon) and at elevated temperatures such as about 70° C. or greater, although reaction temperatures may vary depending on the reactivity of the particular reagents employed and the boiling point of the reaction solvent (if a solvent is employed). Suitable reaction solvents include e.g. a halogenated solvent such as a fluorinated solvent or a chlorinated solvent and the like. Suitable reaction temperatures for any particular system can be readily determined empirically by those skilled in the art based on the present disclosure. A variety of free radical initiators may be employed. For example, azo compounds may be employed such as azo-bis-2,4-dimethylpentanenitrile. Peroxides, peresters, peracids and persulfates also could be employed.  
     [0070] Other monomers that can be reacted to provide a polymer of the invention can be identified by those skilled in the art. For example, to provide photoacid-labile units, suitable monomers include e.g. methacrylate or acrylate that contains the appropriate group substitution (e.g. tertiary alicyclic, t-butyl, etc.) on the carboxy oxygen of the ester group. Suitable acrylate monomers with tertiary alicyclic groups for synthesis of polymers useful in the resists of the invention also are disclosed in U.S. Pat. No. 6,306,554 to Barclay et al.  
     [0071] Resist compositions of the invention also comprise one or more photoacid generators (i.e. “PAG”) that are suitably employed in an amount sufficient to generate a latent image in a coating layer of the resist upon exposure to activating radiation. Preferred PAGs for imaging at 157 nm, 193 nm and 248 nm imaging include imidosulfonates such as compounds of the following formula:  
                 
 
     [0072] wherein R is camphor, adamantane, alkyl (e.g. C 1-12  alkyl) and perfluoroalkyl such as perfluoro(C 1-12 alkyl), particularly perfluorooctanesulfonate, perfluorononanesulfonate and the like. A specifically preferred PAG is N-[(perfluorooctanesulfonyl)oxy]-5-norbornene-2,3-dicarboximide.  
     [0073] Sulfonate compounds are also suitable PAGs, particularly sulfonate salts. Two suitable agents for 193 nm and 248 nm imaging are the following PAGS 1 and 2:  
                 
 
     [0074] Such sulfonate compounds can be prepared as disclosed in European Patent Application 96118111.2 (publication number 0783136), which details the synthesis of above PAG 1.  
     [0075] Also suitable are the above two iodonium compounds complexed with anions other than the above-depicted camphorsulfonate groups. In particular, preferred anions include those of the formula RSO 3 — where R is adamantane, alkyl (e.g. C 1-12  alkyl) and perfluoroalkyl such as perfluoro (C 1-12 alkyl), particularly perfluorooctanesulfonate, perfluorobutanesulfonate and the like.  
     [0076] For imaging at 157 nm, a triphenyl sulfonium PAG is particularly preferred, complexed with anions such as the sulfonate anions mentioned above, particularly a perfluoroalkane sulfonate such as perfluorobutane sulfonate.  
     [0077] A preferred optional additive of resists of the invention is an added base, particularly tetrabutylammonium lactate, which can enhance resolution of a developed resist relief image. Other suitable added bases include diazabicycloundecene or diazabicyclononene. The added base is suitably used in relatively small amounts, e.g. about 0.03 to 5 percent by weight relative to the total solids.  
     [0078] Photoresists of the invention also may contain other optional materials. For example, other optional additives include anti-striation agents, plasticizers, speed enhancers, etc. Such optional additives typically will be present in minor concentrations in a photoresist composition.  
     [0079] The resists of the invention can be readily prepared by those skilled in the art. For example, a photoresist composition of the invention can be prepared by dissolving the components of the photoresist in a suitable solvent such as, for example, 2-heptanone, cyclohexanone, ethyl lactate, propylene glycol monomethyl ether; and propylene glycol monomethyl ether acetate. Typically, the solids content of the composition varies between about 2 and 20 percent by weight of the total weight of the photoresist composition. The resin binder and photoactive components should be present in amounts sufficient to provide a film coating layer and formation of good quality latent and relief images. See the examples which follow for exemplary preferred amounts of resist components.  
     [0080] The compositions of the invention are used in accordance with generally known procedures. The liquid coating compositions of the invention are applied to a substrate such as by spinning or other conventional coating technique. When spin coating, the solids content of the coating solution can be adjusted to provide a desired film thickness based upon the specific spinning equipment utilized, the viscosity of the solution, the speed of the spinner and the amount of time allowed for spinning.  
     [0081] The resist compositions of the invention are suitably applied to substrates conventionally used in processes involving coating with photoresists. For example, the composition may be applied over silicon wafers or silicon wafers coated with silicon dioxide, SiON or Si 3 N 4  for the production of microprocessors and other microelectronic device substrates.  
     [0082] As discussed above, the photoresists are particularly useful for applying over inorganic surface coatings, including SiON and Si 3 N 4 .  
     [0083] Following coating of the photoresist onto a surface, a resist coating layer is suitably dried by heating to remove the solvent until preferably the photoresist coating is at least essentially free of solvent. Thereafter, it is imaged through a mask in conventional manner. The exposure is sufficient to effectively activate the photoactive component of the photoresist system to produce a patterned image in the resist coating layer and, more specifically, the exposure energy typically ranges from about 1 to 100 mJ/cm 2 , dependent upon the exposure tool, radiation type and the components of the photoresist composition  
     [0084] As discussed above, coating layers of the resist compositions of the invention are preferably photoactivated by a short exposure wavelength, particularly a sub-300 and sub-200 nm exposure wavelength. 193 nm and 157 nm are preferred exposure wavelengths. However, the resist compositions of the invention also may be suitably imaged at higher wavelengths.  
     [0085] Following exposure, the film layer of the composition is preferably baked at temperatures ranging from about 70° C. to about 160° C. Thereafter, the film is developed. The exposed resist film is rendered positive working by employing an aqueous based developer such as quaternary ammonium hydroxide solutions such as a tetraalkyl ammonium hydroxide solution, preferably a 0.26 N tetramethylammonium hydroxide aqueous solution; or various amine aqueous solutions such as a solution containing ethyl amine, n-propyl amine, diethyl amine, di-n-propyl amine, triethyl amine, or methyldiethyl amine; alcohol amines such as diethanol amine or triethanol amine; cyclic amines such as pyrrole, pyridine, etc. In general, development is in accordance with procedures recognized in the art.  
     [0086] Following development of the photoresist coating over the substrate, the developed substrate may be selectively processed on those areas bared of resist, for example by chemically etching or plating substrate areas bared of resist in accordance with procedures known in the art. For the manufacture of microelectronic substrates, e.g., the manufacture of silicon dioxide wafers, suitable etchants include a gas etchant, e.g. a halogen plasma etchant such as a chlorine or fluorine-based etchant such a Cl 2  or CF 4 /CHF 3  etchant applied as a plasma stream. After such processing, resist may be removed from the processed substrate using known stripping procedures.  
     [0087] All documents mentioned herein are incorporated herein by reference. The following non-limiting examples are illustrative of the invention.  
     EXAMPLE 1  
     [0088] Polymer Synthesis  
     [0089] An adhesion-promoting tetrapolymer polymer was prepared by reaction of 1) norbornene having a ring substituent of —OCH 2 C(OH)(CF 3 ) 2 ; 2) tetrafluoroethylene (TFE); 3) t-butyl acrylate (photoacid labile group); and 4) 2-hydroxyethyl acrylate (non-photoacid-labile, adhesion-promoting group).  
     [0090] The resulting polymer contained units of the substituted norbornene in an amount of 45 mole percent based on total polymer units, tetrafluoroethylene units in an amount of 30 mole percent based on total polymer units, t-butylacrylate units in an amount of about 20 mole percent based on total polymer units, and 2-hydroxyethyl acrylate in an amount of about 5 mole percent based on total polymer units.  
     EXAMPLE 2  
     [0091] Preparation and Lithographic Processing of a Resist of the Invention.  
     [0092] A resist of the invention was prepared by admixing the following components where amounts are expressed as weight percent of solids (all components except solvent) and the resist is formulated as an 84.4 weight percent fluid formulation:  
                                                   Component   Amount                                                    Resin   10           PAG   5.2           Basic Additive   0.3           Surfactant   0.1           Solvent   to 84.4 percent formulation                      
 
     [0093] In the resist, the resin is the polymer prepared in Example 1. The PAG is triphenylsulfonium perfluorobutane sulfonate. The basic additive is tetrabutylammonium lactate. The surfactant is R08. The solvent is 2-heptanone.  
     [0094] The formulated resist composition is spin coated onto 8 inch silicon wafers having an antireflective SiON surface coating. The applied resist is softbaked via a vacuum hotplate at 120° C. for 90 seconds. The resist coating layer is exposed through a photomask at 157 nm, and then the exposed Si wafer is post-exposure baked at 105° C. The imaged resist layer is then developed by treatment with an aqueous 0.26 N tetramethylammonium hydroxide solution. The resulting photoresist relief image is shown in FIG. 1A.  
     [0095] A comparative photoresist formulation was prepared having the same composition as described immediately 1) norbornene having a ring substituent of —OCH 2 C(OH)(CF 3 ) 2 ; 2) tetrafluoroethylene (TFE); and 3) t-butyl acrylate (photoacid labile group). The terpolymer did not contain the further polymer units with adhesion-promoting units. The comparative photoresist formulation was processed on SiON coated wafers in the same manner as described immediately above in this example. The photoresist image resulting after development is shown in FIG. 1B.  
     EXAMPLE 3  
     [0096] Preparation and Lithographic Processing of a Further Resist of the Invention.  
     [0097] A resist of the invention was prepared by admixing the following components where amounts are expressed as weight percent of solids (all components except solvent) and the resist is formulated as an 84.4 weight percent fluid formulation:  
                                                   Component   Amount                                                    Resin   10           PAG   5.2           Basic Additive   0.3           Surfactant   0.1           Solvent   to 84.4                      
 
     [0098] In the resist, the resin is the same as the polymer prepared in Example 1, except 2,2,2-trifluoroethylacrylate is used in place of the 2-hydroxyethyl acrylate. All other resist components are the same as described in Example 2.  
     [0099] The resulting resist is processed in the same manner as described in Example 2 above.  
     [0100] The foregoing description of the invention is merely illustrative thereof, and it is understood that variations and modifications can be effected without departing from the spirit or scope of the invention as set forth in the following claims.