| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | May 6, 2003 |
| PATENT TITLE |
Spin-on-dielectric compositions with coating enhancer |
| PATENT ABSTRACT | This invention is a composition comprising (a) an oligomer or polymer dispersible in an organic solvent, having a low dielectric constant, or being curable to form a material having a low dielectric constant, (b) at least one organic solvent and (c) less than 1000 parts by weight of a polymeric coating additive per million parts by weight of total composition (ppm). The polymeric additive is characterized in that it is miscible with component (a) and the solvent system but becomes incompatible with the mixture of component (a) and solvent during the coating process |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | July 18, 2001 |
| PATENT REFERENCES CITED |
N. H. Hendricks et al., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chm.), vol. 37(1), pp. 150-151 (1996). J. S. Drage et al., Material Res. Soc., Symp. Proc., vol. 476 (Low Dielectric Constant Materials III), pp. 121-128 (1997). Handbook of Coating Additives, Chapter 5, Leveling and Flow Control, by Horst Vltavsky, pp. 119-144 (1987). B. Daniels, et al., SPIE, vol. 631, Advances in Resist Technology and Processing III, Surface Tension Effects in Microlithography--Striations pp. 192-201 (1986). A. Barton, CRC Handbook of Solubility Parameters and Other Cohesion Parameters, pp. 41, 95-99 (1991). S. Paul, ed., Surface Coatings, Science & Technology, 2.sup.nd Edition, 4.2.3 Hansen Solubility Parameters, pp. 419-424 (1996). D. Satas, ed., Coating Technology Handbook, Leveling of Brush and Striation Marks, pp. 40-41 (1991). Z. Wicks, Organic Coatings: Science and Technology, Leveling, pp. 435-439 (1999). |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A composition suitable for coating to form thin films comprising: (a) less than 40 percent by weight based on total weight of the composition of a polymer or oligomer, which is soluble or dispersible in organic solvents, said polymer or oligomer is characterized in that it has a dielectric constant less than 4.0 or it is curable to form a cured polymer having a dielectric constant less than 4.0; (b) a solvent system, comprising at least one organic solvent and (c) a polymeric coating additive in amounts less than about 1000 parts by weight based on one million parts of the total composition, wherein the coating additive is dispersed in the solution but is characterized by incompatibility as solvent is removed during coating. 2. The composition of claim 1 wherein component (a) and the polymeric coating additive each have a total Hansen solubility parameter that differ by at least 1 MPa.sup.1/2. 3. The composition of claim 2 wherein the total Hansen solubility parameter for the polymeric coating additive is at least 1 MPa.sup.1/2 less than the total Hansen solubility parameter for component (a). 4. The composition of claim 2 wherein the polymeric coating additive has a total Hansen solubility parameter at least 1.5 MPa.sup.1/2 less than the total Hansen solubility parameter of component (a). 5. The composition of claim 1 wherein the component (a) is a thermosetting oligomer which is the reaction product of: (i) a biscyclopentadienone of the formula: ##STR10## (ii) a polyfunctional acetylene of the formula: ##STR11## (iii) and, optionally, a diacetylene of the formula: ##STR12## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety and y is an integer of three or more. 6. The composition of claim 1 wherein component (a) has the general formula: [A].sub.w [B].sub.z [EG].sub.v wherein A has the structure: ##STR13## and B has the structure: ##STR14## wherein EG are end groups having one or more of the structures: ##STR15## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety, M is a bond, and y is an integer of three or more, p is the number of unreacted acetylene groups in the given mer unit, r is one less than the number of reacted acetylene groups in the given mer unit and p+r=y-1, z is an integer from 1 to 1000; w is an integer from 0 to 1000 and v is an integer of two or more. 7. The composition of claim 5 wherein the total Hansen solubility parameter of the polymeric coating additive is less than 20.1 MPa.sup.1/2. 8. The composition of claim 6 wherein the total Hansen solubility parameter of the polymeric coating additive is less than 20.1 MPa.sup.1/2. 9. The composition of claim 5 wherein the polymeric coating additive is present in an amount from 0.5 to about 200 ppm. 10. The composition of claim 5 wherein the polymeric coating additive is present in an amount of about 1 to 50 ppm. 11. The composition of claim 1 wherein the solvent system comprises at least a first solvent and a second solvent, wherein the first solvent has a higher vapor pressure than the second solvent and wherein the coating additive is soluble in the first solvent but phase separates to form a substantially contiguous fluid phase in the second solvent. 12. The composition of claim 11 wherein the component (a) is a thermosetting oligomer which is the reaction product of (i) a biscyclopentadienone of the formula: ##STR16## (ii) a polyfunctional acetylene of the formula: ##STR17## (iii) and, optionally, a diacetylene of the formula: ##STR18## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety, and y is an integer of three or more. 13. The composition of claim 12 wherein the first solvent is selected from mesitylene and cyclohexanone and the second solvent is gamma-butyrolactone. 14. The composition of claim 11 wherein the polymeric coating additive is present in an amount from 0.5 to about 200 ppm. 15. The composition of claim 11 wherein the polymeric coating additive is present in an amount from about 1 to about 50 ppm. 16. A composition suitable for coating to form thin films comprising: (a) less than 40 percent by weight based on total weight of the composition of a polymer or oligomer which is soluble or dispersible in organic solvents, said polymer or oligomer is characterized in that it has a dielectric constant less than 4.0 or it is curable to form a cured polymer having a dielectric constant less than 4.0; (b) a solvent system having at least a first solvent and a second solvent, wherein the first solvent has a higher vapor pressure than the second solvent and (c) a polymeric coating additive in amounts less than about 1000 parts by weight per one million parts by weight of total composition, wherein the coating additive is soluble in the first solvent but phase separates to form a substantially contiguous fluid phase in the second solvent. 17. The composition of claim 16 wherein component (a) is a thermosetting oligomer which is the reaction product of (i) a biscyclopentadienone of the formula: ##STR19## (ii) a polyfunctional acetylene of the formula: ##STR20## (iii) and, optionally, a diacetylene of the formula: ##STR21## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety and y is an integer of three or more. 18. The composition of claim 17 wherein the first solvent is selected from mesitylene and cyclohexanone and the second solvent is gamma-butyrolactone. 19. The composition of claim 16 wherein the polymeric coating additive is present in an amount from 0.5 to about 200 ppm. 20. The composition of claim 16 wherein the polymeric coating additive is present in an amount from about 1 to about 50 ppm. 21. The composition of claim 1 wherein the polymeric coating additive is selected from the group consisting of polyisoprenes, polybutenes, polybutadiene, hydrogenated polystyrenes, hydrogenated polystyrene/indene resins, poly(styrene-b-ethylene-co-propylene) and acrylate polymers and copolymers. 22. The composition of claim 21 wherein the component (a) is a thermosetting oligomer which is the reaction product of (i) a biscyclopentadienone of the formula: ##STR22## (ii) a polyfunctional acetylene of the formula: ##STR23## (iii) and, optionally, a diacetylene of the formula: ##STR24## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety and y is an integer of three or more. 23. The composition of claim 21 wherein the solvent system comprises a solvent selected from n-methylpyrrolidinone, gamma-butyrolactone, mesitylene, cyclohexanone and mixtures thereof. 24. A composition suitable for coating to form thin films comprising: (a) less than 40 percent by weight based on total weight of the composition of a polymer or oligomer, which is soluble or dispersible in organic solvents said polymer or oligomer is characterized in that it has a dielectric constant less than 4.0 or it is curable to form a cured polymer having a dielectric constant less than 4.0; (b) a solvent system, comprising at least one organic solvent and (c) a polymeric coating additive in amounts less than about 1000 parts by weight per one million parts by weight of total composition, wherein the coating additive is the group consisting of polyisoprenes, polybutenes, polybutadiene, hydrogenated polystyrenes, hydrogenated polystyrene/indene resins, poly(styrene-b-ethylene-co-propylene), and acrylate polymers and copolymers. 25. The composition of claim 24 wherein component (a) is a thermosetting oligomer which is the reaction product of (i) a biscyclopentadienone of the formula: ##STR25## (ii) a polyfunctional acetylene of the formula: ##STR26## (iii) and, optionally, a diacetylene of the formula: ##STR27## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety and y is an integer of three or more. 26. The composition of claim 24 wherein component (a) has the general formula: [A].sub.w [B].sub.z [EG].sub.v wherein A has the structure: ##STR28## and B has the structure: ##STR29## wherein EG are end groups having one or more of the structures: ##STR30## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety, M is a bond and y is an integer of three or more, p is the number of unreacted acetylene groups in the given mer unit, r is one less than the number of reacted acetylene groups in the given mer unit and p+r=y-1, z is an integer from 1 to 1000; w is an integer from 0 to 1000 and v is an integer of two or more. 27. The composition of claim 25 wherein the oligomer has a number average molecular weight of more than about 6000 and the amount of polymeric coating additive is less than 50 ppm. 28. A method comprising applying the composition of claim 1 to a substrate and spinning the substrate to form a layer of component (a). 29. A method comprising applying the composition of claim 16 to a substrate and spinning the substrate to form a layer of component (a). 30. A method comprising applying the composition of claim 24 to a substrate and spinning the substrate to form a layer of component (a). 31. The method of claim 28 wherein the layer is characterized in that striations are not detectable at a magnification of 100.times.. 32. The composition of claim 1 wherein the polymeric coating additive does not affect the material properties of the thin film. 33. The composition of claim 1 wherein the polymeric coating additive is present in amounts less than 500 parts per million. 34. The composition of claim 1 wherein the polymeric coating additive is essentially free of Si or F. 35. The composition of claim 21 wherein the acrylate copolymer is a copolymer of two different alkyl acrylates. 36. The composition of claim 24 wherein the acrylate copolymer is a copolymer of two different alkyl acrylates. 37. The method of claim 28 further comprising pyrloyzing the polymeric coating additive. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to spin-on-dielectric compositions which have additives, which reduce striations and/or broaden the processing window and, especially, to polyarylene compositions, which include such additives and are useful in making microelectronic devices. BACKGROUND OF THE INVENTION Spin-on-dielectrics include organic polymeric materials, which may be spin coated to form very thin layers useful in microelectronics applications. See, e.g., CYCLOTENE.TM. benzocyclobutene based resins from The Dow Chemical Company; WO 97/10193; WO 98/11149 (disclosing polyarylenes) and EP 0 755 957 B1, Jun. 5, 1999; N. H. Hedricks and K. S. Y. Liu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chm.), 1996, 37(1), pp. 150-151; also, J. S. Drage, et al., Material Res. Soc., Symp. Proc., (1997), Volume 476, (Low Dielectric Constant Materials III), pp. 121-128 (disclosing polyarylene ethers). In many of these microelectronics applications, such as interlayer dielectric, passivation, etc., the coating quality and uniformity are very important. Unfortunately, some compositions are extremely difficult to spin coat without experiencing coating defects, such as striations and cracking. Therefore, compositions are desired that can be coated with minimal defects and/or which have a broader processing window for spin speed and environmental conditions, such as temperature and humidity. Various types of materials have been taught to generally facilitate coating. For example, resins, such as acrylics, ureas, melamines, cellulose acetobutyrates, and polyvinyl butyrals, at typical addition levels between 0.5 and 2.0 percent, have been taught to control surface flow. Silicones and fluorocarbons and other surfactants have also been taught to be useful. See Handbook of Coating Additives, Ch. 5, Leveling and Flow Control, by Horst Vltavsky, pp. 129-131, Ed. Leonard J. Calbo, Marcel Dekker Inc. (1987). An article in SPIE, Vol. 631, Advances in Resist Technology and Processing III, (1986), Surface Tension Effects in Microlithography--Striations by B. Daniels, et al. mentions that for photoresists used in lithography as little as 0.005 percent of an unidentified surface leveling agent can eliminate striations in a Novolak diazoquinone resist but suffered from a negative cratering effect. SUMMARY OF THE INVENTION Applicants have discovered spin-on-dielectric formulations that have a broader processing window and limited or no observable striations with only very low levels of polymeric coating additives. Preferably, these additives are free or substantially free of silicon and fluorine as these materials are perceived as being detrimental in integrated circuit manufacture. This invention is a composition comprising (a) an oligomer or polymer dispersible in an organic solvent, (b) at least one organic solvent and (c) less than 1000 parts by weight of a polymeric coating additive per million parts by weight of total composition (ppm). Component (a) is preferably present in amounts less than 40 percent, preferably less than 30 percent and more preferably less than 20 percent by weight based on total weight of the composition. This oligomer or polymer is preferably curable to form a cured polymer characterized by a dielectric constant less than 4.0, preferably less than 3.0. If said polymer is not curable, the dielectric constant of the polymer itself is less that 4.0, preferably less than 3.0. While a single organic solvent may be used, the solvent system preferably comprises at least a first and second solvent. The polymeric coating additive is preferably used in an amount less than 500 parts by weight, more preferably less than about 200 parts by weight per million parts by weight of the total composition. The polymeric additive is characterized in that it is miscible with component (a) and the solvent system but becomes incompatible with the mixture of component (a) and solvent during the coating process. In other words, as the solvent is removed during the spin coating process, the additive will become incompatible with the remainder of the composition (i.e., component (a) and what remains of the solvent) and, therefore, will migrate to surface interfaces. According to one preferred embodiment, the additive is characterized in that it has a total Hansen solubility parameter, .delta..sub.t, that differs from, and is preferably less than, the solubility parameter of component (a) by at least 1 MPa.sup.1/2. More preferably, the solubility parameter of component (c) differs from, and is most preferably less than, the solubility parameter of component (a) by at least 1.5 MPa.sup.1/2. Note, however, that molecular weights of the polymeric components also have an effect and high molecular weight polymers require lower additive levels to be effective and/or may function with a smaller difference in solubility parameter. Note, also, that if the polymeric coating additive (c) is too soluble in the solvents, the incompatibility may not be sufficient to resolve the striation problem, even if the difference in solubility parameters between component (a) and (c) would seem to be sufficient. Thus, according to a second preferred embodiment, the solvent system comprises at least a first solvent and a second solvent, wherein the first solvent has a higher vapor pressure than the second solvent (or stated alternatively, the first solvent has a lower boiling point than the second solvent) and the coating additive is characterized in that it is soluble in the first solvent but phase separates to form a substantially contiguous fluid phase in the second solvent. According to a third preferred embodiment, the resin is selected from the group consisting of polybutene, polyisoprene, acrylate polymers and copolymers. According to a fourth preferred embodiment, this invention is a method of spin coating the formulation of any of the previous formulations onto a substrate resulting in a film of the curable polymer or oligomer, which is free of striations. This invention is also a process using the previous compositions to form a film of a polymer having a low dielectric constant, said film being substantially free of striations. DETAILED DESCRIPTION OF THE INVENTION The curable polymers or oligomers of this invention are materials, which when cured, form a polymer having dielectric constants of less than 4.0, preferably less than 3.0. Preferred materials are benzocyclobutene based polymers, such as CYCLOTENE.TM. 5021 from The Dow Chemical Company, the bisorthodiacetylene based polymers as disclosed, for example, in WO 97/10193. These polymers are made by the reaction of precursor compounds of the formula: (R--C.dbd.C--).sub.n --Ar--L[--Ar(--C.dbd.C--R).sub.m ].sub.q wherein each Ar is an aromatic group or inertly-substituted aromatic group and each Ar comprises at least one aromatic ring; each R is independently hydrogen, an alkyl, aryl or inertly-substituted alkyl or aryl group; L is a covalent bond or a group which links one Ar to at least one other Ar; preferably a substituted or unsubstituted alkyl group, n and m are integers of at least 2; and q is an integer of at least 1, and wherein at least two of the ethynylic groups on one of the aromatic rings are ortho to one another. Alternatively, polyarylenes as disclosed, for example, in WO 98/11149, and polyarylene ethers, such as, for example, PAE resins--Air Products, are described in EP 0 755 957 B1, Jun. 5, 1999 and/or the FLARE.TM. resins made by Honeywell International, Inc. (see N. H. Hedricks and K. S. Y. Liu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chm.), 1996, 37(1), pp. 150-151; also J. S. Drage, et al., Material Res. Soc., Symp. Proc., (1997), Volume 476 (Low Dielectric Constant Materials III), pp. 121-128 may be used. Thermosetting materials are especially desirable for interlayer dielectric applications. Preferably, the oligomers and polymers and corresponding starting monomers of the present invention are: I. Oligomers and polymers of the general formula: [A].sub.w [B].sub.z [EG].sub.v wherein A has the structure: ##STR1## and B has the structure: ##STR2## wherein EG are end groups having one or more of the structures: ##STR3## wherein R.sup.1 and R.sup.2 are independently H or an unsubstituted or inertly-substituted aromatic moiety and Ar.sup.1, Ar.sup.2 and Ar.sup.3 are independently an unsubstituted aromatic moiety or inertly-substituted aromatic moiety, M is a bond, and y is an integer of three or more, p is the number of unreacted acetylene groups in the given mer unit, r is one less than the number of reacted acetylene groups in the given mer unit and p+r=y-1, z is an integer from 1 to 1000, w is an integer from 0 to 1000 and v is an integer of two or more. Such oligomers and polymers can be prepared by reacting a biscyclopentadienone, an aromatic acetylene containing three or more acetylene moieties and, optionally, a polyfunctional compound containing two aromatic acetylene moieties. Such a reaction may be represented by the reaction of compounds of the formulas (a) a biscyclopentadienone of the formula: ##STR4## (b) a polyfunctional acetylene of the formula: ##STR5## (c) and, optionally, a diacetylene of the formula: ##STR6## wherein R.sup.1, R.sup.2, Ar.sup.1, Ar.sup.2, A.sup.3 and y are as previously defined. The definition of aromatic moiety includes phenyl, polyaromatic and fused aromatic moieties. Inertly-substituted means the substituent groups are essentially inert to the cyclopentadienone and acetylene polymerization reactions and do not readily react under the conditions of use of the cured polymer in microelectronic devices with environmental species, such as water. Such substituent groups include, for example, F, Cl, Br, --CF.sub.3, --OCH.sub.3, --OCF.sub.3, --O--Ph and alkyl of from one to eight carbon atoms and cycloalkyl of from three to eight carbon atoms. For example, the moieties which can be unsubstituted or inertly-substituted aromatic moieties include: ##STR7## ##STR8## wherein Z can be: --O--, --S--, alkylene, --CF.sub.2 --, --CH .sub.2 --, --O--CF.sub.2 --, perfluoroalkyl, perfluoroalkoxy, ##STR9## wherein each R.sup.3 is independently --H, --CH.sub.3, --CH.sub.2 CH.sub.3, --(CH.sub.2).sub.2 CH.sub.3 or Ph. Ph is phenyl. The amount of the curable polymer or oligomer is preferably less than about 40, more preferably less than 30, and most preferably less than about 20 weight percent based on total weight of the polymer (or oligomer) and the solvent system, but greater than 1, more preferably greater than 5 weight percent. The solvent system comprises at least one, preferably at least two, most preferably two, organic solvents. Examples of such solvents include mesitylene, pyridine, triethylamine, N-methylpyrrolidinone (NMP), methyl benzoate, ethyl benzoate, butyl benzoate, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, cyclohexylpyrrolidinone and ethers or hydroxy ethers (such as dibenzylethers, diglyme, triglyme, diethylene glycol ethyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, dipropylene glycol dimethyl ether, propylene glycol phenyl ether, propylene glycol methyl ether, tripropylene glycol methyl ether), toluene, xylene, benzene, dipropylene glycol monomethyl ether acetate, dichlorobenzene, propylene carbonate, naphthalene, diphenyl ether, butyrolactone, dimethylacetamide, dimethylformamide and mixtures thereof. The preferred solvents are mesitylene, N-methylpyrrolidinone (NMP), gamma-butyrolactone, diphenylether, cyclohexanone or mixtures of two or more of the preceding. The polymeric coating additive is selected based on its compatibility with component (a) and the organic solvent system. The additive must be miscible with such other components during storage and during initial dispense of the composition for coating but should become incompatible with the other components as the coating process continues, i.e., as solvent is removed during spinning and/or during any heating for solvent removal. The incompatibility can be determined, in part, by comparing the total Hansen solubility parameters of the additive and component (a). The total Hansen solubility parameter may be determined by observing the solubility data according to the following codes: 1=soluble, 2=almost soluble, 3=strongly swollen, 4=swollen, 5=slightly swollen and 6=insoluble. This data is for the material in a series of 20 to 30 solvents having known parameters. A non-linear least squares procedure is then used to estimate the Hansen solubility parameters and the radius of the solubility envelope around that resin. The total Hansen solubility parameter, .delta..sub.t, may then be calculated as .delta..sub.t.sup.2 =.delta..sub.d.sup.2 +.delta..sub.p.sup.2 +.delta..sub.h.sup.2, where .delta..sub.d is the dispersion parameter, .delta..sub.p is the polar parameter and .delta..sup.h is the h-bonding parameter. For further explanation of Hansen solubility parameters see, e.g., Hansen Solubility Parameter: A User's Handbook, Charles M. Hansen, CRC Press LLC, Boca Raton, Fla., 2000. The difference between the total solubility parameter of component (a) and the polymeric additive is preferably at least 1 MPa.sup.1/2, more preferably at least 1.5 MPa.sup.1/2. Preferably, the solubility parameter of the polymeric additive is at least 1, more preferably at least 1.5, MPa.sup.1/2 less than that for component (a). For the preferred component (a), which is the reaction product of cyclopentadienone functional compounds and acetylene functional compounds, as recited above, the additive preferably has a to al Hansen solubility parameter of less than about 20 MPa.sup.1/2, more preferably less than about 19 MPa.sup.1/2. This preferred component (a) has a total Hansen solubility parameter of about 22.7 at very low degrees of polymerization (degree of polymerization of about 1), which then decreases gradually to about 21.07 at higher degrees of polymerization (Mn of about 8000-9000). Molecular weight effects of both component (a) and the polymeric coating additive can also have a substantial effect, in that higher molecular weight materials will have more incompatibility. Therefore, if higher molecular weight materials are used for either or both of component (a) and the polymeric coating additive, the coating additive may be effective with a smaller difference in solubility parameter and/or may be effective at lower amounts. The solubility of the additive in the solvent system will also have an impact on its effectiveness. If an additive is too soluble in the solvent, it may fail to be an effective coating additive, even if its solubility parameter when compared with that for component (a) would seem to indicate that it would be an effective additive. Thus, according to another preferred embodiment, the solvent system comprises at least two organic solvents having different characteristic vapor pressures. The polymeric coating additive, which provides improved coating characteristics, is soluble in the solvent having the higher vapor pressure (i.e., the solvent that evaporates first during coating), preferably at concentrations of at least 1 weight percent, more preferably at concentrations of at least 5 weight percent, most preferably at concentrations of at least 20 weight percent. However, the polymeric coating additive is somewhat insoluble in the solvent having the higher vapor pressure. "Somewhat insoluble" means that when the polymeric additive is mixed with the second solvent it forms a substantially contiguous second fluid phase. Preferably, this substantially contiguous second fluid phase occurs at concentrations of additive of less than 1 weight percent in the solvent, more preferably at less than about 0.3 weight percent. "Substantially contiguous" means that large second phase domains are formed rather than many dispersed droplets in the larger phase. Examples of suitable polymeric additives include polyisoprenes, polybutenes, polybutadiene, hydrogenated polystyrenes, hydrogenated polystyrene/indene resins, poly(styrene-b-ethylene-co-propylene) and acrylate polymers and copolymers. Polybutenes, preferably, have a number average molecular weight greater than about 500 and less than about 10,000. Polyisoprenes, preferably, have a weight average molecular weight of greater than about 1000 and, preferably, less than about 15,000. Suitable acrylate polymers include ethylacrylates, butylacrylate, ethylacrylate/ethylhexylacrylate copolymers, butylacrylate/ethyl hexyl acrylate copolymers and the like. These acrylate materials are commerically available under the trademark BYK.TM. from Byk Chemie or MODAFLOW.TM. from Solutia, Inc. The polymeric coating additive is effective in surprisingly low amounts. The most effective amount will depend on the solubility parameter of component (a) relative to the polymeric coating additive, the molecular weights of component (a) and the polymeric additive, the particular solvent system used and the additive's compatibility with those solvents. However, the amount is less than 2000 ppm, preferably less than 1000 ppm, more preferably less than 200 ppm, more preferably still less than 100 ppm, and most preferably less than 50 ppm. Preferably, the additive is present in amounts of at least 0.5 ppm, more preferably at least 1 ppm, and most preferably at least 5 ppm. For the preferred polyarylene oligomer having number average molecular weights of more than about 6000 (preferably in a solution of gamma-butyrolactone and cyclohexanone), the additive is preferably selected from acrylate polymers and copolymers, polyisoprene and polybutene and is preferably present in amounts of 1 to 100, more preferably 1-50, and most preferably 2-40 ppm. For a similar oligomer but lower molecular weight oligomer (Mn Spin conditions and environmental conditions (such as temperature and humidity) will also have an effect on the amount of coating aid that is optimal. Note also, that if too much of component (c) is added, coating defects other than striations, such as cracking, will become a problem. Preferably, the polymeric additive is such that it degrades and is pyrolyzed during the process of manufacture of the electronic devices. This is preferred so that the polymeric additive will not effect the material properties of the final film. According to yet another embodiment, this invention is a method of forming a layer comprising predominantly component (a) via spin coating. The method comprises applying the composition of the first embodiment to a substrate and spinning the substrate at speeds of from about 500 to 4500, preferably 1000 to 4000, rotations per minute to form a layer that has no observable striations under magnifications of 100.times.. Preferably, the method also comprises heating the coated substrate to remove any residual solvent and/or cure a thermosetting component (a). |
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