| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | November 11, 2003 |
| PATENT TITLE |
Polyarylene compositions with enhanced modulus profiles |
| PATENT ABSTRACT | This invention is a polyarylene composition in which resin does not undergo a significant drop in modulus at temperatures above 300.degree. C. during cure. This feature enables one to form porous films by avoiding pore collapse and/or using a wider variety of poragen materials. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | January 11, 2002 |
| PATENT REFERENCES CITED |
"Low Dielectric Constant Polymers Having Good Adhesion and Toughness and Articles Made With Such Polymers," U.S. Patent Application No. 09/468,174 (Attorney Docket No. 44465), Applicant: James P. Goldchalx et al. "Macroporous Thermosets by Chemically Induced Phase Separation," Kiefer et al., Advance in Polymer Science, vol. 147, pp. 161-247 (1999). "Templating Nanoporosity in Thin Film Dielectric Insulators," Hedrick et al., Adv. Mater,, vol. 10, No. 13, pp. 1049-1053 (1998). "Nanoporous Polymides," Hedrick et al., Advances in Polymer Science, vol. 141, pp. 1-43 (1999). "Polyphenylene dendrimers: from three-dimensional to two-dimensional structures," Morgenroth et al., Angew. Chem. Int. Ed. Engl., vol. 36, No. 6, pp. 631-634 (1997) Abstract. "Dielectric property and microstructure of a porous polymer material with ultralow dielectric constant," Abstract--Low-Dielectric Constant Materials IV. Symposium Appl. Phys. Lett., vol. 75, No. 6 (1998). "Spherical polyphenylene dendrimers via Diels-Alder reactions: the first example of an A4B Building block in dendrimer chemistry," Chem. Commun. (Cambridge), 10, pp. 1139-1140 (1998) Abstract. "A Study of the Thermal Degradation of Methyl Methacrylate Polymer and Copolymers by Thermal Volatilization Analysis," I.C. McNeil, vol. 4, pp. 21-29 (1968). "Nanocages Derived from Shell Cross-Linked Micelle Templates," Huang et al., J. Am Chem. Soc. , vol. 121, pp. 3805-3806 (1999). "Diels-Arder Reactions of Tetraethynylcyclopentadienones. An Approach to Differentially Sustituted Hexaethynylbenzens of C2v Symmetry," Tobe et al., J. Org. Chem., vol. 62, No. 11, pp. 3430-3431 (1997) Abstract. "Self-Crosslinkable Poly)arylene ether)s Containing Pendent Phenylenetraizine Groups," Lau et al., J. Poly. Sci., Part A: Polym. Chem., vol. 32, pp. 1507-1521 (1994). "Preparation of Poly(Octaphenyl-Tetraphenylene)," Wrasidlo & Augl, J. Polym. Sci., Part B Polymer Letters: vol. 7, pp. 519-523 (1969). "Diels-alder Polymerization between Bis(cyclopentadienones) and Acetylenes. A Versatile Route to New Highly Aromatic Polymers," Kumar et al., Macromolecules, pp. 124-130 (1995). "Divergent Synthesis of Polyphenylene Dendrimers: The Role of core and Branching Reagents upon Size and Shape," Wiesler et al., Macromolecules, vol. 34, No. 2, pp. 187-199 (Jun. 16, 2001) Abstract. "Recent Advances in Low K Polymeric Materials," K.R. Carter, MRS Low K Dielectric Sysposium III, pp. 87-98. "Phenylated Polyphenylenes Containing Hexafluoroisopropylidene Groups," Rosanov et al., Polymer Preprints, 59(2), pp. 794-795 (1998). "New Method of Preparing Polyphenyleneethynylenes," Keshtov et al., Polymer Science Series A, 43, No. 6, pp. 583-587 (Jun. 2001) Abstract. "2,5-diphenyl-3,4-bis[p- (phenylethynyl)phenyl]cyclopentadienone and product of its Diels-Alder homocondensation," Morgenroth et al., Russ. Chem. Bull. vol. 48, No. 5, pp. 944-948 (1999) Abstract. "Dendritic and hyperbranched polyphenylenes via a simple Diels-Alder route," Morgenroth et al., Tetrahedron, vol. 53, No. 45, pp. 15349-15366 (1997) Abstract. |
| PATENT GOVERNMENT INTERESTS | This invention was made with United States Government support under Cooperative Agreement No. 70NANB8H4013 awarded by NIST. The United States Government has certain rights in the invention |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A composition comprising precursors which when cured form a polyarylene material wherein the composition has a modulus profile as measured by torsional impregnated cloth analysis (TICA) characterized by a Minimum Measured Heat-up Modulus at a temperature, Tmin, said Minimum Measured Heat-up Modulus being greater than a value equal to 20 percent of a Measured Cured Modulus at Tmin, provided that when the polyarylene is formed from the reaction of components consisting of a cyclopentadienone functional compound and an acetylene functional compound each of which have at least two functional groups and at least one compound having at least three functional groups and the ratio of cyclopentadienone groups to acetylene groups in the reaction mixture is less than 2:1, the ratio is greater than 1:1. 2. The composition of claim 1 wherein the Minimum Measured Heat-up Modulus is greater than a value equal to 50 percent of the Measured Cured Modulus at Tmin. 3. A composition comprising precursors which when cured form a polyarylene material, wherein the composition has a modulus profile as measured by TICA characterized by a ratio of Measured Heat-up Modulus at 388.degree. C. to Measured Cured Modulus at 388.degree. C. greater than 0.2 provided that when the polyarylene is formed from the reaction of components consisting of a cyclopentadienone functional compound and an acetylene functional compound each of which have at least two functional groups and at least one compound having at least three functional groups and the ratio of cyclopentadienone groups to acetylene groups in the reaction mixture is less than 2:1, the ratio is greater than 1:1. 4. The composition of claim 3 wherein the ratio of Measured Heat-up Modulus at 388.degree. C. to Measured Cured Modulus at 388.degree. C. is greater than 0.5. 5. The composition of claim 3 wherein the ratio of Measured Heat-up Modulus at 388.degree. C. to Measured Cured Modulus at 388.degree. C. is greater than 0.7. 6. A mixture comprising the composition of claim 1, a solvent and a poragen. 7. A mixture comprising the composition of claim 3, a solvent, and a poragen. 8. An article comprising a substrate and on that substrate a film which comprises the cured reaction product of the composition of claim 1. 9. An article comprising a substrate and on that substrate a film which comprises the cured reaction product of the composition of claim 3. 10. A method of making a porous film comprising coating the mixture of claim 6 on a substrate, removing the solvent, curing the resin and decomposing the poragen. 11. A method of making a porous film comprising coating the mixture of claim 7 on a substrate, removing the solvent curing the resin and decomposing the poragen. 12. A composition comprising a poragen and a partially polymerized reaction product of a reaction mixture comprising a compound having two or more cyclopentadienone functional groups and a compound having three or more acetylene functional groups, wherein the composition is further characterized by one or more of the following characteristics (a) the compound having three or more acetylene functional groups is selected from the group consisting of 4',4',4'-tris(phenylethynyl)-1,3,5-triphenylbenzene, and 3',3', 3'-tris(phenylethynyl)-1,3,5-triphenylbenzene, (b) the reaction mixture further comprises a compound selected from the group consisting of bis-ortho-diacetylenes, mono-ortho-diacetylenes, bistriazenes, tetrazines, bisazides, bissulfonylazides and peroxides, or (c) the composition further comprises a multifunctional reagent that can react with the partially polymerized reaction mixture. 13. A method of making a porous film comprising coating the composition of claim 12 on a substrate, removing the solvent, and curing the resin. 14. The composition of claim 12 wherein the multifunctional reagent is selected from the group consisting of bis-ortho-diacetylenes, mono-ortho-diacetylenes, bistriazines, bisazides, bissulfonulazides, and peroxides. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to compositions useful in making low dielectric constant insulating layers in microelectronic devices. BACKGROUND OF THE INVENTION As semiconductor devices become smaller and smaller, and chip packing densities increase correspondingly, undesirable capacitative delays and crosstalk between metal interconnects are more acutely manifested. There has been a movement away from using silicon dioxide with a dielectric constant of about 4.2 to benzocyclobutene based polymers (BCB), such as CYCLOTENE.TM. resins from The Dow Chemical Company, and polyarylene resins, such as those disclosed in WO98/11149, both of which have dielectric constants of about 2.6. Since capacitative delays and crosstalk relate to the dielectric constant of the insulator, additional attention has focused on the creation of ultra-low dielectric constant materials (that is, dielectric materials having dielectric constants of .ltoreq.2.0). Such efforts include creating porous inorganic (for example, silicon dioxide) or thermoplastic polymeric (for example, polyimide) materials. Silicon dioxide, which has been the dominant interlevel dielectric material (ILD) for the past 40 years, can be made porous by well developed sol-gel techniques such as those disclosed in Proc. Mat. Res. Soc. 381, 261 (1995); Proc. Mat. Res. Soc. 443, 91 (1997); and Proc. Mat. Res. Soc. 443, 99 (1997). The inorganic networks which form are highly cross-linked and exhibit substantial modulus at early stages of their formation utilizing relatively low temperature processes. Although the introduction of pores into silicon dioxide causes a reduction of dielectric constant from 4.2 to less than 2.0, the resultant porous material is significantly weakened and the porous coatings are easily damaged during handling and during the processing steps necessary to fabricate microelectronic devices. Thus, porous silicon dioxide is impractical as an ultra-low dielectric constant material. Porous thermoplastic polymers, particularly thermally stable polymers such as polyimides, have also been investigated for use as ultra-low dielectric constant materials. Although these porous thermoplastic materials can be made to have acceptable dielectric constants and are relatively tough, being able to withstand the mechanical processing steps necessary to fabricate microelectronic devices, the pores tend to collapse during subsequent high temperature processing due to the modulus drop associated with being above the glass transition temperature of the resin, thereby precluding the use of these materials for the applications of interest. The initial proposals for developing porous layers generally involve adding a pore generating material, also referred to as a poragen, to a composition comprising a matrix precursor, forming the matrix from the precursor, and then degrading the pore generating material, to form pores in the matrix material. SUMMARY OF THE INVENTION Applicants have discovered that despite being thermosetting resins, certain of the polyarylene resin formulations disclosed in WO98/11149 may suffer from pore collapse when attempting to form a porous structure from the resin by introduction of a poragen into the b-staged formulation, curing and removal of that poragen. This is believed to occur because the poragen degrades before the matrix has sufficiently set. Modifying the formulation so that the resin does not undergo a significant drop in modulus during cure or alternatively shifting the temperature at which the minimum modulus occurs to a lower temperature, enables one to avoid pore collapse and/or use a wider variety of poragen materials. Thus, according to a first embodiment, this invention is a composition comprising a partially polymerized reaction product of a reaction mixture comprising a compound having two or more cyclopentadienone functional groups and a compound having three or more acetylene functional groups, wherein the composition is further characterized by one or more of the following characteristics: (a) the ratio of cyclopentadienone groups to acetylene groups in the reaction mixture is at least about 3:4 and, preferably no greater than 2:1, more preferably the ratio is in the range of 9:10 to 10:9, and most preferably the ratio is about 1:1; (b) the compound having three or more acetylene functional groups is selected from the group consisting of tris(phenylethynyl)diphenyl ethers, tris(phenylethynyl)-ortho-terphenyls, 4',4',4'-tris(phenylethynyl)-1,3,5-triphenylbenzene, and 3',3',3'-tris(phenylethynyl)-1,3,5-triphenylbenzene; (c) the reaction mixture further comprises a compound which has the ability to react with non-functionalized aryl groups; (d) the composition further comprises a reagent selected from the group consisting of bis-ortho-diacetylenes, mono-ortho-diacetylenes, bistriazenes, tetrazines, bisazides, bissulfonylazides and peroxides. Preferably, the composition comprises a solvent and most preferably also comprises a poragen. According to an alternative embodiment, the invention is a composition comprising precursor compound(s) which when cured form a polyarylene material wherein the composition has a modulus profile as measured by torsional impregnated cloth analysis (TICA) characterized in that during heating of the composition a minimum measured modulus observed in the temperature range from 250 to 450.degree. C. occurs at a temperature Tmin, and said minimum measured modulus is greater than a value equal to 20 percent of a measured cured modulus of the composition after heating to a maximum temperature and cooling back down to Tmin. According to a third embodiment, the modulus profile is characterized by having a modulus at 388.degree. C. during heating of the composition which is greater than a value equal to 20 percent of a measured cured modulus of the composition at 388.degree. C. after cure. The invention is also a mixture comprising the composition of the second or third embodiments and a solvent, and preferably, a poragen. Finally, the present invention is a method of making a film comprising coating one of the above compositions onto a substrate, removing the solvent, and curing the resin. Preferably, the composition further comprises a poragen and the method includes a step of removing (e.g. by decomposition) the poragen. The solvent removal, curing, and removing (decomposition) steps may occur separately in stages or may be accomplished by a single heating step. The present invention further includes an article comprising the film made in accordance with the seventh embodiment. Preferably, the article is an integrated circuit article. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-3 are TICA plots for various polyarylene formulations. DETAILED DESCRIPTION OF THE INVENTION A modulus profile of the polyarylene materials during cure may be determined by evaluation of the formulation using torsional impregnated cloth analysis (TICA). In this technique a woven glass cloth (preferably, 0.3 mm thick, 15 mm wide, and 35 mm long) is mounted in a dynamic mechanical analyzer, such as a DuPont 983 DMA, preferably fitted with a Low Mass Vertical Clamp Accessory or equivalent functionality to enhance sensitivity. The ends of the cloth are wrapped in aluminum foil leaving 10 mm in length exposed. The cloth is then mounted in the vertical clamps of the dynamic mechanical analyzer which were set 10 mm apart. The clamps are tightened to about 12 inch pounds using a torque wrench. The cloth is impregnated using a solution comprising the precursor compounds at 10 to 30 percent solids via a pipet. The cloth is thoroughly soaked with the solution and any excess is removed using the pipet. A heat deflector and oven are attached and a nitrogen flow of about 3 standard cubic feet per hour is established. Amplitude of the displacement is set to 1.00 mm and frequency is set to 1 Hz. The sample is heated to 500.degree. C. at 5.degree. C. per minute and then allowed to cool. Data is collected during both the heating and cooling stages. Data analysis may be performed to obtain temperature versus flexural modulus values for the composite of glass and formulation. Prepared software programs such as DMA Standard Data Analysis Version 4.2 from DuPont or Universal Analysis for Windows 95/98/NT Version 2.5H from TA Instruments, Inc., may be used to perform the data analysis. The modulus values themselves are not absolute values for the tested formulation due to the contribution of the glass cloth and the unavoidable variation in sample loading. However, ratioing the modulus value at a point during heating to a modulus of the composite after cure and cool down to some consistent temperature gives a value which can be used to compare different formulations. A typical TICA plot for a control formulation is shown, for example, in FIG. 1. Although not wishing to be bound by theory, the inventors believe it is thought that on heat-up the solvent from the formulation is lost leading to an initial increase in the modulus of the cloth/matrix composite. After further heating the modulus begins to decrease as the temperature of the scan reaches and then exceeds the glass transition temperature of the mixture of precursor compounds. As the precursor compounds begin to react or cure the modulus again increases and then levels out as cure is complete. Upon cool-down the modulus slowly increases in a fairly linear manner. As noted, for the control, a significant drop in modulus is observed between 300 and 400.degree. C. Pore collapse problems can be minimized by raising the modulus in this temperature range. The modulus drop for the formulations of this invention may either be less dramatic or may be moved to a lower temperature, e.g. having the minimum modulus at temperature less than about 325.degree. C. The latter approach helps avoid pore collapse because it is less likely that significant degradation of the poragens will have occurred at these low temperatures. As used herein "Measured Heat-up Modulus" is the modulus at a given temperature detected for the test composite during the heating phase of the test on a plot of modulus versus temperature. "Minimum Measured Heat-up Modulus" is the minimum Measured Heat-up Modulus occurring in the temperature range of 250 to 450.degree. C. "Measured Cured Modulus" is the modulus at a given temperature for the test composite during the cool down phase. The precursor compounds of this invention cure to a polyarylene. By polyarylene is meant aryl moieties or inertly substituted aryl moieties which are linked together by bonds, fused rings, or inert linking groups such as oxygen, sulfur, sulfone, sulfoxide, carbonyl, etc. The precursor composition may comprise monomers, oligomers, or mixtures of monomers and oligomers. Preferably, the precursor composition comprises cyclopentadienone functional compounds and acetylene functional aromatic compounds, and/or partially polymerized reaction products of such compounds, as disclosed in WO98/11149, incorporated herein by reference. The most preferred precursor compositions comprise the following monomers and/or the partially polymerized reaction products of the following monomers: (a) a biscyclopentadienone of the formula: ##STR1## (b) a polyfunctional acetylene of the formula: ##STR2## (c) and, optionally, a diacetylene of the formula: ##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, and y is an integer of three or more. Stated alternatively, the most preferred precursor material comprises a curable polymer of the formula: [A].sub.w [B].sub.z [EG].sub.v wherein A has the structure: ##STR4## and B has the structure: ##STR5## endgroups EG are independently represented by any one of the formulas: ##STR6## 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 M is a bond, 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 about 1000; w is an integer from 0 to about 1000 and v is an integer of two or more. There are a variety of paths which may be used to attain the desired highly branched polyarylene and the polyarylene precursor compositions having the desired modulus profiles during cure. While the preferred polyarylenes are the reaction product of aromatic compounds having two or more cyclopentadienone groups and aromatic compounds having three or more acetylene groups, and this preferred system will be the focus of the discussion, the Inventors contemplate that the same concepts would apply to other aromatic diene and dienophile compounds. First, a high degree of branching may be introduced at the initial stage of polymerization of the monomers (i.e., the partial polymerizing or b-staging). The precursor composition then comprises monomers which form branched curable oligomers and/or those branched oligomers which can cure to form the matrix. To increase the degree of branching during cure one of the following approaches may be used: a) adjusting the ratio of cyclopentadienone groups to acetylene groups in the mixture to values of greater than about 3:4 and, preferably no greater than about 2:1, more preferably the ratio is in the range of 9:10 to 10:9, and most preferably the ratio is about 1:1, provided that at least some of the compounds have three or more reactive functional groups (e.g. cyclopentadienone or acetylene groups) b) using acetylene functional compounds in which the acetylene groups are highly accessible to react with the cyclopentadienone groups, or c) adding additional reaagents that can react with the polyarylene chain and cause further cross-linking or branching. According to one preferred subset of approach a), the monomers are difunctional aromatic cyclopentadienones (CPD) and tri-functional aromatic acetylenes. In order to have the desired ratio of CPD to acetylene, one adjusts the mole ratio of CPD functional compound to acetylene functional compound. Alternatively, a higher functional (3 or more) CPD monomer may be introduced to attain the desired ratio. Suitable higher functional cyclopentadienones include 1,3,5-tris(3-oxo-2,4,5-triphenylcyclopenta-1,4-dienyl)benzene, 4',4',4'-tris(3-oxo-2,4,5-triphenylcyclopenta-1,4-dienyl)1,3,5-triphenylbe nzene, 4',4',4'-tris(3-oxo-2,4,5-triphenylcyclopentadienyl)1,3,5-triphenoxybenzen e, and the like. For approach b), the monomers again are preferably difunctional CPD compounds and tri-functional acetylene compounds. At least some of the acetylene compounds however, have relatively highly accessible acetylene groups. Examples of such accessible acetylene functional compounds include tris(phenylethynyl)diphenyl ethers, tris(phenylethynyl)-ortho-terphenyls, 4',4',4'-tris(phenylethynyl)-1,3,5-triphenylbenzene, 3',3',3'-tris(phenylethynyl)-1,3,5-triphenylbenzene and the like. For approach c) the basic monomers are again preferably difunctional CPD compounds and tri-functional acetylene compounds. The additional reagents may be characterized by the ability to react with non-functionalized aryl groups by, for example, abstraction of protons forming aryl radicals which can combine with other such radicals or radicals on the additional reagent, insertion into aryl-H bonds forming linkages between two polyarylene chains, etc. Examples of such reagents include bis-ortho-diacetylenes as disclosed for example in WO 97/10193, incorporated herein by reference; mono-ortho-diacetylenes; bistriazenes, as disclosed in U.S. Pat. No. 5,155,175, Macromolecules 1992, 25, 7294-7299, incorporated herin by reference; tetrazines, such as 1,3, diphenyltetrazine; bisazides, such as bissulfonylazides as disclosed for example in U.S. Pat. No. 3,282,864, incorporated herin by reference; and peroxides, including diperoxides. The loading levels of the reagents preferably vary from about 1 wt. percent based on solids to about 30 wt. percent based on solids. Alternatively, branching of the polymer may be increased after the initial b-staging. In this case, the precursor composition comprises a polyarylene oligomer and reagents which can lead to branching of the polyarylene oligomer and reagents. The polyarylene oligomer is preferably the reaction product of a difunctional cyclopentadienone compound and a trifunctional acetylene compound. The reagents may be bis-ortho-diacetylenes as disclosed for example in WO97/10193, incorporated herein by reference, mono-ortho-diacetylenes, bistriazenes, tetrazines, bisazides, bissulfonylazides and peroxides. The solvent may be any known solvent useful in processing thermoset polyarylene precursor compositions. The solvent may be a single solvent or a mixture of one or more solvents. Suitable 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 poragen which is preferably also present in the composition may be any compound that can form small domains in a matrix formed from the precursors and cab be subsequently removed, e.g. by thermal decomposition. Examples of suitable poragens may be found in U.S. Provisional Application No. 60/109,110 and in U.S. application Ser. No. 09/447,011, attorney docket number 44398NP, filed concurrently with this application, both of which are incorporated herein by reference. The poragen may be a block polymer, wherein one of the blocks is compatible with cross-linked polymer matrix resin and the other block is incompatible therewith. Useful polymer blocks can include polystyrenes such as polystyrene and poly-a-methylstyrene, polyacrylonitriles, polyethylene oxides, polypropylene oxides, polyethylenes, polylactic acids, polysiloxanes, polycaprolactones, polyurethanes, polymethacrylates, polyacrylates, polybutadienes, polyisoprenes, polyvinyl chlorides, and polyacetals, and amine-capped alkylene oxides (commercially available as Jeffamine.TM. polyether amines from Huntsman Corp.). Thermoplastic homopolymers and random (as opposed to block) copolymers may be utilized as poragens. As used herein, "homopolymer" means compounds comprising repeating units from a single monomer. Suitable thermoplastic materials include polystyrenes, polyacrylates, polymethacrylates, polybutadienes, polyisoprenes, polyphenylene oxides, polypropylene oxides, polyethylene oxides, poly(dimethylsiloxanes), polytetrahydrofurans, polyethylenes, polycyclohexylethylenes, polyethyloxazolines, polyvinylpyridines, polycaprolactones, polylactic acids, copolymers of these materials and mixtures of these materials. The thermoplastic materials may be linear, branched, hyperbranched, dendritic, or star like in nature. The poragen may also be designed to react with the cross-linkable matrix precursor during or subsequent to b-staging to form blocks or pendant substitution of the polymer chain. For example, thermoplastic polymers containing reactive groups such as vinyl, acrylate, methacrylate, allyl, vinyl ether, maleimido, styryl, acetylene, nitrile, furan, cyclopentadienone, perfluoroethylene, BCB, pyrone, propiolate, or ortho-diacetylene groups can form chemical bonds with the cross-linkable matrix precursor, and then the thermoplastic can be removed to leave pores. The poragen may also be a material that has an average diameter of about 1 to about 50 nm. Examples of such materials include dendrimers (available through Dendritech, Inc., and described by Tomalia et al., Polymer J. (Tokyo), vol. 17, 117 (1985), which teachings are incorporated herein by reference); hyperbranched polymer systems, and latex particles. These materials may be nonreactive with the cross-linkable matrix precursor, or reactive as described above. These compositions may be used to make dielectric films and interlayer dielectrics for integrated circuits in accordance with known processes. See e.g. WO98/11149, incorporated herein by reference. To make a porous film the poragen is preferably removed by thermal decomposition of the poragen. |
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