Jeff W. Labadie

Nanopore foams of high-temperature polymers

A method of generating high-temperature polymer foams with pore sizes in the nanometer regime was developed. The nanofoams were prepared by casting a block copolymer composed of a thermally stable and a thermally labile block, followed by a subsequent thermal treatment to degrade the labile material and generate the pores. The morphology of the block copolymer film was made up of a high-temperature polymer matrix, with the labile component as the dispersed phase. Thermolysis of the labile block affords pores where the size and shape of the pores are dictated by the initial copolymer morphology. Nanopore foam formation is described for triblock copolymers of poly(phenylquinoxaline), with poly(propylene oxide) as the labile block. Foam formation led to a 10-15% reduction in density, consistent with the poly(propylene oxide) composition, and a dielectric constant of 2.3. SAXS and TEM (transmission electron microscopy) measurements indicated pore sizes of approximately 10 nm.<<ETX>>

Nanoscopically Engineered Polyimides

Polyimides are currently the materials of choice for interlayer dielectrics in microelectronic applications, since polyimides, as a class of materials, best satisfy the requisite properties to survive the thermal, chemical, and mechanical stresses associated with microelectronic fabrication. As more function is demanded of these polymer dielectrics, e.g., low residual thermal stress, adhesion, photosensitivity, and low dielectric constant, it becomes increasingly difficult to design materials with the desired enhancements without compromising existing properties. This article will describe an approach to modify polyimide with minimal sacrifice to its desirable properties. The preparation of block and graft copolymers provides a means of tailoring the morphology and properties of polyimide through the judicious choice of the coblock, coblock composition, molecular architecture, and block lengths. It is the advent of the poly(amic alkyl ester) intermediate to the polyimide that allows for the controlled synthesis of such block copolymers. The hydrolytic stability of the poly(amic alkyl ester) precursor allows for the isolation and characterization of the copolymers prior to imidization. Such systems represent self-assembling arrays with considerable potential for the preparation of nanostructures, and this article will describe the modification of rigid and semi-rigid polyimides through copolymerization to address favorably such issues as residual thermal stress, dielectric constant, auto-adhesion, and other key design criteria.

Fabrication and performance studies of multilayer polymer/metal interconnect structures for packaging applications

Multilayer copper/polyimide interconnect structures were fabricated using a reactive-ion-etching-based lift-off technique. Conductor cross-sectional area control, planarity, and a gap-free structure were made possible by the use of a novel siloxane-polyimide. The resultant structure consisted of two signal wiring layers between two ground planes with a nominal impedance of 40 Omega . Although redundant metallization processes were found to repair open lines, they resulted in an increase of the number of processing steps and could result in an increase of defects. Stud chain structures were found to survive cooling to 77 K with very little change in their characteristics, while heating of the copper interconnections to 350 degrees C in a reducing environment reduced their resistance by 3%.<<ETX>>

ADHESION PROPERTIES OF A STRUCTURAL ETCH STOP MATERIAL FOR USE IN MULTILAYER ELECTRONIC WIRING STRUCTURES

A thermally stable copolymer of a polyimide and a dianiline terminated polydimethylsiloxane has been developed for use as a structural oxygen etch barrier material in high performance multilayer electronic wiring structures. We report on the preparation of the etch barrier material and on investigations of the etch stop and adhesion properties of this material. Studies on the effects of adhesion-promoting plasma treatments are supported by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) data. Before plasma treatment, it is observed that the siloxane component segregates to the surface. After either an O 2 reactive ion etch treatment or H 2 O plasma exposure, the unusual XPS charging effects are interpreted as a surface layer containing two distinct phases: the etched polyimide fraction and a partial overlayer of a carbon containing SiO 2

Base-catalyzed photosensitive polyimide

A scheme for imaging of polyimide films is described which is based on the amine-catalyzed imidization of poly(amic alkyl ester) precursor polymers. Films containing amine photogenerators along with poly(amic alkyl esters) are patterned by exposure followed by heating to partially imidize the exposed portion of the film. Negative images are developed by taking advantage of the greater solubility of the precursor polymer which is dissolved in an appropriate solvent mixture. A final cure is carried out to complete the imidization of the patterned film.

Synthesis of imide-aryl ether benzoxazole block copolymers

SummaryImide-aryl ether benzoxazole multiblock copolymers were investigated. A key feature of these copolymers was the preparation of bis(amino) terminated aryl ether benzoxazole oligomers (PBO) via a novel nucleophilic aromatic displacement polymerization. Oligomers with number average molecular weights of 10,500 and 26,000 g/mol were prepared, which displayed Tgs of 210 and 227°C, respectively. The oligomers were co-reacted with 4,4′-oxydianaline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in a NMP/ cyclohexanone solvent mixture in the presence of N-methylmorpholine. The resulting amic ester-aryl ether benzoxazole copolymers were isolated and washed to remove homopolymer contamination. Copolymer compositions were analyzed by 13C NMR. Solutions of the copolymers were cast and cured to effect the imidization, affording tough films with high elongations. Multiphase morphologies were obtained for both of the PBO block lengths used in the copolymerization.

Polyimides with reduced dielectric anisotropy

Ordered polyimides have been the subject of considerable interest for thin film applications due to their excellent balance of final properties, however, these polyimides have been shown to have an exceptionally large dielectric anisotropy. Two approaches were examined as a means of obtaining materials with lowered dielectric anisotropies. ATR spectroscopy was used to measure in-plane and out-of-plane refractive indices from which the directional dielectric constant was estimated. In one case, monomers based on hexafluoroisopropylidine were introduced into PMDA at levels /spl les/20 mole%. This afforded some reduction in the in-plane dielectric constant. A more promising approach involved the use of polyimides derived from 2,2-bis(trifluoromethyl)benzidine (BTFB). The PMDA-BTFB polyimide displayed the best combination of properties, including an estimated in-plane dielectric constant of 2.9 and an out-of-plane dielectric constant of 2.6 at 1 MHz.<<ETX>>

Multiphase imide block copolymers: new materials for microelectronics applications

Imide block copolymers were investigated as a means of lowering the dielectric constant and improving the polymer-polymer adhesion of poly(4,4-oxydiphenylenepyromellitimide) (PMDA/ODA). Poly(perfluoroalkylenearyl ether) (PFAAE) was used as a coblock to introduce fluorine and lower the dielectric constant of PMDA/ODA. Poly(aryl ether-phenylquinoxaline) (PQE) coblocks were incorporated to improve polymer-polymer adhesion, since conventional poly(phenylquinoxalines) are known to be excellent hot melt adhesives. The preparation of imide copolymers required the use of poly(amic ester), rather than poly(amic acids), as the imide precursor. PFAAE and PQE were selected as coblocks due to their compatibility with the solvents required for the poly(amic ester) synthesis and processing as well as their excellent thermal stability and mechanical properties. The copolymers could be processed and cured with conventional techniques to afford high-quality coatings. The block copolymers showed excellent final properties, including high dimensional stability and tough, ductile mechanical properties. The materials displayed a heterogeneous morphology with submicron domains of PFAAE or PQE in a polyimide matrix. The PFAAE copolymers showed a reduction in dielectric constant relative to PMDA/ODA ( epsilon approximately=2.8), and the copolymers of PMDA/ODA with approximately=15-wt.% PQE showed excellent self-adhesion, as predicted.<<ETX>>

Synthesis and characterization of phenylquinoxaline-arylene ester block copolymers

SummaryPhenylquinoxaline-arylene ester block copolymers were prepared from phenolic hydroxyl terminated oligomers of defined molecular weight using an oligomer/monomer(s) approach, in which generation of the ester linkage coupling the blocks occurred concomitantly with the growth of the polyester block. The molecular weight of the phenylquinoxaline block was held constant at 12,900, while the stoichiometry of the arylene ester monomers were adjusted to afford copolymers containing 15, 30, and 50 wt% poly(arylene ester). These copolymers represent the first example of PPQ-based block copolymers derived from well defined phenylquinoxaline oligomers.

Solid state properties of phenylquinoxaline-arylene ester copolymers

SummaryThe thermomechanical behavior and mechanical properties were studied for a series of poly (phenylquinoxaline-arylene ester) block copolymers. The copolymers investigated were composed of a phenylquinoxaline oligomer of block length 12,900 g/mol, and the weight percent of the polyester coblock varied from 15 to 50 percent. Both homo-and heterogeneous morphologies were observed depending on the weight percent of polyester incorporated. Improved elongations were observed as the polyester compositions increased at a minimal sacrifice to the bulk properties (i.e., modulus).