Low dielectric constant polymers for microelectronics

Polymer membranes for high temperature proton exchange membrane fuel cell : recent advances and challenges

Modern computer microprocessor chips are marvels of engineering complexity. For the current 45 nm technology node, there may be nearly a billion transistors on a chip barely 1 cm2 and more than 10 000 m of wiring connecting and powering these devices distributed over 9-10 wiring levels. This represents quite an advance from the first INTEL 4004B microprocessor chip introduced in 1971 with 10 μm minimum dimensions and 2 300 transistors on the chip! It has been disclosed that advanced microprocessor chips at the 32 nm node will have more than 2 billion transistors.1 For instance, Figure 1 shows a sectional 3D image of a 90 nm IBM microprocessor, containing several hundred million integrated devices and 10 levels of interconnect wiring, designated as the back-end-of-the-line (BEOL). Since the invention of microprocessors, the number of active devices on a chip has been exponentially increasing, approximately doubling every two years. This trend was first described in 1965 by Gordon Moore,2 although the original discussion suggested doubling the number of devices every year, and the phenomenon became popularly known as Moore’s Law. This progress has proven remarkably resilient and has persisted for more than 50 years. The enabler that has permitted these advances is known as scaling, that is, the reduction of minimum device dimensions by lithographic advances (photoresists, tooling, and process integration optimization) by ∼30% for each device generation.3 It allowed more active devices to be incorporated in a given area and improved the operating characteristics of the individual transistors. It should be emphasized that the earlier improvements in chip performance were achieved with very few changes in the materials used in the construction of the chips themselves. The increase of performance with scaling * Corresponding author. E-mail: gdubois@us.ibm.com. † IBM Almaden Research Center. ‡ Stanford University. Willi Volksen received his B.S. in Chemistry (magna cum laude) from New Mexico Institute of Mining and Technology in 1972 and his Ph.D. in Chemistry/Polymer Science from the University of Massachusetts, Lowell, in 1975. He then joined the research group of Prof. Harry Gray/Dr. Alan Rembaum at the California Institute of Technology as a postdoctoral fellow and upon completion of the one-year appointment joined Dr. Rembaum at the Jet Propulsion Laboratory as a Senior Chemist in 1976. In 1977 Dr. Volksen joined the IBM Research Division at the IBM Almaden Research Center in San Jose, CA, where he is an active research staff member in the Advanced Materials Group of the Science and Technology function.

Low dielectric constant materials.

A review on colorless and optically transparent polyimide films: Chemistry, process and engineering applications

Polyimide gels are produced by cross-linking anhydride capped polyamic acid oligomers with aromatic triamine in solution and chemically imidizing. The gels are then supercritically dried to form nanoporous polyimide aerogels with densities as low as 0.14 g/cm3 and surface areas as high as 512 m2/g. To understand the effect of the polyimide backbone on properties, aerogels from several combinations of diamine and dianhydride, and formulated oligomer chain length are examined. Formulations made from 2,2′-dimethylbenzidine as the diamine shrink the least but have among the highest compressive modulus. Formulations made using 4,4′-oxydianiline or 2,2′dimethylbenzidine can be fabricated into continuous thin films using a roll to roll casting process. The films are flexible enough to be rolled or folded back on themselves and recover completely without cracking or flaking, and have tensile strengths of 4–9 MPa. Finally, the highest onset of decomposition (above 600 °C) of the polyimide aerogels was obtained usi...

Mechanically strong, flexible polyimide aerogels cross-linked with aromatic triamine.

New polyimides have been prepared from 2,2[prime]-bis(fluoroalkoxy)benzidines and several dianhydrides. The new diamines, with fluoroalkoxy groups OCF[sub 3], OCF[sub 2]CF[sub 2]H, and OCF[sub 2]CFHOC[sub 3]F[sub 7], were obtained from the corresponding 3-(fluoroalkoxy) nitrobenzenes by reduction to hydrazo derivatives, followed by benzidine rearrangements. High-quality polyimide films from these diamines have been prepared by standard procedures and their thermal, mechanical, and electrical properties compared to known polyimides, including those derived from 2,2[prime]-bis(trifluoromethyl) benzidine. Polymers from the diamine with OCF[sub 3] substituents show an especially favorable combination of low dielectric constant, moisture absorption, and coefficient of thermal expansion (CTE) and high thermal stability, suggesting promise as a next-generation material for electronics applications. Polymers from diamines with the largest fluoroalkoxy substituents have very low moisture absorption, but surprisingly high CTE.

Synthesis and properties of fluorinated polyimides from novel 2,2'-bis(fluoroalkoxy)benzidines

The mechanical relaxation behavior of polyimides based on a variety of 2,2'-disubstituted benzidines and rigid dianhydides was investigated. Two transitions were observed in these polyimides. The glass relaxation process is relatively weak and occurs at high temperatures due to the linear and rigid nature of these polyimides. The subglass relaxation is very prominent in these polyimides and is due to main-chain rotational motion localized within the diamine (benzidine) sequent. Changes in the dianhydride moiety have little effect on the temperature of the subglass transition and result in only minor changes in the magnitude of this relaxation. The presence of 2,2'-CF 3 substituents on the benzidine moiety increases the magnitude and shifts the subglass relaxation approximately 150 o C to higher temperatures versus Cl or CH 3 in these positions. Incorporating a flexible ether linkage between the phenyl rings of the benzidine and the CF 3 side group (e.g., OCF 3 ) substantially reduces the temperature and to some extent the magnitude of the subglass relaxation. Replacement of the 2,2'-disubstituted benzidine unit (two phenyl rings) with one (benzene) or three (terphenyl) unsubstituted phenyl rings results in a substantial decline in both the temperature and magnitude of the subglass relaxation. Molecular modeling was used to clairify the nature of the subglass relaxation. Rotational energy barriers for the 2,2'-disubstituted benzidines, calculated from both semiempirical and density functional quantum mechanical calculations, are comparable in magnitude to the experimentally determined activation energies for the subglass relaxation

Relaxation Behavior of Polyimides Based on 2,2'-Disubstituted Benzidines

Perfluorinated polyimides (and co-polyimide) compositions, particularly films are disclosed, comprising at least 50 mole percent of a polymeric repeat unit derived from contacting 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BDPA) and 2,2′-bis(trifluoromethyl) benzidine (TFMB) monomers. The perfluorinated polyimide (and co-polyimide) films of the invention have an in-plane coefficient of thermal expansion (CTE) between −5 and +20 ppm/° C. and a average light transmittance percent of from about 65.0 to about 99.0 (on a 75-micron thick film basis). The films of the present invention were converted to a polyimide using a chemical conversion method instead of typically employed thermal conversion step thus yielding these desirable properties. The films of the present invention can be an excellent substrate in an optical display device and can be used to replace rigid glass substrates. Finally, the polyimide films of the invention can also be used to manufacture flexible display devices (e.g., cellular phones, personal digital assistants, portable video games, laptops, and the like).

Low color polyimide compositions useful in optical type applications and methods and compositions relating thereto

The preparation of a range of 9,9-disubstituted xanthene dianhydrides is discussed, as is their use in the separation of poly(amic acid)s and polyimides. Groups in the 9,9-positions include various combinations of phenyl, substituted phenyl, methyl, ethyl, butyl, trifluoromethyl, perfluoroethyl, perfluoropropyl, cyclotetramethylene, cyclopentamethylene, hydroxy, and acetoxy. Polyimide films prepared from some of these new dienhydrides exhibit good mechanical properties, lower dielectric constant, lower moisture absorption, and low coefficient of thermal expansion, demonstrating their potential use in electronic applications. In addition, these new materials may find use in other film, fiber, and part applications

Polyimides Based on 9,9-Disubstituted Xanthene Dianhydrides

The present invention is directed to coverlay compositions derived from two-layer polyamic acid-based composites having a cover layer and adjacent thereto an adhesive layer wherein the cover layer comprises polyamic acid and other additives allowing the composition to be photosensitive and aqueous base developable, and where the adhesive layer can form a polyimide having a glass transition temperature between 170 and 250° C. The two-layer coverlay compositions of the present invention are used to encapsulate metal circuit traces formed on a flexible printed circuit base substrate. These two-layer compositions are particularity useful due to having an overall in-plane CTE between 10 and 40 ppm/° C. a range that is useful in avoiding unwanted curling of a flexible printed circuit when used as a polyimide-based coverlay material.

Brian C. Auman

Papers

Synthesis and properties of fluorinated polyimides from novel 2,2'-bis(fluoroalkoxy)benzidines

Relaxation Behavior of Polyimides Based on 2,2'-Disubstituted Benzidines

Low color polyimide compositions useful in optical type applications and methods and compositions relating thereto

Polyimides Based on 9,9-Disubstituted Xanthene Dianhydrides

Polyimide composite coverlays and methods and compositions relating thereto