Due to recent rapid development of information and communication techniques, astronomical amount of data needs to be processed or stored at a fast rate. As a result, semiconductor chips in one electronic system are required to transform from the mono-chip form to the multi-chip package form connecting several chips by a paratactically treating way. For use in circuits of such multi-chip packages, the development of low dielectric insulating materials with excellent thermal and mechanical properties is essential. Particularly, in view of reducing signal delays and capacitances being critical to the device performance, the timely development of insulating filling materials with lower dielectric constant is required. Moreover, low dielectric materials used as, for example, interlayer dielectric materials of thin film transistors of liquid crystal displays or other electronic devices are the core elements of the devices because such low dielectric materials can function as protecting integrated circuits, increasing the processing rate of the devices, reducing the power consumption, and reducing the weight of the devices. Consequently, the development of such low dielectric materials with properties, which can be compatible with existing and/or future fabrication methods, is crucial.
According to the ITRS (International Technology Roadmap for Semiconductors) prediction of U.S. semiconductor industry, low dielectric materials for multi-chip packages, that are to be developed before the year 2005, must have excellent properties such as a dielectric constant of no more than 2.0, thermal stability above 300° C. and low hygroscopicity among others. In addition, after the year 2005, there will be additional requirement for materials to develop ultrafast data processing systems based on optical circuits as well as on electronic circuits. Organic thin-film materials targeted for such optoelectronic systems must have a relevant index of refraction, high optical transparency, and low loss of light.
Conventionally, silicon oxide films (SiO2) have been dominantly used for the insulating materials of semiconductor packages as well as interlayer insulating elements. However, since SiO2 has a high dielectric constant above 4.0, it has already reached the limitation to be considered as interchip packaging materials of the next generation. Accordingly, various trials have already been conducted to develop low dielectric materials for the next-generation packages. Examples of low dielectric materials developed up until now include polyimides, benzocyclobutenes, polynorbornenes, and so forth.
Polyimides among the group mentioned above have a high dielectric constant of 2.9˜3.5 and high hygroscopicity, and electrical/optical anisotropy occurs in polyimides due to its inherent chemical structures. Benzocyclobutenes developed by Dow also have a high dielectric constant of about 2.7. Moreover, the process to prepare thin films based on benzocyclobutenes is known to be rather complex and their adhesion to metal surfaces are poor.
Polynorbornenes have excellent properties such as high thermal stability, low hygroscopicity, electrical/optical isotropy among others but have poor adhesion to metals. Recently, BF Goodrich synthesized a new class of polynorbornenes by incorporating a silicon compound containing alkoxy groups to the norbornene monomer in order to improve the adhesion to metals. However, the prepared polynorbornene has a high dielectric constant of about 2.7. Thus, materials with excellent thermal and mechanical properties, yet maintaining low dielectric constant, are required for use as an element for semiconductor packages of the next generation.
From the fabrication perspectives, on the other hand, above mentioned low-dielectric materials should also possess excellent solubility to common organic solvents. Conventional norbornene-based copolymers, however, have poor solubility to organic solvents. As a result, when optoelectronic systems are to be fabricated by spin-coating using such conventional norbornene-based copolymers, there are drawbacks such that a certain solvent must be used at a higher temperature. In order to resolve this kind of drawback, various trials have been conducted such as controlling the design of comonomers used in the copolymers, the content of comonomer in the copolymers, molecular weight of the copolymers, and so forth.