Study On The Preparation And Properties Of Nanoporous Polyimide Based Membranes

The application of low dielectric constant(low-k) dielectric materials can greatly reduce the resistance capacitance(RC) time delay, cross-talk and power dissipation in the new generation of high-density and high-speed integrated circuits(IC). In addition to exhibiting low k, the next generation of dielectric materials must satisfy a variety of requirements(i.e. good breakdown voltage, good chemical corrosion resistance and thermal stability, low moisture absorption and good adhesion to the semiconductors and metals). Polyimides(PIs) have been widely used as dielectric and packaging materials in the microelectronics industry because of their good mechanical, thermal, and dielectric properties. However, with dielectric constant of 3.1~3.5, the conventional PIs are insufficient in meeting the requirement of k<2.0 for the dielectric of the near future. In recent years, the introduction of air holes into the interconnection structure, and the introduction of nanoscale porous in polymer matrix become a new method to reduce the dielectric constant.In this paper, nanoporous polyimide membrane was prepared by template method, and then the dielectric constant, electrical properties, thermal properties of the membrane were studied. Monodispersity nanoporous porogens with template was synthesized by the method of emulsion polymerization. The size of the porogens can be controlled through the raw materials ratios, and the initial concentration of monomer, initiator, emulsifier and the polarity of the dispersing agent. So the hydrophilic-lipophilic balance and the size of the porogens can be better controlled. Furthermore, the porogens were introduced into the polyimide precursor, the porogens were then removed in the process of the imidizationg with high temperature.SEM results showed that, the porogen particle size was about 30 nm with a smooth surface, good sphericity and monodisperlity, which can be well spread out in the solvent. The size of the porogens can be controlled through the the change of the reaction condition, so the size of the porogens can be better controlled. According to the TG-DSC analysis, it indicated that the porogens begun to decompose at 180 ?, and almost break down completely at 440 ?, which can ensure that the removal of the porogens by thermal decomposition method and get the nanoporous polyimide membrane. The polyimide membrane had nanoporous structure, and the pores in the membrane had a certain range of size. With the increase of mass fraction of porogen, the porosity increased. While the mass fraction of porogen exceeded a certain value, the number of the holes of the porous polyimide films decreased. The phenomenon was also showed with the dielectric constants. The thermal stability and resistance to electric breakdown performance with different mass fraction of porogen presents had no large difference. The membrane which we get can be applied in the new generation of high-density and high-speed integrated circuits.