Investigation of Charge Neutralization Behavior in Cu∕6FDA-PPD∕Si MIS Capacitors by Capacitance-Voltage Measurement

Abstract

In this work, the capacitance-voltage ͑C-V͒ characteristics of Cu/2,2Ј-bis-͑3,4-dicarboxyphenyl͒ hexafluoropropane dianhydride ͑6FDA͒-p-phenylene diamine ͑PPD͒/Si metal-insulator-semiconductor ͑MIS͒ capacitors after different annealing processes are investigated. During annealing ͑in N 2 + H 2 ambient and in vacuum͒, positive charges are generated in the capacitors and it leads to a shift of flatband voltage ͑V FB ͒ toward the negative-bias direction. However, the V FB of the annealed samples moves backward ͑the positive bias direction͒ after aging at room temperature in air for 1 week. In addition, stretch-out of C-V curves is observed after the annealing process. Nevertheless, the stretch-out behavior is released after aging in air for 1 week. Influence of annealing condition and time aging effect on C-V characteristics of Cu/6FDA-PPD/Si capacitors are discussed.Polymers, with their flexible and insulating nature, are considered as potential materials to be used in the next-generation microelectronics of miniature and flexible devices. 1,2 Among them, fluorine-contained polyimide have been widely investigated because of their good electrical properties, excellent thermal stability ͑Ͼ500°C͒, superior resistance to chemicals, high transparency in visible light region, and good mechanical properties. 3,4 Most commonly, applications of poyimides are for optoelectronic devices, 5 thin-film transistors ͑TFTs͒, 6 and integrated circuits ͑ICs͒. 7 Investigations of polyimides have been reported in many previous researches; however, most of them were focused on the thermal and mechanical properties of the bulk polyimides. 8-10 Research on the electrical properties of polyimides is deficient. Minor changes in polymers after annealing under the glass transition temperature is often neglected. Nevertheless, very small changes in atomic arrangement within the polymers may affect its electrical property and thus impact the device properties. Because the introduction of polymer materials into electronic devices is inevitable, the details of the electrical properties of polymers after various annealing processes should be clarified.In this study, 2,2Ј-bis-͑3,4-dicarboxyphenyl͒ hexafluoropropane dianhydride ͑6FDA͒-p-phenylene diamine ͑PPD͒ fluorine-contained polyimide was synthesized and annealed in the various annealing processes, and applied as the dielectric layer in the metal-insulatorsemiconductor ͑MIS͒ structure. Through the capacitance-voltage ͑C-V͒ measurement, variations of C-V characteristics after different heat treatments and time aging processes are investigated. The correlation between the electrical behavior and the reactions within the Cu/6FDA-PPD/Si capacitor is also discussed.6FDA, PPD, and anhydrous N-methylpyrrolidine ͑NMP͒ were obtained from the commercial source without further purification. The synthesis reaction of the viscous poly͑amic acid͒ precursor was carried out by mixing 6FDA and PPD monomers with a ratio of 1:1 in an appropriate amount of NMP in N 2 atmosphere at room temperature. The precursor wa...