Acetylene-terminated polyimide oligomers as the interlayer dielectric for multilevel interconnects, some basic electrical characterizations

The dielectric constant (E_rPI) and bulk resistivity (ρ) of three different Thermid polyimide thin-film dielectrics were measured. This was accomplished by actually fabricating a microelectronic capacitor device which utilizes the Thermid polyimide film as the dielectric. The dielectric constant for films from all formulations studied was around 2.8 at a 1-MHz frequency with an average bulk resistivity of 10⁸ Ω-cm. It was found that high heat and moisture exposure and cure schedule (time and temperature) had little effect on these values. The only trend noticeable was related to cure atmosphere, with slightly higher values obtained for the dielectric constant of films processed in nitrogen rather than in air. The results of capacitance-voltage (C-V) studies for these thin dielectric films are also presented. The resulting shift in flatband voltage of a biased sample vs. a control leads to the calculation of total mobile cation concentration expressed as [Na] in ppm. Results indicate that the polyimide thin films contain between 3 and 13 ppm total [Na]