Investigations of the low dielectric constant fluorinated polyimide for use as the interlayer dielectric in ULSI

Low dielectric constant interlayer dielectric (ILD) materials are required for the advanced silicon integrated electronics such as those in the ULSI era. We have investigated several such materials. In this paper the results of our investigations of the materials and electrical properties, processing (to form ILD), and applicability of a DuPont fluorinated polyimide are described and discussed. Weight loss, FTIR, and ellipsometric measurements have been carried out. The DuPont fluorinated polyimide thin film was observed to be thermally stable up to 450 °C, which is monitored by using dynamic TGA with a ramping rate of 10 °C/min or 5 °C/min in N₂ Ambient. Also MPOS capacitor characterization, effect of temperature and moisture on these properties have been determined. The dielectric constant was observed to be as low as 2.5 and the refractive index is around 1.63, both being stable up to 450 °C. However, the DuPont Fluorinated polyimide exhibited a flat band voltage shift on C-V curve after 400 °C annealing in vacuum environments for 1 hr. Compatibility with copper as the interconnecting metal has been determined and discussed. It is concluded that this polymer is a possible candidate for ILD application.