Dependence of the dielectric constant on the fluorine content and porosity of polyimides

The trend toward miniaturization in integrated circuit fabrication demands good interlayer dielectric materials. This need can be met by polyimide (PI), which has extreme thermal and chemical stability and, most importantly, a low dielectric constant. Four porous PIs with symmetrically substituted fluorine contents were synthesized. Different porosity levels were achieved with a sol–gel technique through the incorporation of 10 or 20% tetraethyl orthosilicate into the polymer matrix and then acid etching. Their dielectric constants were correlated with the fluorine contents and porosity levels. High porosity levels and higher fluorine contents induced substantial decreases in the PI dielectric constants (2.4–2.7). The resultant values were within the applicable range for dielectric materials in integrated circuits.