Among the more promising approaches to minimizing capacitance in the multilevel interconnect of integrated circuits containing sub-half micron metal spacings is the development of organic polymers which exhibit high performance in key attributes such as thermal stability, low dielectric constant, and low moisture absorption coupled with high outgassing rates of what little moisture may be present. The use of such polymers as the intermetal dielectric can reduce power consumption and cross talk, while increasing signal propagation speed. While polyimides are the most extensively characterized polymer thin film dielectrics, and are in many cases suitable for the intermetal dielectrics in multichip modules, their tendency to absorb significant quantities of moisture, coupled with relatively slow outgas characteristics (presumably due to hydrogen bonding between water molecules and the carbonyls of the polyimide) constitute significant impediments to throughput in the fabrication of IC interconnects.
The search for alternative polymers which incorporate the “good” characteristics of polyimides while exhibiting improvements in electrical, moisture, and processing characteristics led us to the development of nominally 1 μm spin-on films derived from a family of noncarbonyl containing aromatic polyethers. Fluorinated poly(arylethers) based on decafluorobiphenyl exhibit thermal stability comparable to polyimides, from ten to forty times lower moisture absorption, dielectric constants in the mid-two's, and good retention of storage modulus above their glass transition temperatures. The precursor spin-on solutions, formulated in low toxicity organic solvents, exhibit excellent shelf life, and can be prepared with extremely low levels of metallic contamination. This paper describes the synthesis and both solution and film properties of this newly developed class of highly processible thermally stable polymers, first reported by Mercer, et. al. . The characteristics of the polymers when spin-coated on silicon wafers is emphasized. Thermal and thermomechanical properties of nominally 10-25 μm free standing films are also described.