PTFE nanoemulsions as spin-on, low dielectric constant materials for ULSI applications

ULSI Interconnects require insulative materials with as low a dielectric constant as possible in order to minimize crosstalk and parasitic capacitance. Transmission line simulations indicate that crosstalk in parallel interconnect lines can be dramatically reduced by lowering the dielectric constant of the insulation from 4 to 2. Polytetraftuoroethylene (PTFE) has a desirably low dielectric constant (2.05), but has previously been difficult to deposit in thin films suitable for integrated circuit applications. PTFE has other desirable properties, including temperature resistance in excess of 400 C and outstanding chemical resistance. A novel liquid material has been developed which permits the spin coat deposition of full density PTFE films from 0.2 to 1.0 microns thick. The deposition liquid is a solvent-free, stable PTFE nanoemulsion consisting of fully cured < 0.05 micron particles, surfactant, and water. The nanoemulsion is an equilibrium phase which is thermodynamically stable, optically clear, and has low viscosity. These properties are achieved because of the unusually small particle size of the nanoemulsion. The films are uniform in thickness with a standard deviation of < 2% and edge-to-center variation of < 5%. The films have a weight loss rate of less than 0.008%/min at 425 degrees C. Good adhesion to Al, Si3N4, Sir and SiO2 is obtained when the films are evaluated per ASTM D3359-93. Several reseachers have reported methods by which various materials may be deposited onto PTFE with acceptable results.