Deposition of fluoropolymer films on Si(100) surfaces by Rf magnetron sputtering of poly(tetrafluoroethylene)

Dielectric polymer films of about 40-300 nm in thickness were deposited on Si(100) substrates via rf plasma sputtering of a poly(tetrafluoroethylene) (PTFE) target using different sputtering gases, including Ar, CF₄, N₂, and H₂. Oxygen plasma failed to give rise to any significant deposition. X-ray photoelectron spectroscopy (XPS), time-of-fight secondary ion mass spectrometry (ToF-SIMS), water contact angle measurement, and Fourier transform infrared (FTIR) spectroscopy results indicated that the chemical composition and molecular structure of the sputter-deposited polymer films depended strongly on the type of the sputtering gas used. The Ar, CF₄, and N₂ plasmas gave rise to PTFE-like films with a high fluorine content, although N-containing moieties were also found in the N₂ plasma-deposited films. The H₂ plasma, on the other hand, resulted only in the deposition of a polyethylene-like film. The deposition rate and the dielectric constant (κ) of the resulting fluoropolymer films were also found to be dependent on the type of the sputtering gas. The fluoropolymer film deposited from sputtering by CF₄ plasma had a κ value of 1.9, which was lower than that of the pristine PTFE film (κ = 2.0-2.1). On the other hand, the nonreactive Ar plasma gave rise to the highest deposition rate among the five sputtering gases. Peel adhesion test results suggested that all the sputter-deposited films adhered strongly to the Si(100) surfaces.