Structural, thermal and electrical properties of plasma deposited a-C:F films

Flurinated amorphous carbon (a-C:F) films were deposited at room temperature using C4F8 and CH4 as precursor gases by electron cyclotron resonance chemical vapour deposition (ECR-CVD). Chemical compositions and bond structures were investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). CF=C (1680cm(-1)), as well as CF2=CF (1780cm(-1)) that acted as termination groups of the cross-linking film structure were identified in the deposited a-C:F films. C Is peaks were assigned to CF3(295eV), CF2(293eV), CF(291eV), C-O(289eV), C-CFx(x=1 similar to 3) (287cV) and C-C termination bond(285eV), respectively. The CF3 and C-C termination bonds were thermally liable and could induce reduction of film thickness after heat treatment through out-gassing effect. The thermal stability of a-C:F films improved with increasing cross-linking C-CFx, bonds and decreasing CF3 and C-C termination bonds. The dissipation factor of the as-deposited metal-insulator-semiconductor capacitor (MIS-C) was approximately 0.07 at 1MHz. The dielectric constant of a-C:F films increased after heat treatment due to reduced electronic polarization and enhanced film density. The interface trap density decreased from (5 similar to 9) x 10(11) eV(-1) cm(-2) to (4 similar to 6) x 10(11) eV(-1) cm(-2) after 300 degrees C annealing in a nitrogen environment. The current-voltage characteristics for a-C:F films was explained using ohmic conduction at low fields and Poole-Frankel(PF) conduction mechanism at high fields. The trap energy of the traps at band tails formed by the delocalized pi electrons decreased after annealing, which led to increase of leakage current due to field-enhanced thermal excitation of trapped electrons into the conduction band.