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

Abstract

Flurinated amorphous carbon (a-C:F) films were deposited at room temperature using C4F8and CH4as 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 1s peaks were assigned to CF3(295eV), CF2(293eV), CF(291eV), C-O(289eV), C-CFx(x=1∼3) (287eV) and C-C termination bond(285eV), respectively. The CF3and 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-CFxbonds and decreasing CF3and 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∼9) ×10¹¹eV^-1cm^-2to (4∼6) ×10¹¹eV^-1cm^-2after 300°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 π electrons decreased after annealing, which led to increase of leakage current due to field-enhanced thermal excitation of trapped electrons into the conduction band.