Dielectric characterization of microwave plasma enhanced chemical vapor deposition diamond films with Ar–H2–CH4 gas mixture

Dielectric properties of diamond films grown by microwave plasma enhanced chemical vapor deposition (MPECVD) on tungsten carbide (WC) substrates from Ar–H2–CH4 gas mixture were studied using an impedance analyzer. The dielectric dispersion is observed in the frequency range from 100 Hz to 15 MHz. The real and imaginary parts of impedance of diamond films deposited at the different Ar ratios of the reactive gases consist of a semicircle in the complex plane and can be fitted to the theoretical circuit model. The frequency dependence of the imaginary part of the impedance implies different time constants τ, which are closely related to the diamond film’s AC resistivity ρ and dielectric constant ε. The values of the resistivity of diamond films increase with increasing Ar gas ratio, which is an indication of lower graphite content of the samples with higher Ar gas ratio. Raman spectroscopy also confirmed the results. It is found that Ar ions in a microwave plasma possess the ability to remove the unexpected non-diamond phases and improve the diamond quality.