Very Low Dielectric Constants of Diamond-Like Carbon Films Deposited on Ground Electrode by Plasma-Enhanced Chemical Vapor Deposition

Abstract

Hydrogenated diamond-like carbon (g-DLC:H) was deposited using methane (CH4) gas on p-type Si wafers on a grounded electrode using a plasma-enhanced chemical vapor deposition apparatus. The g-DLC:H films were of low dielectric constant <2.4ε0 proportional to the film thickness, and their densities and refractive indexes were approximately 1.25 g/cm3 and 1.56, respectively. Curves of dielectric constant for a sweep of bias voltages suggested the presence of electron traps in the g-DLC:H film near the interface between the g-DLC:H film and the Si substrate. Electric current curves for the sweep of bias voltages below 1.5 V can be approximated with the Poole–Frenkel mechanism showing the participation of traps in electron conduction. The electrical conductivities measured were proportional to the film thickness: the dielectric constant was proportional to the electrical conductivity. Thus, very low dielectric constants and large electrical conductivities for the g-DLC:H films were caused by electron traps, the densities of which varied with the film thickness.