Permittivity of amorphous hydrogenated carbon (a-C:H) films as a function of thermal annealing

Abstract

New metal-insulator-semiconductor structures with a composite insulating layer, consisting of an amorphous hydrogenated carbon (a-C:H) film and a silicon dioxide, were obtained on silicon substrates. Carbon films were deposited on SiO2 layer by radio-frequency plasma-enhanced chemical vapor deposition (rf PECVD) method from methane. The structures were annealed at the annealing temperature Ta = 250, 275, 300, and 350°C. C-V characteristics of the annealed and as-grown metal-amorphous carbon-oxide-semiconductor (MCOS) structures were examined at room temperature at a frequency of 1 MHz and compared with C-V characteristics of the classic metal-oxide-semiconductor (MOS) system. High-frequency C-V curves of both MCOS and MOS structures were used for extracting the permittivity εa-C:H of carbon films before and after thermal annealing. εa-C:H showed no variations with subsequent annealing of the structure up to Ta = 250°C, but it was observed to decrease from 5.6 to 2.8 as the film was annealed from 250°C up to 300°C with the most rapid changes occurring between 275 and 300°C. © 2001 Elsevier Science Ltd.