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

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 T-a = 250, 275, 300, and 350 degreesC. 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 epsilon (a-C:H) of carbon films before and after thermal annealing. epsilon (a-C:H) showed no variations with subsequent annealing of the structure up to T-a = 250 degreesC, but it was observed to decrease from 5.6 to 2.8 as the film was annealed from 250 degreesC up to 300 degreesC with the most rapid changes occuring between 275 and 300 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.