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

New metal-insulator-semiconductor structures with a composite insulating la yer, consisting of an amorphous hydrogenated carbon (a-C:H) film and a sili con dioxide, were obtained on silicon substrates. Carbon films were deposit ed on SiO2 layer by radio-frequency plasma-enhanced chemical vapor depositi on (rf PECVD) method from methane. The structures were annealed at the anne aling temperature T-a = 250, 275, 300, and 350 degreesC. C-V characteristic s 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-semiconduc tor (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 wi th subsequent annealing of the structure up to T-a = 250 degreesC, but it w as observed to decrease from 5.6 to 2.8 as the film was annealed from 250 d egreesC up to 300 degreesC with the most rapid changes occuring between 275 and 300 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.