STRUCTURE STABILITY OF HYDROGENATED AMORPHOUS-CARBON FILM DURING THERMAL ANNEALING

The thermal stability of an a-C:H film deposited by rf magnetron sputtering in a mixture of Ar and C2H2 was studied by measuring the remaining hydrogen concentration profile, the Raman and infrared spectra of the film annealed in vacuum, in steps at different temperatures. The evolution of hydrogen in the a-C:H film during annealing is not limited by diffusion processes of hydrogen and hydrocarbon. Rather, a rapid effusion and desorption of hydrogen and hydrocarbon occurs. The effusion rate increases rapidly at temperatures T > 450 degrees C. During annealing, both sp(3)- and sp(2)-bonded hydrocarbons are desorbed. The sizes of the sp(2)-bonded carbon clusters are reduced by the desorption of hydrogen and hydrocarbon from the clusters edges by annealing at T less than or equal to 450 degrees C, but a cluster reconstruction process takes place at T>450 degrees C, which causes an increase of the cluster size. The reconstruction of the sp(2) clusters occurs preferentially through transformation of the olefinic sp(2)CH structure.