Effects of acetylene addition on mechanical and dielectric properties of amorphous carbon films

The para-xylene added with acetylene from 15% to 50% was plasma polymerized at 50 to 150 W to deposit the a-C:H films. After the films were annealed from 200 to 400 °C, the network structure, hardness and dielectric constant of films were analyzed by FT-IR, Raman, nanoindentor and capacitance–voltage plot, respectively. Those measured results suggest that hydrocarbon bonds and oxygen related bonds of the a-C:H film effectively reduce and the number of ordered aromatic rings increases with decreasing the deposition power after annealing at 400 °C. In addition, both the dielectric constant and the hardness, respectively, increase up to 2.82 and 2.37 GPa, but the adhesion strength decreases with increasing the C₂H₂ concentration and deposition power. Therefore, the a-C:H films not only have a lower dielectric constant, but also have enough mechanical strength for the IC processing.