Organosilicon thin films deposited by plasma enhanced CVD: Thermal changes of chemical structure and mechanical properties

Abstract

Thin organosilicon and silicon oxide films were deposited in r.f. capacitively coupled discharges from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. The concentration of HMDSO was in the range 5–17%. Even for such relatively high dilution of HMDSO the organic–inorganic crossover of the film character was observed due to changes of the HMDSO concentration, but other factors, such as pressure and d.c. self-bias should also be taken into account. When annealed the films changed their composition, chemical structure and mechanical properties. We observed desorption of water, methane and CO or CO 2 from the SiO 2-like films. The hardness of the SiO 2-like film, containing 5% carbon and 25% hydrogen, increased with the increase of annealing temperature from 5.9 (as deposited) to 11.3 GPa ( 500 ∘ C ) . Simultaneously, its fracture toughness was significantly improved. These effects were explained by dehydration and cross-linking of the film. However, the mechanical properties of highly cross-linked SiO 1.9 C 1.6 H 0.6 plasma polymer were superior over the SiO 2-like film containing impurities and such film can be used as a protective coating with a hardness above 9.6 GPa up to the temperature of 400 ∘ C .