Variable-energy Positron Study of Nanopore Structure in Hydrocarbon–Siliconoxide Hybrid PECVD Films

Nanopore formation upon heat treatment of hydrocarbon-siliconoxide hybrid films was investigated by means of the variable-energy positron annihilation γ-ray and lifetime techniques. The films were prepared using plasma enhanced chemicalvapor deposition (PECVD),and nanoscopic poresinthe films weredeveloped throughthe decom positionofasacrificialhydrocarbonous porogenbyannealingthe filmsat temperaturesupto600 °C.Asaresultofthe positron annihilation γ-ray measurements, the line-shape S parameter increases with increasing annealing temperature from 150 °C to 400 °C, while it reduces with further increasing temperature. This suggests that more positronium annihilate with carbonous elements remaining on the wall of pores formed at temperatures up to 400 °C. The lifetime measurements revealed the nanopore sizes in the range from 0.2 nm3 to 2.0 nm3. With increasing the pore size the film refractive index reduced from 1.44 to 1.29. The variable-energy positron techniques were demonstrated to be useful to examine the nanoporosity evolution for porous PECVD films.