Depth profiled porosity and microstructure evolution studied by positron annihilation and Raman spectroscopy in SiOCH low-κ films

Abstract The 3 γ annihilation of ortho-positronium and the Doppler broadening of the positron annihilation line have been measured by implanting low-energy positrons in low dielectric constant (low- κ ) SiOCH films. Positron techniques were used to gather information about the porosity while Raman scattering was employed to study the microstructure of the films. The evolution of both the film porosity and microstructure was monitored as a function of the thermal treatments in the 400–900 °C temperature range. The films were produced by plasma enhanced chemical vapor deposition (PECVD), and after annealing in N 2 atmosphere at 400 °C they were treated in N 2 +He plasma. The treatment in the N 2 plasma was found to seal the pores within a surface layer 45 nm thick. The minimum free volume of the pores in the as-produced samples has been estimated. The chemical environment of the pores probed by positrons was found to be stable up to 600 °C thermal treatment. At 700–900 °C annealing temperature a reduction of the hydrogen content and a change in the chemical environment of the pores has been observed. Raman spectroscopy indicates the formation of carbon inclusions within the film treated at temperatures equal to and higher than 500 °C.