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

摘要

The 3gamma 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-kappa) 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 400-900degreesC temperature range. The films were produced by plasma enhanced chemical vapor deposition (PECVD), and after annealing in N, atmosphere at 400 degreesC they were treated in N-2 + He plasma. The treatment in the N2 plasma was found to seal the pores within a surface layer 45 run 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 degreesC thermal treatment. At 700-900 degreesC 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 degreesC. (C) 2004 Elsevier Ltd. All rights reserved.