The ultimate control on film growth represents a challenge in PECVD: interphase, film structure and surface roughness are affected by the surface energy, growth and ion fluxes and ion energy. Such control is desired for moisture diffusion barriers, where an irregular polymer surface and defects determine the performance. Routes for microstructure control in PECVD SiO2 barrier layers are presented. The addition of ion bombardment to a remote plasma with a gradient in growth flux allows tuning the film microstructure during growth with the purpose of engineering an adhesive interphase and a dense SiO2 barrier. The role of ion bombardment on the film microstructure is here investigated by means of ellipsometric porosimetry, which monitors the refractive index change due to the adsorption (and desorption) of ethanol vapors in the volume of macro-meso-micro pores in the layer. From the analysis of the adsorption isotherm and the presence of hysteresis during the desorption step as a function of the equilibrium partial pressure, the open porosity can be determined. Recently, we have also explored atomic layer deposition (ALD) for a virtually ultimate control on film microstructure. Plasma can assisted ALD (Plasma- assisted ALD) by providing radicals, replacing one precursor (e.g., O radicals replacing H2O in Al2O3 deposition). 20 nmthick plasma- assisted ALD Al2O3 layers are characterized by water vapor transmission rates (WVTRs) as low as 10-3 g/m2day.
|Title of host publication||Proceedings of the 18th international symposium on plasma chemistry (ISPC 18) 26-31 August 2007, Kyoto, Japan|
|Editors||K. Tachibana, O. Takai, K. Ono, T. Shirafuji|
|Place of Publication||Kyoto, Japan|
|Publication status||Published - 2007|