Effect of plasma treatments on a porous low-k material – Study of pore sealing

In microelectronics, porous low-k materials are needed for 65 nm and beyond technology nodes as insulator material between interconnections. During the integration, these low-k are modified by plasma process. Plasma treatments can lead to the formation of a thin and denser layer at the material surface. Porosity measurement by ellipsometric porosimetry (EP) and a kinetic study of ethanol diffusion were performed on unmodified and modified samples to assess the impact of several plasma post-treatments. Results showed a decrease of the solvent diffusion rate into the modified porous dielectric material that depends on plasma treatment. A vapor permeation model was used in order to quantify the barrier effect of sealed surface pores. NH3 plasma post-treatment leads to a denser modified top layer which is the most efficient for surface pore sealing effect.The low-k materials were characterized by X-ray reflectometry, ellipsometry and ellipsometric porosimetry. Ellipsometry coupled with solvent adsorption is a convenient technique to characterize porosity of low-k material. It is here demonstrated that ellipsometric porosimetry is also an efficient tool for quantifying pore sealing effect. Calculated permeability gave a quantitative classification of the pore sealing effect. NH3 plasma treatment induces a thin top layer with the lowest permeability coefficient, thus this plasma is the most efficient for surface pore sealing. The NH3 plasma treatments lead to the formation of a thin denser layer at the low-k material surface. This pore sealing effect is required in integration step in order to prevent moisture up-take and to avoid metal diffusion inside pores of the low-k material compromising the integrated k value. Neutron reflectometry coupled with solvent adsorption in controlled atmosphere will be soon performed on the same samples in order to better understand diffusion mechanisms through such sealant top layers.