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. (c) 2007 Elsevier Inc. All rights reserved.