Study of solvent penetration inside a porous low k material by neutron reflectometry - Influence of material surface modifications and of solvent properties

Porous low k materials are used as insulator in integrated circuits interconnection levels. The impact of plasma post-treatments on such material was studied by neutron reflectometry coupled with deuterated solvents penetration. The porosity of the non-modified material determined by the CD₃CD₂OD adsorption isotherm is 28%. The CD₃CD₂OD and D₂O distributions inside the material modified by plasma were determined during their penetration. Whatever the plasma, even in steady state conditions, the modified materials are not completely filled by the solvents. For the sample modified by NH₃/N₂ plasma, whatever the solvent, the equilibrium is instantaneously reached. The CD₃CD₂OD diffused in all the material whereas the D₂O diffuse only in the modified zone due to its higher hydrophilic property compared to that of the zone located underneath. After fluorocarbon-based and oxidizing plasma the material shows a continuous penetration of the CD₃CD₂OD solvent with a saturation obtained after 150 min whereas, the saturation is reached after 100 min with D₂O. Moreover, D₂O penetrates the zone located underneath the modified surface of the sample which should be hydrophobic. This observation highlights a chemical modification of this zone by the plasma treatment.