Revealing the Porous Structure of Low-k Materials Through Solvent Diffusion

Conclusions

We propose a simple and effective method for studying the porous structure of a thin film. The method is based on the observation of lateral diffusion of solvents inside a porous film using an optical microscope. The diffusion coefficients of solvents calculated from such observations can be used for revealing the pore interconnection structure of the porous film in question.

Diffusion studies could also be used for characterization of other properties of a porous film. A known diffusion coefficient allows calculation of pinhole density of a barrier deposited on a porous film, when the film is filled with solvent that penetrates through the pinholes and then diffuses inside the film beneath the barrier.

The ratio of diffusion coefficients of polar and nonpolar solvents could be used as a measure for the film affinity for water adsorption. Polar centers inside a porous film could act as attraction sites for polar water molecules, which is detrimental for low-k properties of the film. The presence of polar centers causes polar solvents to diffuse slower than nonpolar ones.