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Nondestructive Characterization of a Series of Periodic Porous Silica Films by in situ Spectroscopic Ellipsometry in a Vapor Cell

Pore size distributions in a series of periodic porous silica low-dielectric-constant (low-k) films were determined by the analysis of adsorption/desorption isotherms of heptane. The isotherms were obtained from in situ spectroscopic ellipsometric measurements at room temperature in a vapor cell. The porous silica low-k films were prepared by the spin coating of a mixture of silica precursor and alkyltrimethylammoniumchloride surfactant template solutions. A systematic increase in pore diameter with an increase in the alkyl chain length of the template molecules was observed. It is concluded that the in situ spectroscopic ellipsometry in a vapor cell as a nondestructive technique of characterizing pore structures in porous low-k films has the potential to clearly distinguish such a slight difference in pore diameter as is caused by only –(CH2)2– in a template molecular structure.