Ionic additives for extreme low dielectric constant chemical formulations

Abstract

A process for depositing porous silicon oxide-based films using a sol-gel approach utilizing a precursor solution formulation which includes a purified nonionic surfactant and an additive among other components, where the additive is either an ionic additive or an amine additive which forms an ionic ammonium type salt in the acidic precursor solution. Using this precursor solution formulation enables formation of a film having a dielectric constant less than 2.5, appropriate mechanical properties, and minimal levels of alkali metal impurities. In one embodiment, this is achieved by purifying the surfactant and adding ionic or amine additives such as tetraalkylammonium salts and amines to the stock precursor solution. In some embodiments, the ionic additive is a compound chosen from a group of cationic additives of the general composition [NR(CH ) ] A , where R is a hydrophobic ligand of chain length 1 to 24, including tetramethylammonium and cetyltrimethylammonium, and A is an anion, which may be chosen from the group consisting essentially of formate, nitrate, oxalate, acetate, phosphate, carbonate, and hydroxide and combinations thereof. Tetramethylammonium salts, or more generally tetraalkylammonium salts, or tetraorganoammonium salts or organoamines in acidic media are added to surfactant templated porous oxide precursor formulations to increase the ionic content, replacing alkali ion impurities (sodium and potassium) removed during surfactant purification, but which are found to exhibit beneficial effects in promoting the formation of the resulting dielectric.