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(CH3)3]+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.