Process for producing nanoporous dielectric films at high pH

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention forms a reaction product of at least one alkoxysilane with a relatively high volatility solvent composition, a relatively low volatility solvent composition, optional water and an optional catalytic amount of an acid such that the reaction product has a pH in the range of from about 2 to about 5.
Water is preferably included to provide a medium for partially hydrolyzing the alkoxysilane.
Thereafter, a low volatility base, such as an amine is added to raise the pH to about 8 or above.
This reaction product is applied onto a substrate.
The high volatility solvent evaporates during and immediately after deposition of the reaction product and the reaction product is further hydrolyzed and condensed until it forms a gel layer.
The second solvent is then removed by increasing the temperature.
Useful alkoxysilanes for this invention include those which have the formula: ##STR1## balance, if any, are independently selected from the group consisting of hydrogen, alkyl, phenyl, halogen, substituted phenyl.
For purposes of this invention, the term alkoxy includes any other organic group which can be readily cleaved from silicon at temperatures near room temperature by hydrolysis.
R groups can be ethylene glycoxy or propylene glycoxy or the like, but preferably all four R groups are methoxy, ethoxy, propoxy or butoxy.
The most preferred alkoxysilanes nonexclusively include tetraethoxysilane (TEOS) and tetramethoxysilane.
The relatively high volatility solvent composition is one which evaporates at a temperature below, preferably significantly below that of the relatively low volatility solvent composition.
The relatively high volatility solvent composition preferably has a boiling point of about 120.
degree.
C.
or less, preferably about 100.
degree.
C.
or less.
Suitable high volatility solvent composition nonexclusively include methanol, ethanol, n-propanol, isopropanol, n-butanol and mixtures thereof Other relatively high volatility solvent compositions which are compatible with the other ingredients can be readily determined by those skilled in the art