Preparation of low-density xerogels at ambient pressure for low K dielectrics

Low density ceramic aerogels have numerous properties which suggest their use as a low dielectric constant material in microelectronics applications. However, the feasibility of aerogels has been limited by microelectronics process integration difficulties associated with drying at supercritical pressures, low stability to water vapor, low mechanical strength, and pore sizes on the same order as microelectronics feature sizes. Recently, a new process has been developed to control capillary pressure and gel matrix strength by employing a series of aging and pore chemistry modification steps such that shrinkage is minimal during rapid drying at ambient pressure. An additional advantage of this approach is that the final gels are hydrophobic. This process is used to make thin films on silicon wafers with thickness of 0.5 μm to 2.0 μm. The porosity is from 50% to 84%. The index of refraction varied from 1.067 to 1.233. (dielectric constant at optical frequency is from 1.138 to 1.520; the extrapolated dielectric constant at 1 MHz is from 1.364 to 2.372.)