Abstract
Silica xerogel films with good uniformity and various thicknesses were successfully prepared by a two-step acid-base catalyst procedure and spin coating. After the addition of ammonia catalyst, the sol changes gradually from a Newtonian fluid to a shear-thinning one due to the progress of polymerization reactions. An empirical equation using the relative ratio of aging time to gel time can give successful prediction of sol viscosity. Our systematic study of the coating process indicates the existence of a process window in terms of t/tgel and spin speed can be defined for obtaining uniform and defect-free films. It is difficult to obtain films with good quality when the viscosity of the sol is either too high or too low. Another parameter that also exhibits strong influence on film thickness is the concentration of TEOS in the starting solution. Finally, the film thickness was found to correlate well with sol viscosity and spin speed as h = A h0.45 v-0.62.The thermal stability of xerogel film is also an important factor. The film thickness decreased as thermal treated temperature increased. According to FTIR and RBS analysis, the film porosity decreased because the structure was destroyed as the treatment temperature increased. The optimal temperature was found to be around 400℃.The low dielectric constant of porous silica films comes mainly from its porosity. However, due to the hydrophilic nature of Si-OH groups on the surface, moisture may be adsorbed from the air to increase its dielectric constant. By immersing the silica film in TMCS, we hope to replace as much Si-OH with Si-C surface groups. As a result, the dielectric constant and leakage can be significantly improved. However, due to incomplete replacement, the dielectric constant has not reached our goals yet.