Low dielectric constant porous silica films formed by photo-induced sol-gel processing

The formation of porous silicon dioxide films on Si (100) and quartz substr ates at low temperatures (25-300 degreesC) by photo-induced sol-gel process ing using 172 nm radiation from an excimer lamp has been investigated. The effects of substrate temperature, total gas pressure and lamp exposure time on the properties of the film formed have been studied using ellipsometry, UV spectrophotometry and Fourier transform infrared spectroscopy (FTIR). T he FTIR spectra revealed a Si-O-Si stretching vibration peak at 1070cm(-1) after UV irradiation at 200 degreesC which is similar to that recorded for oxides grown thermally at temperatures between 600 and 1000 degreesC. The f ilms exhibited optical transmittance of around 90% in the visible and UV re gion of the spectrum. Capacitance measurements indicated that the dielectri c constant of the films strongly depended on the substrate temperature duri ng irradiation. Dielectric constant values as low as 1.7 are readily achiev able at room temperature. (C) 2001 Elsevier Science Ltd. All rights reserve d.