From low- k to ultralow- k thin-film deposition by organosilicon glow discharges

Continuous and modulated discharges, fed with divinyltetramethyldisiloxane mixed with oxygen and argon, were used to deposit carbon-doped silica-like (SiCOH) low- k to ultralow- k films. The effect of various process parameters on the dielectrical and thermal properties of films as well as on their chemical composition were investigated. As deposited, the SiCOH films exhibited dielectric constants from 4.45 to 2.70. Thermal annealing in the 400-450°C temperature range was found to be necessary to reach ultralow-permittivity values, but the temperature must be controlled in order to prevent an excessive collapse of the silicate matrix, which leads to poor thermal stability and mechanical properties. Lowering the oxygen content in the discharge allowed for a continuous decrease in k values down to 2.32 when low radio frequency power was used, with a limited film thickness loss upon annealing of 11%. Fourier transform infrared spectra of ultralow- k film exhibited intense absorptions from C-containing moieties, like C Hx and Si (C H3) x. Upon annealing at 400°C, the organic content considerably decreases, though the loss of Si (C H3) x groups is quite limited. Thermogravimetric analysis coupled with mass spectrometry revealed that during thermal treatment, silicon-containing fragments were lost from the matrix along with hydrocarbon ones.