Rapid SiO₂ Atomic Layer Deposition Using Tris(tert-pentoxy)silanol

Rapid SiO 2 atomic layer deposition (ALD) can deposit very thick and conformal SiO 2 films by silanol exposure to surfaces covered with Al catalysts. In this study, we have explored the growth of rapid SiO 2 ALD films using liquid tris( tert -pentoxy)silanol (TPS). The SiO 2 film thicknesses were determined using quartz crystal microbalance and X-ray reflectivity measurements. The SiO 2 film thicknesses deposited during one silanol exposure were dependent on the substrate temperature, silanol pressure, and silanol exposure time. The dependence of the SiO 2 growth on these parameters helped to establish the mechanism of rapid SiO 2 ALD. For TPS exposures of 1 s, the SiO 2 ALD growth rate was larger at lower temperatures and higher TPS pressures. SiO 2 ALD thicknesses of 125−140 Å were observed at the highest TPS pressures of ∼1 Torr at lower temperatures of 150 and 175 °C. Rapid SiO 2 ALD is believed to result from the growth of siloxane polymer chains at the Al-catalytic sites and the cross-linking of these polymer chains to form a dense SiO 2 film. The results indicated that higher TPS fluxes increase the siloxane polymerization rates. Likewise, the lower temperatures reduce the cross-linking rates between the siloxane polymers that self-limit the SiO 2 deposition. To explore the rate of cross-linking between the siloxane polymers, experiments were conducted where small TPS micropulses were employed with different delay times between the micropulses. The SiO 2 ALD thicknesses decreased with increasing delay times. This behavior suggested that the longer delay times produced more cross-linking that self-limits the SiO 2 deposition. Other experiments showed that higher temperatures produced faster nucleation of the rapid SiO 2 ALD. The nucleation was nearly immediate at the higher temperatures and could be as long as 10 s at the lower temperatures. The growth kinetics of rapid SiO 2 ALD can be understood in terms of the temperature dependence of nucleation and cross-linking and the pressure dependence of the siloxane polymerization rate. Rapid SiO 2 ALD was also dependent on the presence of pyridine derivatives in the TPS. These Lewis base impurities catalyze both the initial nucleation and the cross-linking reaction during rapid SiO 2 ALD.