| AVS 55th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoA |
| Session: | ALD: Functionalization and Surface Chemistry |
| Presenter: | S.M. George, University of Colorado |
| Authors: | S.M. George, University of Colorado B.B. Burton, University of Colorado |
| Correspondent: | Click to Email |
Rapid SiO2 ALD can deposit very thick, ~100 Å, conformal SiO2 films by exposure of various silanol precursors to surfaces covered with Al-catalysts. Rapid SiO2 ALD with tris(tert-butoxy)silanol (TBS) was reported at temperatures from 200─300°C and deposited SiO2 film thicknesses as large as 120 Å [R.G. Gordon and coworkers (Science 298, 402 (2002)]. In this study, we have explored the growth of rapid SiO2 ALD films using liquid tris(tert-pentoxy)silanol (TPS). TPS can deposit even thicker SiO2 films at lower temperatures. The rapid SiO2 ALD growth is believed to result from the growth of siloxane polymer chains at Al-catalytic sites and the cross-linking of these polymer chains to form a dense SiO2 film. The SiO2 film thicknesses deposited during one silanol exposure are dependent on the temperature, silanol pressure, and silanol exposure time. SiO2 film thicknesses were determined using quartz crystal microbalance and x-ray reflectivity measurements. For TPS exposures of 1 second, the SiO2 ALD growth rate was larger at lower temperatures and larger TPS pressures. SiO2 ALD thicknesses of 125─140 Å were observed at the highest TPS pressures of ~1 Torr at the lower temperatures. These 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-limits the SiO2 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 final limiting SiO2 ALD mass gains decreased with increasing delay times. This behavior suggested that the longer delay times produced more cross-linking that self-limits the SiO2 deposition. Other experiments showed that higher temperatures produced faster nucleation of the rapid SiO2 ALD. The nucleation was nearly immediate at the higher temperatures and could be as long as 10 seconds at the lower temperatures. The growth kinetics of rapid SiO2 ALD can be understood in terms of the temperature dependence of nucleation and cross-linking and the pressure dependence of the siloxane polymerization rate.