| AVS 57th International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | ALD/CVD: Surface Chemistry and Fundamentals |
| Presenter: | J.W. Elam, Argonne National Laboratory |
| Authors: | A. Yanguas-Gil, Argonne National Laboratory J.W. Elam, Argonne National Laboratory |
| Correspondent: | Click to Email |
In this work we explore the effect that alkyl alcohols (ROH) have on the saturation growth rate during the ALD of metal oxides. The traditional dosing sequence for metal oxide ALD is: M/O/M/O… where M is the metal precursor and O is the oxygen source. We find that by dosing organic molecules prior to dosing the metal precursor (e.g. ROH/M/O…) we can modify the surface chemistry and control the saturation growth rate. We will present results describing the effect of alkyl alcohols (R=Me, Et, iPr, and Bu) using H2O as the oxygen source and the metal precursors Ti(iPr)4 for TiO2 ALD, TMA for Al2O3 ALD, and DEZ for ZnO ALD. Furthermore, we demonstrate this effect in the ALD of doped metal oxides.
Our results show that the ROH/M/H2O sequence causes a substantial reduction in the growth per cycle for all of the ALD systems studied. For instance, the growth per cycle reduces from 0.31 to 0.06 Å/cycle in the case of TiO2 ALD using MeOH/Ti(iPr)4/H2O, and from 1.2 to 0.4 Å/cycle in the case of Al2O3 ALD using MeOH/TMA/H2O at 200°C.
Previous studies in the literature indicate that ROH reacts with basic sites on the metal oxide surface. Alcohol deprotonation followed by metal oxygen heterolytic bond formation leads to the formation of alkoxide functional groups bound to metal cations. To investigate this process, we performed in situ mass spectrometry and quartz crystal microbalance studies during the ROH/M/H2O dosing sequence. We discovered that the ROH adsorbed on the surface desorbs intact as ROH during the subsequent water pulse, but no alcohol is released during the metal precursor pulse. Furthermore, the reduction of the growth rate per cycle is not affected by purge times, suggesting that the ROH molecules bond strongly to the metal oxide surface. Finally, no reduction in growth per cycle is observed using the dosing sequence: ROH/H2O/TMA/H2O. This finding suggests that the ROH and H2O are able to displace one another, and signifies an almost complete elimination of the alkoxide groups during the water pulse. This observation agrees with the many reports of successful metal oxide ALD using metal alkoxide and water.
The ability to tune the saturation growth rate by modifying the surface chemistry can be of great utility for the ALD of doped materials where a homogenous distribution of dopants at a low concentration is desired.