The surface reaction kinetics of Er(TMHD)(3) and Y(TMHD)(3) with O radicals in radical-enhanced atomic layer deposition (ALD) of Er2O3 and Y2O3 was investigated in situ using a quartz crystal microbalance (QCM). The adsorption isotherms were fitted with the Langmuir-Hinshelwood adsorption model and the extracted adsorption rate coefficient was found to decrease with increasing temperature, exhibiting a negative apparent activation energy of -0.24 +/- 0.09 eV for Er(TMHD)3 and -0.14 +/- 0.05 eV for Y(TMHD)(3). The corresponding activation energies for desorption were determined to be 0.29 +/- 0.03 and 0.16 +/- 0.03 eV. Exposing the adsorbed Er(TMHD)(3) precursors to O radicals at 533 K resulted in a rapid mass decrease followed by saturation, indicating that the reactions proceeded in a self-limiting manner. The critical O radical exposure needed to reach this saturation increased with increasing adsorbed mass and approached approximately 2 minutes as the adsorbed mass increased towards the saturation level. The net mass change ratio per cycle decreased with increasing temperature and reached 0.27 at 603 K for deposition of pure Er2O3. In addition to effectively removing the beta-diketonate ligands, the O radicals were found to create reactive sites for precursor adsorption. Specifically, when the O radical pulse time was shorter than the critical oxygen radical exposure, the removal of beta-diketonate ligands by the O radicals was incomplete, and consequently, less reactive sites were created. This ultimately led to a decrease in adsorption during the subsequent precursor pulse. Finally, radical-enhanced ALD of Er2O3 thin films was achieved at temperatures ranging from 473 to 573 K, using alternating pulses of metal beta-diketonate precursors and O radicals. (c) 2004 Elsevier B.V. All rights reserved.