Surface reaction kinetics of metal b-diketonate precursors with O radicals in radical-enhanced atomic layer deposition of metal oxides

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 b-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 b-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, radicalenhanced ALD of Er2O3 thin films was achieved at temperatures ranging from 473 to 573 K, using alternating pulses of metal b-diketonate precursors and O radicals