Radical-enhanced atomic layer deposition of Y2O3 via a β-diketonate precursor and O radicals

Thin films of Y2O3 were deposited on Si(1 0 0) by radical-enhanced atomic layer deposition (ALD), using Y(TMHD)3 and O radicals. First, the self-limiting mechanism of this process was investigated in situ from 473 to 573 K, using a quartz crystal microbalance. Specifically, adsorption of Y(TMHD)3 can only be initiated after reactive sites are created on the surface by the exposure to O radicals. However, due to the bulky β-diketonate ligands, only a sub-monolayer of metal oxide was achieved after these ligands were removed by a subsequent O radical exposure. These alternating reactions were found to be self-limiting and temperature insensitive from 473 to 573 K. A reactant pulse time of 7 min was required for both Y(TMHD)3 and O radicals to achieve saturation, yielding a maximum deposition rate of 0.5 Å/cycle in the ALD temperature window from 473 to 573 K. A lower deposition rate of 0.3 Å/cycle was obtained when both reactant pulse times were reduced to 30 s. X-ray photoelectron spectroscopy analysis suggests the formation of a thin yttrium silicate interfacial layer between Y2O3 and Si. The compositional analysis indicates stoichiometric Y2O3 films were deposited, with the carbon content decreased from 24 at.% at 473 K to 4 at.% at 623 K. The atomic force microscopy images revealed fairly smooth surfaces of films deposited at 573 K, showing a small root mean square roughness of 5 Å for a 115-Å Y2O3 film. Excellent conformal deposition of an 800-Å Y2O3 film over 0.5 μm features with an aspect ratio of 2 was accomplished. These results demonstrate that radical-enhanced ALD is a viable technique for conformal low-temperature deposition of stoichiometric and smooth metal oxide thin films with minimal carbon contamination.