Gadolinium oxide thin films by atomic layer deposition

Gadolinium oxide thin films have been deposited on Si(1 0 0) by atomic layer deposition (ALD) using as precursors either a β-diketonate-type chelate, namely Gd(thd)3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione) and ozone or a true organometallic (CpCH3)3Gd (Cp=cyclopentadienyl, −C5H5) together with water. Self-limiting ALD growth mode was detected for the Gd(thd)3/O3 process at 300 °C with a growth rate of 0.3 Å/cycle. In the case of the (CpCH3)3Gd/H2O process, partial decomposition of the metal precursor affected the film growth mechanism. However, at 250 °C, the uniform films obtained from (CpCH3)3Gd and H2O showed almost an ideal stoichiometry with low impurity contents (e.g. 0.5 at% of C) as analyzed by time-of-flight elastic recoil detection analysis (TOF-ERDA). X-ray diffraction data indicated that Gd2O3 films obtained by the Cp-based process were crystalline with cubic C-type structure when deposited even at 150 °C. The strongest reflection changed from (4 0 0) to (2 2 2) at deposition temperatures around 200 °C. Oxygen-rich films grown by the Gd(thd)3/O3 process were amorphous at deposition temperatures below 250 °C but crystalline with (4 0 0) dominant reflection at temperatures exceeding 250 °C. The films were smooth with both processes at the optimized deposition temperatures. In addition, the dielectric properties were analyzed showing effective permittivity of about 13 for the (CpCH3)3Gd/H2O-processed Gd2O3 films.