Paper TF-TuA4
Nucleation of Al₂O₃ Atomic Layer Deposition with Water or H₂O₂

Tuesday, October 31, 2017, 3:20 pm, Room 20

Aluminum oxide (Al₂O₃) is a suitable replacement for SiO₂ in electronic devices such as flash memory due to its wide band gap and higher dielectric constant. Atomic layer deposition (ALD) using sequential pulses of trimethylaluminum (TMA) and an oxidant is a leading method for the formation of nano-scale Al₂O₃ layers. Al₂O₃ layers grown by ALD have been demonstrated with leakage currents of less than 1 nA/cm³. The quality of the layers depends on both the deposition temperature and choice of oxidant, which is commonly water or oxygen atoms generated using a plasma.

An oxidant more reactive than water, such as H₂O₂, could produce a denser Al₂O₃ film. The growth of Al₂O₃ on hydrogen-terminated silicon using TMA and H₂O₂ was compared to that using TMA and water as a reference. Spectroscopic ellipsometry was used to determine the growth per cycle (GPC), and in situ x-ray photoelectron spectroscopy (XPS) was recorded before and after each precursor dose. The O 1s XPS peak at 531.8 eV and the Al 2p peak at 75.5 eV were used to monitor the formation of the Al-O bond and the C 1s peak at 284.5 eV was used to monitor the persistence of the Al-C bond after each half cycle. A second state in O 1s XPS at 533.3 eV assigned to the O-H bond was used to estimate the number of reactive sites present after each oxidant pulse.

The growth-per-cycle (GPC) was equal to 1.2 Å at H₂O₂ pulse times above 0.3 s, which is similar to reported ALD growth rates using water. The Al 2p XPS peak appeared after 4 ALD cycles using anhydrous H₂O₂ and after 7 cycles using water. The aluminum coverage after 10 ALD cycles was 40 % greater for anhydrous H₂O₂ compared to water, although the GPC was similar for each co-reactant. The O-H coverage doubled with each pulse of H₂O₂. The O 1s peak assigned to O-H also broadened with subsequent ALD cycles due to the presence of additional surface states. Each pulse of water increased the O-H coverage by about 1.5 times compared to the subsequent pulse. The ratio between C 1s and Si 2p peak areas showed twice as much carbon present on the surface during H₂O₂ ALD. The C 1s/Si 2p ratio increased during pulses of TMA and decreased during pulses of H₂O₂ due to surface reactions that desorb CH₄. Greater OH densities and C coverages indicate that H₂O₂ activates more surface sites for the metal precursor than water, improving Al₂O₃ film density.