AVS 59th Annual International Symposium and Exhibition
    Thin Film Tuesday Sessions
       Session TF-TuM

Paper TF-TuM6
Growth Inhibition of Al2O3 on InGaAs by Atomic Layer Deposition

Tuesday, October 30, 2012, 9:40 am, Room 11

Session: ALD Reactions and Film Properties
Presenter: B. Granados, University of Arizona
Authors: B. Granados, University of Arizona
A.J. Muscat, University of Arizona
Correspondent: Click to Email
The chemical composition of the In0.53Ga0.47As(100) interface during the growth of an aluminium oxide (AlOx) layer deposited by ALD was studied after each half-cycle using in-situ X-ray photoelectron spectroscopy (XPS) to understand film nucleation and interface formation. Native oxide was removed from InGaAs using liquid HF (49%, followed by water rinse) and gas phase HF and compared to deposition directly on native oxide. In situ gas phase HF/H2O etching was run at 29°C and 100 Torr with an HF to water partial pressure ratio of 1.23. The ALD process consisted of pulses of trimethylaluminum (TMA) and H2O at 170°C. The AlOx film thickness was estimated from the Al 2p peak area and the attenuation of the As 3d bulk signal due to an assumed homogenous Al2O3 overlayer. An AlOx film with a thickness of 11.2 ± 2.5 Å was deposited during the first pulse of TMA on both liquid and gas phase HF treated samples and a film with a thickness of 12.8 ± 2.5 Å was deposited on InGaAs covered by native oxide. These thicknesses correspond to approximately 3 ML of Al2O3, which could indicate the formation of islands. Remarkably the thickness was equivalent starting from an As-rich interface in the case of liquid HF, a Ga-rich interface in the case of gaseous HF that contained both oxides and fluorides, and an nearly stoichiometric surface in the case of native oxide. After three complete ALD cycles the thickness of the AlOx film was 12.9 ± 2.5 Å on liquid HF treated, 9.2 ± 2.5 Å on gas phase HF treated, and 14.1 ± 2.5 Å on the native oxide of InGaAs, indicating that the first pulse reacts with most of the sites on the surface. The density of methyl groups after the first pulse was estimated to be 12 methyl groups/nm2 on the liquid HF treated surface based on XPS. Approximately half of the methyl groups were hydrolyzed by the first water pulse, depositing an estimated 6 hydroxyl groups/nm2. The second TMA pulse returned the methyl density to approximately the same value after the first TMA pulse. After the first ALD cycle the samples entered into a growth inhibition period. The growth rate per cycle (GPC) during cycles two and three dropped from 2.5 ML/cycle to 0.4 ML/cycle on the liquid HF treated surface and to 0.0 ML/cycle on the gas phase HF treated surface, and from 3.4 ML/cycle to 0.2 ML/cycle on the native oxide of InGaAs. This growth inhibition after the first pulse of TMA must be caused by the formation of Al-CH3 moieties on the surface that are less reactive than both the initial surface and Al2O3. Understanding the surface reactions involved in the nucleation phase and early cycles of ALD is important in achieving control of the III-V-dielectric interface.