Nucleation and Interface Formation of Al2O3 on HF-treated InGaAs(100) by Atomic Layer Deposition
Tuesday, November 1, 2011, 5:40 pm, Room 107
III–V compound semiconductors are alternative channel materials for high-speed, low-power digital logic devices because their electron transport and breakdown properties are superior to that of Si. However, robust surface passivation processes and thermodynamically stable interfaces are barriers to its wider adoption. Additionally, the scaling down of integrated circuits has prompted the use of alternative high-k dielectric films to replace SiO2 as the gate in metal-oxide-semiconductor field effect transistors (MOSFETs). Recent work demonstrated oxide removal and passivation of III-V surfaces by depositing high-k dielectrics using atomic layer deposition (ALD).
In this study, the ALD of Al2O3 was investigated on liquid and vapor HF-etched In0.53Ga0.47As(100) samples. Both half and complete ALD cycles of trimethylaluminum (TMA) and H2O at 170°C were used to better understand nucleation and film growth. Aqueous HF etching was performed by a 49% HF dip 1 min and 15 s water rinse. 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 initial 8.0±1.4 Å-thick native oxide contained 21% In, 27% Ga, and 52% As oxides and was reduced to a 4.3±1.5 Å-thick oxide containing 91±7% As by aqueous HF. In contrast, the gas phase HF produced ~7 Å-thick mixed oxide and fluoride overlayer containing 30% In, 40% Ga, and 30% As.
Large reductions of substrate oxides were observed after the first TMA pulse on both liquid and gas phase HF-treated samples. The intensity of the O 1s XPS peak was constant but the peak shifted by 1 eV to higher binding energy (BE) due to the conversion of the oxide to Al2O3. On the gas phase HF-treated samples removal of In, Ga and As atoms in the fluoride-rich overlayer layer was also observed after the first TMA pulse. The intensity of the F 1s peak was reduced and the peak shifted by 2.2 eV to higher BE, indicating the etching of fluoride as well as the conversion of the bonding from substrate fluorides to Al-F.
Subsequent H2O and TMA pulses up to three cycles of TMA/H2O revealed a systematic peak shift of the overlayer atom signals. F 1s, O 1s and Al 2p peaks shifted 0.9 eV, 0.4 eV and 0.2 eV, respectively, towards lower BE after a H2O pulse and shifted back to their original positions after a TMA pulse. The systematic shifts could be attributed to the change in surface termination after every half-cycle reaction, methyl termination after the TMA pulse and hydroxyl termination after a water pulse. Understanding surface reactions involved in the nucleation phase and early cycles of ALD is important in achieving control of the III-V-dielectric interface.