One of the current challenges in fabricating III-V-based electronics is the growth of an interfacial layer during the atomic layer deposition (ALD) of high-k dielectrics on III-V substrates, which has led to poor quality electrical properties. A process that can mitigate this problem is the “clean-up” effect that occurs when trimethylaluminum (TMA) is deposited by atomic layer deposition during the formation of Al2O3. A recent theoretical study suggests that the principal pathway in the “clean-up” effect of TMA on the native oxides of GaAs and InGaAs involves oxygen gettering1. In this work, in-situ infrared absorption spectroscopy has been used to investigate the temperature dependence of the native oxide and the interface formation during Al2O3 deposition using TMA and deuterium oxide (D2O) on chemically-treated InP(100) surfaces. Upon annealing a degreased sample to 300°C, compositional changes are observed, as evidenced by new absorption features in the region of 900-1250 cm-1 of the infrared spectrum prior to TMA exposure. The initial native oxide, comprised in part of In(PO3)3 is transformed into an InPO4-rich surface. Upon TMA exposure at 300°C, there is a clear loss of In(PO3)3 and gain of InPO4 (at 1007 and 1145 cm-1, respectively) along with the formation of Al-O bonds (absorption band at 800 cm-1)2. These observations are consistent with the “clean up” effect observed on GaAs3 and InGaAs4, and on InP(100)5 where TMA preferentially withdraws oxygen from the native oxide forming Al-O bonds. However, the TMA reduces In(PO3)3 and forsters the formation of InPO4. Furthermore, TMA exposure of the native oxide at lower deposition temperatures (150°C) gives rise to methoxy (CH3) formation as evidenced by the appearance of a band centered at 1475 cm-1. This indicates that TMA not only withdraws oxygen from the native oxide but also transfers a methyl group to the surface oxygen, which may lead to carbon contamination at the interface. Al2O3 oxide films are formed after 10 TMA and D2O cycles on both degreased native oxide and chemically treated (HF and (NH4)2S) InP(100) substrates, although the quality is higher on the (HF and (NH4)2S)-treated surface. A more clearly defined LO phonon mode is detected for that surface, suggesting that a denser oxide is formed.

1 S. Klejna et. al, J. Phys. Chem. C, 116, (2012) 643-654

2 M. M. Frank et. al , Appl. Phys. Lett.82 (2003) 4758

3 C. L. Hinkle et. al, Appl. Phys. Lett., 92 (2008) 071901

4 M. Milojevic,et. al Appl. Phys. Lett., 93, (2008) 202902

5 B. Brennan et. al, Appl. Phys. Exp.,4 (2011) 125701