Interfacial chemistry of hydrofluoric acid-treated In_0.53Ga _0.47As(100) during atomic layer deposition of aluminum oxide

Atomic layer deposition (ALD) of aluminum oxide on In 0.53 Ga 0.47 As (100) prepared with aqueous or gas phase hydrofluoric acid (HF) was followed using x-ray photoelectron spectroscopy after each pulse of trimethylaluminum (TMA, Al (CH₃) and water at 170 ° C up to three cycles. On the surface prepared using aqueous HF, the primary oxide was As ₂ O₃, which was removed by the first TMA pulse depositing about two layers of AlO _x and leaving residual As + 1 oxide at the interface that persisted even after three complete ALD cycles. The aluminum oxide AlO _x film was O deficient but was closed off, trapping the As + 1 oxide at the interface. The C and O coverages were modulated by TMA and water pulses supporting the expected near 1 Å per cycle growth during the second and third ALD cycles. The larger absolute change in the C than the O coverage suggests that the reaction of TMA with O-H groups is more facile than the reaction of water with Al - CH ₃ moieties, explaining the less than monolayer growth per cycle intrinsic to ALD processes. On the surface prepared using gas phase HF, the fluorides and oxides of all substrate atoms were removed after one complete ALD cycle and a second TMA pulse, which also deposited about two layers of AlO _x. Yet, the surface was passivated by the residual F left from the gas phase HF process and by the large increase in C deposited in the first TMA pulse. There is clear evidence for Al-F bonding, and the locations of the Al 2p peaks combined with the large peak widths indicate that the Al atoms deposited in a variety of local bonding environments. The film was not closed off by the first ALD cycle because F and C capped reaction sites, inhibiting further growth of aluminum oxide up to three ALD cycles.