Atomic Layer Deposition of Al2O3 Thin Films Using Dimethyl Aluminum sec-Butoxide and H2O Molecules

Abstract

Aluminum oxide (Al2O3) thin films were grown by atomic layer deposition (ALD) using a new Al metalorganic precursor, dimethyl aluminum sec-butoxide (C12H30Al2O2), and water vapor (H2O) as the reactant at deposition temperatures ranging from 150 to 300 oC. The ALD process showed typical self-limited film growth with precursor and reactant pulsing time at 250 oC; the growth rate was 0.095 nm/cycle, with no incubation cycle. This is relatively lower and more controllable than the growth rate in the typical ALD-Al2O3 process, which uses trimethyl aluminum (TMA) and shows a growth rate of 0.11 nm/ cycle. The as-deposited ALD-Al2O3 film was amorphous; X-ray diffraction and transmission electron microscopy confirmed that its amorphous state was maintained even after annealing at 1000 oC. The refractive index of the ALD-Al2O3 films ranged from 1.45 to 1.67; these values were dependent on the deposition temperature. X-ray photoelectron spectroscopy showed that the ALD-Al2O3 films deposited at 250oC were stoichiometric, with no carbon impurity. The step coverage of the ALD-Al2O3 film was perfect, at approximately 100%, at the dual trench structure, with an aspect ratio of approximately 6.3 (top opening size of 40 nm). With capacitance-voltage measurements of the Al/ALD-Al2O3/p-Si structure, the dielectric constant of the ALDAl2O3 films deposited at 250 oC was determined to be ~8.1, with a leakage current density on the order of 10−8 A/cm2 at 1 V.