Plasma-enhanced and thermal atomic layer deposition of Al2O3 using dimethylaluminum isopropoxide, [Al(CH3)2(μ-OiPr)]2, as an alternative aluminum precursor

The authors have been investigating the use of [Al(CH3)(2)(mu-(OPr)-Pr-i)](2) (DMAI) as an alternative Al precursor to [Al(CH3)(3)] (TMA) for remote plasma-enhanced and thermal ALD over wide temperature ranges of 25-400 and 100-400 degrees C, respectively. The growth per cycle (GPC) obtained using in situ spectroscopic ellipsometry for plasma-enhanced ALD was 0.7-0.9 angstrom/cycle, generally lower than the > 0.9 angstrom/cycle afforded by TMA. In contrast, the thermal process gave a higher GPC than TMA above 250 degrees C, but below this temperature, the GPC decreased rapidly with decreasing temperature. Quadrupole mass spectrometry data confirmed that both CH4 and (HOPr)-Pr-i were formed during the DMAI dose for both the plasma-enhanced and thermal processes. CH4 and (HOPr)-Pr-i were also formed during the H2O dose but combustion-like products (CO2 and H2O) were observed during the O-2 plasma dose. Rutherford backscattering spectrometry showed that, for temperatures > 100 degrees C and > 200 degrees C for plasma-enhanced and thermal ALD, respectively, films from DMAI had an O/Al ratio of 1.5-1.6, a H content of similar to 5 at. % and mass densities of 2.7-3.0 g cm(-3). The film compositions afforded from DMAI were comparable to those from TMA at deposition temperatures >= 150 degrees C. At lower temperatures, there were differences in O, H, and C incorporation. 30 nm thick Al2O3 films from the plasma-enhanced ALD of DMAI were found to passivate n- and p-type Si floatzone wafers (similar to 3.5 and similar to 2 Omega cm, respectively) with effective carrier lifetimes comparable to those obtained using TMA. Surface recombination velocities of < 3 and < 6 cm s(-1) were obtained for the n- and p-type Si, respectively. Using these results, the film properties obtained using DMAI and TMA are compared and the mechanisms for the plasma-enhanced and thermal ALD using DMAI are discussed. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3683057]