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

Abstract

The authors have been investigating the use of [Al(CH3)2(μ-OiPr)]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 °C, respectively. The growth per cycle (GPC) obtained using in situ spectroscopic ellipsometry for plasma-enhanced ALD was 0.7–0.9 Å/cycle, generally lower than the >0.9 Å/cycle afforded by TMA. In contrast, the thermal process gave a higher GPC than TMA above 250 °C, but below this temperature, the GPC decreased rapidly with decreasing temperature. Quadrupole mass spectrometry data confirmed that both CH4 and HOiPr were formed during the DMAI dose for both the plasma-enhanced and thermal processes. CH4 and HOiPr were also formed during the H2O dose but combustion-like products (CO2 and H2O) were observed during the O2 plasma dose. Rutherford backscattering spectrometry showed that, for temperatures >100 °C and >200 °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 ∼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 °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 (∼3.5 and ∼2 Ω 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.

Revisiting the growth mechanism of atomic layer deposition of Al2O3: A vibrational sum-frequency generation study

“…36 This trend is also reflected in the stoichiometry of the films which are slightly O rich at high temperatures. 6,7,21,32,37 At lower temperatures, the films become even more O rich, 6,7,21,32,36,37 in line with the AlO(OH) structure. The films prepared with thermal ALD are generally carbon free, even when deposited at low temperatures.…”

“…The deposition temperature has a significant influence on the ALD process. 6,13,[30][31][32] The lowest practical temperature for thermal Al 2 O 3 ALD is $150 C. At lower temperatures, the ALD cycle becomes quite long because H 2 O is difficult to remove at low temperatures resulting in extremely long purge steps. Also the mass density of the deposited Al 2 O 3 decreases significantly for deposition temperatures below 150 C. 6 For example, Groner et al showed that a deposition at 33 C requires a cycle time of $200 s (compared to, e.g., 4 s) and the mass density of the film is $20% less than for films grown at high temperatures.…”

“…The Al 2 O 3 films have been reported to be carbon-free even when deposited at low temperatures. 6,7,21,32 This suggests that the persistent -CH 3 groups are not incorporated into the film. Therefore, a dedicated experiment was designed to test the hypothesis that -CH 3 groups are not incorporated into the film.…”

Status and prospects of Al2O3-based surface passivation schemes for silicon solar cells

“…A saturated process was developed for plasma and thermal ALD in our OpAL reactor. 199 Slightly longer dosing times ($100 ms) were required for DMAI than for TMA, which can be A negative Q f of $4 Â 10 12 cm À2 was obtained. Wafers with a resistivity of $2 X cm (p-type) were used as substrates.…”

A Process‐Structure Investigation of Aluminum Oxide and Oxycarbide Thin Films prepared by Direct Liquid Injection CVD of Dimethylaluminum Isopropoxide (DMAI)

“…Dimethylaluminum isopropoxide (DMAI) was proposed by a few groups as an alternative CVD precursor to produce alumina films using evaporation or bubbling systems . DMAI was also tested for atomic layer deposition (ALD) of alumina in a few instances . This molecule consists of an Al atom linked to two methyl and one isopropyl groups, and has an intermediate structure between ATI and TMA.…”