Preparation of Al2O3 thin films by atomic layer deposition using dimethylaluminum isopropoxide and water and their reaction mechanisms

Al2O3 thin films were grown on H-terminated Si(001) substrates using dimethylaluminum isopropoxide [DMAI: (CH3)(2)AlOCH(CH3)(2)], as a new Al precursor, and water by atomic layer deposition (ALD). The self-limiting ALD process by alternate surface reactions of DMAI and H2O was confirmed from measured thicknesses of the aluminum oxide films as functions of the DMAI pulse time and the number of DMAI-H2O cycles. Under optimal reaction conditions, a growth rate of similar to1.06 Angstrom per ALD cycle was achieved at the substrate temperature of 150 degreesC. From a mass spectrometric study of the DMAI-D2O ALD process, it was determined that the overall binary reaction for the deposition of Al2O3 [2(CH3)(2)AlOCH(CH3)(2) + 3H(2)O --> Al2O3 + 4CH(4) + 2HOCH(CH3)(2)] can be separated into the following two half-reactions: (A) (AlOH)-H-double dagger* + (CH3)(2)(AlOCH)-C-dagger(CH3)(2) --> Al-O-double dagger-Al[(OCH)-C-dagger(CH3)(2)]* + CH(4)up arrow (B) Al[(OCH)-C-dagger(CH3)(2)]* + H2Odouble dagger --> (AlOH)-H-double dagger* + (HOCH)-C-dagger(CH3)(2)up arrow where the asterisks designate the surface species. Growth of stoichiometric Al2O3 thin films with carbon incorporation less than 1.5 atomic % was confirmed by depth profiling Auger electron spectroscopy. Atomic force microscopy images show atomically flat and uniform surfaces. X-ray photoelectron spectroscopy and cross-sectional high resolution transmission electron microscopy of an Al2O3 film indicate that there is no distinguishable interfacial Si oxide layer except that a very thin layer of aluminum silicate may have been formed between the Al2O3 film and the Si substrate. C-V measurements of an Al2O3 film showed capacitance values comparable to previously reported values.