Chemical vapor deposition precursor chemistry. 5. The photolytic laser deposition of aluminum thin films by chemical vapor deposition

Thin films of very high purity aluminum were formed from the laser photolysis of trimethylamine alane (TMAA) using both ultraviolet (pulsed nitrogen) and visible (argon ion) laser irradiation on a variety of substrates including gold, Si(111), GaAs(110) and Teflon (PTFE). At thicknesses of up to 1 μm, nearly linear growth rates of 377 Ås^-1 and 112Ås^-1 were observed. The formation of volatile species formed during the deposition of aluminum from TMAA was investigated by quadrupole mass spectrometry (QMS) of the reactant gas stream. The highest intensity post-deposition mass fragments were observed at m/z 58, 43 and42amucorresponding to [NC₃H₈]⁺, [NC₂H₅]⁺ and [NC₂H₄]⁺, respectively. These species arise from the dissociation and subsequent fragmentation of the trimethylamine ligand from the starting TMAA complex. Semi-empirical quantum chemical calculations (MNDO) for TMAA provided further support that photolysis of this precursor should result in principally ligand dissociation processes since the LUMO orbital is primarily an aluminum-nitrogen antibonding interaction. The deposited materials were also characterized by X-ray emission spectroscopy (XES), scanning electron microscopy (SEM), and Laser Microprobe Mass Analysis (LAMMA) techniques.