Argon-ion laser direct-write Al deposition from trialkylamine alane precursors

Laser direct writing of aluminum lines on Si, GaAs and Al₂O₃ substrates using the trialkylamine alane precursors, (C₂H₅)₃N · AlH₃ (TEAA) and (CH₃)₃N · AlH₃ (TMAA), is reported. Deposition, carried out with a continuous wave Ar⁺ laser working at 514 nm, results from the thermal decomposition of the precursor via laser-induced surface heating at temperatures in excess of 360 K. It proceeds in two steps: surface nucleation, which occurs typically in 0.01 to 0.1 s depending on the laser power and the substrate nature; and the successive Al growth. Uniform lines are produced at scanning speeds up to 300 μm/s. Higher deposited heights are obtained with TMAA due to its higher vapor pressure when compared to TEAA. 7 μm wide, 0.7 μm thick Al lines are generated by a single surface scan at a scanning speed of 100 μm/s and a high power density (1.55 MW/cm²). Passing N₂ or He gas through a TEAA bubbler increases the deposited height by a factor 1.6 in comparison to deposition without the bubbler. Al lines deposited from TEAA and TMAA are polycrystalline. The rate of crystallite growth is greater than the rate of nucleation, leading to an increase of the surface roughness with the line thickness. Adhesion of the deposit to the substrates is good and Al lines with resistivities down to 4.5 μΩ cm, i.e. twice the bulk value are obtained.