LASER DIRECT-WRITE AL DEPOSITION ON SI, GAAS AND DIAMOND FROM TRIALKYLAMINE-ALANE PRECURSORS

Laser direct writing of aluminium on silicon, gallium arsenide and diamond film substrates using the Al precursors (C2H5)3N . AlH3 (TEAA) and (CH3)3 N . 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 at the laser-heated surface. Estimated temperature thresholds for Al deposition from TEAA and TMAA are similar: about 370 K on Si(111) and 385 K on GaAs(100) for both precursors. The deposited height increases with laser power density but decreases with scanning speed. Uniform lines are produced at scanning speeds up to 250 and 400 mum/s, using TEAA and TMAA precursors, respectively. The height of the deposited line is also strongly dependent on the precursor pressure in the processing chamber. Larger deposited heights are obtained with TMAA due to its higher vapour pressure compared to TEAA. 7 mum wide, 0.7 mum thick Al lines are generated by a single surface scan at a scanning speed of 100 mum/s and a high power density (1.55 MW/cm2). Deposited 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 aluminium lines to the substrates is good and their resistivities range from 4.5 to 7 muOMEGA . cm for both precursors (bulk: 2.8 muOMEGA . cm).