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Keywords:

  • Laser chemical vapour deposition;
  • Al deposition;
  • Photolysis;
  • Pyrolysis;
  • Trimethylamine alane;
  • Laser direct writing

Abstract

Aluminium microstructures (dots or strips) have been photodeposited on GaAs substrates via the decomposition of a solid precursor, the 2:1 hydride adduct of Al, called trimethylamine alane (TMAA).

The dissociation of TMAA, the vapour pressure of which can be varied between 0.4 and 1 mbar by dilution in hydrogen carrier gas, has been achieved via a pyrolytic process using a CW Ar+ laser operating in the visible range (488–514 nm). This decomposition reaction occurs at laser powers higher than 0.3 W, i.e. at laser-induced temperatures higher than 130°C, and leads to the formation of high-purity aluminium strips as observed from Auger electron spectroscopy (AES) and energy-dispersive X-ray analysis (EDX) data. The deposition rates are in the range 50–1400 Å s−1. The minimum of line resistivity measured versus scanning speed and laser power is 6.5 μΩ cm.

The photolytic decomposition of TMAA has been performed at room temperature within the laser spot area using a CW UV laser (intracavity frequency doubler emitting at 257 nm). The formation of aluminium clusters has been observed at very low deposition rates (20 Å s−1). However, these tiny clusters react quickly with oxygen and are transformed into alumina clusters.

All these results have been tentatively explained on the basis of the surface reactivity of H2 and TMAA regarding GaAs or Al, as obtained by other workers through surface science techniques and mass spectrometry.