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Enhanced Desorption of Surface Methyl Groups in Time-Resolved Chemical Vapour Deposition of Aluminium Nitride from Trimethylaluminum

Aluminium nitride (AlN) is a semiconductor with a wide range of
applications from light emitting diodes to high frequency transistors. Electronic
grade AlN is routinely deposited at 1000 °C by chemical vapour deposition (CVD)
using trimethylaluminium (TMA) and NH3 while low temperature CVD
routes to high quality AlN are scares and suffer from high levels of carbon
impurities in the film. We report on an ALD-like CVD approach with
time-resolved precursor supply where thermally induced desorption of methyl
groups from the AlN surface is enhanced by the addition of an extra pulse, H2,
N2 or Ar between the TMA and NH3 pulses. The enhanced
desorption allowed deposition of AlN films with carbon content of 1 at. % at
480 °C. Mass spectrometry combined
with kinetic- and quantum chemical modelling show that the extra pulse between
TMA and NH3 enhances the desorption and prevents re-adsorption of the
methyl groups, terminating the AlN surface after the TMA pulse. The surface
methyl groups are found to desorb as CH3, CH4 and C2Hx.