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 C₂H_x.