PEALD AlN: Controlling growth and film crystallinity

We report on the growth kinetics and material properties of aluminium nitride (AlN) films deposited on Si(111), with plasma enhanced atomic layer deposition (PEALD). Tri-methyl aluminium (TMA) and NH3-plasma were used as the precursors. The ALD window was identified in terms of the process parameters, and it showed that a 0.1 s of TMA pulse, 8 s of NH3-plasma pulse, and 350 oC were the optimal conditions for ALD to occur. In-situ spectroscopic ellipsometry (SE), using a Cauchy optical model, was used to monitor the film growth in real time. The composition of the as-grown AlN films were determined by X-ray photoelectron spectroscopy (XPS), which revealed Al/N compositions of approximately 46% and 53%, also with low impurity (O, C) levels. The film crystallinity, measured with grazing incidence X-ray diffraction (GIXRD), showed polycrystalline hexagonal (wurtzitic) crystalline planes. Finally, several techniques were employed to influence the film crystallinity. These included: ALD at different plasma powers and temperatures, in-situ treatment of the Si(111) wafer with different plasma parameters (composition, power, duration) prior to deposition, and ALD on Si(100) and SiO2 substrates.