Batch processing of aluminum nitride by atomic layer deposition from AlCl3 and NH3

Batch processing of aluminum nitride (AlN) by thermal atomic layer deposition (ALD) was studied at high temperatures of 500–550 °C using aluminum chloride (AlCl3) and ammonia (NH3) as metal and nitrogen precursors. The growth behavior, chemical composition, morphology, crystallinity, and residual stress of the AlN films were characterized by ellipsometry, x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, x-ray diffraction, and the wafer curvature method, respectively. The deposited AlN films at 525 °C had a good batch thickness uniformity of 2.6%, a low surface roughness of ∼1 nm, a low Cl impurity level of ∼1.2%, and a hexagonal polycrystalline structure with a preferential (002) orientation. An obvious dependence between film properties and deposition temperature was found. The evaluation in deposition temperature from 500 to 550 °C resulted in an increase of the growth-per-cycle, refractive index, and tensile stress as well as a decrease of Cl and O impurity levels in the AlN films. Based on these findings, the authors concluded that high quality polycrystalline AlN films with a preferential (002) orientation can be grown with ALD in a large batch reactor at high temperatures (500–550 °C).