Atomic layer deposition of Al2O3 interlayer for improving AlN growth on silicon substrates

Ultrathin Al2O3 interlayers have been grown on silicon (111) substrates using atomic-layer deposition (ALD) and investigated as interlayers prior to AlN growth by metalorganic chemical vapor deposition. The ALD process is carried out at low temperatures with the interlayer thickness systematically varied from 0.9 to 5.1 nm. A reference sample with the standard SiNx interlayer is also investigated. Thin Al2O3 layers (<2 nm) are found to significantly improve the crystal quality of AlN. X-ray diffraction measurements show the total dislocation density is decreased by nearly one order of magnitude for an Al2O3 thickness of 1.7 nm compared with the standard SiNx interlayer. The impact of the interlayer on the AlN strain is studied by x-ray diffraction and Raman spectroscopy measurements. Some reduction in stress is observed when incorporating the 1.7 nm interlayer. A Raman stress factor of −2.6 ± 0.1 cm−1/GPa is obtained for AlN. Surface and interface analysis studied by atomic force microscopy, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy indicates sharp atomic alignment between AlN and silicon with a 1.7 nm Al2O3 interlayer.