Nucleation and growth during the atomic layer deposition of W on Al2O3 and Al2O3 on W

Nucleation and growth are critical during the atomic layer deposition (ALD) of ultra thin films and nanolaminates. This study examined the nucleation and growth during tungsten (W) ALD on aluminum oxide (Al2O3) surfaces and Al2O3 ALD on W surfaces using Auger electron spectroscopy (AES). W ALD was performed using alternating exposures of WF6 and Si2H6. Al2O3 ALD was performed using alternating exposures of Al(CH3)(3) and H2O. AES signals were measured after each WF6 and Si2H6 exposure during W ALD on Al2O3 and after each Al(CH3)(3) and H2O exposure during Al2O3 ALD on W The AES measurements revealed that 3 WF6/Si2H6 reaction cycles were required to nucleate the W ALD film on Al2O3 Surfaces at 473 K. Subsequently, the W ALD film grew linearly at a rate of 2.6-3.5 Angstrom per WF6/Si2H6 reaction cycle. The AES measurements also revealed that only one H2O/Al(CH3)(3) cycle was needed to nucleate Al2O3 ALD on W at 450 K. Subsequently, the Al2O3 ALD film grew linearly at the rate of 1.0 Angstrom per Al(CH3)(3)/H2O reaction cycle. As expected from the W ALD surface chemistry, the W and Si AES signals oscillated dramatically during the sequential WF6 and Si2H6 exposures. Many parameters were varied to determine their effect on the W ALD nucleation period. The WF6 surface reaction was surprisingly insensitive to the Al2O3 substrate temperature and the initial hydroxyl coverage on the Al2O3 surface. These results for the nucleation and growth during W ALD on Al2O3 and Al2O3 ALD on W are relevant to the growth of W/Al2O3 nanolaminates that have potential as X-ray mirrors, thermal barrier coatings and tribological films. (C) 2004 Elsevier B.V. All rights reserved.