Nucleation and growth during the atomic layer deposition of W on Al 2O 3 and Al 2O 3 on W

Abstract

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 (Al 2O 3) surfaces and Al 2O 3 ALD on W surfaces using Auger electron spectroscopy (AES). W ALD was performed using alternating exposures of WF 6 and Si 2H 6. Al 2O 3 ALD was performed using alternating exposures of Al(CH 3) 3 and H 2O. AES signals were measured after each WF 6 and Si 2H 6 exposure during W ALD on Al 2O 3 and after each Al(CH 3) 3 and H 2O exposure during Al 2O 3 ALD on W. The AES measurements revealed that 3 WF 6/Si 2H 6 reaction cycles were required to nucleate the W ALD film on Al 2O 3 surfaces at 473 K. Subsequently, the W ALD film grew linearly at a rate of 2.6–3.5 Å per WF 6/Si 2H 6 reaction cycle. The AES measurements also revealed that only one H 2O/Al(CH 3) 3 cycle was needed to nucleate Al 2O 3 ALD on W at 450 K. Subsequently, the Al 2O 3 ALD film grew linearly at the rate of 1.0 Å per Al(CH 3) 3/H 2O reaction cycle. As expected from the W ALD surface chemistry, the W and Si AES signals oscillated dramatically during the sequential WF 6 and Si 2H 6 exposures. Many parameters were varied to determine their effect on the W ALD nucleation period. The WF 6 surface reaction was surprisingly insensitive to the Al 2O 3 substrate temperature and the initial hydroxyl coverage on the Al 2O 3 surface. These results for the nucleation and growth during W ALD on Al 2O 3 and Al 2O 3 ALD on W are relevant to the growth of W/Al 2O 3 nanolaminates that have potential as X-ray mirrors, thermal barrier coatings and tribological films.