Kinetics of the WF 6 and Si 2H 6 surface reactions during tungsten atomic layer deposition

Abstract

The atomic layer deposition (ALD) of tungsten (W) films has been demonstrated using alternating exposures to tungsten hexafluoride (WF 6) and disilane (Si 2H 6). The present investigation explored the kinetics of the WF 6 and Si 2H 6 surface reactions during W ALD at 303–623 K using Auger electron spectroscopy techniques. The reaction of WF 6 with the Si 2H 6-saturated W surface proceeded to completion at 373–573 K. The WF 6 reaction displayed a reactive sticking coefficient of S=0.4 and required an exposure of 30 L (1 L=1×10 −6 Torr s) to achieve saturation at 573 K. The WF 6 exposures necessary to reach saturation increased with decreasing temperature. At surface temperatures <373 K, the WF 6 reaction did not consume all the silicon (Si) surface species remaining from the previous Si 2H 6 exposure. The reaction of Si 2H 6 with the WF 6-saturated W surface displayed three kinetic regimes. In the first region at low Si 2H 6 exposures⩽50 L, the Si 2H 6 reaction was independent of temperature and had a reactive sticking coefficient of S∼5×10 −2. In the second kinetic region at intermediate Si 2H 6 exposures of 50–300 L, the Si 2H 6 reaction showed an apparent saturation behavior with a Si thickness at saturation that increased with substrate temperature. At high Si 2H 6 exposures of 300–1×10 5 L, additional Si was deposited with an approximately logarithmic dependence on Si 2H 6 exposure. The Si 2H 6 reaction in this third kinetic region had an activation energy E=2.6 kcal/mol and the Si thickness deposited by a 1.6×10 5 L Si 2H 6 exposure increased with temperature from 3.0 Å at 303 K to 6.6 Å at 623 K. These kinetic results should help to explain W ALD growth rates observed at different reactant exposures and substrate temperatures.