Kinetics of the WF6 and Si2H6 surface reactions during tungsten atomic layer deposition

The atomic layer deposition (ALD) of tungsten (W) films has been demonstrated using alternating exposures to tungsten hexafluoride (WF6) and disilane (Si2H6). The present investigation explored the kinetics of the WF6 and Si2H6 surface reactions during W ALD at 303–623 K using Auger electron spectroscopy techniques. The reaction of WF6 with the Si2H6-saturated W surface proceeded to completion at 373–573 K. The WF6 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 WF6 exposures necessary to reach saturation increased with decreasing temperature. At surface temperatures <373 K, the WF6 reaction did not consume all the silicon (Si) surface species remaining from the previous Si2H6 exposure. The reaction of Si2H6 with the WF6-saturated W surface displayed three kinetic regimes. In the first region at low Si2H6 exposures⩽50 L, the Si2H6 reaction was independent of temperature and had a reactive sticking coefficient of S∼5×10−2. In the second kinetic region at intermediate Si2H6 exposures of 50–300 L, the Si2H6 reaction showed an apparent saturation behavior with a Si thickness at saturation that increased with substrate temperature. At high Si2H6 exposures of 300–1×105 L, additional Si was deposited with an approximately logarithmic dependence on Si2H6 exposure. The Si2H6 reaction in this third kinetic region had an activation energy E=2.6 kcal/mol and the Si thickness deposited by a 1.6×105 L Si2H6 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.