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

The atomic layer deposition (ALD) of tungsten (W) films has been demonstrat ed using alternating exposures to tungsten hexafluoride (WF6) and disilane (Si2H6) The present investigation explored the kinetics of the WF6 and Si2H 6 surface reactions during W ALD at 303-623 K using Auger electron spectros copy techniques. The reaction of WF6 with the Si2H6-saturated W surface pro ceeded to completion at 373-573 K. The WF6 reaction displayed a reactive st icking coefficient of S = 0.4 and required an exposure of 30 L (1 L = 1 x 1 0(-6) Torr s) to achieve saturation st 573 K. The WF6 exposures necessary t o reach saturation increased with decreasing temperature. At surface temper atures < 373 K, the WF6 reaction did not consume all the silicon (Si) surfa ce species remaining from the previous Si2H6 exposure. The reaction of Si2H 6 with the WF6-saturated W surface displayed three kinetic regimes. In the first region at low Si2H6 exposures less than or equal to 50 L, the Si2H6 r eaction was independent of temperature and had a reactive sticking coeffici ent of S similar to 5 x 10(-2). In the second kinetic region at intermediat e Si2H6 exposures of 50-300 L, the Si2H6 reaction showed an apparent satura tion behavior with a Si thickness at saturation that increased with substra te temperature. At high Si2H6, exposures of 300-1 x 10(5) L, additional Si was deposited with an approximately logarithmic dependence on Si2H6 exposur e. The Si2H6, reaction in this third kinetic region had an activation energ y E = 2.6 kcal/mol and the Si thickness deposited by a 1.6 x 10(5) L Si2H6 exposure increased with temperature from 3.0 Angstrom at 303 K to 6.6 Angst rom at 623 K. These kinetic results should help to explain W ALD growth rat es observed at different reactant exposures and substrate temperatures. (C) 2001 Published by Elsevier Science B.V.