Cell and dendrite growth of tungsten by atmospheric pressure chemical vapor deposition

In this study, tungsten coatings are deposited at 300-610 degrees C from WF6 and H-2 by atmospheric pressure chemical vapor deposition (APCVD). Tungsten powders adheres to the furnace walls (cold wall furnace) in every deposition, regardless of whether the coating is dense or not. These tungsten powders are proved to be produced by homogeneous reactions in gas phase near the substrate and adheres to the furnace inner wall as they move with the fluid. The presence of tungsten powders when depositing dense tungsten coatings indicates that the homogeneous reactions contribute to the growth of dense tungsten coatings; with this premise, the kinetics, structure and growth mode of tungsten coatings in APCVD system are discussed. Activation energy of 28.7 and 61.9 kJ/mol corresponded to rate-limiting steps of the diffusion of the tungsten atoms in gas phase, and the dissociation of H-2. The < 100 > orientated columnar grains along the growth direction (GD) are main-branches. Not all but majority of the small grains intercalated between the columnar grains orient in the direction close to < 111 > along the GD, and these small grains are proved to be parts of second-branches. In the early stage of deposition, the < 100 > orientated grains compete with each other due to the growth of the cell tips in width. Raised areas are found on the surfaces of pyramids, and the microstructure of the growth interface shows that flat interface is prone to curved when there are more favorable growth conditions ahead. These results reveal that homogeneous reactions lead to the cell and dendrite growth mode of tungsten coatings in APCVD system. (C) 2022 Published by Elsevier B.V.