Shapes of agglomerates in plasma etching reactors
Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogou...
On form and flow in dusty plasmas
Microscopic cauliflowers have been observed in a surprisingly diverse range of dusty plasmas. Their microstructure, as analysed by electron microscopy, is consistent with growth by ballistic deposition rather than diffusion limited aggregation. The morphology of the grains supports the inference from dust growth kinetics that they form by accretion of positive ions rather than neutral radicals. The dense, amorphous structure is capped by a fractal surface whose texture is concisely described by a recursion based on the modified midpoint method. The surface texture may be reconstructed by ion bombardment, providing a quantitative link between growth kinetics and roughness through a Mullins-Sekerka stability analysis of Laplacian growth.
Wall-to-bed heat transfer in circulating fluidized beds
Heat Transfer from the wall of a circulating fluidized bed to the fast bed suspension has been investigated for several materials. The range of investigation includes dense and dilute phase fast fluidization and pneumatic transport. The overall heat transfer coefficient was found to be a function mainly of cross-sectional average suspension density. Effects of superficial velocity and solids mass flux were obscured by their interrelationship to the suspension density. Two models from the literature are evaluated using present and published data.