Supercritical Fluids (SCFs) are unique solvents that posses thermodynamic and transport properties intermediate of those of the liquid- and gas-like states. These unusual solvents have previously been used to thermally batch deposit thin metal films within micro- and meso-scale templates [for example 1,2]. We have developed a new continuous flow reactor that allows deposition of metals and metal oxides from SCFs, which opens the possibility of rapid multi-layered conformal growth without the need to depressurize. However, the engineering of performing this task in flow is not straightforward. SCFs are highly dynamic, where changes in temperature or pressure lead to large thermal and diffusion gradients that strongly influence flow patterns. The use of SCFs and high-pressures also introduces obvious analytical challenges. We have deposited Cu and Ag thin films from SCF-soluble MOCVD reagents, with an aim to understand, predict and effectively utilize the SCF flow.

In order to design successful tubular SCF-MOCVD flow reactors, we have incorporated custom thermodynamic FORTRAN routines into a commercially available CFD package, CFD-ACD+; this allows us to calculate many SCF properties. We will present simulations and experimental validations of flow and metal deposits from MOCVD reagents within these reactors. Reactor development, in combination with ACE+ calculations, has led to several generations of warm- and hot-walled reactors. Hot-walled reactors allow for much higher temperatures to be achieved, i.e. >500°C inside SCF reactors, and hence semi-conductor materials may be rapidly deposited. However, as we will demonstrate, their use further increases the need for specialized engineering solutions.

1. Watkins, J et al., Microelec. Eng., 2002, 64, p53
2. Holmes J et al., J.Phys:Condens. Matter, 2003, 15, p8303

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1. Facile synthesis of uniform NH₄TiOF₃ mesocrystals and their conversion to TiO₂ mesocrystals by topotactic transformation