Fluidized bed as a solid precursor delivery system in a chemical vapor deposition reactor

Chemical vapor deposition (CVD) using precursors that are solids at operating temperatures and pressures, presents challenges due to their relatively low vapor pressures. In addition, the sublimation rates of solid state precursors in fixed bed reactors vary with particle and bed morphology. In a recent patent application, the use of fluidized bed (FB) technology has been proposed to provide high, reliable, and reproducible flux of such precursors in CVD processes. In the present contribution, we first focus on the reactor design which must satisfy fluidization,sublimation and CVD reactor feeding constraints. Then, we report masstransport results on the sublimation of aluminium acetylacetonate, a common precursor for the CVD of alumina films. Finally, we discuss the efficiency of the precursor feeding rate, we address advantages and drawbacks of the invention and we propose design modifications in order to meet the process requirements

Combined plasma gas-phase synthesis and colloidal processing of InP/ZnS core/shell nanocrystals

Indium phosphide nanocrystals (InP NCs) with diameters ranging from 2 to 5 nm were synthesized with a scalable, flow-through, nonthermal plasma process at a rate ranging from 10 to 40 mg/h. The NC size is controlled through the plasma operating parameters, with the residence time of the gas in the plasma region strongly influencing the NC size. The NC size distribution is narrow with the standard deviation being less than 20% of the mean NC size. Zinc sulfide (ZnS) shells were grown around the plasma-synthesized InP NCs in a liquid phase reaction. Photoluminescence with quantum yields as high as 15% were observed for the InP/ZnS core-shell NCs

Liquid and Solid Precursor Delivery Systems in Gas Phase Processes

Due to attractive surface properties and to intrinsic brittleness of Complex Metallic Alloys (CMAs), most of their potential applications involve materials with high surface-to-volume ratios, including thin films and coatings. While physical vapor deposition techniques are efficient for the processing of CMA films on line-of-sight surfaces, chemical vapor deposition (CVD) is well positioned for their application on complex surfaces. However, for CVD process to be implemented efficiently in the processing of CMA films a number of challenges must be addressed. Because numerous CVD reagents, commonly called precursors, are low vapor pressure liquids or solids, one of these challenges is the production of vapors of such precursors, which are decomposed in the deposition chamber to provide the desired film. Such a production has to be ensured at high rate and must be reproducible and stable during the whole process. Actual solutions to this question involve (i) bubbling inert gas through thermally regulated liquid precursors, (ii) leaching the surface of fixed precursor powder beds, and (iii) in situ generating the precursor flow by passing a reactive gas through a thermally regulated bed of the metallic element to be transported. Such solutions neither may be satisfactory for actual R&D needs nor may be transferable to industrial environments. These reasons are in part responsible for the limited implementation of advanced materials (including CMA-based ones) in numerous industrial and hence societal needs. More recently, innovative solutions have been proposed to feed deposition systems based on vapor phase chemical techniques (CVD and Atomic Layer Deposition, ALD). Such solutions are Direct Liquid Injection (DLI) of dissolved solid precursors and also sublimation of the latter in fluidized beds or in elaborated fixed beds. Such technological responses show promise for industrial applications of CVD, especially for the deposition of metals and ceramic compounds for which the available molecular and inorganic precursors present low vapor pressures. This review provides an overview of the methods by which precursor vapors are transported to the deposition chamber. Early and recent patents dedicated to such technologies will be revisited and considered in the light of the deposition of multimetallic alloy coatings