Chemical Vapor Deposition (CVD)
Chemical vapor deposition (CVD) is a wet chemistry-free process in which one or more volatile molecular (either organic or inorganic) precursors decompose either in the gas phase or at the substrate surface. This delivers radical species to the substrate surface, which allow the deposition of thin (ranging from few nms up to ms in thickness), high-purity, high-performance films. Volatile, stable molecular by-products are also produced, which are then removed by gas flow through the reaction chamber or by a pumping unit. CVD processes are categorized on the basis of the energy source selected for the decomposition of the precursor(s) into radicals. The most common are the application of heating (e.g. in furnaces and hot-wire CVD) and of electric field (e.g. in plasma-enhanced CVD). At PMP we cover the following CVD processes.
In thermal CVD, energy in the form of heat is supplied to activate the required gas and gas-solid phase reactions. In all thermal CVD processes the reactant gases are delivered to a reactor. An oven or hot lamps typically supply the thermal energy. By-products are removed by the gas flow or by a pumping unit. At PMP we have both atmospheric and low pressure thermal CVD set-ups. These set-ups are used to synthesize for example carbon nanotubes and graphene.
Also known as catalytic CVD (Cat-CVD), this process adopts a hot filament/grid to chemically decompose the precursor molecules. The grid temperature and substrate temperature are independently controlled, allowing low temperatures at the substrate for better adsorption rates at the substrate as well as compatibility with thermally sensitive substrates (e.g. polymers) and higher temperatures at the grid for enhanced precursor decomposition.
The generation of a plasma, i.e. through the application of a DC or RF electric field to a gap between two metal electrodes and containing the deposition precursor gases, allows the decomposition/dissociation of the molecules into depositing radicals by means of electron impact reactions. The high reactivity achieved in the plasma phase allows for low substrate temperatures, compatible with processing of thermally sensitive substrates (e.g. polymers). At PMP we investigate deposition processes in direct plasma configurations (parallel plate RF capacitively coupled plasma), remote configurations (inductively RF coupled plasma) and operating at atmospheric pressure (roll-to-roll atmospheric pressure glow discharge).