Specifications for ALD precursors

ALD precursors must be transported in the gas phase from the storage container, which is usually heated, over distances of varying length depending on the reactor architecture, before finally reacting chemically with the substrate, which is also heated to a different temperature. High volatility is therefore a major prerequisite for the precursor, but without compromising thermal stability or chemical reactivity. First and foremost, these inorganic (metallic) precursors must therefore have a finite structure, i.e. be molecular and not polymeric or a crystalline ionic network. Thermal stability over a range of temperatures is also desirable, to avoid decomposition during transport, which would generate particles and clogging of injectors in the case of...