Atomic layer deposition (ALD) is a modified chemical vapour deposition (CVD) process. Two successive, self-limiting surface reactions are characteristic for the process, so that extremely thin, defect-free and highly homogeneous films can be deposited. Plasma atomic layer deposition is a special version in which plasma is used for the activation of the second precursor. This allows less reactive precursors to be used, or alternatively the substrate temperature can be lowered, for example to coat sensitive substrates. Compared to other PVD and plasma-CVD deposition processes, the component being coated is not damaged by the plasma.