High layer conformity at high aspect ratios as well as an exact control of the layer thickness itself require a special coating process which is very different to standard CVD or PVD processes. The process of Atomic Layer Deposition (ALD) as a special CVD process fulfils the above mentioned requirements.

The basic principle of ALD is a chemical reaction of two or more reactants on the substrate to obtain the desired layer material. To control of the growth of the desired layer the precursors (which form reactants) are injected sequentially and homogeneously over the substrate separated by an Argon-flush. The appropriate time of the precursor-inlet as well as the time of the Argon-flushing guarantee a layer growth of the material for each process cycle. Because of the fact that chemisorption is taking place homogeneously over the complete substrate-surface an excellent homogeneous layer thickness distribution without pinholes is being achieved even at 3D-surfaces.