Atomic layer deposition: basic principles and preparation of thin films for energy applications

Atomic layer deposition (ALD) is chemical method based on a sequential introduction of chemical precursors and reactants. Compared to chemical vapour deposition distinctive and clear feature of ALD lies in the self-limiting nature of precursor adsorption and reaction. ALD growth consists of the four steps: 1) precursor adsorption, 2) purging, 3) reactant exposure and 4) purging. These steps constitute an ALD cycle. ALD takes place in conditions where precursor adsorption is the self-limiting step, i.e. only 1 molecular layer is adsorbed at the surface. Theoretically, exposure to reactant gives rise to formation of 1 atomic layer of the reaction product. Consequently, ALD is a surface-controlled process, where parameters other than reactants, substrate and temperature have little influence. ALD application in microelectronics as well as ALD films for energy application are discussed. (authors)