Atomic layer deposition (ALD), is a discontinuous variation of CVD which seperates the different chemistries of CVD into distinct steps. The alternating precursor and co-reactant pulses are seperated by inert gas purging pulses to remove excess reactants and by-products together forming a so-called “ALD” cycle. Thus, the thin films are grown layer by layer, in self-limiting surface reactions. This growth behavior allows uniform coating of complex patterned substrates and structures as well as atomic level thickness control. Due to process and precursor design, ALD is usually conducted at significantly lower temperatures than CVD, commonly with substrate temperatures below 300 °C, also facilitating film depositions on temperature sensitive substrates.
Schematic of the ALD process.
Thin films deposited via ALD.