Film Uniformity in Atomic Layer Deposition

The sources of non-uniformity in thin films produced using atomic layer deposition (ALD) have been investigated by reviewing the mechanical hardware of ALD reactors, precursors, and the by-products of surface reactions. The most common causes of non-uniformity are overlapping pulses, thermal self-decomposition of precursors, and non-uniform gas distribution. Less studied, however, are the consequences of downstream surface reactions of gaseous by-products. In particular, titanium nitride films have been found to be significantly less uniform than those of transition metal oxides deposited from metal halides. The influence of reaction by-products on the TiN film growth has been studied by comparing the deposition in the cross-flow and showerhead style reactors. Finally, the sources of non-uniformity in plasma enhanced (PE) ALD are illustrated by studying the TiN deposition process.