Surface chemistry and film growth during TiN atomic layer deposition using TDMAT and NH 3

Abstract

Surface chemistry and film growth were examined during titanium nitride (TiN) atomic layer deposition (ALD) using sequential exposures of tetrakis-dimethylamino titanium (TDMAT) and NH 3. This ALD system is shown to be far from ideal and illustrates many potential problems that may affect ALD processing. These studies were performed using in situ Fourier transform infrared (FTIR) techniques and quartz crystal microbalance (QCM) measurements. Ex situ measurements also analyzed the properties of the TiN ALD films. The FTIR studies revealed that TDMAT reacts with NH x * species on the TiN surface following NH 3 exposures to deposit new Ti(N(CH 3) 2) x * species. Subsequent NH 3 exposure consumes the dimethylamino species and regenerates the NH x * species. These observations are consistent with transamination exchange reactions during the TDMAT and NH 3 exposures. QCM studies determined that the TDMAT and NH 3 reactions are nearly self-limiting. However, slow continual growth occurs with long TDMAT exposures. In addition, the TiN ALD growth rate increases progressively with growth temperature. The resistivities of the TiN ALD films were ⩾10 4 μΩ cm and the densities were ⩽3 g/cm 3 corresponding to a porosity of ∼40%. The high porosity allows facile oxidation of the TiN films and lowers the film resistivities. These high film porosities will seriously impair the use of these TiN ALD films as diffusion barriers.