Surface chemistry and film growth during TiN atomic layer deposition using TDMAT and NH3

Surface chemistry and film growth were examined during titanium nitride (TiN) atomic layer deposition (ALD) using sequential exposures of tetrakis-dimethylamino titanium (TDMAT) and NH3. 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 NHx* species on the TiN surface following NH3 exposures to deposit new Ti(N(CH3)2)x* species. Subsequent NH3 exposure consumes the dimethylamino species and regenerates the NHx* species. These observations are consistent with transamination exchange reactions during the TDMAT and NH3 exposures. QCM studies determined that the TDMAT and NH3 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 ≥104 μΩ cm and the densities were ≤3 g/cm3 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