In advanced multi-level metallization schemes, the application of copper as interconnect metal requires the prevention of Cu diffusion into the active area and into interlevel dielectrics by total encapsulation of Cu with barrier films. Critical requirements for diffusion barriers are very small thicknesses, low resistivity, low deposition temperature and conformality on high aspect ratio trenches and vias. For this application, we have studied TiN films deposited by atomic layer chemical vapour deposition (ALCVD) at 400°C and 350°C. This paper discusses the ALCVD TiN films properties and compares them to the properties of TiN deposited by ionized physical vapour deposition (I-PVD).
The ALCVD TiN deposited at 400°C exhibits a resistivity comparable to I-PVD TiN resistivity. However, the ALCVD films deposited at 350°C show higher resistivity. The Cl residue in ALCVD films is 1.5% at 400°C and 3% at 350°C. The microstructure is fine-grained. A very high level of conformality on trenches characterizes the ALCVD TiN films. We believe this property gives a clear advantage over the sputtered I-PVD TiN since its coverage in high aspect ratio trenches and vias is expected to be limited for the future devices interconnection scheme.