Characterisation of TiN thin films using the bulge test and the nanoindentation technique

Abstract In-plane mechanical properties of titanium nitride (TiN x ) thin films have been investigated by performing bulge test experiments on square membranes of side of approximately 2 a =4 mm. A layer of about 1 μ m thickness of TiN x ( x =0.84–1.3) was deposited onto an n-type Si(100) wafer using radio frequency magnetron sputtering. Prior to TiN x deposition, free-standing low-stress LPCVD silicon nitride (SiN y ) thin films were fabricated by means of standard micromachining techniques. The edges of windows were aligned with the [110] directions of underlying silicon wafer in order to make perfect squares bounded by (111) planes. The bulge test was first conducted on the silicon nitride films to determine its proper residual stress and Young's modulus, being σ i =227±15 MPa and E =225±10 GPa, respectively. Then, the composite membrane made of TiN x together with underlying SiN y was bulged and the related load-displacement variation was measured. Finally, using a simple rule of mixtures formula, the elastic mechanical properties of TiN x coatings were determined and compared to those obtained during nanoindentation measurements. Both the Young's modulus and residual stress showed increasing values with increasing bias voltage, nitrogen-to-titanium ratio and coating density. The effect of substrate temperature below 600°C was found to be less significant compared to other parameters. These results are presented and discussed in terms of coating porosity, microstructure and chemical composition determined by means of electron probe microscopy.