Laser-assisted atom probe tomography of Ti/TiN films deposited on Si

Laser-assisted atom probe tomography (L-APT) was used to examine superconducting TiN/Ti/TiN trilayer films with nominal respective thicknesses of 5/5/5 (nm). The trilayers were deposited on Si substrates by reactive sputtering. Electron energy loss microscopy performed in a scanning transmission electron microscope (STEM/EELS) was used to corroborate the L-APT results and establish the overall thicknesses of the trilayers. Three separate batches were studied where the first (bottom) TiN layer was deposited at 500 ⁰C (for all batches) and the subsequent TiN/Ti bilayer was deposited at ambient temperature, 250 ⁰C, and 500 ⁰C, respectively. L-APT rendered an approximately planar TiN/Si interface by making use of plausible mass-spectral assignments to N31+, SiN1+, and SiO1+. This was necessary since ambiguities associated with the likely simultaneous occurrence of Si1+ and N21+ prevented their use in rendering the TiN/Si interface. The non-superconducting Ti2N phase was revealed by L-APT and was most prominent near the bottom Ti/TiN interface. Neither L-APT nor STEM/EELS rendered sharp Ti/TiN interfaces and the contrast between these layers diminished with increased film deposition temperature. L-APT also revealed that hydrogen was present in varying degrees in all samples including control samples that were composed of single layers of Ti or TiN.