Composite structures based on Ti - Si and TiN_x - SiN_x materials are interesting for photonic, optoelectronic and sensor techniques. The TiN_x - SiN_x multilayers were deposited on Si(100)-wafers by laser ablation of the Ti and Si targets in ambient nitrogen gas in range of pressures ranging from 3x10^-3 to 5x10^-3 mbar. The layer thickness and composition was controlled by parameters of the excimer laser pulses (wavelength at 193 nm), ambient gas species and gas pressure.
Processing of Ti - Si and TiN_x - SiN_x multilayers at high temperature (HT) lead to uniform metastable phase of composite films. The effect of HT treatment (typically for 10 min by rapid thermal process, RTP) at 870 K on structural transformation in multilayers were investigated by X-ray reflectrometry (XRR), X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM) and ellipsometric measurements. Morphology of samples was characterised by atomic force microscopy (AFM).
The Ti - Si multilayers show the superlattice with bilayer period Λ = 31 nm and Si thickness t_Si = 2.9 nm. Due to the very thin layers, the interfacial and surface energies dominate both the bulk and the strain-energy terms, which encourages the formation of metastable phase with a low interfacial energy. Then the inter facial energy term becomes less important and bulk formation energies dominate. These energetic arguments can only give a preference for phase formation and are most valid when growth occurs at near-equilibrium conditions.