Reactive Magnetron Sputter Deposition and Characterization of Thin Films from the Ti-Al-N and Sc-Al-N Systems

Sammanfattning: This Thesis treats the growth and characterization of ternary transition metal nitride thin films. The aim is to probe deeper into the Ti-Al-N system and to explore the novel Sc-Al-N system. Thin films were epitaxially grown by reactive magnetron sputtering from elemental targets onto single-crystal substrates covered with a seed layer. Elastic recoil detection analysis and Rutherford backscattering spectroscopy were used for compositional analysis and depth profiling. Different x-ray diffraction techniques were employed, ex situ using Cu radiation and in situ during deposition using synchrotron radiation, to identify phases, to obtain information about texture, and to determine the thickness and roughness evolution of layers during and after growth. Transmission electron microscopy was used for overview and lattice imaging, and to obtain lattice structure information by electron diffraction. Film properties were determined using van der Pauw measurements of the electrical resistivity, and nanoindentation for the materials hardness and elastic modulus. The epitaxial Mn+1AXn phase Ti2AlN was synthesized by solid-state reaction during interdiffusion between sequentially deposited layers of (0001)-oriented AlN and Ti thin films. When annealing the sample, N and Al diffused into the Ti, forming Ti3AlN at 400 ºC and Ti2AlN at 500 ºC. The Ti2AlN formation temperature is 175 ºC lower than earlier reported results. Ti4AlN3 thin films were, however, not possible to synthesize when depositing films with a Ti:Al:N ratios of 4:1:3. Substrate temperatures at 600 ºC yielded an irregularly stacked Tin+1AlNn layered structure because of the low mobility of Al adatoms. An increased temperature led, however, to an Al deficiency due to an out diffusion of Al atoms, and formation of Ti2AlN phase and Ti1-xAlxN cubic solid solution. In the Sc-Al-N system the first ternary phase was discovered, namely the perovskite Sc3AlN, with a unit cell of 4.40 Å. Its existence was supported by ab initio calculations of the enthalpy showing that Sc3AlN is thermodynamically stable with respect to the binaries. Sc3AlN thin films were experimentally found to have a hardness of 14.2 GPa, an elastic modulus of 21 GPa, and a room temperature resistivity of 41.2 ??cm.