Modeling of metastable phase formation diagrams for sputtered thin films

Abstract

A method to model the metastable phase formation in the Cu–W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu–W and Cu–V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

Compositional and Tribo‐Mechanical Characterization of Ti‐Ta Coatings Prepared by Confocal Dual Magnetron Co‐Sputtering

“…In terms of the composition, the solubility limit reported for Ta in α ‐Ti solid solutions varied from 0 to 2 at% at room temperature (RT) to 6.2 at% at 600 °C (see Figure ). According to our data, α‐ Ti remains the predominant phase at Ta content as high as 7.9 at%, as it can be seen in Figure , which could be explained as a consequence of the non‐equilibrium growth conditions, which causes changes in the solubility limits of alloys; as has been demonstrated by Chang et al The metastable α″ phase is obtained in the bulk after quenching from the β phase once the solubility limit of Ta in α ‐Ti is exceeded; α ″ is usually found for Ta contents between 7 and 21 at% . However, for these sputtered deposited Ti‐Ta coatings, the coexistence of α″ and β phases was observed without need of a high temperature treatment with Ta contents between 7.9 and 30 at%.…”

“…In this work, we propose the synthesis of an improved light‐alloy metallic coating investigating the formation of metallic alloys at the nanoscale as a possible route to increase the hardness due to the Hall–Petch effect and obtain larger H / E ratios by tailoring the crystalline phase adequately . Therefore, we propose the synthesis of Ti‐Ta coatings based on the interesting properties observed for bulk Ti‐Ta alloys .…”

Unprecedented thermal stability of inherently metastable titanium aluminum nitride by point defect engineering

“…On the other hand, the nitrogen content in the solid is defined by equal chemical potential of nitrogen in the solid phase and the vapor at given pressure, µ N,film = µ N,gas phase . Decomposition of (Ti,Al)N into the thermodynamically stable phases TiN and AlN during growth is kinetically hindered since metal diffusion over the length scale of many tens or even hundreds of atomic distances [24] is required. Hence, to enable diffusion metal atoms need to overcome an activation energy in the order of one electronvolt many tens or even hundreds of times [24,25].…”

“…Decomposition of (Ti,Al)N into the thermodynamically stable phases TiN and AlN during growth is kinetically hindered since metal diffusion over the length scale of many tens or even hundreds of atomic distances [24] is required. Hence, to enable diffusion metal atoms need to overcome an activation energy in the order of one electronvolt many tens or even hundreds of times [24,25]. Nitrogen adsorption and desorption on the other hand are single-step processes with activation energy in the same order of magnitude [26,27].…”

“…The here proposed existence of a paraequilibrium between the gas phase and the film during synthesis is the basis for a first theory to describe stoichiometry and hence defect formation besides growth defects of all reactively deposited thin films: Even though it is accepted that the extreme quenching rates ( ∼ 10 15 K/s: from metal vapor to solid within fs [29]) allow for growth of thermodynamically metastable phases [22,30], (Ti,Al)N being an excellent example [6,23,31], we propose that the amount of incorporated nitrogen is defined by a paraequilibrium between nitrogen in the gas phase and in the metastable film surface during growth, µ N,gasphase = µ N,film . Based on the gas-solid paraequilibrium notion we introduce a methodology utilizing defect energies from ab initio calculations for thermodynamic calculations, allowing stoichiometry and thus point defect concentrations remaining after healing out growth defects by annealing [22,28] of reactively grown films to be predicted.…”