Impurity dominated thin film growth

Abstract

Magnetron sputter deposition was applied to grow thin metal films in the presence of impurities. These impurities are ambient gas molecules and/or atoms from the residual gas present in the vacuum chamber. Seven materials were investigated: four single element metals (Al, Ag, Cu, and Cr), two widely applied alloys (Cu 55 Ni 45 and Ni 90 Cr 10), and one high entropy alloy (CoCrCuFeNi). The thin films were analyzed using X-ray diffraction to determine the domain size, the film texture, and the lattice parameter. The same trend for all studied materials is observed. When the ratio between the impurity and metal flux towards the substrate is low, the domain size is not affected by the presence of the impurities. In this regime, the incorporation of the impurities affects the lattice parameter. At high flux ratios, the change of the domain size can be described by a power law with the exponent equal to À1/2 for all studied materials. A kinetic Monte Carlo code is used to demonstrate this observed trend.

The Seebeck Coefficient of Sputter Deposited Metallic Thin Films: The Role of Process Conditions

“…The domain size in the high-impurity regime (τ 1) is strongly refined by the presence of the impurities during growth. Based on previous research [24], we expect a relation D ∼ τ −1/2 in this regime. This relation is represented by the striped line and further consolidated by the gray markers taken from the previous work.…”

“…As already discussed in previous work [24], atmospheric gas impurities present in the vacuum chamber during film growth can act as grain refiners. In general, in the high-impurity regime (τ 1), the average domain size D decreases in a material-independent way with an increasing impurity-to-metal impingement flux ratio τ according to D ∼ τ −1/2 [24]. This effect was experimentally verified in Figure 4 (right).…”

“…This specific description of |∆S| as function of the impurity-to-metal ratio τ embodies the thought of a relation between |∆S| and the domain size D, more specifically 1/D. The idea for this relation originates from a previous work [24], where we elaborated a model that accounts for the experimental observation D ∼ τ −1/2 in the high-impurity regime. The agreement between the experiment and the proposed relation |∆S| ∼ τ 1/2 is evaluated by means of a chi-squared test.…”

“…The material flux was calculated from the measured thickness (Taylor-Hobson profilometer, Leicester, UK), the deposition time, and the film density as measured by x-ray reflectometry (Bruker D8). The impurity flux was calculated based on the Maxwell-Boltzmann distribution as presented in previous work [24].…”

“…Figure 4b is based on the same data for the domain size as in Figure 4a but presented in a normalized way and as function of the impurity-to-metal impingement flux ratio τ. The data for the domain size have been normalized in order to allow a better comparison with the additional data set (gray circles) included in Figure 4b which originates from a previous experiment [24]. The uppermost dotted line in the figures indicate the averaged domain size in this low-impurity regime.…”