Effects of nitrogen flow rate on the preferred orientation and phase transition for niobium nitride films grown by direct current reactive magnetron sputtering

Abstract

We deposit niobium nitride (NbN) thin films on Si(1 0 0) substrates using direct current (dc) reactive magnetron sputtering in discharging a mixture of N2 and Ar gas, and explore the effects of nitrogen flow rate ( ) on the preferred orientation (PO), phase transition and mechanical properties for the obtained films by virtue of x-ray diffraction and nanoindentation measurements. We find that with increasing the biaxial compressive stress increases, which leads to a pronounced change in the PO and phase structure for the film. A phase transition from δ (face-centred cubic) to δ′ (hexagonal) occurs in the film as the biaxial stress increases to a critical value of about 3.9 GPa, which can be attributed to a decrease in the strain energy. With a further increase in the biaxial stress, the fraction of the δ′ phase in the film increases, and finally the film only has a single phase, δ′-NbN, resulting in a consistent increase in hardness.

Microstructure, mechanical properties and oxidation behaviors of magnetron sputtered NbNx coatings

“…However, in previous studies, the obtained results on the hardness of the NbN x coatings are often contradictory. The hardness of d-NbN was lower than those of b-Nb 2 N and d 0 -NbN [5,7,14,16,18], or higher than those of b-Nb 2 N and d 0 -NbN [5,6,12], or almost equal to those of b-Nb 2 N and d 0 -NbN [10]. These scattered results suggest that the phase structure of the NbN x coatings may be an important factor affecting the hardness, but not the only one, for example the morphologies of the coatings which have been less studied in previous studies.…”

Growth and mechanical properties of epitaxial NbN(001) films on MgO(001)

“…In addition, NbN has potential as a hard protective coating [11,12]. Therefore various researchers have studied the microstructure and mechanical properties of NbN coatings deposited using ion beam assisted deposition [13], pulsed laser deposition [14], cathodic arc deposition [11,12], and reactive magnetron sputtering [15][16][17][18][19].…”

“…Deposition using a high ion flux, as obtained by unbalanced magnetron sputtering results in a strong 111 preferred orientation [20], and increasing the nitrogen partial pressure in a Ar/N 2 mixture during deposition leads to an increasing N/Nb ratio in the NbN x films from x = 0.61 to 1.06 and a transition from a pure cubic δ-NbN rocksalt structure to a mixed phase structure including a hexagonal δ′-NbN phase [15]. The reported hardness H of NbN ranges from 7-48.5 GPa [11,12,[14][15][16][17][18]21]. We attribute this large range to a combination of microstructural effects including open grain boundaries, layer density, texture, and intrinsic stress, but is likely also related to the phases and the N/Nb-ratio, as a transition from the δ to the δ′ phase with an associated increase in x from 0.92 to 1.08 is reported to cause an increase in H from 25 to 40 GPa [15], while an even higher hardness of 48.5 GPa is reported for highly stressed cathodic arc deposited layers [12].…”

Sputter deposited NbCxNy films: Effect of nitrogen content on structure and mechanical and tribological properties

“…Among the transition metal nitrides and carbides, Nb-based coating materials have been extensively studied and evaluated with respect to industrial applications [5,6]. NbN has gained some interest due to its relatively high superconducting transition temperature of T c = 17.3 K [7].…”

“…NbN has gained some interest due to its relatively high superconducting transition temperature of T c = 17.3 K [7]. It is also promising as a protective coating material due to its high chemical stability, high hardness of 38 GPa, and high melting point of 2204 K [5,[8][9][10][11]. NbN layers have been proposed as wear protective coatings at high temperature [12], but the friction coefficient of 0.7 is rather large [13].…”