Extended metastable Al solubility in cubic VAlN by metal-ion bombardment during pulsed magnetron sputtering: film stress vs subplantation

Abstract

The self-archived version of this journal article is available at Linköping University Electronic Press: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-139557 N.B.: When citing this work, cite the original publication.Greczynski, G., Mraz, S., Ruess, H., Hans, M., Lu, J., Hultman, L., Schneider, J. M., (2017) AbstractDynamic ion-recoil mixing of near-film-surface atomic layers is commonly used to increase the metastable solubility limit xmax in otherwise immiscible thin film systems during physical vapor deposition. Recently, Al subplantation achieved by irradiating film growth surface with Al + metalion flux was shown to result in an unprecedented xmax for VAlN, far above values obtained with gas ion irradiation. However, it is reasonable to assume that ion irradiation necessary for subplantation also leads to a compressive stress σ buildup. In order to separate the effects of Al + bombardment on σ and xmax, and realize low-stress high-xmax nitride alloys, we grow metastable

Time evolution of ion fluxes incident at the substrate plane during reactive high-power impulse magnetron sputtering of groups IVb and VIb transition metals in Ar/N2

“…The approach described above has been used to grow N-doped bcc-CrN0.05 nanostructured films combining metallic and ceramic properties; 18 hard, stress-free Ti0.39Al0.61N; 19 single-phase NaCl-structure Ti1-xSixN with extremely-high SiN concentrations; 20 unprecedented AlN supersaturation in single-phase cubic V1-xAlxN; 21,22 and hard, dense Ti0.92Ta0.08N and Ti0.41Al0.51Ta0.08N alloys grown with no external heating. 23,24 In each of these examples, the crucial step was synchronization of the substrate bias pulse to the metal-ion portion of the HiPIMS pulse, which requires detailed knowledge, typically provided by the time-resolved mass spectrometry, of the time evolution of metal-and gas-ion fluxes incident at the substrate.…”

Control over the Phase Formation in Metastable Transition Metal Nitride Thin Films by Tuning the Al+ Subplantation Depth

“…This effectively suppresses the formation of the thermodynamically stable w-AlN phase as the activation energy for bulk diffusion is larger than for surface diffusion. The volume fraction χ of the second-phase w-AlN precipitates, estimated from NaCl phase 002 and wurtzite 1010 peak intensities integrated over all sample title angles and normalized to random powder diffraction values, is plotted in Figure 5 as a function of Al concentration x for three series of V 1−x Al x N films grown with (a) conventional DCMS and dc bias of −100 V, (data points from [20]) (b) hybrid Al-HiPIMS/V-DCMS co-sputtering with -60 V bias pulses synchronized to the metal-ion rich portions of the HiPIMS pulses, and (c) hybrid Al-HiPIMS/V-DCMS co-sputtering with V s = −300 V. Linear extrapolations of χ(x) data plots towards the χ = 0 horizontal line are used to estimate the critical Al concentration value x max , above which w-AlN phase is detected, corresponding to metastable solubility limit of Al in the NaCl crystal lattice. Clearly, solubility is lowest for the V 1−x Al x N films grown with conventional DCMS technique and with a DC substrate bias of -100 V, x max = 0.52.…”

“…For example, for the TiAlN material system, x max~0 .40 at the growth temperature T s = 500 • C [14,15]. In the case of ZrAlN, values between 0.13 and 0.43 are reported [16][17][18], while x max is in the range 0.52-0.54 for VAlN [19][20][21].…”

“…The powering of the DCMS source is chosen such that the film surface, where high adatom mobility and gas-ion-induced mixing drives the system towards thermodynamic equilibrium, is dominated by V atoms, which arrive predominantly between HiPIMS pulses and form NaCl-structure VAlN crystallites with low Al content. To avoid precipitation of the thermodynamically favored w-AlN phase, high-energy Al + ions deposited exclusively during thẽ 100-µs-long metal-ion rich HiPIMS phase are directly subplanted into cubic low-x V 1−x Al x N grains buried below the high-mobility surface zone, where the activation energy for diffusion is larger than at the very surface, which enables formation of single-phase VAlN solid solution with record-high x max of 0.75 [20,22,28].…”

Stress-Dependent Elasticity of TiAlN Coatings

“…Recently, it has been demonstrated for Cr 0.8 Al 0.2 N that a compressive stress state of −4 GPa results in an elastic modulus increase of 150 GPa, when compared to the stress-free material [4]. In addition, compressive residual stresses are utilized to stabilize the metastable cubic phase of MAlN (M = Ti, V, Cr) [5,6].…”