A review of metal-ion-flux-controlled growth of metastable TiAlN by HIPIMS/DCMS co-sputtering

Abstract

We review results on the growth of metastable Ti1-xAlxN alloy films by hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) using the time domain to apply substrate bias either in synchronous with the entire HIPIMS pulse or just the metal-rich portion of the pulse in mixed Ar/N2 discharges. Depending upon which elemental target, Ti or Al, is powered by HIPIMS, distinctly different film-growth kinetic pathways are observed due to charge and mass differences in the metal-ion fluxes incident at the growth surface. Al + ion irradiation during Al-HIPIMS/Ti-DCMS at 500 C, with a negative substrate bias Vs = 60 V synchronized to the HIPIMS pulse (thus suppressing Ar + ion irradiation due to DCMS), leads to single-phase NaCl-structure Ti1-xAlxN films (x ≤ 0.60) with high hardness (> 30 GPa with x > 0.55) and low stress (0.2-0.8 GPa compressive). Ar + ion bombardment can be further suppressed in favor of predominantly Al + ion irradiation by synchronizing the substrate bias to only the metal-ion-rich portion of the Al-HIPIMS pulse. In distinct contrast, Ti-HIPIMS/Al-DCMS Ti1-xAlxN layers grown with Ti + /Ti 2+ metal ion irradiation and the same HIPIMS-synchronized Vs value, are two-phase mixtures, NaCl-structure Ti1-xAlxN plus wurtzite AlN, exhibiting low hardness (≃18 GPa) with high compressive stresses, up to -3.5 GPa. In both cases, film

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

“…18,19 It was shown for Ti1-xAlxN and Ti1-xSixN films deposited in a hybrid high-power pulsed and DC magnetron (HIPIMS/DC) co-sputtering configuration that film nanostructure, phase composition, and stress evolution exhibit distinct differences depending upon which metal target was powered by HIPIMS. 20,21,22 The effects were ascribed to differences in mass and charge state of metal-ions incident on the growing film surface, 23 and the detrimental role of intense fluxes of doubly-ionized Ti atoms, resulting from the fact that the second ionization potential 2 of Ti is lower than the first ionization potentials of Ar and N2.…”

Strategy for tuning the average charge state of metal ions incident at the growing film during HIPIMS deposition

“…This provides increased capability for controlling film microstructure, and hence physical properties, while minimizing ionbombardment-induced compressive stress (such as obtained from rare-gas ion irradiation) during HIPIMS film growth utilizing a substrate bias synchronized to the metal-ion dominated portion of the pulses. 2,3,5 Metal, as opposed to the noble-gas, ions primarily end on lattice sites. 5 HIPIMS discharges are complex, time-dependent, and operate far from equilibrium.…”

“…2,3,5 Metal, as opposed to the noble-gas, ions primarily end on lattice sites. 5 HIPIMS discharges are complex, time-dependent, and operate far from equilibrium. In order to qualitatively describe the general trends observed in these experiments, we use time-averaged parameters (e.g., electron temperature, discharge voltage, and sputter-ejected atom thermalization distance) corresponding to steady-state plasmas.…”

“…Low-energy metal-ion irradiation of growing films during high-power pulsed magnetron sputter deposition (HIPIMS), 1 with the substrate bias synchronized to the metal-ion-rich portion of the pulses, 2,3 has recently been shown to provide microstructure densification and surface smoothening, without introducing the large increases in film compressive stress reported for noblegas ion irradiation during dc magnetron sputter deposition, 4,5 provided that the metal-ion flux incident at the substrate is primarily singly-ionized. In contrast, multiply-charged metal-ion irradiation, even at floating potential, can result in films with high defect densities and high compressive stresses.…”

In-situ observation of self-cleansing phenomena during ultra-high vacuum anneal of transition metal nitride thin films: Prospects for non-destructive photoelectron spectroscopy

“…HIPIMS is operated at the average power of 1.3 kW, the pulsing frequency of 600 Hz, and the duty cycle of 12%. Substrate bias is applied in the form of 200-ls-long pulses synchronized with HIPIMS cathode and the amplitude of À60 V. 12,13 The target-to-substrate distance is 6 cm, while the total pressure during deposition is 3 mTorr (0.4 Pa). Following film growth, the samples are allowed to cool down to 180 C before the deposition chamber is ventilated, which allows for a better control of surface chemistry upon air exposure.…”