Role of Tin+ and Aln+ ion irradiation (n=1, 2) during Ti1-xAlxN alloy film growth in a hybrid HIPIMS/magnetron mode

Abstract

Metastable Ti 1-x Al x N (0.4 ≤ x ≤ 0.76) films are grown using a hybrid approach in which high-power pulsed magnetron sputtering (HIPIMS) is combined with dc magnetron sputtering (DCMS). Elemental Al and Ti metal targets are co-sputtered with one operated in HIPIMS mode and the other target in DCMS; the positions of the targets are then switched for the next set of experiments. In both cases, the AlN concentration in the co-sputtered films, deposited at T s = 500 °C with R = 1.5-5.3 Å/s, is controlled by adjusting the average DCMS target power. Resulting films are analyzed by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, elastic recoil detection analysis, and nanoindentation.Mass spectroscopy is used to determine ion energy distribution functions at the substrate. The distinctly different flux distributions obtained from targets driven in HIPIMS vs. DCMS modes allow the effects of Al n+ and Ti n+ (n = 1, 2) ion irradiation on film growth kinetics, and resulting properties, to be investigated separately. Bombardment with Al n+ ions (primarily Al + in the Al-HIPIMS/Ti-DCMS configuration) during film growth leads to NaCl-structure Ti 1-x Al x N (0.53 ≤ x ≤ 0.60) films which exhibit high hardness (> 30 GPa) with low stress (0.2 -0.7 GPa tensile). In contrast, films with corresponding AlN concentrations grown under Ti n+ metal ion irradiation (with a significant Ti 2+ component) in the Ti-HIPIMS/Al-DCMS mode have much lower hardness, 18-19 GPa, and high compressive stress ranging up to 2.7 GPa. The surprisingly large variation in mechanical properties results from the fact that the kinetic AlN solubility limit x max in 2 Ti 1-x Al x N depends strongly on, in addition to T s and R, the target power configuration during growth and hence the composition of the ion flux. AlN with x max  64 mol% can be accommodated in the NaCl structure under Al n+ ion flux, compared with  40 mol% for growth with Ti n+ flux. The strong asymmetry in film growth reaction paths is due primarily to the fact that the doubly-ionized metal ion flux is approximately two orders of magnitude higher from the Ti target, than from Al, powered with HIPIMS. This asymmetry becomes decisive upon application of a moderate substrate bias voltage, -60 V, applied synchronously with HIPIMS pulses, during growth.

Direct current magnetron sputtered ZrB2 thin films on 4H-SiC(0001) and Si(100)

“…A range of dc bias voltages between -20 V and -80 V was applied to the substrate and the deposition time was 100 s, yielding 300 nm thick films, corresponding to a growth rate of about 8 unit cells/s in the c-axis direction. The typical floating potential for a DCMS process is around -10 V in this deposition system [23]. The power of the heater was 0 W, 5 000 W or 10 000 W, corresponding to approximately room temperature (RT), 400 °C, and 550 °C respectively, as calibrated by thermocouple.…”

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.…”

“…This has been shown, for example, to be essential for controlling phase composition, while minimizing compressive residual stresses, in pseudobinary TM nitride thin films. 2,3,8 The approach is based on controllably adjusting plasma electron-energy distributions g(Ee) by the proper choice of sputtering-gas mixtures, since the ionization probability of sputtered metal atoms during HIPIMS is determined by the g(Ee) high- of the sputtering gas (Ne, Ar, Kr, or Xe). The average target power P and total gas pressure P were maintained constant at 1 kW and 0.4 Pa (3 mTorr).…”

“…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 contrast, multiply-charged metal-ion irradiation, even at floating potential, can result in films with high defect densities and high compressive stresses. 2,3 Synchronized-bias HIPIMS CrN films deposited in mixed Ar/N2…”