Development of preferred orientation in polycrystalline TiN layers grown by ultrahigh vacuum reactive magnetron sputtering

Abstract

The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over-stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Contrary to previous models, the present results establish that TiN preferred orientation can be controlled without introducing large in-plane compressive stress and/or changes in the strain energy as a function of layer thickness.

Effect of Al substitution on Ti, Al, and N adatom dynamics on TiN(001), (011), and (111) surfaces

“…Thus, with continued deposition, (1 1 1) grains slowly and inexorably overgrow (0 0 1) grains in a competitive growth mode leading to increasingly strong (1 1 1) preferred orientation as observed by x-ray diffraction studies as a function of film thickness and cross-sectional transmission electron microscopy analyses. [60,62] We find that Al adatoms also have a higher mobility on TiN(0 0 1) than on TiN(1 1 1) (Sec. 4.2).…”

“…This is also consistent with experimental results for TiN/SiO 2 film deposition carried out under conditions of minimal intrinsic growth stress. [60,62] However, once island coalescence occurs, the effect is reversed. Since Ti adatoms have longer residence times on (1 1 1) than (0 0 1) surfaces, adatoms deposited near grain boundaries have a much higher probability of being captured on (1 1 1) grains.…”

“…This is consistent with experimental observations showing that nucleation of TiN on amorphous (i.e., non-orientationally biased) substates is dominated by approximately equal number densities of (0 0 1) and (1 1 1) islands with almost no (0 1 1) islands detected. [60,62] The considerably higher Ti adatom mobility, hence chemical potential, of Ti adatoms on TiN(0 0 1) compared to (1 1 1) surfaces (see Sec. 4.1) implies that Ti adatoms have a higher chance of moving off (0 0 1) islands compared to low-potential-energy, low-surface-diffusivity, (1 1 1) islands.…”

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

“…26 The incident ion energy Ei and ion-to-metal flux ratio Ji/JMe are decisive parameters controlling nanostructural evolution during low temperature (< 500 o C; Ts/Tm < 0.3 for TiN) physical vapor deposition of transition-metal (TM) nitrides by conventional reactive DCMS. 17,25,27,28,29,30,31 The dominant ion species incident at the growth surface during DCMS with N2/Ar gas mixtures optimized to obtain stoichiometric films is typically Ar + , with N2 + and N + both contributing a few percent. 32, 33 The N2 + /N + ratio increases with increasing N2/Ar fraction, while in pure N2 discharges the dominant ion species is N2 + .…”

“…32, 33 The N2 + /N + ratio increases with increasing N2/Ar fraction, while in pure N2 discharges the dominant ion species is N2 + . 32 For magnetron sputtering, in which anode sheaths are typically ≤ 1 mm (that is, essentially collisionless), the average energy Ei of ions incident at the growing film is Ei = o i E + ne(Vs -Vpl), 25,27 in which o i E denotes the average energy of ions entering the anode sheath, n accounts for the charge state of the ion, and Vpl is the plasma potential (typically 3-10 V). 26 o i E corresponds to the mean value of the SigmundThompson energy distribution function for sputter-ejected atoms 34 convolved with (i) the probability function for electron impact ionization, 35 and (ii) the probability function for collisions with Ar neutrals between the target and the substrate.…”