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- Greczynski, Grzegorz, et al.
(author)
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Metal versus rare-gas ion irradiation during Ti1-xAlxN film growth by hybrid high power pulsed magnetron/dc magnetron co-sputtering using synchronized pulsed substrate bias
- 2012
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 30:6
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Journal article (peer-reviewed)abstract
- Metastable NaCl-structure Ti1-xAlxN is employed as a model system to probe the effects of metal versus rare-gas ion irradiation during film growth using reactive high-power pulsed magnetron sputtering (HIPIMS) of Al and dc magnetron sputtering of Ti. The alloy film composition is chosen to be x = 0.61, near the kinetic solubility limit at the growth temperature of 500 degrees C. Three sets of experiments are carried out: a -60V substrate bias is applied either continuously, in synchronous with the full HIPIMS pulse, or in synchronous only with the metal-rich-plasma portion of the HIPIMS pulse. Alloy films grown under continuous dc bias exhibit a thickness-invariant small-grain, two-phase nanostructure (wurtzite AlN and cubic Ti1-xAlxN) with random orientation, due primarily to intense Ar+ irradiation leading to Ar incorporation (0.2 at. %), high compressive stress (-4.6 GPa), and material loss by resputtering. Synchronizing the bias with the full HIPIMS pulse results in films that exhibit much lower stress levels (-1.8GPa) with no measureable Ar incorporation, larger grains elongated in the growth direction, a very small volume fraction of wurtzite AlN, and random orientation. By synchronizing the bias with the metal-plasma phase of the HIPIMS pulses, energetic Ar+ ion bombardment is greatly reduced in favor of irradiation predominantly by Al+ ions. The resulting films are single phase with a dense competitive columnar structure, strong 111 orientation, no measureable trapped Ar concentration, and even lower stress (-0.9 GPa). Thus, switching from Ar+ to Al+ bombardment, while maintaining the same integrated incident ion/metal ratio, eliminates phase separation, minimizes renucleation during growth, and reduces the high concentration of residual point defects, which give rise to compressive stress.
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| 2. |
- Greczynski, Grzegorz, et al.
(author)
-
Novel strategy for low-temperature, high-rate growth of dense, hard, and stress-free refractory ceramic thin films
- 2014
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 32:4, s. 041515-
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Journal article (peer-reviewed)abstract
- Growth of fully dense refractory thin films by means of physical vapor deposition (PVD) requires elevated temperatures T-s to ensure sufficient adatom mobilities. Films grown with no external heating are underdense, as demonstrated by the open voids visible in cross-sectional transmission electron microscopy images and by x-ray reflectivity results; thus, the layers exhibit low nanoindentation hardness and elastic modulus values. Ion bombardment of the growing film surface is often used to enhance densification; however, the required ion energies typically extract a steep price in the form of residual rare-gas-ion-induced compressive stress. Here, the authors propose a PVD strategy for the growth of dense, hard, and stress-free refractory thin films at low temperatures; that is, with no external heating. The authors use TiN as a model ceramic materials system and employ hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS and DCMS) in Ar/N-2 mixtures to grow dilute Ti1-xTaxN alloys on Si(001) substrates. The Ta target driven by HIPIMS serves as a pulsed source of energetic Ta+/Ta2+ metal-ions, characterized by in-situ mass and energy spectroscopy, while the Ti target operates in DCMS mode (Ta-HIPIMS/Ti-DCMS) providing a continuous flux of metal atoms to sustain a high deposition rate. Substrate bias V-s is applied in synchronous with the Ta-ion portion of each HIPIMS pulse in order to provide film densification by heavy-ion irradiation (m(Ta) = 180.95 amu versus m(Ti) = 47.88 amu) while minimizing Ar+ bombardment and subsequent trapping in interstitial sites. Since Ta is a film constituent, primarily residing on cation sublattice sites, film stress remains low. Dense Ti0.92Ta0.08N alloy films, 1.8 mu m thick, grown with T-s less than= 120 degrees C (due to plasma heating) and synchronized bias, V-s = 160 V, exhibit nanoindentation hardness H = 25.9 GPa and elastic modulus E = 497 GPa compared to 13.8 and 318 GPa for underdense Ti-HIPIMS/Ti-DCMS TiN reference layers (T-s less than 120 degrees C) grown with the same V-s, and 7.8 and 248 GPa for DCMS TiN films grown with no applied bias (T-s less than 120 degrees C). Ti0.92Ta0.08N residual stress is low, sigma = -0.7 GPa, and essentially equal to that of Ti-HIPIMS/Ti-DCMS TiN films grown with the same substrate bias.
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