[en] Laser textured substrates enable a combinatorial study of strained layer growth morphology as a function of substrate miscut. Si(001) substrates with miscut θ<15 deg. off (001) are produced by texturing with nanosecond laser pulses. Ge_0.8Si_0.2 growth rates are varied over a wide range, 1.7-90 monolayers per minute, at a fixed substrate temperature of 600 deg. C. Film morphologies at all growth rates show strong dependence on the local miscut θ within the dimpled regions of the substrate: the results demonstrate the importance of anisotropy in surface stiffness for the formation of epitaxial nanostructures. The length scales of all structures display a similar trend of decreasing size with increasing growth rate due to the suppression of coarsening at high growth rates

[en] 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/N₂ mixtures to grow dilute Ti_1−xTa_xN 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 Ti_0.92Ta_0.08N alloy films, 1.8 μm thick, grown with T_s ≤ 120 °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 < 120 °C) grown with the same V_s, and 7.8 and 248 GPa for DCMS TiN films grown with no applied bias (T_s < 120 °C). Ti_0.92Ta_0.08N residual stress is low, σ = −0.7 GPa, and essentially equal to that of Ti-HIPIMS/Ti-DCMS TiN films grown with the same substrate bias

[en] Highly textured epitaxial metallizations will be required for the next generation of devices with the main driving force being a reduction in electromigration. Herein a model system of 190 nm of Al on a 140 nm layer of W grown on MgO <00l> substrates was studied. The W layer was <00l> oriented and rotated 45 degree sign with respect to the MgO substrate to minimize the misfit; the remaining strain was accommodated by dislocations, evident in transmission electron microscopy images. From high-resolution x-ray diffraction (XRD) measurements, the out-of-plane lattice parameter was determined to be 3.175 Aa, and the in-plane parameter was 3.153 Aa, i.e., the W film sustained a strain resulting in a tetragonal distortion of the lattice. XRD pole figures showed that the Al had four fold symmetry and two dominant orientations, <016> and <3 9 11>, which were twinned with multiple placements on the epitaxial W layer. The driving force for the tilted <001> and <011> orientations of Al on W is due to strain minimization through lattice matching. These results show that <00l> Al deposited at ambient conditions onto W is difficult to achieve and implies that electromigration difficulties are inherent. (c) 2000 American Institute of Physics

[en] Metastable NaCl-structure Ti_1−xAl_xN 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 °C. Three sets of experiments are carried out: a −60 V 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 Ti_1−xAl_xN) 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 (−1.8 GPa) 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.