ALBERT

Notes: The effects of incident ion/metal flux ratio Ji/JMe and ion energy Ei on the microstructure, texture, and phase composition of polycrystalline metastable Ti0.5Al0.5N films produced by reactive magnetron sputtering have been investigated using x-ray diffraction (XRD), plan-view and cross-sectional transmission electron microscopy, and Rutherford backscattering spectroscopy. The films, typically (approximately-equal-to)1 μm thick, were deposited at a pressure of 20 mTorr (2.67 Pa) in pure N2 on thermally oxidized Si(001) substrates at 250±25 °C. The N2+ ion flux to the substrate was controlled by means of a variable axial magnetic field superimposed on the permanent magnetic field of the magnetron. Films deposited at Ei=20 eV ((approximately-equal-to)10 eV per incident accelerated N) with Ji/JMe=1 exhibited a complete (111) texture with a porous columnar microstructure and an average column size of (approximately-equal-to)30 nm. Increasing Ei from 20 to 85 eV, while maintaining Ji/JMe constant at 1, resulted in a small change in texture as the XRD intensity ratio I002/(I111+I002) increased from (approximately-equal-to)0 to 0.14, a decrease in average column size to 25 nm, and a reduction in intracolumn porosity.The stoichiometric ratio N/(Ti+Al) increased from 1 at Ei=20 eV with Ji/JMe=1 to 1.23 at Ei=85 eV indicating trapping of excess N while the lattice constant a0 increased from 0.4157 to 0.4188 nm due to compressive stress. Ei values ≥100 eV led to alloy phase separation. In contrast, maintaining Ei at (approximately-equal-to)20 eV and increasing Ji/JMe from 1 to ≥5.2 resulted in a change from a porous (111) texture to a dense completely (002)-oriented microstructure with an increase in the average column size to 35 nm. N/(Ti+Al) and a0 remained essentially constant and the alloy remained single phase. Mechanistic pathways leading to microstructure and texture changes through variations in Ei at constant Ji/JMe and in Ji/JMe at constant Ei were found to be quite different. The average energy deposited per metal atom, 〈Ed〉=Ei(Ji/JMe), is therefore not a universal parameter, as has been previously proposed, for describing film growth.

Notes: Ti0.5Al0.5N alloy films, typically 1.5 μm thick, were grown on MgO(001) at temperatures Ts between 400 and 850 °C by ultra-high-vacuum reactive magnetron sputtering in pure N2. Films grown at Ts between (approximately-equal-to)480 and 560 °C were single crystals in which the lattice misfit strain was partially relieved by glide of 〈001〉 misfit dislocations, with Burgers vector =a0/2〈011〉, on {011¯} planes. Cross-sectional transmission electron microscopy investigation showed no evidence of residual extended defects in the films until thicknesses of (approximately-equal-to)150 nm at which point threading dislocations, oriented along the [001] growth direction, were observed. Surface-initiated spinodal decomposition, resulting in the formation of compositionally modulated NaCl-structure platelets along [001] with width (approximately-equal-to)1 nm, occurred over a narrow growth temperature range between 540 and 560 °C as a precursor to bulk phase separation of wurtzite-structure AlN at Ts≥560 °C. The alloy was continuously depleted of AlN at higher growth temperatures until the equilibrium two-phase structure, cubic TiN and wurtzite AlN, was obtained at Ts≥750 °C.

Notes: The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si1−xGex layers were grown by molecular-beam epitaxy (MBE) and the silicides formed by different postdeposition reaction paths, were investigated using a combination of high-resolution cross-sectional transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. In two of the three sample configurations investigated, Co was deposited either (S1) directly on a strained Si1−xGex layer or (S2) on a sacrificial MBE Si overlayer on Si0.9Ge0.1. In the third sample configuration (S3) Si1−xGex was grown on a Si(001) substrate containing a buried ion-implanted CoSi2 layer. Only in sample configuration S2 was it possible to obtain a fully strained nearly defect-free CoSi2/Si0.9Ge0.1 structure. A high density of threading dislocations, corresponding to ≈60% relaxation at the Si0.9Ge0.1/Si interface, was observed in S1 while S3, in addition to the dislocations, exhibited a pronounced faceting at the CoSi2/Si interface. © 1995 American Institute of Physics.

Notes: 2H–AlN(0001) layers have been grown on Si(111) by reactive magnetron sputtering from an Al target in Ar+N2 gas mixtures at temperatures Ts=400–900 °C. Variations in reactive gas consumption, target voltage, and current–voltage characteristics versus nitrogen partial pressure were used to determine deposition parameters required to yield stoichiometric AlN with growth rates ≥2 μm h−1. High-resolution cross-sectional transmission electron microscopy (XTEM) analyses of films grown at 900 °C showed that the initial 6–8 monolayers were (111)-oriented cubic 3C before transforming to the (0001)-oriented 2H polytype. The epitaxial relationship was found by XTEM and x-ray diffraction (XRD) to be 2H–AlN(0001)//3C–AlN(111)//Si(111) with 2H–AlN[12¯10]//3C–AlN[110]//Si[110]. High-resolution XRD ω−2aitch-theta and ω rocking curve widths for films grown at Ts=900 °C were 70 and 500 arc sec, respectively, the lowest values yet reported. © 1995 American Institute of Physics.

Notes: The mechanical properties of (001)-, (011)-, and (111)-oriented MgO wafers and 1-μm-thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N2 and Ar discharge, were investigated using nanoindentation. A combination of x-ray-diffraction (XRD) pole figures, high-resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three-sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as-received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasing loads, increased in the order (011)〈(001)〈(111). After a 30 s postdeposition anneal at 1000 °C, however, hardness was found to be independent of load except at displacements 〉100 nm where substrate effects were apparent. TiN(001) and (111) films had hardnesses of 20±0.8 and 21±1 GPa, respectively, while data obtained from (011) layers exhibited large scatter due to surface roughness effects. Young's moduli for annealed samples, calculated from the elastic unloading curves, were found to be 307±15 GPa for MgO (001) and 445±38 and 449±28 GPa for TiN (001) and TiN (111), respectively. © 1996 American Institute of Physics.

Notes: The effects of the incident ion/metal flux ratio (1≤Ji /JTi≤15), with the N+2 ion energy Ei constant at (approximately-equal-to)20 eV ((approximately-equal-to)10 eV per incident accelerated N), on the microstructure, texture, and stoichiometry of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputtering have been investigated. The layers were deposited in pure N2 discharges on thermally oxidized Si(001) substrates at 350 °C. All films were slightly overstoichiometric with a N/Ti ratio of 1.02±0.03 and a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Films deposited with Ji/JTi=1 initially exhibit a mixed texture—predominately (111), (002), and (022)—with competitive columnar growth which slowly evolves into a pure (111) texture containing a network of both inter- and intracolumn porosity with an average column size of (approximately-equal-to)50 nm at t=1.6 μm. In contrast, films grown with Ji/JTi≥5 do not exhibit competitive growth. While still columnar, the layers are dense with an essentially complete (002) preferred orientation and an average column size of (approximately-equal-to)55 nm from the earliest observable stages. The normalized x-ray diffraction (002) intensity ratio in thick layers increased from (approximately-equal-to)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 for all Ji/JTi. Thus, contrary to previous models, strain is not the dominant factor in controlling the development of preferred orientation in these films. Moreover, once film texture is fully evolved—whether it be (002) or (111)—during deposition, changing Ji/JTi has little effect as preferred orientation becomes controlled by pseudomorphic forces. Film porosity, however, can be abruptly and reversibly switched by increasing or decreasing Ji/JTi. © 1995 American Institute of Physics.

Notes: Two-dimensional reciprocal space mapping with high-resolution x-ray diffraction has been used to characterize the strain in as-grown and annealed Sb-doped Si. Si(100) layers with Sb concentrations 1×1019–3×1021 cm−3 were grown by molecular-beam epitaxy at a growth temperature of 310 °C. High-resolution transmission electron microscopy has been applied to determine the critical thickness for epitaxial growth, growth morphology, and defect structure. The critical thickness for low-temperature epitaxial growth decreases with increasing Sb concentration from ∼1000 A(ring) for CSb≈2×1020 cm−3 to ∼25 A(ring) for CSb≈2×1021 cm−3. Following the defect-free epitaxial layer was a (100)-oriented layer with stacking faults and facets to the final amorphous phase. The strain in as-grown Si layers increased with increasing Sb concentration CSb up to 1×1021 cm−3. The thermal stability for concentrations above 2×1020 cm−3 was poor, resulting in Sb precipitation. The lattice expansion obtained due to Sb-doping in Si was β=5.4×10−24 cm3 atom−1. Electrical characterization of the samples showed that doping concentrations ≤4×1020 cm−3 could be obtained.

Notes: The influence of Ti ion bombardment on the intrinsic stress and microstructure of TiN films during deposition by arc evaporation of Ti in pure N2 has been investigated. Ions with an average charge of +1.6 were accelerated from the arc discharge by a negative substrate bias Vs between 5 and 540 V which yielded a steady-state substrate temperature between 300 and 600 °C, respectively. The compressive intrinsic stresses in the films, as determined by the x-ray-diffraction (XRD) sin2 ψ method after subtracting the thermal stress contribution at room temperature, changed abruptly from 1.9 to a maximum of 6.5 GPa as Vs increased from 5 to 100 V. The compressive stress then decreased monotonically to ∼1.6 GPa as Vs increased to 540 V. Broadening of XRD peaks (β) showed accompanying inhomogeneous strain with a maximum values for Vs=100 V. Cross-sectional transmission electron microscopy showed a dense columnar film microstructure. Electron microdiffraction showed a distorted structure within the same columns for Vs=100 V and better defined grains for Vs=500 V. The observed reduction in intrinsic stress with increasing Ti ion energy is in addition to what is normally observed in sputter-deposited TiN films with the same ion energy range of predominantly Ar-ion bombardment. A comparison with published work of magnetron sputtered TiN showed that defects created by Ti ions are more easily annihilated than defects created using Ar ions. Ar atoms tend to be strongly bound to lattice defects and forming thermally stable complexes and prevent stress relief at high Vs as is observed for arc-evaporated films. The obtained results are compared to models for stress generation during steady-state conditions in the competition between collisionally induced point defect formation and defect annihilation during deposition. © 1995 American Institute of Physics.

Notes: Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm−2, were investigated by multicrystal x-ray diffraction, reciprocal space mapping (RSM), high-resolution transmission electron microscopy, and secondary-ion-mass spectrometry (SIMS). For Sn doses up to 3.30×1015 cm−2, annealing at 600 °C for 30 min under dry N2 atmosphere resulted in recrystallization by solid-phase epitaxy (SPE) to a layer thickness of more than 50 nm. These SPE-grown layers were shown to be free of extended defects and Sn redistribution was negligible. As measured by x-ray diffraction, the Sn-induced strain in Si increased with the implant dose. From RSM measurements, this strain was shown to be tetragonal with negligible in-plane relaxation. Mosaicity and defect-related effects were shown to be negligible. Instead, limited thickness effects and strain variation due to the implantation profile appeared to be the major sources of the observed broadening in the diffraction peaks. The lattice expansion coefficient for Sn in Si was estimated from the measurements to be 2.5×10−24 cm3/atom. For Sn doses above 3.3×1015 cm−2, a reduction in the Sn-induced strain in Si was observed despite the fact that Sn concentrations were higher. In this high-dose regime, the SPE growth under the same annealing conditions was limited to ∼10 nm. The remainder of the structure showed a succession of layers dominated by twinned Si(001), polycrystalline Si, nanocrystalline Si:Sn, and an untransformed amorphous top layer. In addition, Sn redistribution was detected in the SIMS measurements at levels much higher than expected from trace-diffusivity values at the employed annealing conditions. The observed SPE retardation was related to the high concentrations of Sn in these structures. © 1995 American Institute of Physics.

Notes: Suppression of three-dimensional (3D) island nucleation during growth of InAs on Si (100), achieved by using very low energy, high-flux Ar ion irradiation, reduced planar defect densities. For 13 eV ion irradiation, 3D islands nucleated after ∼2 monolayers (ML) of deposition, similar to conventional molecular beam epitaxy. High-resolution transmission electron microscopy studies of nominally 18-ML-thick films showed 3D InAs islands with {111} facets. A high density of {111} twins and stacking faults was observed adjacent to many of the {111} facets. Most of these defects propagated into the film upon further growth. When nucleation was carried out with 28 eV ion irradiation, flat InAs films were observed for thicknesses up to ∼10 ML. The 3D islands that nucleated at higher thicknesses were flatter with less faceting than in the 13 eV case. The density of planar defects in the initial nucleation layer and in thicker InAs films was reduced when 3D island nucleation was suppressed. These results indicate that planar defects formed directly on the {111} facets of the 3D islands.