Joshua Pelleg

Reactive-sputter-deposited TiN films on glass substrates

Abstract Sputter-deposited TiN thin films on glass substrate were investigated by X-ray diffraction analysis. The lattice parameter determined on the basis of (200) and (220) peaks is smaller than that determined on the basis of (111) peaks. A decrease in lattice parameter with increasing temperature was observed on annealing. The films exhibited preferred orientation. The tendency towards a specific preferred orientation is discussed on the basis of strain and surface energies. At low substrate temperatures and/or at small film thicknesses surface energy controls growth and a (100) preferred orientation is expected. At large film thicknesses and at high substrate temperatures the strain energy predominates and the (111) orientation is expected.

Lattice distortion in thin films of IVB metal (Ti, Zr, Hr) nitrides

Abstract Nitride films of IVB metals (titanium, zirconium and hafnium) exhibit non-conventional lattice distortion which is displayed in the expansion of the lattice parameter calculated from the (111) diffraction peak. It is commonly assumed that this phenomenon may be explained in terms of rhombohedral distortion of the cubic lattice. However, our experimental data do not agree with the shift and broadening of the peak that are characteristic of rhombohedral distortion. We propose an alternative model for the observed expansion which is based on selective trapping of interstitial atoms in various crystallographic planes. It is shown that entrapment of interstitial atoms in the (111) plane is favorable, in comparison with the (100) plane. Entrapped atoms cause hydrostatic lattice expansion which varies with the different orientations of the grains. Non-uniform lattice expansion seems to be the main source of intrinsic microstrains and macrostrains usually observed in thin sputtered films.

Reactions in the matrix and interface of the Fe–SiC metal matrix composite system

Abstract Fe–SiC metal matrix composite (MMC) was produced by the use of hot isostatic pressing (HIP) or sintering for consolidation. The SiC in the MMC was in the forms of particulates and chopped fibers. The effect of exposure of the MMC to high temperatures for long time, up to 1.4×10 4 s, was obtained by heat treatment of the HIPed or sintered specimens. A small reaction zone of ∼0.5–1 μm, composed of iron silicides, was observed in specimens HIPed at 1173 K at a pressure of 150 MPa. Cursory mechanical tests indicate an increase in the ultimate tensile strength and the yield strength of 33.1 and 12.6% of the as HIPed specimens, respectively, when the SiC content was 3% by volume. C, originating from the SiC and dissolved in Fe, induces changes in the matrix when the MMC is exposed to high temperatures, leading to the formation of the familiar transformation products. Strengthening by modification of the Fe matrix under controlled conditions is a unique feature of the Fe–SiC MMC system. The kinetics of the reaction zone formation was investigated and it was found that its growth is diffusion controlled and occurs with an activation energy of 205.4 kJ mol −1 . The reaction zone might act as a diffusion barrier preventing fiber degradation as long as the conditions of thermal effects are reasonable, but exposure of the MMC to high temperatures for extended time can result in severe fiber damage. A mechanism is suggested for the reaction zone formation.

RGa6 (R≡ rare earth atom), a common intermetallic compound of the R-Ga systems

Abstract A number of new RGa 6 compounds (where R is a rare earth atom) with the tetragonal PuGa 6 structure are reported. The lattice parameters of these compounds decrease on replacing the rare earth atoms in the order of increasing atomic number. The RGa 6 compounds are formed by a peritectic reaction at temperatures which decrease in the order mentioned. The thermal instability of these compounds as expressed by the decrease in peritectic temperature is discussed. Also the failure to detect these intermetallic compounds by other investigators is explained.

The influence of a third element on the interface reactions in metal-matrix composites (MMC) : Al-graphite system

Abstract The basic concept of achieving reduced reactions at a matrix–fiber interface by decreasing fiber solubility in the matrix of a metal matrix composite (MMC) was implemented on the Al–graphite system. Alloying the matrix of the Al–C system with small amounts of additional constituent can do this. According to theoretical calculations, Si should be the most effective constituent to reduce the reactions in the binary Al–C system. Small quantities of Si added to Al–C are effective both in decreasing C solubility in the Al matrix and limiting the formation of Al 4 C 3 by reducing interface reactions. Fe or Ga additives should not reduce interface reactions at the matrix–fiber interface of this system, but rather augment them, leading to accelerated deterioration. Experiments were carried out on the Al–C MMC system with and without the addition of a third component. The theoretical calculations were verified by the experimental results. In the absence of Si in the Al–C MMC, the reactions at the fiber–matrix interface occur at a rapid rate with an activation energy of 62 kJ mol −1 . The kinetics of degradation of the fiber in the Al–C is discussed. Si limits such reactions. Ga as an additive to Al–C provided further substantiation of the validity of the theory. According to our experimental results, Ga as an additive to Al–C has a detrimental effect on the reaction, which was also predicted by the theoretical calculations.

Control of the reaction at the fibre-matrix interface in a Cu/SiC metal matrix composite by modifying the matrix with 2.5 wt.% Fe

Abstract Metal matrix composites (MMCs) of Cu/SiC can be produced directly by hot isostatic pressing (HIP) by eliminating the reaction at the fibre-matrix interface via small additions of Fe. No further heat treatment is required if the HIP is performed at about 925 K for approximately 7.2 × 103 s at a pressure of 100 MPa. The interface resulting from the application of the processing technique is almost perfect. Without Fe addition a reaction at the fibre-matrix interface was observed, despite the high temperatures and extended times used. The effect of high temperatures on the quality of the interface has been investigated and it seems that an MMC based on Cu/SiC alloyed with Fe can be exposed in use to the temperature range 870–1135 K. Exposure of the Cu/Fe/SiC composite for extended times at 1135 K or above is detrimental because of interface reactions.

Stress changes in chemical vapor deposition tungsten silicide (polycide) film measured by x-ray diffraction

Stresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) were evaluated at each stage of the fabrication. The individual layers of the Si/SiO2/poly-Si/WSi2/poly-Si multilayered structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were either heat treated at 1193 K for 30 min or capped with a 25 nm thermal oxide and the strain in the WSi2 film was also analyzed by x-ray diffraction. The change in strain of the WSi2 layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The stress is affected by the layers of the multilayered film. An as deposited poly-Si layer on top of WSi2 reduces its stress, since it introduces a compressive component. The stress in WSi2 is further reduced upon annealing. Poly-Si also maintains a Si supply at ...

Co-sputtered TiB2 as a diffusion barrier for advanced microelectronics with Cu metallization

Abstract Titanium boride thin films were deposited from separate Ti and B targets by magnetron co-sputtering and the conditions for obtaining good diffusion barrier properties were evaluated. The best diffusion barrier properties against Cu penetration were obtained when the film was amorphous and deposited with RF bias. Auger electron spectroscopy (AES) and plan-view scanning electron microscopy (SEM) revealed that Cu penetration into amorphous titanium boride is appreciably greater in the unbiased specimen. The as-deposited amorphous film has a resistivity of 450–500 μΩ · cm, but after following annealing at ∼ 723°C for 1 h a substantial decrease in resistivity was obtained while the structure of the boride remained amorphous. The amorphous boride is stable up to 890°C. The crystallization temperature can be decreased by RF bias application, and under these conditions microcrystalline TiB 2 can be formed already at ∼ 400°C. Crystalline TiB 2 has a strong (001) preferred orientation. TiSi 2 (C-54) is also formed during annealing at temperatures exceeding 765°C as a result of the reaction of titanium boride containing free Ti with the silicon substrate.

Structural analysis of (Ti1−xAlx)N graded coatings deposited by reactive magnetron sputtering

Abstract Graded (Ti1−xAlx)N coatings were prepared by reactive magnetron co-sputtering of Ti and Al on silicon and glass substrates in an Ar+N2 atmosphere. The N2 content was kept constant in the gas mixture and the composition of the (Ti1−xAlx)N film was controlled by the power applied to the targets. The composition of the graded films was determined by Auger electron spectroscopy (AES) depth profiling and by energy dispersive spectroscopy (EDS) of their cross sections. Phase determination was performed by X-ray diffraction (XRD) and by selected area electron diffraction (SAED). Transmission electron microscopy (TEM) of the cross sections was used to determine the microstructure of the graded films. Interfaces between the films and substrates and within the films were investigated by high resolution TEM (HRTEM). The microstructural observations as well as the composition analysis, performed by AES depth profile and by EDS measurements, show that the graded films are continuous. XRD patterns have shown a strong preferred orientation with the (111) planes parallel to the surface of the film. Splitting of the (111) peak or its broadening reflect reduction in the lattice parameter with increasing Al content. TEM images show that the films posses columnar structure with an average grain size of ∼50 nm. HRTEM images reveal randomly oriented grains near the Si substrate and semi-coherent grain boundary between neighboring columnar grains.

The gallium-rich side of the Nd-Ga and Ce-Ga systems

Abstract The existence of an intermetallic compound of the type RGa6 (R  rare earth) on the gallium-rich side of the Nd-Ga and Ce-Ga systems was established. The compounds NdGa6 and CeGa6 have a primitive tetragonal structure with the following lattice parameters: NdGa6 a = 5.996 ± 0.001 A b = 7.620 ± 0.001 A CeGa6 a = 6.03 A b = 7.632 A A large solid solubility range exists between the RGa2-type compound and Nd-80at.%Ga or Ce-78at.%Ga. This phase has a hexagonal structure, the lattice parameters of which increase with the concentration of gallium.