In many cases the stability of amorphous films is influenced by interaction with metallic crystalline overlayers. Such interactions between Au, Ni, Nb and Ta overlayers and a-(Ni-Nb) films are reported. During interdiffusion Au overlayers reacted with a-(Ni-Nb) to form two different adjacent crystalline layers. In order to study the influence of relaxation of the amorphous film on overlayer reaction several a-(Ni-Nb) samples were pre-annealed prior to Au deposition. High depth resolution Rutherford Backscattering Spectrometry (RBS) demonstrates that preannealing lowers the diffusion poefficient of Au in a-(Ni-Nb) at 4500C from 7.5×10−22 m2/s to 8.7×10−23 m22/s. During interdiffusion Ta was discovered to be substantially more inert than Au. For example, negligible interdiffusion between Ta and a-(Ni-Nb) at 505°C after 25 hours implies a diffusivity of less than 5×10−24 m2/s. These observations allow assessment of some of the requirements for increasing the stability of crystalline-amorphous metal film layered structures.

In studying the growth of epitaxial layers in III-V compounds, it is advantageous to obtain information on the early stage of the growth that takes place at the substrate-epitaxial layer interface. In this paper, we describe a method of measuring the recombination velocity at this interface, as well as the minority carrier diffusion length in the bulk of the epitaxial layer. A bi-directional diffusion of excess carriers was modeled, with layer thickness, diffusion length and recombination velocity as variables. Layer thickness was determined using spreading resistance, the other two variables can be separated by measuring layers of several thicknesses. Some carriers diffuse from the point of generation toward the surface and are collected at a Schottky barrier depletion layer, The remaining carriers diffuse from the point of generation toward the epi-substrate interface where they recombine.

Most of the papers in this symposium have dealt with superlattices formed from semiconductors with the diamond or zinc blende structure or derivative structures such as fluorite in which one sublattice has the diamond structure. Such superlattices are often called compositionally modulated alloys (CMA) because the two components have the same or related structures and because the two components have some mutual solubility. In these cases, depending on the differences in the lattice parameters, the resulting CMA will be almost a perfect single crystal, and the sharpness of the interfaces between the two alternating components will depend on the amount of interdiffusion during growth.

Following the earlier multilayer work of Ovshinsky and colleagues, we have fabricated thin-film samples consisting of alternating periodic layers of a transition metal (Nb, Mo, W) and a semiconducting element (Si, Ge, C) by sequential sputtering from two targets onto room-temperature substrates. The regular repeat spacing has been varied from 10 Å to more than 100 Å, with as many as several hundred layer pairs. Crystalline epitaxy was not required or even desired; many samples were largely amorphous as determined from x-ray scattering. Electrical transport measurements of superconducting properties have been carried out parallel to the layers. Samples exhibited highly anisotropic superconducting critical magnetic fields, with some values in excess of 200kG parallel to the layers. Evidence suggesting an asymmetric interface profile will be presented.

By means of metal MBE technique with in-situ RHEED characterization, high-quality single crystal rare earth metal films of yttrium and gadolinium were grown as a necessary requirement for studying Gd/Y superlattices. The key step of this successful growth is the employment of the single-crystal Nb film as a buffer layer to eliminate the interaction of rare earth metals with most substrates. Structural analyses by X-ray diffraction and ion channeling show that these crystals exhibit not only complete texture of [00.1], but also narrow rocking curves both perpendicular (00.2) and parallel (10.0) to the film.

Films of Nb3Sn vapor deposited at low rates and high temperatures on (1102) sapphire form an epitaxial <100> single crystal matrix with a domain structure of misoriented regions bounded by low-angle dislocation boundaries. Nucleation of other orientations at the interface result in a highly oriented but polycrystalline film through approximately the first thousand Angstroms of film thickness. After this point random orientations become overgrown by epitaxial <100> regions. At slightly lower temperatures many small <100> grains with a second epitaxial relationship also nucleate at the interface. These rotated grains persist through greater thicknesses than random orientations. The misorientation defect structure of the single crystal matrix is analyzed by transmission electron microscopy.

We report the observation of a higher degree of preferred crystalline orientation in Nb/rare earth superlattices for modulation wavelengths in the range of 200 Å to 500 Å than that exhibited by single component films. All films and multilayers are sputter deposited onto room temperature sapphire substrates. Electronic transport measurements also show that the residual resistance ratio is higher and the room temperature resistivity is lower than for multilayers of either greater or lower periodicities. Transmission electron micrographs (TEM) showing excellent layering, grain size comparable to the layer thickness, and evidence of some degree of epitaxy are presented.

The enhanced elastic modulus effect was found in composition modulated Cu/NiFe foils. Young's modulus was measured via tensile testing on thin foils containing short-wavelength composition modulations of 1.4–10. nm. The foils, of 53% Cu -40% Ni -7% Fe composition, were produced by vapor deposition using a three-source evaporator. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase (up to 300%) in modulus for two distinct ranges of compositon wavelength: 2.1–2.7 nm and 3.6–4.1 nm. Results of x-ray diffraction and Mossbauer spectroscopy studies suggest the concept of interfacial coherency, accommodating the lattice misfit between the composition layers, is the underlying structural feature responsible for the enhanced modulus effect.

Composition modulated (with wavelengths between 1.6 to 4.98 nm) Cu/NiFe ternary alloy thin films containing 53 at % Cu, 40 at % Ni, and 7 at % Fe were prdduced by the vapor-phase growth technique. The inter-diffusivities in these films were measured at temperatures 320°C, 345°C, and 400°C from the growth or decay rate of satelite peak intensities. as a function of dispersion relation B2 exhibited anomalous behavior at certain wavelengths at which an enhanced elastic modulus effect is also observed. This anomalous behavior was directly attributed to the long range interaction.

The properties of strained superlattices can be studied in a tunable fashion by dissolving hydrogen interstitially in strain free Nb/Ta metal superlattices. We report on a first investigation of a Nb/Ta 20 Å superlattice loaded with hydrogen in-situ in a high temperature x-ray furnace. After hydrogen uptake the ± 1 satellite reflections show pronounced asymmetries, indicating a hydrogen density distribution which is modulated by the superlattice periodicity.

We have prepared sputtered metallic films comprised of alternating layers of pure Ni and Zr to a total thickness of several microns. Due to the negative beat of mixing of crystalline Ni and Zr and a significant intermixing rate we have been able to form an amorphous Ni-Zr phase by a solid state reaction. In this work we report the conditions under which a substantial fraction of amorphous material may be formed. The extent of the reaction itself as a function of time has also been monitored.

Formation of an amorphous zirconium-nickel phase by solid state reaction of a layered crystalline structure has been studied by in-situ resistivity, x-ray diffraction, and Auger depth profiling. The reaction was studied as a function of layer thickness and reaction temperature.

Samples with a layer thickness of less than 4 atomic planes had x-ray diffraction spectra with one broad maximum characteristic of amorphous material. As the layer thickness increased, the maximum broadened and separated into two resolved peaks corresponding to crystalline nickel and zirconium. These structures were transformed to an amorphous nickel-zirconium alloy by an anneal at temperatures below the crystallization temperature of the amorphous phase. The reaction occured by a layer growth process, where the thickness of the layer evolved linearly with the square root of time.

Ion mixing of multilayered Ru-Zr and Ru-Ti at different compositions and substrate temperatures produced various metastable phases. The applicability of previously proposed rules regarding amorphous phase formation are examined. Effects of point defect in amorphous phase formation by ion mixing are discussed.

Nickel and cobalt silicides have been formed by raster-scanned electron beam and flash-lamp irradiation of thin metal films on single crystal (100) and (111) silicon wafers. RBS and channelling measurements indicate that the NiSi2 is epitaxial and of good crystalline quality (Xmin 4% on (111)); epitaxial CoSi2 was more difficult to form and of somewhat poorer quality. The elastic recoil technique has been used to determine bulk and interfacial light element contamination. These measurements have been correlated with resistivity and SEM studies of the surface textures.

The redistribution of arsenic during CrSi2 formation and its influence on the growth rate of the silicide have been investigated with Rutherford backscattering and ion channeling spectroscopy and electron microscopy. Arsenic was introduced by implantation in the metal films or in the silicon substrates. When arsenic was initially in chromium, it was incorporated in CrSi2 during silicide formation and significantly reduced the reaction rate; when arsenic was initially in silicon, it accumulated at the silicon/silicide interface with a less pronounced retarding effect than that if arsenic was present in chromium. The redistribution of dopant atoms is attributed to the fact that silicon is the dominant moving species in CrSi2 formation. The influence of dopant atoms is related to their chemical and physical state.

The formation of silicides via a solid state reaction of silicon and transition metal thin film is characterized by the sequential appearance of the various compounds rather than the simultaneous formation of all possible compounds [1]. Thin films of refractory metals will form disilicides on a single crystal silicon substrate (unlimited supply of silicon) and since they are stable with silicon, no other silicides will form. This situation is illustrated in Fig. la) by the formation of VSi2 in the case of vanadium on silicon. On the other hand, which silicide will form in the case where there is an excess amount of refractory metal is unknown. The objective of this work was to study this case utilizing the vanadium silicon binary system [2].

We report on contacts to p-type GaAs formed by a GaAs/Pt/TiN/Ag system. Ohmic behavior in this system is believed to be accomplished by the solidstate reaction of Pt with GaAs. This reaction is confined by the TiN film which is thermally stable. In addition, the TiN film acts as an excellent diffusion barrier in preventing the intermixing of the top Ag layer with GaAs or Pt. Contacts formed with such controlled reaction have important implications for the stability of shallow p-n junction devices.

X-ray diffraction was used in situ to study the phase transitions which occurred in 1500 Å Au/GaAs(100) upon heating and cooling. The reaction between Au and GaAs took the form Au + Ga → α Au-Ga. Upon heating, α Au-Ga completely dissolved in liquid Au-Ga. Upon subsequent cooling, β Au-Ga (or Au7Ga2) formed. In 1 atm of nitrogen, phase transitions were observed reversibly at 525 ± 25°C (due to the complete dissolution of α Au-Ga upon heating) and 415 ± 5°C (due to the peritectic transformation of β Au-Ga to α Au-Ga and liquid Au-Ga upon heating). In a vacuum of 425 μ (0.031 Kg/2m) similar phase transitions were observed at 425 ± 25°C and 387 ± 13°C, respectively.

Results are presented for the kinetics of growth of Pd2Si interfacial layers obtained by an X-ray diffraction technique. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222°C. The parabolic rate law observed is in qualitative agreement with those reported by investigators using other techniques (RBS, AES, Electron Microprobe). There appear to be two kinetics regimes distinquished by diffusion paths with different activation energies (1.35±0.10 eV vs. 1.05± 0.10 eV). The presence of impurities and the detailed Pd 2Si microstructure will influence how the reacting species are transported through the lattice.

Titanium nitride is an ideal barrier to silicon migration into aluminium metallisations in MOS devices. Various means by which a TiN,TiSi2 contact structure can be achieved to give low resistivity interconnects and stable contacts are outlined. It is shown that TiN/ TiSi2 contact structures self aligned to contact holes cut down to the TiSi2 can be simply achieved. Results showing the stability of the nitride film against silicon diffusion are presented.