B. Y. Tsaur

Ion‐beam‐induced silicide formation

Rutherford‐backscattering spectrometry and x‐ray‐diffraction analysis have been used to investigate intermixing between thin metal films (Pt, Ni, and Hf) and silicon substrates as a result of inert‐gas ion bombardment. Silicide phases (Pt2Si, Ni2Si, and HfSi) were observed near the interface as long as the ion range exceeds the film thickness. For a fixed dose, the silicide thickness increases with the atomic mass of both ion and metal and is greater for Pt2Si than HfSi. The growth of Pt2Si showed a square‐root dependence on ion dose for Ar, Kr, and Xe ions. The phenomenon of ion‐induced silicide formation is similar to formation resulting from thermal anneal until the whole metal film is consumed in the reaction, at which point a progressive intermixing to redistribute the metal into deeper regions of the sample occurred along with the disappearance of the structure diffraction patterns.

Continuous series of metastable Ag‐Cu solid solutions formed by ion‐beam mixing

Metastable Ag‐Cu solid solutions have been formed by ion‐beam mixing of thin deposited Ag and Cu layers of various compositions. X‐ray diffraction measurements indicated that the lattice parameters of the ion‐induced Ag‐Cu alloys vary almost linearly with composition, with a slight positive deviation from Vegard’s law for ideal solid solutions. The microstructures of the alloyed layers were studied by transmission electron microscopy and their stability was examined by thermal annealing up to 250u2009°C. The present results are compared with those obtained previously by rapid quenching techniques.

Microalloying by ion-beam mixing

Abstract We have investigated ion-induced atomic mixing process as an alternative approach to conventional rapid quenching techniques for producing thin film metastable alloys. Multi-layered samples consisting of thin alternate layers of two elements were bombarded with energetic Xe ions. Formation of metastable phases such as supersaturated solid solutions and amorphous alloys were obtained as a result of atomic mixing. The systems under investigation are binary couples of Au and one of the fourth-period transition metals, Ni, Co, Fe or V. For samples irradiated at R.T., metastable crystalline phases were usually formed. In the Auue5f8Ni and Auue5f8Co systems, single-phase f.c.c. solid solutions over an entire range of composition have been produced. In the Auue5f8Fe and Auue5f8V systems, the Au-rich alloys showed a f.c.c. structure while the Fe (or V)-rich alloys showed a b.c.c. structure. The simultaneous presence of a f.c.c. phase and a b.c.c. phase was found in alloys with compositions Au 38 Fe 62 and Au 40 V 60 . For samples irradiated at LN 2 temperature, the structures of the alloys were found to be more random in nature. Amorphous phases of compositions Au 25 Co 75 and Au 40 V 60 were obtained. Comparisons of results observed on various systems indicate that the formation and structure of metastable phases are strongly influenced by the equilibrium nature of the system.

Sequence of phase formation in planar metal‐Si reaction couples

A correlation is found between the sequence of phase formation in thin‐film metal‐Si interactions and the bulk equilibrium phase diagram. After formation of the first silicide phase, which generally follows the rule proposed by Walser and Bene, the next phase formed at the interface between the first phase and the remaining element (Si or metal) is the nearest congruently melting compound richer in the unreacted element. If the compounds between the first phase and the remaining element are all noncongruently melting compounds (such as peritectic or peritectoid phases), the next phase formed is that with the smallest temperature difference between the liquidus curve and the peritectic (or peritectoid) point.

Supersaturated metastable Ag‐Ni solid solutions formed by ion beam mixing

Extension of terminal solid solubilities has been achieved by ion beam mixing in the almost completely immiscible Ag‐Ni system. Multi‐layered samples of thin deposited Ag‐Ni films of various compositions were bombarded with energetic Xe ions at temperatures from −190 to 250u2009°C. Supersaturated Ag‐ and Ni‐rich fcc solid solutions were obtained, as indicated by x‐ray and electron diffraction. Analyses of lattice parameters showed that the solubility range for the metastable solid solutions produced by low‐temperature bombardment was wider than for those formed at high temperature. Maximum solubilities were determined to be 4.5 at.u2009% Ni in Ag and 16 at.u2009% Ag in Ni if one assumes the ion‐induced fcc phases to be ideal solid solutions. The effects of implantation temperature on the formation of metastable phases are discussed.

Phase transformations in laser‐irradiated Au‐Si thin films

Laser‐pulse‐induced melting, interdiffusion, and rapid resolidification are applied to deposited Au‐Si thin films of various compositions. It is found that, if 30‐ns pulses are used, amorphous Au‐Si films can be produced over a compositional range 9–91 at.% Au. The stability of the amorphous phases varies with their composition. Thermal decomposition involves the formation of a single‐metastable silicide with a hexagonal structrue. Application of 300‐μs laser pulses directly leads to formation of the same compound.

Phase separation in alloy‐Si interaction

Phase separation has been found to be a general phenomenon among many alloy‐Si interactions at temperatures as high as 800u2009°C. We have studied these interactions with alloys consisting of a near‐noble metal of Ni, Pd, and Pt, and a refractory metal of Cr, V, and W. The interaction produces a silicide of the near‐noble metals next to the Si and an outer layer of silicide of the refractory metals. No evidence for ternary formation has been found.

Phase formation in Cr‐Si thin‐film interactions

Silicide formation has been studied in Cr‐Si thin‐film samples by MeV 4He+ backscattering and glancing‐incidence x‐ray diffraction. Samples of SiO2/Cr/Si configuration were prepared by sequential e‐gun deposition of Cr and Si onto SiO2 substrates with the relative film thicknesses adjusted to Cr:Si ratios of 3.0 (Cr3Si), 1.67 (Cr5Si3), and 1.0 (CrSi). In the early stage of phase formation when both unreacted Cr and Si are present, the CrSi2 phase is formed. The phase grows until the Si is completely consumed, and then a metal‐rich phase, Cr5Si3, is formed at the Cr‐CrSi2 interface. Upon further heating of samples with a Cr:Si ratio of 3.0, Cr5Si3 reacts with Cr to form a more Cr‐rich phase, Cr3Si. The CrSi phase was observed only in samples with a Cr:Si ratio of 1. All the compounds present in the phase diagram were observed. The end phases are determined by the availability of Cr and Si in the reactions and can be predicted from the phase diagram.

Ion-beam induced epitaxy of silicon

Abstract Epitaxial regrowth of an amorphous Si layer on a 〈100〉 Si crystal held at 200–400°C is achieved under bombardment with Si, Kr, or Xe ions. Channeling measurements with MeV He ions show the regrowth proceeds from the amorphous-crystalline interface, and has an initially linear dose dependence. The annealing beam, however, introduces additional damage centered at or beyond the ion range. Amorphous layers obtained by low-temperature self-ion bombardment regrow much more readily than amorphous deposited layers.

Epitaxial alignment of polycrystalline Si films on (100) Si

We demonstrate that fine‐grained polycrystalline Si films obtained by chemical vapor deposition can be aligned expitaxially with respect to the underlying (100) Si substrate upon furnace annealing at temperatures of 1000–1150u2009°C. The alignment proceeds basically by the formation of epitaxial columns which subsequently grow laterally to consume the remaining polycrystalline Si. The rates of alignment are measured to be 20–200 A/min in the temperature interval of annealing with an activation energy of 4.7 eV. The epitaxial layers so obtained are of reasonably good crystal quality and contains only a small amount of planar crystallographic defects.