Cosputtered W70Zr30 and W40Zr60 films are investigated as diffusion barriers between Al and Si. W-Zr alloys of both compositions were determined by x-ray diffraction to crystallize at 900°C on Al2O3 substrates. On <111>Si the W-Zr alloy reacts with the substrate above 700°C, forming a uniform, polycrystal line layer of W and Zr suicides. Despite the high crystallization temperatures, an Al overlayer interacts with W-Zr and the Si substrate at ∼500°C. MeV He backscattering spectrometry, SEM and EDAX indicate that this reaction is laterally nonuniform with the formation of deep pits penetrating into the Si substrate. We believe this to be a consequence of fractures in the W-Zr layer induced by reaction with Al. Electrical measurements on shallow junction diodes with <Si>/W-Zr/Al contacts show that the device junctions were thermally stable after a 30 min annealing at 450°C but were all shorted after heat treatments at 500°C or above.

Thin film interactions between a-(Ni-Nb) and polycrystalline Au over-layers have been studied with high depth resolution (≤1.7nm) Rutherford backscattering (RBS) and TEM to obtain information on the early stages of reaction at the interface. The RBS spectra from Au indicated that the interdiffused samples consisted of two layers: an Au-Nb binary layer on the surface and a ternary Au-Ni-Nb compound layer beneath the binary layer. The growth kinetics of the ternary compound layer differed in samples which had been relaxed prior to Au deposition from the kinetics for unrelaxed samples. Furthermore, cross section TEM micrographs showed that relaxed and unrelaxed samples exhibit different microstructures after the early stages, of annealing. We interpret this result to indicate that the reaction stages in relaxed samples are not as advanced as those in the unrelaxed samples.

Interdiffusion, reactions and microstructure in Ti-Cu-Ti trilayer thin films deposited on silicon wafers have been investigated by Rutherford backscattering, and cross-sectional TEM techniques in the temperature range of 350 to 500 °C. The formation of intcrmetallic compounds was found to be symmetric at both interfaces in Ti-Cu-Ti film package. TiCu compound formed first at low temperature and was followed by TiCu3 at higher temperatures. The stress in Ti-Cu film has also been measured in-situ as functions of both temperature and annealing time by thin fused quartz bending-cantilever beam technique. The stress in metallic Ti-Cu film couple on fused quartz was tensile. The stress increased as both annealing time and temperature increased and followed a parabolic relationship with time due to the growth of the intermetallic compound TiCu3 It was possible to calculate stress in the TiCu3 layer from the changes of stress in the bilayer thin film. The stress in TiCu3 was computed to be at about 3 times larger than the stress in the unreacted Ti-Cu thin film couple.

The reaction of Ni- refractory metal alloys with silicon has been studied by backscattering spectrometry and transmission electron microscopy. The analysis of the as-deposited sample revealed solid solutions for Ni-Cr and amorphous phases for Ni-Ta and Ni-Ti. In situ annealing resulted in crystallization of Ni43 Ta57 at 750 °C, a value above the reaction temperature of the alloy with silicon. The amorphous alloy of Ni48Ti52 was transformed into the equilibrium compound of NiTi at 450 °C, much below the reaction temperature. Phase separation has been observed in the Ni-Cr and Ni-Ta systems with a Ni- silicide layer next to the Si substrate and a refractory disilicide layer on the other side. In contrast, Si reacts with the NiTi compound to form a uniform mixed layer with a composition of NiTiSi2. The different behavior is explained based on considerations of both thermodynamic and kinetic terms.

The Al-Cu system has been used to test the application of grazing incidence EXAFS and x-ray reflectivity measurements to interface systems. Both techniques have been found to be sensitive to compound formation and interdiffusion, and with further development of analysis procedures should be very useful complements to more traditional techniques.

Interfacial reactions in bimetallic thin films have been studied by in-situ glancing angle X-ray diffraction which enables us to monitor all stages of the interface reaction in the temperature range 35 °-950° C Results are presented on new phase formation in evaporated Ag-Al and Cu-Al thin film couples, sputtered bimetallic Nb-Sn and Nb-Pb films and magnetic alloy films. New phases as well as phase transitions which are not known to exist in the bulk phase diagrams, were observed. These results provided evidence that phases other than those predicted by the first nucleation rule, grow during the initial metal-metal thin film interface reaction.

The displacements of Mo, Zr and Pd markers have been monitored by backscattering of MeV He+ to study the growth of the amorphous HfNi phase by solid-state reaction. We find that the Ni is the dominant moving species in this reaction.

The microstructure and properties of thin films depends strongly upon the alloy composition. A study was made of the metallurgical aspects of homogeneous Al alloy films, particularly the binary Al-Ti and the ternary Al-Ti-Si systems. Electrical resistivity, grain size morphology, second phase formation and electromigration have been studied as a function of the alloy composition and its heat treatment.

Significant polymer weight loss has been observed due to environmental ashing by atomic oxygen at low earth orbital (LEO) altitudes. Static charging during deployment and charging caused by the space plasma in LEO polar orbits may cause electromagnetic interference (EMI) problems on insulating polymer materials that are integral to such applications as high voltage solar arrays. Simultaneous ion beam sputter deposited coatings of indium-tin-oxide (ITO) with polytetrafluoroethylene (PTFE), carbon, air, or methane were investigated as potential solutions to these problems. The purpose of this research was to improve the flexibility of ITO coatings with these additives and to study the effect the addition of these materials had not only on the flexibility of ITO sputter deposited thin films but also on the conductivity and optical properties.

The moving species in near-noble metal suicide formation was investigated using embedded markers and Rutherford backscattering. With thermal annealing of Ni-silicides, Ni is the dominant diffusing species while in ion-induced reactions both Ni and Si diffuse across the suicide. This difference in behavior is not a result of the formation of amorphous Si during ion irradiation nor is it caused by release of Si. We propose that the diffusion of Si is associated with the formation of defects in the suicide layer generated within the collision cascade.

Ion beam mixing effects on metals and highly doped semiconductors on GaAs for formation of ohmic contacts have been studied. In this study, we have principally selected Pt as metal and Ge as semiconductors electrodes for GaAs. In Pt/GaAs system, we observed alloying phenomena induced by Si+, Ar+, Ge+ ion mixing effects. The amount of GaAs reacted with Pt was found to be proportional to the mass of the incident ions for constant dose. Concernig with the formation of ohmic contacts, only in the case of Si implantation through Pt films, the conversion from Schottky- to ohmic-contact was observed due to ion beam mixing effects. In Ge/GaAs system, we observad the solid state epitaxy for implanted Ge layer by the first annealing at 450°C in the two step annealing, but no activation of the implanted species. For activating implanted species, the second annealing at 800°C was effective. Concerning with the formation of ohmic contacts, we observed that the ohmic I-V characteristics for Ge/GaAs system could be obtainable when the following conditions were satisfied at the same time: 1) high dose implantation of As+ into Ge layer, 2) low dose implantation of Si into Ge/GaAs boundary and 3) relatively short period annealing in the second annealing step. From such study, it is concluded that ion beam mixing in conjunction with rapid annealing would be most promising for forming stable and reproducible ohmic contacts.

The extended Structural Difference Rule for amorphous phase formation states that an amorphous phase can be obtained by ion mixing with an alloy with a composition lying in a two-phase region in the equilibrium phase diagram. This criterion has to respond to the challenge that no amorphous alloy has been formed in some early studied systems exhibiting a two-phase region character, e.g. Ag-Cu(typical eutec-tic),Ag-Ni(almost entirely immiscible),etc‥

We performed ion mixing experiments for several systems at liquid nitrogen temperature using Xe ions with low current density. Amorphization was indeed observed in both Ag-Cu and Ag-Ni samples, as two halos were seen by TEM SAD immediately after adequate doses ion mixing. These not only support our two-pnase region rule, but also show the possibility of amorphization in a system(Ag-Ni) that has large positive heat of formation.

We studied ion beam mixing of thin Mo films on monocrystalline Si by As “implantation at room temperature. The results differ significantly from those obtained for implantation at elevated temperature (T > 200°C). where ion beam mixing results in hexagonal MoSi2 formation. Room temperature implantation results in the formation of an amorphous mixed layer. The composition of this layer varies with depth from Mo-rich to Si-rich. The mixed layer thickness increases linearly with implanted dose and energy. An increase of the implantation temperature with 100°C gives rise to a factor of 2 larger mixed layer thickness and to the formation of amorphous MoSi2 near the interface with Si. These phenomena indicate that at elevated temperature ion beam mixing is controlled by radiation-enhanced diffusion whereas, at room temperature ballistic mixing is the dominant mechanism.

In ion beam mixing, the subject on the marker evolution of Si/Pt/Si target during 300 keV Xe ion irradiation has been an interesting topic of recent years. A cottputer simulation for this system by using the Monte Carlo code TCIS-4 is reported here. Dynamic target model was employed. Some radiation-enhanced diffusion and relaxation of the displacement cascades were also considered. Results of this simulation study reveal the evolution of Pt marker profile with fluences during bombardment. The shifts of Pt marker and the dispersions evaluated from the profiles agree fairly well with experimental date, demonstrating a reslistic model of the target being irradiated is important.

Alternating layers of Ni and Nb with a total thickness of 1060Å, and Ni and Cr with a total thickness of 840Å were deposited by electron beam evaporation on silicon. The individual layer thicknesses were adjusted in such a way as to obtain 50/50 at% compositions of Ni-Nb and Ni-Cr; the thicknesses were around 100Å for Ni and 170Å for Nb, and 100Å of Ni and 110Å of Cr. The films were bombarded with 350 keV Cr+ ions at a dose of 2 × 10 ions cm. RBS and TEM techniques were used to study the mixing and microstructure. Almost complete mixing and amorphization have been observed for the Ni-Nb system. Ni-Cr film has revealed very little mixing compared to Ni-Nb film and the microstructure remained polycrystalline. Sputter (rf) deposited Ni-Cr film also remained polycrystalline both before and after ion irradiation. The Ni-Cr System appears to be an exception to the structural difference rule for amorphous phase formation by ion irradiation.

The effect of the heat of mixing, ΔHm, on the ion beam mixing of marker systems was studied. The matrices for tne experiment were Mo and Ru, and marker atoms were Ti, Cr, Mn, Ni, Hf, Ta, Pt, and Au. These markers and matrices have heat of mixing ranging from +65 to -227 kJ/mol. Irradiations were done with 300 keV Kr at 77 and 300 K, with room temperature backscattering spectrometry analysis. There was no correlation between the mixing results and heat of mixing, which is consistent with the idea of ion beam mixing of dilute marker system.

Recent progresses in the epitaxial growth of refractory metal suicides, FeSi2 and manganese suicides on silicon are reviewed.

The formation and structures of epitaxial suicides are described. Factors affecting the suicide epitaxy are examined. The lattice match criteria for the growth of epitaxial suicides are assessed. The effects of anharmonicity in the interatomic force of overlayer on the heteroepitaxial growth and pseudomorphism are discussed. The properties and possible applications of epitaxial suicides are summarized. Prospects for the study of epitaxial suicides are addressed.

The initial nucleation processes for reactions of Pd and Ti on Si are studied by Raman scattering, and Auger electron spectroscopy. The epitaxial nature of the structures is verified by high resolution TEM. A model of the interface reaction is presented which describes the initial interdiffusion and subsequent nucleation. The aspects of nucleation in a thin film reaction are compared to nucleation processes in vacuum deposition. For Pd/Si a critical depostion thickness is observed which is related to a critical nuclei size. For Ti/Si higher annealing temperatures are required to bring about conditions for nucleation of the suicide.

Rapid electron beam and lamp heating have been used to form thin epitaxial films of rare-earth suicides by reacting overlayers of the rare earths with (111) Si substrates. Of the metals Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, all but Gd are found to form epitaxial suicide layers by rapid solid-phase reaction, while suicides of Gd, Dy, Tm, Yb and Lu have been formed epitaxially by liquid phase reaction. For all but Er this is the first demonstration of epitaxial growth on Si. Details obtained from ion beam channeling analysis and transmission electron microscopy confirm the expected epitaxial structure and also show that the Si vacancies in the suicide form an ordered superlattice, rather than a random array as had been assumed before.

Single-crystal silicon layers and doping multilayers have been grown by liquid phase qpitaxy on silicon substrates. The substrates were either partially masked by SiO2, with via holes of various shapes and sizes, or patterned with SiO2 stripes, or profiled with grooves and ridges. The via holes and grooves were just refilled, or they acted as seeding areas for lateral overgrowth of the oxidized wafer up to 100μm. The silicon layers, interfaces and heterointerfaces were free of defects. With appropriate growth conditions the surfaces and interfaces of the epitaxial Si were outstandingly planar.