Formation Of Pd2Si Research Articles

Transmission electron microscope study of the initial stage of formation of Pd2Si and Pt2Si

Transmission electron microscopy of the compounds formed from the reaction between amorphous Si and thin (0.5–20 nm) layers of Pd and Pt reveals the early formation of crystalline silicides. The presence of phase in an amorphous state prior to crystallization is not observed. These results appear to be in agreement with earlier results of surface electron spectroscopy studies on these systems.

The Influence of Predeposition of Nonolayer Thin Titanium Filns Upon the Crystallography of Subsequently Formed Pd2Si Layers on (100) Silicon

ABSTRACTThis paper reports upon a new technique for the formation of epitaxial Pd2Si on (100) silicon using thin predeposited titanium layers. Improvements in the quality of epitaxy in Pd2Si on {111} silicon by this technique will also be shown. A preliminary model for the formation of epitaxy will be given. Discrepancies between this model and results in the literature will be discussed and experiments suggested to resolve the uncertainties.

Effect of Ion-Irradiation on Silicide Formation in Metal-Silicon System with Interfacial Silicon Dioxide Layer

The thermal and ion-induced formation of Pd2Si in a Pd-Si system with an interfacial SiO2 layer has been investigated. It is found that the blocking of the thermal silicide formation by the SiO2 layer is partially removed by pre-irradiation with ions, inducing a quadratic, laterally non-uniform thermal growth of the silicide. The growth of the silicide layer under irradiation with light ions is found to be a linear function of the ion fluence. Light ion irradiaticn is shown to induce laterally non-uniform silicide formation, whereas uniform silicide is formed by heavy ions. The result is analyzed using a model in which the blocking of the reaction by SiO2 is partially destroyed by ion-irradiation. A criterion for uniform silicide growth from a contaminated metal-silicon system is presented.

Formation of palladium silicide by rapid thermal annealing

The formation of palladium silicide Pd2Si by rapid thermal annealing of Pd layers on silicon has been studied as a function of annealing time (1–60s) in the temperature range 350–500 °C. It is shown that the results found for conventional furnace annealing (long duration, low temperature) can be extrapolated for rapid thermal annealing (shorter time, higher temperature) when taking into account the exact time dependence of the short temperature cycle. The growth rate is essentially diffusion limited and the activation energy is close to 1.1±0.1 eV. Silicide resistivity of about 30–40 Ω cm was obtained for 200–400 nm thick Pd2Si layers formed at 400 °C for a few seconds.

The effects of implanted oxygen on Pd 2Si formation

A systematic study of the effects of implanted oxygen on the formation of Pd 2Si has been carried out using 4He + backscattering spectrometry and the 16O( d, α) 14 N nuclear reaction for the analysis. Palladium ∼ 2000 Å thick were e-baum evaporated on Si〈100〉 substrates and implanted with 2 × 10 16 O/cm 2 halfway through the film. Upon anneling in vacuum, Pd 2Si grows identically in both implanted and unimplanted samples. The implanted oxygen has no effect on the growth kinetics of Pd 2Si. We also find that after Pd 2Si formation is complete, the implanted oxygen is incorporated into the silicide in a deep-lying band near the Pd 2SiSi interface. Substantial additional oxygen is also found at the surface. The results are interpreted by assuming that oxygen is mobile in the Pd at the annealing temperature of 250°C, but is immobile once incorporated into the silicide. A simple model can then explain the observed redistribution of the implanted oxygen. The major parameters in this model are the chemical affinities of oxygen relative to the reacting species and the dominant diffusing species during Pd 2Si formation. The redistribution of the implanted oxygen is consistent with Si as the dominant diffusing species. This result is compared with previous marker experiments.

Transmission electron microscopy investigation of silicide formation on slightly oxidized silicon substrates

The formation of PtSi and Pd2Si on chemically cleaned and on slightly oxidized Si substrates had been investigated by TEM with cross-sectional specimens. The oxide has been found to influence the silicide-Si interface roughness, the silicide surface roughness,and the corrosion behavior of the silicide layer. The formation of PtSi is more sensitive to the presence of oxide than Pd2Si and may even be suppressed. Remnants of the oxide are identified within the silicide using Auger sputter profiling technique. They can be interpreted as diffusing markers and provide information about the diffusing atomic species. Results of such marker experiments for formation of Pd2Si and PtSi are disussed.

Epitaxial Silicides

The formation and structures of epitaxial CoSi2, NiSi2, Pd2 Si and PtSi films on silicon are reviewed. Polycrystalline films of reasonable epitaxial quality can be grown with sharp interfaces on Si(111) by conventional deposition and heating techniques. The interfaces on (100) substrates, however, are faceted. Perfect singlecrystal CoSi2 films can be grown on Si(111) substrates by ultrahigh vacuum techniques using conventional deposition and annealing at about 900°C and molecular beam epitaxy codeposition at about 600°C. The single-crystal films are rotated 180° with respect to the substrate. Novel defect arrays are observed at the interface. Resistivities in epitaxial films are lower than those reported in polycrystalline layers. High quality silicon films can be grown on the silicides to form semiconductor/metal/semiconductor heterostructures.

Silicide formation using a scanning cw laser beam

A scanning cw laser has been used to react e-beam-deposited Pd, Pt, and Nb thin films with single-crystal silicon substrates. A single laser scan is capable of reacting 1300 Å of Pd with Si to form either Pd2Si or PdSi, depending on the laser power. Multiple laser scans are necessary to completely react 1100 Å of Nb to form NbSi2. X-ray diffraction analysis shows that the Pd and Nb silicides formed are essentially single phase. The formation of Pd2Si and NbSi2 can be understood by a solid-phase diffusion mechanism. However, it is suggested that a nucleation-reaction-controlled process is occurring in the formation of the PdSi compound. The formation of a superconducting Pt2Si3 is also shown.

Calculation of solid-phase reaction rates induced by a scanning cw laser

An analytical model is presented for solid-phase reactions induced by a scanning cw laser. The results are applicable for both rate-limited reactions, such as the regrowth of implanted amorphous Si, and diffusion-limited reactions, such as the formation of metal silicides. The effect of the laser is interpreted in terms of a furnace anneal at an ’’effective temperature,’’ Teff, for an ’’effective time,’’ teff. Teff is shown to be equal to the maximum laser-induced surface temperature, while teff equals the laser dwell time multiplied by a ’’dwell-time reduction factor’’ which is a rational function of several material and annealing parameters and is typically on the order of (1)/(3) . A comparison of theory and experiment is made for the specific case of the formation of Pd2Si.

Silicide formation with Pd-V alloys and bilayers

Solid phase reactions in the temperature range between 250 and 600 °C between Si and V-Pd bilayers as well as alloy layers have been studied by MeV 4He+ backscattering and x-ray diffraction techniques. When a Pd layer is interposed between Si and V, the bilayer system starts to react at <300 °C with the formation of Pd2Si. Annealing at higher temperatures (∼600 °C) leads to a uniform layer of VSi2 formed on top of the Pd2Si. Reversing the bilayer sequence (Si/V/Pd) raises the reaction temperature of the system to ∼500 °C with V mixing into the Pd layer. Annealing at higher temperature leads to the formation and accumulation of Pd2Si at the interface and a mixed (nonuniform) structure of Pd2Si and VSi2 in the outer surface region. For a Pd-rich alloy (Pd80V20), a reaction started at about 300 °C and produced Pd2Si by depleting Pd from the alloy. This resulted in a mixed structure of Pd2Si and VSi2 in the outer region, similar to the final stage of the Si/V/Pd system. For a V-rich alloy (Pd90V10), the formation temperature of Pd2Si is raised to ∼500 °C and again leads to a mixed structure. The amount of accumulation of Pd2Si at the substrate-silicide interface increases with the Pd content in the alloy.

Auger spectroscopy analysis of palladium silicide films

The formation of Pd2Si in Pd films sputter deposited on Si substrates and heated up to 400 °C has been studied by measuring the depth profile using Auger electron spectroscopy (AES) and Ar+ ion sputtering. Significant chemical effects in the silicon LVV Auger peak shape have been observed, enabling the easy differentiation of the silicide from elemental silicon. The depth profile indicated that the silicide phase is formed at the Pd/Si interface even in the unannealed films. In forming the silicide, the silicon atoms diffuse through the film and on arrival at the surface oxidize to form a thin layer of SiO2. Some of the problems encountered in the determination of the depth scale from the AES data are pointed out.

Formation kinetics and structure of Pd 2Si films on Si

Backscattering and X-ray techniques have been used to study properties of palladium silicide (Pd 2Si) formed by evaporating thin Pd layers on Si followed by heat treatment. The rate of formation of Pd 2Si in the temperature range of 200–275°C has been measured by 2-MeV 4He + ion backscattering. The Pd 2Si layer is found to grow at a rate proportional to the square root of time for thicknesses ranging from approximately 200–4000 Å. The rate of growth is found to be independent of Si substrate orientation or doping type and the rate constant is found to fit a single activation energy of E a = 1·5±0·1 eV over the temperature range measured. X-ray diffraction indicates the structure to be Pd 2Si with the basal plane roughly parallel to the substrate surface for films formed on 〈111〉, 〈110〉, 〈100〉 and evaporated (amorphous) silicon substrates. The degree of preferred orientation is markedly stronger on [111] Si. Ion channeling measurements confirm that in this case the c-direction of the Pd 2Si is parallel with the [111] direction in the underlying Si.

The growth and transformation of Pd 2Si on (111), (110) and (100) Si

Thin Pd films on (111), (110), (100) and amorphous Si substrates form [001] fiber textured Pd 2Si in the temperature range 100°–700°C. The degree of texture is a function of substrate orientation, increasing in the order amorphous Si, (100) Si, (110) Si and (111) Si. Only on the (111) Si substrate is the Pd 2Si film epitaxially oriented. Temperature-dependent growth on this orientation can be characterized by [001] textured growth, epitaxial azimuth orientation at the Si interface and progressive layer by layer formation of the mosaic crystal to the thin film surface. During Pd deposition, rapid non-diffusion-controlled growth of epitaxial Pd 2Si on (111) Si occurs at substrate temperatures of 100° and 200°C. An unidentified palladium silicide of low crystallographic symmetry forms during Pd deposition onto a 50°C substrate. The diffusion-controlled growth of Pd 2Si on (111) Si follows a t 0.5 dependence. The velocity constant is k = 7 × 10 −2 exp − 29200±800 RT cm 2/ sec Palladium deposited on 100°C (111) Ge substrates reacts during deposition to form epitaxially oriented Pd 2Ge. However, growth of this phase at higher temperatures results in a randomly oriented film. The transformation of Pd 2Ge to PdGe is kinetically controlled. After a 15 min anneal at 560°±10°C in N 2 only PdGe is detectable on (111) Ge. The high temperature stability of thin film Pd 2Si is controlled by time- temperature kinetics. For a given annealing cycle, the nucleation and growth rates of the PdSi phase are inversely related to the crystalline perfection of Pd 2Si. Decreasing transformation rates follow the order (100), (110), (111) Si. formation of thin film Pd 2Si occurs by the formation of PdSi and subsequent growth of Si within the PdSi phase. After a 30 min N 2 anneal, initial transformation occurs at 735°C on (100) Si, 760°C on (110) Si and 840°C on (111) Si. Extended high temperature annealing produces a two-phase structure of highly twinned and misoriented Si and small PdSi grains that penetrate as much as 3 μm into the Si.