Au Diffusion Research Articles

Dissolution and interfacial reactions of thin-film Ti/Ni/Ag metallizations in solder joints

The dissolution and interfacial reactions involving thin-film Ti/Ni/Ag metallizations on two semiconductor devices, diode and metal-oxide-semiconductor field-effect transistor (MOSFET), a Sn–3.0Ag–0.7Cu solder, and a Au-layer on the substrates are studied. To simulate the dissolution kinetics of the Ag-layer in liquid solder during the reflow process, the computational thermodynamics (Thermo-Calc) and kinetics (DICTRA: DIffusion Controlled TRAnsformations) tools are employed in conjunction with the assessed thermochemical and mobility data. The simulated results are found to be consistent with the observed as-reflowed microstructures and the measured Ag contents in the solder. In the as-reflowed joints two different intermetallic compounds (IMC) are found near the diode/solder interface. Both are in the form of particles of different morphologies, not a continuous layer, and are referred to as IMC-I and IMC-II. The former corresponds to Ni 3Sn 4 with Cu atoms residing in the Ni sublattice. It is uncertain whether IMC-II is Cu 6Sn 5 phase with Ni atoms residing in the Cu sublattice or a Cu–Ni–Sn ternary phase. Near the as-reflowed MOSFET/solder interface, both particles and a skeleton-like layer of Ni 3Sn 4 are observed. The primary microstructural dynamics during solid state aging are the coarsening of IMC particles and the reactions involving the unconsumed (after reflow) Ni- and the Ti-layer with Sn and Au. While the reaction with the Ni-layer yields only Ni 3Sn 4 intermetallic, the reaction involving the Ti-layer suggests the formation of Ti–Sn and Au–Sn–Ti intermetallics. The latter is due to the diffusion of Au from the substrate side to the die side. It is postulated that the kinetics of Au–Sn–Ti layer is primarily governed by the diffusion of Au through the Ni 3Sn 4 layer by a grain boundary mechanism.

Moisture influence and geometry effect of Au and Pt electrodes on CO sensing response of SnO 2 microsensors based on sol–gel thin film

Undoped tin oxide-based gas microsensors have been prepared by the sol–gel deposition technique. The influence of the gaseous atmosphere (humidity and carbon monoxide) on the electrical conductance of the samples has been investigated. Then, the variation of the geometry and the nature of the electric contacts has been considered as interesting factor that can modulate the selectivity. SEM observations of the surface have shown a good quality of the electrodes. A pre-deposited Ti thin layer improves the adhesion of the contacts to the SnO 2 film. A diversification of the sensors, when exposed to CO, was observed depending on two different electrodes materials (Au and Pt) arranged in two different geometric configurations of the interdigitated fingers. Preliminary results have shown that CO response is enhanced by the use of interdigitated electrodes with a short separation gap (200 μm) as compared to those with wider one (400 μm) for both Pt and Au electrodes, while the use of gold contacts seems to reduce the working temperature of our sensors, probably due to some effects related to the diffusion of Au into the Ti and/or the active layer, but other drawbacks could also arise.

Diffusion of Au along <100> Symmetrical Tilt Boundaries in Copper: Grain-Boundary Roughening?

Diffusion of Au along <100> Symmetrical Tilt Boundaries in Copper: Grain-Boundary Roughening?

Au−Ni−Sn intermetallic phase relationships in eutectic Pb−Sn solder formed on Ni/Au metallization

Recent work has shown that a Au−Ni−Sn ternary compound with a nominal composition of Au0.5Ni0.5Sn4 redeposits and grows at the interface between eutectic Pb−Sn solder and Ni/Au metallization during aging at 150°C. The present work verifies the existence of the Au0.5Ni0.5Sn4 phase by examining the Sn-rich corner of the Au−Ni−Sn ternary phase diagram. The reconfiguration mechanism of the AuSn4 from the bulk solder is also discussed, with detailed observations of the Au0.5Ni0.5Sn4 microstructure. The results show that the Ni solubility limit in the AuSn4 phase is approximately 12 at.% at 150°C and thus, the Au0.5Ni0.5Sn4 phase is a ternary AuSn4-based compound with high Ni solubility. Due to the slight solubility and the fast diffusion of Au in the eutectic Pb−Sn at 150°C, the AuSn4 intermetallics in the bulk solder can reconfigure to form a AuxNi1−xSn4 compound at the interface where Ni is available. The AuxNi1−xSn4 compound layer consists of nanocrystals arranged in a larger grainlike morphology. It appears that the inherent lattice strain of the AuxNi1−xSn4 compound and the volume change due to its formation results in a nanocrystalline microstructure.

Investigation of Au–CdZnTe contacts using photovoltaic measurement

It is well known that a pure Au–CdZnTe contact will produce a Schottky barrier of height 0.7–0.8 eV depending on the Zn concentration. However, the actual barrier height in detector grade material has been measured to be around 0.9 eV. We have developed a model that explains the additional 0.2 eV barrier in terms of Au diffusion between the contact and the intrinsic CdZnTe bulk material. In this work, we have also analysed this contact structure to provide additional validation of our contact model. In this context, we operated the crystal in photovoltaic mode with illumination by a sub-bandgap (850 nm) IR laser point beam through the contact region. The photogenerated potential was measured using a constant current supply to null the photocurrent, and the corresponding potential across the current source was recorded by a digital voltmeter. By illuminating at varying depths into the crystal and with carefully controlled light intensities, we have produced further evidence for the lightly doped region just below the metal contact that is required by our model.

Grain Boundary Motion during Ag and Cu Grain Boundary Diffusion in Cu Polycrystals

Grain boundary (GB) motion in high-purity Cu material (5N8 and 5N Cu) is investigated using the results of radiotracer GB diffusion measurements with tracers exhibiting fundamental differences in the solute-matrix atom interactions. The results on GB solute diffusion of Ag (revealing a miscibility gap in the Ag-Cu phase diagram) and Au (forming intermetallic compounds with Cu) in Cu and on Cu self-diffusion are analyzed. The initial parts of the Ag and Cu penetration profiles turned out to be substantially curved. The profile curvature is explained via the effect of GB motion during 110m Ag and 64Cu GB penetration. The activation enthalpies of GB motion in these two independent measurements occurred to be very close, 95 and 103 kJ/mol, respectively. Moreover, these values turn out to be close, but still somewhat larger than the activation enthalpy of Cu GB self-diffusion in Cu material of the same very high purity, Q Cu gb = 72 kJ/mol. Although tracer diffusion measurements of Au GB diffusion in Cu yielded only limited information on GB motion, the absolute values of GB velocities are consistent with those calculated from the Ag and Cu GB diffusion data.

Grain Boundary Diffusion in C 60 Thin Films

This paper focuses on the effect of grain boundaries on the diffusion processes in polycrystalline C60 thin films. Electrically induced diffusion of Au was investigated by in situ measurements of the film conductivity. Electron Paramagnetic Resonance (EPR) spectroscopy was used to study diffusion of oxygen. Increase in grain sizes in polycrystalline C60 thin films was found to result in the acceleration of gold and oxygen diffusion. The results are interpreted assuming that these impurities diffuse in C60 films dominantly along grain boundaries.

Effect of the first antimony layer on AuZn ohmic contacts to p-type InP

The electrical properties of the Sb/Zn/Au/Nb ohmic contacts to p-type InP were investigated, where a slash (/) indicates the deposition sequence. The first Sb layer improved the contact resistivity and reduced the optimum annealing temperature, compared with the Au/Zn/Au/Nb contacts whose first layer was Au. The minimum contact resistivity of 4×10−5 Ω cm2 was obtained from the Sb(3 nm)/Zn(5 nm)/Au(10 nm)/Nb(50 nm) contacts annealed at 325 °C for 2 min. The interfacial microstructure was studied using the cross-sectional transmission electron microscope. It was considered that the deposited Sb deoxidized and removed the native oxides of the InP surface and that facilitated the upper Au and Zn diffusion into InP.

Admetal-induced substrate surface restructuring during metal-on-metal electrochemical deposition studied by in situ scanning tunneling microscopy

Based on time-dependent in situ scanning tunneling microscopy (STM) studies, we demonstrate that for Ni on Ag(111) and Ru on Au(111), electrochemical metal-on-metal deposition can result in pronounced substrate surface restructuring. For Ni/Ag(111), we observe that at low deposition flux and low coverage, Ni submonolayer islands at steps are partly embedded in the Ag terraces, whereas at higher deposition flux and higher coverage, substrate restructuring results in the formation of monolayer bays in the Ag terraces. We suggest that this restructuring process proceeds predominantly via step edge diffusion of Ag atoms. For Ru/Au(111), the formation of fjords and monolayer holes in the Au terraces is observed at low and high Ru coverage, respectively. The importance of the Au surface mobility for the restructuring process is demonstrated by comparing experiments in H 2SO 4 and HCl solutions, in which Au exhibits strongly different surface mobilities. For this system, restructuring involves Au diffusion along Au steps, Au atom detachment from the Au steps, and upward exchange diffusion. According to these observations and their comparison with similar findings for vacuum deposition, we conclude that this restructuring requires (i) a high substrate surface mobility and (ii) a stronger bonding of substrate atoms to deposit islands than to the substrate.

MBE grown BeTe and ZnBeTe films as a new p-contact layer of ZnSe-based II–VI lasers

Non-alloyed Au/p-ZnSe/p-BeTe ohmic contact layers for ZnSe-based blue–green laser diodes with contact resistivity as low as 4.2×10 −4 Ω cm 2 are reported. This contact layer is basically dislocation free due to small lattice misfit as long as the thickness is thinner than 500 Å, as confirmed by transmission electron microscopy (TEM) observation. The ZnSe layer serves as a contact layer for BeTe and protecting layer against oxidation as well. The electrical properties of the contact layers are strongly dependent on the ZnSe layer thickness. Au diffusion through the ZnSe layer down to the BeTe layer at room temperature is found to be responsible for ohmic properties. A series of ZnBeTe epilayers with different x values have been grown on GaAs by molecular beam epitaxy (MBE). We can easily control the composition by changing the Zn or Be cell temperatures. Hall effect measurement was performed on as-grown Zn 0.05Be 0.95Te epilayer doped with nitrogen. Hole concentration as high as 2×10 19 cm −3 has been achieved.

Diffusion and solubility of Au implanted into the AZ1350 photoresist

In the present paper we report diffusion and solubility results for Au into the photoresist AZ1350. Au was implanted into AZ1350 films at very low energy (E=20keV) and fluences (Φ=1012 and 5×1012 Au/cm2). In this way the radiation damage introduced by the implantation process was minimized and cluster formation was avoided. Annealing was performed in the 150–300°C temperature range and the as implanted and thermal treated samples were analyzed using the Rutherford backscattering (RBS) technique. For the lowest implantation fluence the results have shown a regular atomic diffusion process characterized by an activation energy of Ea=640meV. Instead, for Φ=5×1012 Au/cm2 the diffusional mechanism has revealed the effects of the radiation damage. In addition solubility measurements indicate that the solubility limit at 250°C is of the order 0.3 at.%.

Defect complexes induced by diffusion of group I acceptors into CdTe

The formation of defects following the diffusion of the group I acceptors Cu, Ag, or Au into CdTe was investigated by perturbed γγ-angular correlation (PAC) using the radioactive donor 111InCd. The formation of A-centres (InCd–VCd pairs) with the donor 111InCd was observed, indicating that the incorporation of the group I acceptors Cu, Ag, or Au is accompanied by the generation of cation vacancies. In addition, the formation of InCd–AgCd or InCd–AuCd pairs was observed in CdTe. The concentration of cation vacancies formed after diffusion of Cu, Ag, or Au was found to depend only weakly on the respective group I element. In contrast, the migration energy of the cation vacancy was observed to be different in CdTe crystals doped with Ag or Au, yielding 0.76 (3)eV and 0.84 (3)eV, respectively. In Ag-doped CdTe the binding energies of the InCd–VCd pair and the InCd–AgCd pair were determined to 0.18 (2)eV and 0.19 (2)eV, respectively.

Surface alloying at the Cd∣Au(100) interface in the upd region. Electrochemical studies and in situ EC-AFM observation

The surface alloy formation during Cd underpotential deposition (upd) on Au(100) in sulfuric acid solution was investigated by means of long-time polarization experiments and in situ electrochemical atomic force microscopy (EC-AFM). The dynamics of the surface alloying were found to depend on polarization conditions and to compete with surface diffusion and further adsorption processes. A turnover mechanism is proposed for the surface alloying process that was observed to take place mainly on the terraces. For long polarization times, the extent of 2D alloy formation into the surface is governed by solid-state diffusion of either Cd or Au through the alloyed phase. The time dependence of the surface phase stability and composition, which was formed at a certain potential in the upd region, is discussed in thermodynamic terms derived for the surface.

Non-alloyed Au/ p -ZnSe/ p -BeTeohmic contact layersfor ZnSe-based blue-green laser diodes

Non-alloyed Au/p-ZnSe/p-BeTe ohmic contact layers for ZnSe based blue-green laser diodes with contact resistivity as low as 4.2/spl times/10/sup -4/ /spl Omega/cm/sup 2/ are reported. This contact layer is basically dislocation free due to the low level of lattice misfit, as confirmed by TEM observations. The ZnSe layer serves as a contact layer and also as a protection layer for BeTe against oxidation. The electrical properties of the contact layers are strongly dependent on the ZnSe layer thickness. Au diffusion through the ZnSe layer down to the BeTe layer at room temperature is found to be responsible for the ohmic properties.

Organic and Inorganic Contamination on Commercial AFM Cantilevers

It has been found that a common shipping and packaging material for commercial AFM cantilever tips, poly(dimethylsiloxane) (PDMS), causes a thin layer of silicone oil contamination on AFM cantilever tips. Due to the similarity of elemental compositions between silicone oils and AFM cantilevers (both contain silicon and oxygen), it is difficult to detect such contaminants with the widely used surface characterization technique, X-ray photoelectron spectroscopy (XPS), since XPS provides mainly elemental and short-range chemical information. However, by using static time-of-flight secondary-ion mass spectrometry (TOF-SIMS), a technique that is extremely surface-sensitive, silicone oils on AFM cantilevers can easily be identified by their molecular fragments. A simple dip cleaning procedure using a mixture of concentrated sulfuric acid and hydrogen peroxide (piranha solution) was found to be an easy and effective way to remove organic contamination, including silicone oils, from AFM cantilever tips. It has also been shown, in both XPS and TOF-SIMS spectra, that a small amount of Au is present on the tip side of AFM cantilevers. This is most likely due to thermal diffusion of Au during the deposition of Au on the back side of the cantilevers, placed there to enhance laser reflectivity in the detection system of AFM instruments. No simple dipping approach was found to remove Au contamination on the tip side without also damaging the required Au coating on the back side of the cantilevers.

Evidence for structural multiplicity of the Σ = 3 incoherent twin boundary in Cu from grain-boundary diffusion measurements

ABSTRACT Grain-boundary impurity diffusion of Au along the incoherent twin boundary in a diffusion-bonded Cu bicrystal has been studied by the serial sectioning technique. The measured penetration profiles had a rather atypical shape which we interpreted in terms of structural multiplicity of the grain-boundary structure. A method of processing such profiles has been suggested and the relative fraction of the grain-boundary structural modification exhibiting the lowest diffusion coefficient has been estimated as 60% . The difference between the energies of the two structural modifications has been estimated as being less than 17%, which is in good agreement with the results of computer simulations of the grain-boundary energy in Cu.

Slip Diffusion and Lévy Flights of an Adsorbed Gold Nanocluster

Anomalous diffusion of a gold nanocrystal Au{sub 140} , adsorbed on the basal plane of graphite, exhibiting L{acute e}vy-type power-law flight-length and sticking-time distributions, is predicted through extensive molecular dynamics simulations. An atomistic collective slip-diffusion mechanism is proposed and analyzed. {copyright} {ital 1999} {ital The American Physical Society}

Pulsed laser deposition of multilayer TiN/Pb(Zr xTi 1− x)O 3 for piezoelectric microdevices

Multilayer Pb(ZrTi)O 3 (PZT)/TiN/Si structures were grown by two subsequent laser ablation processes in reactive atmosphere. First, a fcc-oriented TiN film was deposited by laser ablation of a Ti target in high-purity nitrogen reactive gas. Subsequently, a crystalline, piezoelectric PZT film was grown by reactive ablation of a PZT target in oxygen atmosphere. Both deposition processes were conducted at quite low Si(100) substrate temperature: 350°C for TiN and 370°C for PZT, in the same experimental setup (Nd-YAG laser, λ=1060 nm, energy/pulse 0.3 J, t FWHM=10 ns). TiN film properties were analyzed by XRD and electric measurements. After the deposition of the PZT layer, the obtained structure was first characterized by XRD, SEM and SIMS techniques. Testing measurements performed after the deposition by thermal evaporation of an Al layer as top electrode on the PZT/TiN/Si structure confirm that they can be used as sensor transducer element. The TiN (as high conductive nitride) layer replaces the former Au layer used as bottom electrode. In this way, the Au diffusion inside the Si substrate, as well as in the deposited layer, is avoided, as could be observed from a comparative study of the SIMS spectra recorded for PZT/TiN/Si and PZT/Au/Si configurations.

The inclination dependence of gold tracer diffusion along a Σ3 twin grain boundary in copper

Grain boundary impurity diffusion of Au in diffusion bonded Σ3〈011〉 Cu bicrystals has been studied by the radiotracer serial-sectioning technique using the 195Au isotope with high specific activity. The dependence of the grain boundary diffusion parameter sδD b on the inclination angle Φ of the grain boundary plane with respect to the close-packed (111) plane of the coherent twin boundary has been determined for the temperatures of 673 and 773 K (here s, δ and D b are the segregation factor, the grain boundary width and the grain boundary diffusion coefficient, respectively). At both temperatures sδD b exhibits a minimum at Φ=70.5° and a maximum at Φ=82.0°. It is shown that there is no direct correlation between the energy and diffusivity of the grain boundaries in this system and that the periodicity in the grain boundary plane has a significant influence on the grain boundary diffusivity.

Diffusion of Au in ZnSe and its dependence on crystal quality

Diffusion of gold in zinc selenide has been studied by using a C12 and He12 ion backscattering technique. The samples were thin films grown by molecular beam epitaxy on bulk GaAs (100) substrates and on GaAs (100) epitaxial layers followed by evaporation of gold and annealing in the temperature range 400–800 °C. The surface properties of the samples were studied with scanning electron microscopy and atomic force microscopy. The crystal quality of the samples was studied with He4 ion channeling. The gold diffusion was found to depend significantly on the crystal quality of the ZnSe. An empirical model for calculating the diffusion coefficient for different crystal quality ZnSe is presented.