Platinum Diffusion Research Articles

Platinum contamination issues in ferroelectric memories

The contamination risk of processing with platinum electrodes on device performance in ferroelectric memories is assessed in this work. Details of platinum diffusion to the active regions at annealing temperatures of 800 °C are investigated by secondary ion mass spectroscopy, deep level transient spectroscopy, and Rutherford backscattering spectrometry techniques. Cross sectional transmission electron microscopy and local elemental analysis by energy dispersive x-ray spectroscopy were used to examine the precipitation of Pt in defect free silicon as an eventual cause of gate oxide degradation. The impact of platinum contamination on device performance is evaluated under the typical ferroelectric memory processing conditions. Results from leakage current and charge to breakdown measurements of intentionally contaminated diode and metal–oxide–semiconductor (MOS) structures, respectively, are presented. The results show that the degradation depends strongly on device design and configuration. A phosphorus doped polysilicon plug, which has the function of connecting the select transistor to the capacitor module, provides effective gettering regions and prevents the diffusion of Pt atoms to the active regions. Under typical processing conditions, no evident Pt precipitates were observed and up to a concentration level of 4×1014 atoms/cm2, the leakage current of intentionally contaminated diodes does not increase, if the contamination occurs after front-end phosphorus doped poly-Si processing. Results from constant current charge to breakdown show a small number of breakdown events due to redeposition of Pt at the periphery of the MOS structure. The risk of processing with Pt electrodes in ferroelectric memories requires great care. Precautions like sealing the back surface and incorporating phosphorus doped polysilicon as the plug material are necessary to avoid the detrimental effects of Pt.

High temperature stability of indium tin oxide thin films

A robust high temperature strain gage based on indium-tin-oxide (ITO) has been used to measure static and dynamic strains at temperatures up to 1400 °C. These thin film, ceramic strain gages have several advantages over metal strain gages including a large gage factor and increased chemical and electrical stability at very high temperatures. Electron spectroscopy for chemical analysis (ESCA) of ITO films deposited onto high purity alumina substrates and subjected to temperatures up to 1400 °C indicated that the ITO films had undergone an interfacial reaction with the substrate. In addition, the interfacial reaction appears to have been responsible for high temperature stabilization through the formation of an ITO/Al 2O 3 solid solution. When similar ITO films were deposited onto alumina with a platinum diffusion barrier, there was no evidence of an interfacial reaction. Thermodynamic calculations indicated that bulk ITO may not be stable in air ambients at temperatures above 1300 °C but the alumina substrates stabilized the ITO to temperatures well beyond this value.

Influence of the Applied Cooling Rate on the Type Conversion of Platinum Diffused N-Type Silicon

In this work we show that the temperature and the applied cooling rate during a platinum diffusion process strongly influence the electrical conductivity in weakly phosphorus doped silicon. Diffusions were done in the range of 800–950°C for several hours. Spreading resistance profile analyses clearly show an n-type to p-type conversion under the surface when samples are slowly cooled (5°C/min). Only a compensation of the phosphorus donors is observed when samples are quenched. This mechanism is reversible. Five Pt related deep levels, including the acceptor level at 0.23 eV from the conduction band, are observed. One of them is located at 0.427 eV from the valence band and can be related to the acceptor state at the origin of the type conversion mechanism. This acceptor state can be associated with a complex defect based on the association of a substitutional Pt atom with interstitial atoms (Pt, O) or intrinsic point defects.

Silver and platinum diffusion in alumina single crystals

Silver and platinum diffusion in α-alumina single crystals have been investigated using SIMS technique in 800–1150°C and 900–1200°C temperature ranges. Previous radiotracer measurements yielded higher diffusion coefficients of silver than those presented here. This difference is attributed to the resolution differences between the SIMS and the radiotracer techniques. The former allows us to obtain the bulk diffusion coefficients while the latter the dislocation ones. Silver and platinum diffusion coefficients are one to two orders of magnitude higher than those of chromium and aluminium. It is suggested that such a difference can be related to the ability of low valency cations to occupy interstitial sites, allowing a proportion of the noble elements to dissolve in alumina through the self-compensating mode. Hence, a diffusion mechanism involving correlated jumps of interstitial and substitutional foreign atoms (Ag, Pt) is proposed.

Bonding of Bulk Piezoelectric Material to Silicon Using a Gold-Tin Eutectic Bond

AbstractA class of MEMS devices, which utilizes microfabrication technology and bulk piezoelectric material, is currently being developed to produce high power density transducers. A thin-film gold-tin eutectic solder bond has been developed to bond electrically and mechanically bulk piezoelectric elements to microfabricated silicon structures in these devices. A 4.3 [.proportional]m thick multilayer film structure, consisting of a titanium adhesion layer, a platinum diffusion barrier, a gold-tin (80 wt.% Au - 20 wt.% Sn) alloy layer, and a pure gold capping layer, was sputter deposited on the piezoelectric components to be bonded. Bonding was accomplished by mating the piezoelectric components with silicon components metallized with a titanium-platinum-gold multilayer film and heating to approximately 300°C in a reducing atmosphere. The bonding technology allows thin, electrically conductive bonds to be formed between dissimilar materials with minimal amounts of applied pressure during bonding. Successful bonding has been achieved between single crystal silicon and polycrystalline lead-zirconate-titanate (PZT-5H) as well as between silicon and single crystal lead zinc niobate-lead titanate (PZN-PT). The process was optimized to produce mechanically robust, void-free bonds. The absence of voids was verified through scanning electron microscope examinations of bond cross-sections. Tensile tests conducted on representative structures indicated that the strength of the bond was limited by the strength of the titanium – PZT-5H interface.

X-ray study of Co/Ni and Co/Pt/Ni/Pt multilayers

Magnetic multilayers consisting of repeated bilayers of cobalt and nickel or quadrilayers of cobalt, platinum, nickel and platinum were investigated using reflection and diffraction of X-rays. It was found that ultra-thin Co/Ni multilayers deposited with dual electron beam evaporation grow with poor interface quality, which is partly caused by high interdiffusion of Co and Ni, partly by cumulative interface roughness. The low interface quality destroyed the superlattice structure after a few bilayers in our samples. The quality of superlattice in Co/Pt/Ni/Pt multilayers was substantially better, which was mainly due to the lower mutual diffusion of platinum and cobalt, and platinum and nickel. For the Co/Pt/Ni/Pt multilayers, X-ray reflectivity measurements yielded information on thickness and interface roughness of individual layers. These characteristics were compared with thickness and interface roughness obtained from X-ray diffraction. X-Ray diffraction was also applied to get information on atomic ordering in individual layers (mean interplanar spacing and atomic disorder).

Influence of Au and Pt on the concentration profile of Mn in Si

The influence of diffusion of gold and platinum from the layer deposited on the silicon surface on the concentration profile of 54Mn in the bulk is investigated using the radiochemical technique. The data obtained indicate that the manganese concentration in the bulk of silicon is reduced due to annealing of the samples Si〈54Mn〉 with the gold or platinum layer on the surface.

The evolution of interstitial-type defects in silicon during platinum diffusion from 400 to 600°C following 2-MeV electron irradiation

Platinum has been diffused into epitaxial n-type silicon for 30 min at temperatures from 400 to 600°C following room temperature irradiation with 2-MeV electrons at a dose of 1×10 17 e − cm −2. Platinum has only been detected by deep level transient spectroscopy (DLTS) following the highest diffusion temperature. For lower temperatures defects, not previously reported, arise which are thought to be of interstitial nature. The two principal defect levels are determined to be located at 0.29 and 0. 41 eV below the conduction band. The compensation for the two lowest diffusion temperatures is observed to be extremely strong as manifested by a strong reduction of the steady state reverse bias capacitance during the DLTS measurements. Following thermal treatment at 500°C this capacitance, however, increases. DLTS measurements down to 20 K detected thermal donors as well as a number of other defects not previously reported. Their signatures have been determined by DLTS and TSCap (thermally stimulated capacitance) measurements. The nature of the observed defects is discussed with reference to recent results concerning interstitial defects.

Platinum overlayers on Co(0001) and Ni(111): numerical simulation of surface alloying

The surface alloying of one and two monolayers (ML) of platinum deposited on Ni(111) and Co(0001) were studied by means of the ECT-BFS method. The 1ML deposit appears to be very stable on both substrates. Platinum can diffuse at high temperature only, the large activation barrier being represented by the first substrate layer. On the contrary, the stability of the 2ML deposit is poor so that alloying is easily obtained. In both cases, the platinum diffusion produces metastable states. The lowest-energy states exhibit a propensity for platinum dilution in a limited region below the surface. The initial platinum thickness determines not only the features of the alloyed region, but also the surface concentration. The surface alloys have features qualitatively similar to those reported for the (111) surface of bulk Pt–Ni and Pt–Co alloys: a platinum-rich surface and oscillating concentration profiles.

Chitosan Sorbents for Platinum Sorption from Dilute Solutions

Chitosan has proved efficient at removing platinum in dilute effluents. The maximum uptake capacity reaches 300 mg/g (almost 1.5 mmol/g). The optimum pH for sorption is pH 2. A glutaraldehyde cross-linking pretreatment is necessary to stabilize the biopolymer in acidic solutions. Sorption isotherms have been studied as a function of pH, sorbent particle size, and the cross-linking ratio. Surprisingly, the extent of the cross-linking (determined by the concentration of the cross-linking agent in the treatment bath) has no significant influence on uptake capacity. Competitor anions such as chloride or nitrate induce a large decrease in the sorption efficiency. Sorption kinetics show also that uptake rate is not significantly changed by increasing either the cross-linking ratio or the particle size of the sorbent. Mass transfer rates are significantly affected by the initial platinum concentration and by the conditioning of the biopolymer. Gel-bead conditioning appears to reduce the sorption rate. While for molybdate and vanadate ions, mass transfer was governed by intraparticle mass transfer, for platinum, both external and intraparticle diffusion control the uptake rate. In contrast with the former ions, platinum does not form polynuclear hydrolyzed species, which are responsible for steric hindrance of diffusion into the polymer network.

Study on the evolution and nature of interstitial-type defects following proton and alpha particle implantation during low-dose proximity gettering of platinum

Platinum has been diffused into epitaxial n-type silicon at 600°C, 650°C and 700°C for 30 min following implantation with 3.3 MeV alpha particles. The doses employed were between 1 × 10 11 and 1 × 10 14 He + cm −2. Also an implantation involving protons at 850 keV with doses of 5 × 10 13 and 5 × 10 14 H + cm −2 has been performed followed by an annealing at 600°C or 700°C. Thereafter the samples were characterized using Deep Level Transient Spectroscopy (DLTS). Apart from the platinum deep level at 0.23 eV below the conduction band, other deep levels (so-called K-lines) may appear in the deep level transient spectroscopy spectrum depending on the respective implantation dose or annealing temperature. We have traced the evolution of these spectra from the state without a platinum deep level to its appearance by varying the implantation dose and the annealing parameters. It was thus possible to determine which defects might influence platinum diffusion. In addition, one of the observed defects was observed only after the proton implantation and is thus considered to be hydrogen-related. Possible identities of the other defects are discussed.

2 MeV electron irradiation of silicon at elevated temperatures: Influence on platinum diffusion and creation of electrically active defects

Platinum has been diffused at 300–800 °C for 30 min into n-type epitaxial silicon samples during 2 MeV electron irradiation using a dose of 1×1017 e− cm−2. Thereafter the samples were characterized by capacitance–voltage measurements and deep level transient spectroscopy. The samples with irradiation temperatures of 500, 600, and 700 °C could be analyzed, while the compensation in the others was too high. Most of the observed deep levels were characterized using the Arrhenius method. Their possible identities are discussed. The deep level of substitutional platinum first appears in the sample irradiated at 600 °C and is the dominant defect level at even higher temperatures. We observe that at a chosen distance from the sample surface (17 μm), the concentration of electrically active platinum after an irradiation at 700 °C is a factor of 1000 higher than in an ordinarily diffused sample. Taking into account experiments where platinum was diffused into pre-irradiated samples, the observed behavior is attributed to a reduced correlated recombination of interstitials and vacancies.

Diffusion of platinum, vanadium and manganese in Ni3Al phase under high pressure

Diffusion of platinum, vanadium, and manganese in the Ni3Al phase is investigated under high pressure. Platinum atoms occupy cubic face centred sites (α) in the L12 ordering structure. Vanadium atoms occupy cubic corner sites (β). Manganese atoms occupy both sites. Activation volumes ΔV for diffusion of these diffusing atoms to the molar volume of the Ni3Al phase V0 are as follows: $$\Delta V/V_0 {\text{ for Pt:}}{\kern 1pt} {\text{ 0}}{\text{.75, }}V{\kern 1pt} :\;\,0.97 - 1.08,{\text{ Mn: 1}}{\text{.01}} - {\text{1}}{\text{.03}}$$ These values mean that the diffusion of platinum is mediated by single vacancies, that of vanadium is done by divacancies or other complex mechanisms, and that of manganese via single vacancies plus other mechanisms.

Enhanced diffusion of platinum in electron-irradiated silicon

Platinum has been diffused at 600, 700 and 800°C into n-type epitaxial silicon samples with and without prior 2 MeV electron irradiation at doses of 1×10 14–1×10 17 cm −2. Without prior electron irradiation, diffusion at 700 and 800°C for 30 min resulted in the presence of a single deep level in the DLTS (Deep Level Transient Spectroscopy) spectrum, which is attributed to the platinum acceptor level at 0.23 eV below the conduction band edge. At lower diffusion temperatures no deep level was detected. However, after prior electron irradiation and subsequent in-diffusion at 600°C this platinum level is again present in the DLTS spectrum. Depth profiling shows, that the platinum concentration increases with electron dose. Its value after in-diffusion without prior irradiation at 750°C is comparable to the one after in-diffusion at 600°C following a dose of 1×10 17 cm −2. A tentative explanation of this enhanced diffusion is proposed and the influence of the irradiation induced vacancies and silicon self-interstitials is discussed.

Diffusion of Pt in molecular beam epitaxy grown ZnSe

Diffusion of platinum in zinc selenide has been studied by the use of the He4 and C12 ion backscattering techniques. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 500–800 °C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4×10−6 cm2/s, respectively.

Electron irradiation for adjusting the reverse recovery time and forward voltage drop characteristics of fast diodes

The electron linear accelerator ALIN-10 has been used to irradiate at room temperature and high temperature silicon diodes type BA159, BAX157 and 6DRR1 (manufacturer – Baneasa S.A.-factory 2300, Romania). The influence of 10 MeV electron irradiation upon the main electrical characteristics (reverse recovery time, forward voltage, reverse current) has been examined for different absorbed doses (10–50 kGy) and different irradiation temperatures (25°C, 175°C, 250°C). The dependence of the minority carrier lifetime, reverse recovery time and forward voltage on the radiation dose, and the percentage distribution (%) of the reverse recovery time and of the reverse current for the irradiated diodes are presented. A comparison between the electrical performances of the fast diodes obtained by electron irradiation and the electrical performances of the fast diodes obtained by gold or platinum diffusion has been made.

Study on microstructure and interdiffusion behavior in Pb(Fe [formula omitted]Nb [formula omitted])O 3/Pt/Ti/SiO 2/Si(100) multilayer films

Pb(Fe 1 2 Nb 1 2 )O 3 (PFN) films on Pt/Ti/SiO 2/Si(100) substrates were fabricated by pulsed laser deposition (PLD), and Pt/Ti/SiO2/Si(100) were formed by the deposition of Pt and Ti on SiO 2/Si(100) using ion-beam sputtering technique. PFN/Pt/Ti/SiO 2/Si(100) multilayer structure has been studied using Auger electron spectroscopy (AES), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The diffusion of platinum into PFN film and Ti layer has been observed. The formation of a TiO 2 phase was Confirmed.

Determination of vacancy concentrations in the bulk of silicon wafers by platinum diffusion experiments

Diffusion of platinum at low temperatures is a convenient way to characterize vacancy profiles in silicon. This article summarizes the experiments performed to find a standard procedure, discusses the pitfalls and limitations, and shows the applicability of the method. The results of experiments with float-zone and Czochralski-grown samples in the temperature range from 680 to 842 °C were found to disagree with the predictions of models published in the literature. Therefore, parameters governing the diffusion of point defects and platinum in silicon were determined for this temperature range.

Point Defect Properties from Metal Diffusion Experiments — What Does the Data Really Tell Us?

Point defect properties, including diffusivities and equilibrium concentrations for both interstitials and vacancies, are commonly extracted from metal diffusion experiments, and these values are widely used in process simulation software. However, in many cases, these parameter values were extracted using oversimplified models which ignore interactions between interstitial and vacancy diffusion mechanisms. Questions about the accuracy of these parameters have come from ab-initio defect calculations which conclude that vacancies diffuse faster than interstitials, in contrast with published reports on metal diffusion which find vacancies diffuse much more slowly than interstitials. We have reanalyzed published data for zinc and platinum diffusion and find that it is possible to match all of the data using fast vacancy diffusivity. The most direct evidence for slow vacancy diffusion (and a high equilibrium concentration) comes from platinum diffusion experiments. However, we are able to reproduce these results with fast V diffusion and carbon/interstitial clustering, using carbon concentrations typical of Czochralski and float zone silicon (1016cm−3). We evaluate the effectiveness of metal diffusion experiments in determining point defect parameters, and find that it is not possible to reliably determine both diffusivities and equilibrium concentrations for both interstitials and vacancies from metal diffusion results.

Influence of RTP on Vacancy Concentrations

ABSTRACTThe increase and reduction of the vacancy concentration by rapid thermal processing (RTP) was investigated by platinum diffusion. Direct experimental evidence is presented for the consumption of vacancies during oxidation and for the introduction of vacancies during processing in ammonia and nitrogen. These results confirm the indirect conclusions from dopant diffusion and from the growth and shrinkage of extended defects. In addition, it was possible to establish an upper limit for the equilibrium concentration of vacancies at 1180 °C which is lower than previously reported values.