Iridium Silicide Research Articles

RBS characterization of the iridium diffusion in silicon

In this work, the Ir diffusion in Si has been studied in the high concentration regime. Si (1 0 0) samples were preamorphized by Si implantation and implanted with Ir with a peak concentration of 8×10 21 cm −3 , below the minimum necessary to the formation of a continuous layer of iridium silicide. The amorphized region of the substrate was regrown by solid phase epitaxy at 550°C. This procedure eliminates the effect of the end of range region of the Ir implant on the diffusion process. After regrowth, the samples were annealed at temperatures in the 800–1000°C range for different times. The Ir concentration profiles and the crystal quality were determined from random and aligned RBS spectra. Annealing at high temperatures causes a snow plow effect of Ir toward the surface of the sample, with a segregation coefficient close to 1. An Ir diffusion mechanism through the defect-free region of the Si substrate is also clearly identified, and a constant value of the diffusion coefficient D is derived for each temperature. The values of D follow an Arrhenius behavior with an activation energy E a =3.3±0.2 eV . This value agrees with the typical ones found in vacancy assisted diffusion mechanisms reported for other species. Comparison of these results with the previously reported activation energy E a =1.3 eV for Ir diffusion from the vapour phase at low concentrations shows that the diffusion mechanism is dependent on the concentration level. The values of D at high concentrations are 6 to 7 orders of magnitude lower than the ones reported for low concentrations.

Thermal Stability of Ir/TaN Electrode/Barrier on Thin Gate Oxide for MFMOS one Transistor Memory Application

AbstractThe Metal-Ferroelectric-Metal-Oxide-Silicon (MFMOS) one transistor memory requires a metal electrode directly on top of the thin gate oxide. The gate oxide used in our present MFMOS one transistor memory processing is 30 Å SiO2. Ir has been chosen for the bottom electrode and TaN was used as the barrier layer between the Ir and thin gate oxide. It has been shown from previous studies that a TaN barrier layer can effectively prevent the formation of iridium silicide and can enhance the adhesion between Ir and Si or SiO2 substrates. But it is more important that the TaN itself is stable and will not react with the gate oxide during ferroelectric material deposition, annealing and subsequent processing. In this paper, TaN barriers with different deposition conditions have been deposited on 30 Å gate oxide. 1500 Å Ir was deposited on the TaN barrier layer. Capacitors of Ir/TaN/gate SiO2/Si were defined by dry etching. Series RTP annealing were performed in oxygen from 500 to 650 °C with annealing times from 5 min to 90 min. The capacitor was also annealed in a nitrogen ambient at 1000°C for 10s. C-V and I-V studies were used to characterize the stability of the Ir/TaN/Gate SiO2 structure. It was observed that the Ir/TaN/Gate SiO2 is very stable during the above mentioned annealing conditions. The consumption and further oxidation of the gate oxide is negligible and would depend on the deposition condition of the TaN barrier layer. With optimized deposition conditions, a 220 Å TaN barrier layer can effectively prevent any iridium silicide formation and will not degrade the gate oxide during annealing processing. The interfaces between the TaN and gate SiO2 and between the gate SiO2 and Si substrate can be further improved by forming gas annealing.

Infrared Optical Properties of Iridium Silicides

Amorphous (a-IrSi) and crystalline (c-IrSi, Ir3Si4) iridium silicide layers (1 to 80 nm) are fabricated by evaporation of iridium metal onto Si(100) substrates and subsequent annealing at various temperatures in the range from 440 to 530 °C. The infrared transmission and reflection are measured for the layer system as a function of the wavelength in the range from 2 to 6 μm and as a function of the film thickness. The dielectric permittivity of the silicide films is determined by taking into account multiple reflections in the thin film. All the silicides investigated show metallic behavior. The crystalline iridium silicide phases c-IrSi and Ir3Si4 are well described by the Drude model; the amorphous a-IrSi exhibits a reduced absorption indicating a reduced density of states near the Fermi energy.

Infrared Optical Properties of Iridium Silicides

Amorphous (a-Irsi) and crystalline (c-IrSi, Ir 3 Si 4 ) iridium silicide layers (1 to 80 nm) are fabricated by evaporation of iridium metal onto Si(1000) substrates and subsequent annealing at various temperatures in the range from 440 to 530°C. The infrared transmission and reflection are measured for the layer system as a function of the wavelength in the range from 2 to 6 μm and as a function of the film thickness. The dielectric permittivity of the silicide films is determined by taking into account multiple reflections in the thin film. All the silicides investigated show metallic behavior. The crystalline iridium silicide phases c-IrSi and Ir 3 Si 4 are well described by the Drude model; the amorphous a-IrSi exhibits a reduced absorption indicating a reduced density of states near the Fermi energy.

RBS and SIMS study of the simultaneous phase growth of iridium silicides formed by RTA in vacuum

Quantitative analysis of the kinetics of growth of IrSi and IrSi 1.75 by RTA in vacuum, taking into account that the formation of the two compounds proceeds simultaneously, are reported. The composition and thickness of the different silicides as a function of annealing temperature and time has been obtained by RBS measurements. We have used a multiphase system model based on the simultaneous growth of the two phases, assuming that silicon is the moving reactant in the Ir Si system, to obtain the interfacial reaction constant K and the diffusion coefficient D of silicon in both silicides as a function of annealing temperature. With the help of the layer thickness vs. annealing time plots at different temperatures, we have calculated, using numerical analysis techniques, two pairs of constants related to K and D. SIMS characterization of the samples has been necessary to estimate the silicon concentration gradient values, so that we have been able to obtain the final values of K and D at different processing temperatures, and, as a consequence, to determine their activation energies.

Noble metal silicide formation in metal/Si structures during oxygen annealing: Implications for perovskite-based memory devices

This paper investigates the potentially undesirable noble metal silicide formation reactions that may occur in noble metal electrodes deposited directly on silicon without an intervening diffusion barrier. Metal (90–100 nm)/Si structures of Pt/Si, Rh/Si, Ir/Si, and Ir/Ti/Si were annealed in oxygen or nitrogen ambients at temperatures of 640–700 °C. Metalysilicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, x-ray diffraction, and electrical resistance measurements. While complete silicidation was observed in the Rh/Si, Pt/Si, and Ir/Si samples after 640 °C/6 min anneals in nitrogen, some Pt and most of the Ir remained after equivalent anneals in oxygen. More detailed studies of the Ir/Si samples indicated that some Ir is left unsilicided even after a 700 °C/6 min anneal in O2, and that the iridium silicide formed is the semiconducting IrSi1.75. The formation of this silicide can be delayed, but not prevented, with the use of a 5 nm Ti adhesion layer between the Ir and Si.

Buried, self-aligned barrier layer structures for perovskite-based memory devices comprising Pt or Ir bottom electrodes on silicon-contributing substrates

The integration of noble metal electrodes into semiconductor memory devices incorporating ferroelectric or high dielectric constant ε materials is expected to require deposition of a conductive, oxidation-resistant barrier material between the noble metal and the silicon contact. Described is an alternative type of barrier layer structure which is formed as buried, self-aligned layer during oxygen-ambient annealing after noble metal deposition on silicon-contributing substrates. Reactions of Pt(20 nm) and Ir(20 nm) films with substrates of single crystalline silicon (c-Si), polycrystaline silicon (poly-Si), and tungsten silicide (WSix/Si with x=2.4–2.8) were examined after anneals in atmospheric pressure ambients of oxygen or nitrogen at temperatures of 640–700 °C, a temperature range of interest for high-epsilon materials deposition. While Pt(20 nm) films reacted with silicon and WSix/Si during oxygen annealing to form a mixture of Pt silicides and Pt, Ir(20 nm) films on the same substrates did not form any iridium silicides during oxygen annealing. In all cases, unreacted noble metal M was left due to the formation of an oxygen-containing M–O–Si barrier which interfered with the silicidation reaction. In contrast to these results for oxygen annealing, the Pt and Ir films were completely consumed by silicidation reactions during anneals in nitrogen. Qualitative through-film resistance measurements indicated that the M–O–Si barrier layers formed during oxygen annealing were at least moderately conductive for the cases of M=Ir on silicon and M=Ir or Pt on WSi2.8(300 nm)/Si, a prerequisite for the use of these electrode barrier structures in high-density dynamic random access memory.

RBS characterization of iridium silicides formed by RTA in vacuum

The growth kinetics of the iridium silicides, IrSi, IrSi 1.75 and IrSi 3, formed by RTA in vacuum has been characterized, by RBS, as a function of the annealing temperature and time for Ir films of different thicknesses. To ensure an accurate temperature measurement and control during the annealing, the sample temperature was calibrated by evaluating the recrystallization rates in vacuum of amorphized (100) silicon in the same RTA system. IrSi and IrSi 1.75 were the only compounds formed for temperatures up to 675°C. Both phases grow simultaneously and coexist with the Ir metal. RBS spectra show wide intermixing regions between the different phases. Kinetics of silicide formation is independent of the as deposited Ir film thickness as long as unreacted Ir remains in the film. However, when the annealing time is long enough to convert all the Ir metal into silicide, the IrSi 1.75 continues growing at the expense of the IrSi phase that shrinks and even disappears. IrSi 3 phase starts to be formed at 920°C, coexisting with the IrSi 1.75 phase. For temperatures higher than 950°C only the IrSi 3 phase was present.

SIMS characterization of thin layers of IR and its silicides

To apply Secondary Ion Mass Spectrometry (SIMS) to the characterization of very thin films one needs to quantify the ionic intensity signals in non-steady-state conditions, that is, when the bombardment induced atomic mixing layer is not yet completely developed. Unfortunately, there is not enough information available about the complex stabilization processes taking place when analyzing thin films of iridium silicides by SIMS. We present data for the quantitation of SIMS signals taken from these silicides and the process that we have followed to obtain and to apply them. We begin with the characterization of thick silicide layers paying special attention to the signal behavior at their interfaces, and proceed to thinner layers. Some effects related to the presence of native intermixing layers are also shown.

Comparison between furnace and rapid thermal annealed iridium silicide Schottky barrier diodes

AbstractIridium silicide Schottky barrier diodes fabricated by low temperature rapid thermal annealing (R TA) either in vacuum or in an argon atmosphere are investigated. A comparison with furnace annealed diodes is made in terms of their electrical characteristics. An ideality index close to unity has been obtained. Measured values of Schottky barrier height were close to that reported for Ir1Si1/n type silicon diodes. An increase in series resistance with annealing time is detected for diodes fabricated in the gas atmosphere by either furnace annealing or RTA: this effect seems to be related to oxygen diffusion through the iridium layer. The effect of atmosphere control on the grown material is also significant: silicidation and a phase change from Ir1 Si1 to Ir1 Si1-75 occur at lower temperatures when the reaction atmospheres contain a lower oxygen concentration. Complete silicidation to Ir1Si1 is obtainedfor all the 400°C RTA samples, but temperatures above 450°C are required for open tube furna...

Iridium Silicides Formed by RTA in Vacuum

AbstractThe growth kinetics of the iridium silicides, IrSi and IrSi1.75 formed by RTA in vacuum has been characterized as a function of the processing temperature, up to 675°C, and annealing time for iridium films of different thickness. The sample temperature was measured using as a reference the SPE growth rate of amorphized silicon processed in the same RTA conditions. The samples were characterized by RBS, HREM, XRD and microdiffraction. RBS spectra show that the transition region between IrSi and IrSi1.75 is slightly gradual, while the interface between the IrSi and the iridium metal is sharp. The layer thickness of each silicide as a function of temperature and time was obtained from the RBS spectra. The activation energy of the diffusion coeficient of Si in IrSi and IrSi1.75 are about 1.3 eV and 3.9 eV respectively. Phase kinetics are the same for both thin and thick samples processed at the same temperature and annealing time when unreacted iridium remains in the film. However, the phase evolution is different when the annealing time is long enough to convert all the iridium metal into silicide in the thin film sample but not in the thick one. In this case, IrSil.75 is the only phase found if the annealing time is long enough. Silicides formed at 525°C consist mainly of polycrystalline IrSi, with grain size between 3 and 10 nm, and some isolated grains of IrSi 1.75. The interface between the IrSi and the Si is flat, very sharp, and well oriented grains grow from it. In order to avoid the IrSi1 75 formation and to obtain IrSi layers at reasonable rates, an RTA process at 500°C is proposed.

Polycrystalline Iridium Silicide Films. Phase Formation, Electrical and Optical Properties

Electrical and optical properties of thin IrxSi1−x films are investigated in the composition range 0.25 ≦ x ≦ 0.55 in dependence on the crystallization stage. The films are prepared by dc-magnetron codeposition and annealed at temperatures between 400 and 1170 K. The X-ray diffraction measurements show phase formation sequences in dependence on annealing which are in general agreement with the phase diagram of Ir-Si bulk material. According to the dominant phases (IrSi, Ir4Si5, Ir3Si5, and IrSi3 with decreasing x) films are obtained with metallic or semiconducting properties. Films with the semiconducting compound Ir3Si5 as main phase show a large thermopower only in a small composition range depending on grain size. The optical gap of Ir3Si5 is determined by absorption measurements to be 1.56 eV. Es werden elektrische und optische Eigenschaften dunner IrxSi1−x-Schichten in Abhangigkeit vom Kristallisationsgrad und im Bereich 0.25 ≦ x ≦ 0,55 untersucht. Die Schichten werden durch DC-Magnetron-Codeposition hergestellt und einer Warmebehandlung zwischen 400 und 1170 K unterzogen, was zu einer schrittweisen Bildung von Silizidphasen fuhrt. Die mittels Rontgenbeugung untersuchte Phasenbildung entspricht generell dem Phasendiagramm von Ir-Si-Volumenmaterial. Abhangig von der jeweils dominierenden Verbindung (IrSi, Ir4Si5, Ir3Si5 bzw. IrSi3 mit abnehmendem x) wird metallisches oder halbleitendes Verhalten beobachtet. Schichten, in denen das halbleitende Silizid Ir3Si5 dominiert, zeigen nur in einem engen Bereich der Zusammensetzung hohe Thermokrafte, die ihrerseits von der Ir3Si5-Korngroβe abhangen. Das optische Gap von Ir3Si5 wurde mittels Absorption zu Eg = 1,56 eV neu bestimmt.

Determination of iridium silicides using matrix effects in SIMS

Secondary Ion Mass Spectrometry (SIMS) matrix effects can serve as a way of showing stoichiometric changes in thin iridium silicide layers. In this work iridium relative emission from several iridium silicides has been established. Layers were formed by Rapid Thermal Annealing (RTA) of Ir on Si. Quantification of relative Ir emission and sputtering rates at several energies has been carried out in a group of samples with annealed 240 nm deposited Ir. Ir 1Si 1 and Ir 1Si 1.75 phases were identified by Rutherford Backscattering Spectroscopy (RBS) and X-ray Diffraction (XRD) analysis. Ir + emissions from each phase up to 10 and 5 times the Ir + emission from pure Ir were found. Results are applied to the depth profile of thin Ir layers (< 20 nm as deposited) processed under several conditions.

Infrared optical absorption of iridium silicide films on silicon

Optical constants and absorption data of thin iridium silicide films on silicon substrates are presented for incident light between 4 and 11 μm. The data were obtained from reflection and transmission measurements made on samples with IrSi thicknesses from 8 to 350 Å. The optical constants n and k are those that best fit the reflection and transmission data over the wavelength and thickness ranges.

Epitaxial iridium silicide formation during deposition of Ir on Si(100) at high temperature under ultrahigh vacuum

The iridium silicide formation has been examined by depositing Ir on Si(100) at different substrate temperatures under ultrahigh vacuum. An epitaxial Ir3Si4 film was formed when an Ir film of 100 Å was directly deposited on Si(100) at 475 °C and annealed at the same temperature for 1.5 h. The Ir3Si4 was not observed in the conventional annealing process at 475 °C. In contrast, a polycrystalline IrSi film was formed after deposition of an Ir film of 100 Å on Si(100) at room temperature and followed by annealing at 475 °C for 1.5 h under ultrahigh vacuum. Formation of the epitaxial Ir3Si4 on Si(100) is attributed to the interfacial energy of the Ir3Si4/Si(100) interface.

Growth and structure of IrSi3 on Si(111)

Molecular-beam epitaxy has been used to grow films that are almost entirely IrSi3 by codeposition of Si and Ir in a 3:1 ratio on Si(111) substrates. Bragg–Brentano and Seemann–Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 490 °C, the lowest temperature yet reported for growth of this iridium silicide phase. Above 580 °C this hexagonal phase becomes textured, with as many as seven preferred growth orientations on Si(111). Samples codeposited on Si(111) between 680 and 780 °C consist almost entirely of IrSi3 with its c axis perpendicular to the substrate’s surface. At higher substrate temperatures, near 830 °C growth of IrSi3 with its c axis in the plane of the substrate dominates. Atomic force microscopy shows that there is a difference in the surface morphology of the c-axis in-plane and perpendicular growth modes. Transmission electron microscope diffraction and in situ low-energy electron diffraction verify that both of these IrSi3 growth modes are epitaxially registered with their substrates. To check the quality of this epitaxy ion-beam channeling and x-ray rocking curves were used. The data from the epitaxial samples have channeling χmin ratios as low as 0.64. The x-ray rocking curves for these IrSi3 films are narrow, with full-width-at- half-maxima of as little as 0.07°.

Iridium Silicide Formation by Rapid Thermal Annealing

AbstractIridium silicides formation by rapid thermal annealing (RTA) under vacuum at several temperatures in the range of 350 to 650°C has been investigated. The substrates and the silicide films were analyzed by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). At 350°C, no distinguishable phase was detected for 240 seconds of annealing time. At 400°C, for processing time up to 45 seconds only Ir1Si1 was formed, for longer processing time Ir1Si1.75 was formed too. At higher temperatures even for very short processing time, Ir1Si1.75 was formed. Ir, Ir1Si1 and Ir1Si1.75 were present simultaneously if the iridium film was thick enough and the processing time was long enough too. For thin iridium layers, the Ir1Si1 formed was totally converted to Ir1Si1.75, if the annealing time was long enough. Formation rates were observed to be three to five orders of magnitude faster than the reported for furnace annealing.

Influence of Oxygen on the Iridium Silicide Formation by Rapid Thermal Annealing

AbstractIridium silicide formation by rapid thermal annealing (RTA) in an Ar atmosphere or under vacuum has been investigated. The evolution of the silicide front and the identification of the phases were monitored by Auger Electron Spectroscopy (AES) and Rutherford Backscattering Spectrometry (RBS). Oxygen was incorporated during the RTA process in an Ar atmosphere. The oxygen effect is to slow down the silicide formation and eventually to stop it. In all the cases, the oxygen piled-up at the iridium-iridium silicide interface. No distinguishable phase was formed by RTA in an Ar atmosphere. No oxygen contarsi'nation was detected when the RTA was performed under a vacuum lower than 2×10−5 Torr. In this case Ir1Si1 and Ir1Si1.75 phases were formed.

Growth of MBE-Codeposited IrSi3 on Si(111) and Si(100)

AbstractWe have used Molecular Beam Epitaxy (MBE) to successfully grow films that are predominantly IrSi3 on both Si(111) and Si(100) substrates by codeposition of Si and Ir in a 3:1 ratio. Bragg-Brentano and Seemann-Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 450 °C. This is the lowest temperature yet reported for growth of this iridium silicide phase. These x-ray diffraction techniques, along with Transmission Electron Microscope (TEM) diffraction and in situ Low Energy Electron Diffraction (LEED), show that at higher deposition temperatures codeposition can form IrSi3 films on Si(111) that consist predominantly of a single epitaxial growth orientation. Ion beam channeling and x-ray rocking curves show that the epitaxial quality of IrSi3 films deposited on Si(111) is superior to that of IrSi3 films deposited on Si(100). We also present evidence for several new epitaxial IrSi3 growth modes on Si(111) and Si(100).

Iridium silicides obtained by rapid thermal annealing

Iridium silicides formation by RTA in an Ar atmosphere or under vacuum has been studied for several temperatures in the range of 350–500°C. For the samples annealed in argon atmosphere, oxygen is incorporated during the RTA process, slowing down the reaction at the interface or even stopping it. In this case, no clear compound, Ir 1Si 1 or Ir 1Si 1.75, could be identified neither from the RBS spectra nor from the AES profiles. On the other hand, when the anneal is performed under vacuum, silicidation takes place. In samples processed at 400°C in these conditions and processing time shorter than 45 s only the Ir 1Si 1 compound was formed. For longer annealing time, Ir 1Si 1.75 appeared too. At higher temperatures, even for very short processing time, Ir 1Si 1.75 was formed.