PtSi Films Research Articles

Beem and UHV-TEM Studies of PtSi/Si(001)

AbstractRecent work using ballistic electron emission microscopy (BEEM) and ultra-high vacuum transmission electron microscopy (UHV-TEM) to study structure-property correlations of PtSi/Si(001) contacts is described. The spatial uniformity of the Schottky barrier height (SBH) for diodes grown at room temperature and 350°C was compared with the interface microstructure using TEM. Narrow SBH distributions with standard deviations of 7–12 meV were obtained independent of the deposition system and temperature. Analysis of the distributions compared well with standard current-voltage and capacitance-voltage measurements on the same diode. These low temperature depositions produced fine grained PtSi films (10–20 nm) with an interface roughness dependent on the cleaning process. Probable orientation effects on the SBH distribution were apparently screened out because of the low doping of the substrates that were used. As the deposition temperature is increased the PtSi tends towards polycrystalline epitaxy with island growth beginning at 700°C. Grains are rectangular and develop a large shape anisotropy of great interest for future investigations.

Process Windows of Nickel and Platinum Silicides in Deep Sub-Micron Regime

AbstractIt has been observed that the sheet resistance of a Ti-salicided polysilicon-gate electrode or source/drain region increases significantly as the dimension reaches the lower sub-micron range. The resistance of platinum and nickel silicide (PtSi and NiSi), however, does not increase with reduced linewidth. We have studied PtSi and NiSi films with deep sub-micron linewidths on single crystal or poly-Si substrates. In this study, the material properties such as sheet resistance, grain structure and surface morphology of these silicide films in confined geometries are reviewed and compared with TiSi2. Process windows for forming and maintaining these silicides are explored.

Characterization of Ultra-Thin PtSi Films for Infrared Detectors

AbstractTransmission electron microscopy and grazing incidence X-ray diffraction are used for the structural characterization of ultra-thin PtSi layers on (100) silicon prepared by a two-step rapid thermal annealing process. The roughness of the layers is investigated with atomic force microscopy. Two deposition techniques for the initial Pt layer are compared.

Thickness dependence of the properties and thermal stability of PtSi films

The phase growth sequence, structural, electrical and optical properties and thermal stability of platinum silicide films were investigated as a function of silicide film thickness in the range 133–2506 Å. The platinum silicide films were formed by ex situ silicidation of Pt films sputter-deposited onto n--Si (100) substrates. Films of all thickness were polycrystalline but exhibited columnar growth morphology and strong orientation effects. The orientation, grain size, electrical resistivity, specular reflectance and thermal stability were observed to be strongly thickness dependent. The temperature at which the film properties degraded increased with film thickness. The degradation mechanism appeared to be Pt diffusion into Si accompanied by the disintegration of the PtSi layer and the formation of an additional Pt3Si phase.

Superconductivity in PtSi ultrathin films

Normal and superconducting properties of PtSi films with thicknesses of d=2–20 nm have been investigated. The superconducting transition has been observed on the thin films down to d=4 nm. The systematic reduction of the transition temperature with decreasing d (increasing the sheet resistance) has been explained by the localization and Coulomb interaction effects on superconductivity. The temperature dependence of the upper critical field indicates that the PtSi films behave as homogeneous superconductors.

Epitaxial orientation of PtSi grown by Pt deposition on heated Si(001) substrate

PtSi film epitaxial orientation and morphology depend greatly on the Si(001) substrate temperature during Pt deposition. 15 nm Pt films were evaporated on the heated substrate in room-temperature to the 1100 K range. The PtSi on the Si substrate forms a continuous film below 850 K and forms islands at above 920 K. In the entire heated range, except for around 1000 K, the dominant epitaxial orientation is PtSi(11̄0)‖‖Si(001) (A orientation). At around 1000 K, the dominant orientation is PtSi(12̄1)‖‖Si(001) (called B orientation). In the range from 920 to 950 K, B orientation grains partially exist in the predominant A orientation. Below 1000 K, the predominant factor governing the epitaxial orientation is area mismatch, which is the difference between the PtSi and Si superlattice areas at the interface. The predominantly A-oriented grains observed at above 1050 K can be explained by the superlattice area mismatch concept.

AES-depth-profiling of thin annealed Pt-films on Si(100)

Thin PtSi films can be grown by evaporating Pt on Si(100) at RT and subsequent annealing of the system at 600–700 K. Contaminants like oxygen are known to have a strong influence on this reaction. In the present study we concentrate on the effect of oxygen partial pressure during the annealing on the silicide growth process. Under proper vacuum conditions annealing at 500 K leads to a homogeneous Pt2Si film which reacts around 600 K completely to PtSi. A substantial oxygen partial pressure (≈ 0.1 mbar) in contrast results in an incomplete reaction in the same temperature range: unreacted platinum remains at the surface separated from the silicide by an oxygen enriched layer.

A silicon homojunction infrared detector having an active metal film on an n/sup ++/ layer

A silicon n/sup ++/pn homojunction infrared detector, in which a degenerate n/sup ++/ layer is backed by a metal film forming an ohmic contact, has been proposed and studied. The metal film is a photoelectric conversion region along with the n/sup ++/ layer. Although, for an n/sup ++/pn detector without the metal film, very poor rectifying properties are observed when the n/sup ++/ layer thickness is extremely reduced, the new detector, employing a thin PtSi film as the metal film, shows normal diode I-V characteristics, since the PtSi film provides increased surface conductivity. The new detector has achieved an increase in operatable temperature, or an extension of cutoff wavelength, and operated with cutoff wavelengths of 11.9 /spl mu/m, 18.7 /spl mu/m and about 30 /spl mu/m at 70 K, 50 K, and 30 K, respectively, because the saturation current density for the new detector has been reduced to about one tenth that for the previously reported n/sup ++/pn detector. The responsivity for the new detector has increased to 1.1-3.8 times as large as that for the previously reported n/sup ++/pn detector, when both detectors have the same cutoff wavelength. >

Hot-carrier scattering in a metal: A ballistic-electron-emission microscopy investigation on PtSi

Ballistic-electron-emission microscopy (BEEM) has been used to study the PtSi/n-type Si(100) interface. Hot-electron transport has been investigated by measuring the ballistic-electron transmission as a function of position (BEEM imaging), energy (BEEM spectroscopy), and PtSi thickness (BEEM attenuation length). Hot-hole transport and electron-electron scattering have also been investigated as a function of these parameters. This study has been conducted on in situ fabricated PtSi/n-type Si(100) Schottky diodes in UHV with the silicide thickness ranging from 20 to 500 \AA{}. The PtSi films were granular and the BEEM transmissivity was found to be homogeneous on individual grains but strongly varying from one grain to another. We attempt to compare the absolute BEEM current level with existing models and find its limiting value for small silicide thicknesses to be close to 1 depending on the model considered, indicating efficient transmission due to strong forward focusing of the electrons in the base or enhancement due to multiple scattering within the grains. BEEM current as a function of silicide thickness shows a change from a rapid to a slower decrease at about 150 \AA{}. Reverse BEEM (RBEEM) attenuation lengths also show this qualitative behavior, but the attenuation with increasing PtSi thickness is distinctly weaker, indicating that BEEM and RBEEM intensities are differently influenced by the elastic and inelastic hot-carrier mean free paths. RBEEM spectra are found to be anomalous, indicating an anomalous distribution of the tunnel-injected hot holes in the base.

Measuring the opaque substrate temperature by infrared laser beams : Y. H. Shen and Z. J. Xing. Vacuum43(11), 1079 (1992)

Platinum silicide thin films formed via solid–solid reaction of Pt–Si interfaces play an important role as interconnects in microelectronics. This “self-aligned” silicide formation, however, is diffusion-limited and only Pt2Si and PtSi phases form. Also, their usefulness in electronic applications at high temperatures is limited due to agglomeration effects. Here, e-beam co-evaporation is presented as a means of fabricating well-defined films of Pt3Si as well as the Pt2Si and PtSi phases familiar to conventional, self-aligned silicide technology. Pt–Si films with a range of compositions (silicon atomic fractions of XSi = 0.00–0.77) were grown on r-sapphire substrates by co-deposition of independently controlled Pt and Si evaporant fluxes at 400 °C. Phase, morphology, and electronic properties were analyzed upon deposition and after vacuum annealing for 48 h at 1000 °C. As-deposited films with XSi < 0.70 are polycrystalline and at higher Si concentrations are fully amorphous. Valence spectra from Pt, Pt2Si, and PtSi films confirm previous reports and a valence spectrum is presented for the stoichiometric Pt3Si phase; these data provide experimental support for recently proposed revisions to the standard transition metal–silicon bonding model. As-deposited films, nominally 200 nm thick, are electrically conductive in the range 0.1–4.0 × 106 S/m and remain so after vacuum annealing for 48 h at 1000 °C. The phase, morphological, and electrical stabilities are attributed to the finely grained as-deposited morphologies of co-evaporated Pt silicide films, which hinder agglomeration at 1000 °C for much greater times than do morphologies of traditional, self-aligned silicides grown via solid-state reaction.

Stability of Silicide Films Under Post-Annealing: a Dopant Effect

AbstractThe formation of PtSi films by rapid thermal processing of e-beam evaporated Pt on &lt;100&gt; Si has been studied. The current study found that PtSi films have the potentially useful property of oxidizing, i.e., forming a surface layer of Si02 which may be useful for patterning. Rapid oxide formation is found with, possibly, linear growth rates when the film is doped with As to 8E15 atoms/cm2 at 80 KeV but insignificant oxidation if the film is undoped or B-doped. Rutherford backscattering analysis shows significant redistribution of the As during silicidation and oxidation with As excluded from the silicide, diffusing to the oxide and especially the oxide surface. Post-silicidation anneals have been done in a conventional tube furnace at 650ºC for up to 60 minutes and form an oxide thickness of up to 200 nm. NiSi films appear stable if Bdoped, oxidize with Ni piling up at the Si02/Si interface if undoped, and are unstable with Ni diffusing deep into the Si if As-doped.

Interactions of Cu with PtSi and TiSi2 with and without Como Barrier Layers

ABSTRACTInteractions of Cu with PtSi and TiSi2 films grown on Si (100) substrates have been studied in the temperature range of 250-500°C with Rutherfold backscattering spectrometry, Auger electron spectrometry, and x-ray diffraction. Upon annealing Cu migrates across the intermediate PtSi or TiSi2 layers and reacts with Si substrates to form Cu silicides. Unlike what were reported in the literature, no indications of the reaction of Cu with PtSi or TiSi2 have been observed. Both PtSi and TiSi2 retain their original thicknesses and compositions during Cu penetration. The structural integrity of the metal suicides in contact with Cu films is attributed to low formation energies of Cu-silicides. A 50-nm thick amorphous CoMo barrier impedes Cu diffusion up to 550°C, but fails as a diffusion barrier at higher temperatures due to CoMo-Si reaction.

Microstructure Analysis of Agglomerated Epitaxial Columns of Si/PtSi/Si(111) Double Heterostructure

ABSTRACTMicro structures and interface structures of epitaxially grown PtSi and over-capping Si films on Si(111) substrates prepared by MBE were studied by RHEED, HREM, SEM and XRD. An epitaxially grown Si layer on the PtSi layer, which was fabricated by coevaporation of Pt and Si with the stoichiometric ratio (Pt/Si=l/1), was obtained as a Si(111)/PtSi(010)/Si(111) double heterostructure at the substrate temperature of 400°C. On the other hand, it was found that the PtSi layer transformed into epitaxial columns and/or walls when a Si over-capping layer was grown on the PtSi layer at a substrate temperature of 600°C or higher. These columns and/or walls were surrounded by a Si matrix which showed epitaxial relations to the Si substrate with stacking faults.

Infrared absorption and carrier generation in very thin PtSi film on p-type Si crystal

Abstract From the measurement of infrared transmittance and refractance for very thin platinum silicide films on a silicon substrate, the absorption coefficient of the PtSi films was examined. The coefficients at wavelengths of 3.0 and 6.0 μm depend on the film thickness, and increase strongly in the ultra-thin region. When the sample was cooled at liquid nitrogen temperature and a low positive potential applied to the PtSi film, a small photocurrent was observed by infrared irradiation with a wavelength below 4.6 μm. The height of the infrared responsivity on the PtSi-Si (p-type) structure is related to its infrared absorption. The generation of electrons and holes in the PtSi film occurs by incident photons and a part of holes drifts to the PtSi-Si interface which has the Schottky barrier with an estimated height 0.27 eV by the photo-response.

Heteroepitaxy of PtSi/SiGe on Si(100) by dual electron gun co-deposition at high temperatures

Co-deposition of both PtSi and SiGe layers on a p-Si(100) substrate has been performed at high temperatures in a dual electron gun deposition chamber at a base pressure of 10 -10 Torr. Reflection high energy electron diffraction, transmission electron microscope, and X-ray diffraction have been used in characterizing the epitaxial film. The PtSi/SiGe film co-deposited at a substrate temperature of 450°C had four types of epitaxial modes. Two of them were the same as the epitaxial modes for the PtSi film formed by depositing Pt on Si with sequential annealing. The other two epitaxial modes were observed in the PtSi/SiGe/p- Si(100) for the first time. The PtSi film co-deposited at 550°C showed polycrystalline structures, corresponding to three-dimensional island growth.

Infrared photoemission of holes from ultrathin (3?20 nm) Pt/Ir-compound silicide films into silicon

The infrared responsivity is measured at low temperature on Schottky barrier detectors having ultrathin (3–20 nm) PtSi, IrSi, and compound silicide films as a metal electrode on p-type silicon. The total yield for internal hole photoemission is 1% per incident photon for PtSi and 0.1% for IrSi at a wavelength of λ=4 μm. The cut-of wavelengths are λ=5.4 μm and λ=8.2 μm for PtSi and IrSi, respectively. The compound silicides fabricated by sequential evaporation of Pt and Ir and subsequent annealing at T=450° C show characteristics identical to that of PtSi.

Infra-red surface plasmons on platinum silicide

It is shown that surface plasmons (SPs) are supported on thin PtSi films. Using a prism-air gap-sample configuration, p-polarised infra-red light (3.39 μm) has been coupled with ̃95% efficiency to SPs on the silicide electrode of PtSi-Si Schottky barrier structures. Stimulating SPs offers both a means of optically characterising silicide films and of enhancing optical absorption with a view to significantly increasing the Schottky barrier photoresponse.

Formation of PtSi-contacted p+n shallow junctions by BF+2 implantation and low-temperature furnace annealing

This work investigates the characteristics of PtSi-silicided p+n shallow junctions fabricated by implanting BF+2 ions into either the Pt/Si (ITM scheme) or the PtSi/Si (ITS scheme) structure followed by annealing in N2 furnace at temperatures from 650 to 800 °C. For a structure with Pt film of 30 nm thickness or PtSi film of 60 nm thickness, the implantation energy ranges from 40 to 80 keV with a dose ranging from 1×1015 to 1×1016 cm−2. For the ITS samples with BF+2 implantation at 40 keV, all ions are confined in the PtSi layer; therefore, only a modified Schottky junction is formed by the diffusion of boron atoms from the PtSi film during the annealing. The junction depth may be as shallow as 30 nm from the PtSi/Si interface. A complete p+n junction is formed for the ITM samples with implantation at 40 keV as well as all the samples implanted at 80 keV. The junction thus obtained has a forward ideality factor lower than 1.02 and a reverse current density less than 0.2 nA/cm2 at −5 V. Activation energy measurement indicates that most of the implantation damages have been recovered after annealing at a temperature as low as 700 °C. The reverse area and peripheral leakage current density are separated by measuring diodes of different perimeter/area ratio. For good samples, the reverse peripheral current comes from the surface generation current within the depletion region underneath the field oxide. All of the experimental results reveal that either Pt or PtSi film can be employed as an efficient barrier film in the ITM/ITS technique to form excellent and ultrashallow junctions with a low thermal budget.

Formation and characterization of a PtSi contacted n+p shallow junction

Ion implantation through metal (ITM) or metal silicide (ITS) appears to be an attractive technique for self-aligned silicided shallow junction formation. Since most of the implanted ions are confined in the barrier film, the damage generated in the silicon substrate is reduced and so is the required post-implant annealing temperature. The purpose of this work is to study the capability of using Pt and PtSi in the ITM/ITS technique. As+ ions were implanted through 30-nm Pt or 60-nm PtSi at 80 keV with doses ranging from 1×1015 to 1×1016 cm−2. The implanted samples were annealed from 650 to 800 °C. Junction depths measured by spreading resistance and secondary-ion mass spectroscopy on 750 °C annealed samples are about 0.11 and 0.13 μm for the ITS and ITM schemes, respectively. The reverse area and peripheral leakage current density (JRA and JRP) are separated by measuring diodes of different size. All samples with a dose of 1×1015 cm−2 failed due to an insufficient amount of dopants which were incorporated into Si. For a dosage greater than 5×1015 cm−2, the JRA at −5 V is less than 0.2 nA/cm2 and the forward ideality factor is lower than 1.02 for the ITS samples annealed at 750 °C. Activation energy measurement shows that the JRA is diffusion-component dominated while the JRP is generation-component dominated at room temperature. Surface generation current and lateral implantation damage-induced current are examined and discussed in detail. A possible reason is that the lateral junction depth is less than the vertical junction depth and the depletion region may be extended to near the PtSi/Si interface. Annealing at 800 °C degrades the junction characteristics because the Pt from PtSi diffuses into the junction region. Based on the experimental results and analysis we conclude that either Pt or PtSi film can be employed as an efficient barrier film in the ITM/ITS technique. A high-quality and ultrashallow junction can be fabricated using furnace annealing at temperature as low as 750 °C. The peripheral current generated at the silicide/silicon interface dominates the reverse junction current and cannot be avoided for the silicided junction with a junction depth less than 50 nm from the interface. This factor acts as a physical limitation as the junction depth scales down.

High-temperature stability of platinum silicide associated with fluorine implantation

High-temperature stability of the F+- or BF+2 -implanted PtSi thin film was investigated. For the PtSi films that received F+ implantation, the film characteristics remain unchanged even after annealing at 800 °C for 90 min, while for those without F+ implantation, the film properties begin to degrade after annealing at 750 °C as observed by scanning electron microscopic inspection, Auger electron spectroscopy analysis, Rutherford backscattering spectroscopy analysis, and sheet resistance measurement. The secondary ion mass spectroscopy analysis indicates that the fluorine atoms are segregated to the PtSi/Si interface. A fluorine barrier model is proposed to explain the absence of Pt in-diffusion induced deterioration for the F+-implanted PtSi film.