PtSi Formation Research Articles

Self-aligned formation of superconducting sub-5 nm PtSi films

Platinum silicide (PtSi) presents a promising superconductor for achieving silicon-based Josephson field-effect transistors (JoFETs). In a viable process flow to realize self-aligned PtSi formation, thermal oxidation at 600 °C is required to form a protective oxide layer on the surface of the as-formed PtSi selectively against Pt to facilitate subsequent selective etch in aqua regia. However, sub-10 nm PtSi films tend to agglomerate and even break into discrete PtSi islands upon thermal treatments above 500 °C. To achieve nanoscale JoFETs, we have developed a simple alternative with chemical oxidation at room temperature leading to the formation of homogeneous sub-5 nm PtSi films. The critical temperature of the resultant superconducting PtSi films is found to increase from 0.66 to 0.90 K when the PtSi thickness is raised from 3.1 to 12.7 nm, while, concurrently, the PtSi grains grow larger in thicker films. The critical temperature also increases from 0.53 to 0.66 K for the 3.1 nm PtSi film when the formation temperature is raised from 400 to 500 °C.

Raman spectroscopy of silicon, doped with platinum and irradiated by protons

In this work, the influence of proton irradiation and platinum impurities on the crystal structure of silicon samples was studied by Raman spectroscopy. It has been established that the doping of single crystals of Si with platinum leads to minor changes and the appearance of new vibrations in the Raman spectra. The intensity of the main silicon peak at 521 cm–1 decreases by a factor of 1.6, while its FWHM practically does not change and is about 4.0 cm–1. Such a decrease in the intensity of the peak is probably due to the weakening and breaking of bonds in the structure of the silicon crystal lattice due to the diffusion of Pt. It is shown that the appearance of new vibrations in the range 60–280 cm–1 in the spectra of Si<Pt> is associated with the presence of elemental Pt and the formation of PtSi. It has been found that irradiation of Si<Pt> samples with 600 keV protons leads to a change in the Raman spectra, and the peaks from Pt and/or PtSi disappear.

Athermal Solid Phase Reaction in Pt/SiO x Thin Films Induced by Electron Irradiation.

Microelectronics based on Si requires metal silicide contacts. The ability to form platinum silicide (Pt2Si) by electronic excitation instead of thermal processes would benefit the field. We studied the effects of electron irradiation on Pt2Si formation in composite films—composed of Pt and amorphous silicon oxides (a-SiOx)—by transmission electron microscopy and electron diffraction. Pt2Si formed in Pt/a-SiOx bilayer and a-SiOx/Pt/a-SiOx sandwiched films by 75 keV electron irradiation, at 298 and 90 K. The reaction is attributable to dissociation of SiOx triggered by electronic excitation. In a-SiOx/Pt/a-SiOx sandwiched films, reflections of pure Pt were not present after irradiation, i.e., Pt was completely consumed in the reaction to form Pt2Si at 298 K. However, in Pt/a-SiOx bilayer films, unreacted Pt remained under the same irradiation conditions. Thus, it can be said that the extent of the interfacial area is the predominant factor in Pt2Si formation. The morphology of Pt islands extensively changed during Pt2Si formation even at 90 K. Coalescence and growth of metallic particles (Pt and Pt–Si) are not due to thermal effects during electron irradiation but to athermal processes accompanied by silicide formation. To maintain the reaction interface between metallic particles and the dissociation product (i.e., Si atoms) by electronic excitation, a considerable concomitant morphology change occurs. Elemental analysis indicates that the decrease in Si concentration near Pt is faster than the decrease in O concentration, suggesting formation of a Si depletion zone in the amorphous silicon oxide matrix associated with formation of Pt2Si.

In situ atomic-level observation of the formation of platinum silicide at platinum-silicon oxide interfaces under electron irradiation

In situ atomic-level observation of the formation of Pt2Si at Pt/SiOx interface by electronic excitation under electron irradiation was performed by using scanning transmission electron microscopy. Scanning of an electron-beam probe stimulates silicide formation at the Pt/SiOx interface; the change in the Pt column corresponding to Pt2Si formation with a crystallographic orientation of (001)Pt//(001)Pt2Si and [110]Pt//[110]Pt2Si was observed in high-angle annular dark-field images.

Self-assembled patches in PtSi/n-Si (111) diodes

Using the effect of the temperature on the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of PtSi/n-Si (111) Schottky diodes the profile of apparent doping concentration (NDapp), the potential difference between the Fermi energy level and the bottom of the conduction band (Vn), apparent barrier height (ΦBapp), series resistance (Rs) and the interface state density Nss have been investigated. From the temperature dependence of (C–V) it was found that these parameters are non-uniformly changed with increasing temperature in a wide temperature range of 79–360 K. The voltage and temperature dependences of apparent carrier distribution we attributed to the existence of self-assembled patches similar the quantum wells, which formed due to the process of PtSi formation on semiconductor and the presence of hexagonal voids of Si (111).

Spatially-resolved spectroscopic investigations on the formation of PtSi by annealing on a silicon surface

We report spatially-resolved spectroscopic investigations on the effect of annealing a Pt (100Å)/Si interface in the presence of a native silicon oxide layer. Scanning photoelectron microscopy showed a spatially non-uniform growth pattern of PtSi depending on the annealing temperature and annealing time. Pt 4f and Si 2p core-level spectra measured using different photon energies and at different points suggest both in-plane and out-of-plane inhomogeneous growth of PtSi at 773K.

Pt co-catalyst effect on photoelectrochemical properties of 3C-SiC photo-anode

The effect of Pt co-catalyst fabricated with various annealing temperatures on photoelectrochemical (PEC) properties of 3C-SiC photo-anode was investigated. 3C-SiC with Pt co-catalyst shows the greater PEC reaction compared with bare 3C-SiC. A further enhancement is found by annealing process due to the Pt particle structure and enhanced contact of 3C-SiC and Pt. The formation of Pt particles improves the PEC reaction of samples annealed at 500 and 700 °C. Here, 3C-SiC with the Pt annealed at 500 °C shows the largest photocurrent, 3.47 mA/cm2 at an applied bias of 1 V (vs Ag/AgCl) and the lowest onset potential, 0.74 V with the optimum particle size. It is also considered to have appropriate contact by the proper Pt2Si formation, revealed by X-ray photoelectron microscopy. Although photocurrent is improved after anneal at 700 °C, the onset potential becomes almost same as bare 3C-SiC. Furthermore, the photo-activity after anneal at 900 °C is even degraded compared to the bare 3C-SiC because of the evolution of immoderate carbon compounds suppressing Pt co-catalyst effect.

Formation of Pt silicide on doped Si: Kinetics and stress

In situ experiments based on X-ray diffraction, sheet resistance and differential scanning calorimetry were performed on Pt thin films deposited on Si either undoped or doped with As (n type) or B (p type). In all cases, these measurements show a sequential formation of Pt2Si followed by PtSi phases. Simulations of the kinetics show that the growth is controlled by both the interface and the diffusion through the growing silicide. A slowdown of the formation of Pt2Si has been observed at the end of Pt consumption; this might be due to the accumulation of impurities in the Pt film. The in situ measurements show a delay between the end of the growth of Pt2Si and the formation of PtSi that is related to the strain relaxation in Pt2Si: i.e. the growth of PtSi starts when most of the strain in Pt2Si is relaxed. Anisotropy in the magnitude of strain value and gradient was found for two grain orientations of Pt2Si. The dopants (B and As) do not significantly influence the silicide formation properties (phase sequence, strain and sheet resistance). Boron addition has almost no influence on the formation kinetics while Arsenic slightly slows it down. The sheet resistance of Pt2Si is lower than that of PtSi, which remains stable until 800°C.

Interfacial structure of ferromagnetic Fe-Pt thin films grown on a Si substrate

In order to understand the Fe-Pt phase transformation, Fe-Pt films were sputtered on HF-treated, untreated Si substrates, and SiO 2 substrates and the magnetic and structural properties were analyzed by XRD, VSM, and XPS. The formation of Pt 2Si on the interface between Fe-Pt films and a Si substrate could be clearly observed with a shift of Pt4f 7/2 binding energy. Native oxide on the surface of Si substrate slowed the transformation of the disordered Fe-Pt phase to the ordered phase. The Pt 2Si phase was easily formed during sputtering on an HF treated Si substrate; moreover, a formation of a very small amount of Pt 2Si phase could be observed on the interface of Fe-Pt films and a SiO 2 substrate. Thus, the formation of Pt silicide assumes an important role in the transformation of Fe-Pt films grown on Si substrates.

The thermal stability of Pt/Ir coated AFM tips for resistive switching measurements

Abstract In this paper, we focus on the thermally treated atomic force microscope tips used in the investigation of the resistive switching phenomenon. Since the resistive switching phenomenon is often connected with the red-ox process, it is crucial to investigate the influence of oxidizing and reducing conditions at elevated temperatures on typical AFM tips. To fully characterize the influence of different conditions on the tip properties we used several techniques such as: X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and local-conductivity atomic force microscopy. The chemical composition as well as the topography and morphology of the most popular Pt/Ir coated silicon tips were investigated. The influence of thermal treatment on the tip apex was also imaged and the changes in the electrical behavior of the tip coating were observed. Applied temperatures ranges were: 500–700 ° C for oxidizing conditions (air) and 300–700 ° C for reducing conditions (vacuum 10 −6 Torr), the annealing time was set to 0.5 h. Results yielded the formation of Pt 2Si and SiO 2 on the tip surface. The Pt tends to agglomerate into particles over time, depending on the temperature and conditions. The tip apex radius increases while the electrical conductivity decreases with the temperature. In conclusion, even the lowest applied temperature leads to changes in the tip properties, while these changes are much more pronounced under oxidizing conditions.

On the kinetics of platinum silicide formation

In this work, the kinetics of platinum silicide formation for thin Pt films (50 nm) on monocrystalline ⟨100⟩ silicon is investigated via in situ resistance measurements under isothermal (197–275 °C) conditions. For Pt2Si diffusion limited growth was observed. For PtSi formation, however, no linear relation between silicide thickness and √t was found. PtSi growth over time could be described using the Avrami relation rendering Avrami exponent n=1.4±0.1. Additionally, an effective activation energy EA=1.7±0.1 eV was derived using the Avrami k values. The findings are important for obtaining well defined silicide films and silicide-to-silicon contacts.

Nanoelectronic Devices from Nanowire Heterostructures

In this manuscript we report the formation of single crystal PtSi and MnSi nanowires, silicide/silicon/silicide nanowire (NW) heterostructures and studies of the electron and spin transport in silicon nanostructure. Single crystal silicide contact is grown by converting the silicon nanowire into single crystal silicide nanowire through controlled solid state reaction, wherein a coherently and automatically flat silicide/Si interface is maintained. Electrical transport studies of PtSi and MnSi nanowires show a metallic behavior for both, and show that MnSi displays ferromagnetic properties at low temperature. More importantly, a high performance intrinsic-Si NW transistor has been demonstrated with PtSi/Si/PtSi heterostructures, and spin injection and detection are demonstrated in MnSi/Si/MnSi nanowire heterostructure with an ultra-short Si channel ~20 nm. These studies demonstrate for the first time the realization of normally-off intrinsic Si p-type transistor, as well the spin injection and detection in a Si nanostructure.

Growth of vertically aligned bamboo-like carbon nanotubes from ammonia/methane precursors using a platinum catalyst

Vertically aligned multi-walled carbon nanotubes have been synthesized by microwave plasma enhanced chemical vapor deposition using ammonia/methane source gas mixtures and a platinum thin film catalyst on thermally oxidized silicon substrates. The SiO 2 layer served as a diffusion barrier to reduce PtSi formation and aide the formation of well dispersed catalytic nanoparticles. Nevertheless, some degree of substrate–catalyst interaction occurred even with this diffusion barrier present. Carbon nanotube growth using a relatively thick catalyst film was either inhibited or prevented altogether when increasing the duration of plasma pretreatment or by moving the substrate closer to the center of the plasma. This was primarily attributed to increased substrate–catalyst interactions resulting in catalyst poisoning. Decreasing the plasma pretreatment time or moving the substrate away from the center of the plasma improved the growth, increasing the length of the nanotubes. Varying the catalyst film thickness enabled control of the diameter and density of the carbon nanotubes. Transmission electron microscopy revealed a bamboo-like structure with the orientation of internal compartments consistent with a base-growth mode.

Phonon density of states of self-assembled isolated Fe-rich Fe-Pt alloy nanoclusters

The Fe-projected phonon density of states (PDOS) of monolayer-thick films of self-assembled, size-selected, isolated ${^{57}\text{F}\text{e}}_{1\ensuremath{-}\text{x}}{\text{Pt}}_{\text{x}}$ alloy nanoclusters (NCs) (height: $\ensuremath{\sim}2\text{ }\text{nm}$, diameter: $\ensuremath{\sim}8\text{ }\text{nm}$) supported on flat ${\text{SiO}}_{2}/\text{Si}(111)$ substrates has been measured by nuclear resonant inelastic x-ray scattering. The samples were characterized by atomic force microscopy (AFM), transmission electron microscopy, and x-ray photoelectron spectroscopy (XPS). Surface segregation of Pt and PtSi formation at the NC surface due to the sample-preparation process is inferred from the XPS data. As compared to the bulk, pronounced modifications of the PDOS beyond the bulk cut-off energy are observed in bcc ${^{57}\text{F}\text{e}}_{0.8}{\text{Pt}}_{0.2}$ (core)/PtSi(shell) NCs. By contrast, the PDOS of fcc ${^{57}\text{F}\text{e}}_{0.75}{\text{Pt}}_{0.25}$ (core)/PtSi(shell) NCs retains features of bulk ordered ${\text{Fe}}_{3}\text{Pt}$ Invar alloys (presumably due to a thicker PtSi shell), in particular, the transverse-acoustic [110] ${\text{TA}}_{1}$ mode near 9 meV. Apparently, this mode is not affected by size effects. The existence of the [110] ${\text{TA}}_{1}$ phonon mode is a prerequisite for the persistence of Invar-related effects in ${\text{Fe}}_{3}\text{Pt}$ NCs. Important thermodynamic properties of the NCs are derived, such as the vibrational entropy per atom.

Tuning of the Platinum Silicide Schottky Barrier Height on n-Type Silicon by Sulfur Segregation

The Schottky barrier height PhiB of platinum silicide (PtSi) contacts on n-type silicon was tuned by sulfur segregation at the PtSi/Si interface. Sulfur was implanted prior to Pt deposition and segregated at the interface during PtSi formation. It was observed that the barrier height could be tuned by changing the sulfur dose. A minimum barrier height of 0.12 eV was obtained on n-type (100) Si substrates. Since PtSi naturally provides a small PhiB of 0.2 eV on p-type Si, it carries the potential to serve as the single metal source/drain contact metal in a CMOS integrated circuit with PhiB tuning on n-channel transistors.

Silicidation of Silicon Nanowires by Platinum

The solid-state reaction between platinum and silicon nanowires grown by the vapor-liquid-solid technique was studied. The reaction product PtSi is an attractive candidate for contacts to p-type silicon nanowires due to the low barrier height of PtSi contacts to p-type Si in the planar geometry, and the formation of PtSi was the motivation for our study. Silicidation was carried out by annealing Pt on Si nanowires from 250 to 700 degrees C, and the reaction products were characterized by transmission electron microscopy. Strikingly different morphologies of the reacted nanowires were observed depending on the annealing temperature, platinum film thickness, silicon nanowire diameter, and level of unintentional oxygen contamination in the annealing furnace. Conversion to PtSi was successfully realized by annealing above 400 degrees C in purified N2 gas. A uniform morphology was achieved for nanowires with an appropriate combination of Si nanowire diameter and Pt film thickness to form PtSi without excess Pt or Si. Similar to the planar silicidation process, oxygen affects the nanowire silicidation process greatly.

A study of the formation and oxidation of PtSi by SR–PES

In the paper we present the results on the formation of platinum silicide (PtSi) by means of synchrotron radiation photoelectron spectroscopy (SR–PES) and show the effect of a Pt/Si sample exposure to both a low and high-pressure oxygen atmosphere at the end of an annealing process. We have carried out a detailed analysis of high resolution photoelectron spectra of the Pt 4f and Si 2p peaks which were taken during the sample annealing at specific temperatures. In addition to the generally known Pt 2Si and PtSi phases we have recognized an additional intermediate phase during the formation of Pt 2Si and attributed it to the Pt 3Si phase. We have proved that silicon diffuses towards the sample surface. The results of a low-pressure oxygen experiment have shown that oxygen binds only to surface silicon, however, in the case of a PtSi sample prepared externally in the ON Semiconductor labs under nitrogen/oxygen atmosphere oxygen binds not only to surface silicon but also takes over Si atoms out of the PtSi phase which results in the formation of a SiO 2 layer on almost pure platinum.

STM studies of PtSi formation on Si(111) by solid state epitaxy

Formation process and surface structure of platinum silicide thin layers have been studied using scanning tunneling microscopy. The investigated structures have been grown by solid state epitaxy upon deposition of 5 and 10 monolayers (ML) of platinum on the Si(111) surface and annealing at temperatures between $250\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $1100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Platinum silicide exhibits a tendency to form islands as the annealing temperature increases. At a coverage of 5 ML the platinum silicide grows epitaxially with the relation of $\mathrm{Pt}\mathrm{Si}(010)\ensuremath{\Vert}\mathrm{Si}(111)$. In contrast, for 10 ML coverage the $\mathrm{Pt}\mathrm{Si}(100)\ensuremath{\Vert}\mathrm{Si}(111)$ growth was found. New types of surface reconstruction were observed on the both surfaces. Models successfully explaining investigated reconstructions are proposed. The electronic structure of platinum silicide in the vicinity of the Fermi level has been deduced from the scanning tunneling spectroscopy measurements.

Effect of Pt Interlayer on Thermal Stability of NiSi Films

In this paper, the effect of a thin interlayer of Pt on thermal stability of NiSi films on Si(111) has been studied. The Ni/Pt/Si(111) bilayered samples with the same film thickness were annealed by rapid thermal annealing at 640 °C-900 °C. Both the X-ray diffraction analysis and four-probe measurements show a remarkable improvement in the thermal stability NiSi as a result of Pt interlayer. The possible reason for the enhanced NiSi thermal stability is attributed to the formation of the Ni(Pt)Si solid solution and its preferred orientation, leading to the decrease in the driving force of NiSi2 nucleation and the increase in the interfacial energy change respectively. The experimental results are explained in terms of Miedema’s Model and Thomas-Fermi-Dirac (TFD) equations in detail.

Effect of Pt film thickness on PtSi formation and film surface morphology

The effect of Pt film thickness on the formation of platinum silicide (PtSi) phase, distribution of silicides, and surface morphology of PtSi/Si films was investigated with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). It was shown that when the film structure was changed from PtSi/Si to Pt/Pt 2Si+PtSi/PtSi/Si, the film morphology changed from a smooth surface to a coarse columnar structure with the increase of the Pt film thickness.