Ni Silicide Formation Research Articles

Effect of alloying elements Mo and W on Ni silicides formation

The effect of alloying Mo and W elements on the formation and stability of the Ni silicides are studied using in situ and ex situ measurements by X-ray diffraction (XRD), sheet resistance (Rs) and Rutherford back scattering (RBS). The results show that a low Mo concentration in Ni layer does not affect the sequence, texture and resistivity compared to the Ni/Si system. However, the addition of 10% Mo and 5% W in Ni layer leads to the suppression of a transient phase. For Ni (10%W), a (NixSiy) phase appears in the end of Ni consumption and the sheet resistance increases when this phase is formed. In all cases, ex situ XRD and RBS shows that, at high temperature, MoSi2 and WSi2 are formed at the surface before NiSi2. Low resistances films are obtained even for temperatures as high as 900°C for the samples containing 10% Mo, 5% and 10% W.

Formation of nickel-platinum silicides on a silicon substrate: Structure, phase stability, and diffusion from ab initio computations

The formation of Ni(Pt)silicides on a Si(001) surface is investigated using an ab initio approach. After deposition of a Ni overlayer alloyed with Pt, the calculations reveal fast diffusion of Ni atoms into the Si lattice, which leads initially to the formation of Ni2Si. At the same time, Si atoms are found to diffuse into the metallic overlayer. The transformation of Ni2Si into NiSi is likely to proceed via a vacancy-assisted diffusion mechanism. Silicon atoms are the main diffusing species in this transformation, migrating from the Si substrate through the growing NiSi layer into the Ni2Si. Pt atoms have a low solubility in Ni2Si and prefer Si-sites in the NiSi lattice, thereby stabilizing the NiSi phase. The diffusivity of Pt is lower than that of Ni. Furthermore, Pt atoms have a tendency to segregate to interfaces, thereby acting as diffusion barriers.

Improvement of Ni Silicide Thermal Stability By Using Vanadium Elements

Ni silicide thermal stability is improved by the use of a Ni-V (nickel vanadium) alloy target. The relationship between the formation temperature and the thermal stability of Ni silicide is investigated. The sheet resistance after the formation of Ni silicide with the Ni-V shows stable characteristics up to a rapid-thermal-process temperature of 700°C, while degradation of sheet resistance starts at that temperature in the case of pure-Ni. Moreover, the thermal stability improvement is demonstrated by the post-silicidation annealing. It is considered that the thermal robustness of Ni-V silicide is highly dependent on the formation temperature. With the increasing silicidation temperature (around 700°C), more thermally stable Ni silicide is formed in comparison to the low-temperature case using the Ni-V. A Ni-V alloy target is utilized to form Ni silicide. The V and the V-trap complexes are explained to block the transformation from NiSi to NiSi2 so as to improve the Ni silicide thermal stability.

Formation of pre-silicide layers below Ni1−xPtxSi/Si interfaces

The formation of a pre-silicide layer below Ni1−xPtxSi films is reported with structure and composition distinctly different from previously observed diffusion layers. It was found that during two-step rapid thermal annealing Ni interstitial diffusion can kinetically dominate over the formation of Ni silicide, which results in a metastable pre-silicide layer. Aberration corrected scanning transmission electron microscopy experiments have revealed Ni to occupy interstitial and substitutional sites in the pre-silicide layer. Rapid thermal annealing and Pt alloying determines the stoichiometry and thickness of the layer, while the point defect configurations give rise to lowering of the associated Schottky barrier heights. The pre-silicide layer effectively limits diffusion of Ni into the substrate and therefore allows for the low-temperature growth of Ni2Si and NiSi.

Combined in situ x-ray scattering and electrical measurements for characterizing phase transformations in nanometric functional films

This paper presents a combination of in situ synchrotron techniques (diffraction and reflectivity of x-rays) and sheet resistance measurements to study the phase transformations in functional thin films. The association of the three techniques enables simultaneously extracting structural and electrical characteristics of thin films during thermal annealing. For illustrating such combined experiments, two different examples are presented and discussed: the first one deals with solid phase reactions involved in the formation of Ni-based silicides with Pd alloy element, while the second one refers to amorphous-to-crystalline phase transition in chalcogenide materials. For the first case, it is shown that the combined experiments enable measuring the kinetics of Ni-silicide formation by detecting growing and consumed phases (crystallized or amorphous) exhibiting different electrical properties. In the second case, the correlated changes in film density, thickness and sheet resistance are evidenced upon Ge2Sb2Te5 (GST) thin film crystallization. A spread of transition temperature deduced from the different measured parameters is also demonstrated for the thinner GST films.

Effect of Pd on the Ni2Si stress relaxation during the Ni-silicide formation at low temperature

The thermally induced solid-state reaction between a 50-nm-thick Ni(6%Pd) layer and a Si(100) substrate was investigated using in situ and simultaneous x-ray diffraction and sheet resistance. The reaction begins with the growth of the stressed δ-Ni2Si phase, and the transient θ-Ni2Si. At the end of the θ-Ni2Si consumption, a NiSi seed is formed. Then, the δ-Ni2Si relaxation occurs simultaneously with its subsequent growth and the Pd out diffusion from the unreacted Ni(Pd) layer. It is suggested that the driving force for the Pd diffusion out of the metal layer is linked to both the higher solubility of Pd in NiSi compared to Ni2Si and to the Ni2Si relaxation.

Self-aligned Ni-P ohmic contact scheme for silicon solar cells by electroless deposition

We report a Ni-P metallization scheme for low resistance ohmic contacts to n-type Si for silicon solar cells. As-deposited Ni-P contacts to n-type Si showed a specific contact resistance of 6.42 × 10−4 Ω·cm2. The specific contact resistance decreased with increasing thermal annealing temperature. When the Ni-P contact was annealed at 600°C for 30 min in ambient air, the specific contact resistance was greatly decreased, to 6.37 × 10−5Ω·cm2. The improved ohmic property was attributed to the decrease in the work function due to the formation of Ni-silicides from Ni in-diffusion during the thermal annealing process. Effects of the annealing process on the electrical and crystal properties of the contacts were investigated by means of various resistivity measurements (circular transmission line method (c-TLM), 4-point probe), glancing angle x-ray diffraction (GAXRD), and x-ray photoelectron spectroscopy (XPS).

Conformal Ni-silicide formation over three-dimensional device structures

This letter reports on conformal formation of ultrathin Ni-silicide films over a three-dimension structure relevant to the most advanced tri-gate transistor architecture. This is achieved by combining ionization of the sputtered Ni atoms with application of an appropriate bias to the Si substrate during the sputter-deposition of Ni films. In comparison, use of ordinary DC sputtering for Ni deposition results in thinner or less uniform silicide films on the vertical sidewalls than on the top surface of the three-dimensional structure. The roughened Si sidewall surface is ascribed to be responsible for a deteriorated thermal stability of the resultant silicide films.

Arsenic clustering during formation of the transient Ni silicide

The redistribution of arsenic during the reaction of Ni thin films with arsenic-doped Si(1 0 0) substrates is studied by in situ X-ray diffraction (XRD) and atom probe tomography. In situ XRD showed the formation of a transient phase that forms isolated grains at the δ-Ni 2 Si/Si interface. Arsenic is not incorporated in δ-Ni 2 Si but accumulates at the δ-Ni 2 Si/Si interface. Clusters containing 10 at.% As are present only in the transient phase. The As clustering might have important consequences for devices.

Ni-silicide growth kinetics in Si andSi/SiO2 core/shell nanowires

A systematic study of the kinetics of axial Ni silicidation of as-grown and oxidized Si nanowires(SiNWs) with different crystallographic orientations and core diameters ranging from ∼ 10 to 100 nm is presented. For temperatures between 300 and 440 °C the length of the total axial silicide intrusion varies with the square root of time,which provides clear evidence that the rate limiting step is diffusion of Ni throughthe growing silicide phase(s). A retardation of Ni-silicide formation for oxidizedSiNWs is found, indicative of a stress induced lowering of the diffusion coefficients.Extrapolated growth constants indicate that the Ni flux through the silicidedNW is dominated by surface diffusion, which is consistent with an inverse squareroot dependence of the silicide length on the NW diameter as observed for⟨111⟩ orientated SiNWs. In situ TEM silicidation experiments show thatNiSi2 is the first forming phase for as-grown and oxidized SiNWs. The silicide–SiNW interface isthereby atomically abrupt and typically planar. Ni-rich silicide phases subsequentlynucleate close to the Ni reservoir, which for as-grown SiNWs can lead to a completechannel break-off for prolonged silicidation due to significant volume expansion andmorphological changes.

Kinetics of reactions of Ni contact pads with Si nanowires

Abstract

Formation of Ni-Silicide at the Interface of Ni/4H-SiC

We report the relationship between the formation of Ni-silicide compounds and the change of the electrical behavior under different post-annealing conditions. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques were employed to study the formation of the various Ni-silicide compounds at the interface between Ni and 4H-SiC. Also, the electrical properties of the device were analyzed based on its current-voltage (I-V) characteristics under the same conditions. In our experiments, Ni2Si began to form at a post-annealing condition about 700°C. However, a good Ohmic behavior was observed at a post-annealing condition of 1000°C.

Redistribution of Alloy Elements during Nickel Silicide Formation: Benefit of Atom Probe Tomography

The unique capabilities of atom probe tomography (APT) to characterize internal interfaces and layer chemistry with sub-nanometer scale resolution in three dimensions have been recently opened up to materials with poor electrical conductivity by the use of ultrafast laser pulses. The progress in sample preparation (focused ion beam) as well as in instrument performance enable now the analysis of relatively large volumes with typical diameters of 100 to 200 nm and depths of several hundred nm (this corresponds to an increase by several order of magnitude compared to the former instrument) of site specific samples. In this work, APT is used to study the effects of Pt on the formation and stability of Ni silicides. The precise location of this alloy element has been determined at the nanometer scale: In particular, APT allows us to quantify the amount of Pt in the grain boundaries (GB) of Ni2Si for about 100 different grain boundaries and thus to better characterize the GB diffusion and segregation.

Characterizations of NiSi2-Whisker Defects in n-Channel Metal–Oxide–Semiconductor Field-Effect Transistors with Channel on Si(100)

Electrical and physical characteristics of nickel disilicide (NiSi2)-whisker defects in n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs) on Si(100) have been investigated. NiSi2-whisker defects are easily generated in narrow-channel-width nMOSFETs with the <110> channel on Si(100) and anomalously increase the leakage current between the drain and the source. A NiSi2 whisker elongates toward the <110> direction along the trench edge and pierces the channel region. These physical properties of NiSi2-whisker defects were revealed by detailed failure analyses. The influence of the recessed depth of trench-fill oxides on NiSi2-whisker defects was also investigated. Furthermore, it is found that trench-edge defects, such as Si(111) stacking faults, are generated in the <110> channel before the Ni silicide formation. These trench-edge defects were not observed in the <100> channel. We also propose a generation model for NiSi2-whisker defects. The nucleation of NiSi2 precipitates might be generated at trench-edge defects, and Ni atoms diffuse toward the <110> direction during the silicidation annealing. As a result, NiSi2-whisker defects are generated toward the <110> direction at the trench edge.

Ni silicide formation on epitaxial Si 1 − yC y/(001) layers

The formation of Ni silicides on Si 1 − y C y ( y = 0.01 and 0.018) epilayers grown on Si(001) has been investigated. The presence of C atoms was found to significantly retard the growth kinetics of NiSi and enhances the thermal stability of thin NiSi films. For Ni(11 nm)/Si 0.982C 0.018 samples, the process window of NiSi was shifted and extended to 450–700 °C. Moreover, there was an additional strain introduced into the Si 1 − y C y epilayers during Ni silicidation. This work shows the potential of Ni silicidation on Si 1 y C y for device applications.

Influence of Incorporating Rare Earth Metals on the Schottky Barrier Height of Ni Silicide

Characterized herein is a different physical mechanism for the formation of Ni silicide by incorporating rare earth (RE) metals such as ytterbium (Yb), erbium (Er), and dysprosium (Dy). Although the incorporation of any RE metal increases the Schottky barrier height (SBH) for holes in Ni silicide due to the formation of a ternary phase silicide, Yb induced the greatest increase in SBH because, unlike the other metals, Yb atoms accumulated at the silicide/silicon interface.

C Redistribution during Ni Silicide Formation on Si1 − yCy Epitaxial Layers

This study investigates the formation of Ni silicides on epilayers grown on Si(001). The presence of C atoms retards the growth kinetics of NiSi and significantly enhances the thermal stability of NiSi thin films. In particular, an abnormal redistribution of C atoms in the NiSi thin films was observed during Ni silicidation. The NiSi layer was split into two sublayers by an obvious pileup of C atoms. This study proposes a mechanism to elucidate this phenomenon in terms of the C solubility. C atoms accumulated at the interfaces and NiSi grain boundaries may act as diffusion barriers, effectively hindering the grain growth and agglomeration of NiSi and extending the process window of low resistivity NiSi silicides.

Three-dimensional composition mapping of NiSi phase distribution and Pt diffusion via grain boundaries in Ni 2Si

The formation of Ni silicide alloyed with Pt has been analyzed by atom probe tomography. A 300 °C/1 h anneal results in simultaneous growth of the NiSi and Ni2Si phases: the Ni2Si phase is a continuous layer with columnar grains, while the NiSi phase forms a discontinuous layer. Direct evidence of Pt diffusion short-circuits via Ni2Si grain boundaries is shown. The presence of Pt in the grains and interphase boundaries may explain the change in the Ni silicide formation for the Ni(5% Pt)/Si system.

Effect of Pt addition on Ni silicide formation at low temperature: Growth, redistribution, and solubility

The formation of Ni silicide during the reaction between Ni(5% Pt) and a Si(100) substrate has been analyzed by differential scanning calorimetry (DSC), in situ x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and H4e+ Rutherford backscattering. The DSC measurements show evidence of the Ni2Si nucleation followed by lateral growth formation. In situ XRD and TEM have been used to investigate the sequence of formation of the silicides. These experiments show that the formations of Ni2Si and NiSi occur simultaneously in the presence of the Pt alloy. The redistribution of platinum at different stages of the Ni silicide growth has been determined. We have estimated the solubility limit of platinum (1 at. % at 573 K) in the Ni2Si phase by extrapolation from a measured value at 1073 K. This redistribution is explained in terms of the solubility limits and the diffusion of Pt in the Ni2Si and NiSi phases. Pt is more likely to reside at the silicide grain boundaries and the interfaces where it can slow down the silicide growth kinetics.

Kinetic study of interfacial solid state reactions in the Ni/4H–SiC contact

Investigation of the relatively low temperature reaction between Ni nanolayer film and 4H–SiC substrate provides valuable insights into studies of the fundamental properties of SiC Schottky diodes. A quantitative description of chemical kinetics of Ni/SiC contact formation has been studied via deposition of about 50 nm Ni film on 4H–SiC (Si terminated surface) by magnetron sputtering and subsequent annealings at temperatures of 500–700 °C. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) techniques were used to investigate the interface reaction products upon annealing and element distribution across the reaction layer. It is found that the thermodynamically stable silicide Ni 2Si begins to form at the contact interface as a result of sample annealing above 600 °C, which associated with producing carbon distributed at the surface and at the interface of the silicide with the SiC substrate. The kinetic process is described to mainly include the solid state interface reactions and the diffusion of components through the produced layer of silicides. When the diffusion layer is thick enough (more than 100 nm), the kinetic feature is thought to be diffusion controlled, which follows the parabolic law. The active energy of Ni silicide formation was derived as (135.0 ± 19.51) kJ mol −1.