NiSi Films Research Articles

Influence of the annealing schemes on the formation and stability of Ni(Pt)Si thin films: Partial, laser, total, and one-step annealings

In this study, the impact of various annealing schemes on the formation and agglomeration mechanisms of ultrathin Ni(Pt)Si films is investigated. To this end, 11 ± 1 nm-thick Ni(Pt)Si films are grown on 300 mm Si(100) wafers using various traditional rapid thermal annealing procedures as well as laser annealing. The obtained silicide films are then subjected to additional annealing between 500 and 800 °C, to evaluate their stability at high temperature. The correlation between the as-grown Ni(Pt)Si film properties and their capability to withstand agglomeration is analyzed via a complementary approach of several techniques (Rs, ellipsometry, TEM-EDX, SEM, and EBSD). Texture comparison for ultrathin films give deeper insights into the role of the NiSi-(010) and NiSi-(013) orientations in the agglomeration phenomenon. Depending on the annealing schemes used during the silicide formation, there is a strong correlation between the initial microstructure of Ni(Pt)Si films and their subsequent degradation. Indeed, cross-analysis of these different key parameters indicates that the presence of small Ni(Pt)Si grains (40 nm) obtained after laser annealing, and a high ratio of Ni(Pt)Si grains oriented along the (013) direction appears to be more efficient in delaying the agglomeration to higher temperatures.

A comparative study of C, N and Xe pre-amorphization implantation processes for improving the thermal stability of NiSi films

In this paper, a comparative study of C-, N- and Xe-based pre-amorphization implantation (PAI) processes is proposed. The impact of the use of such processes on the agglomeration resistance and physical properties of the final Ni(Pt)Si layer, as well as the formation mechanisms via solid-state reactions and electrical performances via the transfer length measurement (TLM) method, is evaluated. It is shown that although all species are able to increase the agglomeration temperature of Ni(Pt)Si layers (up to more than 100 °C), the underlying mechanisms are different. For C- and N-based PAI processes a strong chemical effect is observed, while for Xe-based processes the amorphization depth plays an important role. Consequently, the beneficial effect of stabilizing Ni(Pt)Si layers at high temperatures using C- and N-based PAI processes has to be balanced with an increased layer resistivity (up to 30%) combined with a strong deterioration of the associated specific contact resistivity (which is multiplied by almost a factor 10). In this sense, Xe-based PAI processes seem to be a better option as they could allow to combine both requirements.

Oxidation behaviour of NiSi–NiCr thin film thermocouples and antioxidation effect of SiNxOy film

NiSi–NiCr thin film thermocouples (TFTCs) have significant application value as contact temperature sensors in cutting temperature measurements owing to their fast response and negligible volume. However, due to the relatively high chemical activity of Ni-based alloys, high-temperature oxidation strongly affects the operational reliability of NiSi–NiCr TFTCs. In this respect, depositing an anti-oxidation coating onto the surface of NiSi–NiCr TFTCs is considered an effective way to protect them in high-temperature environments. In this study, NiSi and NiCr films were deposited on cemented carbides and annealed at 200 °C–600 °C in air. Scanning electron microscope, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and four-probe resistivity tests were used to characterize the microstructure and resistivity of NiSi and NiCr film. Then SiNxOy films were deposited onto the NiSi and NiCr films and compared with uncoated samples after annealing at 600 °C. The effect of SiNxOy films on the thermal stability and thermoelectric output of NiSi–NiCr TFTCs was investigated. The results show that the NiSi film was partially oxidized at 200 °C and entirely oxidized when the temperature exceeded 400 °C. The completely oxidized NiSi films had evident defects and cracks, and the resistivity increased by a factor of over 1000. The NiCr film could not be completely oxidized at 600 °C, which is attributed to the formation of Cr2O3 as an external oxide barrier layer. Below 600 °C, SiNxOy films could effectively protect NiSi and NiCr films from oxidation. Thus, the addition of SiNxOy film increases the maximum temperature at which NiSi–NiCr TFTCs can be used.

On the influence of Ni(Pt)Si thin film formation on agglomeration threshold temperature and its impact on 3D imaging technology integration

Ni(10 at.% Pt) monosilicide is used as contact in microelectronics but suffers from degradation at relatively low temperatures due to agglomeration. Recent results obtained on 28 nm-FDSOI (Fully Depleted Silicon On Isolator) microelectronics devices have demonstrated severe yield loss after an anneal at 550 °C/2 h linked to Ni(Pt)Si film dewetting. Such agglomeration thermal budget is 100 °C lower than the ones measured on blanket wafers with in-situ or ex-situ four-point probe measurements. In this context, the aim of this paper is to investigate the effect Ni(Pt)Si formation process on the Ni(Pt)Si agglomeration using different approaches as (i) the classical one in which one anneal is applied to form silicide and leads also to agglomeration, (ii) the silicide formation through the standard SALICIDE process, “Self-Aligned Silicide”, and a subsequent anneal to induce agglomeration, and (iii) the standard SALICIDE process for silicide formation followed by an encapsulation of the top silicide surface by a SiN layer as applied in devices, and submitted finally to the agglomeration anneal. Our work demonstrated that the film thermal stability is influenced by the sequencing of the Selective Etch (SE) in the formation process and whether it is formed by a single or a double anneal. For single anneal, the thermal budget needed to agglomerate Ni(Pt)Si film is higher i.e., agglomeration occurs at around 700 °C/30 s in single anneal as compared to double anneal at around 550 °C/30 s. Another conclusion of this work is that four-point probe measurements are not sensitive enough to well estimate the real starting point of agglomeration phenomenon which is detrimental for devices (holes formation at the triple junctions). Some additional characterizations such as tilted Scanning Electron Microscopy (tilted SEM) are deeply needed for an accurate determination of agglomeration thermal budget. This study allows clarifying the main parameters leading to agglomeration: the film thickness and the grain size appear to be the more important ones.

The preliminary exploration on change mechanism of Seebeck coefficient for NiCr/NiSi thin film thermocouple with different thickness

By controlling the thickness of NiCr and NiSi films, a series of NiCr/NiSi thin film thermocouples (TFTCs) were prepared by the sputtering technique. With the standard static calibration procedure for wire thermocouple, the temperature difference mainly happened between NiCr/NiSi compensation wires, but not between pad and hot junction of NiCr/NiSi TFTCs. The incorrect temperature difference resulted in the distorted Seebeck coefficient of NiCr/NiSi TFTCs, which was close to the standard NiCr/NiSi wire thermocouple. Only considering the temperature difference between pad and hot junction of NiCr/NiSi TFTCs, Seebeck coefficient of NiCr/NiSi TFTCs were accurately obtained. Seebeck coefficient of NiCr/NiSi TFTCs was about ∼10 μV/°C, which was obviously lower than that of standard K type NiCr/NiSi wire thermocouple (∼40μV/°C). Besides, Seebeck coefficient of NiCr/NiSi TFTCs gradually increased from 7.32 to 13.36 μV/°C with the increase of NiCr/NiSi film thickness from 400 to 2000 nm. NiCr and NiSi films with different thickness displayed the similar crystal structure, grain size, metal bonds structure, Ni/Cr and Ni/Si atom ratio, as well as similar surface morphology and roughness, which have little influence on Seebeck coefficient of NiCr/NiSi TFTCs. With the increase of NiCr and NiSi film thickness, the sheet concentration of free electron increased gradually, which resulted in the increase of Seebeck coefficient of NiCr/NiSi TFTCs. Because of the limited thickness of NiCr and NiSi film, all Seebeck coefficient values of NiCr/NiSi TFTCs were lower than that of standard K type thermocouple. NiCr/NiSi TFTCs with small thickness NiSi film and large thickness NiCr film could display the relative higher Seebeck coefficient value. And, NiCr/NiSi TFTCs with 800 nm NiSi and 2000 nm NiCr films displayed Seebeck coefficient value of 21.30 ± 0.69 μV/°C. o

Adaptive Thin Film Temperature Sensor for Bearing's Rolling Elements Temperature Measurement.

With the continuous improvement of train speeds, it is necessary to find the possible problems of bearings in time, otherwise they will cause serious consequences. Aiming at the characteristics of rapid temperature change of bearings, a thin film thermocouple temperature sensor was developed to measure the real-time temperature of the bearing’s rolling elements during train operation. Using dc pulse magnetron sputtering technology, Al2O3 film, NiCr film, NiSi film, and SiO2 film were successively deposited on an aluminum alloy substrate. We studied their microstructure, static characteristics, dynamic characteristics, and repeatability. Finally, we installed an adaptive film temperature sensor on the bearing testing machine to measure the temperature of the rolling elements. The results show that the developed temperature sensor has good linearity in the range of 30~180 ℃. The Seebeck coefficient is 40.69 μV/℃, the nonlinear fitting error is less than 0.29%, the maximum repeatability error is less than 4.55%, and the dynamic response time is 1.42 μs. The temperature of the measured rolling elements is 6~10 ℃ higher than that of the outer ring, which can reflect the actual temperature of the bearing operation.

Dewetting of Ni silicide thin film on Si substrate: In-situ experimental study and phase-field modeling

In this paper, the in-situ Scanning Electron Microscopy (in-situ SEM) technique and three-dimensional (3-D) phase-field simulation were combined to perform a comprehensive study on the kinetics and mechanisms of dewetting (or agglomeration) of a 30 nm NiSi films on Si(100) substrate at 600 °C. The evolution of texture during agglomeration of the polycrystalline NiSi thin film was also studied by ex-situ Electron BackScattered Diffraction (EBSD). The phase-field simulation results showed that abnormal grain growth plays an important role in the dewetting process of polycrystalline films, while the misorientations between the NiSi grains and the Si substrate are the main reason for the agglomeration of NiSi polycrystalline thin film on the monocrystal Si substrate. Moreover, 3-D phase-field simulations coupled with experimental information on misorientation distribution and initial grain size were also performed, and the simulated Ni silicide grain morphology is in good agreement with the in-situ SEM results during agglomeration. In order to slow down or to suppress the agglomeration, it is highly recommended to increase the volume fraction of low angle grains, and/or to decrease the misorientation between the NiSi grain and the Si substrate or between the NiSi grains.

Low contact resistivity of Ti/TiN/Al for NiSi2 on epitaxial Si:P structure at full low-temperature process below 450 °C

Combined with Ti/TiN/Al for ultra-thin NiSi2 and in situ-doped Si:P, an ultra-low contact resistivity of 4.6 × 10−9 Ω cm2 was achieved under a low thermal budget (⩽450 °C). The in situ-doped Si:P layer was grown by molecular beam epitaxy at 350 °C with a high doping concentration of 1.2 × 1021 cm−3 exceeding the solid solubility. On the Si:P substrate, ultra-thin NiSi2 film of 12.8 nm was formed by low-temperature drive-in diffusion and alloying at 180 °C and 450 °C, respectively. The Ti/TiN/Al-NiSi2-Si:P scheme provides a solution to the dilemma between performance boosting and reliability degradation in advanced very-large-scale integration manufacturing technology. It can also be applied in future monolithic three-dimensional integration.

Ion beam modification of the Ni-Si solid-phase reaction: The influence of substrate damage and nitrogen impurities introduced by ion implantation

We report on the growth of thin NiSi films via the thermal reaction of Ni layers (13–35 nm) with Si(100) substrates modified by ion implantation. By introducing substrate damage or nitrogen impurities prior to the solid-phase reaction, several properties of the NiSi films can be modified: the formation temperature, texture, diffusion-limited growth rate and morphological stability. As some of the modifications to the NiSi films are rooted in the early silicide phases preceding the NiSi phase, particularly its formation temperature, special attention is devoted to the growth of the amorphous Ni-Si alloy and the crystalline δ-Ni2Si and θ-Ni2Si phases.We employed a number of experimental techniques, including in situ synchrotron x-ray diffraction (XRD), in situ Rutherford backscattering spectrometry (RBS), in situ sheet resistance measurements, ex situ ion beam channelling and ex situ pole figure measurements. We show that both the formation temperature of the NiSi films and the intensity of epitaxial and axiotaxial components of the NiSi texture can be either lowered or raised by selecting appropriate implantation conditions. Agglomeration of the NiSi films at high temperature (> 700 °C) can be slowed down, either by slowing down the mobility of the Ni and Si atoms, or by removing the morphologically destabilizing axiotaxial texture. Our results emphasize the strong interwoven nature of phase formation, texture and morphological degradation. We illustrate that the kinetics of the early stages of thin film reactions consist of more than just diffusion, i.e. nucleation can also play a crucial role.

EFFECT OF RAPID THERMAL TREATMENT ТЕMPERATURE ON ELECTROPHYSICAL PROPERTIES OF NICKEL FILMS ON SILICON

Present work is devoted to determination the regularity of change of specific resistance and Schottky barrier height of nickel films on n-type silicon (111) at their rapid thermal treatment in the temperatures range from 200 to 550 °C. Nickel films of about 60 nm thickness were deposited by magnetron sputtering onto the silicon substrates having a resistivity of 0.58 to 0.53 Ohms×cm. The rapid thermal treatment was carried out in the range of 200 to 550 °C under heat balance mode by irradiating the backside of the substrates with non-coherent light flux in nitrogen ambient for 7 seconds. The thickness of the nickel films was determined by scanning electron microscopy. The sheet resistance of the samples was measured by a four-probe method. The Schottky barrier height was determined from I-V plots. It is shown that at a temperatureы of rapid thermal treatment of Ni/n-Si (111) 200–250 °C nickel will be transformed to Ni2Si, increasing in thickness by 1.15–1.33 times, specific resistance increases to 26–30 μOhm×cm, and Schottky barrier height decreases from 0.66 to 0.6 V. At a rapid thermal treatment temperature of 300°C the initial nickel film thickness increases by 1.93 times, the resistivity and Schottky barrier height decrease to 26–30 μOhm×cm and 0.59 V respectively due to the conversion of the Ni2Si into NiSi and the fixation of the barrier height by surface states at the silicidesilicon interface. Rapid thermal treatment of 350–550 °C transforms the original nickel film into NiSi, increases its thickness by 2.26–2.67 times, reduces its resistivity to 15–18 μOhm×cm and increases the Schottky barrier height to 0.62–0.64 V. The minimum defects and better reproducibility of electrophysical properties are characterized by NiSi films formed by rapid thermal treatment of nickel films on n-type silicon at a temperature of 400–450 °C. The results obtained can be used in the technology of integrated electronics products containing rectifying contacts.

Ultra-thin and conformal epitaxial NiSi2 film on Si fins by barrier-induced phase modulation (BPM) technique

In this work, a barrier-induced phase modulation scheme to realize an ultra-thin and conformal epitaxial NiSi2 film for wrapped-around contact beyond the 7 nm technology node, is proposed and experimentally demonstrated. The 1 nm thick Al2O3 barrier inserted between the Ni film and the substrate can limit the amount of nickel diffusing into silicon and establish an initial Si-rich region consisted of only a few atomic layers during a rapid thermal annealing treatment, so that NiSi2 can grow epitaxially as the first phase at a temperature as low as 600 °C. Additionally, thanks to the barrier layer, a relatively thick (50 nm) Ni film can be used, which not only ensures the continuity of NiSi2 formed on sidewalls of three-dimensional structures, but also reduces the process complexity. As a result, a conformal 3.3 nm NiSi2 shell with ΦBn = 0.33 eV is successfully obtained on Si fins.

Surface Morphology of NiSi2/Si Films Obtained by the Method of Solid-Phase Deposition

Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy are used to study the formation of epitaxial layers of NiSi2 during Ni–Si deposition followed by annealing. It is shown that the formed NiSi2 film has an island structure when its thickness is h ≤ 150 A and at h ≥ 200 A the film is continuous. The band gap of the island and solid films is ~0.6 eV, while the values of the resistivity ρ differ by several orders of magnitude. It is found that the photoelectron spectrum of the NiSi2 film with h = 50 A has peaks characteristic of both Si and NiSi2. The formation of the main peaks in the photoelectron spectrum of NiSi2 is explained by hybridization of the M1, M2, M3 states of Si with the М3, М4, М5 states of Ni.

Microstructural Analysis of Ti/Ni Bilayer Ohmic Contacts on 4H-SiC Layers

The micro-structural analysis of Ti/Ni bilayer as Ohmic contacts to n-type 4H-SiC is reported. There was no carbon segregation at the interface between the NiSi layer and the 4H-SiC layer for Ti/Ni contacts, unlike pure Ni contacts. The diffraction pattern image shows the presence of the cubic NiSi film which grows on the SiC surface. The film interface with the SiC was uniform and more planar. An optimized contact in terms of contact morphology was achieved using a bilayer contact Ti/Ni (20/100nm) annealed at 1100 °C for 5 minutes in vacuum.

Thermal stability study of Ni–Si silicide films on Ni/4H-SiC contact by in-situ temperature-dependent sheet resistance measurement

We investigate the Ni–Si film silicidation process on 4H-SiC and Si substrates and compare the thermal stability of the films grown on each substrate. The Ni–Si films were subjected to rapid thermal annealing (RTA) in the temperature range 575 °C–975 °C for 90 s, and their thermal stability was characterized by in-situ temperature-dependent sheet resistance measurements at temperatures of 25 °C–550 °C. The sheet resistance of a 40 nm thick Ni film was observed to increase sharply above 330 °C in the Ni/Si (100) interface, but slightly decrease at approximately 480 °C in the Ni/4H-SiC interface. The thermal stability of the films was found to be significantly dependent on the RTA temperature. Thermally stable Ni–Si silicide films with excellent Ohmic properties (no hysteresis behavior) can be obtained on 4H-SiC substrates at RTA temperatures of 925 °C–975 °C and can used for application in MOSFET devices.

Electronic and Optical Properties of NiSi2/Si Nanofilms

Optimum conditions for ion implantation and subsequent annealing for the fabrication of NiSi2/Si (111) nanofilms with a thickness of 3.0–6.0 nm are determined. It is demonstrated that the energy-band parameters and optical properties typical of thick NiSi2 films start to set in at d = 5.0–6.0 nm.

The Effect of the Formation of Silicides on the Resistivity of Silicon

The effect of the formation of thin films of nickel silicides on the migration of intrinsic p-type impurities in silicon was studied for the first time. It was found that bulk resistance $${{\rho }_{{v}}}$$ of a single Si crystal increases by a factor of 3–4 if a NiSi2 film with thickness θ ≥ 50–100 A forms on its surface. This is attributable to the migration of boron atoms toward the silicide film. The Si layer thickness enabling measurable boron migration was estimated at 800–1000 A.

Pt-doped Ni-silicide films formed by pulsed-laser annealing: Microstructural evolution and thermally robust Ni1-xPtxSi2 formation

Pulsed-laser annealing (PLA) was performed on a preformed Pt-doped Ni-rich silicide film (Ni2Si phase), and its microstructural and phase evolution were studied from submelting to melting condition by varying the laser power density (P). Vertically nonuniform compositional profile with an interfacial intermixing was observed under a solid state reaction regime (P < 400 mJ/cm2) due to a limited atomic diffusion. At higher P condition, melting/resolidification occurred with a continuous increase in the Si concentration, and various microstructures of the film evolved with increasing P: amorphous structure and nucleation/growth of NiSi and NiSi2 phases form in that order on the Si interface. Lastly, by applying additional rapid thermal annealing on the polycrystalline mixture of NiSi and NiSi2 phases formed by PLA, a uniform Pt-doped NiSi2 film with strong epitaxial growth tendency on the Si(001) substrate and high thermal stability (up to 900 °C) was synthesized.

Impurity-enhanced solid-state amorphization: the Ni–Si thin film reaction altered by nitrogen

Solid-state amorphization, the growth of an amorphous phase during annealing, has been studied in a wide variety of thin film structures. Whereas research on the remarkable growth of such a metastable phase has mostly focused on strictly binary systems, far less is known about the influence of impurities on such reactions. In this paper, the influence of nitrogen, introduced via ion implantation, is studied on the solid-state amorphization reaction of thin (35 nm) Ni films with Si, using in situ x-ray diffraction (XRD), ex situ Rutherford backscattering spectrometry, XTEM, and synchrotron XRD. It is shown that due to small amounts of nitrogen (<2 at.%), an amorphous Ni–Si phase grows almost an order of magnitude thicker during annealing than for unimplanted samples. Nitrogen hinders the nucleation of the first crystalline phases, leading to a new reaction path: the formation of the metal-rich crystalline silicides is suppressed in favour of an amorphous Ni–Si alloy; during a brief temperature window between 330 and 350 °C, the entire film is converted to an amorphous phase. The first crystalline structure to grow is the orthorhombic NiSi phase. We demonstrate that this impurity-enchanced solid-state amorphization reaction occurs only under specific implantation conditions. In particular, the initial distribution of nitrogen upon implantation is crucial: sufficient nitrogen impurities must be present at the interface throughout the reaction. Introducing implantation damage without nitrogen impurities (e.g. by implanting a noble gas) does not cause the enhanced solid-state amorphization reaction. Moreover, we show that the stabilizing effect of nitrogen on amorphous Ni–Si films (with a composition ranging from 40% to 50% Si) is not restricted to thin film reactions, but is a general feature of the Ni–Si system.

Lamellar-structured Ni-silicide film formed by eutectic solidification

Abstract Pt-doped NiSi‒NiSi2 thin films in a uniform lamellar structure with a periodicity on the scale of a few tens of nanometers were formed on Si(001) substrates using a continuous laser scanning process. When the Pt-doped NiSi film was melted at high temperatures and was supercooled at high solidification rates (a high scanning speed of over 200 mm/s), a NiSi‒NiSi2 lamellar structure evolved while interacting with the underlying Si substrate and following the classical eutectic solidification path. The lamellar spacing could be easily controlled by the laser scanning speed. In addition, the periodically formed, nearly single-crystalline NiSi and NiSi2 phases exhibited epitaxial relationships with each other and also with the Si(001) substrate. It is believed that this novel NiSi‒NiSi2 lamellar structure can be used as a template for application areas requiring an electrode with a line/space pattern on the scale of a few tens of nanometers that can be prepared without using costly photolithographic processes.

Controlling the formation and stability of ultra-thin nickel silicides - An alloying strategy for preventing agglomeration

The electrical contact of the source and drain regions in state-of-the-art CMOS transistors is nowadays facilitated through NiSi, which is often alloyed with Pt in order to avoid morphological agglomeration of the silicide film. However, the solid-state reaction between as-deposited Ni and the Si substrate exhibits a peculiar change for as-deposited Ni films thinner than a critical thickness of tc = 5 nm. Whereas thicker films form polycrystalline NiSi upon annealing above 450 °C, thinner films form epitaxial NiSi2 films that exhibit a high resistance toward agglomeration. For industrial applications, it is therefore of utmost importance to assess the critical thickness with high certainty and find novel methodologies to either increase or decrease its value, depending on the aimed silicide formation. This paper investigates Ni films between 0 and 15 nm initial thickness by use of “thickness gradients,” which provide semi-continuous information on silicide formation and stability as a function of as-deposited layer thickness. The alloying of these Ni layers with 10% Al, Co, Ge, Pd, or Pt renders a significant change in the phase sequence as a function of thickness and dependent on the alloying element. The addition of these ternary impurities therefore changes the critical thickness tc. The results are discussed in the framework of classical nucleation theory.