Ni Silicide Phases Research Articles

Role of interfacial nickel silicides in shaping magnetic anisotropy in nickel films grown on Silicon substrates

Using different experimental techniques such as X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and magneto-optical Kerr effect (MOKE) microscopy, the structural and magnetic properties of Ni films grown on Si substrates are investigated. Various Ni-silicide phases are found to be formed at the Ni–Si interface as a function of depth following the sequence Ni-Ni2Si-NiSi-NiSi2 from the nickel to silicon side. This has been explained in terms of the effective heat of formation and inter-diffusion of the elements at the interface. In-plane magnetic anisotropy of the system is investigated by measuring in-plane magnetization using MOKE microscopy. The film exhibits an uniaxial in-plane magnetic anisotropy. An anomalous behavior, i.e., the collapse of the hard axis, has also been observed. This anomaly has been explained in terms of the creation of V-state domains during the magnetization reversal process at the hard axis. Interestingly, in-plane magnetic anisotropy could not be found in a Ni film grown with a Pt buffer layer on the Si substrate. Ni-silicide phases could not be detected in this system. This may suggests that the formation of silicides and diffusion at the interface causes the atypical magnetic anisotropy in Ni–Si sample.

In situ TEM study of Ni-silicides formation up to 973K

Low-temperature solid-state reactions between Ni and Si were studied using in situ transmission electron microscopy (TEM). In the experiments thin amorphous silicon (a-Si) films were laid on Ni micro-grids and heated up to 973 K. In our approach the supporting Ni-grid serves as an unlimited source of nickel to successively form the whole range of Ni-silicide phases while diffusing into amorphous silicon. Unlike other thin film experiments where Ni and Si are layered on top of each other, our arrangement enables lateral diffusion of Ni along the Si layer and therefore enables the formation and study of successive Ni-Si phases side by side. That allowed us to observe in situ α-NiSi2 as the first reaction product, in contrast to most studies that had reported either δ-Ni2Si or θ-Ni2Si as the first phase to form. α-NiSi2 was continuously present at the reaction front propagating into the a-Si film. The phase sequence followed the increasing Ni concentration from a-Si towards the Ni-grid: α-NiSi2, NiSi, Ni3Si2, δ-Ni2Si, γ-Ni31Si12 and Ni3Si. Almost all known Ni-silicide phases were found to form at relatively low temperatures except the θ-Ni2Si, β-NiSi2 and β3-Ni3Si. The dominant phase was γ-Ni31Si12 which appeared in three structural modifications, differing in lattice periodicity along the c-axis. The periodicity of the basic γ-Ni31Si12 structure along the c-axis is ~12 Å (c0 = 12.288 Å) and that of the other two modifications were ~18 Å and ~36 Å, denoted by S12, S18 and S36 respectively. Of the three, only S12 has a structural model, S18 had been previously observed by Chen, but S36 had not been documented in previous works. During our in situ heating experiments, in addition to the Ni-silicide layer formation a new phenomenon was observed, namely the appearance, growth and transformation of Ni-silicide whiskers which was attributed to the accumulation of compressive stress in the thin layer.

Towards Reconfigurable Electronics: Silicidation of Top-Down Fabricated Silicon Nanowires

We present results of our investigations on nickel silicidation of top-down fabricated silicon nanowires (SiNWs). Control over the silicidation process is important for the application of SiNWs in reconfigurable field-effect transistors. Silicidation is performed using a rapid thermal annealing process on the SiNWs fabricated by electron beam lithography and inductively-coupled plasma etching. The effects of variations in crystallographic orientations of SiNWs and different NW designs on the silicidation process are studied. Scanning electron microscopy and transmission electron microscopy are performed to study Ni diffusion, silicide phases, and silicide–silicon interfaces. Control over the silicide phase is achieved together with atomically sharp silicide–silicon interfaces. We find that {111} interfaces are predominantly formed, which are energetically most favorable according to density functional theory calculations. However, control over the silicide length remains a challenge.

Fast in situ X‐ray analysis of Ni silicide formation

Metal silicides are the preferred contact materials for metal‐oxide semiconductor (MOS) structures. With further technology development, the materials changed within the last decades toward lower resistivity and lower thermal budget. Currently NiSi partly further stabilized with Pt or Pd is the material of choice. The understanding of phase transformation processes and structural features is of great importance for production process optimization. Here we present a fast laboratory‐based in situ X‐ray diffraction method with two different experimental arrangements (Bragg–Brentano and grazing incidence) optimized concerning the materials texture. Its application is demonstrated for the transformation of Ni to different Ni silicide phases starting with a 46 nm thick Ni layer sputtered on a Si(001) substrate and covered with TiN. Activation energies for the Ni to Ni2Si (1.55 ± 0.13) eV and the Ni2Si to NiSi transition (1.30 ± 0.15) eV are measured by repeating fast diffraction scans over a limited angular range under isothermal conditions and analyzing the diffraction peak height versus time.

Interfacial reactions and microstructural evolution of periodic Ni nanodot arrays on N2+-implanted amorphous Si substrates

We report here on the results of a systematic investigation of the interfacial reactions and microstructural evolution of nanoscale Ni metal dots on N2+-implanted amorphous Si (a-Si) substrates under different annealing conditions. During annealing, Ni2Si was the first phase to form, followed by NiSi and NiSi2. The three Ni-silicide phases formed were polycrystalline and the average sizes of the annealed nanodots were observed to increase with the annealing temperature, up to 500°C. After a further increase of the annealing temperature and/or time, it is interesting to note that the NiSi2 grains gradually migrated outward from their original nanodot positions to the a-Si regions, which resulted in the formation of a remarkable NiSi2 nanoring structure. The inner regions of the NiSi2 nanorings were found to be comprised of a single crystalline Si phase, indicating mediation of the epitaxial crystallization of N2+-implanted a-Si by the lateral migration of the NiSi2 nanodots. Furthermore, the annealing temperature required for complete recrystallization of the a-Si layer in the Ni nanodot/N2+-implanted a-Si sample could be significantly reduced to 550°C, 200°C lower than that which was required the blank N2+-implanted a-Si sample. It is suggested that the formation of these remarkable NiSi2 nanoring structures and the enhancement of N2+-implanted a-Si recrystallization in the presence of NiSi2 nanodots were due to the silicide-induced crystallization mechanism.

Improved ohmic contacts for SiC nanowire devices with nickel-silicide

The effect of annealing temperature has been investigated to obtain a low ohmic contact for silicon carbide nanowire field-effect transistor (SiC NW FET). Fabrication of two types of SiC NW FET has been studied using cylinder and needle shapes of SiC NW. The experimental results show that an annealing temperature of 650 °C leads to the lowest ohmic contact resistance on SiC NW FET. It is believed that the Ni silicide phases formed on SiC NWs make low resistance ohmic contacts. Ni silicide phases begin to intrude into the SiC NW channel after an annealing step at 700 °C for 30 s and consequently, it forms either a SiC/Ni silicide heterostructure or a fully Ni silicidized SiC NW depending on the channel length. A fully silicidized SiC NW exhibits a low channel resistance (740 Ω) and a high current density (1.46 × 107 A cm−2 at 1.4 V). The needle shape of SiC NWs is transformed into a bead necklace like morphology after Ni silicide intrusion.

Influence of Ni concentration on the crystallization of amorphous Si films and on the development of different Ni-silicide phases

The crystallization mechanism was the subject of the present study which reports on the structure, and the Ni-silicide formation, of Si films containing different concentrations of Ni. The films were prepared by sputtering and were analyzed by compositional and structural characterization techniques. Additional information was obtained by thermal annealing the films up to 800 °C. The experimental results indicated that, in the as-deposited form, the films are amorphous, homogeneous, and with Ni contents in the ∼0–40 at. % range. Moreover, the development of Si and/or Ni-silicide crystalline structures was susceptible to factors like the Ni concentration, the annealing temperature and the annealing process (if cumulative or not, for example).

Kinetics of reactions of Ni contact pads with Si nanowires

Abstract

Growth, optical, and electrical properties of silicon films produced by the metal-induced crystallization process

Amorphous Si (a-Si) and Ni films were deposited by electron beam evaporation on to borosilicate glass (BSG) substrate maintained at ambient temperature. The BSG/a-Si/Ni stack was subjected to post deposition annealing in air at various temperatures from 200 to 500 °C for 1 h. Electron diffraction was employed to characterize the crystallographic phases appearing on the stacks that were depending on initial conditions. Clear evidence of the formation of hexagonal Si and fcc NiSi2 was shown by TEM. In parallel, an increase of refraction index was observed. Electrical resistivity measurements showed that resistance is of the order of kilo ohms in the as-deposited films, increasing sharply to giga ohms in films annealed at T higher than 300 °C. A large band gap of 2.23 eV which is the combined contribution from a-Si, wurtzite-Si, and Ni silicide phases, is observed.

Characterization of nickel silicides using EELS‐based methods

The characterization of Ni-silicides using electron energy loss spectroscopy (EELS) based methods is discussed. A series of Ni-silicide phases is examined: Ni₃Si, Ni₃₁Si₁₂, Ni₂Si, NiSi and NiSi₂. The composition of these phases is determined by quantitative core-loss EELS. A study of the low loss part of the EELS spectrum shows that both the energy and the shape of the plasmon peak are characteristic for each phase. Examination of the Ni-L edge energy loss near edge structure (ELNES) shows that the ratio and the sum of the L₂ and L₃ white line intensities are also characteristic for each phase. The sum of the white line intensities is used to determine the trend in electron occupation of the 3d states of the phases. The dependence of the plasmon energy on the electron occupation of the 3d states is demonstrated.

Metastable phase formation during the reaction of Ni films with Si(001): The role of texture inheritance

The thermally induced solid-state reaction between a 10-nm-thick Ni film and a Si(001) substrate was investigated using in situ x-ray diffraction and ex situ pole figure analyses. The reaction begins with the appearance of orthorhombic Ni2Si grains characterized by a strong fiber texture. The formation of the metastable hexagonal θ phase—which inherits the fiber texture of Ni2Si—is then observed. This phase has been observed in every sample studied regardless of dopant, film thickness, deposition method, and anneal profile (>2000 conditions). Texture inheritance allows a reaction pathway with a lower activation energy than the expected formation through thermodynamically stable Ni silicide phases.

Chemical analysis of nickel silicides with high spatial resolution by combined EDS, EELS and ELNES

The purpose of this study is to develop methodologies for the characterization of Ni-silicides by analytical TEM techniques. The measurements are performed in STEM mode to allow a good spatial resolution. Initial examination of the Ni-silicide phases is done by energy-dispersive X-ray spectroscopy (EDS). It is shown that quantification results with high accuracy and precision are obtained when a Ni-silicide reference layer is used as a standard, and an absorption correction is applied to the data. The EDS quantification results are then used as a reference for the quantitative electron energy-loss spectroscopy (EELS) analysis. It is shown that EELS analysis yields quantification results with high accuracy and precision, when the EELS data are treated with a model based approach. The EELS analysis is combined with a study of the Ni-L2,3 near-edge structure (ELNES). The ELNES of the phases can be distinguished either visually or by calculating the branching ratio from the spectra with the model based approach. This paper shows that the different Ni-silicide phases can be distinguished with these EELS based methods. The accuracy and precision of the EDS and EELS results are compared.

In situ study of the formation of silicide phases in amorphous Ni–Si mixed layers

In this paper, we investigated Ni silicide phase formation when Si is added within an as deposited 50 nm Ni film. A series of 22 samples with a Si content varying from 0 to 50 at. % was prepared and systematically investigated with in situ x-ray diffraction. The inert oxide substrate was used to identify the phases which first crystallize in an amorphous Ni–Si mixture of a given concentration. The noncongruent silicides Ni3Si and Ni3Si2 are never observed to crystallize readily out of the mixture. A remarkable observation is the initial crystallization at low temperature of a hexagonal Ni-silicide, observed over a broad mixed layer composition [35–49%Si]; this hexagonal phase nucleates readily as a single phase [39–47%Si] or together with Ni2Si [35–38%Si] or NiSi [49%Si]. This low-temperature phase is related to the high temperature θ-phase, but covers a wide composition range up to 47%Si. For the same Ni–Si films deposited on Si(100), the initial nucleation of the Ni(Si) mixture is similar as for the samples deposited on SiO2, such that the complex sequence of metal-rich Ni-silicide phases typically observed during Ni/Si reactions is modified. For samples containing more than 21%Si, a simpler sequential phase formation was observed upon annealing. From pole figures, the phase formation sequence was observed to have a significant influence on the texture of the technologically relevant NiSi phase. For mixture composition ranging from 38% to 43%Si, the initial transient θ-phase appears extremely textured on Si(100). The observed transient appearance of a hexagonal phase is of importance in understanding the phase formation mechanisms in the Ni–Si system.

AI 이온 주입된 p-type 4H-SiC에 형성된 Ni/AI 오믹접촉의 전기 전도 특성

Ni/Al (`/` denotes deposition sequence) contacts were deposited on Al-implanted 4H-SiC for ohmic contact formation, and the conduction properties were characterized and compared with those of Ni-only contacts. The thicknesses of the Ni and Al thin film were 30 nm and 300 nm, respectively, and the films were sequentially deposited bye-beam evaporation without vacuum breaking. Rapid thermal anneal (RTA) temperature was varied as follows : , , and . The specific contact resistivity of the Ni contact was about , However, with the addition of Al overlayer, the specific contact resistivity decreased to about , almost irrespective of RTA temperature. X-ray diffraction (XRD) analysis of the Ni contact confirmed the existence of various Ni silicide phases, while the results of Ni/Al contact samples revealed that Al-contaning phases such as , , , and were additionally formed as well as the Ni silicide phases. Energy dispersive spectroscopy (EDS) spectrum showed interfacial reaction zone mainly consisting of Al and Si at the contact interface, and it was also shown that considerable amounts of Si and C have diffused toward the surface. This indicates that contact resistance lowering of the Ni/Al contacts is related with the formation of the formation of interfacial reaction zone containing Al and Si. From these results, possible mechanisms of contact resistance lowering by the addition of Al were discussed.

Influence of Ni silicide phases on effective work function modulation with Al-pileup in the Ni fully silicided gate/HfSiON system

Influences of Ni silicide phases on the effective work function (Φeff) modulation effect with Al incorporation has been investigated in the Ni silicide/HfSiON systems. We formed metal-insulator-semiconductor capacitors with Al incorporated Ni silicide (NiSi, Ni2Si, and Ni3Si) gates on HfSiON by Al solid-phase diffusion (Al-SPD) process or Al ion implantation (I/I) process. In the Al-SPD process, Al is deposited on Ni silicide gate. In the Al-I/I process, Al ions were doped in the upper part of Ni silicide layer. In both cases, we performed Al drive-in annealing under the condition of 450 °C for 30 min in N2 ambient. It is found that the flat-band voltage (Vfb) values of Al incorporated NiSi and Ni2Si gates shift negatively and identical independent of Al incorporation processes. A highly concentrated Al piled-up layer, which induces Φeff modulation to Al-Φeff value, seems to correspond to the Vfb modulation. On the other hand, Al incorporation has little influence on Φeff at the Ni3Si/HfSiON interface. We revealed that a lower Al diffusion coefficient in Ni3Si phase reduces the Al interface density at the Ni3Si/HfSiON interface. In addition, Al piled-up layer is inherently unstable at the Ni3Si/HfSiON interface, which is confirmed from the detailed investigation about thermal stability of Al piled-up layer by using phase change process from NiSi to Ni3Si phase.

Backside Nickel Based Ohmic Contacts to n-Type Silicon Carbide

This work focuses on Ni ohmic contacts to the C-face (backside) of n-type 4H-SiC substrates. Low-resistive ohmic contacts to the wafer backside are important especially for vertical power devices. Ni contacts were deposited using E-beam evaporation and annealed at different temperatures (700-1050 °C) in RTP to obtain optimum conditions for forming low resistive ohmic contacts. Our results indicate that 1 min annealing at temperatures between 950 and 1000 °C provides high quality ohmic contacts with a contact resistivity of 2.3x10-5 Ωcm2. Also our XRD results show that different Ni silicide phases appear in this annealing temperature range.

Influence of film thickness on the crystallization of Ni-doped amorphous silicon samples

This work reports on the crystallization of amorphous silicon (a-Si) films doped with 1 at. % of nickel. The films, with thicknesses ranging from 10 to 3000 nm, were deposited using the cosputtering method onto crystalline quartz substrates. In order to investigate the crystallization mechanism in detail, a series of undoped a-Si films prepared under the same deposition conditions were also studied. After deposition, all a-Si films were submitted to isochronal thermal annealing treatments up to 1000 °C and analyzed by Raman scattering spectroscopy. Based on the present experimental results, it is possible to state that (a) when compared to the undoped a-Si films, those containing 1 at. % of Ni crystallize at temperatures ∼100 °C lower, and that (b) the film thickness influences the temperature of crystallization that, in principle, tends to be lower in films thinner than 1000 nm. The possible reasons associated to these experimental observations are presented and discussed in view of some experimental and thermodynamic aspects involved in the formation of ordered Si–Si bonds and in the development of Ni-silicide phases.

Stress evolution during Ni–Si compound formation for fully silicided (FUSI) gates

The stress (force) evolution during the formation of different Ni silicide phases was monitored by in situ curvature measurements, for the reaction of thin Ni films of various thicknesses with 100 nm polycrystalline-Si deposited on oxidized (1 0 0) Si substrates. The silicide phase formation was also monitored by in situ X-ray diffraction, allowing to match and interpret the stress evolution in terms of the formation of the different silicide phases. We found that stresses developed during the formation of the different silicides can be explained qualitatively in terms of the corresponding volume changes at the reacting interfaces. Furthermore, the matching between XRD and force curve reveals that the highest compressive stress is related to the formation of the Ni 31Si 12 phase, and that the stress formed is relaxed when the reaction is completed.

Impact of surface preparation on nickel–platinum alloy silicide phase formation

Nickel based silicide films were prepared by annealing nickel–platinum layers deposited on n-doped Si substrates. We report on the evolution of the crystallography, the phase formation and the redistribution of contaminants on blanket wafers during silicide formation as a function of the silicon surface preparation prior to Ni(Pt) deposition. In situ argon sputtering etch creates a contamination layer which modifies phase texture during the formation of the first Ni silicide phases. Using remote pre-clean results in a predominant Ni 2Si phase with preferential grain orientation after a first anneal. After a second anneal, the monosilicide forms, regardless of what nickel rich silicide phase was initially formed and regardless of the surface preparation prior to metal deposition.

Phase effects and short gate length device implementation of Ni fully silicided (FUSI) gates

A study of the implementation of Ni fully silicided (FUSI) gates to scaled devices is presented, addressing the issue of phase control at short gate lengths. A linewidth effect for Ni FUSI gates is found for non-optimized processes targeting NiSi, with formation of NiSi at long gate lengths and Ni-rich silicides at short gate lengths. This is attributed to Ni diffusion from areas surrounding the gates, resulting in a larger reacted Ni–Si ratio at short gate lengths. The linewidth dependence of the Ni FUSI phase results in an undesirable kink in the V t roll-off characteristics, due to the difference in effective work function between the Ni silicide phases, which is particularly large for HfSiON dielectrics. An optimized 2-step RTP silicidation process is shown to eliminate this problem allowing the formation of NiSi gates uniformly at all gate lengths. The application and scalability of Ni-rich silicides to PMOS devices is also demonstrated, as well as a scheme for CMOS integration of dual WF phase controlled FUSI (NiSi for NMOS and Ni-rich silicides for PMOS), using an etch back step to reduce the poly-Si height on PMOS electrodes before full silicidation.