Study of nickel silicide formation on Si(1 1 0) substrate

Nickel silicide formation on Si(1 1 0) and Si(1 0 0) substrate was investigated in this paper. It is confirmed that nickel monosilicide (NiSi) starts to form after 450 °C annealing for Si(1 0 0) substrate, but a higher annealing temperature is required for NiSi formation on Si(1 1 0) substrate, which is demonstrated by X-ray diffraction (XRD) and Raman scattering spectroscopy. The higher formation temperature of NiSi is attributed to the larger Ni₂Si grain size formed on Si(1 1 0) substrate. Ni silicided Schottky contacts on both Si(1 0 0) and Si(1 1 0) substrates were also fabricated for electrical characteristics evaluation. It clearly reveals that the rectifying characteristics of NiSi/n-Si(1 1 0) Schottky contacts is inferior to that of NiSi/n-Si(1 0 0) Schottky contacts, which is attributed to a lower Schottky barrier height and a rougher contact interface. The formation kinetics for nickel silicide on Si(1 1 0) substrate is also discussed in this paper.     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Study of Ni/Si(1 0 0) solid-state reaction with Al addition

The characteristics of Ni/Si(1 0 0) solid-state reaction with Al addition (Ni/Al/Si(1 0 0), Ni/Al/Ni/Si(1 0 0) and Al/Ni/Si(1 0 0)) is studied. Ni and Al films were deposited on Si(1 0 0) substrate by ion beam sputtering. The solid-state reaction between metal films and Si was performed by rapid thermal annealing. The sheet resistance of the formed silicide film was measured by four-point probe method. The X-ray diffraction (XRD) was employed to detect the phases in the silicide film. The Auger electron spectroscopy was applied to reveal the element profiles in depth. The influence of Al addition on the Schottky barrier heights of the formed silicide/Si diodes was investigated by current-voltage measurements. The experimental results show that NiSi forms even with the addition of Al, although the formation temperature correspondingly changes. It is revealed that Ni silicidation is accompanied with Al diffusion in Ni film toward the film top surface and Al is the dominant diffusion species in Ni/Al system. However, no Ni_xAl_y phase is detected in the films and no significant Schottky barrier height modulation by the addition of Al is observed.     

Oxygen distribution in nickel silicide films analyzed by time-of-flight secondary ion mass spectrometry

The oxygen distribution in Ni₂Si and NiSi films formed during a two-step silicidation process was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS mass spectra revealed that both silicon and nickel reacted with oxygen at the Ni₂Si surface. In addition, silicon nitride was formed at the surface by the reaction of silicon with nitrogen in the TiN capping layer during the first silicidation annealing. The amount of nitrogen at the NiSi surface varied with silicidation annealing temperature and with the formation conditions of the TiN capping layer. We also showed that a small amount of oxygen was penetrated into the NiSi film and strongly affected the level of junction leakage current in n⁺–p junctions in n-channel MOSFETs. The oxygen concentration in the NiSi film decreased with an increase in the amount of nitrogen at the NiSi surface.     

Silicidation in Ni/Si thin film system investigated by X-ray diffraction and Auger electron spectroscopy

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni₂Si, NiSi and NiSi₂ phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi₂ phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.     

Structural and electrical characterization of the nickel silicide films formed at 850 °C by rapid thermal annealing of the Ni/Si(1 0 0) films

Nickel di-silicide formation induced by RTA process at 850 °C for 60 s in the Ni/Si(1 0 0) systems are investigated as a function of the initial Ni film thickness of 7-89 nm using XRD, RBS, SEM, X-SEM and AFM. Based on the XRD and RBS data, in the silicide films of 400-105 nm, NiSi and NiSi₂ silicide phases co-exist, indicating that Ni overlayer is completely transformed to NiSi and NiSi₂ silicide phases. SEM reveals that these films consist of large grains for co-existence of NiSi₂ and NiSi phases, separated from one another by holes, reflecting that NiSi₂ grows as islands in NiSi matrix. These films have low sheet resistance, ranging from 1.89 to 5.44 Ω/□ and good thermal stability. For thicknesses ≤ 80 nm RBS yields more Si-rich silicide phases compared to thicker films, whereas SEM reveals that Si-enriched silicide islands with visible holes grow in Si matrix. As the film thickness decreases from 400 to 35 nm, AFM reveals a ridge-like structure showing a general trend of decreasing average diameter and mean roughness values, while sheet resistance measurements exhibit a dramatic increase ranging from 1.89 to 53.73 Ω/□. This dramatic sheet resistance increase is generated by substantial grain boundary grooving, followed by island formation, resulting in a significant phase transformation from NiSi₂-rich to Si-rich silicide phases.     

Identification of nickel silicide phases on a silicon surface from Raman spectra

We have demonstrated the effectiveness of Raman spectroscopy for monitoring nickel silicide formation processes on the surface of silicon wafers, with deposition of a composite metal layer (nickel, platinum, and vanadium) under industrial process conditions in microelectronics. The observed shift of all the NiSi lines toward lower energies is associated with formation of the metastable silicide phase Ni_1?x Pt _x Si, which leads to the presence of stresses in the lattice as a result of the increase in the distances between atoms.     

掺Mo对NiSi薄膜热稳定性的改善

报导了在镍薄膜中掺入少量Mo提高了镍硅化物的热稳定性.结果表明，经650— 800℃快速热 退火形成的Ni(Mo)Si硅化物薄膜电阻值较低，约为2．4(Ω／□).XRD分析表明薄膜中只存在 NiSi相，而没有NiSi₂生成.由吉布斯自由能理论分析表明在Ni薄膜中掺人5．9 ％Mo对改善 Ni硅化物热稳定性起到至关重要的作用.经650—800℃快速热退火后的 Ni(Mo)Si／Si肖特基 二极管电学特性良好，势垒高度Φ_B为0．64—0．66eV，理想因子接近于1，更 进一步证明掺少量的Mo能够改善NiSi薄膜的热稳定性. 关键词： 镍硅化物 快速热退火 x射线衍射分析 卢瑟福背散射     

Low-temperature diffusion of silicon atoms in the nickel-nickel silicide-silicon system

The diffusion of Si atoms from a silicon substrate through a layer of nickel monosilicide into a Ni film is investigated in the temperature interval 470–670°K by the method of radioactive isotopes. The distribution profile of Si in NiSi and Ni is derived. The GB-diffusion parameters of Si in NiSi are determined. It is shown that when T>570°K there is an increase in the thickness of the initial NiSi layer, and a kink appears on the in D=f(1/T) curve. The associated change in the activation energy of diffusion from 0.43 (470–570°K) to 0.72 eV (570–670°K) is explained by the formation of Ni-Si and Si-O type complexes. The diffusion of silicon atoms accompanied by complex-formation processes determines the evolution of the resistivity of the Ni-NiSi-Si contact.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 78–83, March, 1985.     

Synthesis and charge storage properties of double-layered NiSi nanocrystals

Based on bidirectional diffusion of Ni atoms, double-layered nickel silicide (NiSi) nanocrystals (NCs) for multilevel charge storage were fabricated, and their charge storage properties were examined. The double layer was produced by long-term thermal annealing (for 4 h at 900 °C) of a sandwich structure comprised of a thin Ni film of 0.3 nm sandwiched between two silicon-rich oxide (SiO_1.36) layers. Transmission electron microscopic image clearly exhibits a distinct NiSi nanocrystal double layer with a gap of about 7 nm between the mean positions of particle distribution in each NC layer. Capacitance–voltage measurements on the metal/oxide/semiconductor (MOS) capacitors with the double-layered NiSi nanocrystals are shown to have the apparent two plateaus of charge storage, the large memory window of about 9 V and the improved charge retention stability.     

Spectroscopic ellipsometric evidence of the solid-state reactions in Ni/Si multilayered films,induced by ion-beam mixing and thermal annealing

Solid-state reactions, induced by ion-beam mixing (IBM) and thermal annealing, in Ni/Si multilayered films (MLF) with an overall stoichiometry of Ni2Si, NiSi and NiSi2, while keeping the nominal thickness of Ni sublayer constant (3.0 nm), were studied by using spectroscopic ellipsometry as well as X-ray diffraction (XRD). The mixing was performed with Ar+ ions of an energy of 80 keV and a dose of 1.5× 1016 Ar+/cm2. Unlike the results of our previous study on Fe/Si MLF [Y.V. Kudryavtsev et al., Phys. Rev. B 65, 104417 (2002)], it was shown that an amorphous phase of NiSi in the B20 phase was formed during deposition independent of the overall stoichiometry of MLF, i.e., the nominal thickness of Si sublayer. IBM leads to some structural changes in the Ni/Si MLF, which cannot be detected by XRD but are confidently recognized by optical tools. A thermal annealing at 673 K of the Ni/Si MLF with an overall stoichiometry of NiSi and NiSi2 causes formation of the -NiSi phase. The first trace of NiSi2 phase on the background of the -NiSi phase was detected by XRD after an annealing at 1073 K, while, according to the optical results, NiSi2 turned out to be the dominant phase for the annealed Ni/Si MLF with an overall stoichiometry of NiSi2.     

Formation of the Si/Ti interface

The formation of the Si/Ti interface during the deposition of silicon on titanium polycrystalline substrates has been studied at room temperature (RT) using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), ultraviolet photoelectron spectroscopy (UPS) and ion scattering spectroscopy (ISS). The experimental results are consistent with a two-stage mechanism for Si growth: a first stage characterized by the simultaneous formation of a uniform titanium silicide layer, that reaches a limiting thickness of ∼3 monolayer (ML), and pure silicon islands 1 ML thick that grow on top of this layer up to coalescence, followed by a second stage in which pure silicon islands, with an average thickness of 9 ML, grow on top of the uniform titanium silicide layer + pure silicon ML structure formed during the first stage. As a whole, pure silicon species grows according to a Stranski-Krastanov mechanism, where the first ML is formed during the first stage and the islands during the second stage. The comparison of Ti/Si and Si/Ti interfaces shows that the structure and composition of the interface do not depend substantially on the deposition sequence, suggesting that the bulk chemistry of the compound formed at the interface dominates over the surface kinetics and the bulk substrate chemistry in determining the composition and structure of the interface.     

Growth of an Eu-Si(111) thin film structure: The stage of silicide formation

Silicide formation in thin films produced by depositing Eu atoms on the Si(111) surface is studied using LEED, Auger electron spectroscopy, contact potential difference, and isothermal thermal-desorption spectroscopy. It is shown that if Eu is deposited on a substrate at room temperature, the growing film is disordered and consists of almost pure Eu. At high temperatures (T≥500 K), the Eu-Si(111) system forms through the Stranski-Krastanow mechanism; namely, first a two-dimensional transition layer (reconstruction) with the (2×1) structure forms and then three-dimensional silicide crystallites grow on it. A specific feature of this system is a low rate of diffusion of Si atoms in the europium silicides. This feature accounts for the concentration gradient of Si atoms across the silicide film thickness and, as a consequence, the multiphase film composition.     

Control of the interfacial reactivity in the Ni/Si system

The reactivity at the Ni/Si interface is studied as a function of the sputtering conditions of the nickel film. Four systems are considered, by combining two different sputtering rates and two distinct base pressures for the deposition of the nickel 10 nm-thick film. The formation of Ni₂Si is revealed at the four interfaces by an X-ray emission spectroscopy study of the interfacial Si 3p occupied valence states. Increasing the sputtering rate is herein evidenced to decrease the quantity of silicide formed at the interface. Moreover, the combination of a high sputtering rate and a low base pressure advantageously prevents against the oxidization of the silicon surface during the metal deposition.     

Enhanced formation of periodic arrays of low-resistivity NiSi nanocontacts on (0 0 1)Si0.7Ge0.3 by nanosphere lithography with a thin interposing Si layer

In this study, we demonstrated significant enhancement of the formation of low-resistivity NiSi nanocontacts with controlled size on (0 0 1)Si_0.7Ge_0.3 substrates by combining the nanosphere lithography with the use of a new Ni/a-Si bilayer nanodot structure. Low-resistivity NiSi with an average size of 78 nm was observed to be the only silicide phase formed in samples annealed at 350-800 °C. The presence of the interposing Si layer with appropriate thickness was found to effectively prevent Ge segregation and maintain the interface stability in forming NiSi nanocontacts on (0 0 1)Si_0.7Ge_0.3. As the annealing temperature was increased to 900 °C, amorphous SiO_x nanowires were observed to grow from silicide nanocontact regions. The NSL technique in conjunction with a sacrificial Si interlayer process promises to be applicable in fabricating periodic arrays of other low-resistivity silicide nanocontacts on Si_1−xGe_x substrates without complex lithography.     

Interaction of iron atoms with the silicon surface coated with a native oxide layer

The solid-phase epitaxy of iron silicide on the Si(111) surface coated with a native oxide layer is studied by high-resolution photoelectron spectroscopy using synchrotron radiation and by atomic force microscopy. The iron deposition dose changes up to 1 nm, and the annealing temperature changes up to 500°C. At room temperature, the native oxide layer is shown to be impermeable to Fe atoms and an iron film grows on the sample surface. An increase in the annealing temperature to ～100°C results in a change in the film morphology, increasing its heterogeneity. As the annealing temperature increases to ～250°C, Fe and Si atoms diffuse through the oxide layer and undergo a solid-phase reaction. As a result, stable iron monosilicide ?-FeSi forms.     

Epitaxial growth of uniform NiSi2 layers with atomically flat silicide/Si interface by solid-phase reaction in Ni-P/Si(1 0 0) systems

As metal-oxide-semiconductor field-effect transistor (MOSFET) devices are shrunk to the nanometer scale, flat shallow metal/Si electrical contacts must be formed in the source/drain region. This work demonstrates a method for the formation of epitaxial NiSi₂ layers by a solid-phase reaction in Ni-P(8 nm)/Si(1 0 0) samples. The results show that the sheet resistance remained low when the samples were annealed at temperatures from 400 to 700 °C. P atoms can be regarded as diffusion barriers against the supply of Ni to the Si substrate, which caused the formation of Si-rich silicide (NiSi₂) at low temperature. Furthermore, elemental P formed a stable capping layer with O, Ni and Si during the annealing process. A uniform NiSi₂ layer with an atomically flat interface was formed by annealing at 700 °C because of the formation of a Si-Ni-P-O capping layer and a reduction in the total interface area.     

Effect of erbium interlayer on nickel silicide formation on Si(1 0 0)

To reveal the influence of erbium interlayer on the formation of nickel silicide and its contact properties on Si substrate, Er(0.5-3.0 nm) and Ni(20 nm) are successively deposited onto Si(1 0 0) substrate and are treated by rapid thermal annealing in pure N₂ ambient. The NiSi formation temperature is found to increase depending on the Er interlayer thickness. The formation temperature of NiSi₂ (700 °C) is not influenced by Er addition. But with 2 nm Er interlayer, the formed NiSi₂ is observed textured with preferred orientation of (1 0 0). During the formation of NiSi, Er segregates to the surface and little Er remains at the NiSi/Si(1 0 0) interface. Therefore, the Schottky barrier height of the formed NiSi/n-Si(1 0 0) contact is measured to be 0.635 ∼ 0.665 eV which is nearly invariable with different Er addition.     

Surface Morphology of NiSi 2 /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 Å and at h ≥ 200 Å 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 Å 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.