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.     

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.     

XRD and XPS characterisation of transition metal silicide thin films

Binary transition metal silicides based on the systems Ti–Si, Fe–Si, Ni–Si and Cr–Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti–Si, Fe–Si and Ni–Si systems, single phase thin films of TiSi₂, β-FeSi₂ and NiSi₂ were generated as the model predicts, while a mixture of CrSi + CrSi₂ phases was obtained for the Cr–Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p_3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0 eV for Ni 2p_3/2 peak of NiSi₂ is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3 eV for the Fe 2p_3/2 level was shown for β-FeSi₂ and negative binding energy shifts of 0.1 and 0.3 eV were determined for CrSi + CrSi₂ and TiSi₂, respectively.     

Growth of size-tunable periodic Ni silicide nanodot arrays on silicon substrates

The fabrications of size-tunable periodic arrays of nickel metal and silicide nanodots on (0 0 1)Si substrates using polystyrene (PS) nanosphere lithography (NSL) and heat treatments have been investigated. The growth of epitaxial NiSi₂ was found to be more favorable for the Ni metal nanodot arrays. The effect becomes more pronounced with a decrease in the size of the Ni nanodots. The sizes of the epitaxial NiSi₂ nanodots were tuned from 38 to 110 nm by varying the diameter of the PS spheres and heat treatment conditions. These epitaxial NiSi₂ nanodots formed on (0 0 1)Si were found to be heavily faceted and the faceted structures were more prone to form at higher temperatures. Based on TEM, HRTEM and SAED analysis, the faceted NiSi₂ nanodots were identified to be inverse pyramids in shape. Compared with the NiSi₂ nanodot arrays formed using single-layer PS sphere masks, the epitaxial NiSi₂ nanodot arrays formed from the double-layer PS sphere templates exhibit larger interparticle spacings and smaller particle sizes. Since the nanoparticle sizes, shapes and interparticle spacings can be adjusted by tuning the diameter of the PS spheres, stacking conditions, and heat treatment conditions, the PS NSL technique promises to be an effective patterning method for growth of other nanostructures.     

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.     

Positron beam studies of cobalt silicides

Silicide formation in Co/Si thin structures synthesized using thermal evaporation, sputter deposition and ion implantation, has been investigated using depth-resolved positron annihilation spectroscopy (PAS) together with other corroborative experimental techniques. S vs. E_p curves and S-W correlation plots have revealed important processes such as defect annealing, interdiffusion, silicide formation and recrystallization of amorphous Si. These studies have shown that there exist differences in the formation temperature of the silicide phases, the sequence of silicide phase formation and defect generation owing to the nature of the deposition methods employed.     

Improved electrical and thermal properties of nickel silicides by using a NiCo interlayer

We have investigated the effects of a NiCo interlayer on the electrical and thermal properties of nickel silicide as a function of the annealing temperature. For the interlayered samples, 3 nm-thick NiCo(10 at.% Co) films are electron-beam evaporated on Si substrates, on which 27 nm-thick Ni films are deposited without breaking the vacuum. It is shown that all the samples exhibit a distinctive increase in the sheet resistance at temperatures above 900 ^°C. However, the NiCo interlayer sample produces the lowest sheet resistance at 900 ^\circC. X-ray diffraction results show that the Ni only and NiCo interlayer samples produce NiSi and NiSi₂ phases, while NiCo full samples give NiSi and Ni_1−xCo_xSi₂ phases. Scanning electron microscopy results exhibit that for all the samples, the surfaces become degraded with numerous arbitrarily-shaped spots, corresponding to areas uncovered by the silicides. The areal fractions of the silicides for the Ni only, NiCo full, and NiCo interlayer samples are about 57%, 72%, and 81%, respectively. The temperature dependence of the electrical properties of the silicide samples is explained in terms of the formation of resistive phases and the agglomeration of the silicide.     

Phase transformation of Ni/Si thin films induced by nanoindentation and annealing

Thin Ni/Si films are prepared by depositing a Ni layer with a thickness of 100 nm on a Si (100) substrate. The as-deposited thin-film specimens are indented to a maximum depth of 500 nm using a nanoindentation technique and are then annealed at temperatures of 200°C, 300°C, 500°C and 800°C for 2 min. The microstructural changes and phases induced in the various specimens are observed using transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). Based on the load-displacement data obtained in the nanoindentation tests, the hardness and Young’s modulus of the as-deposited specimens are found to be 13 GPa and 177 GPa, respectively. The microstructural observations reveal that the nanoindentation process prompts the transformation of the indentation-affected zone of the silicon substrate from a diamond cubic structure to a mixed structure comprising amorphous phase and metastable Si III and Si XII phases. Following annealing at temperatures of 200∼500°C, the indented zone contains either a mixture of amorphous phase and Si III and Si XII phases, or Si III and Si XII phases only, depending on the annealing temperature. In addition, the annealing process prompts the formation of nickel silicide phases at the Ni/Si interface or within the indentation zone. The composition of these phases depends on the annealing temperature. Specifically, Ni₂Si is formed at a temperature of 200°C, NiSi is formed at a temperature of 300°C and 500°C, and NiSi₂ is formed at 800°C.     

Oxidation behaviour of nickel silicides investigated by AES and XPS

The oxygen interaction with Ni silicide surfaces in a wide range of composition, from NiSi₂ to Ni₃Si, has been investigated at room temperature by AES and XPS techniques. It has been found that the Si oxidation is enhanced over that of pure Si in all the Ni-Si compounds, and that the strongest oxidation occurs in Ni richer silicides. In general, oxygen bonds with Si leaving the metal unoxidized, but in Ni₃Si evidence for the occurrence of Ni oxidation has been found at high exposures.     

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.     

Epitaxial growth and surface structure of NiSi2{0 0 1} on Si{0 0 1}

LEED (low-energy electron diffraction) intensity measurements were done to monitor the formation of epitaxial NiSi₂ on the {0 0 1} surface of Si. The resulting silicide surface, although possibly reconstructed, was subjected to LEED intensity analysis as NiSi₂{0 0 1}1×1. Several structural models involving bulk-like terminations, and variants thereof, failed the LEED test. However, one model, with Si adatoms in the four-fold symmetrical sites of the Si bulk-like termination, provides reasonable agreement with experiment and is therefore tentatively proposed as containing the main features of the real structure. The model may explain the failure of double epitaxy, i.e., the failure to grow epitaxial Si films on the silicide surface.     

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     

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     

Investigation on the 773 K isothermal section of Dy–Ni–Si ternary phase diagram by X-ray powder diffraction

The 773 K isothermal section of the Dy–Ni–Si ternary system was investigated and constructed by X-ray powder diffraction in this paper. Eighteen ternary phases (DyNiSi, DyNi₂Si₂, DyNiSi₂, Dy₂Ni₃Si₅, DyNiSi₃, Dy₂NiSi₃, Dy₃Ni₆Si₂, DyNi₁₀Si₂, Dy₄NiSi₇, DyNi₂Si, DyNi₅Si₃, DyNi₄Si, Dy₃NiSi₂, DyNi₆Si₆, Dy₈Ni₃₁Si₁₁, Dy₃Ni₂Si₄, Dy₄Ni₅Si and Dy₉Ni₂Si₁₄) were confirmed to exist in this work. In those ternary phases, Dy₉Ni₂Si₁₄ is a new phase, Dy₂NiSi₃ and Dy₄NiSi₇ have solid solution phenomena and the solid solution ranges are Dy_33.3Ni_14.7–18.7Si_52–48 and Dy₄Ni_0.3–1.2Si_7.7–6.8, respectively. We constructed 14 two phase regions and 52 three phase regions in the Dy–Ni–Si ternary phase diagram at 773 K. Because the phase relation is not very clear between 66.7 and 50 Si at.% in the Dy–Si binary system, we use dot lines to estimate tentative phase regions in this region.     

Ion beam modification of silicide-silicon interfaces

We have modified the contact interface between Pd₂Si and n-Si by ion implantation and investigated the effect of the implantation on Schottky barrier height and rate of silicide formation by electrical current-voltage measurements and Rutherford backscattering spectroscopy. Various ions, As. P, B. O and Si at 50 keV and up to a dose of 5 × 10¹⁴ ions/cm² were implanted into Si wafers before the Pd-deposition to form Pd₂Si. In the case of As and P, the implantation showed a large erect on the subsequent Pd₂Si formation; the formation is enhanced in the as-implanted samples, but it is retarded if an annealing at 600°C precedes the Pd-deposition. Silicide formation was found generally to help reduce the implantation damage (with or without the 600°C annealing) and showed improvements on the electrical characteristics of the contact interface. Consumption of the entire implanted region by silicide formation is found necessary for obtaining a good diode performance. In the case of As implantation, a lowering of the Schottky barrier height of Pd₂Si has been observed.     

The Ba/Si(100)-2 × 1 interface I. XPS and XAES studies of silicide formation

In two complementary papers we present the results and analysis of an extended study of the Ba/Si(100)−2 × 1 interface. In this paper, we will discuss X-ray excited Auger electron spectroscopy- and X-ray photoelectron spectroscopy chemical shifts, as well as plasmon losses, which have been studied to answer the question whether silicide formation occurs at this interface. It is found that no silicide formation takes place at room temperature. Two Ba-Si phases are detected as reaction products upon annealing the Ba/Si(100) system at ˜ 550 K.     

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.     

Formation of high-conductivity NiSi2 layers on Si at zero-mismatch temperature by high-current Ni-ion implantation

2 and Si lattices at 380 °C, which was defined as zero-mismatch temperature. The implantation was conducted with a metal vapor vacuum arc (MEVVA) ion implanter at an extraction voltage of 45 kV. Based on a thermal conduction estimation, a temperature rise of 380 °C required the Ni-ion current density to be 35 μA/cm². For the Si(111) wafers, the high conducting NiSi₂ layers were indeed directly formed after Ni-ion implantation with this specific current density to a normal dose of 2×10¹⁷ ions/cm² and the resistivity was as low as 9 μΩ cm. For the Si(111) wafers pre-covered with a 10-nm Ni overlayer, the resistivity of the NiSi₂ layers obtained under the same conditions decreased down to about 6 μΩ cm. The superior electrical property of the NiSi₂ was thought to be related to its formation temperature, i.e. at a zero-mismatch temperature of 380 °C, which resulted in minimizing the stress and stress-induced defects involved in its formation as well as cooling process. Received: 27 April 1998 / Accepted: 26 October 1998     

The interface reaction of high-k La2Hf2O7/Si thin film grown by pulsed laser deposition

The La₂Hf₂O₇ films have been deposited on Si (1 0 0) substrate by using pulsed laser deposition (PLD) method. X-ray diffraction (XRD) demonstrates that the as-grown film is amorphous and crystallizes after 1000 °C annealing. The interface structure is systematically studied by Synchrotron X-ray reflectivity (XRR), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Silicide, silicate and SiO_x formations from interfacial reaction are observed on the surface of the Si substrate in the as-grown film. The impact of silicide formation on the electrical properties is revealed by capacitance-voltage (C-V) measurements. By post-deposition annealing (PDA), silicide can be effectively eliminated and C-V property is obviously improved.     

Silicide formation in Co/Si system investigated by depth-resolved positron annihilation and X-ray diffraction

The transformation of Co/Si to CoSi₂/Si in the temperature range of 300-1170 K has been investigated using depth-resolved positron annihilation and Glancing incidence X-ray diffraction (GIXRD). The different silicide phases formed are identified from the experimental positron annihilation characteristics, which are consistent with the GIXRD results. The present study clearly indicates the absence of vacancy defects in the silicide overlayer.