Ni Silicide Formation Research Articles

Effect of a Ge interlayer on the high-temperature behavior of NiSi films

The effect of a thin Ge interlayer on the formation of Ni silicides on (100)Si substrates has been investigated. X-ray diffraction shows a remarkable increase of the nucleation temperature of NiSi2 in the presence of the Ge interlayer. Four-probe measurements show that the sheet resistance of silicide formed in Ni∕Ge∕Si system remains stable up to 850 °C, while the sheet resistance of silicide formed in Ni∕Si system presents a significant increase at 750 °C. Scanning electron microscopy indicates that island formation is not observed in the NiSi film grown on Ge∕Si substrate annealing at 800 °C. The classical nucleation theory is employed to explain the increased temperature of the nucleation of NiSi2 in the Ni∕Ge-Si system.

The effects of Ta on the formation of Ni-silicide in Ni 0.95xTa x0.05/Si systems

We investigated a comparative study on the silicide formation in the Ni 0.95Ta 0.05/Si alloy systems and Ni/Si systems. Ni and Ni 0.95Ta 0.05 films were deposited on Si(1 0 0) substrate by DC magnetron sputtering and processed at various silicidation temperatures. The sheet resistance of the silicide from the Ni 0.95Ta 0.05/Si alloy systems was obtained at lower values than those in pure Ni/Si systems at any temperature. Using RBS and TEM analyses, we confirmed the presence of a Ta rich layer at the top of the Ni-silicide layer and the presence of small amounts of Ta in the silicide layer. The stability of the silicide layer for the Ni 0.95Ta 0.05 systems is explained by the presence of the Ta rich layer on top of the Ni-silicide layer, as well as by the presence of the small amount of Ta in the Ni-silicide layer. The Ni-silicide using Ni 0.95Ta 0.05/Si system displayed a stable sheet resistance value of ∼5 Ω/sq which was maintained during the anneal process at 600 °C.

Formation of ternary Ni-silicide on relaxed and strained SiGe layers

Ni germanosilicide formation on Si1−xGex layers with different elastic strain was investigated by sheet resistance measurements and cross-sectional transmission electron microscopy. Ni–Si–Ge silicide layers with low resistivity were obtained by depositing 20 nm Ni with an 8 nm Ti cap on the Si1−xGex layers and rapid thermal annealing within the temperature range of 400–500 °C. The sheet resistance and the thermal stability of the silicide layers depends on the elastic strain of the SiGe layer. Best uniformity of the silicide layers was obtained on relaxed SiGe layers. High strain produces rough silicide layers. Strain relaxation was observed in initially pseudomorphically strained Si0.73Ge0.27 layers during silicidation at 600 °C.

Low temperature spike anneal for Ni-silicide formation

Excessive Ni-silicide formation is observed at the edges of poly gates and source/drain lines. The excessive silicidation results in locally completely silicided poly gates and in very high junction leakage in small source/drain islands. It was studied whether the excessive Ni-silicide formation in narrow features can be reduced in a two-step Ni-silicide process in which the thermal budget of the first RTP step is just enough to fully react the Ni. It was found that the excessive silicidation can be avoided either by reducing the anneal temperature or by reducing the anneal time. Reducing the thermal budget of the first RTP step was found to significantly improve the junction leakage in small source/drain islands for As junctions. No improvement was observed for B junctions. The latter is thought to be related to the presence of NiSi2 pyramids.

Thermal stability, phase and interface uniformity of Ni-silicide formed by Ni–Si solid-state reaction

Thermal stability, phase and interface uniformity of Ni-silicide are some key issues for NiSi Salicide technology. The improved stability of NiSi was achieved by Ni/Pt/Si and Ni/Pd/Si reaction. The increase of thermal stability can be explained by classical nucleation theory. The phase and interface uniformity of Ni-silicides formed by Ni–Si solid-state reaction were characterized by X-ray diffraction (XRD) and temperature-dependent current–voltage ( I– V– T) techniques. Results show that the Schottky barrier height (SBH) inhomogeneity characteristic has strong dependence on annealing temperature for Ni-silicide formation. Deep level transient spectroscopy (DLTS) measurement shows that annealing at relatively low temperature may cause electrically active deep level defects in the film. These results show that choosing a proper annealing temperature for Ni/Si silicidation will be very important for device performance.

Study of TiW/Au Thin Films Metallization Stack for High Temperature and Harsh Environment Devices on 6H Silicon Carbide

Study of TiW/Au Thin Films Metallization Stack for High Temperature and Harsh Environment Devices on 6H Silicon Carbide

Effects of Ti Interlayer on Ni/Si Reaction Systems

The effects of Ti interlayer on the formation of Ni silicides on Si(100) substrate was investigated. The phase and microstructure of Ni silicides during isochronal annealing treatment are monitored in situ by curvature measurement and characterized ex situ by other measurements. The addition of a thin Ti layer which formed an amorphous layer with the Si substrate acted as a diffusion barrier for the Ni atom in the early phase transformation process. The transformation temperature for the NiSi is significantly increased in an isochronal annealing process. When the NiSi phase is formed, the Ti-related layer moves to the surface of the silicide film. The temperature for the transformation of NiSi to is relatively irrelevant to the presence of the Ti interlayer. A preferential orientation of (200) and (002) was found in the NiSi phase formed via the Ti interlayer, which significantly improved the epitaxial quality of on Si(100) substrate with a stepwise interface bounded by (111) and (100) planes. The top continuous Ti-related layer causes the incomplete accommodation of the thermal stress for the system. Upon disintegration of the Ti-related layer, the thermal stress of the system could be completely accommodated by relaxation of the NiSi layer. © 2004 The Electrochemical Society. All rights reserved.

Nickel nanoparticles in silica glass fabricated by 60 keV negative-ion implantation

Magnetic nanoparticles are fabricated in silica glass (SiO 2) using high-flux implantation of 60 keV negative nickel ions Ni −. Photo-absorption measurements and cross-sectional transmission electron microscopy (XTEM) observation confirm the formation of metallic Ni nanoparticles in SiO 2, and exclude the possible formation of Ni silicides (Ni 3Si, Ni 2Si, NiSi) and oxides (NiO) as major products. The mean diameter of the nanoparticles was ∼2.9 nm, and the observed depth distribution was similar to a prediction from the TRIDYN code when sputtering was accounted for. Temperature- and field-dependences of magnetization show that the nanoparticles are in the superparamagnetic state at T>∼50 K. From the peak temperature of the zero-field cooling (ZFC) magnetization, which is ∼27 K, and the mean diameter determined from XTEM, it is suggested that the magnetic anisotropy constant K of the nanoparticles is enhanced by ∼8 times as compared to the bulk value.

Suppression of Ni Silicide Formation by Se Passivation of Si(001)

ABSTRACTValence mending of a semiconductor surface, such as the Se-passivated Si(001) surface, improves the chemical and thermal stability of the surface as compared to the bare Si(001) surface. In this paper, we report the suppression of Ni silicide formation between Ni and Si(001) through monolayer passivation of Si(001) by Se. Ni was deposited on both Se-passivated and bare Si(001) surfaces. The samples were annealed at temperatures from 400°C to 700°C. Cross-sectional TEM (Transmission Electron Microscopy) revealed that Ni on bare samples reacted with Si at 400°C and formed silicide, whereas Ni on Se-passivated samples did not react with Si at 500°C. Surface composition analysis by XPS (X-Ray Photoelectron Spectroscopy) showed pure Ni surface on Se-passivated samples annealed at 400°C and 500°C, but silicide surface on bare samples annealed at the same temperatures. Hence, Se passivation suppresses the formation of Ni silicide on the Si(001) surface by over 100°C as compared to the bare Si(001) surface. These results may have important implications in source/drain engineering in sub-100 nm Si CMOS (Complementary Metal Oxide Semiconductor) devices.

Analysis of laterally non-uniform layers and sub-micron devices by Rutherford backscattering spectrometry

A method for analyzing sub-micron devices by Rutherford backscattering spectrometry is presented. Using simplifying assumptions, we are able to simulate the backscattering spectrum of laterally non-uniform samples. The method has been verified with Ni/Pt laterally non-uniform layers on (1 0 0)Si substrate and has been applied to characterize the formation of Ni silicide in structures similar to metal oxide semiconductor (MOS) transistors. It is shown that the analysis of devices with a linewidth as low as 0.25 μm is possible using micro RBS and the method of simulation that we have developed.

Low-Temperature Growth of Carbon Nanotube by Plasma-Enhanced Chemical Vapor Deposition using Nickel Catalyst

Carbon nanotubes (CNTs) were grown on silicon (Si) substrates with a native oxide layer using a nickel (Ni) catalyst by the plasma-enhanced chemical vapor deposition method at 550 and 650°C. Multiwall CNTs with a large inside hollow core were observed with samples deposited on Si substrates with a native oxide layer. However, no CNT growth was observed with samples deposited on Si substrates without a native oxide layer due to the formation of Ni-silicide. The native oxide layer was believed to act as the diffusion barrier and to suppress the formation of Ni-silicide. The typical diameter and length of CNTs ranged from about 30 to 100 nm and 2 to 3 µm, respectively. The size of CNTs was more strongly dependent on the thickness of the Ni layer than on the growth temperature. The surface roughness and amount of surface defects decreased with increasing process temperature. We performed a post hydrogen plasma treatment for the purification of raw CNTs. The post hydrogen plasma treatment successfully removed residual graphite particles and/or metallic impurities without significant damage to the CNTs.

Effects of stress on the interfacial reactions of metal thin films on (0 0 1)Si

The influences of stress on the interfacial reactions of Ti and Ni metal thin films on (0 0 1)Si have been investigated. Compressive stress present in the silicon substrate was found to retard significantly the growth of Ti and Ni silicide thin films. On the other hand, the tensile stress present in the silicon substrate was found to enhance the formation of Ti and Ni silicides. For Ti and Ni on stressed (0 0 1)Si substrates after rapid thermal annealing, the thicknesses of TiSi 2 and NiSi films were found to decrease and increase with the compressive and tensile stress level, respectively. The results clearly indicated that the compressive stress hinders the interdiffusion of atoms through the metal/Si interface, so that the formation of metal silicide films was retarded. In contrast, tensile stress facilitates the interdiffusion of atoms. As a result, the growth of Ti and Ni silicide is promoted.

Layer Inversion of Ni(Pt)Si on Mixed Phase Si Films

The formation of Ni silicides has been improved with Ni(Pt)-silicidation on the mixed phase Si films which were grown using the rapid thermal chemical vapor deposition technique. The Ni(Pt)Si was stabilized up to 800°C and layer inversion was retarded beyond 600°C. The enhanced stability of Ni(Pt)Si is attributed to the change in Gibbs free energy. The reduced layer inversion is due to the modification of the Si microstructure that has played an important role in the layer inversion. The enlarged poly-Si grains from the mixed phase films are due to the silicide enhanced mediated crystallization using NiSi 2 precipitates as seeds besides the preexisting Si crystallites.

In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines

The formation of Ni silicides is studied by transmission electron microscopy during in situ heating experiments of 12 nm Ni layers on blanket silicon, or in patterned structures covered with a thin chemical oxide. It is shown that the first phase formed is the NiSi2 which grows epitaxially in pyramidal crystals. The formation of NiSi occurs quite abruptly around 400 °C when a monosilicide layer covers the disilicide grains and the silicon in between. The NiSi phase remains stable up to 800 °C, at which temperature the layer finally fully transforms to NiSi2. The monosilicide grains show different epitaxial relationships with the Si substrate. Ni2Si is never observed.

Formation of Ni silicides on (001)Si with a thin interposing Pt layer

The formation of Ni silicides on (001)Si with a thin interposing Pt layer has been investigated. NiSi was observed to be the only silicide phase for the samples annealed at 500–800 °C with a thin interposing Pt layer. The sheet resistance maintained the same low level in a wide temperature range. Pt addition was found to retard significantly the formation of nickel silicides and enhance the thermal stability of NiSi thin films on (001)Si. For Ni(30 nm)/Pt(1.5 nm)/(001)Si, the process window of NiSi was extended to 500–800 °C. The effects of a thin interposing Pt layer on the formation of Ni silicides on (001)Si are discussed.

On the Ni–Si phase transformation with/without native oxide

This study has been carried out to check the effect of native oxide on the formation of Ni silicides. Ni films of various thickness were sputter deposited on Si(100) wafer without oxide, with native oxide and with oxide grown by rapid thermal oxidation, and subjected to rapid thermal annealing in nitrogen ambient for 1 min at temperatures ranging from 250 to 900°C. For the samples with native oxide, phase identification by X-ray diffraction and composition analysis by Auger electron spectroscopy showed that the Ni films do not react below 800°C. At 800 and 900°C, NiSi 2 was found to form. Cross transmission electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the layer of native oxide that caused the inhibition of Ni–Si reaction. For the Si substrate with oxide grown by rapid thermal oxidation, the formation of nickel oxide was observed. A Ni–Si–O ternary phase diagram has been constructed to interpret the results observed. The annealed unreacted Ni films show improved etch resistance and lower resistivity as compared to the as-deposited Ni film. This is attributed to the observed change in microstructure, e.g., grain growth.

Surfactant effect of atomic hydrogen on suicide-formation of nickel on Si(110) surfaces

In this report Ni-silicide formation processes are described using LEED-Auger and a high resolution FE-scanning electron microscope. Eight monolayers (ML) of Ni atoms were deposited on the clean and hydrogen-terminated (H-terminated) Si(110) surfaces. Ni atoms reacted strongly with silicon atoms at room temperature on the bare Si(110). However, on the H-terminated Si(110) surface Ni atoms reacted gradually with Si atoms with increasing annealing temperature, and formed a uniform layer and flat suicide surface. In contrast, on the bare Si surface, the silicide formed non-uniform but precipitous islands along the [12] direction with elevating temperatures.

Silicon Crystal Growth on a Ni Silicide Seeding Layer by DC Magnetron Sputtering

AbstractDirect current (d.c.) magnetron sputtering was applied to polycrystalline Si growth and yielded a uniform Si film at a deposition temperature below the glass softening point. The approach involved the deposition of a thin Ni film over SiO2 prior to Si sputtering. The interaction of a fine-grained metallic Ni with an atomic Si provided by a sputtering gun resulted in the formation of Ni silicide at the Ni-Si interface immediately after the onset of Si deposition. The phase composition of the nickel silicide was controlled by the temperature of deposition and the Si-to-Ni concentration ratio. The silicide region exhibited a layered structure where the bottom layer consisted of the mixture of several NixSiy phases and the top layer represented the pure NiSi2 phase. This Ni disilicide layer provided the nucleation sites for the epitaxial Si crystal growth. As a result, the polycrystalline silicon film consisted of 0.1-0.5µm grains with preferred (11) or (110) orientation without an indication of an amorphous phase. The carrier lifetime of 11 µs indicated good electrical properties which make the film potentially applicable to fabrication of thin film transistors and solar cells. The Ni prelayer thickness in the 5-100nm range dramatically influenced the crystal size and preferential crystal orientation. Possible mechanisms responsible for the nickel silicide induced grain growth of silicon and the correlation between the Ni silicide and silicon microstructure is discussed.

Formation and Stability of NI(PT) Silicide on (100)SI and (111)SI

AbstractThe effect of a small amount of Pt (5 at.%) on the thermal stability of NiSi film on (100)Si and (111 )Si has been investigated. Rutherford back scattering, Scanning Electron Microscopy, and X-ray diffraction have been used to study the formation, microstructure and orientation of the silicide. The addition of platinum results in increasing the disilicide nucleation temperature to 900°C and thus leads to a better stability of NiSi at high IC processing temperatures. The presence of Pt also induced a texture of the NiSi film both on (11 1)Si and (100)Si. The increase in thermal stability is explained in terms of nucleation controlled reaction concept and should open new possibilities for the use of NiSi in self aligned silicidation. The redistribution of Pt in the silicide is examined and explained in terms of kinetics and thermodynamics considerations. The addition of Pt also increases the temperature of agglomeration of NiSi.

Coplanar amorphous silicon thin film transistor fabricated by inductively coupled plasma chemical vapor deposition

The electrical and optical properties of the hydrogenated amorphous silicon (a-Si:H) films deposited by inductively coupled plasma (ICP) chemical vapor deposition (CVD) have been investigated. The ICP-CVD a-Si:H films deposited at the pressure of 30 mTorr exhibited the hydrogen content of 17 at. %, a photosensitivity of 106 at 100 mW/cm2 and a conductivity activation energy of 0.9 eV. A novel coplanar self-aligned a-Si:H thin film transistor was fabricated using Ni-silicide gate and source/drain electrodes. The simultaneous Ni-silicide formation of gate and source/drain regions using the stacked layers of thin a-Si:H, silicon nitride (SiNx) and a-Si:H reduces the offset length between gate and source/drain, which leads to the coplanar a-Si:H thin film transistor (TFT). This self-aligned a-Si:H TFT exhibited a field effect mobility of 0.44 cm2/V s, threshold voltage of 5.3 V and subthreshold slope of 0.5 V/dec. The coplanar geometry reduces the parasitic capacitance and parasitic resistance compared with those of conventional staggered a-Si:H TFTs.