Ni Silicide Formation Research Articles

On the high-temperature reactions between advanced ceramics and a cobalt-base alloy

Abstract The incorporation of advanced ceramics or ceramic composites into land-based turbines may potentially increase their efficiency due to increased gas inlet temperatures and/or reduced cooling requirements. In some proposed designs, incorporation of ceramics would require intimate contact of the ceramic and a metallic structure at elevated temperatures. Since many advanced ceramics contain Si, and since turbines are usually constructed out of Ni or Co-base alloys, the formation of Co or Ni silicides is expected at the ceramic/metallic interfaces. The goals of the present work are (a) an assessment of the microstructures and reaction products formed at ceramic/metallic interfaces during annealing at elevated temperatures and (b) a description of the kinetics of the reaction zone formation. Reaction couples consisting of the Co-base alloy ECY 768 and various advanced ceramics were prepared by hot-pressing in vacuum and subsequent annealing in vacuum or air at temperatures ranging from 1173 to 1323 K and for times ranging between 10 and 1000 h. Two types of silicon nitride (NT154 and AS800) and four whisker-reinforced alumina ceramics containing different weight fractions of SiC whiskers (ARtuff CC5500, S7, SX and CC7000) were investigated. The reaction zones consisted primarily of (Cr, Co)carbosilicides. The maximum reaction zone thicknesses after 1000 h at 1323 K were in most cases below 50 μm. Whereas the reaction zones were well defined in the case of the silicon nitrides, the Al 2 O 3 /SiC w materials developed multiple silicide layers within the reaction zone. With increasing SiC whisker content, the reaction zones increased in thickness for a given heat treatment. A non-linear fitting procedure was employed to describe the reaction zone thicknesses in terms of apparent activation energies and pre-exponential factors. Whereas this procedure worked well for the silicon nitrides annealed in a vacuum, substantial scatter occurred for air anneals. The ARtuff materials always showed substantial scatter which is attributed to their layered reaction microstructure.

Intrinsic Gettering of Nickel and Copper for Advanced Low Temperature Device Processes

AbstractThe formation and dissolution of Ni and Cu silicides were investigated to determine effective intrinsic gettering (IG) for low temperature processes. Ni formed silicides easily at low contamination levels and these silicides formed the nuclei for OSF during subsequent annealing at temperatures above 1000°C. Ni silicides were dissolved and gettered during low temperature deposition of a poly-back seal (PBS) at 620°C, whereas Cu silicides, once formed, easily induced secondary defects on further annealing even at low temperatures and could not be dissolved or gettered by PBS. The sizes and densities of oxygen precipitates necessary to intrinsically getter Ni and Cu contamination levels of 1012atoms/cm2 were also investigated with respect to generation lifetime. Cu contamination at this level did not degrade generation lifetime or gate oxide integrity (GOI) yield. For Ni contaminated samples, a strong dependence of generation lifetime on both oxygen precipitate density and size was observed. Effective IG for Ni during a low temperature process was demonstrated using a 2-step low temperature process simulation.

Formation of Ni silicide from Ni(Au) films on (111)Si

The solid state reaction between a Ni (7 at. % Au) film and a Si substrate at temperatures ranging from 250 to 800 °C is examined by scanning electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry. Compared to the usual features for thin film reaction of Ni with Si, we observed the following. (i) The simultaneous growth of Ni2Si and NiSi, and the growth of NiSi at the expense of both Ni2Si and Ni. This is related to Au accumulation in the metal layer. (ii) Au precipitation at 300 °C followed by the dissolution of the clusters thus created above the Au–Si eutectic temperature (370 °C). (iii) A decrease of the temperature of formation of NiSi2 and the appearance of thickness oscillations that are characteristic of nucleation. These different effects are interpreted by taking into account the metallurgy of the system: segregation of Au in the Ni film, Au solubility in the different silicides, change in surface and interface energies, and chemical interactions with Si.

Numerical simulation of the formation of Ni silicides induced by pulsed lasers

Pulsed laser-induced solid-state chemical reactions in an Ni-Si system are studied in the paper. Physico-chemical and mathematical models of the Ni-silicides formation are formulated, a numerical solution using the Galerkin finite-element method is described, and a computational algorithm is developed. Further, the XeCl excimer laser irradiation of a thin nickel film (1 nm to 2000 nm)-silicon system is simulated, with energy densities of the laser pulse which are insufficient to melt the surface of the sample. Typical results of the numerical experiments are presented and the influence of the diffusion coefficients of Ni in Si and Si in Ni recommended by various authors on the calculated temperature and concentration fields is studied. A comparison of the results of numerical simulations with experimental findings previously published in the literature reveals that the lattice diffusion cannot explain the experimental data of laser synthesis of silicides and that grain-boundary diffusion is probably the dominant mechanism of mass transfer at the laser irradiation of Ni-Si systems.

Ni-Silicide Formation: Dependence on Crystallographic Orientation of Si Substrates

We have analyzed the influence of the crystalline orientation of Si substrates on Ni-silicide formation. Ni-silicide/Si(111) and (100) samples formed through solid-phase reaction (SPR) were examined using soft X-ray emission spectroscopy (SXES), transmission electron microscopy (TEM) and grazing incidence X-ray diffraction. The formation of δ-Ni2Si and NiSi on Si(100) substrate occurs at a lower temperature than that on Si(111). However, the NiSi2 region is found to be formed only on the Si(111) substrate at a lower temperature (Ta=500°C) than previously reported. The NiSi2 regions are located at the interface region of NiSi/Si(111) and have a small island structure. On Si(100) substrates, only the NiSi layer is stably formed in the heat-treatment temperature range of 250-700°C.

Thermal and ion-beam-induced reactions in titanium thin films on boron phosphide (100)

The potential use of the boron phosphide (BP) as a refractory semiconductor (bandgap Eg = 2.1 eV) has motivated the investigation of Schottky barrier diodes [1], ion-beam-induced epitaxial crystallization [2] and metal-BP interfacial reactions in this system [3]. This novel material has several unique properties, such as the high melting temperature of 3000 °C, high. decomposition temperature of about 1130 °C and high oxidation resistance at high temperature. The future application of this material in the microelectronics industry requires sophisticated contacting schemes (both ohmic and Schottky). A detailed knowledge about metal-BP interactions and the thermal stability of metal-BP interfaces is of primary importance. A thorough characterization and understanding of the reactivity and thermal stability is therefore crucial in the design of BP devices. The investigation of the thermal and ion-beaminduced reactions in the Ni/BP(100) system revealed some striking outcomes. The thermal reaction temperature in Ni on BP system is found to be around one-fifth of the melting point (in K) [4]. Ion-beam mixing can significantly enhance the interfacial reaction and lower the reaction temperature. The reaction products are a mixture of NiB and Ni3P at 450 °C. The reaction progress in the thermal process depends linearly on the duration of the annealing. A linear dependence of the reacted thickness on the ion fluence was also observed between room temperature and 300 °C in this system. It is also interesting to investigate the refractory metal-BP interfacial reactions. Ti is of specific interest since it is known to form silicides at higher temperature than the formation of Ni silicide. Furthermore, interesting comparisons can be made with the Ni/BP system. In this letter we present the first observation of both thermal and ion-beaminduced reactions of Ti thin films of BP(100). Compared with the reaction in the Ni/BP system, the reaction temperature in the Ti/BP system is about 400 ~C higher. BP wafers with film thickness of about 1/xm were prepared by the thermal decomposition of B2H 6 and PH3 in a hydrogen atmosphere on Si(100) sub-

Thin Ni Silicide Formation by Low Temperature-Induced Metal Atom Reaction with Ion Implanted Amorphous Silicon

ABSTRACTWe have extended our recent work [1,2] on buried suicide formation by Ni diffusion into a buried amorphous silicon layer to the case where silicide formation is at lower temperatures on silicon substrates which have been preamorphized. The reaction of metal atoms from a 12 nm Ni film evaporated on top of a 65 nm thick surface amorphous layer formed by 35 keV Si+ ion implantation has been investigated at temperature ≤400 °C. Rutherford Backscattering Spectrometry (RBS) with channeling, cross-sectional transmission electron microscopy (XTEM), X-ray diffraction and four-point-probe measurements were used to determine the structure, interfacial morphology, composition and resistivity of the silicide films. It has been found that an increased rate of silicidation occurs for amorphous silicon with respect to crystalline areas permitting a selective control of the silicon area to be contacted during silicide growth. Vacuum furnace annealing at 360 °C for 8 hours followed by an additional step at 400 °C for one hour produces a continuos NiSi2 layer with a resistivity 44 μΩ cm.

TEM and SXES study of Ni-silicide/Si interface: crystallographic relationship with the Si substrates

We have analyzed the microstructure of Ni-silicides/Si(111) and (100) samples formed by heat-treating Ni(film)/Si(substrate) at 750°C for 30 min by means of soft X-ray emission spectroscopy (SXES), transmission electron microscopy (TEM) with cross-sectional mode and scanning electron microscopy (SEM) observation. Several differences appear between a sample on Si(111) and the one on Si(100) in view of Ni-silicides formation. It is worth describing that NiSi 2 and Si are included in the NiSi layer grown on Si(111) and Si(100) substrate, respectively.

Nickel and cobalt silicides on silicon: Thin-film reaction and interface structure

The latest developments in our understanding of the initial stages of Ni and Co silicide formation are described. Particular attention is given to the composition and structure of the ultrathin silicide layer which forms upon room temperature deposition of Ni or Co on atomically clean Si(111). The role of these as-deposited silicide layers as precursors to the formation of epitaxial NiSi 2 and CoSi 2 at higher temperature will be discussed in some detail. Finally, our current state of knowledge concerning the geometric and electronic structures of the NiSi 2Si(111) and CoSi 2Si(111) interfaces will be reviewed.

Depth analysis of oxygen and gold in thin film semiconductor structures using RBS, AES, SIMS and resonant scattering

The redistribution and the effect of oxygen on Co and Ni silicide formation were measured as a function of concentration and initial location by RBS, resonant scattering, AES and SIMS. RBS depth profiling was also used to study the effect of gold on Co silicide formation.

Phosphorus redistribution during nickel silicide formation

Nickel silicide was formed by heat treating Ni film on a single-crystal Si(100) substrate. The Schottky barrier height of Ni silicide was examined in relation to the phosphorus dose implanted into the Si substrate. The reduction of the Schottky barrier height during the Ni silicide formation indicates phosphorus redistribution.

Epitaxial growth of NiSi2 on ion-implanted silicon at 250–280 °C

Striking effects of dopant atoms on the formation of Ni silicides were observed. Epitaxial NiSi2 was found to grow on both BF+2- and B+-implanted (001) and (111)Si at 250–280 °C. The formation of Ni2Si was suppressed. It is conjectured that the presence of dopant atoms may lower the activation energy substantially to promote the formation of epitaxial NiSi2 at low temperatures. The effects may be exploited to grow other epitaxial silicides on silicon at low temperatures.

A comparison between thermal annealing and ion mixing of multilayered Ni-W films on Si. II

The reactions between bilayered Ni/W films and Si〈100〉 substrates induced by thermal annealing and ion mixing were investigated and compared. Samples were prepared by electron-beam sequential deposition of Ni and W onto the Si〈100〉 substrates and following by either furnace annealing (∼200–900 °C) or ion mixing (∼2×1015–4×1016 86Kr+ ions/cm2). The reactions were analyzed by Rutherford backscattering and x-ray diffraction (Read camera). Thermal annealing of both W/Ni/Si〈100〉 and Ni/W/Si〈100〉 samples led to the formation of Ni silicide next to the Si substrate and W silicide on the sample surface (layer reversal between Ni and W in the Ni/W/Si〈100〉 case). Ion mixing of W/Ni/Si〈100〉 samples led to the formation of Ni silicide with a thin layer of Ni-W-Si mixture located at the sample surface. For Ni/W/Si〈100〉 samples a ternary amorphous mixture of Ni-W-Si was obtained with ion mixing. These reactions were rationalized in terms of the mobilities of various atoms and the intermixings between layers.

NiSi mixing: A new model for low temperature silicide formation

High-resolution ion backscattering has been used to study the initial stages of Ni silicide formation on Si(111). NiSi mixing is observed, following Ni deposition on clean Si(111) at room temperature, up to coverages of ∼ 8 × 10 15 Ni atoms/ cm 2. The ultra-thin mixed layers are disordered and have a composition close to Ni 2Si. Ion backscattering and high-resolution cross-section TEM observations show the films to grow out from small 3D silicide islands which are formed at the initial deposition stage. A new cluster growth model for the formation of silicide films on clean Si is derived from the results.

Low-temperature redistribution of As in Si during Ni silicide formation

We have investigated the redistribution of implanted As during Ni2Si formation at 275 and 300 °C and NiSi formation at 400 to 700 °C with neutron activation analysis and Hall effect measurement. Some of the implanted As atoms were found to redistribute themselves near the silicide-Si interface during both Ni2Si and NiSi formation. The depth of the redistribution extends about 100 Å into Si and is affected slightly by the formation temperature of NiSi. A fraction of the redistributed As is electrically active and the fraction increases with the annealing temperature. The maximum electrical activity of redistributed As during NiSi formation at 700 °C is estimated to be 6.5%.

Thermal and ion-induced reaction of Ni–Au dilute alloys on Si

Redistribution of Au in Ni silicide formation by thermal annealing or ion beam mixing of Ni films with 1.4 at. % Au deposited on 〈100〉 Si was investigated using Rutherford backscattering spectrometry and glancing-angle x-ray diffraction. Annealing at temperatures of 300–350 °C results in the formation of Ni2Si with accumulation of Au at the Ni2Si/Ni interface. A similar redistribution of Au has also been found when the samples are irradiated with Xe ions at doses ≥2×1015 ions/cm2. This accumulation is contrary to the dispersion that one would anticipate in ballistic collisions and we believe that the Au accumulation is a result of thermodynamic forces in ion-induced reactions. In thermal annealing, the accumulation of Au impedes the supply of Ni and the second phase NiSi begins to form before the Ni film is consumed. With ion beam mixing, however, the accumulation of Au does not block silicide formation and Ni2Si continues to grow. We attribute the continued growth of Ni2Si to Au–Ni demixing within the collision cascade.

Lateral Silicide Growth

ABSTRACTSilicide formation and growth kinetics have been investigated with lateral diffusion couples formed by deposition of Ni and Cr layers on patterned Si substrates and by deposition of Ni patterns on Si films. For annealing temperatures between 520 and 650°C the growth of CrSi2follows a (time)½ dependence with an activation energy of 1.4± 0.1 eV. In Ni-silicide formation at temperatures below 600°C, Ni was the predominant moving species. As the temperature increased, the motion of Si became significant. The apparent activation energy for silicide formation varied from Ea ≅ 1.4 eV for Ni motion at relatively low temperatures to Ea≅ 2.3 eV for Si motion that occurs at high temperatures. Lateral diffusion in device geometry structures resulted in degradation of contact planarity due to the penetration of metal silicides in Ni-Si structures or the erosion of silicon in Cr-Si structures.

Alteration of Ni silicide formation by N implantation

The possibility of controlling the growth of nickel silicide by implanting N into thin Ni films evaporated on Si substrates has been studied using 4He backscattering spectrometry. The reaction between Ni and Si is completely halted below annealing temperatures of ∼375 °C by implanted doses of 5×1016 N/cm2. At higher annealing temperatures, localized intermixing takes place. For low doses ≲0.5×1016 N/cm2, the reaction between Ni and Si is that observed for unimplanted samples both in the phase formed (Ni2Si) and in rate of growth. For intermediate doses ∼0.9×1016 N/cm2, the first phase formed corresponds to NiSi, and the growth rate is greatly reduced. These results are explained in terms of a silicon nitride barrier to Ni diffusion forming at the Ni/Si interface.

Effect of Ion Irradiation on the Formation of Ni, Cr and Pt Silicide

ABSTRACTThe influence of Xe+, As+ and Si+ irradiation on the Ni, Cr and Pt-silicide formed upon subsequent thermal annealings has been investigated. Helium MeV backscattering spectrometry and x-ray diffraction have been used to analyze the samples. The effect of silicon-metal interface contamination has been observed using an intentionally formed thin silicon oxide layer. The oxide layer was thick enough to prevent thermal silicide formation in unirradiated samples. In irradiated samples, the silicide forms thermally in spite of the presence of this oxide layer for Ni and Cr, but not for Pt. Similar results were obtained for Xe+, As+ and Si+ irradiations. We attribute this effect to ion mixing of the interfacial layer. The differences between results obtained with Ni, Cr and Pt are discussed. These results demonstrate that a low-dose irradiation can render the process of silicide formation upon thermal annealing tolerant to interfacial impurities. On the other hand, we also show that ion irradition can inhibit Pt and Ni silicide formation.

On the formation of Ni and Pt silicide first phase: The dominant role of reaction kinetics

4He+ backscattering spectrometry and x-ray diffractometry have been used to study the formation of Ni and Pt silicides in Si(xtl)/M film structures with different metal film thicknesses ranging from 800 to 5000 Å. Results clearly show that first the phase richer in metal (Ni2Si, Pt2Si) grows and continues to grow until all available metal is reacted, then the phase richer in Si (PtSi, NiSi) starts to grow. Present results prove that in Si(xtl)/Pt or Ni interactions the growth phase is determined by the reaction kinetics and that diffusion of metal atoms through Pt2Si and Ni2Si is fundamental in keeping the reaction going.