NiSi Films Research Articles

Pure and conformal CVD nickel and nickel monosilicide in high-aspect-ratio structures analyzed by atom probe tomography

Low-resistance and uniform contacts are needed for modern 3-D silicon transistors. The formation of high-quality and conformal nickel silicide at the interface between silicon and metal contacts is a possible solution. Direct-liquid-evaporation chemical vapor deposition is used to deposit nickel films conformally inside narrow silicon trenches. The deposited Ni is then reacted with a silicon substrate to form nickel monosilicide. Atom probe tomography (APT) is used to find and count the atoms in nanoscale regions inside these 3-D structures. APT shows that these NiSi films are stoichiometrically pure, single-phase, and conformal even inside trenches with high aspect ratios. The APT technique measures all impurities, including carbon, nitrogen, and oxygen, to have concentrations less than 0.1 at. %.

Characterization and crystallization kinetics of sputtered NiSi thin films for blue laser optical recording application

In this study, Ni31Si69, Ni43Si57 and Ni63Si37 thin films with the thickness of 16 nm were deposited at room temperature by co-sputtering using Ni and Si targets. From the result of reflectivity-temperature measurement, it was found the NiSi layers possessed two temperature ranges of reflectivity change, i.e. 150–270 °C and 320–370 °C. Microstructural analysis indicated that the NiSi2 nano-crystalline phase was formed in the as-deposited state. After annealing at 270 and 500 °C, the crystallinity of NiSi2 phase was improved and the Ni2Si phase appeared, respectively. By measuring the optical reflectivity at a wavelength of 405 nm, the optical contrasts of these films before and after annealing at 270 °C were determined to be 24%, 16% and 26% with the Ni contents of 31, 43 and 63 at.%, respectively. The optimum jitter values of Ni31Si69 blu-ray disc were 7.7% at 5.7 mW and 8.2% at 7 mW, respectively, for 1× and 2× recording speeds. It reveals that the NiSi films have high potential in the application of blue laser recording media.

Enhanced thermoelectric property and stability of NiCr–NiSi thin film thermocouple on superalloy substrate

Thin film thermocouples (TFTCs) can provide fast and accurate surface temperature measurement with minimal impact on the physical characteristics of the supporting components. In this study, NiCr and NiSi films were prepared with radio frequency (RF) magnetron sputtering and the influences of vacuum annealing on the resistivity of the films were investigated. Afterward, NiCr–NiSi films were deposited on Ni-based superalloy substrates to form TFTCs. The overall dimension of the thermocouple is 64 mm in length, 8 mm in width and 30 μm in thickness. Compared with those of as-deposited sample, the thermoelectric property and stability of the TFTC are significantly improved by vacuum annealing of NiCr and NiSi films. The variation of the Seebeck coefficient of TFTC was discussed based on the size effect of NiCr and NiSi films. And a lower Seebeck coefficient of TFTC of 38.4 μV·°C−1 is obtained.

Microstructural properties of Ni-silicide films formed on epitaxially grown strained Si:P layer

As a future-generation source/drain contact structure, NiSi films were formed on a strained and epitaxial Si:P layer (P concentration of ~1.9at.%), and their unique microstructural properties were characterized as a function of the annealing temperature (400–800°C). Unlike the NiSi film formed on Si, those formed on the strained Si:P consisted of many abnormally large grains with a rather uniform thickness and flat-bottom interface, most likely because of the strain effect caused by the underlying Si:P layer. The strain energy built at the NiSi/Si:P interface is believed to have significantly affected the microstructure and morphology of the subsequently grown NiSi film, which eventually led to retardation of thermal agglomeration.

Improvement of the thermal stability of nickel silicide using a ruthenium interlayer deposited via remote plasma atomic layer deposition

In this study, the effects of a thin Ru interlayer on the thermal and morphological stability of NiSi have been investigated. Ru and Ni thin films were deposited sequentially to form a Ni/Ru/Si bilayered structure, without breaking the vacuum, by remote plasma atomic layer deposition (RPALD) on a p-type Si wafer. After annealing at various temperatures, the thermal stabilities of the Ni/Ru/Si and Ni/Si structures were investigated by various analysis techniques. The results showed that the sheet resistance of the Ni/Ru/Si sample was consistently lower compared to the Ni/Si sample over the entire temperature range. Although both samples exhibited the formation of NiSi2 phases at an annealing temperature of 800 °C, as seen with glancing angle x-ray diffraction, the peaks of the Ni/Ru/Si sample were observed to have much weaker intensities than those obtained for the Ni/Si sample. Moreover, the NiSi film with a Ru interlayer exhibited a better interface and improved surface morphologies compared to the NiSi film without a Ru interlayer. These results show that the phase transformation of NiSi to NiSi2 was retarded and that the smooth NiSi/Si interface was retained due to the activation energy increment for NiSi2 nucleation that is caused by adding a Ru interlayer. Hence, it can be said that the Ru interlayer deposited by RPALD can be used to control the phase transformation and physical properties of nickel silicide phases.

Characterization of ultra-thin nickel–silicide films synthesized using the solid state reaction of Ni with an underlying Si:P substrate (P: 0.7 to 4.0%)

The solid state reaction of an ultra-thin Ni film (6nm) with Si:P epi layers (P: 0.7 to 4.0%), grown on 300-mm Si wafers, is studied as a function of different rapid thermal process (RTP) annealing temperatures (250–550°C) before and after applying a selective etch. The films are characterized using sheet resistance (Rs), mass, glancing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR) atomic force, scanning electron and transmission electron microscopy (AFM, SEM and TEM) analyses to follow the onset of the Ni reaction, the evolution of the different phases formed within the Ni–Si system and to investigate the NiSi film properties. Results demonstrate that, though the Ni conversion to form an intermediate Ni-rich silicide phase is complete at 300°C, showing no dependency on the P content, the complete transformation (to form low resistive NiSi) shows a temperature dependence with P content (350°C vs 400°C for 0.7% P and 2.0–4.0% P). Despite the delay in silicidation completion, the NiSi films exhibit comparable layer properties, for all P contents. All films show a uniform conversion with a similar volume expansion (2.1), good interface properties, comparable resistivity (18–20μΩ·cm) and exhibit a smooth morphology with limited rms roughness increase (0.37 to 0.56nm). The thermal stability studies carried out on NiSi, post RTP anneals, shows a different Rs stability (650 and 575°C for 0.7% and 2.0–4.0% P), while the morphological and phase stability is found to be similar (≤500°C) for all P contents. The contact resistance measured using Circular Transmission Line Model (CTLM) structures for the synthesized NiSi films is found to be 4.8×10−8 and 1.2×10−8Ω·cm2 for 0.7% and 4.0% P respectively, the latter meeting the requirements for 10-nm CMOS technology node as predicted by International Technology Road Map for Semiconductors (ITRS).

Thermal Stability Improvement Induced by Laser Annealing for 50-Å Ni(Pt) Film Silicidation

The significant thermal stability improvement induced by laser annealing (LA) is demonstrated for 50-A Ni(Pt) film silicidation. For the first time, it is revealed that LA may induce less stress in ultrathin Ni(Pt)Si film during silicidation, which can directly improve the thermal stability of the film. The local area annealing model is proposed to discuss the origin of stress relief. Besides, it is discovered that LA can result in a higher Pt concentration at the Ni(Pt)Si film surface, which will also enhance the resistance of Ni(Pt)Si film agglomeration.

Structural and electrical characterization of platinum (~15 at%) doped nickel silicides on Si(100) and SiGe/Si(100) substrates

Ni(Pt~15at%)Si/Si(100) and Ni(Pt~15at%)SiGe/SiGe/Si(100) films corresponding to rapid thermal annealing (RTA1) temperatures of 220, 230 and 240°C with constant RTA2 (at 420°C) have been investigated for sub 20nm devices. X-ray reflectometry (XRR), X-ray diffraction (XRD), four point probe, and atomic force microscopy (AFM) techniques were employed for the characterization of NiSi and NiSiGe films. XRR results indicated that NiSi and NiSiGe film thicknesses increased with RTA1 temperatures. NiSi films densities increased with layer thickness but NiSiGe films displayed an opposite trend. The diffractograms revealed that NiSi and NiSiGe layers contain identical phases and possessed fiber texture at 220°C. Whereas, the peaks shift were observed for NiSi (211) and NiSi (021) at higher RTA1 temperatures which appear due to Pt diffusion (hexagonal structures of larger grain size were noted). NiSiGe crystallites self-alignment was observed because of strained SiGe/Si(100) substrate. At 240°C, NiSiGe layer showed the smallest crystallites. This is believed to be due to Pt distributed along the silicide grain boundaries which obstructs silicide grain growth. NiSi and NiSiGe sheet resistance decreased significantly with increase in RTA1 temperatures and found to correlate with multiple grain orientation. AFM revealed a smooth-stable surface morphology for all films.

Phase analysis and thermal stability of thin films synthesized via solid state reaction of Ni with Si1 − xGex substrate

The products of the solid state reaction involving ultra-thin Ni film (6nm) and Si1−xGex layers (Ge 25 and 55at.%), were analysed using sheet resistance (Rs), glancing angle X-ray diffraction (GIXRD), scanning electron and atomic force microscopy (SEM, AFM) techniques. The reaction was carried out via rapid thermal process (RTP) annealing using two different steps (RTP1 and RTP2) while applying a selective etch (SE) in between them. The intermediate and the end reaction products resulting after RTP1 and RTP2 were found to be dependent on the Ge content, forming Ni-rich silicide (Ni2Si) and NiSi on Si75Ge25, while Ni-rich germanide (Ni5Ge3) and NiGe were obtained by using Si45Ge55. Though the onset of intermediate Ni-rich silicide or germanide phase formation occurs at similar RTP1 temperature (275°C), the reaction completion to yield low resistive phase NiSi or NiGe phase results at different RTP2 temperatures (400°C vs 350°C). Based on the volume expansion, a resistivity value of 25μΩcm was obtained for the synthesized NiGe (12nm) and NiSi (14nm) layers. Independent of the phases obtained, the films were found to be closed and homogeneous and exhibit rms roughness of 0.5–0.8nm as evidenced by SEM and AFM analysis. Thermal stability studies carried out on NiSi and NiGe thin films, post RTP1/RTP2, show the latter phase to have limited stability and result in Rs degradation starting already at 475°C due to phase decomposition.

NixSi1-x Alloy Negative Electrodes for Li-Ion Batteries

Introduction Si containing alloys are promising candidates as anode materials for lithium ion batteries. This is owing to the high theoretical capacity of Si (2194 Ah/L, compared to 764 Ah/L for graphite) [1]. Pure Si, however, suffers from severe volume expansion (280% in the fully lithiated state) during the lithiation/delithiation process [2]. High internal stress in the electrode can lead to particle cracking, poor electrical contact and thus poor cycling stability. The use of active/inactive composites is an efficient way to reduce volume expansion and improve cycling performance [1,3]. In the present study, NixSi1-x (0≤x≤0.65) thin film libraries were synthesized by combinatorial sputtering. A structural and compositional analysis of the films and the effect of composition on their electrochemical behavior are presented. It was found that the capacity of NixSi1-x thin films could not be explained by the lithiation mechanisms proposed in any of the previous studies of Si-TM films. Instead, it was found that increasing Ni content suppressed the average lithiation voltage, resulting in capacity reduction, however all the Si in the alloy remained active. Experimental Thin film libraries of Ni-Si were fabricated using sputtering. Cu foil discs with sputtered thin films were assembled in 2325-type coin cells with Li metal foil (99.9%, Sigma-Aldrich) counter electrodes. 1M LiPF6 (BASF) in a solution of ethylene carbonate, diethyl carbonate and monofluoroethylene carbonate (volume ratio 3:6:1, all from Novolyte Technologies) was used as electrolyte. Cells were galvanostatically cycled at 30.0 ± 0.1 °C between 5 mV and 0.9 V with a Maccor Series 4000 Automated Test System. Results Selected XRD patterns of two Ni-Si thin films are shown in Figure 1. All the patterns have two broad diffraction peaks at around 28° and 49°, indicating the amorphous nature of sputtered thin films. With the increase of Ni content, the intensity of the peak at 49° increases and its position shifts slightly to lower angle. Figure 2 shows the differential capacity curves of the same Ni-Si thin films shown in Figure 1. Two broad peaks during lithiation (denoted as peak A and B) and two corresponding peaks during delithiation (denoted as peak A' and B') can be clearly observed for the Ni0.04Si0.96 thin film. The two lithiation peaks shift to less positive voltages for Ni0.35Si0.65 thin film while the B' peak position remains unchanged. The apparent suppression in discharge voltage by increasing Ni content causes a reduction in the film capacity. This would suggest that some of the Si is becoming inactive, but this is not the case. While peak B becomes truncated by the voltage suppression the capacity of peaks A/A' remain unaffected and therefore can be used as a measure of active Si in the alloy. Figure 3 shows the percent active Si present in the Ni-Si films calculated on the basis of the capacity under peak A'. According to this model all Si atoms are active to Li. Above x = 0.4 the amount of active Si decreases only because peak A also becomes truncated for these compositions. The model reported by Fleischauer et al. [4] does not explain the behavior observed here and is also shown in Figure 3 for comparison. Here the electrochemistry of Ni-Si films will be discussed. It will be suggested the lithiation voltage suppression observed in these films arises from internal stress that arises between the expanding Si active phase and the inactive Ni phase. This has important consequences for other Si/inactive alloy negative electrodes.

Electroless Ni Layer: Influence of Growth Steps and Annealing Temperature on NiSi Formation

Nowadays in the photovoltaic field, the research aim is to develop cheaper solar cells with efficiency more and more higher. For both the silicon and thin film solar cells, one of enhancement ways concerns the front-side collect lines. Traditionally made by screen-printed silver paste, the current development of these lines are focused on the reduction of the silver quantity inside the paste [1,2], the modification of the deposit techniques [3,4], the contact design [5] or several modifications in the same time [6], as for our work. Indeed, our objective is to replace silver lines by nickel/copper lines, respectively deposited by electroless and electrolytic processes. From this method, the electroless nickel ensures a barrier role against the copper diffusion throughout the silicon, which would damage the solar cell efficiency. This nickel layer is first annealed to obtain specifically NiSi composite, necessary to guarantee the desired contact adherence and the low contact resistance (14 µΩcm). However, the thickness and the composition of this composite must be monitored. This research work is focused on the nickel annealing under Ar/5% H2 atmosphere. In a first part, the Ni coverage ratio as a function of the plating time and the influence of the initial Ni thickness on the diffusion depth throughout the silicon are studied. A second part is devoted to the importance of the annealing duration on the diffusion depth, including the sample cooling and the furnace extraction. Moreover, the composition of the NixSiy layer depends on the annealing temperature [7,8,9]. The NiSi film is obtained for a temperature between 350°C and 700°C. Therefore, in a final part, the impact of the annealing temperature on the NiXSiYcomposition is presented. This work has been made on polished silicon substrate [100] and monitored using complementary surface equipments: SEM (imaging), EDS (bulk chemical analyses in surface and cross-section) and XPS (surface chemical information and composition profiling). Figure 1 shows an example of this analysis complementarity. SEM micrographs of a Ni layer deposited during 1 min are presented in surface (a) and on cross-section (b). Figure 1 c) shows the surface sample after annealing at 370°C under Ar/5%H2atmosphere. EDS analyses in cross-section (d and e) prove the Ni diffusion throughout the Si substrate, generating the NiSi layer, and allow its thickness measurement. XPS profile analyses (f) confirms these results. ACKNOWLEDGMENTS This work has been carried out in the frame of the BIFASOL project supported by the “Agence Nationale de la Recherche” (ANR-11-PRGE-004). The authors would like to thanks INES (Institut National de l’Energie Solaire) for providing silicon substrates. REFERENCES S. Olweya, A. Kalio, A. Kraft, E. Deront, A. Filipovic, J. Bartsch and M. Glatthaar, Energy Procedia, vol. 43, pp. 37 – 43, 2013Rene Hoenig, Michael Duerrschnabel, Willem van Mierlo, Zainul Aabdin, Joerg Bernhard, Johannes Biskupek, Oliver Eibl, Ute Kaiser, Juergen Wilde, Florian Clement and Daniel Biro, Energy Procedia, vol. 43, pp. 27-36, 2013M. Beutel, A. Lewis, M. Prondzinski, F. Selbmann, P. Richter, F. Bamberg, P. Raschtschepkin, A. Krause, C. Koch, M. Hentsche, K.-H. Stegemann, E. Schneiderlöchner, and H. Neuhaus, Solar Energy Materials and Solar Cells, in press, corrected proof, DOI: 10.1016/j.solmat.2014.06.006Do-Hyung Kim, Sung-Soo Ryu, Dongwook Shin, Jung-Han Shin, Jwa-Jin Jeong, Hyeong-Jun Kim and Hyo Sik Chang, Materials Science and Engineering: B, vol. 177, issue 2, pp. 217–222, 2012E. Kurtz and W. Zhang, Energy Procedia, vol. 8, pp. 620-624, 2011M. Balucani, K. Kholostov, P. Nenzi, R. Crescenzi, D. Ciarniello, D. Bernardi, L. Serenelli, M. Izzi and M. Tucci, Energy Procedia, vol. 43, pp. 54-65, 2013E.J. Lee, D.S. Kim and S.H. Lee, Solar Energy Materails and Solar Cells, vol. 74, pp. 65-70, 2002L. Tous, D.H. Van Dorp, R. Russell, J. Das, M. Aleman, H. Bender, J. Meersschaut, K. Opsomer, J. poortmans and R. Mertens, Energy Procedia, vol. 21, pp. 39-46, 2012J. Foggiato, W.S. Yoo, M. Ouaknine, T. Murakami and T. Fukada, Materials Science and Engineering B, vol 114-115, pp. 56-60, 2004 Figure 1

Electroless Ni Layer: Influence of Growth Steps and Annealing Temperature on NiSi Formation

For the improvement of the silicon solar cell and competitiveness, one of the today challenges is to process Ni/Cu contact lines by chemical way. The study presented in this article is focused on the annealing of electroless nickel-phosphorous layers to create the NiSi film necessary for the good adhesion of the Ni/Cu stack and to guaranty the low contact resistance of these lines. The impact of the initial Ni-P layer thickness and the annealing temperature were particularly taken into account. Thanks to a combination of characterization techniques (SEM, EDS and XPS), the thickness and the composition of the NiSi layer were well established and monitored enabling to optimize the contact line procedure.

Effect of a Ti capping layer on thermal stability of NiSi formed from Ni thin films deposited by metal–organic chemical vapor deposition using a Ni(iPr-DAD)2 precursor

Ni films were deposited by metal–organic chemical vapor deposition (MOCVD) using a novel Ni precursor, bis(1,4-di-isopropyl-1,3-diazabutadienyl)nickel [Ni(iPr-DAD)2], and NH3 gas. To optimize process conditions, the deposition temperature and reactant partial pressure were varied from 200 to 350 °C and from 0.2 to 0.99 Torr, respectively. Ni films deposited at 300 °C with a reactant pressure of 0.8 Torr exhibited excellent quality, and had a low carbon impurity concentration of around 4%. In addition, a sacrificial Ti capping layer was deposited by an in situ e-beam evaporator on top of the Ni films to enhance the thermal stability of the subsequently formed NiSi films. Both the Ti-capped and uncapped Ni films were annealed by a two-step method, with a first annealing conducted at 500 °C, followed by wet etching and then a second annealing carried out from 500 to 900 °C. The Ti capping layer did not affect the silicidation kinetic process, but by acting as an oxygen scavenger, it did enhance the morphological stability of the NiSi films and thus improve their electrical properties.

Combinatorial Investigations of Ni-Si Negative Electrode Materials for Li-Ion Batteries

Sputtered thin films in the Ni-Si system (0 ≤ x ≤ 0.65 in NixSi1-x) were studied for use as anode materials in Li-ion cells. All compositions were found to be amorphous. The Ni in Ni-Si films was found to suppress the lithiation voltage, resulting in a reduction in capacity. The delithiation voltage was not affected. No capacity was observed when Ni content was more than 50 at% because at this composition the lithiation voltage was suppressed to 0 V. In contrast to previous models of capacity in transition metal-Si films, all Si atoms were found to be active in Ni-Si films at all compositions. Capacity reduction is only caused by a suppression of the Si lithiation voltage. We attribute this voltage suppression to internal stress in the thin film during lithiation from the presence of Ni.

Phase Formation and Morphology of Nickel Silicide Thin Films Synthesized by Catalyzed Chemical Vapor Reaction of Nickel with Silane

The synthesis of nickel silicide thin films via a vapor–solid reaction has been studied by exposing thin (10 nm) Ni films to silane (SiH4). The crystalline phases, the Ni/Si stoichiometric ratios, as well as the surface and interface properties of the resulting silicide films were investigated as a function of the growth parameters such as the SiH4 partial pressure, the reaction temperature, and the exposure time. At low temperature (300 °C), SiH4 exposure led to the self-limiting deposition of Si on Ni by catalytic decomposition of SiH4 but not to silicate formation. Between 350 and 400 °C, phase pure orthorhombic NiSi films were obtained that were formed directly without any apparent intermediate Ni-rich silicide phases. A transformation to NiSi2 occurred at 450 °C and above, and at 500 °C phase pure NiSi2 was obtained. Here, the transient formation of NiSi was observed that transformed into NiSi2 for prolonged SiH4 exposure. The results indicate that the Si solubility governs the phase formation sequen...

Cold Silicon Preamorphization Implant and Presilicide Sulfur Implant for Advanced Nickel Silicide Contacts

We report the first demonstration of a nickel silicide (NiSi) contact formation technique using cold silicon (Si) preamorphization implant (PAI) combined with presilicide sulfur (S) implant. The cold Si PAI suppresses the agglomeration of NiSi film at elevated temperatures. Presilicide S implant and its segregation at the interface of NiSi and n-type Si (n-Si) after silicidation significantly lowers the effective Schottky barrier height (Φ n B ) for electrons at the NiSi/n-Si contact. The S atoms in Si could be modeled as donor-like traps near the NiSi/n-Si interface, and a simulation study was performed to explain the reduction of Φ n B caused by S.

Nano-scale NiSi and n-type silicon based Schottky barrier diode as a near infra-red detector for room temperature operation

The fabrication of nano-scale NiSi/n-Si Schottky barrier diode by rapid thermal annealing process is reported. The characterization of the nano-scale NiSi film was performed using Micro-Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The thickness of the film (27 nm) has been measured by cross-sectional Secondary Electron Microscopy and XPS based depth profile method. Current–voltage (I–V) characteristics show an excellent rectification ratio (ION/IOFF = 105) at a bias voltage of ±1 V. The diode ideality factor is 1.28. The barrier height was also determined independently based on I–V (0.62 eV) and high frequency capacitance–voltage technique (0.76 eV), and the correlation between them has explained. The diode photo-response was measured in the range of 1.35–2.5 μm under different reverse bias conditions (0.0–1.0 V). The response is observed to increase with increasing reverse bias. From the photo-responsivity study, the zero bias barrier height was determined to be 0.54 eV.

Improvement of thermal stability of nickel silicide film using NH3 plasma treatment

In this study, the effects of NH3 plasma pre-treatment on the characteristics of NiSi films were investigated. Nickel film was deposited on a Si(100) substrate by meal-organic chemical vapor deposition (MOCVD) using Ni(iPr-DAD)2 as a Ni precursor and NH3 gas as a reactant. Before the Ni deposition, silicon substrate was treated by NH3 plasma with various flow rates to adjust the amount of inserted hydrogen and nitrogen atoms. The Ni films showed a considerable low sheet resistance around 12 Ω/□, irrespective of the NH3 plasma pre-treatment conditions. The sheet resistance of the all Ni films was decreased after annealing at 500 °C due to formation of a low resistive NiSi phase. NiSi films with a high flow rate of NH3 plasma pre-treatment exhibited a lower sheet resistance and smoother interface between NiSi and the Si substrate than the low flow rate of the NH3 plasma pre-treated NiSi films because lots of nitrogen atoms incorporated at grain boundary of NiSi which result in reduce total surface/interface energy of NiSi and enhancement interface characteristics.

Impact of additional Pt and NiSi crystal orientation on channel stress induced by Ni silicide film in metal–oxide–semiconductor field-effect transistors

The impact of additional Pt and Ni monosilicide (NiSi) crystal orientation on channel stress from Ni silicide in metal–oxide–semiconductor field-effect transistors (MOSFETs) has been demonstrated. The channel stress generation mechanism can be explained by the NiSi crystal orientation. In pure Ni silicide films, the channel stress in the p-type substrate is much larger than that in the n-type one, since the NiSi a-axis parallel to the channel direction is strongly aligned on the p-type substrate compared with on the n-type one. On the other hand, in NiPt silicide films, the difference in the channel stress between the p- and n-type substrates is small, because the NiSi crystal orientation on the p-type substrate is similar to that on the n-type one. These results can be explained by the Pt segregation at the interface between the NiSi film and the Si surface. Segregated Pt atoms cause the NiSi b-axis to align normal to the Si(001) surface in the nucleation step owing to the expansion of the NiSi lattice spacing at the NiSi/Si interface. Furthermore, the Pt segregation mechanism is considered to be caused by the grain boundary diffusion in the Ni2Si film during NiSi formation. We confirmed that the grains of Ni2Si on the p-type substrate are smaller than those on the n-type one. The Ni2Si film on the p-type substrate has more grain boundary diffusion paths than that on the n-type one. Therefore, the amount of Pt segregation at the NiSi/Si interface on the p-type substrate is larger than that on the n-type one. Consequently, the number of NiSi grains with the b-axis aligned normal to the Si(001) in the p-type substrate is larger than that in the n-type one. As a result, the channel stress induced by NiPt silicide in PMOS is larger than that in NMOS. According to this mechanism, controlling the Pt concentration at the NiSi/Si interface is one of the key factors for channel stress engineering.

High-Temperature and Anodic Oxidation of Thin NiSi and NiSi2 Films

The high-temperature and anodic oxidation of thin NiSi and NiSi2 films produced by thermal annealing of Ni film on single-crystalline silicon is studied. Both types of oxidation lead to the formation of thin protective SiO2 layers. The high-temperature oxidation of NiSi films begins at 930 K, which is 100 K lower than that of NiSi2 films. When temperature increases, the mass increment of NiSi films becomes greater than that of NiSi2 films. This difference is three times as great at 1273 K, which is due to the difference in structure and stoichiometry. It is shown that the electrochemical corrosion resistance of films increases from Ni to NiSi and to NiSi2.