TiSi2 Thin Films Research Articles

Evaluation of bias voltage-dependent mechanical properties of amorphous TiSi2 thin films on PEEK by nano-characterization techniques

Thin films on PEEK have been designing by magnetron sputtering, using bias voltages ranging from −31 to −157 V. The X-ray diffraction and EDX show how the amorphous films resulting have an elemental composition very close to the stoichiometry TiSi2. The AFM and SEM performed on top and cross-section, respectively, of film reveal a smooth and uniform surface, free of pores and cracks, and a compact microstructure. The evaluation of the resolved shear stress, yield strength, hardness, scratch resistance, and fracture toughness show how these values increase in the TiSi2/PEEK system as the bias voltage increase. The development of these hard and tough thin films has enabled the fracture toughness achieved by the TiSi2/PEEK system increase when a bias voltage equal to or higher than −108 V is used during the deposition process. For these bias conditions, the compressive residual stresses generated are large enough to prevent crack nucleation. The increase of the crack resistance gives as a result that KI reaches values above 32 MPa*m1/2. This value is much greater than those values corresponding to the classic ceramic coatings, such as Al2O3 (4.6 MPa*m1/2) and ZrO2 (7.6 MPa*m1/2).

Synthesis of TiN, Ti, and TiSi2 Thin Films for the Contact System of Solar Cells

The influence of deposition parameters, such as: the magnetron power in the range 690–1400 W, the silicon substrate temperature 23–170°C, the N2 gas flow rate 0.9–3.6 L/h, the Ar gas flow rate 0.06‒3.6 L/h, the ratio of N2/Ar gas flows 1–60 on the thickness, the density, and the composition of the deposited films is analyzed. The maximum density 5.247 g/cm3 corresponding to the TiN0.786 = Ti56N44 composition has been achieved at the following deposition parameters: 1200 W, N/Ar = 1.8/0.06 L/h = 30, 0.8 Pa, 320 s, and 100°C. At temperatures 700–800°C, the mutual diffusion of titanium and silicon atoms through the interface leads to the active nucleation, the formation of nanocrystals and low-resistance metallization layers. X-ray diffraction shows that, during annealing at 700°C (30 min, Ar), the formation of phase TiSi2 due to the diffusion of Ti atoms into silicon is twice more intense than the formation of Ti5Si3 due to the diffusion of silicon atoms into titanium as a result of high hardness of titanium. The average sizes of TiSi2 decreases from 7.1 to 5.6 nm at 750°C due to the crystallization of the nuclei and increase to 9.2 nm at 800°C.

Effects of Ag addition on phase transformation and resistivity of TiSi2 thin films

In this study, the effects of adding Ag to TiSi2 thin films are examined. It is demonstrated that both the C49→C54 transformation temperature and the electric resistivity are appreciably lowered with Ag addition. Due to the presence of Ag nanocrystals precipitated at the C49 grain boundaries, the overall grain boundary density would increase to result in the higher nucleation rate of C54 and the lower transformation temperature. The precipitation of pure Ag network can provide another electric current conductive path except for the TiSi2 grains. Due to the lower vacuum condition and the higher oxygen content in the current sputtered and annealed films, the C49→C54 transformation temperature and the resistivity of the TiSi2–20at%Ag films can only be reduced by ∼100°C and 10μΩcm, as compared with the non-Ag additive films. With better fabrication vacuum, the transformation temperature and resistivity might be lowered to a level below 700°C and 15μΩcm, which are highly applausive for engineering applications.

Nucleation and growth of TiSi2 thin films deposited on glass by atmospheric pressure chemical vapor deposition

Titanium silicide (TiSi2) thin films were prepared on glass substrate by atmospheric pressure chemical vapor deposition using SiH4 and TiCl4 as the precursors. The phase structure of the thin films was identified by x-ray diffractometry. The surface morphology and thickness of the thin films were observed by field emission scannig electron microscopy and the sheet resistance of the thin films was measured using the four point probe method. The results show that the TiSi2 thin films are formed in a face-centered orthorhombic structure. Due to the influence of the amorphous glass substrate, an amorphous layer is initially formed on the substrate and the TiSi2 crystalline phase grows on top of it. As the thickness and content of TiSi2 crystalline phase increase with deposition time, the resistivity of the thin film decreases. Besides, the growth rate and thus the size of TiSi2 crystalline phase increase as the deposition temperature increases. The stack density decreases when the deposition temperature increases above 700°C because the rapid growth at the higher temperatures causes more irregular shape of crystalline particles. The maximal stack density of the crystalline phase and thus the minimum resistivity of the thin films are obtained at the deposition temperature of 700°C. The expressions of the stack density of crystalline phase and the resistivity of the thin films as functions of the deposition conditions are theoretically deduced which are well consistent with the experimental results.

Fabrication of C54-TiSi2 Thin Films Using Cathodic Arc Deposition and Rapid Thermal Annealing

AbstractDue to its low electrical resistivity and high thermal stability, C54-TiSi2 thin films can be used in some MEMS application, such as RF MEMS, to reduce RC delay and improve dynamic performance. In this paper, TiSi2 thin films have been prepared for the first time by using cathodic arc deposition to study the impact of energetic ion bombardment on the film microstructure and subsequent C49-C54 phase transformation during annealing. TiSi2 compound was used as the cathode and a substrate bias was varied to control kinetic energy of the ions during the film growth. Rutherford backscattering spectrometry and transmission electron microscopy were utilized to characterize the film composition and microstructure. The composition of the resultant TiSix thin films varies from x=2.4 to x=1.4 when the substrate bias was varied from floating to –200V. The as-deposited TiSix films are amorphous under no substrate heating and a phase separation at nano scale with inhomogeneous distribution of Ti and Si atoms was observed within the amorphous phase. Si atoms are seen to segregate on the boundary of Ti-rich domains and the domain size increased with the substrate bias. For a 90nm-thick TiSi2 film deposited on a SiO2/Si substrate, kinetics of the C49-C54 phase transformation was studied by measuring the change of film resistivity upon rapid thermal annealing. It was found that the C49-C54 phase transition temperature is higher (>900°C) for the arc-deposited TiSi2 thin films compared to evaporated and sputtered films and the activation energy for the transformation was calculated to be 6.1±0.2eV.

Application of edge-to-edge matching model to understand the in-plane texture of TiSi2 (C49) thin films on (001)Si surface

The edge-to-edge matching model, which was originally developed for predicting crystallographic features in diffusional phase transformations in solids, has been used to understand the formation of in-plane textures in TiSi2 (C49) thin films on Si single crystal (001)si surface. The model predicts all the four previously reported orientation relationships between C49 and Si substrate based on the actual atom matching across the interface and the basic crystallographic data only. The model has strong potential to be used to develop new thin film materials. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Defect structures in cosputtered thin films of transition-metal disilicides with C11 b , C40 and C54 structures

Defect structures in crystallites of the stable phases in thin films of transition-metal (TM) disilicides (C11b MoSi2, C40 TaSi2, and C54 TiSi2) produced by cosputtering and subsequent annealing have been investigated by transmission electron microscopy (TEM). Crystallites in thin films of MoSi2, TaSi2, and TiSi2 all contain planar faults parallel to hexagonally arranged TMSi2 planes, which are a characteristic feature commonly observed in all three crystal structures. These planar faults are twin boundaries in all cases. Twins in thin films of these disilicides, thus, have a common characteristic that the twin habit plane is parallel to hexagonally arranged TMSi2 stoichiometric planes. For twins in thin films of C11b MoSi2, and C54 TiSi2, the twining elements can be deduced and the twin habit plane is found not to be parallel to the twinning (K1) plane, but to be perpendicular to it. Twins formed in C40 TaSi2 thin films are different from those formed in C11b MoSi2 and C54 TiSi2 thin films, in that the crystal orientation of the twin is exactly the same as that of the matrix, since they are racemic twins that are only enantiomorphically (space groups of P6222 or P6422) related to each other.

Dependence of Structural and Electrical Properties on Substrate Temperature for Annealed C54 TiSi2 Thin Films Grown on p-Si Substrates

Substrate temperature effects on the structural and electrical properties of annealed C54 TiSi2 thin films grown on p-Si (100) substrates using a sputtering method were determined with the objective of improving the properties of the films. The results of scanning electron microscopy, energy-dispersive X-ray fluorescence, and X-ray diffraction measurements showed that the thickness of the C54 TiSi2 thin films increases with increasing substrate temperature and that the sheet resistance decreases with increasing substrate temperature up to 200°C. These results indicate that the structural and electrical properties of annealed C54 TiSi2 thin films grown on p-Si (100) substrates using a sputtering method can be improved by increasing substrate temperature, and that these films grown on p-Si(100) substrates using a high-temperature sputtering method hold promise for potential applications in Si-based ultralarge-scale integration devices.

RF-plasma enhanced CVD of TiSi2 thin films: effects of TiCl4 flow rate and RF power

The effects of TiCl4 flow rate and RF power on PECVD of TiSi2 thin films using TiCl4/H2 gas mixture have been investigated. In the reaction system used, the low-resistivity phase C54-TiSi2 film with homogeneous composition and smooth interface was obtained when the TiCl4 flow rate and the RF power were optimized at 0.4sccm and 200W. The film surface and the film/substrate interface became rough at higher TiCl4 flow rate whereas the deposition rate was slow and the Ti5Si3 was formed at lower TiCl4 flow rate. At higher RF power, Ti5Si3 and TiSi phases were formed while at lower RF power the film surface became rough. These results are discussed with reference to the optical emission intensity of the plasma and the estimated temperature of hydrogen atom in the plasma.

Nucleation and growth kinetics of preferred C54 TiSi2 orientations: time-resolved x-ray diffraction measurements

The transformation from the C49 to the C54 phase in TiSi2 thin films has been studied for more than a decade because of its importance to the semiconductor industry. In previous work we identified three dominant C54 orientations in TiSi2 thin films on Si(001) substrates using x-ray pole figure analysis. In the current study the evolution of the three prominent C54 texture components was further examined using synchrotron based time-resolved in situ x-ray diffraction. The kinetics results show significant differences in the nucleation and growth kinetics of the individual orientations. Simulations suggest that this could be explained by an inhomogeneous nucleation of different texture components in the thin film, but not by simple differences in nucleation and/or growth rates. Classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis of nucleation and growth was applied to model the C49–C54 phase transformation kinetics for each C54 orientation. These results showed a systematic decrease of the Avrami exponent n from 3 to 2 with increasing annealing temperature. Within a JMAK approach this could be explained by the presence of a limited number of C54 nucleation sites coupled with a faster increase in nucleation rate than in growth velocity with increasing anneal temperature.

Texture of TiSi2 thin films on Si (001)

The texture of blanket C49 and C54 phase TiSi2 films on Si (001) substrates was examined with x-ray pole figure analysis. Textures were studied both in films with initial Ti deposited by sputtering and by low-temperature, plasma assisted chemical vapor deposition. Detailed differences were observed between silicide films grown by subsequently annealing films deposited with the two different methods. However, in both cases, the dominant C49 phase orientational relationships develop with respect to the substrate (001) planes. In contrast, we find that the dominant crystallographic relationships of the C54 phases in both cases are not with the surface (001) plane of the substrate, but instead with the Si (111) planes. Texturing in the case of the sputtered films is particularly complex with one prominent orientation having C54 (11¯0)‖(1¯11) Si with C54 (3̄3̄1̄)‖(011̄) Si and a second having C54 (1¯03¯)‖(1̄1̄1) Si with C54 (040)‖(11¯0) Si. These orientations, which suggest local epitaxy of the disilicide with the Si {111} planes, have not been previously identified for C54 TiSi2 growth on Si (001) substrates. This strong orientational relationship suggests that significant {111} faceting of the Si surface may occur during the silicide formation.

Electrical resistivity and Hall coefficient of C49, C40, and C54 TiSi2 thin-film phases

The electrical resistivity and Hall coefficient of C49, C40, and C54 TiSi2 thin films were studied in the temperature range of 4–350 K. The residual resistivity was the highest (52–72 μΩ cm) for the C49 phase, lower for the C40 (22–33 μΩ cm), and the lowest for the C54 phase (2.8–3.8 μΩ cm). On the other hand, the Debye temperature decreases from the C54 phase (470–490 K), to the C49 (451 K), and finally to the C40 phase (420 K). The Hall coefficient of the C49 and C40 phases exhibits a temperature independent value. A change of sign for the Hall coefficient occurs in the case of C54 at a temperature of about 80 K indicating that a multicarrier conduction mechanism exists in C54 TiSi2. The value of the scattering length le for the C54 samples is two to three times larger than for the C49 and C40 samples. This difference in the scattering length is suggested to be due to the presence of intrinsic defects in the C49 and C40 phases and/or to the large amount of grain boundaries.

Influence of Substrate Temperature During Sputter Deposition on the Subsequent Formation of Titanium Disilicide

ABSTRACTWe examine how the substrate temperature during Ti film sputter deposition influences the subsequent texture formation in TiSi2 thin films. Titanium films of 32 nm thickness were sputtered onto Si(001) at elevated substrate temperatures varying between 100 °C and 900 °C. After the depositions, in situ x-ray diffraction (XRD) measurements were performed to study the thin film reactions in real time, as the samples were annealed. The XRD results show that the substrate temperature significantly influences the texture of the initial Ti film as well as the texture of the resulting C54-phase TiSi2. The preferred Ti orientation gradually changes from (002) to (101) fiber texture as the deposition temperature increases up to 500 °C. Films deposited at 600 °C transformed into the C49 phase during deposition while films deposited at 700 °C and higher temperatures transformed into the C54 phase during deposition. The series of deposited films was annealed up to 1000 °C in He to complete the C54 phase formation while monitoring the texture evolution in situ using a position sensitive x-ray detector. The XRD results show that the final C54 phase texture changes from a dominant (311) orientation normal to the substrate to a (010) orientation for substrate temperatures between 600 °C and 700 °C. The C49-C54 phase transformation temperature is also lowered for these deposition temperatures. Ex situ pole figure analysis of the film deposited at 700 °C confirms the dominant C54 (010) texture and shows an in-plane orientation with C54 [001] ∥ Si [110]. For substrate temperatures between 800 °C and 900 °C, the C54 texture changes dramatically. In this case, θ - 2 θ scans do not show a preferred C54 orientation, but pole figure analysis indicates weak inplane orientations.

Effects of deposition conditions on preparation of TiSi2 thin films by PECVD

Effects of deposition conditions on preparation of TiSi2 thin films by PECVD

Preparation and properties of TiSi2 thin films from TiCl4/H2 by plasma enhanced chemical vapor deposition

Titanium silicide films were successfully prepared from TiCl4/H2 by plasma enhanced chemical vapor deposition. X-ray diffraction measurements showed that the films were polycrystalline and have the low resistivity phase C54-TiSi2. Contamination with chlorine could not be detected, however, oxygen contamination on the film surface was detected by X-ray photoelectron spectroscopy. The films were uniform and the TiSi2/substrate interface was clear and smooth. An excessive silicon substrate etching was observed when the substrate was heated by plasma. By controlling the reaction temperature and/or introducing hydrogen to the reaction gas system, it could be possible to deposit homogenous titanium silicide film and reduce silicon etching. These results could be explained reasonably based on thermodynamic calculations.

Nucleation and growth of C54 grains into C49 TiSi2 thin films monitored by micro-Raman imaging

The first-order C49–C54 allotropic-phase transition has been studied in TiSi2 thin films by electrical measurements and micro-Raman spectroscopy. To evaluate the parameters describing the kinetics of the transition and the barrier energy for the nucleation, micro-Raman spectroscopy has been used as a microscopy technique: spectra have been acquired scanning large silicide areas (100×50 μm2) and have been processed to obtain images which show the morphological evolution of the C54 grains during the transition. For temperatures between 680 and 720 °C, the converted area fraction has been determined at different annealing times and compared with electrical measurements. The two methods agree quite well. Both density and size of the C54 grains have been measured, thus allowing to separately determine the nucleation and growth parameters as a function of temperature. A nucleation and growth model has been fitted to data obtaining an activation energy of 4.9±0.7 eV for the nucleation rate and 4.5±0.9 eV for the growth velocity. Such values, coincident within experimental errors, indicate that the nucleation barrier energy for the transition to the C54 phase is very low.

Retarded C54 transformation and suppressed agglomeration by precipitates in TiSi2 films

We report the effects of excess Si phase on the C54 transformation and the thermal stability of TiSi2 thin films as a function of Si/Ti (x) ratio. The resistivity and x-ray diffraction data of TiSix(x=2.1–2.4) films showed a retardation of C54–TiSi2 transformation with incremental molar ratio x; the TiSix (x=2.1–2.3) films were completely transformed to C54-TiSi2 with rapid thermal annealing (RTA) of 750 °C, while the TiSix (x=2.4) films were transmuted to C54–TiSi2 over the RTA of 800 °C. Transmission electron microscopy study revealed that the growth of Si precipitates in the Si-rich TiSix films competes with the grain growth during the transformation of C49 to C54 TiSi2 phase, resulting in the increase of C54 transformation temperature. An excellent sheet resistance (Rs) and its standard deviation in concert with a reliable gate oxide integrity were attained from the Si-rich TiSi2/polycrystalline-Si (poly-Si) structure up to the solid state annealing of 850 °C for 60 min. These attributes are due to the reduced solid state reaction at TiSi2/Si interface and the suppressed TiSi2 agglomeration by Si precipitates. The average Rs of the 0.12-μm-wide TiSi2(800 Å)/poly-Si gate lines is lower than 4.5 Ω/□, demonstrating a robust gate electrode structure for gigabit scale device application.

Effects of stress on the growth of TiSi2 thin films on (001)Si

Tensile stress induced by backside CoSi2 films on a silicon substrate has been found to enhance the growth of C54–TiSi2 on (001)Si. In contrast, compressive stress induced by backside oxide films on the silicon substrate was found to retard significantly the growth of C54–TiSi2 on (001)Si. For Ti on stressed (001)Si after rapid thermal annealing at 800 °C for 30 s, the thickness of the C54– TiSi2 films was found to increase and decrease with the tensile and compressive stress levels, respectively. The retarded growth is attributed to the hindrance of the migration of Si through the Ti/Si interface by the compressive stress. On the other hand, the presence of tensile stress promotes the Si diffusion to facilitate the formation of Ti silicide thin films.

Kinetic Analysis of the C49-to-C54 Phase Transformation in TiSi2 Thin Films by In Situ Observation

The C49-to-C54 phase transformation of TiSi2 has been studied by in situ observation using a transmission electron microscope (TEM) and by thermal desorption spectroscopy (TDS). In situ TEM observation reveals that the interface of the transformation moves parallel to the Si substrate. The results indicate that the transition is a diffusional transformation that occurs via the short-distance diffusion of atoms, and is not a diffusionless shear transformation. Through TDS study, H2 is found to be desorbed during the transformation. The activation energy for the transformation is calculated to be 4.1 eV from the relationship between the desorption temperature and the heating rate of TDS. The phase transformation is thought to occur via lateral and massive growth, and is not simply limited by the growth rate.

Formation of Tisi2 Thin Films from Chemical Vapor Deposition Using TiI4

ABSTRACTThe formation of TiSi2 films by chemical vapor deposition was investigated for the application as a contact plug material because of its low resistivity, low contact resistance with n+ and p+ Si, and good chemical stability with Si. TiI4 and SiH4 were used as source gases. Since TiI4 is thermodynamically less stable than TiCl4, the deposition temperature of TiSi2 with TiI4 precursor could be lower than that of TiSi2 from TiCl4 precursor. TiSi2 thin films with C49 phase were formed at 650°C on Si (100) wafer, while a Ti5Si3 phase was formed at 650°C on SiO2 substrate. The resistivity of the C49 phase films was 210 μΩ-cm. The C49 phase was completely transformed into a C54 phase above 800°C annealing in an N2 atmosphere and the resistivity reduced to 34 μΩ-cm. We were able to deposit TiSi2 films at lower temperature using TiI4 precursor, compared to TiCl4 precursor. The Cl and HCI byproducts originated from TiCl4 can be excluded using TiI4 precursor.