Preparation and characterization of TaAlOx high-κ dielectric for metal-insulator-metal capacitor applications

Metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated using high-κ TaAlO_x-based dielectrics. TaAlO_x films having thickness of 11.5-26.0 nm, with equivalent oxide thickness (EOT) of ~ 2.3-5.3 nm were deposited on top of Au/SiO₂ (180 nm)/Si (100) structures by radio frequency magnetron co-sputtering of Ta₂O₅ and Al₂O₃ targets. The surface chemical states of the as-deposited TaAlO_x films were characterized by high-resolution X-ray photoelectron spectroscopy. The crystallinity of the TaAlO_x films for various post-deposition annealing treatments was characterized by grazing incident X-ray diffraction, which reveals that an amorphous phase is still retained for rapid thermal annealing up to 500 °C. Besides a high capacitance density (~ 5.4 to 6.6 fF/μm² at 1 kHz), a low value of voltage coefficients of capacitance and a stable temperature coefficient of capacitance have also been obtained in MIM capacitors with TaAlO_x films. Degradation phenomenon of TaAlO_x-based MIM capacitors under constant current stressing at 20 nA is found to be strongly dependent on dielectric thickness. It is shown that Al-incorporated Ta₂O₅ (TaAlO_x) films with high band gap and good thermal stability, low leakage current and good voltage linearity make it one of the most promising candidates for metal-insulator-metal capacitor applications.     

Sol–gel deposited ceria thin films as gate dielectric for CMOS technology

In this work, cerium oxide thin films were prepared using cerium chloride heptahydrate, ethanol and citric acid as an additive by sol–gel spin-coating technique and further characterized to study the various properties. Chemical composition of deposited films has been analysed by FTIR which shows existence of CeO₂. The samples have been optically characterized using ellipsometry to find refractive index of 2·18 and physical thickness which is measured to be 5·56 nm. MOS capacitors were fabricated by depositing aluminum (Al) metal using the thermal evaporation technique on the top of CeO₂ thin films. Capacitance–voltage measurement was carried out to calculate the dielectric constant, flat-band voltage shift of 18·92, 0·3–0·5 V, respectively and conductance–voltage study was carried out to determine the D_it of 1·40 × 10¹³ eV^???1 cm^???2 at 1 MHz.     

Mössbauer study of Fe magnetic state at the interface between Fe-Al-Si thin films and crystallized glass substrate

The magnetic state of Fe atoms at or near the interface between Fe_74.3Al_9.8Si_15.9 sendust magnetic thin films and SiO₂-based crystallized glass substrate (Fotoceram, Corning Co.) has been examined using conversion electron Mössbauer spectroscopy. The thicknesses of sputtered films are 0.05–2.0 m, and annealing conditions are at 500 C for 1 H. The excellent soft magnetic properties are not obtained for films with a thickness of less than 0.5 m. The presence of ferromagnetic Fe atoms with internal magnetic fields of 24.3–24.9 MAm^–1 is confirmed at or near the interface, indicating the formation of an Fe-rich phase such as Fe₉₀Si₁₀. The fraction of Fe atoms forming the Fe-rich phase at or near the interface is estimated to be around 20.... The formation of the Fe-rich phase is one of the main reasons for the degradation of the soft magnetic properties of sendust films deposited on SiO₂-based crystallized glass substrate, even though the DO₃-type ordered structure has also been formed.     

Electrical characteristics of lead-free Mn-doped BiFeO3–SrTiO3 thin films deposited on silicon substrate using pulsed laser deposition

Journal of Materials Science: Materials in Electronics - Lead-free 0.4(BiFe0.995Mn0.005O3)–0.6(SrTiO3) thin films were deposited on boron-doped silicon (p-Si) through pulsed laser deposition....     

Study of electrical and micro-structural properties of high-κ gate dielectric stacks deposited using pulse laser deposition for MOS capacitor applications

The electrical properties of hafnium oxide (HfO₂) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO₂–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (V_fb) and oxide-charge density (Q_ox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La₂O₃ into HfO₂ to fabricate HfO₂/La₂O₃ dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO₂–La₂O₃–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO₂ based MOS capacitors using the PLD deposition technique.     

Growth and properties of HfxZn1−xO thin films on flexible PET substrate using pulsed laser deposition

Hf-doped ZnO thin films with different Hf contents of target (Hf_xZn_1?xO 0 ≤ x ≤ 10 at.%) were deposited on flexible PET substrates under different oxygen pressure using pulsed laser deposition. Microstructures, optical and electrical properties of the films were studied. The results show that the as-deposited Hf_xZn_1?xO (0 ≤ x ≤ 5 at.%) films crystallized in ZnO hexagonal wurtzite structure with a highly preferred c-axis orientation. The films exhibited a transmission of higher than 80 % in the visible region. With increasing Hf content, the lattice constants increased; the morphology of the films deteriorated. The sheet resistance reached a minimum value of 16 Ω/□ when the doping level was about 0.5 at.%.     

Electrical transport properties of as evaporated and annealed amorphous GexSe1−x thin films

D.C. conductivity measurements were made on evaporated and annealed amorphous Ge_xSe_1−x thin films as a function of temperature (80–330K) and composition (x = 1.0, 0.9, 0.7, 0.5, 0.3, 0.1). It was observed that for Ge-rich films (x = 1.0, 0.9, 0.7) the conduction in the high temperature region takes place due to thermally assisted tunneling of charge carriers in localized states at the band edges and at low temperatures conduction is due to variable range hopping in localized states near the Fermi level. For Se-rich films (x=0.5, 0.3, 0.1) the conduction is intrinsic in the entire temperature range of measurements. It was observed that annealing reduces the density of states at the Fermi level. At the highest annealing temperature films become polycrystalline.     

Growth of CZTS thin films by sulfurization of sputtered single-layered Cu–Zn–Sn metallic precursors from an alloy target

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing single-layered metallic Cu–Zn–Sn precursors which were deposited by DC magnetron sputtering using a Cu–Zn–Sn ternary alloy target. The composition, microstructure and properties of the CZTS thin films prepared under different sputtering pressure and DC power were investigated. The results showed that the sputtering rate of Cu atom increases as the sputtering pressure and DC power increased. The microstructure of CZTS thin films can be optimized by sputtering pressure and DC power. The CZTS thin film prepared under 1 Pa and 30 W showed a pure Kesterite phase and a dense micro-structure. The direct optical band gap of this CZTS thin film was calculated as 1.49 eV with a high optical absorption coefficient over 10⁴ cm^?1. The Hall measurement showed the film is a p-type semiconductor with a resistivity of 1.06 Ω cm, a carrier concentration of 7.904 × 10¹⁷ cm^?3 and a mobility of 7.47 cm² Vs^?1.     

Growth of β-FeSi2 thin films on silicon (100) substrate for different annealing times by pulsed laser deposition

Single-phase β-FeSi₂ films were fabricated on silicon (100) substrates by pulsed laser deposition (PLD) technique and post-annealing process. The X-ray diffraction (XRD) showed that the diffraction intensity reached a certain threshold and then decreased with the increase of annealing time. The scanning electron microscopy (SEM) observations revealed surface morphologies of the films for different annealing times. The optimal photoluminescence (PL) of the films was obtained after 9 h annealing process. Based upon all the experimental results, it was found that the luminous properties were associated with the crystalline quality and surface morphologies.     

Influence of thickness on nanomechanical behavior of Black Diamond™ low dielectric thin films for interconnect and packaging applications

In the present study, we have investigated the thickness dependence of mechanical properties of the Black Diamond? (SiOC:H, BD, Low-k) films, which are of great interest in current Cu/low-k Back End of the Line (BEOL) interconnect/packaging technologies. For this investigation the BD thin films of six different thicknesses 100, 300, 500, 700, 1,000 and 1,200 nm were deposited on the 8″ Si wafer by using plasma enhanced chemical vapor deposition (PECVD) technique. Nanoindentation and nanoscratch tests of the BD films were performed by using the Nano Indenter^® XP (MTS Corp. USA). In nanoindentation testing of the BD films, significant differences in the elastic modulus of the BD films were observed. In nanoscratch testing, it is found that the critical load (Lc) and scratch width increases as the thickness of the film increases. Cross-sectional analysis of residual nanoindentation impressions was carried out using atomic force microscopy (AFM) to study the deformation behavior. The nanoindentation and nanoscratch responses of the BD thin films of six different thicknesses are different and they are expected mainly due to the molecular reorganization in thin/ultra thin films.     

Higher order Cauchy–Born rule based multiscale cohesive zone model and prediction of fracture toughness of silicon thin films

In this work, we extend the multiscale cohesive zone model (MCZM) (Zeng and Li in Comput Methods Appl Mech Eng 199:547–556, 2010), in which interatomic potential is embedded into constitutive relation to express cohesive law in fracture process zone, to include the hierarchical Cauchy–Born rule in the process zone and to simulate three dimensional fracture in silicon thin films. The model has been applied to simulate fracture stress and fracture toughness of single-crystal silicon thin film by using the Tersoff potential. In this study, a new approach has been developed to capture inhomogeneous deformation inside the cohesive zone. For this purpose, we introduce higher order Cauchy–Born rules to construct constitutive relations for corresponding higher order process zone elements, and we introduce a sigmoidal function supported bubble mode in finite element shape function of those higher order cohesive zone elements to capture the nonlinear inhomogeneous deformation inside the cohesive zone elements. Benchmark tests with simple 3D models have confirmed that the present method can predict the fracture toughness of silicon thin films. Interestingly, this is accomplished without increasing of computational cost, because the present model does not require quadratic elements to represent heterogeneous deformation, which is the inherent weakness of the previous MCZM model. Quantitative comparisons with experimental results are performed by computing crack propagation in non-notched and initially notched silicon thin films, and it is found that our model can reproduce essential material properties, such as Young’s modulus, fracture stress, and fracture toughness of single-crystal silicon thin films.     

Effects of Bi doping on dielectric and ferroelectric properties of PLBZT ferroelectric thin films synthesized by sol–gel processing

[Pb _0·95(La_1???y Bi _y ) _0·05][Zr_0·53Ti_0·47]O₃ (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content ${\mathit{y}}$ is not more than 0·4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0·6, the pyrochlore phase appears and the remnant polarization P _r of PLBZT thin films is smaller than that of $\left({Pb}_{{1-x}} {\bf La}_{x}\right)\!\!\left({Zr}_{{1-y}} {Ti}_{y}\right){O}_{3}$ (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.     

Single and multiple doping effects of silicon–boron and fluorine on ZnO thin films deposited with sol–gel spin coating technique

Undoped, Si and B single doped, Si–B co-doped and Si–B–F triple doped ZnO thin films were grown by sol–gel spin coating method. Effects of these doping elements on microstructural, morphological and optical properties were investigated. X-ray diffraction studies showed that all films had hexagonal wurtzite structure. Although Si doping increased crystallinity of ZnO, single boron doping, Si–B co-doping and Si–B–F triple doping gave rise to a decreasing in crystallinity. Scanning electron microscope micrographs indicated that the grain size and morphological characters of ZnO depended on doping element type and their concentrations. The micrographs also demonstrated that Si doping deteriorated grain size and their distribution on film surface of ZnO structure. Although single B, doubly Si–B and triple Si–B–F doping at low contents improved grain distribution and film morphology, when their content increased, film morphology started to deteriorate. Optical band gap value of undoped film increased with Si doping irrespective of Si doping content. Although single B, doubly Si–B and triple Si–B–F doping at low contents caused an increase in optical band gap of undoped ZnO, more doping content brought about a decrease in optical band gap. From the optical parameters such as absorption coefficient, the Urbach energy values of the films were calculated by using ln α vs. photon energy graphs. In generally, Urbach energies of the films changed reversely with the band gap energies of the films.     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Effect of lead on formation and dielectric tunability of (Pbx,Sr1–x)0.85Bi0.1TiO3 thin films

(Pb_x,Sr_{1 x})_0.85Bi_0.1TiO₃ thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pb_x, Sr_{1 x})_0.85KBi_0.1TiO₃ thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb²⁺ and Sr²⁺. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing Pb²⁺ content because the radius of Pb²⁺ is larger than that of Sr²⁺. It appears at room temperature when the content of Pb²⁺/Sr²⁺ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb²⁺ ions increase due to its high polarization. The higher tunability of the (Pb_x,Sr_{1 x})_0.85Bi_0.1TiO₃ thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric phases. Pb²⁺ions show a dominant factor to affect the Curie point of the system and then changing tunability.     

Electrical and optical properties of ZrxLa1−xOy nanocrystallites as an advanced dielectric for the next FET devices

In the present work, the spatial distribution of the leakage current through Zr_xLa_1?xO_y thin films with different degrees of crystallinity temperatures was investigated. Zr_xLa_1?xO_y nanocrystallites were prepared by sol–gel method, in that Zr atomic fractions in the combined is at the range of x = 5–60 %. The nanocrystallite’s phases and properties were characterized with using X-ray diffraction, fourier transfer infrared radiation, scanning electron microscopy, atomic force microscopy and transmission electron microscopy techniques. Electrical property characterization was also performed with cyclic-voltameter (C-V) technique in TRIS solution (pH = 7.3, with the formula (HOCH₂)₃CNH₂). C-V measurements showed current flow through the TRIS reduces at higher temperatures. Moreover, elemental qualitative analysis was performed with map and energy dispersive X-ray spectra confirmed above claims.     

The effects of native and light induced defects on optoelectronic properties of hydrogenated amorphous silicon–germanium (a-SiGe:H) alloy thin films

Effects of native and light induced defects states in hydrogenated amorphous silicon–germanium alloy thin films with different Ge concentrations have been investigated by using steady-state photoconductivity, dual beam photoconductivity (DBP), transmission spectroscopy and photothermal deflection spectroscopy (PDS) techniques. In the annealed state, sub-bandgap absorption spectra obtained from both PDS and DBP overlap very well at energies above 1.4 eV. However, differences in α (hν) spectrum exist in the lower energy part of absorption spectrum. The α (hν) value measured at 1.0 eV is the lowest for 10% Ge sample and increases gradually as Ge content of the sample increases. In the light soaked state, time dependence of photoconductivity decay obeys to t ^−x power law, where x changes from 0.30 to 0.60 for samples with low Ge content and 0.05–0.1 for samples with high Ge content. Correspondingly, the increase of the sub-bandgap absorption coefficient at lower energies obeys to t ^y power law, where y values are lower than the x value of the same sample. It can be inferred that sub-bandgap absorption and photoconductivity measurements are not controlled by the same set of defects created in the bandgap of alloys.     

The effects of the aluminium concentration on optical and electrical properties of AZO thin films as a transparent conductive layer

In this paper, we studied the effects of the aluminium dopant concentration on the optical and electrical properties of aluminium doped zinc oxide (AZO) thin films grown on soda-glass substrates by a simple chemical method. The amount of aluminium in the compound was varied from 0 to 5 atomic percent (at.%), and the typical thickness of the films produced was about 300 nm. The thin films were characterized by scanning electron microscopy and X-ray diffraction to investigate the morphology and crystallinity of the samples. The optical properties of the thin films were studied by UV–Vis spectroscopy to determinate absorption, transmittance, and the diffuse reflectance. In addition, the photoluminescence properties of the thin films, excited with a 320 nm UV laser beam, were investigated. The effects of the aluminium concentration on these optical properties are discussed. The films with 2 and 5 % doping had excellent optical transmittance (~85–90 %) in the 400–1100 nm wavelength range. The photoluminescence spectra of the AZO films revealed UV near band edge emission peaks in the 378–401 nm range and an oxygen-vacancy related peak around 471 nm. The addition of aluminium changed the band gap of zinc oxide from 3.29 to 3.41 eV, and the appearance of a new level was observed in the band gap at the higher aluminium doping concentrations. The AZO thin films showed good conductivity (in the order of 10^?2 Ω cm) which allows their use as transparent electrodes. Moreover, the AZO thin films were stable in open air for 30 days.