Atomic Vapor Depositions of Ti-Ta-O thin films for Metal-Insulator-Metal applications

Atomic Vapor Deposition technique was applied for the depositions of Ti-Ta-O oxide films for Metal-Insulator-Metal capacitors used in back-end of line for Radio Frequency applications. Composition, crystallinity, thermal stability and electrical properties were studied. Ti-Ta-O films, with the ratio of Ta/Ti ~ 1.5, deposited at 400 °C on TiN electrodes, were amorphous and possessed a dielectric constant of 50 with low voltage linearity coefficients and leakage currents densities as low as 10^− 7 A/cm² at 1 V. The films, deposited on Si wafers, were amorphous up to the annealing temperature of 700 °C and crystallized in orthorhombic Ta₂O₅ phase at higher temperatures.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Hysteresis-free HfO2 film grown by atomic layer deposition at low temperature

Hysteresis-free hafnium oxide films were fabricated by atomic layer deposition at 90 °C without any post-deposition annealing, and their structures and properties were compared with films deposited at 150 °C and 250 °C. The refractivity, bandgap, dielectric constant and leakage current density all increase with deposition temperature, while the growth rate and breakdown field decrease. All films are amorphous with roughly the same composition. Although the thin films deposited at the above-mentioned temperatures all show negligible hysteresis, only the 90 °C-deposited films remain hysteresis-free when the film thickness increases. The 90 °C-deposited films remain hysteresis-free after annealing at 300 °C. The hysteresis in films deposited at high temperatures increases with deposition temperature. Evidences show such hysteresis originates in the HfO₂ film instead of the interface. Based on a careful structure analysis, middle-range order is suggested to influence the trap density in the films. HfO₂ films deposited at low temperature with negligible hysteresis and excellent electrical properties have great potential for the fabrication and integration of devices based on non-silicon channel materials and in applications as tunneling and blocking layers in memory devices.     

Effects of annealing temperature on the characteristics of ALD-deposited HfO2 in MIM capacitors

We have investigated the annealing effects of HfO₂ films deposited by an atomic layer deposition (ALD) method on the electrical and physical properties in the Si/SiO₂/Pt/ALD-HfO₂/Pd metal-insulator-metal (MIM) capacitors. If the annealing temperature for HfO₂ films was restricted below 500 °C, an annealing step using a rapid thermal processor (RTP) improves the electrical properties such as the dissipation factor and the dielectric constant. On the other hand, annealing at 700 °C degrades the electrical characteristics in general; the dissipation factor increases over the frequency range of 1∼4 MHz, and the leakage current increases up to 2 orders at the low electric field regions. We found that the degradation of electrical properties is due to the grain growth in the HfO₂ film (i.e., poly-crystallization of the film) by the high temperature annealing processing. We suggested that the annealing temperature must be restricted below 500 °C to obtain the high quality high-k film for the MIM capacitors.     

Reduction of crystallization temperature of the Aurivillius phase in Nd-doped SrBi2Ta2O9 thin films via substrate bias

Nd-doped SrBi₂Ta₂O₉ films were sputtered on Pt/Ta/SiO₂/Si substrates under various substrate biases. The radio frequency bias results in the reduction of the Aurivillius phase crystallization temperature. At 48 W, the crystallization temperature of film is lowered at a magnitude of about 80 °C. When the bias further increases, Aurivillius phase formation is suppressed due to too deficient Bi in film. The film deposited at 48 W after annealing at 670 °C shows ferroelectric characteristics. The remnant polarization of the films increases as the annealing temperature is increased.     

High performance metal-insulator-metal capacitors with atomic vapor deposited HfO2 dielectrics

Thin HfO₂ films were grown as high-k dielectrics for Metal-Insulator-Metal applications by Atomic Vapor Deposition on 8 inch TiN/Si substrates using pure tetrakis(ethylmethylamido)hafnium precursor. Influence of deposition temperature (320-400 °C) and process pressure (2-10 mbar) on the structural and electrical properties of HfO₂ was investigated. X-ray diffraction analysis showed that HfO₂ layers, grown at 320 °C were amorphous, while at 400 °C the films crystallized in cubic phase. Electrical properties, such as capacitance density, capacitance-voltage linearity, dielectric constant, leakage current density and breakdown voltage are also affected by the deposition temperature. Finally, TiN/HfO₂/TiN stacks, integrated in the Back-End-of-Line process, possess 3 times higher capacitance density compared to standard TiN/Si₃N₄/TiN capacitors. Good step coverage (> 90%) is achieved on structured wafers with aspect ratio of 2 when HfO₂ layers are deposited at 320 °C and 4 mbar.     

HfO2 gate insulator formed by atomic layer deposition for thin-film-transistors

We have investigated the effects of annealing temperature on the physical and electrical properties of the HfO₂ film deposited by an atomic layer deposition (ALD) method for high-k gate oxides in thin-film-transistors (TFTs). The ALD deposition of HfO₂ directly on the Si substrate at 300 °C results in the formation of thin HfSi_xO_y interfacial layer between Si and HfO₂. The subsequent low temperature N₂-annealing of HfO₂ films (i.e., 300 °C) using a rapid thermal processor (RTP) improves the overall electrical characteristics of HfSi_xO_y-HfO₂ films. Based on the current work, we suggest that HfO₂ film deposited by the ALD method is suitable for high-k gate oxides in TFTs, which have to be fabricated at low temperature.     

Structural investigation of thin TiO2 films prepared by evaporation and post‐heating

Thin films of TiO₂ have been prepared by reactive evaporation of Ti₂O₃ at substrate temperatures from 150 °C to 350 °C and by post‐heating at 150 °C to 850 °C. The mass density of the films increases with increasing substrate and annealing temperature. The crystalline structure of the film prepared at 350 °C is anatase and becomes rutile upon annealing at 850 °C. All other films are amorphous as‐prepared and become anatase upon annealing above 250 °C. The crystallinity is higher for films prepared at lower temperature and does not increase with annealing temperature. Coatings with reproducible optical properties are obtained when deposited and post‐annealed at 250 °C.     

Nanocluster evolution in Ge ion implanted Ta2O5 layers

Ion implantation-induced nanoclusters were synthesized in reactive sputtered Ta₂O₅ films by Ge⁺ implantation and subsequent annealing. The effects of ion fluence and post-implantation thermal treatment on the kinetics of the nanoclustering were investigated. Ge⁺ ions with energy of 40 keV and fluences of 5 × 10¹⁵, 1 × 10¹⁶ and 5 × 10¹⁶ cm^− 2 were implanted in the Ta₂O₅ layers at room temperature. The samples were thermally treated by rapid thermal annealing in vacuum at 700 °C and 1000 °C for 30, 60 and 180 s. Structural studies of all samples were done by Cross-sectional Transmission Electron Microscopy in diffraction and phase contrast mode. Under optimized conditions (high implantation fluence, subsequent annealing) nanoclusters are formed around the projected ion range of the implanted Ge⁺ ions. The structure of the implanted Ta₂O₅ matrix changes from amorphous to orthorhombic when the annealing was performed at 1000 °C. Although the Ta₂O₅ matrix crystallizes, no evidence is obtained for crystallization of the embedded nanoclusters even after annealing at 1000 °C.     

Effect of doping and substrate temperature on the structural and optical properties of reactive pulsed laser ablated tin oxide doped tantalum oxide thin films

5% SnO₂ doped tantalum oxide (Ta₂O₅) films are deposited on quartz substrates at different substrate temperatures of 300 K, 773 K, 873 K and 973 K using pulsed laser deposition in an oxygen ambient of 0.002 mbar. Undoped Ta₂O₅ films are also deposited on quartz substrates kept at substrate temperature 973 K under the same oxygen ambient using PLD. The films are characterized using GIXRD, AFM, FTIR, micro-Raman and UV-visible spectroscopy. Undoped films show an amorphous nature even at a substrate temperature of 973 K, whereas, SnO₂ doped films show crystalline nature even for deposition at 300 K. As far as our knowledge goes, this is the first report of crystalline Ta₂O₅ films deposited at room temperature. The average size of the crystallites calculated using the Debye-Scherrer formula, shows that the size of the crystallite decreases with increase in substrate temperature. FTIR and micro-Raman spectroscopic analysis reveals the presence of Ta-O-Ta, O-Ta and O-Ta-O vibrational bands in the films. Raman analysis indicates that the addition of SnO₂ suppresses the bond formation and changes the magnitude of bonds in Ta₂O₅. AFM patterns reveal the formation of Ta₂O₅ nanorods of diameter about 100 nm for the doped film deposited at 973 K. Optical transmittance of the films is found to be sensitive to substrate temperature as well as to the presence of SnO₂. A blue shift in the band-gap of the doped films is observed. The decrease of band-gap with decrease of particle size observed for SnO₂ doped films can be due to a band-bending effect. The transmittance of the films is found to depend on SnO₂ doping and substrate temperature.     

Properties of Ce-doped ITO films deposited on polymer substrate by DC magnetron sputtering

Ce-doped indium tin oxide (ITO:Ce) films were deposited on flexible polyimide substrates by DC magnetron sputtering using ITO targets containing various CeO₂ contents (CeO₂ : 0, 0.5, 3.0, 4.0, 6.0 wt.%) at room temperature and post-annealed at 200 °C. The crystallinity of the ITO films decreased with increasing Ce content, and it led to a decrease in surface roughness. In addition, a relatively small change in resistance in dynamic stress mode was obtained for ITO:Ce films even after the annealing at high temperature (200 °C). The minimum resistivity of the amorphous ITO:Ce films was 3.96 × 10^− 4 Ωcm, which was deposited using a 3.0 wt.% CeO₂ doped ITO target. The amorphous ITO:Ce films not only have comparable electrical properties to the polycrystalline films but also have a crystallization temperature > 200 °C. In addition, the amorphous ITO:Ce film showed stable mechanical properties in the bended state.     

Stability and effect of annealing on the optical properties of plasma-deposited Ta2O5 and Nb2O5 films

Tantalum and niobium oxide optical thin films were prepared at room temperature by plasma-enhanced chemical vapor deposition using tantalum and niobium pentaethoxide (M(OC₂H₅)₅) precursors. We studied the evolution of their optical and microstructural properties as a result of annealing over a broad temperature range from room temperature up to 900 °C. The as-deposited films were amorphous; their refractive index, n, and extinction coefficient, k, at 550 nm were n = 2.13 and k < 10^− 4 for Ta₂O₅, and n = 2.24 and k < 10^− 4 for Nb₂O₅. The films contained a small amount of residual carbon (∼ 2-6 at.%) bonded mostly to oxygen. During annealing, the onset of crystallization was observed at approximately T_C1 = 650 °C for Ta₂O₅ and at T_C1 = 450 °C for Nb₂O₅. Upon annealing close to T₁ (300 °C for Nb₂O₅ and 400 °C for Ta₂O₅), n at 550 nm decreased by less than 1%. This was correlated with the decrease of carbon content, as suggested by Fourier transform infrared spectroscopy, elastic recoil detection and static secondary ion mass spectroscopy (SIMS) results. During annealing, we observed phase transition from the δ- (hexagonal) phase to the L- (orthorhombic) phase between 800 °C and 900 °C for Ta₂O₅, and between 600 °C and 700 °C for Nb₂O₅. The structural changes were also marked by silicon diffusion from the substrate into the oxide layer at annealing temperatures above 500 °C for Ta₂O₅ and above 400 °C for Nb₂O₅. As a consequence of oxygen, silicon and metal interdiffusion, the interface between the Si substrate and the metal oxide (Ta₂O₅ or Nb₂O₅) is characterized by its broadening, well documented by spectroscopic ellipsometry and SIMS data.     

Optical and electrical properties of heat-resistant Sb-doped Sn1 − xHfxO2 transparent conducting films

To examine variations in the transparent conducting properties after annealing at high temperatures, 300-nm thick Sb-doped Sn_1 − xHf_xO₂ (x = 0.00-0.10) films were deposited onto silica glass substrates by the RF sputtering method and annealed in air up to 1000 °C at 200 °C increments. After annealing, all the Sb-doped SnO₂ films were transparent and electrically conductive, but large cracks, which decreased the electrical conductivity, were generated in several films due to crystallization or the thermal expansion difference between the film and substrate. Only the film deposited at room temperature in an Ar and O₂ mixed atmosphere did not crack after annealing, and its electrical conductivity exceeded 100 S cm^− 1 even after annealing at 1000 °C in air. Hf-doping blue shifted the fundamental absorption edges in the UV region in the Sb-doped Sn_1 − xHf_xO₂ films. Additionally, the optical transmission at 310 nm, T₃₁₀, increased as the Hf concentration increased, whereas the electrical conductivity was inversely proportional to the Hf concentration. On the other hand, thinner films (150-nm thick) with x = 0.00 showed both a high electrical conductivity over 100 S cm^− 1 and a high transparency T₃₁₀ = 65% after high temperature annealing.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

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.     

Annealing effects on structural and electrical properties of fluorinated amorphous carbon films deposited by plasma enhanced chemical vapor deposition

The annealing effects on the structural and electrical properties of fluorinated amorphous carbon (a-C:F) thin films prepared from C₆F₆ and Ar plasma are investigated in a N₂ environment at 200 mTorr. The a-C:F films deposited at room temperature are thermally stable up to 250 °C, but as the annealing temperature is increased beyond 300 °C, the fluorine incorporation in the film is reduced, and the degree of crosslinking and graphitization in the film appears to be enhanced. At the annealing temperature of 250 °C, the chemical bond structures of the film are unchanged noticeably, but the interface trapped charges between the film and the silicon substrate are reduced significantly. The increased annealing temperature contributes the decrease of both the interface charges and the effective charge density in the a-C:F film. Higher self-bias voltage is shown to reduce the charge density in the film.     

Influence of annealing temperature on the structural, mechanical and wetting property of TiO2 films deposited by RF magnetron sputtering

TiO₂ films have been deposited on silicon substrates by radio frequency magnetron sputtering of a pure Ti target in Ar/O₂ plasma. The TiO₂ films deposited at room temperature were annealed for 1 h at different temperatures ranging from 400 °C to 800 °C. The structural, morphological, mechanical properties and the wetting behavior of the as deposited and annealed films were obtained using Raman spectroscopy, atomic force microscopy, transmission electron microscopy, nanoindentation and water contact angle (CA) measurements. The as deposited films were amorphous, and the Raman results showed that anatase phase crystallization was initiated at annealing temperature close to 400 °C. The film annealed at 400 °C showed higher hardness than the film annealed at 600 °C. In addition, the wettability of film surface was enhanced with an increase in annealing temperature from 400 °C to 800 °C, as revealed by a decrease in water CA from 87° to 50°. Moreover, the water CA of the films obtained before and after UV light irradiation revealed that the annealed films remained more hydrophilic than the as deposited film after irradiation.     

A study of amorphous and crystalline phases in In2O3-10 wt.% ZnO thin films deposited by DC magnetron sputtering

We report on the processing, phase stability, and electronic transport properties of indium oxide (In₂O₃) doped with 10 wt.% zinc oxide (ZnO) deposited to a thickness of 100 nm using DC magnetron sputter deposition at room temperature and 350 °C. We compare the optimum oxygen content in the sputter gas for pure In₂O₃ and doped with (i) 10 wt.% ZnO and (ii) 9.8 wt.% SnO₂. Amorphous IZO films were annealed at 200 °C in air and N₂/H₂ and resistivity, Hall mobility, and carrier density along with molar volume change were monitored simultaneously as a function of time at temperature. We report that annealing the amorphous oxide in air at 200 °C does not lead to crystallization but does result in a 0.5% decrease in the amorphous phase molar volume and an associated drop in carrier density. Annealing in forming gas leads to an increase in carrier density and a small decrease in molar volume. We also report that when annealed in air at 500 °C, the amorphous IZO phase may crystallize either in the cubic bixbyite or in a recently observed rhombohedral phase.     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.     

Medium-term thermal stability of amorphous Ge2Sb2Te5 flash-evaporated thin films with regards to change in structure and optical properties

The stability of flash-evaporated amorphous Ge₂Sb₂Te₅ thin films has been studied under medium-term temperature treatment (30 - 80 °C, with a step of 10 °C) in ten subsequent heating and cooling cycles. The significant changes in structure and optical properties are reported. The temperature cycling of the films resulted in formation of an isolated 5 - 7 nm nano-crystalline phase in the amorphous phase. The corresponding increase in refractive index and change in optical bandgap energy and sheet resistance are also presented. The formation of Ge₂Sb₂Te₅ nano-crystals (~ 5 - 7 nm) even under temperature below 80 °C could contribute to the explanation of mechanism of resistivity fluctuation (drift) of the “amorphous phase” films. We also show that the optical and electrical properties of flash evaporated Ge₂Sb₂Te₅ thin films are very similar to those reported for sputtered films.