Optische und mechanische Eigenschaften von RLVIP HfO2‐Schichten

Optical and mechanical properties of RLVIP HfO₂ films In this paper HfO₂‐films were deposited on unheated fused silica, borosilicate glass, and silicon wafer substrates by reactive low voltage ion plating (RLVIP). Optical film properties, i. e. refractive index and absorption as well as mechanical properties, particularly film stress, were investigated. Their dependence on deposition parameters, i. e. arc current and oxygen partial pressure was studied. The film refractive index was calculated from spectrophotometric measurements. The low absorption was determined by photothermal deflection spectrometry. Stress measurements were performed by bending disc method with uncoated and coated silicon wafer substrates.     

Ferroelectricity and Antiferroelectricity of Doped Thin HfO2‐Based Films

The recent progress in ferroelectricity and antiferroelectricity in HfO₂‐based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O₃, BaTiO₃, and SrBi₂Ta₂O₉, which are considered to be feasible candidate materials for non‐volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si‐compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si‐doped HfO₂ thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro­electricity or antiferroelectricity in thin HfO₂ films. They have large remanent polarization of up to 45 μC cm^?2, and their coercive field (≈1–2 MV cm^?1) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field‐effect‐transistors and three‐dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid‐state‐cooling, and infrared sensors.     

Antireflecting coating from Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> and SiO<Subscript>2</Subscript> multilayer films

Sol-gel method is important for depositing antireflective coating that allows control over thickness as well as the index of refraction. Antireflective coatings which are produced from Ta₂O₅ and SiO₂ multi-layer thin films using sol-gel spin coating method are presented. The refractive index and the thickness are controlled by the composition and the concentration of the solution respectively. The thickness, refractive index and extinction coefficient of the films were calculated through transmission and reflection measurement by an NKD analyser. Mechanical properties of the films were checked by the cross tape test and dry sun test at 760 W/m². The result shows that the sample heat treated at 450^∘C for 15 min approaches a reflectance with less than 0.5% at around 840 nm.     

ITO‐coatings by reactive low‐voltage ion plating: film properties and plasma analysis

Transparent conductive oxides (TCO) are widely used materials for multifarious applications. According to today's state of knowledge, indium‐tin‐oxide (ITO) still offers the best electrical properties among numerous TCOs. However, ITO films produced by ion plating have only rarely been reported to be investigated. For most coating processes, ITO films need to be deposited under high temperature conditions (some 100 °C substrate heating) or require post‐deposition heat treatment in order to obtain high film quality. In this study, reactive low‐voltage ion plating (RLVIP) was used, which allows ‐ due to plasma assistance during the coating process ‐ deposition of ITO films at temperatures below 100 °C. Essential film properties, i.e. resistivity and optical transmission, were optimised by variation of arc current, gas pressure and deposition rate. These quantities ‐ particularly arc current and gas pressure ‐ have huge influence on the characteristics of the supporting plasma. This was shown by analysing the plasma with a mass‐spectrometric plasma monitoring system and with a Langmuir probe. In comparison with formerly studied coating materials (Ta₂O₅,Nb₂O₅,HfO₂), different plasma compositions regarding the presence of metal oxide ions were determined, which could be attributed to elemental and molecular energy properties (ionisation and binding energies).     

Influence of Relevant Gas Pressure on the Properties of Ionplated Ta2O5 Films. Einfluss relevanter Gasdrücke auf die Eigenschaften ionenplattierter Ta2O5 Schichten

Ta₂O₅ films were deposited onto unheated fused silica substrates (Suprasil®) by reactive low voltage ion plating (RLVIP). From these films of about 200 nm thickness the optical properties (refractive index n and the absorption coefficient k) and also the mechanical properties (density ρ and intrinsic stress σ) were investigated in dependence of the working gas pressure (Ar) and the reactive gas pressure (O₂). The experiments show a reasonable correlation between refractive index, density and intrinsic stress of the films. With low total pressure high refractive indices (up to n₅₅₀=2.25), high compressive film stress and high relative film density were found. However the film density, the refractive index and also the intrinsic stress decreased with films prepared under raising total gas pressure. The optical absorption depends on the amount of oxygen in the gas phase during deposition. By adding more oxygen to the Ar/O₂ gas mixture primarily the absorption could clearly be decreased.     

Optical properties of TiO2 thin films deposited on polycarbonate by ion beam assisted evaporation

TiO₂ thin films were deposited on polycarbonate (PC) substrate by ion beam assisted evaporation. The grain size increased with the ion anode voltage and film thickness. The TiO₂ thin films had an amorphous structure. Moiré deflectometry was used to measure the nonlinear refractive indices of TiO₂ thin films on PC substrates. The nonlinear refractive index was measured to be of the order of 10^− 8 cm² W^− 1 and a change in refractive index was of the order of 10^− 5. Dense TiO₂ films exhibited high linear refractive indices, red-shift of the optical absorbance, and absorbance in the near-IR region.     

Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

HiPIMS ‐ Technologie und Anwendungsfelder

HiPIMS‐technology and field of application Starting wi^th the introduction of planar magnetron cathodes in the mid seventies magnetron sputtering has taken nearly all industrial branches, dealing wi^th thin film coatings, which are in assault. Numerous milestones within the last 30 years were set, whereas some of the most important were the development of rotary cathodes (?CMAG”?) and the introduction of pulsed plasmas. H igh P ower I mpulse M agnetron S puttering (HiPIMS) or H igh P ower P ulse M agnetron S puttering (HPPMS) is a further innovative step towards coatings wi^th superior quality. HiPIMS typically uses pulses in the megawatt range, resulting in power densities of 1000 W/cm² and higher (compared to typically 20 – 50 W/cm²). The major benefit of the new technology is a very high degree of ionised target material of 50 – 90%, leading to superior coating properties like high density, very smoo^th surfaces, and high refractive index for optical coatings. Besides the introduction in highly ionised pulse plasmas the potential of this new technology will be demonstrated by recent results of applied research for applications in different industrial branches.     

Phase‐Engineered PtSe2‐Layered Films by a Plasma‐Assisted Selenization Process toward All PtSe2‐Based Field Effect Transistor to Highly Sensitive,Flexible, and Wide‐Spectrum Photoresponse Photodetectors

The formation of PtSe₂‐layered films is reported in a large area by the direct plasma‐assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 °C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe₂‐layered film (five monolayers) exhibits a metallic behavior. A clear p‐type semiconducting behavior of the PtSe₂‐layered film (≈trilayers) is observed with the average field effective mobility of 0.7 cm² V^?1 s^?1 from back‐gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe₂ field effect transistor is demonstrated where the thinner PtSe₂, exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe₂, exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe₂‐layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 µA under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.     

Modulation of the structural and optical properties of sputtering-derived HfO2 films by deposition power

High-k gate dielectric HfO₂ thin films have been deposited on Si and quartz substrate by radio frequency magnetron sputtering. The structural and optical properties of HfO₂ thin films related to deposition power are investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), ultraviolet–visible spectroscopy (UV–Vis), and spectroscopic ellipsometry (SE). Results confirmed by XRD have shown that the as-deposited HfO₂ thin films are not amorphous state but in monoclinic phase, regardless of deposition power. Analysis from FTIR indicates that an interfacial layer has been formed between the Si substrate and the HfO₂ thin film during deposition. AFM measurements illustrate that the root mean square (RMS) of the as-deposited HfO₂ thin films’ surface demonstrates an apparent reduction with the increase of deposition. Combined with UV–Vis and SE measurements, it can be noted reduction in band gap with an increase in power has been observed. Additionally, increase in refractive index (n) has been confirmed by SE.     

Reactive Low Voltage Ion Plating (RLVIP). Prozess‐, Plasma‐ und Schichteigenschaften am Beispiel von Ta2O5/SiO2

Reactive Low Voltage Ion Plating (RLVIP) is a process for production of chemical compound films mainly by direct synthesis from the elements. It can be used for deposition of single layer and multilayer oxide coatings onto unheated glass and other unheated substrates. An introduction to the RLVIP process will be given, together with some relevant plasma process data and optical and mechanical film properties of Ta₂O₅ films and Ta₂O₅/SiO₂ multilayers. The process plasma was analysed by plasma monitoring (PPM421), a Langmuir probe system (Smartprobe) and a Faraday Cup System (MIEDA). A correlation between plasma data and optical/mechanical properties will be shown.     

Synthesis and characterization of HfO2 and ZrO2 thin films deposited by plasma assisted reactive pulsed laser deposition at low temperature

A plasma assisted reactive pulsed laser deposition process was demonstrated for low-temperature deposition of thin hafnia (HfO₂) and zirconia (ZrO₂) films from metallic hafnium or zirconium with assistance of an oxygen plasma generated by electron cyclotron resonance microwave discharge. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared spectroscopy, which reveals the monoclinic phases of HfO₂ and ZrO₂ in the films with no interfacial SiO_x layer between the oxide film and the Si substrate. The optical properties of the deposited films were investigated by measuring the refractive indexes and extinction coefficients with the aid of spectroscopic ellipsometry technique. The films deposited on fused silica plates show excellent transparency from the ultraviolet to near infrared with sharp ultraviolet absorption edges corresponding to direct band gap.     

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

Investigations of bilayer and trilayer Al₂O₃/SiO₂ and Al₂O₃/HfO₂/SiO₂ antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10^?3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al₂O₃, 0.6 nm ? 0.8 nm/s for HfO₂ and 0.6 nm/s for SiO₂. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al₂O₃/SiO₂ and 78 nm/156 nm/78 nm for Al₂O₃/HfO₂/SiO₂. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.     

Far-infrared laser measurement of the refractive index of polypropylene

The refractive index of polypropylene in the far infrared (FIR) is measured by means of a suitably modified laser of a FIR spectrometer. When thin polypropylene films of 12.7-microm nominal thickness are introduced in the optical cavity of a laser at the Brewster angle, the radiation ceases because of the change in the optical path of the laser beam. This change is measured from the displacement of one of the laser mirrors, which is necessary to restore the laser resonance. The refractive index of polypropylene is deduced from this measurement and from the film thickness, as obtained from an independent measurement based in pycnometry. The value obtained for the refractive index is 1.492(15) for the wavelengths between 118.834 and 251.140 microm, for a polypropylene film of 12.71(2)-microm thickness and 0.9049(7) g/cm3 density.     

Reflectance spectra and refractive index of a Nd:YAG laser-oxidized Si surface

The reflectance spectra and refractive index of Nd:YAG laser-oxidized SiO₂ layers with thicknesses from 15 to 75 nm have been investigated with respect to the laser beam energy density and substrate temperature. Thickness and refractive index of films have been determined from reflectance measurements at normal light incidence in the spectral range 300–800 nm. It was found that the oxide-growth conditions at higher substrate temperatures and laser powers greater than 3.36 J cm⁻² provides a better film quality in terms of both optical thickness and refractive index. However, the refractive indices of the films are smaller in the whole spectral range studied as compared to that of conventional thermally grown SiO₂. This might be due to the porous structure formed during the laser-assisted oxidation. The results suggest the need of post-oxidation annealing to improve the refractive indices of the films, suitable for Si-device applications.     

Oxide thickness measurements by infrared ellipsometry

Current interest' in anodized aluminum surfaces as substrates for adhesive bonding has created a need to measure the properties of the oxide layer in a non-contacting manner. Visible light ellipsometry is a very sensitive non-contacting technique for measuring the thickness of very thin films on smooth surfaces whose optical constants are known. However, the method is limited to film thicknesses which are generally less than 2000 Å and validity is lost when there is appreciable scattering caused by the roughness of the substrate and the structure of the oxide itself. These objections become much less severe if the operating wavelength is in the infrared region. Such an infrared ellipsometer has been developed to measure the thickness of oxides produced by anodization of aluminum with production-finished surfaces. The instrument operates with a 10.6 μm beam from a low power CO₂ laser and uses a 6328 Å beam from a He-Ne laser for alignment and location of the measurement region. The oxides were formed on unclad 7075 aluminum by anodization in an ammonium pentaborate solution at constant current to termination voltages of from 25 to 275 V in 25 V increments. The measured ellipsometric quantities Δ and ψ were used to compute the corresponding metal oxide film thicknesses using a complex refractive index N = 2.39?i41.36 for the substrate. The results for a film refractive index of 1.50 were in close agreement with those measured with a scanning electron microscope. Elemental concentration profiles for each surface were made by Auger electron spectroscopy.     

Deposition Temperature Effect on the Structure and Optical Property of RF‐PACVD‐Derived Hydrogenated SiCNO Film

Amorphous hydrogenated silicon oxocarbonitride (SiCNO:H) films have been deposited by plasma‐assisted chemical vapour deposition (PACVD) using bis(trimethylsilyl)carbodiimide (BTSC) as a single source precursor in a argon (Ar) radio‐frequency plasma. In this work the SiCNO:H films deposited at different deposition temperatures were studied in terms of deposition rate, refractive index, surface roughness, microstructure, and chemical composition including bonding state. The results showed that a higher deposition temperature enhanced the formation of Si‐N bonds, and disfavoured the formation of N=C=N, Si‐NCN, C‐H and Si‐CH₃ bonds. A higher deposition temperature also decreased the deposition rate and increased the refractive index of the resulting SiCNO:H film. With increasing temperature a denser film was formed, indicating a change of the deposition mechanism, i.e., transformation from particle precipitation to heterogeneous surface reaction. Except for the coatings deposited at room temperature, the surface of the films was smooth with a roughness of around 4 nm at the centre in the range of 5 μm x 5 μm area. Moreover, the films contained 8 ～ 16 at.% oxygen bonded to Si, which originated from the remnant H₂O in the deposition chamber.     

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents

In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (?-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by ¹H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.     

A 1D Vanadium Dioxide Nanochannel Constructed via Electric‐Field‐Induced Ion Transport and its Superior Metal–Insulator Transition

Nanoscale manipulation of materials' physicochemical properties offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the present semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future. Here, a superior metal–insulator transition (MIT) of a 1D VO₂ nanochannel constructed through an electric‐field‐induced oxygen ion migration process in V₂O₅ thin film is reported for the first time. A sharp and reliable MIT transition with a steep turn‐on voltage slope of <0.5 mV dec^?1, fast switching speed of 17 ns, low energy consumption of 8 pJ, and low variability of <4.3% is demonstrated in the VO₂ nanochannel device. High‐resolution transmission electron microscopy observation and theoretical computation verify that the superior electrical properties of the present device can be ascribed to the electroformation of nanoscale VO₂ nanochannel in V₂O₅ thin films. More importantly, the incorporation of the present device into a Pt/HfO₂/Pt/VO₂/Pt 1S1R unit can ensure the correct reading of the HfO₂ memory continuously for 10⁷ cycles, therefore demonstrating its great possibility as a reliable selector in high‐density crossbar memory arrays.