Influences of poly[(styrene)x-stat-(chloromethylstyrene)y]s additives on dewetting behaviors of polystyrene thin films: effects of polar group ratio and film thickness

This contribution investigates the addition of poly(styrene-stat-chloromethylstyrene (ClMS))s as dewetting inhibitors of polystyrene (PS) thin films with thicknesses ranging from 12 to 38 nm. The ClMS ratios in the copolymers are 5, 25 and 45 mol%. Atomic force microscopy and optical microscopy are utilized to follow morphological changes of blended PS/copolymer films upon annealing above their glass transition temperatures. We have found that thermal stability of the PS films is greatly improved when a small amount of the copolymers is added into the system. The polar ClMS groups provide anchoring sites with the polar SiO_x/Si substrate while the styrene segments favorably interact with the PS matrix. The effectiveness of the copolymers as dewetting inhibitors is also found to increase with mole ratio of ClMS group. While the stability of PS films is systematically improved upon addition of the highly substituted copolymers, using the copolymer with relatively low ratio of ClMS group could lead to the opposite result. This class of copolymers can be utilized for improving thermal stability of ultrathin PS films. The fundamental knowledge from this study is also important for designing or selecting structure of additives used to improve the stability of polymeric thin films.     

Optical and structural properties of SiOx films from ion-assisted deposition

This study investigates the optical and structural properties of SiO_x (x ∼ 1) films prepared by an ion-assisted deposition (IAD) process. The films were prepared by evaporating silicon monoxide, with and without simultaneous Ar⁺ bombardment. The stoichiometry of each film was determined as measured by the infrared spectrometry and X-ray photoelectron spectrometry. The variation in the stoichiometry revealed that the oxygen content of the SiO_x thin films varied slightly under the different conditions of the Ar⁺ bombardment. The results of the X-ray diffraction and transmission electron microscopy (TEM) measurements illustrated that all of the films had amorphous structures. However, a different interfacial appearance between the film and the substrate was observed from the TEM image. The optical constants of the SiO_x thin films were determined by a spectroscopic ellipsometry. The extinction coefficient of all of the films approached zero in the infrared wavelength range from 2 to 7 μm, but the refractive index was varied by the IAD process. The variation of these refractive indices is mainly related to the packing density of the films.     

Characteristics of high-k gate oxide prepared by oxidation of multi-layered Hf/Zr/Hf/Zr/Hf metal films

We investigated the physical and electrical properties of Hf-Zr mixed high-k oxide films obtained by the oxidation and annealing of multi-layered metal films (i.e., Hf/Zr/Hf/Zr/Hf, ∼ 5 nm). We demonstrated that the oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf-Zr mixed oxide film was formed on the top of silicate film due to inter-diffusion between Hf and Zr layer. This film shows the improved dielectric constant (k) and the raised crystallization temperature. Compared with HfO₂ and ZrO₂ gate dielectric, the crystallization temperature of Hf-Zr mixed oxides was raised by more than 200 °C. Using AES and XPS, we observed that Zr oxide has more fully oxidized stoichiometry than Hf oxide, irrespective of annealing temperatures. We also found that the thickness of an interfacial layer located between Hf-Zr mixed oxide and Si substrate also increases as annealing temperature increases. Especially, the thin SiO_x interfacial layer starts to form if annealing temperature increases over 700 °C, deteriorating the equivalent oxide thickness.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Interfacial layer growth of ZrO2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO₂ thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO₂/SiO₂/Si, the thickness of a SiO₂-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO₂ film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7-50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO₂/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi_xO_y overlayer and the SiO_x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.     

Effects of cetyltrimethylammonium bromide on redox deposition and rectification properties of silicon oxide thin film

Silicon oxide (SiO_x) thin film was deposited onto fluorine-doped tin oxide (FTO) and silicon wafer substrate by the reduction of an aqueous solution containing ammonium hexafluorosilicate, dimethylamine borane and cetyltrimethylammonium bromide (CTAB). Characterization of the films by X-ray photoelectron spectroscopic depth profile and infrared spectroscopy proved that the addition of CTAB into the film enhanced the aggregation of silica particles and the growth rate. The SiO_x films (resistivity: 3.2 × 10⁸ Ω cm) remarkably improved the rectification properties of FTO/SiO_x/poly(3,4-ethylenedioxythiophene) derivative diodes. A rectification mechanism based on conduction of electron and ions was investigated.     

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr_1−xSi_xN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N₂/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200 °C and post-deposition annealing up to 1000 °C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200 °C growth temperature. After the annealing treatment, films with Si content x < 0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x > 0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000 °C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100 nm thick films have an average roughness < 2 nm, except for Si content near x = 0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV-visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x > 0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x < 0.15), there is no band gap and the films are highly conductive.     

Effect of the interface on the electrical properties of an indium zinc oxide/SiOx multilayer

In this work, indium zinc oxide (IZO) films have been deposited on a polyethylene terephthalate substrate coated with an SiO_x film. Based on a comparative investigation of an IZO monolayer and an IZO/SiO_x multilayer, it is shown that oxygen has a great effect on the electrical properties of the thin films. A mechanism is described to explain the influence of the introduced SiO_x buffer layer. It is considered that an interfacial layer has come into being at the interface between the SiO_x layer and IZO layer, and the properties of this layer have been evaluated. Moreover, the electrical properties of the IZO/SiO_x multilayer have been successfully improved by controlling the oxygen content of the interfacial layer.     

Application of plasma polymerized siloxane films for the corrosion protection of titanium alloy

Organosilicon film and SiO_x-like film are deposited on titanium alloy (Ti6Al4V) surfaces by atmospheric pressure (~ 10⁵ Pa) dielectric barrier discharge to improve its corrosion resistance in Hanks solution. Hexamethyldisiloxane (HMDSO) is used to be the chemical precursor. The organosilicon film deposited in Ar/HMDSO system has high growth rate (75 nm/min) and low surface roughness (3 nm), while the SiO_x-like film deposited in Ar/O₂/HMDSO system has lower growth rate (35 nm/min) and slightly higher surface roughness (9 nm). The potentiodynamic polarization tests show that both the two siloxane films coated Ti6Al4V samples have more positive corrosion potential and one order of magnitude lower corrosion current density than the substrate, indicating the corrosion resistance of Ti6Al4V can be improved by depositing siloxane film on its surface. In particular, as the surface is more compact and cross-linked, the SiO_x-like film has better corrosion resistance than the organosilicon film.     

Deposition and characterization of ultra-high barrier coatings for flexible electronic applications

A barrier structure consisting of SiO_x and SiN_x films was deposited on the polymer substrate at 80 °C via plasma-enhanced chemical vapor deposition (PECVD). However, the low radius of curvature (R_c) of the barrier-coated substrate may cause the inconvenience of the following fabrication processes. By depositing a 150 nm-SiN_x film, the R_c of the barrier-coated polycarbonate (PC) substrate can increase from 80 to 115 mm without inducing any cracks in the barrier structure. Furthermore, the thermal stress of the barrier structure can be adjusted via extending the PECVD process duration in the chamber and replacing PC by the polyethersulone (PES) substrate. The R_c can increase to ∼356 mm by depositing the 150 nm-SiN_x film on the other side of the PES substrate. Finally, the calcium test result of the barrier films/PES/SiN_x sample was calculated to be around 3.05 × 10⁻⁶ g/m²/day, representing that the barrier structure did not fail after modification.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

Diamond nanocrystals and amorphous SiOx nanowires formed by rapid thermal annealing of carbon film

Rapid thermal annealing (RTA) has been performed on the carbon films prepared by radio frequency plasma-enhanced chemical vapor deposition on Si substrate. The RTA at 800 °C for 60 s leads to the formation of many diamond nanocrystallites agglomerating on the film surface. Higher temperature RTA at 1100 °C for 60 s induces the high-density amorphous SiO_x (x = 1.2) nanowires on the film surface without diamond nanocrystallites. At both the RTA temperatures, a well-oriented SiC interlayer is also formed simultaneously. The sp³ sites in the carbon film and the oxygen during the RTA treatment as well as the RTA temperature are considered to play important roles in determining the final reaction products.     

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiN_x) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiN_x thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiN_x films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiN_x thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiN_x thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiN_x layer during SiO₂ removal.     

Ferroelectricity of ultrathin ferroelectric Langmuir-Blodgett polymer films on conductive LaNiO3 electrodes

LaNiO₃ (LNO) films with a surface roughness rms of 0.384 nm and a sheet resistance of about 200 Ω were prepared on SrTiO₃ and Si/SiO₂ substrates respectively by rf magnetron sputtering technique. The surface of LNO on Si/SiO₂ substrate is smoother than that on SrTiO₃ substrate. A nominal 2-monolayer (ML) poly(vinylidenefluoride-trifluoroethylene) film with a thickness of about 3 nm was deposited on LNO coated Si/SiO₂ substrate by Langmuir-Blodgett (LB) technology. Piezoresponse force microscopy (PFM) measurements show that the LB films demonstrate an obvious feature of polarization switching and good voltage durability. The results suggest that the ultrathin polymer films may be utilized to explore ferroelectric tunnel junctions.     

Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

Effect of yttrium doping on the dielectric properties of CaCu3Ti4O12 thin film produced by chemical solution deposition

Pure and yttrium substituted CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0, 0.02, 0.1) thin films were prepared on boron doped silica substrate employing chemical solution deposition, spin coating and rapid thermal annealing. The phase and microstructure of the sintered films were examined using X-ray diffraction and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using electrochemical impedance spectroscopy. Highly ordered polycrystalline CCTO thin film with bimodal grain size distribution was achieved at a sintering temperature of 800 °C. Yttrium doping was found to have beneficial effects on the dielectric properties of CCTO thin film. Dielectric parameters obtained for a CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0.02) film at 1 KHz were k ∼ 2700 and tan δ ∼ 0.07.     

Plastic substrate with gas barrier layer and transparent conductive oxide thin film for flexible displays

A novel plastic substrate for flexible displays was developed. The substrate consisted of a polycarbonate (PC) base film coated with a gas barrier layer and a transparent conductive thin film. PC with ultra-low intrinsic birefringence and high temperature dimensional stability was developed for the base film. The retardation of the PC base film was less than 1 nm at a wavelength of 550 nm (film thickness, 120 µm). Even at 180 °C, the elastic modulus was 2 GPa, and thermal shrinkage was less than 0.01%. The surface roughness of the PC base film was less than 0.5 nm. A silicon oxide (SiO_x) gas barrier layer was deposited on the PC base film by a roll-to-roll DC magnetron reactive sputtering method. The water vapor transmission rate of the SiO_x film was less than 0.05 g/m²/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m² day atm at 40 °C and 90% RH. As the transparent conductive thin film, amorphous indium zinc oxide was deposited on the SiO_x by sputtering. The transmittance was 87% and the resistivity was 3.5 × 10^− 4 ohm cm.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Fabrication of a n-ZnO/p-Si heterojunction diode by ultra-high vacuum magnetron sputtering

Heterojunction diodes of n-type ZnO were fabricated on a p-type Si(100) substrate using an ultra-high vacuum radio frequency magnetron sputtering method at room temperature. A short-time post-annealing process was performed to prevent inter-diffusion of Zn, dopants, and Si atoms. The post-annealing process at 600 °C enhanced the crystallinity of ZnO films and produced a high forward to reverse current ratio of the heterojunction diode with a barrier height of approximately 0.336 eV. A thin SiO_x layer at the interface of the ZnO film and Si substrate appeared distinctly at the 600 °C annealing, however the post-annealing at 700 °C showed an a-(Zn_2xSi_1 − xO₂) structure caused by diffusion of silicon into the ZnO film. In the n-ZnO/p-Si sample annealed at 700 °C, a rapid change in the barrier height was considered due to the effect of the dopant segregation from the substrate and deformation of the a-SiO_x structure.