Annealing temperature dependence on the structural and optical properties of sputtering-grown high-k HfO2 gate dielectrics

High-k gate dielectric HfO₂ thin films have been deposited on Si and quartz substrates by radio frequency magnetron sputtering. The structural characteristics, surface morphology, and optical properties of the HfO₂/Si gate stacks at various post-annealing temperatures were examined by X-ray diffraction (XRD), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis spectroscopy), and spectroscopic ellipsometry (SE). XRD measurement indicates that the 80 W-deposited HfO₂ films demonstrate a polycrystalline structure. AFM measurements illustrate that the root mean square of the HfO₂ thin films demonstrates an apparent increase with increasing the annealing temperature. Analysis from FTIR indicates that the Si–O–Si bonds vibration peak position shift toward lower wave numbers with increasing the annealing temperature. Combined with UV–Vis spectroscopy and SE measurements, it can be noted reduction in band gap with an increase in annealing temperature has been confirmed. Additionally, increase in refractive index (n) has been confirmed by SE.     

Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films

HfO₂ thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O₂/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO₂ grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO_x suboxide layer at the HfO₂/Si interface is unavoidable. The HfO₂ thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O₂/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO₂, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO₂ to form HfO₂, leaving Si-Si bonds behind.     

Preparation and characterization of Ba2TiSi2O8 ferroelectric films produced by sol–gel method

Fresnoite (Ba₂TiSi₂O₈, BTS) thin films were grown on polished Si(100) substrates by sol–gel method. The films were characterized using Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy, X-ray diffraction (XRD) and atom force microscopy (AFM). The results reveal that the crystallinity of fresnoite thin films increases and their structures become more compact as post-annealing temperature increases. Combined with XRD data, the strong FTIR peaks and Raman bands assigned to Ti–O and Si–O vibration indicate the formation of fresnoite phase in the films at a temperature of 750 °C. Besides, the AFM observation showed the films have a smooth surface, fine grains and dense structure.     

Influence of RF power on structural optical and electrical properties of hydrogenated nano-crystalline silicon (<Emphasis Type="Italic">nc</Emphasis>-Si:H) thin films deposited by PE-CVD

We report synthesis of hydrogenated nanocrystalline silicon (nc-Si:H) thin films by using conventional plasma enhanced chemical vapor deposition (PE-CVD) system from gas mixture of pure silane (SiH₄) and hydrogen (H₂). We investigated the effect of RF power on structural, optical and electrical properties using various characterization techniques including Raman spectroscopy, FTIR spectroscopy, UV–visible spectroscopy etc. Low angle XRD and Raman spectroscopy analysis revealed that the RF power in PE-CVD is a critical process parameter to induce nanocrystallization in Si:H films. The FTIR spectroscopy analysis results indicate that with increase in RF power the predominant hydrogen bonding in films shifts from Si–H to Si–H₂ and (Si–H₂)_n bonded species bonded species. However, the bonded hydrogen content didn’t show particular trend with change in RF power. The UV–visible spectroscopy analysis shows that the band tail width (E₀₄–E_Tauc) with increase in RF power. The defect density and Urbach energy also increases with increase in RF power. The highest dark conductivity (and lowest charge carrier activation energy) was obtained for the film deposited at RF power of 125 W indicating that 125 W is optimized RF power of our PE-CVD unit. At this optimized RF power nc-Si:H films with crystallite size ~3.7 nm having good degree of crystallinity (~86.7 %) and high band gap (E_Tauc ~ 2.01 eV and E₀₄ ~ 2.58 eV) were obtained with a low hydrogen content (6.2 at.%) at moderately high deposition rate (0.24 nm/s).     

Microstructure,electrical and humidity sensing properties of TiO<Subscript>2</Subscript>/polyaniline nanocomposite films prepared by sol–gel spin coating technique

High sensitive resistive type humidity sensor based titanium oxide/polyaniline (TiO₂/PANI) nanocomposite thin films prepared by a sol–gel spin coating technique on an alumina substrate. The resultant nanocomposites were characterized by using X-ray diffraction (XRD), Field emission electron microscopy, Fourier transform infrared spectroscopy (FTIR), UV–Vis absorbance and energy dispersive spectra analysis. In the XRD patterns of both pure and TiO₂/PANI composite confirms the deposition of PANI on TiO₂ and the average size of the composite particle was found to be 32 nm. Large number of nano grain surface being covered by PANI, which agrees very well with the results obtained by XRD studies. FTIR and UV–Vis spectra reveal that the PANI component undergoes an electronic structure modification as a result of the TiO₂ and PANI interaction. The room temperature resistivity was found to be for TiO₂ and TiO₂/PANI nanocomposite films 1.42?×?10⁶ and 2.56?×?10³ Ω cm respectively. The obtained TiO₂/PANI nanocomposites sensor exhibited higher humidity sensing performance such as high sensitivity, fast response (20 s) and recovery time (15 s) and high stability.     

Growth of ZnO thin films at low temperature by plasma-enhanced atomic layer deposition using H2O and O2 plasma oxidants

Zinc oxide (ZnO) thin films were grown at 70 °C by plasma-enhanced atomic layer deposition using H₂O and O₂ plasmas. Plasma oxidants were used in order to improve the ZnO crystallinity and optoelectronic properties, avoiding high-temperature synthesis. The deposition parameters were optimized to achieve saturation in each reaction step. X-ray photoelectron spectroscopy (XPS) reveals high purity of the obtained ZnO films. X-ray diffraction (XRD) measurements indicate that the grown layers are polycrystalline and that the H₂O plasma synthesis leads to better crystallinity than the O₂ plasma as inferred from the intensity of the (100) and (002) peaks. The films are with high optical transmission, ~90%, as inferred from UV–visible (UV–Vis) transmittance measurements, and optical band gaps of 3.22 and 3.23 eV for H₂O and O₂ plasma, respectively. Atomic force microscopy (AFM) indicates that the films are smooth, with an average roughness of ~?0.22 nm. The growth rate was found to be in the range of 1.2–1.4 Å/cycle. The XPS, XRD, UV–Vis, and AFM results prove the possibility to obtain high-quality ZnO films by O₂ and H₂O plasma processes at 70 °C with chemical, structural, and optical properties promising for flexible electronics. ZnO films were successfully deposited on polyethylene terephthalate substrates using the optimal conditions for H₂O plasma process. No damage of the film surface or substrate was observed.

     

Influence of filament-to-substrate distance on the spectroscopic,structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp ² bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.     

Structural and optical properties of yttrium trioxide thin films prepared by RF magnetron sputtering

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (111) at different RF powers and the sputtering pressures by RF magnetron sputtering. The influences of the RF power and the sputtering pressures on the structural and optical properties of Y₂O₃ thin films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM) and spectroscopic ellipsometer (SE). The results show that chemical composition of as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio and it is crystallized but crystallinity is poor. The monoclinic and cubic fluorite-like structure can coexist in as-deposited Y₂O₃ film. A four-layer-structured optical model consisting of silicon substrate, silicon dioxide (SiO₂) interlayer, Y₂O₃ layer and a surface roughness (SR) layer is built for interpreting preferably the results measured by spectroscopic ellipsometry. With the increase of RF power or decrease of sputtering pressure, the refractive index and optical bandgap of sputtered Y₂O₃ film is increased and the extinction coefficients is decreased.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Structural and optical properties of yttrium trioxide thin films prepared by RF magnetron sputtering

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (111) at different RF powers and the sputtering pressures by RF magnetron sputtering. The influences of the RF power and the sputtering pressures on the structural and optical properties of Y₂O₃ thin films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM) and spectroscopic ellipsometer (SE). The results show that chemical composition of as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio and it is crystallized but crystallinity is poor. The monoclinic and cubic fluorite-like structure can coexist in as-deposited Y₂O₃ film. A four-layer-structured optical model consisting of silicon substrate, silicon dioxide (SiO₂) interlayer, Y₂O₃ layer and a surface roughness (SR) layer is built for interpreting preferably the results measured by spectroscopic ellipsometry. With the increase of RF power or decrease of sputtering pressure, the refractive index and optical bandgap of sputtered Y₂O₃ film is increased and the extinction coefficients is decreased.     

Optical properties of silicon thin films related to LPCVD growth condition

In this paper we study the changes in the microstructural and optical properties of silicon thin films produced by the variation of the parameters (temperature and pressure) of the low-pressure chemical vapour deposition (LPCVD) process. Silicon thin films prepared by LPCVD on oxidized silicon substrates over a large range of process parameters (T_dep=500-615°C, p_dep=20-100 Pa) have been characterized by Raman spectroscopy, spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. The phase transition of as-deposited silicon from an amorphous to a crystalline phase via an intermediate mixed phase (few grains in amorphous silicon matrix) can be monitored by the changes in the optical properties and in the Raman spectra. LPCVD parameters, which control the deposition kinetics, are able to influence the optical properties, the structure and/or morphology of the as-deposited LPCVD silicon films. The SE and Raman results prove that it is possible to grow by LPCVD (from pure silane), a silicon film in a (poly)crystalline state at a temperature as low as 500°C.     

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.     

Structural,morphological, optical and electrical properties of spray deposited zinc doped copper oxide thin films

Nanostructured spray deposited zinc (Zn) doped copper oxide (CuO) thin films were characterized by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy. XRD patterns of CuO and Zn doped CuO thin films indicated monoclinic structure with the preferred orientation along \(\left( {\bar 111} \right)\) plane. Maximum value of crystallite size is found about 28.24 nm for 5 at% Zn doped CuO thin film. In FESEM images, nanoparticles were observed around the nucleation center. EDX analysis confirms the presence of all component elements in CuO and Zn doped CuO thin films. Analysis by AFM of CuO and Zn doped CuO thin films figured out decrease of surface roughness due to Zn doping. UV–Vis–NIR spectroscopy showed that CuO and Zn doped CuO thin films are highly transparent in the NIR region. Optical band gap of CuO thin films decreased with substrate temperature and that of Zn doped CuO thin films increased with Zn concentration. Refractive index of CuO and Zn doped CuO thin films raised with photon wavelength and became constant in the NIR region. 5 at% Zn doped CuO thin film showed the highest optical conductivity and the lowest electrical resistivity at room temperature.     

Photocatalytic properties of Au/TiO2 thin films prepared by RF magnetron co-sputtering

Au/TiO₂ thin films with various Au doping contents were deposited on quartz substrates by radio frequency (RF) magnetron co-sputtering. The as-deposited Au/TiO₂ films were characterized by energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), XRD, and UV-vis techniques. Au doping and UV treatment enhanced the photocatalytic efficiency of TiO₂ thin films. The optimal RF power of the Au target and UV treatment time were 5 W and 1 h, respectively. The enhanced photoactivity of Au(5 W)/TiO₂ thin films with UV treatment is found to result from the increased hydroxyl concentration.     

Atomic layer deposition of TiO2 thin films on glass fibers for enhanced photocatalytic activity

Photocatalytic wastewater treatment is expected to become a sustainable way of eliminating toxic chemicals. Due to the surface-driven mechanism of the photocatalysis, surface area of the catalyst material plays a crucial role in the efficiency of the process, which is usually achieved by nanoparticles. However, using powder materials introduces a new problem: removing the catalyst materials out of clean water. As an alternative, atomic layer deposition (ALD) can form conformal thin films on high surface area substrates providing an immobilization route with high photocatalytic activity. Textile materials are inexpensive and accessible therefore good candidates for the substrate materials. Here, we deposit thin films on TiO₂ on fiberglass fabrics and investigate the photocatalytic activity. Since the as-deposited ALD TiO₂ films are amorphous, they have very limited photocatalytic activity. Upon thermal treatment of the films after deposition, photocatalytic activity is achieved. After four hours of exposure to the solar simulator and UV lamp, TiO₂-coated fibers demonstrated much higher photocatalytic activity than films on planar substrates previously described in the literature. The photocatalytic activity and structure of the coated fibers were investigated using XRD, XPS, UV–Vis, and PL analyses.

     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Low temperature preparation of transparent, antireflective TiO2 films deposited at different O2/Ar ratios by microwave electron cyclotron resonance magnetron sputtering

A serial of crystalline titanium oxide ceramic films were deposited at low temperature using microwave electron cyclotron resonance (MW-ECR) magnetron sputtering with different O₂/Ar ratios. The influences of O₂/Ar ratio on the deposition rate, morphology, crystalline nature, optical adsorption property of the obtained titanium oxide thin films were investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-Vis spectra. Therefore, the optimum O₂/Ar ratio for deposition of anatase TiO₂ thin films on unheated glass substrate was realized in a MW-ECR magnetron sputtering process. The as-deposited anatase TiO₂ films were transparent and were antireflective in the visible region.     

Preparation of rare earth CeO<Subscript>2</Subscript> thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO₂ thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO₂ films with atomic percentage of 19.39 and 54.82% of Ce and O₂, respectively. Thickness of 60.11 nm of CeO₂ film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400?°C annealed CeO₂ films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO₂/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Q_eff), interface trap density (D_it) and dielectric constant (k) and are 2.48?×?10¹² cm^?2, 1.26?×?10¹² eV^?1cm^?2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.     

Spectroscopic ellipsometry and positron annihilation investigation of sputtered HfO2 films

Hafnium oxide (HfO₂) films were prepared using a pulsed sputtering method and different O₂/(O₂ + Ar) ratios, deposition pressures, and sputtering powers. Spectroscopic ellipsometry (SE) and positron annihilation spectroscopy (PAS) were used to investigate the influence of the deposition parameters on the number of open volume defects (OVDs) in the HfO₂ films. The results reveal that a low O₂/(O₂ + Ar) ratio is critical for obtaining films with a dense structure and low OVDs. The film density increased and OVDs decreased when the deposition pressure was increased. The film deposited at high sputtering power showed a denser structure and lower OVDs. Our results suggest that SE and PAS are effective techniques for studying the optical properties of and defects in HfO₂ and provide an insight into the fabrication of high-quality HfO₂ thin films for optical applications.     

The influence of thermal processing on microstructure of sol–gel-derived SrSnO<Subscript>3</Subscript> thin films

Polycrystalline SrSnO₃ thin films were fabricated using the aqueous sol–gel process and deposited on the single crystal sapphire (R-Al₂O₃ and C-Al₂O₃) and Si substrates by spin coating technique. Two different processing of thermal treatment was explored to produce SrSnO₃ thin films of different porosity. The XRD analysis showed that polycrystalline films with preferential growth of SrSnO₃ (200) plane were obtained on C-Al₂O₃ substrates, while films deposited on R-Al₂O₃ demonstrated a random polycrystalline growth. FE-SEM analysis revealed that the higher porosity of SrSnO₃ films can be achieved by introducing additional thermal treatment step during the deposition procedure. The UV–Vis reflectance spectroscopy was used to study the effect of porosity on optical properties of the films.