Effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films

The effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films were investigated using spectroscopic ellipsometry in the UV-visible range, reflectance-transmittance spectra at normal incidence in the infrared range, electrical resistivity measurements, and X-ray diffraction. It was found that annealing at 300 °C produces an overall shift to lower photon energies of the optical constant spectra, which is related to the increase in electrical resistivity. The electrical measurements performed in the 25-300 K range show a metallic behavior with large residual resistivity, quantity that increases with annealing temperature and is closely related with the change in the relative intensity of the main diffraction peaks. Also it is shown that under certain conditions of film deposition onto indium-tin oxide, some of its properties can change in a similar way as in air-annealing processing.     

First-principles calculations-based model for the reactive ion etching of metal oxide surfaces

A model for the RIE process design of metal oxide surfaces based on density functional theory-based total energy calculations has been developed. Cluster and periodic systems were employed in order to develop the model and hence gain a deeper understanding of the process mechanisms on an atomic scale. In the present study, Fe₃O₄ was used for the cluster system, and NiO for the periodic system as metal oxide surfaces. Possible gas combinations and by-products were studied with the aim of producing a more efficient and effective RIE process for metal oxide thin films. This study can be considered as fundamental groundwork required for the understanding of the reactivity in the etching of metal oxide surfaces and a means of decreasing the processing period of RIE for metal oxide thin films by optimum selection of gas combinations with a knowledge of their probable by-products.     

fabrication of diamond membranes for MEMS using reactive ion etching of silicon

Polycrystalline diamond thin film has been grown on a silicon substrate using high pressure microwave plasma-assisted chemical vapor deposition from a gas mixture of methane and hydrogen at a substrate temperature of 950°C. A simple process flow has been developed to fabricate optically transparent polycrystalline synthetic diamond membranes/windows employing reactive ion etching (RIE) of a single crystal silicon substrate using an electron beam evaporated aluminum thin film mask pattern formed by photolithography. Scanning electron microscopy has been used to study the morphology of as-grown diamond thin films.     

反应离子刻蚀工艺仿真模型的研究

以ＳＦ６／Ｎ２混合气体对Ｓｉ反应离子刻蚀工艺研究为例提出干法刻蚀计算机工艺模拟的方法：在分段拟合优化工艺条件下采用人工神经网络该当建立干法刻蚀仿真模型,可以预测绘定射频功率、总气流量下刻蚀速率和纵横比,并且以仿真实验数据训练模型学习,模型具有通用性,与设备无关。     

Periodic arrays of deep nanopores made in silicon with reactive ion etching and deep UV lithography

We report on the fabrication of periodic arrays of deep nanopores with high aspect ratios in crystalline silicon. The radii and pitches of the pores were defined in a chromium mask by means of deep UV scan and step technology. The pores were etched with a reactive ion etching process with SF(6), optimized for the formation of deep nanopores. We have realized structures with pitches between 440 and 750?nm, pore diameters between 310 and 515?nm, and depth to diameter aspect ratios up to 16. To the best of our knowledge, this is the highest aspect ratio ever reported for arrays of nanopores in silicon made with a reactive ion etching process. Our experimental results show that the etching rate of the nanopores is aspect-ratio-dependent, and is mostly influenced by the angular distribution of the etching ions. Furthermore we show both experimentally and theoretically that, for sub-micrometer structures, reducing the sidewall erosion is the best way to maximize the aspect ratio of the pores. Our structures have potential applications in chemical sensors, in the control of liquid wetting of surfaces, and as capacitors in high-frequency electronics. We demonstrate by means of optical reflectivity that our high-quality structures are very well suited as photonic crystals. Since the process studied is compatible with existing CMOS semiconductor fabrication, it allows for the incorporation of the etched arrays in silicon chips.     

Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

The etching characteristics of a LiNbO₃ single crystal have been investigated using plasma reactive ion etching (RIE) with a mixture of CF₄/Ar/H₂. The etching rate of LiNbO₃ with the mixture of CF₄/Ar/H₂ gases was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy methods. The rate-determining process of RIE is the supply of F radicals in RIE. The surface morphology of the etched LiNbO₃ changed with the increase in the H₂ gas flow ratio. The surface profile became flat, on optimizing the etching conditions, similar to the surface of non-etched LiNbO₃. The X-ray diffraction peakfor etched LiNbO₃ using the mixture of CF₄ and Ar gases did not appear, because a non-crystalline layer was formed. It was found that the crystallinity of the surface is dependent on both, the flow rate of H₂ gas and the etching time. F atoms exist in the contamination layer of the sample etched, using the mixture of CF₄, Ar and H₂ gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, were determined.     

Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

The etching characteristics of a LiNbO₃ single crystal have been investigated using plasma reactive ion etching (RIE) with a mixture of CF₄/Ar/H₂. The etching rate of LiNbO₃ with the mixture of CF₄/Ar/H₂ gases was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy methods. The rate-determining process of RIE is the supply of F radicals in RIE. The surface morphology of the etched LiNbO₃ changed with the increase in the H₂ gas flow ratio. The surface profile became flat, on optimizing the etching conditions, similar to the surface of non-etched LiNbO₃. The X-ray diffraction peak for etched LiNbO₃ using the mixture of CF₄ and Ar gases did not appear, because a non-crystalline layer was formed. It was found that the crystallinity of the surface is dependent on both, the flow rate of H₂ gas and the etching time. F atoms exist in the contamination layer of the sample etched, using the mixture of CF₄, Ar and H₂ gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, were determined.     

Modification of AZO thin-film properties by annealing and ion etching

Effects of annealing and ion etching on the structural, electrical and optical properties of sputtered ZnO:Al (AZO) thin films were investigated. The post-deposition annealing at temperatures T_A = 200-400 °C in the forming gas (80% N₂/20% H₂) for 1 h and ion RF-sputter etching after annealing were used. Ion-sputter etching rate was 7 nm/min. The surface topography changed noticeably after ion-sputter etching: the surface of the sample was rougher (R_a = 33 nm) in comparison with annealed sample only (R_a = 9 nm). After the post-deposition annealing temperature T_A = 400 °C and ion-sputter etching thin films have higher integral transmittance (in the range of λ = 400-1000 nm) than non-etched samples. The figure of merit (F) became higher with increase of annealing temperature and the maximum value was F = 8%/Ω at T_A = 400 °C (R_s = 10 Ω, T_int = 86%).     

Effect of annealing temperature on the crystal phase fraction in silicon nanoclusters in a silicon oxide matrix

A model of the annealing-induced crystallization of amorphous clusters in a solid matrix is proposed. The calculated dependence of the crystallized phase fraction on the annealing temperature agrees with the available experimental data.     

Effect of argon plasma etching damage on electrical characteristics of gallium nitride

Effect of Ar plasma etching damage on electrical characteristics of n-GaN is significantly dependent on gas pressure. At a low gas pressure (5 mTorr), physical etching effect contributes to degradation of a reverse leakage current through a Au/n-GaN Schottky contact. At a high gas pressure (50 or 100 mTorr), UV radiation effect from the Ar plasma (ArII whose energy corresponds to GaN band-gap energy) seems to contribute to the degradation.     

Improved electrical and reliability characteristics in metal/oxide/nitride/oxide/silicon capacitors with blocking oxide layers formed under the radical oxidation process

We propose a Metal-Oxide-Nitride-Oxide-Silicon (MONOS) structure whose blocking oxide is formed by radical oxidation on the silicon nitride (Si3N4) layer to improve the electrical and reliability characteristics. We directly compare the electrical and reliability properties of the MONOS capacitors with two different blocking oxide (SiO2) layers, which are called a "radical oxide" grown by the radical oxidation and a "CVD oxide" deposited by chemical vapor deposition (CVD) respectively. The MONOS capacitor with a radical oxide shows a larger C-V memory window of 3.6 V at sweep voltages from 9 V to -9 V, faster program/erase speeds of 1 micros/1 ms at bias voltages of -6 V and 8 V, a lower leakage current of 7 pA and a longer data retention, compared to those of the MONOS capacitor with a CVD oxide. These improvements have been attributed to both high densification of blocking oxide film and increased nitride-related memory traps at the interface between the blocking oxide and Si3N4 layer by radical oxidation.     

Etch characteristics of FePt magnetic thin films using inductively coupled plasma reactive ion etching

Etch characteristics of L10 FePt thin films masked with TiN films were investigated using an inductively coupled plasma (ICP) reactive ion etching in a CH₃OH/Ar plasma. As the CH₃OH gas was added to Ar, the etch rates of FePt thin films and TiN hard mask gradually decreased, and the etch profile of FePt films improved with high degree of anisotropy. With increasing ICP rf power and dc-bias voltage to substrate and decreasing gas pressure, the etch rate increased and the etch profile becomes vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of FePt thin films in a CH₃OH/Ar gas does not follow the reactive ion etch mechanism but the chemically assisted sputter etching mechanism, due to the chemical reaction of FePt film with CH₃OH gas.     

Direct comparison of the electrical properties in metal/oxide/nitride/oxide/silicon and metal/aluminum oxide/nitride/oxide/silicon capacitors with equivalent oxide thicknesses

We examine the electrical properties of metal/oxide/nitride/oxide/silicon (MONOS) capacitors with two different blocking oxides, SiO₂ and Al₂O₃, under the influence of the same electric field. The thickness of the Al₂O₃ layer is set to 150 Å, which is electrically equivalent to a thickness of the SiO₂ layer of 65 Å, in the MONOS structure for this purpose. The capacitor with the Al₂O₃ blocking layer shows a larger capacitance-voltage memory window of 8.6 V, lower program voltage of 7 V, faster program/erase speeds of 10 ms/1 μs, lower leakage current of 100 pA and longer data retention than the one with the SiO₂ blocking layer does. These improvements are attributed to the suppression of the carrier transport to the gate electrode afforded by the use of an Al₂O₃ blocking layer physically thicker than the SiO₂ one, as well as the effective charge-trapping by Al₂O₃ at the deep energy levels in the nitride layer.     

Photovoltaic junctions between indium tin oxide and silicon

Photovoltaic junctions solar cells were made between indium tin oxide (ITO) and polycrystalline p-Si (poly-Si), or between ITO and single-crystal p-Si. A model based on the assumption that the grain boundaries in poly-Si introduce ionized energy states equivalent to an effective doping density is considered. The cell performance was calculated from current-voltage characteristics and capacitance-voltage measurements at various frequencies. From transient photovoltage decay measurements, an effective lifetime τ_eff of (300–400) × 10⁻⁹ s was found in the poly-Si/ITO junction, whereas in the single-crystal-Si/ITO junction τ_eff was 5 μs. The shorter lifetime of the injected carriers is one of the reasons for the lower conversion efficiency of these cells.Prior to ITO deposition, iodine ions were introduced to neutralize the trap states at the surface of the single-crystal silicon and to neutralize the traps at both the surface and grain boundaries of the poly-Si. An increase in the open-circuit voltage factor was observed.     

Scaling down lateral dimensions of silicon nanopillars fabricated by reactive ion etching with Au/Cr self-assembled clusters as an etch mask

Nanodot and nanopillar structures and precisely controlled reproducible fabrication thereof are of great interest in common nanoelectronic devices, including photonic crystals and surface plasmon resonance instruments. In this work, fabrication process of the silicon nanopillar structures is described. It includes self-organization of gold and chromium clusters at thickness close to that of one atomic diameter to serve as etching masks followed by the reactive ion etching to form silicon nanopillars. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize self-organized gold and chromium clusters as well as the final silicon nanopillars. This method was found to produce silicon nanopillars of sub-10 nm lateral dimensions and the diameter-to-height aspect ratio of up to 1:14.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

Effect of plasma treatment on the microstructure and electrical properties of MIM capacitors with PECVD silicon oxide and silicon nitride

Metal–insulator–metal (MIM) capacitors with plasma enhanced chemical vapor deposited (PECVD) nitride exhibit trap-induced dispersive behavior and electrical hysteresis, which lead to degradation in capacitor linearity at low frequencies. The dominant defect was suggested to be silicon dangling bonds originated from nitrogen deficiency. Previous methods to eliminate the dispersive behavior and electrical hysteresis include use of oxide–nitride–oxide (ONO) stacks and/or plasma pre-treatment of silicon substrate before nitride deposition [Van Huylenbroeck S, Decoutere S, Venegas R, Jenei S, Winderickx G (2002) IEEE Electron Device Lett 23:191; Lau WS (1990) Jpn J Appl Phys 29:L690]. In this study, the plasma post-treatment method was employed; MIM capacitors with PECVD oxide and nitride were treated with N₂O and SiH₄/NH₃ plasma, respectively, after deposition of the dielectric layer. No apparent change in film microstructure is observed after plasma treatment. Plasma post-treatment is effective in eliminating the electrical hysteresis shift of the nitride capacitors. Fourier transform infrared (FTIR) absorption spectra suggest an increase of the Si–H bond after SiH₄/NH₃ plasma bombardment of the nitride films. Auger depth profiling indicates a slight increase of nitrogen to silicon ratio after plasma treatment. The increase of the Si–H bonds as well as the raise of nitrogen to silicon ratio are two possible causes for the elimination of the hysteresis shift of the plasma-treated nitride capacitors. The time dependent dielectric breakdown testing indicates a decrease in both the leakage current and the lifetime of the MIM capacitors treated with plasma. Possible dielectric degradation mechanism is explored.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

Submicron-patterning of bulk titanium by nanoimprint lithography and reactive ion etching

Nanopatterns on titanium may enhance endosseous implant biofunctionality. To enable biological studies to prove this hypothesis, we developed a scalable method of fabricating nanogrooved titanium substrates. We defined nanogrooves by nanoimprint lithography (NIL) and a subsequent pattern transfer to the surface of ASTM grade 2 bulk titanium applying a soft-mask for chlorine-based reactive ion etching (RIE). With respect to direct write lithographic techniques the method introduced here is fast and capable of delivering uniformly patterned areas of at least 4 cm(2). A dedicated silicon nanostamp process has been designed to generate the required thickness of the soft-mask for the NIL-RIE pattern transfer. Stamps with pitch sizes from 1000 nm down to 300 nm were fabricated using laser interference lithography (LIL) and deep cryogenic silicon RIE. Although silicon nanomachining was proven to produce smaller pitch sizes of 200 nm and 150 nm respectively, successful pattern transfer to titanium was only possible down to a pitch of 300 nm. Hence, the smallest nanogrooves have a width of 140 nm. An x-ray photoelectron spectroscopy study showed that only very few contaminations arise from the fabrication process and a cytotoxicity assay on the nanopatterned surfaces confirmed that the obtained nanogrooved titanium specimens are suitable for in vivo studies in implantology research.     

Effects of annealing on optical and electrical characteristics of p-type semiconductor copper (II) oxide electrodeposits

The 1.35-eV-bandgap energy-CuO film with the optical absorption coefficient of 2.2 × 10⁴ cm^− 1 has been prepared on a conductive glass substrate by anodic electrodeposition in an aqueous solution containing copper (II) nitrate and ammonium nitrate at 298 K followed by annealing at 573 K and above in air. The as-deposited CuO film with a monoclinic lattice showed p-type conduction with resistivity of 2.2 × 10⁵ Ω cm and slightly expanded bandgap energy of 1.46 eV with the absorption coefficient of 1.3 × 10⁴ cm^− 1. The annealing induced changes in the grain morphology, bandgap energy, absorption coefficient, and resistivity, and the resistivity of 3.3 Ω cm could be obtained by annealing at 773 K.