Wet etching mechanisms of ITO films in oxalic acid

This study examines how oxalic acid solutions affect indium tin oxide (ITO) etching. Experimental results show that the etching rate of ITO films increased linearly with the concentration of . The open circuit potentials included in the potential-pH diagrams for indium and tin in aqueous oxalic acid systems helped determine that ITO films was dissolved by the formation of in oxalic acid. However, the tin oxide in ITO films was difficult to dissolve, but could be removed by stripping. The EDS analysis and optical microscopic images indicate that the removal rate of SnO₂ in oxalic acid etchants was slower than that of In₂O₃, and many residues were distributed around the ITO bars after the etching process. Moreover, kinetic experiments reveal the high activation energy of ITO etching, and it was found stirring or ultrasonic vibration of the etchants had no influence on the dissolution rate of ITO films at all. Therefore, the rate-determining step should be the chemical reaction on ITO surface. A mechanism including protonation and ligand adsorption was proposed to explain the observed results.     

Iron nitride mask and reactive ion etching of GaN films

One of the major GaN processing challenges is useful pattern transfer. Serious photoresist mask erosion and hardening are often observed in reactive ion etching of GaN. Fine pattern transfer to GaN films using photoresist masks and complete removal of remaining photoresist after etching are very difficult. By replacing the etch mask from conventional photoresist to a sputtered iron nitride (Fe-8% N) film, which is easily patterned by wet chemical etching and is very resistive to Cl based plasmas, GaN films can be finely patterned with vertical etched sidewalls. Successful pattern transfer is realized by reactive ion etching using Cl (H) containing plasmas. CHF₃/Ar, C₂ClF₅/Ar, C₂ClF₅/Ar/O₂, SiCl₄, and CHCl₃ plasmas were used to etch GaN. The GaN etch rate is dependent on the crystalline quality of GaN. Higher crystalline quality GaN films exhibit slower etch rates than GaN films with higher dislocation and stacking fault density.     

Etch damage evaluation on (Bi4−xLax)Ti3O12 thin films during the etch process using inductively coupled plasma sources

The etching mechanism of (Bi_4−xLa_x)Ti₃O₁₂ (BLT) thin films in Ar/Cl₂ inductively coupled plasma (ICP) and plasma-induced damages at the etched surfaces were investigated as a function of gas-mixing ratios. The maximum etch rate of BLT thin films was 50.8 nm/min of 80% Ar/20% Cl₂. From various experimental data, amorphous phases on the etched surface existed on both chemically and physically etched films, but the amorphous phase was thicker after the 80% Ar/20% Cl₂ process. Moreover, crystalline “breaking” appeared during the etching in Cl₂-containing plasma. Also the remnant polarization and fatigue resistances decreased more for the 80% Ar/20% Cl₂ etch than for pure Ar plasma etch.     

Using the photolysis of chemically modified gel films preparing ITO fine patterned thin films

A novel technique for the fabrication of tin-doped indium oxide (ITO) fine patterning in sol-gel technology is presented in this paper. The fabricated ITO fine patterning could be obtained through a process which combines film fabrication with film etching. ITO films have good comprehensive property of visible transmittance and electrical conductivity, consequently they have been extensively used as coating electrodes. Indium nitrate (In(NO/sub 3/)/sub 3/.4.5H/sub 2/O) and stannic chloride ( SnCl/sub 4/.5H/sub 2/O) were used as starting materials which were modified with benzytone (BzAcH). The chelate complexes containing indium ions were produced during the process which of forming photosensitive ITO/BzAcH gel films through sol-gel technique. It was found that the gel films are sensitive to both the ultraviolet (UV) light irradiation and their solubility on solvents as well. For example, ethanol was reduced remarkably while the UV absorption peak disappeared with the dissociation of the chelate complexes correspondingly by means of UV-vis and IR spectrophotometers. Utilizing these characteristics, a fine pattern was obtained by irradiation of UV light on the ITO/BzAcH gel films through a pattern mask. of the fine patterned ITO films were heat treated at 500/spl deg/C for 15 min, the optical, electrical properties and the surface element components were examined by X-ray photoelectron spectroscopy (XPS) spectra in this work.     

Flexible organic light-emitting diodes on a polyestersulfone (PES) substrate using Al-doped ZnO anode grown by dual-plasma-enhanced metalorganic deposition system

This study proposes flexible organic light-emitting diodes (OLEDs) grown on polyestersulfone (PES) using Al-doped zinc oxide (AZO) as the anode, fabricated by the dual-plasma-enhanced chemical vapor deposition (DPEMOCVD) system. The experimental results including crystalline structure, optical, and electrical characteristics indicate that the quality of AZO films grown on PES depends on the deposition temperature and Al content. The optimal deposition temperature and Al content for AZO film are 185  C and 2.88 at%, respectively. Further increasing or decreasing the deposition temperature and Al content degrades the quality of AZO films. The optimal AZO film deposited on the PES substrate was used as the anode for flexible OLED. It shows a similar performance compared to OLEDs using commercial indium–tin-oxide (ITO) as the anode on glass, and represents enhanced characteristics to that of the commercial ITO anode on a flexible polyethylene naphthalate (PEN) substrate. This indicates that the DPEMOCVD-deposited AZO film on the PES substrate can be the anode for flexible OLEDs.     

Luminescent chemically-etched porous poly-crystalline silicon on insulating substrates

Polycrystalline silicon deposited on insulating substrates has been chemically-etched to form thin films of porous material exhibiting room temperature visible photoluminescence with emission wavelengths of around 650 nm. Material of 4000 ? thickness was quickly converted to porous silicon within 15 s of etching, with an etch rate of 1–1.5 μm/h. In contrast to anodization, chemical-etching parameters have little effect on modulating the resultant peak wavelength. Peak photoluminescence intensity was achieved 8–12 s of etching in 1:3:5 parts HF:HNO₃:H₂O at room temperature with ambient lighting. The chemical etching process and its etch characteristics have been discussed in relation to its suitability for large area thin film devices.     

Effect of NaOH solution on surface textured ZnO: Al films prepared by pulsed direct current magnetron sputtering

Transparent conducting Al-doped ZnO (ZnO:Al, AZO) thin films were prepared at substrate temperature of 270 °C by pulsed direct current magnetron sputtering. NaOH solution (5 wt%) was employed to etch the AZO films at room temperature, and the surface textured AZO films were obtained successfully. The relationship between the surface textured structures and the etching process controlled by etching time was discussed. The textured morphology of the etched AZO films became clear as increasing the etching time, and the AZO film etched for 30 min exhibited uniformly and distinctly crater-like surface textured structure. Correspondingly, the haze and the resistivity increased with the increasing etching time. And the resistivity of the AZO film etched for 30 min was 3.2×10⁻³ Ω cm.     

An a-Si:H vacuum-compatible photoresist process for fabricating device structures in HgCdTe

A process for transferring patterns into HgCdTe epilayers using a hydrogenated amorphous silicon (a-Si:H) photomask has been demonstrated. a-Si:H films were grown using plasma enhanced chemical vapor deposition (PECVD). A latent image of a projected mask pattern was created at the a-Si:H surface by ultraviolet enhanced oxidation in the load lock of the PECVD vacuum chamber. This image was transformed into a mask by hydrogen plasma removal of the unexposed areas. A hydrogen plasma etch selectivity value greater than 500:1 for oxide and a-Si:H allows patterns as thick as 700 nm to be generated. a-Si:H masks were used to create arrays of mesas in planar HgCdTe epilayers by etching in an electron cyclotron resonance (ECR) plasma reactor. Etch selectivity between a-Si:H and HgCdTe during an ECR hydrogen plasma etch was measured to be greater than 18:1. R_oA values > 10³ were obtained for mid-wavelength infrared diodes made from HgCdTe heterojunctions using a-Si:H masks.     

The dry etching of TEOS oxide for poly-Si cantilevers in supercritical CO2

Dry etching of p-tetraethylorthosilicate (TEOS) with HF/H₂O in supercritical carbon dioxide (scCO₂) was studied. The etch rate of TEOS increased with HF concentration and reaction temperature, while the concentration of H₂O and processing pressure were found to have little effect on the etch rate. Finally, poly-Si cantilevers with high aspect ratios (1:150) were released using this technique without stiction and residue on the surface.     

Excimer laser patterning of high-Tcsuperconducting thin films of YBCO

The patterning by excimer laser ablative etching of thin superconducting films of YBCO on MgO and fused silica substrates which were fabricated by laser sputtering is discussed. The etch rate as a function of laser fluence, wavelength, and number of pulses has been investigated. Although etched film surfaces were found to be considerably smoother than annealed films, the laser etching itself was found not to be a totally thermal process     

Reactive ion etching of gallium nitride films

Reactive ion etching (RIE) was performed on gallium nitride (GaN) films grown by electron cyclotron resonance (ECR) plasma assisted molecular beam epitaxy (MBE). Etching was carried out using trifluoromethane (CHF₃) and chloropentafluoroethane (C₂ClF₅) plasmas with Ar gas. A conventional rf plasma discharge RIE system without ECR or Ar ion gun was used. The effects of chamber pressure, plasma power, and gas flow rate on the etch rates were investigated. The etch rate increased linearly with the ratio of plasma power to chamber pressure. The etching rate varied between 60 and 500Å/min, with plasma power of 100 to 500W, chamber pressure of 60 to 300 mTorr, and gas flow rate of 20 to 50 seem. Single crystalline GaN films on sapphire showed a slightly lower etch rate than domain-structured GaN films on GaAs. The surface morphology quality after etching was examined by atomic force microscopy and scanning electron microscopy.     

CHF3-O2 reactive ion etching of 4H-SiC and the role of oxygen

Reactive ion etching of 4H-SiC was performed using a CHF₃-O₂ plasma. The etch rate and mean surface roughness were investigated as a function of the ratio of the O₂ flow rate to the total gas flow rate. It was found that oxygen plays an indirect role in contributing to the etching of SiC. An optimum O₂ fraction of 20% was found to give a maximum etch rate of 35 nm/min. On the other hand, the root-mean-square (RMS) surface roughness was found to increase from 1.31 to 2.34 nm when the O₂ fraction increased from 0% to 80%. Auger electron spectroscopy results for the samples etched at the optimum condition of 20% O₂ fraction revealed the presence of oxygen on the etched surface in a form of an oxide-like layer (SiO_x). No carbon residue (carbon rich-layer) and aluminum were found. Based on our results, the role of O₂ in the reactive ion etching of 4H-SiC will be presented.     

Selective silicon epitaxy by photo-chemical vapor deposition at a very low temperature of 160°C

We have grown epitaxial Si films by the photo-chemical vapor deposition (photo-CVD) technique with SiH₄ and H₂ at a very low-temperature of 160°C. Epitaxial films were grown on silicon substrates, while amorphous-like films were deposited on glass substrates. Furthermore, it was found from the atomic hydrogen etching which was produced by photo-dissociation of hydrogen that the etching rate of amorphous silicon was much higher than that of crystal silicon. By using these selectively, we have demonstrated selective epitaxial growth of silicon by the photo-CVD technique followed by the atomic hydrogen photo-etching. Furthermore, heavily phosphorus-doped silicon films (>1 × 10²¹ cm¹⁻³) were also selectively grown by this novel technique.     

绒面AZO最新研究进展及应用

掺铝氧化锌(AZO)透明导电膜作为一种光电性能优异的透明导电膜(TCO)受到研究人员的广泛关注,并被认为是当前大规模使用的传统铟锡氧化物(ITO)的替换材料。绒面AZO薄膜因其电阻率低、高透过率且具有良好的陷光效果,可以提高太阳能电池的光电转换效率,而被认为是太阳能电池前电极的理想材料。综述了绒面AZO透明导电膜的制备方法和性能研究现状,并针对AZO的国内外研究状况提出了今后的发展趋势和研究方向。     

Electrophotographic patterning of thin-film silicon on glass foil

We report the patterning of thin films of amorphous silicon (a-Si:H) using electrophotographically applied toner as the etch mask. Using a conventional xerographic copier, a toner pattern was applied to 0.1 μm thick a-Si:H films deposited on ~50 μm thick glass foil. The toner then served as the etch mask for a-Si:H, and as the lift-off material for the patterning of chromium. This technique opens the prospect of roll-to-roll, high-throughput patterning of large-area thin-film circuits on glass substrates     

Selective chemical etching of polycrystalline SiGe alloys with respect to Si and SiO2

Polycrystalline SiGe etches that are selective to silicon dioxide as well as silicon are needed for flexibility in device fabrication. A solution of NH₄OH, H₂O₂, and H₂O has been found to selectivity etch polycrystalline silicon-germanium alloys over both silicon and silicon dioxide. Optimum composition of the solution was determined by maximizing etch rates for SiGe films with several germanium compositions. The dependence of etch rates on germanium content, etching temperature, and doping concentration are reported. The etch rate and selectivity are approximately exponentially proportional to the germanium content. Etching was found to be insensitive to deposition method, doping method, and annealing conditions of the SiGe films. In addition, etching leaves a smooth silicon substrate surface after removal of SiGe films.     

Plasma deposition of aluminum oxide films

A plasma deposition technique for amorphous aluminum oxide films is discussed. A 450 kHz or 13.56 MHz power supply was used to generate the plasma and the deposition of the film was achieved at low plasma power using trimethyl-aluminum and carbon dioxide reactant sources. It has been found that for the low frequency plasma the growth is strongly dependent upon TMA concentration, indicating that the growth process is mass transport limited. On the other hand using the 13.56 MHz discharge results in a surface controlled growth rate. An increase in the deposition temperature up to 300° C makes the films more dense and lowers their etching rate. FTIR and ESCA measurements showed that oxidation is only completed with high CO₂ concentrations and a deposition temperature above 250° C. The dielectric films were found to have a dielectric constant in the range 7.3=2-9 and a refractive index between 1.5–1.8 depending upon deposition conditions.     

Pulsed-magnetron-sputtered low-temperature indium tin oxide films for flat-panel display applications

In this paper, indium tin oxide (ITO) thin films were prepared by unipolar and bipolar direct current (DC)-pulsed magnetron sputtering in a mixture of argon and oxygen onto unheated glass substrates. The target of ITO with 10 wt.% tin is used. The influences of polar modes (unipolar and bipolar); output frequencies (0 to 33 kHz); and times and off times on the optical, electrical, and structural properties of ITO films are investigated. The correlations between the deposition parameters and the film properties are discussed. It is found that the resistivity with 10⁻³ Θ-cm and transmittance with ≥90% of amorphous ITO films can be prepared by the reactive bipolar DC-pulsed sputtering with t _on ⁻ between 45 μs and 85 μs (i.e., t _on ⁻ /t _on ⁺ is 9–17), and t _on ⁺ , t _off ⁻ and t _off ⁺ are constant at 5 μs, 10 μs, and 5 μs, respectively. An optimal condition, based on the polar mode and frequency of reactive-pulsed sputtering, for obtaining the high transmittance and low resistivity of ITO films is suggested.     

Role of N2 during chemical dry etching of silicon oxide layers using NF3/N2/Ar remote plasmas

In this work, the role of N₂ gas during the chemical dry etching of silicon oxide layers in NF₃/N₂/Ar remote plasmas was investigated by analyzing the species in the plasma, the reaction by-products in the exhaust, and the chemical properties of the etched surface. Increasing the N₂ gas flow rate resulted in an initial increase in the oxide etch rate up to a maximum value, followed by a subsequent decrease. The increased etch rate of the silicon oxide layers was not ascribed to the increased surface arrival rate of fluorine, but to the enhanced oxygen removal from the silicon oxide caused by the formation of NO₂ molecules. Presumably, the NO radicals formed from the added N₂ gas react chemically with the oxygen in the oxide, leading to the breaking of the Si-O bonds and the effective removal of oxygen, which in turn enhances the formation of SiF₄ resulting in an increased etch rate.     

低真空下射频磁控溅射法制备ITO薄膜

在低真空(2.3×10-3 Pa)下采用射频磁控溅射法制备了ITO薄膜.溅射温度200 ℃,溅射气氛为氩气和氧气的混合气,溅射靶材为90 %氧化铟、10 %氧化锡的陶瓷靶.用场发射扫描电子显微镜和X衍射仪研究了薄膜的显微结构, 用X射线光电子能谱表征了薄膜的成分.ITO薄膜在可见光范围内有较高的透射率(80 %～95 %).在低工作气压(1 Pa)下,氧气流量比率[O2/(O2+Ar)]越小,薄膜的透射率越高、导电性越好.在高工作气压(2 Pa)下,制备得到低质量、低透射率的无定形薄膜.