Tadashi Shinmura

Study on Surface Modification of Indium Tin Oxide and Resist Surfaces Using CF4/O2 Plasma for Manufacturing Organic Light-Emitting Diodes by Inkjet Printing

We studied a surface modification technique for indium tin oxide (ITO) anodes without precleaning and resist banks for manufacturing organic light-emitting diodes (OLEDs) by inkjet printing. The ITO surface modified by inductively coupled plasma (ICP) with an optimized CF4/O2 (7:3) gas mixture improved both its hydrophilicity and its work function, while the resist surface treated by the plasma became hydrophobic. The resist and ITO surfaces treated by plasmas of various gas mixtures (i.e., CF4, CF4/Ar (1:2), CF4/O2 (x:1; x=1, 7/3, 4, and 9) were analyzed by X-ray photoelectron spectroscopy (XPS) of the C 1s, F 1s, O 1s, and In 3d5/2 core levels. On the uncleaned ITO surfaces modified by CF4/O2 plasmas, organic contaminants were removed more efficiently and the deposition of CFx on the remaining contaminants decreased with increasing oxygen. The amount of F in the form of InFx increased using the CF4/O2 (7:3) plasma in comparison with that using the CF4/Ar and CF4 plasmas. We investigated the effect of adding oxygen to CF4 on the change in gaseous species produced in the plasma chamber by mass spectrometry. In the CF4/O2 (7:3) plasma, the peak intensities of F+, HF+, F2+, O+, and O2+ were higher than those in the CF4 plasma. The results suggest that In2O3 was generated by the oxidation of indium with O, and InFx was generated by the fluoridation of indium with HF. By introducing InFx onto ITO surfaces using the CF4/O2 plasma, the hole-injection energy barrier could be reduced.

Topography Simulation of Reactive Ion Etching Combined with Plasma Simulation, Sheath Model, and Surface Reaction Model

We developed an oxide-film reactive ion etching (RIE) topography simulation which consists of a plasma simulation, a sheath model, and a surface reaction model. In the plasma simulation, the plasma parameters were calculated in two dimensions using the particle-in-cell/Monte Carlo collision (PIC/MCC) method. In the surface reaction model, the motion of particles in the etching trench was simulated by the Monte Carlo method. This topography simulation was applied to the etching by a capacitively coupled plasma (CCP). Etching conditions were as follows:gas pressure 5.3–10.6 Pa and RF power 1.1–1.7 kW in the gas mixture of C4F8, CO, O2, and Ar. The calibration method for such simulation parameters as the ion reflection ratio, the etch rate and the polymer etch rate was established based on the experimental results. As a result, the change of the etching profile was reproduced according to the change of the gas pressure and RF power with high accuracy. Furthermore, it was shown that the simulator can predict the profile change corresponding to the process change.

Improvement in downflow etching rate using Au as a catalyst

We studied the improvement in the polycrystalline silicon (poly-Si) etching rate in the downflow etching process using microwave-excited CF4/O2 plasma by enhancing the dissociation reaction of the etching gas and the etching reaction on the poly-Si film surface through the use of a catalyst. A piece of platinum (Pt), gold (Au) or silver (Ag) was placed in a quartz tube as a potential catalyst for the downflow etching of poly-Si films. The results revealed that the etching rate using Au was up to 3.6 times higher than that without any catalyst. The mechanism for the improvement in the etching rate using a Au catalyst was analyzed by evaluating the plasma and etching species in transportation paths using optical emission spectral analysis and mass spectrometry, and by examining the poly-Si film with thermal desorption spectrometry, scanning electron microscopy and x-ray photoelectron spectroscopy. The Au placed between the plasma and the sample is oxidized by the active gas dissociated from CF4/O2 gas, and Au oxides and their compounds including F and CFx are transported and deposited onto the surface of the poly-Si film. Although, the precise mechanism of these reactions is not clear, it was presumed that the gold oxides and their reaction compounds acted as catalysts in the etching reaction of the poly-Si film and significantly accelerated the etching rate.We studied the improvement in the polycrystalline silicon (poly-Si) etching rate in the downflow etching process using microwave-excited CF4/O2 plasma by enhancing the dissociation reaction of the etching gas and the etching reaction on the poly-Si film surface through the use of a catalyst. A piece of platinum (Pt), gold (Au) or silver (Ag) was placed in a quartz tube as a potential catalyst for the downflow etching of poly-Si films. The results revealed that the etching rate using Au was up to 3.6 times higher than that without any catalyst. The mechanism for the improvement in the etching rate using a Au catalyst was analyzed by evaluating the plasma and etching species in transportation paths using optical emission spectral analysis and mass spectrometry, and by examining the poly-Si film with thermal desorption spectrometry, scanning electron microscopy and x-ray photoelectron spectroscopy. The Au placed between the plasma and the sample is oxidized by the active gas dissociated from CF4/O2 gas, and ...

Selective Plasma Surface Modification of Resist for Patterning Hydrophobic and Hydrophilic Regions

A plasma surface modification process was investigated to realize a fine pattern on a surface that consists of highly controlled hydrophilic and hydrophobic areas. Capacitively and inductively coupled plasmas (CCP and ICP) using CF4 and argon gases were used to increase the hydrophobicity of a resist surface selectively on an indium tin oxide (ITO) surface. By plasma exposure, both the hydrophobicity of the resist and the hydrophilicity of the ITO surface were increased. The difference between the contact angle of water on the plasma-exposed surface of the resist and that on the ITO surface was larger in ICP than in CCP. On the basis of the results of the plasma analyses and X-ray photoelectron spectroscopy of the surfaces, this difference is considered to be due to the high densities of CF3 and CF3+ generated in ICP with the generation of CF2, CF, CF2+, and CF+ at reduced amounts because of the low electron temperature in ICP.

Deposition and characterization of gold thin films on Si by CF4+O2 gas microwave plasma

Thin films of Au deposited on Si[(100), n type] wafers using a solid Au source and CF4+O2 microwave plasma were studied. Solid Au heated at 200 °C in a vacuum crystal reactor was vaporized in a CF4+O2 microwave (2.45 GHz power 200 W) plasma flow, and the Au film was deposited on a Si wafer heated to 270 °C in a low-pressure (10 mTorr) O2 atmosphere. The density of Au in this film was about 91.7% as analyzed by x-ray photoelectron spectroscopy, and the film resistivity was 2.8 μΩ cm, which is almost the same as that of the initial bulk Au (2.4 μΩ cm). The deposition mechanism was deduced. The heated solid Au reacts with O2 and (CF2)n from the CF4+O2 microwave plasma, and then the Au is converted into AuO(CF2)n. This Au compound carries Au atoms to the vacuum chamber. In the O2 atmosphere, vaporized AuO(CF2)n is oxidized and changed into oxides such as AuO and COFx. AuO is deposited on the Si wafer heated to 270 °C, and then reduced into Au and O2 by heating. This process results in a high purity deposited ...

Simulations and Experiments on O Density and Distribution in Ashing Process Using Surface Plasma Excited by Microwave

Simulation methods for the density and spatial distribution of O atoms have been developed to analyze high-density plasma (1011 cm-3) excited by two microwave sources. The density of O atoms, that react with photoresist, was calculated in a gas mixture of CF4 and O2, and the density has a maximum value at 10% CF4 partial pressure. For the distribution simulation, the rate of reaction between O atoms and photoresist was measured in a small cell, and the sticking coefficient was estimated to be 0.002. The O atom distribution on a glass substrate was calculated by the simulator, where the sticking coefficient was input, focusing on the density under a beam that connected the microwave sources and had no plasma source. The results of both the simulations are in good agreement with the experimental results. The simulations were applied to optimize the chamber configuration and process conditions. As a result, a high ashing rate of over 1430 nm with a uniformity of ±9.3% was obtained.