Seiji Noda

Development of a Photoresist Removal Method Using Ozone Gas with Water Vapor for LCD Manufacturing

A photoresist removal method for liquid crystal display manufacturing, using highly concentrated ozone gas and water vapor, has been developed. This method overcomes limitations of conventional ozone processing for resist removal, and obtains a resist removal rate over 1 μm/min at substrate temperatures lower than 100°C. In our experiment, ozone gas was bubbled into water, and water vapor concentration in the gas phase was controlled by the water temperature (T w ). The influence of treatment parameters, such as substrate temperature (T s ), water vapor concentration, and residence time (τ), on the removal rate has been experimentally examined. The treatments were performed at T, = 25-83°C, T w = 27-92.5°C, T = 0.5-2 min, ozone concentration [O 3 ] 0 = 4.2-10.7 vol % (90-230 g/m 3 ), gas flow rate 1-12.5 slm, and total pressure 100 kPa. The observed removal rate was 1.4 μm/min for a sample with a dry etching treatment at T s = 83°C, T w = 90°C, and [O 3 ] = 10.7 vol %. It was also shown that the difference between the water and the substrate temperatures, T w - T s , was a critical parameter for determining the removal rate. The removal rate in this process is more than ten times greater than that of the conventional ozone processing, such as ozone gas ashing and ozonized water treatment. A higher removal rate was realized by optimizing the amount of condensed water with respect to a resist oxidation rate and the diffusion rate of ozone into the resist in the water.

Development of a Method for Resist Removal by Ozone with Acetic Acid Vapor

A method of removing the photoresist using ozone gas with acetic acid vapor has been developed. Glass substrates (size 100 X 100 mm 2 ) coated with I-line resist were treated under the conditions of substrate temperature, (T S ) 27-50°C; acetic acid vapor, 2-18 vol %; ozone, 0-9.3 vol % (0-200 g/m 3 ); total gas flow rate, 2 L/min; and gas pressure, 100 kPa. A previous ozone treatment with oversaturated water vapor or sprayed water overcame the limitation of ozone diffusion into the resist by the control of the water film on the resist. In this study, pure acetic acid vapor has been first applied for the resist removal by ozone in order to improve the oxidation rate of the resist, because acetic acid is an inactive solvent in the ozonization, and the solubility of ozone is much higher than water. It was observed that the resist removal rate increased with acetic acid and ozone concentration, and reached at 6 μm/min at Ts = 50°C, which was about six times greater than that of the previous ozone treatment. Metal corrosion of molybdenum and aluminum electrodes was found negligible during the ozone treatment with acetic acid vapor. The mechanism of resist removal without the metal corrosion by ozone with acetic acid vapor is also discussed, based on the solubility of ozone in acetic acid and the corrosion current in ozonized solutions.

Densification of Chemical Vapor Deposition Silicon Dioxide Film Using Ozone Treatment

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with ozone (O3) or oxygen (O2) gas ambient at 450 °C. Density depth profiles of the SiO2 films were investigated using X-ray reflectivity analysis with synchrotron radiation. The density depth profile of the base CVD-SiO2 film without the O3 or O2 treatment is low (~2.03 g/cm3) and constant. That of the CVD-SiO2 film with the O3 treatment is not constant. The O3-treated CVD-SiO2 film is composed of a middle-density top layer (~2.13 g/cm3), a low-density center layer (~2.03 g/cm3), and a high-density bottom layer (~2.24 g/cm3). The density depth profile of the CVD-SiO2 film treated with O2 gas agrees with that of the base CVD-SiO2 film. The temperature or presence of O2 molecules during the O3 treatment at 450 °C does not affect the densification of the base CVD-SiO2 film. Therefore, the active species that densify the base CVD-SiO2 film during the O3 treatment are oxygen (O) radicals generated by the thermal decomposition of O3 molecules. The middle-density top layer near the SiO2 surface is formed by the reconstruction of a Si–O network with the oxidation of oxygen vacancies in the base CVD-SiO2 film with O radicals. The high-density bottom layer near the SiO2/Si interface is formed by the oxidation of the silicon substrate with O radicals that diffuse through the low-density base CVD-SiO2 film. The penetration length of O radicals in the base CVD-SiO2 film is very large because the thickness of the high-density bottom layer does not depend on the thickness of the base CVD-SiO2 film up to 16.8 nm at least. Therefore, this densification method for the CVD-SiO2 film with O3 treatment can be applied to the formation of either thin or thick SiO2 films.

Generation of Highly Ozonized Water Using a Microporous Hollow Fiber Module

The generation of an environmentally friendly and highly ozonized water has been investigated. This was achieved by contacting highly concentrated ozone gas and water through a microporous hollow fibers module. According to the experimental results, it was observed that the ozone mass transfer in this system was controlled by the liquid phase. The maximum gradient approach was then used to model the ozone transfer within the module in both wetted and non-wetted modes. The corresponding validity was checked through the agreement between our experimental results and the calculated results under the gas-filled pore assumption. Furthermore, this model was used for a parameter study, and revealed that the connection of modules in series was more effective than that in parallel for the production of highly ozonized water.

Method for real-time measurement of nitrogen atom density in atmospheric pressure post-discharge flows

A method has been developed for real-time measurement of nitrogen atom density in atmospheric pressure post-discharge flows. In this method, nitric oxide is supplied to the downstream of a nitrogen discharge as a reactant. Our chemical simulation has revealed that the injected nitric oxide is consumed mainly by reductive reaction with nitrogen atoms or oxidative reaction with oxygen atoms. The number density of atomic nitrogen is determined almost instantaneously through the measurement of nitric oxide and nitrogen dioxide densities with a gas analyser. The experimental verification was carried out with a dielectric barrier discharge unit as a nitrogen atom source, and the results showed good agreement with simulation predictions.

Effect of Ammonia Addition on Photo-Resist Removal Characteristics by Ozone/Water Vapor Treatments

Abstract A photo-resist removal process, using highly-concentrated ozone gas and water vapor, has been investigated in the presence of ammonia. Test substrates (size 520 mm × 410 mm) coated with I-line resist and with pretreatment (140°C baking in 3000 sec and SF6/O2 dry etching) are chosen from a real manufacturing process for TFT-LCD (Thin film transistor Liquid Crystal Display) panel fabrication. The resist removal rate was measured under the conditions of substrate temperature (Ts) 59-83°C, ammonia 0-6.4vol%, ozone 10.7 vol%, total gas flow rate 12.5 slm, and gas pressure 100 kPa. It was found that the removal rate increased with ammonia concentration and reached at 2.1μm/min at Ts= 74°C. It is suggested that ammonia neutralizes acids to form ammonium salts, improving the dissolving rate of the decomposed resist into water. The corrosion of Al electrode on a substrate was also evaluated, when the resist was completely removed by the moist ozone treatment. Ammonia addition was found to maintain pH value of water on the substrate around neutrality and prevent the Al corrosion.