Arata Toyoda

A new method for treating fluorine wastewater to reduce sludge and running costs

Reduction of the sludge generated in fluorine wastewater treatment is a critical problem for the semiconductor industry. We have developed a new method for treating fluorine wastewater in order to reduce sludge and running costs. This method utilizes a small amount of Al(OH)/sub 3/ not only as an aggregator for CaF/sub 2/ generated from fluoride ions in the wastewater but also as an effective fluorine adsorbent. The Al(OH)/sub 3/ as fluorine adsorbent is used repeatedly through an AI(OH)3 reclamation process. This method can effectively treat the concentrated fluorine wastewater to achieve an exceedingly low concentration in one-step treatment. We constructed a practical treatment system using this method by modifying part of an existing conventional system. This new treatment system is able to reduce both the total sludge and running costs to about one-tenth those of a conventional system.

A novel treatment technique for DMSO wastewater

We have developed an efficient treatment technique for wastewater containing dimethyl sulfoxide [DMSO, (CH/sub 3/)/sub 2/SO], a compound used as a photoresist stripping solvent in semiconductor manufacturing processes. Generally, wastewater containing organic compounds can be treated biologically, but with DMSO wastewater, biological treatment is not available because noxious compounds are produced that harm the environment. Here, we present an effective DMSO wastewater treatment technique in which we add an oxidizing agent and irradiate the wastewater with ultraviolet light to prevent damage to the environment. The use of hydrogen peroxide (H/sub 2/O/sub 2/) as an oxidizing agent in combination with ultraviolet irradiation causes DMSO to decompose promptly into methanesulfonic acid (MSA, CH/sub 3/SO/sub 2/OH). With continued treatment, the resultant MSA decomposes gradually into the inorganic compound sulfuric acid (H/sub 2/SO/sub 4/). In this reactive route, no noxious compounds are generated. We confirmed that MSA can be biologically treated comparatively easily, and that by combining the initial ultraviolet irradiation/H/sub 2/O/sub 2/ addition treatment to rapidly produce MSA with a biological treatment to convert the MSA to H/sub 2/SO/sub 4/, the total processing can be treated at very low cost. These treatment techniques make use of the characteristically high reactivity of DMSO and are very effective as a means of treating DMSO wastewater.

An efficient treatment technique for TMAH wastewater by catalytic oxidation

Developers used in photolithography contain toxic tetramethylammoniumhydroxide (TMAH) and this creates a problem of how to properly treat developer wastewater. We have developed a TMAH wastewater treatment technique that consists of a combination of two novel decomposition processes: pyrolyzing TMAH to TMA and decomposing TMA to N/sub 2/, H/sub 2/O, and CO/sub 2/ by means of a selective oxidation catalyst for nitrogenous compounds. We have tested a system using this technique in long-term treatment of the actual wastewater and have found it to be sufficiently practical. The running cost of a treatment system using our technique would be about one-ninth that of disposing of the wastewater as industrial waste but about 2.3 times that of biological treatment. Compared with biological treatment, however, our system is tolerant to many treatment conditions and operation management is much easier. Furthermore, it occupies only about one-sixth the area of a biological treatment system.

A novel tungsten light-shield structure for high-density CCD image sensors

A novel tungsten light-shield structure has been developed. Tungsten film properties, the device configuration with the tungsten light-shield structure, and experimentally achieved results regarding device characteristics are described. Optical measurement clarified that tungsten film has a sufficiently low transmittance value for practical use for more than 200-nm-thick film and is stable up to 1000 degrees C. The good step coverage and low reflectance, such as 20-40% for aluminum, required for light-shield film were also obtained. A tungsten light-shield structure was applied to a 1/2-in format 668(H)-pixel*575(V)-pixel charge coupled-device (CCD) image sensor. An extremely low smear value, less than 0.001%, was obtained for a 300-nm film thickness. >

A 1-inch 2-M pixel HDTV CCD image sensor with tungsten photo-shield and H-CCD shunt wiring

A 1-inch 2-million pixel FIT-CCD image sensor for HDTV has been developed, which features a tungsten photo-shield and horizontal CCD (H-CCD) shunt wiring. Tungsten photo-shield, which has low reflectance and good step coverage characteristics, reduces smear level to -110 dB, combined with a frame-interline-transfer (FIT) scheme. The tungsten photo-shield also acts as a shunt busline, supplying transfer pulses to vertical CCD (V-CCD) electrodes, so that a 1.2/spl times/10/spl circ/5 electron charge handling capability is obtained at a frame transfer frequency of 1 MHz. Newly developed H-CCD shunt wiring suppresses vertical line pair FPN, even with smaller transfer pulse amplitudes. H-CCD shunt wiring also helps reduce power consumption in the H-CCD by 2/3 as compared to that achieved with conventional wiring. >

A new technique for treating fluorine wastewater to reduce sludge and running costs

This technique utilizes a small amount of Al(OH)/sub 3/ not only as an aggregator for CaF/sub 2/ but also as an effective fluorine adsorbent. The Al(OH)/sub 3/ is used repeatedly through an Al(OH)3 reclamation process. This technique can effectively treat the concentrated fluorine wastewater and eliminate the high-level treatment step. We constructed a practical treatment system simply by modifying part of an existing conventional system. This new treatment system reduced both the total sludge and running costs to about one tenth those of a conventional treatment system.

A high level treatment of fluorine wastewater to reduce sludge

A novel technique for treating fluorine wastewater has been developed in order to reduce sludge. This technique utilizes the dependence of solubility and adsorption characteristics of Al(OH)/sub 3/ gel on pH, and uses Al(OH)/sub 3/ gel itself repeatedly as a fluorine adsorbent. The reclamation process of Al(OH)/sub 3/ gel involves varying the pH level of its slurry to allow Al(OH)/sub 3/ gel to desorb fluorine and be dissolved as an aluminate ion. This technique can treat fluorine wastewater to several ppm at low-cost, and reduce the resulting volume of sludge to a level one-thirtieth the amount produced by the conventional treatment method.

Ozone treatment of persistent organic chemical wastewater

We developed an ozone treatment process for wastewater containing persistent organic chemicals that are not easily treated by conventional processes. These include alkylbenzenesulfonic acids (ABS), phenol, and dimethylsulfoxide (DMSO). We confirmed that there are different optimal pH conditions with respect to the efficiency of ozone treatment for different types of organic compounds. The potential of the process was convincingly demonstrated; with proper pH adjustment it is extremely effective. Organic compounds, for which biological treatment is not suitable, can be converted to biologically degradable compounds without generating hazardous byproducts. Ozone treatment can be extremely cost-effective, particularly, for high-level wastewater.

A 2 M pixel HDTV CCD image sensor with tungsten photo-shield and H-CCD shunt wiring

A 1-in optical lens format, 2-Mpixel FIT-CCD (charge coupled device) image sensor is described. The low reflectance and good step coverage characteristics of a tungsten photoshield, combined with a frame-interline-transfer scheme, reduces the smear level to -110 dB. The tungsten photoshield also acts as a shunt bus line, supplying transfer pulses to vertical CCD (V-CCD) electrodes, so that a 1.2*10/sup 5/-electron charge-handling capability is obtained at a frame transfer frequency of 1 MHz. Tungsten-and-aluminum-shunt (TAS) wiring, used in a horizontal CCD (H-CCD), suppresses vertical line pair fixed-pattern noise, even at a smaller transfer pulse amplitudes. TAS wiring also helps reduce power consumption in the H-CCD by 2/3 compared to that achieved with conventional wiring.<<ETX>>