Tatsuya Koito

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.

Effective and environmentally friendly remover for photo resist and ashing residue for use in Cu/low-k process

The authors have developed an effective removal solvent for photo resist and its ashing residue for use in copper wire/low-dielectric interlayer devices that significantly lowers the risk of harming the environment. The inhibition of Cu corrosion is very important in these devices, and benzotriazole (BTA, C/sub 6/H/sub 5/N/sub 3/) is usually used as the corrosion inhibitor. However, BTA creates mutagenicity and biodegrades poorly. The authors investigate several typical heterocyclic nitrogen compounds as Cu inhibitors to replace BTA and study their optimum compositions. It has been found that uric acid (C/sub 5/H/sub 4/N/sub 4/O/sub 3/) is the best corrosion inhibitor for Cu. Moreover, this remover, which was composed mainly of amino alcohol, uric acid, and H/sub 2/O, can be applied to low-k films by optimizing its H/sub 2/O ratio. It not only effectively removed the ashing residue on Cu/low-k devices but also effectively reduced the environmental impact because the rinse wastewater containing remover can be completely treated at the fabrication site with ordinary biological processes.

An environmentally friendly photoresist and ashing residue remover for Cu/low-k devices

Developed an effective removal solvent for photoresist and its ashing residue for use in copper wire/low-dielectric interlayer devices that significantly lowers the risk of harming the environment. The inhibition of Cu corrosion is very important in these devices, and benzotriazole (BTA, C/sub 6/H/sub 5/N/sub 3/) is usually used as the corrosion inhibitor. However, BTA creates mutagenicity and biodegrades poorly. We investigated several typical heterocyclic nitrogen compounds such as Cu inhibitor to replace BTA and studied their optimum compositions. We found that uric acid (C/sub 5/N/sub 4/O/sub 3/) was the best corrosion inhibitor for Cu. Moreover, this remover which is composed mainly of amino alcohol, uric acid, and H/sub 2/O can be applied to low-k films by optimizing its H/sub 2/O ratio. It not only effectively removes the ashing residue on Cu/low-k devices, but also effectively reduces the environmental impact because the rinse wastewater containing remover can be completely treated at the fabrication site with ordinary biological processes.

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.