Keiji Hirano

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.

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.