Chemistry of inorganic compounds – Oxygen or compound thereof – Peroxide
Reexamination Certificate
2000-10-23
2003-07-15
Gupta, Yogendra N. (Department: 1751)
Chemistry of inorganic compounds
Oxygen or compound thereof
Peroxide
C510S175000
Reexamination Certificate
active
06592840
ABSTRACT:
The present invention relates to highly pure aqueous hydrogen peroxide solutions, which are in particular essentially free from organics, a process for the preparation of such solutions and their use.
Hydrogen peroxide is widely used in many industrial sectors, for example in chemical synthesis, paper and pulp bleaching, wastewater treatment and as a constituent of chemical polishing fluids. A large part of the hydrogen peroxide is currently prepared by the anthraquinone process. In this process, an anthraquinone derivative, such as a 2-alkylanthraquinone, is reduced to the corresponding alkylanthrahydroquinone in a water-immiscible organic solvent mixture over a hydrogenation catalyst. Subsequent oxidation of this hydroquinone solution with air or oxygen and recovery of the starting 2-alkylanthraquinone yields hydrogen peroxide which is usually extracted with water to form a crude aqueous hydrogen peroxide solution. This crude solution contains numerous inorganic impurities, such as silicon compounds and metals, e.g. Al, Fe, Cr, and Ni, which generally originate from the material of the reactors and synthesis equipment used. Furthermore, the crude solution also contains numerous organic impurities, such as anthraquinone, residual organic solvent and the degradation products of these substances. It is necessary to subject the aqueous hydrogen peroxide solutions to various purifying and/or concentrating steps, depending on their intended use. Examples of known purification processes are distillation, membrane filtration, adsorption on resins and the use of ion exchange resins, which may be employed individually or in combination. The solutions purified in this way may then be concentrated by evaporation and rectification to give a hydrogen peroxide content of about 10-70% by weight of hydrogen peroxide. The quality of the hydrogen peroxide solutions obtained in this way is sufficient for many industrial applications which are not very demanding in terms of removal of inorganic and/or organic impurities, for example for use in wastewater treatment and paper and pulp bleaching.
Owing to the continuing miniaturization of electronic components, it is necessary to provide more and more powerful microchips having higher and higher integration levels. These chips can only be produced from highly pure silicon wafers which generally contain impurities in an amount of 1 ppb or less and sometimes far less than 1 ppb. The production of such electronic components involves process steps, such as wet processing, in which the semiconductors are treated with various cleaning chemicals. This often involves the use of hydrogen peroxide solutions.
A substantial problem in the production of these large-scale-integrated circuits is that the semiconductor surfaces may be contaminated by inorganic or organic compounds present in the cleaning chemicals. All solutions contacting semiconductor elements are therefore required to be extremely pure and should, for example, have a very low ionic impurities content. Said solutions should preferably have a total metal content of 300 ppt or less and, for some metal species, sometimes less than 10 ppt. It is also necessary to avoid contamination by anions, since some anions form complexes with metal ions and may thus interfere with the intentional doping of the semiconductor.
Another substantial problem is that the semiconductor surfaces may be contaminated by organic compounds which may have deleterious effects on subsequent processing steps, such as etching. Therefore, aqueous hydrogen peroxide solutions which are essentially free from organics are much needed.
Processes for the removal of inorganic impurities from hydrogen peroxide solutions are known. WO-A 96/39237 discloses a process for the preparation of ultrapure, aqueous hydrogen peroxide for the production of semiconductors. An anion exchange resin and a cation exchange resin are used to purify an about 30% strength aqueous hydrogen peroxide solution by removal of the cations and anions contained therein. This process has the disadvantage that the resulting hydrogen peroxide solutions may still contain organic impurities in an amount of up to 20 ppm.
The organics contained in the hydrogen peroxide solutions is usually referred to as toc (total organic carbon) and is indicated in units of ppm, i.e. parts of impurity in 10
6
parts of substance, or ppb (10
9
) etc. However, the removal of organic impurities is still not satisfactory. For example, hydrogen peroxide obtained by the anthraquinone process cannot be purified by distillation only since it contains volatile or steam-volatile organics. In the case of such a distillate, the hydrogen peroxide solution may still contain organics in an amount of up to 150 mg/l.
U.S. Pat. No. 5,456,898 describes a method for enrichment and purification of a crude aqueous hydrogen peroxide solution obtained by the anthraquinone process. This process comprises adsorbing organic impurities on a synthetic adsorber resin and subsequently concentrating the resulting solution by partial condensation and subsequent fractionated distillation. An aqueous hydrogen peroxide solution is obtained which contains organic impurities in an amount not exceeding 50 ppm.
U.S. Pat. No. 4,999,179 discloses a method for purifying an aqueous hydrogen peroxide solution by removal of metal cations, anions and organic impurities using a combination of a cation exchanger, an anion exchanger and a further halogen-containing porous resin, e.g. a bromine-containing styrene/divinylbenzene copolymer. It is possible to purify hydrogen peroxide solutions which have been produced according to the anthraquinone process. The resulting purified solutions generally have a toc content of 5 ppm or less.
U.S. Pat. No. 5,342,602 likewise discloses a process for reducing the amount of organic impurities in aqueous hydrogen peroxide solutions which have been produced according to the anthraquinone process. In this process, the organic impurities are adsorbed on dealuminized H-Y zeolites or H mordenites. These adsorption agents can be regenerated by calcining at up to 1000° C. According to the examples, toc was reduced to as little as 44 ppm.
All adsorptive methods for removing organic impurities have the disadvantage that they are very complicated. For example, it is generally necessary to subject the adsorber medium to a complicated pretreatment procedure and to regenerate it at a later stage. Furthermore, adsorption processes are demanding from a safety point of view since hydrogen peroxide tends to decompose exothermally.
JP-A-09 100 106 discloses a process for removing organic impurities from hydrogen peroxide solutions without any adsorption step. This process comprises bubbling air or an inert gas through a crude hydrogen peroxide solution to reduce toc from 34.2 mg/l to 10.4 mg/l. A similar process is disclosed in JP-A-09 278 416. JP-A-09 075 605 discloses a process for removing organic impurities from hydrogen peroxide solutions by fractional crystallizations. This energy-intensive and technically very complicated process makes it possible to reduce toc from 64 to 2.7 ppm. A similar process is disclosed in JP-A-09 278 417.
U.S. Pat. No. 5,112,702 discloses a process for making hydrogen peroxide by electrochemical reduction of oxygen. U.S. Pat. No. 5,496,532 discloses a process for producing hydrogen peroxide by catalytic conversion of hydrogen and oxygen in the presence of a catalyst which comprises a platinum group metal. It is also known to prepare hydrogen peroxide by electrolysis of ammonium peroxodisulfate.
None of these processes yields aqueous hydrogen peroxide which fulfills the current purity requirements of the electronics industry, in particular the requirements of excluding, as substantially as possible, inorganic and organic substances. The prior art hydrogen peroxide solutions therefore produce too many rejects in the treatment of electronic component substrates.
It is an object of the present invention to provide highly pure aqueous hydrogen peroxide solutions for treating electronic compo
Fischer Martin
Quaiser Stefan
Stammer Achim
BASF - Aktiengesellschaft
Gupta Yogendra N.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Petruncio John M.
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