Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2000-10-18
2003-04-01
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S691000, C210S806000, C210S263000, C210S284000, C423S584000
Reexamination Certificate
active
06540921
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 99 13435 filed in France on Oct. 27, 1999; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The invention relates to a process for the purification of aqueous hydrogen peroxide solutions using ion-exchange resins. More particularly, the invention relates to a process for the production of aqueous hydrogen peroxide solutions containing very small amounts of impurities, especially metallic impurities, and intended for the fabrication of semiconductors, this production process being carried out very close to or at the point of use of the aqueous solution.
The invention also relates to a plant for producing aqueous hydrogen peroxide solutions containing very small amounts of impurities.
2. Description of the Related Art
Increasing the capacity of memories produced in the form of integrated circuits goes hand in hand with increasing purity of the chemicals used for the fabrication of chips on which these integrated circuits are produced.
Between 1985 and 1990, the capacity of on-chip memories was between 1 Mbits and 16 Mbits for an etching line thickness of between 1.5 &mgr;m and 0.8 &mgr;m, and required hydrogen peroxide solutions each with an impurity concentration that had to be less than 100 ppb.
At the present time, producing a 64 Mbit memory on a chip of the same size requires a line width of approximately 0.35 &mgr;m and in general uses a grade of hydrogen peroxide having a maximum degree of impurity for each impurity lying within the range from 0.1 to 1 ppb.
Semiconductor manufacturers hope in the near future to be able to market 256 Mbit and 1 Gigabit memories with a minimum etching geometry of less than 0.18 &mgr;m. The increase in memory capacity will then require a product for which the amount of each impurity will have to be less than 50 ppt.
Hydrogen peroxide is generally manufactured by auto-oxidation of an anthraquinone derivative or of a mixture of such derivatives. The said anthraquinone derivative(s) is (are) used dissolved in a complex mixture of organic solvents, such as an aromatic hydrocarbon mixed with an ester or an alcohol. This solution forms the working solution. This working solution is firstly hydrogenated in the presence of a catalyst, which converts the quinones into hydroquinones. It is then oxidized by bringing it into contact with air or with oxygen-enriched air. During this oxidation, the hydroquinones are oxidized, again, into quinones, with the simultaneous formation of hydrogen peroxide. The said hydrogen peroxide is extracted with water and the working solution undergoes a regeneration treatment before being used again.
The raw aqueous hydrogen peroxide solution is generally concentrated by rectification and purified in aluminium or stainless-steel distillation columns.
After this step, the aqueous hydrogen peroxide solution still contains impurities such as organic substances coming from the anthraquinone derivatives, solvents as well as degraded products from these compounds, and metallic elements such as aluminium, iron, chromium and zinc coming from the surface of the materials and pipes used. This hydrogen peroxide solution must therefore undergo a subsequent treatment in order to achieve the degree of purity required by the semiconductor industry.
Various techniques may be used to purify such a solution, such as distillation, crystallization, passage over beds of adsorbent resins and/or ion exchanges, reverse osmosis, filtration, ultrafiltration, etc.
In general, the organic substances are well purified by a distillation process and/or a process involving an adsorbent resin. For more details about these processes, reference may be made to Patents FR-A-2,710,045, EP-A-835,842, EP-A-502,466 and/or FR-A-1,539,843. The metallic elements, present in not insignificant amounts for applications in microelectronics, as well as anions such as nitrates or sulphates for example, are generally removed by passage over beds of ion-exchange resins.
Various methods of purifying aqueous hydrogen peroxide solutions using ion-exchange resins have been proposed in the literature. In general, these methods comprise making the solutions come into contact with at least one highly acid cation-exchange resin, obtained by polymerization of styrene and crosslinking by divinylbenzene followed by a sulphuric acid treatment, as well as at least one highly basic anion-exchange resin, obtained by the reaction of a tertiary amine, for example trimethylamine, with polychloro-methylstyrene.
In general, a person skilled in the art knows that the hydroxide form of the anionic resin is to be proscribed, since hydrogen peroxide very rapidly decomposes when in contact with it. The carbonate CO
3
2−
and bicarbonate HCO
−
3
forms of lower basicity may be used and are described, for example, in U.S. Pat. No. 3,294,488, U.S. Pat. No. 3,305,314 and/or U.S. Pat. No. 3,297,404.
However, the hydrogen peroxide decomposition reaction, when hydrogen peroxide comes into contact with this slightly basic support, is still possible, particularly if the hydrogen peroxide remains in static contact with the resin for several tens of minutes at room temperature.
Those skilled in the art know that this hydrogen peroxide decomposition reaction is accelerated by certain metals, such as iron and chromium, which may be contained in the resin itself and come from the materials used for its synthesis. For this purpose, special methods of preparing the resins before their use have been developed. Thus, JP-A-08,337,405 describes a process for treating anionic and cationic resins before use by an ultrapure aqueous solution of a mineral acid (for example, HCl). After this acid treatment, the resins are rinsed in ultrapure water. Next, the anionic resin is treated by an aqueous sodium hydroxide solution and then by a sodium carbonate or bicarbonate solution before being rinsed with ultrapure water. These treatments are generally lengthy and particular care has to be taken when carrying them out so as to avoid any contamination.
It is also known that hydrogen peroxide decomposition can gradually increase during purification of the said peroxide by the increase in metals picked up by the resin and carried away by the hydrogen peroxide solution itself. The addition of a mineral acid HX to the hydrogen peroxide solution before it comes into contact with the anionic resin, as described in U.S. Pat. No. 5,200,166, or with the cationic resin, as described in U.S. Pat. No. 5,534,238, makes it possible to reduce the evolution of oxygen due to hydrogen peroxide decomposition.
These methods have the drawback of considerably reducing the volume of hydrogen peroxide that can be purified per litre of resin. For example, in the case of anionic resins, sites are occupied by X, X being added in not insignificant amounts compared with the anionic mineral impurities contained in the hydrogen peroxide. This point is particularly important in the case of industrial plants intended for producing hydrogen peroxide. This is because, for the same volume of hydrogen peroxide, the amount of resin needed for purification will be greater if an HX resin is added to the hydrogen peroxide.
EP-A-846,654 discloses a process and an apparatus for purifying aqueous hydrogen peroxide solutions, in which the unpurified or partially purified solution flows under gravity through anionic and cationic resins. Because of the head losses due to the resins, the operating flow rate is limited because the flow is only created by gravity, thereby considerably reducing the production capacity. In this method of implementation, the cationic resin used is pretreated with an acid so as to remove the traces of metals.
Furthermore, the apparatus described does not benefit from a safety system allowing the unit to be rapidly shut down if the temperature in the latter rises abruptly, with a risk of explosion which must always be under control in hydrogen peroxide treatment units.
Thus, the on-site generation of
Demay Didier
Devos Christine
Dulphy Herve
Burns Doane Swecker & Mathis L.L.P.
Hoey Betsey Morrison
L'Air Liquide Societe Anonyme a Directoire et Conseil de Su
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