Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-03-26
2001-10-09
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S301000
Reexamination Certificate
active
06300518
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a highly-concentrated and highly-purified aqueous solution of free hydroxylamine (which is not in the form of a salt). The invention particularly relates to a highly-concentrated aqueous hydroxylamine solution containing almost no metal components and having such high stability that the solution is advantageously used for processing or washing electronic devices.
BACKGROUND OF THE INVENTION
An aqueous hydroxylamine solution has been hitherto used, for instance, as a processing solution or detergent for producing electronic devices. In particular, a highly-concentrated and highly-purified aqueous hydroxylamine solution containing almost no impurities (particularly, metal components) has been recently required, for example, for washing very small and highly-integrated electronic devices such as semiconductor IC chips.
Hydroxylamine (NH
2
OH) is generally synthesized by a known method. In the method, sodium bisulfite and sodium nitrite are reacted in an aqueous phase to prepare an aqueous solution of sodium hydroxylamine sulfonate, which is then hydrolyzed to obtain an aqueous hydroxylamine sulfate solution. The obtained solution is neutralized with sodium hydroxide to give an aqueous free hydroxylamine solution.
Hydroxylamine normally takes the form of crystals at room temperature, and its melting and boiling points are 33° C. and 57° C. (at 20 mmHg), respectively. The crystals of hydroxylamine are known to be explosive when heated, and an aqueous hydroxylamine solution is also known to be so unstable that it is liable to rapidly decompose. For this reason, an aqueous solution of stable hydroxylamine salt is beforehand prepared, and the free hydroxylamine is produced when it is used in industry. Since this process is troublesome and inconvenient, it has been desired to find out a stabilizing agent specifically effective for free hydroxylamine. Examples of the stabilizing agents hitherto having been proposed include 8-hydroxyquinoline (Japanese Patent Provisional Publication No. 57-100908), 1,10-phenanthroline (Japanese Patent Provisional Publication No. 58-69841), bipyridine (Japanese Patent Provisional Publication No. 58-69842), thiocarboxylic acids (Japanese Patent Provisional Publication No. 58-69843) and quinoline (Japanese Patent Provisional Publication No. 58-69844). Further, WO 97/22549 and U.S. Pat. No. 5,783,161 teach that trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid effectively stabilizes free hydroxylamine.
The already proposed stabilizing agents, however, are not fully effective when used in a normal manner. In addition, a prepared aqueous hydroxylamine solution generally contains impurities such as metal components (e.g., iron, aluminum, alkali metals such as sodium and potassium), which are originally contained in the starting materials or introduced in the preparation process.
In order to prepare a highly-purified aqueous free hydroxylamine solution suitable for processing or washing semiconductor devices, concentration and distillation by heating are indispensable. However, these treatments are liable to cause explosion, and hence it is very difficult to safely distill the aqueous hydroxylamine solution (which is unstable and corrosive) keeping its distillate from contamination with impurities.
SUMMARY OF THE INVENTION
The present invention provides a highly-concentrated and highly-purified aqueous (free) hydroxylamine solution which contains, in particular, almost no metal components such as iron. The invention also provides a process for safely and easily preparing the aqueous hydroxylamine solution.
The inventors already found a stabilizing agent by which an aqueous free hydroxylamine solution is stabilized effectively enough to safely concentrate and distill by heating, which is trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA). The CDTA makes it easy to store and transport an aqueous free hydroxylamine solution. Further, the CDTA makes it possible to safely produce and supply a purified aqueous hydroxylamine solution containing sodium and potassium in an amount of 30 to 100 ppb for each and iron in an amount of 50 to 100 ppb. However, the purity of this level is still not advantageous for treating electronic devices. In order to further purify the aqueous hydroxylamine solution, the solution must be further concentrated and distilled by heating. Such severe distillation procedure is not easy, because a distilling apparatus is easily corroded by hydroxylamine to release new impurities.
The present inventors have further studied and finally discovered that a highly-purified aqueous hydroxylamine solution can be obtained by distilling an aqueous crude hydroxylamine solution (hereinafter, referred to as “crude solution”) in the presence of the specific stabilizing agent (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid) using a stainless steel-made distilling apparatus which preferably has equipment (e.g., spatter separator) for keeping spatters of the concentrated solution from contaminating the resulting solution and which has an inside surface treated with an aqueous hydroxylamine salt so that the surface may not be corroded to release impurities. Thus prepared aqueous hydroxylamine solution is much more pure than the crude solution, and therefore is suitable for the use in washing semiconductor devices.
The invention resides in an aqueous hydroxylamine solution containing hydroxylamine in an amount of not less than 30 weight %, which contains iron in an amount of not more than 10 ppb, metal components other than iron in an amount of not more than 5 ppb for each metal component and trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amount of 0.0005 to 0.5 weight %.
The invention further resides in a process for the preparation of a highly purified aqueous hydroxylamine solution, comprising the steps of:
heating in a vessel an aqueous crude hydroxylamine solution containing 40 to 60 weight % of hydroxylamine and 15 to 200 ppb of iron, in the presence of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amount of 0.0005 to 0.5 weight % based on the weight of the crude solution, to distill water off and to give a concentrated aqueous hydroxylamine solution containing hydroxylamine in an amount of 70 to 95 weight %; and
distilling the concentrated aqueous hydroxylamine solution to give an aqueous hydroxylamine distillate by means of a stainless steel-made distilling apparatus of which inner surface has been previously treated with an aqueous hydroxylamine salt solution.
The preferred embodiments of the invention are as follows.
(1) The aqueous hydroxylamine solution, wherein the amount of iron is not more than 5 ppb (more preferably, not more than 3 ppb).
(2) The aqueous hydroxylamine solution, wherein the amounts of sodium and potassium are not more than 2 ppb (more preferably, not more than 1 ppb) for each.
(3) The aqueous hydroxylamine solution, wherein the amounts of metal components other than iron are not more than 2 ppb (more preferably, not more than 1 ppb) for each.
(4) The distilling apparatus is equipped with a device for keeping a distilled aqueous hydroxylamine solution from contamination with the concentrated solution which spatters in the vessel.
(5) The concentrated aqueous hydroxylamine solution is distilled, while a portion of the concentrated aqueous hydroxylamine solution is taken out from the vessel.
(6) The concentrated aqueous hydroxylamine solution taken out from the vessel is mixed with a freshly supplied aqueous crude hydroxylamine solution to give an aqueous mixture which is then supplied into the vessel.
(7) A portion of the concentrated aqueous hydroxylamine solution taken out from the vessel is wasted before the mixing.
(8) Trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid is supplemented to the aqueous hydroxylamine distillate.
REFERENCES:
patent: 5783161 (1998-07-01), Schneider et al.
patent: 5808150 (1998-09-01), Michelotti
patent: 5906805 (1999-05-0
Imai Naoshi
Toguro Kouzou
Costellia Jeffrey L.
Davis Brian J.
Nissin Chemical Co., Ltd.
Nixon & Peabody LLP
Padmanabhan Sreeni
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