DD281173A5 - METHOD FOR THE PRODUCTION OF HIGH-PURITY, CRYSTALLIZED AMMONIUM FLUORIDE - Google Patents

Abstract

The invention relates to the production of high-purity, crystallized ammonium fluoride ("ammonium fluoride" for use in the microelectronics industry.) The crystallized ammonium fluoride is immediately obtained from the suspension formed by reaction of hydrogen fluoride with ammonia in ultrapure quality The ammonium fluoride used can be used as an additive to compositions for the treatment of semiconductor devices. {ammonium fluoride, crystallized, special-purpose; production; composition; semiconductor device; microelectronics; treatment}

Description

absorbed amounts of the supplied starting materials can be completely retained therein. The feed rates of hydrogen fluoride and ammonia gas are maintained so that in the reaction solution, including intensive cooling, the temperature remains within the specified limits.

Exemplary embodiments

A reaction vessel made of polypropylene with a cooling coil, stirrer, inlet and outlet pipes and a bottom valve was charged with 44% hydrofluoric acid and ammonia gas was introduced with stirring and cooling while maintaining the temperature between 293 and 298K. After complete neutralization, the suspension was drained and the crystallized ammonium fluoride separated from the mother liquor by centrifugation. The mother liquor, a saturated ammonium fluoride solution, was returned to the reaction vessel and hydrogen fluoride was passed to a level of 25 to 30%, maintaining the temperature below 298K by stirring and intensive cooling. Thereafter, ammonia gas was again introduced at 293 to 298 K until neutralization, the resulting suspension was worked up as described above and the mother liquor returned again. The recirculation took place mehr.ach, at least 5 times, until there were signs that the Fe or sulfate content threatens to increase. Steady ι batches were obtained with a content of ammonium fluoride of more than 99.5%.

During the introduction of ammonia gas or hydrofluoric acid, the reaction vessel jet was followed by another jet with a newly prepared batch in order to take up the small amounts of non-absorbed constituents. The following table summarizes the results (averages of several cycles). Column 1 shows values of conversions with ammonia gas at temperatures between 320 and 325K (not according to the invention), in column 2 those of conversions between 298 and 301K. Column 3 contains the results (means) of Ansätzon up to 5 times the recycle of ammonium fluoride solution. From the table it can be seen that at lower reaction temperature, the proportion of ionic impurities significantly reduce and can be maintained at these low values even with multiple recycling.

table Levels of foreign ions in ammonium fluoride (in ppm)

column smaller 1 smaller 2 smaller 3 Verunr. smaller smaller al 0.17 0.10 0.03 Ag smaller 0.007 · smaller 0.007 " smaller 0.007 " Cu 0.02 smaller 0.003 " smaller 0.003 " Fe 0.26 smaller 0.14 smaller 0.05 Mn 00:03 · 0.03 " 0.03 " Ni 0.05 smaller 0.014 " smaller 0.014 " N / A 0.12 0.035 " 0.035 " pb smaller 0.02 smaller 0.02 smaller 0.02 Zn smaller 0.08 smaller 0.007 " smaller 0.007 " Si 30 30 30 chloride 5 · 5 · 5 » sulfate 10 · 10 » 10 »

Column 1: first batch at 320-325K, Column 2: first batch at 298-301K, Column 3: up to 5 times recycling, 298-301K,

* = Detection limit.

Claims (2)

claims: 1. A process for the preparation of high purity, crystallized ammonium fluoride from hydrogen fluoride and gaseous ammonia, characterized in that highly concentrated hydrofluoric acid or hydrogen fluoride containing ammonium fluoride solution neutralized with gaseous ammonia, while maintaining the temperature of the reaction solution in the range between 293 and 308 K, from the resulting suspension separated out crystallized ammonium fluoride and the remaining ammonium nfluoridlösung is recycled to re-salt formation. 2. The method according to claim 1, characterized in that the recirculated ammonium fluoride first hydrogen fluoride fed to a content of about 25 to 30%, the temperature of the reaction medium is maintained in the range between 293 and 298 K and then neutralized with ammonia gas. Field of application of the invention The invention is used in the chemical industry for the production of ammonium fluoride ("ammonium fluoride spezialrein"), which meets the purity requirements of the semiconductor industry.The product produced according to the invention is used in the manufacture of semiconductor devices as an additive to etchant compositions.To avoid unwanted side reactions, all must Components of Ätzmittelkompositionen extremely high purity. Characteristic of the known state of the art Ammonium fluoride is usually prepared by reacting hydrogen fluoride or hydrofluoric acid with gaseous ammonia or with aqueous ammonium hydroxide. Due to the high solubility in water, it is difficult to obtain high yields in this way, ie to recover crystallized Pr oi Λ from the solution. Upon concentration of these solutions decomposition occurs, so that gaseous cleavage products and unwanted Ammoniumbifluorid arise. Another preparation method is the extraction by ammoniacal hydrolysis of sodium fluorosilicate by a mixture of hydrogen fluoride, ammonia, ammonium fluoride and Ammoniumbifluorid is aborted in the range up to about 500K. The absorption of this mixture takes place at 340 to 360K in aqueous ammonium fluoride solution, from which then forms a suspension of ammonium fluoride crystals. This procedure, apart from the high temperatures to be used, is not suitable for preventing the entrainment of impurities (PL 62513). New procedures are proposed in CS 160414 and CS 164687. In particular, this describes the subsequent purification with organic solvents. With the exclusion of atmospheric moisture, the ammonium fluoride is isolated from the aqueous solution with up to 10 times the amount (based on ammonium fluoride) of organic solvents. Despite the high expense of additional auxiliaries, the yields are only between 75% and 88%, or 65%. A high degree of protection of ionic, in particular inorganic, impurities with nonaqueous solvents can not be guaranteed in this way. A procedure for producing high purity, crystallized ammonium fluoride from hydrogen fluoride and ammonia without subsequent purification operations has not previously been described. Object of the invention The aim of the invention is the development of a procedure that leads immediately to high-purity products, requires no auxiliaries or with such a rework and high yields and low environmental impact allowed. Explanation of the essence of the invention Ammonium fluoride, like all ammonium salts, has a high solubility in water. It was therefore the task of achieving a maximum utilization of the starting materials and at the same time to avoid subsequent cleaning operations and to enable a minimization of waste products. The problem has been solved by neutralizing concentrated hydrofluoric acid by introducing ammonia gas at temperatures between 293 K and 308 K. It forms a suspension with crystallized ammonium fluoride. It has surprisingly been found that ammonium fluoride of high purity can be obtained even if the saturated ammonium fluoride solution freed from crystallized ammonium fluoride is again charged with fluorobutane at 293K to 298K and then reintroduced with ammonia gas to form crystallized ammonium fluoride. The ammonium fluoride solution can be recycled several times, without the high purity is thereby reduced. Cycles of up to ten times regression without quality degradation were achieved. In this way, it is possible to use the starting materials practically quantitatively when submitting ammonium fluoride solution. The reaction vessel was followed by a newly prepared batch, so that the low, not in the reaction vessel