JPH03237009A - High purity phosphoric acid and its production - Google Patents

Abstract

PURPOSE:To decrease amts. of various impurity metal elements by adding seed crystal to the raw phosphoric acid in an atmosphere purified by removing suspending fine particles so as to obtain phosphoric acid hemihydrate crystal, subjecting this hemihydrate to purification and then to micro filtration to remove suspending fine particles. CONSTITUTION:Air is purified with using a high-performance filter to remove suspending fine particles so that the purified atmosphere contains 0-10000 fine particles of >=0.3mum size per 1ft<3>. In this atmosphere, the source phosphoric acid of >=70wt.% concn. is kept at a temp. range lower than the saturation temp. by 0-10 deg.C, to which the seed crystal is added by 0.1-2% of the mass of the raw phosphoric acid, and then the temp. is lowered to obtain acicular phosphoric acid hemihydrate crystal having 0.5-10mm major axis. Then this hemihydrate crystal is washed with high-purity water, maintained at a temp. higher than the saturation temp. by 0-10 deg.C, purified by sweating, molten, and subjected to micro filtering so that the purified phosphoric acid contains suspending particles of >=0.5mum particle size by <=50 particles per 1ml. By this method, the obtd. high purity phosphoric acid contains impurities by <=20ppb Fe, <=ppb mun, and <=40ppb Na in terms of 85wt.% H3PO4 concn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to high purity phosphoric acid and a method for producing the same.

Furthermore, the present invention relates to high-purity phosphoric acid for use in the electronic industry, which is used when removing silicon nitride films in the semiconductor manufacturing process, and which does not substantially contain impurities that degrade the electrical characteristics of microelements, and a method for producing the same. It is something. Since this high-purity phosphoric acid has a low content of impurities, it is also suitable as a metal aluminum etching solution, an alumina etching solution for ceramics, and a phosphoric acid glass raw material for optical fiber glass.

[Prior Art] The technique of purifying phosphoric acid by crystallization has been widely known for some time, and can be found in Japanese Patent Publication No. 14692/1983. According to this document, a method is disclosed in which a series of crystallization and purification operations consisting of a crystallization operation, a separation operation from a mother liquor, and a melting operation is repeated three times in order to purify phosphoric acid to a desired purity.

Oita et al.: Toyo Soda Report, 10.2.21 (1966)
revealed basic physical property data for purifying phosphoric acid by crystallization, such as saturation solubility, correlation between supersaturation degree and growth rate, hygroscopicity of phosphoric acid hemihydrate crystals, and crystal sedimentation rate in phosphoric acid. The purity of the phosphoric acid hemihydrate crystal particles obtained was not quantitatively discussed.

Also, for example, see et al.: Proceedings of
aConference of Industry
l Crystallization+pp413-4
20 (1976) shows an example of application in a fluidized bed crystallizer. This fluidized bed crystallizer produces uniform coarse particles, which not only facilitates separation from the mother liquor, but also
The solution is cooled by an external heat exchanger provided in the fluidized bed section, and the heat of crystallization is efficiently removed, thereby increasing the production rate.

Although it is conventionally known that phosphoric acid is purified by crystallization operations in this manner, the purity of phosphoric acid obtained by these operations is not clearly described.

[Problems to be Solved by the Invention] Furthermore, in these methods, the means for preventing the contamination of impurities during purification operations are not clear, and the effects of preventing the contamination of impurities are not clearly specified. do not have.

Therefore, an object of the present invention is to provide high-purity phosphoric acid and a method for producing the same in which the amount of various impurity metal elements is below the detectable limit regardless of whether the state in the liquid is dissolved or not. .

[Means for Solving the Problems] The present invention was completed as a result of intensive research in view of the above-mentioned prior art.

That is, in the present invention, the impurity content is 20 ppb or less for Fe, 3 ppb or less for Mn, and 40 ppb or less for Na when the concentration of I, PO, is converted to 85% by weight, and The present invention relates to high-purity phosphoric acid characterized in that the number of suspended particles having a particle size of 0.5 μm or more is 50 or less per 1 mf.

Additionally, the present invention removes airborne particulates from the air phase.
Reduce the number of particles larger than 3 μm to virtually 0 per ft3
In an atmosphere that has been purified to a temperature range of 10,000 to 10,000 °C, (a) Seed crystals are added while the raw material phosphoric acid with a concentration of 70% by weight or more is maintained at a temperature range of 0 to 10'C lower than the saturation temperature, and then the temperature is lowered. (b) a step of purifying the phosphoric acid hemihydrate crystals by washing and/or sweating the phosphoric acid hemihydrate crystals obtained in (b); ) Then, after melting the purified phosphoric acid hemihydrate crystals,
The present invention relates to a method for producing high-purity phosphoric acid, which comprises a step of removing suspended fine particles with a particle size of 0.5 μm or more contained in phosphoric acid by microfiltration.

The present invention will be explained in detail below.

In the present invention, phosphoric acid is a liquid mixture of components represented by the following general formula and H2O in any ratio, and is highly corrosive to various metals, so it is a suitable substance as an etching liquid for the surfaces of metals, etc. be. Phosphoric acid has a low vapor partial pressure compared to other mineral acids, making it difficult to purify by distillation, and although it is actually a very difficult compound to purify industrially, The high purity phosphoric acid according to the invention is
As mentioned above, it is characterized by low contents of Fe, Mn, and Na.

As mentioned above, the high purity phosphoric acid according to the present invention includes Fe, M
It is a phosphoric acid characterized by a low content of n and Na, that is, iron, manganese and sodium.

Here, the concentration of phosphoric acid is measured by a titration method using sodium hydroxide as shown in JIS K-1449.

The content of Fe, Mn, and Na in phosphoric acid was measured by injecting 0 μl of a sample diluted to a 5-fold dilution rate (100-fold for Na) into a carbon heating furnace and heating it to 800°C. phosphoric acid is removed, and the absorbance of the element that has become atomic at the atomization temperature according to the element shown in Table 1 is compared with the absorbance of a standard sample in dilute hydrochloric acid. Evaluation is performed using so-called flameless atomic absorption spectrometry. Here, the purity of phosphoric acid is expressed as a ratio of the mass of an element per unit of phosphoric acid.

The lower limit of detection of an element by flameless atomic absorption spectrophotometry is calculated using the following formula: Element mass [l?
] was divided by the sample injection amount of 10 μe and the sample density [y/Cm3], and the lower limit of detection was calculated by multiplying by the dilution rate [-] of the injected sample. Here, the sample density was 19/C-.

The detection limits for Fe-Mn and Na were determined using the above formula and are shown in Table ↑.

Table 1: Conditions and lower detection limit M for frameless atomic absorption spectrophotometry
n 279.5 2400 0.00
4 2N a 598.0 20
00 0.001 10 The number of suspended particles is determined by a method in which the test liquid is passed through a sapphire cell placed in the laser beam and the light blocking signal caused by the particles is measured. The number of particles is determined by calculating the light cutoff signal of the test fluid using a calibration curve of the particle density function of the standard particles and the light cutoff signal when using a fluid in which standard particles are dispersed in ultrapure water in the same device. This is the obtained value. Products that implement such a measurement method are commercially available, and here, Hiac/Royc.

company particle counter Model 14100/
4150 was used.

Phosphoric acid hemihydrate crystals are H3P0. - It is a crystalline substance with a composition of 1/2H20.

The supercooling temperature in the crystallization operation and sweating operation is the value obtained by subtracting the saturation temperature shown by the following formula from the temperature of phosphoric acid and the concentration of the phosphoric acid.

Saturation temperature -27,i (91,6-phosphoric acid concentration) (saturation temperature - phosphoric acid concentration -63,7>Here, the unit of saturation temperature is [℃], and the unit of phosphoric acid concentration is [wt%]) Representation, 65
Values range from 89% by weight.

Therefore, the supercooling temperature has a negative value in the crystallization operation, and a positive value in the sweating operation.

The present invention also provides an industrial method for producing such high-purity phosphoric acid, which is based on the following three steps.
In an atmosphere where the number of fine particles of m or more is substantially in the range of 0 to 10,000 per ft3, (a) 70% by weight or more of raw phosphoric acid is maintained at a temperature range of 0 to 10 degrees Celsius below the saturation temperature. In this state, seed crystals are added, and then the temperature is lowered to precipitate phosphoric acid hemihydrate crystals. (b) The phosphoric acid hemihydrate crystals obtained in (a) are washed and/or sweated. a step of purifying phosphoric acid hemihydrate crystals, and (c) then, after melting the purified phosphoric acid hemihydrate crystals,
A step of removing suspended particles with a particle size of 0.5 μm or more contained in phosphoric acid by microfiltration.

Impurities in the high-purity phosphoric acid according to the present invention are affected by fine particles contained in the air that comes into contact with the phosphoric acid crystals or phosphoric acid solution, and must be handled in a clean atmosphere. This means that in the production process of high purity phosphoric acid according to the present invention, which includes operations such as crystallization, separation, washing, sweating, precision P'41, etc.
This means that suspended particles of μm or larger are held at substantially 0 to 10,000 particles per 1 ft'. Such a clean environment can be achieved by passing the air taken into the manufacturing environment through a high-performance filter and by employing manufacturing equipment and manufacturing methods that generate as little dust as possible.

The number of fine particles of 0.3 μm or larger in the air phase can be determined by shining light on dust floating in the air using a light scattering particle counter that satisfies the standards set by the Japanese Industrial Standards, IIS 89921. The density is measured using a method that calculates the number of particles according to size depending on the amount of light, and this results in 1 ft'
The total number of particles with a diameter of 3 μm or more was calculated.

According to the research conducted by the present inventors, the number of suspended particles of 0.1 μm or larger in the air phase is 1 per 1 ft3 in normal air.
It was found that the high purity phosphoric acid according to the present invention cannot be obtained in such an environment.

As the raw material phosphoric acid used as a raw material in the method of the present invention, any phosphoric acid supplied for industrial use can be used, regardless of its production history by the so-called wet method or dry method. The concentration of H3P O< in the raw material phosphoric acid is preferably 70% by weight or more. If the phosphoric acid concentration is less than 70% by weight, the saturation temperature will be low and a large amount of energy will be required to obtain an appropriate degree of supersaturation during crystallization, which is industrially undesirable. In addition, the upper limit is up to the saturated concentration (91.6% by weight), and if it exceeds this, there is a risk that crystals other than phosphoric acid hemihydrate crystals will precipitate, and the viscosity will further increase, making crystallization and separation difficult, which is undesirable. .

In the method of the present invention, the following treatment can be performed as a pretreatment of the raw material phosphoric acid. That is, before crystallizing the raw material phosphoric acid, it is held at a temperature higher than the saturation temperature for a predetermined period of about one hour to remove clusters of phosphoric acid that are contained in the phosphoric acid and tend to have an adverse effect on the subsequent crystallization operation. Can be disassembled. Alternatively, the raw material phosphoric acid may be filtered to remove fine particles in advance. However, although such pretreatment of the raw material phosphoric acid is a preferred operation in the production of high-purity phosphoric acid according to the present invention, it is not an essential requirement for the method of the present invention.

Crystallization is carried out by adding seed crystals to phosphoric acid while maintaining a predetermined liquid temperature using a corrosion-resistant container equipped with a mixing device such as a stirrer and a temperature control mechanism. The seed crystals used here are phosphoric acid hemihydrate crystals, and a part of the crystals obtained in the previous crystallization operation can be used. Publication No. 30607 and Special Publication No. 62-3
Phosphoric acid hemihydrate crystals prepared by the method disclosed in Japanese Patent No. 0608 can be used. For example, 200 g of 85% by weight high-purity phosphoric acid was placed in a PTFE beaker, 300 ml.
When the mixture is cooled to 0° C. while stirring at pm and about 0.1 g of phosphoric acid hemihydrate crystals are added, phosphoric acid hemihydrate crystals of about 100 μm can be precipitated.

This phosphoric acid hemihydrate crystal is in the form of a slurry in high-purity phosphoric acid, and can be used as a seed crystal in the crystallization process according to the method of the present invention.

The amount of seed crystals added is preferably 0.1 to 2% based on the mass of the raw material phosphoric acid, depending on the mass of the raw material phosphoric acid charged to the crystallization tank.
If it is less than 0.1%, the effect will be small, and even if it is added in an amount exceeding 2%, no improvement in the effect commensurate with the amount added will be observed.

The crystallization vessel must be equipped with a mechanism capable of controlling the temperature inside the crystallization tank, but any device used in normal industrial crystallization operations can be employed. The material of the container is preferably one that has corrosion resistance against phosphoric acid in order to prevent contamination of impurities from the container, and for example, a material made of synthetic resin such as polyethylene, polypropylene, or fluororesin can be used. Those made of well-washed borosilicate glass can also be used.

Control of the degree of supersaturation during crystallization can generally be considered in the same way as the crystallization operation, and conditions can be selected as appropriate, but the supersaturation temperature is O to 10°C, preferably -2 to 10°C.
It is best to keep it within the range of -8°C.

If the supersaturation temperature is lower than -10° C., the crystal particles tend to aggregate and more impurities are included, which is undesirable, and it is not an economical condition considering the energy required for cooling. Furthermore, if the supersaturation temperature is O to -2°C, the crystallization rate is relatively low, the production rate is reduced, and a large amount of raw material phosphoric acid is required to obtain the desired production amount, so this is not an optimal condition. .

The crystallization operation according to the method of the present invention may be either a batch operation or a continuous operation as long as the above conditions are satisfied.

The phosphoric acid hemihydrate crystal obtained by the method of the present invention has a major axis of 0.
．． They are needle-shaped crystals with a diameter of 5 to 10 mm, and can be separated and recovered from the mother liquor by ordinary industrial operations such as filtration and centrifugation. Since the crystals thus recovered contain impurities or have mother liquor attached to them, the high purity phosphoric acid according to the present invention cannot be obtained as is. Therefore, it is necessary to purify the crystals by the following two operations.

That is, (1) the crystals separated from the mother liquor and attached thereto are removed by washing with ultrapure water or the high purity phosphoric acid according to the present invention, and phosphoric acid hemihydrate crystals are purified.

■The phosphoric acid hand water crystals separated from the mother liquor are held at a temperature 0 to 10°C higher than the saturation temperature of the attached mother liquor, and the parts containing impurities are selectively melted by sweating, the melted parts are removed, and the phosphoric acid Purify water crystals.

These operations (1) and (2) may be performed individually, or may be performed in combination.

When introducing (1) and (2) together, the order may be an essential requirement of the present invention, and it does not matter which operation is performed first.

The purified crystals are then melted and ultrapure water is added to obtain phosphoric acid at a predetermined concentration.

The phosphoric acid obtained in this way usually contains a large amount of suspended particles and is still unsuitable for use in advanced electronic industry, mainly semiconductor manufacturing, and requires further processing. In the method of the present invention, this phosphoric acid is microfiltered to reduce the number of suspended particles contained in the phosphoric acid with a particle size of 0.5 μm or more to 50 or less per 1+al.

Of course, the precision filtration device itself must not have a structure or material that would release fine particles or elute impurities into the phosphoric acid, but recent technological developments have made it possible to obtain the desired device. It became so. In the method of the present invention,
For example, ChemiBoat [P (, -11000, manufactured by Kurabo Industries, Ltd.)] can be used.

According to research by the present inventors, when the number of suspended particles in high-purity phosphoric acid is in the range of 50 or more per 1+n1 to 155,000 or less, when the number of particles is large, F
Since there was a tendency for the contents of Fe, Mn, and Na to increase, the number of suspended particles and Fe, Mn in high-purity phosphoric acid
There is a correlation between the contents of n and Na, although it is not quantitatively or mechanistically clear, and it is presumed that the removal of suspended particles also contributes to the improvement of purity.

Note that the above-mentioned washing operation, sweating operation, and microfiltration operation can be repeated multiple times as desired to obtain a predetermined high-purity phosphoric acid.

As described above in detail, by employing the production method according to the present invention, it is possible to obtain high purity phosphoric acid according to the present invention. do.

Phosphoric acid was produced by a dry method, which is a conventionally known method for producing phosphoric acid. That is, this is a manufacturing method in which yellow phosphorus is burned in excess air to form P2O5, which is then dissolved in pure water. Phosphoric 6-acid (89% by weight including H3PO4) produced by this method was added to polytetrafluoroethylene (PTFE) with a pore size of 0.8μ.
M membrane filter - [manufactured by Toyo Roshi Co., Ltd.: T
0.8μm by filtering with O80^047^]
The number of these particles was reduced, and in particular, suspended particles with a size of 2 μm or more were removed.

When the amount of metal elements in this phosphoric acid was measured by flameless atomic absorption spectrophotometry, Fe was 180 ppb, M
n was 10 ppb, and Na was 250 ppb.

This phosphoric acid was used as a raw material phosphoric acid in the following examples.

Example 1 (a) 800 g of the raw material phosphoric acid was prepared using PTF as a crystallization container in a purified atmosphere with a particle size of 0.3 μm or more in the range of 10 to 100 particles per 1 ft.
The mixture was poured into a separable flask made by E and a PTFE stirring blade was inserted therein, and the mixture was stirred by rotating it at 100 rpm.

The crystallization container containing this phosphoric acid was immersed in a constant temperature bath to cool the phosphoric acid. The temperature of the phosphoric acid was cooled from 25° C. to 20° C., and 1 g of phosphoric acid hemihydrate crystals with a particle size of 0.5 to 5 mm were added as seed crystals. The temperature of phosphoric acid was gradually lowered and 3 hours after seed crystals were added, the temperature was lowered to 14° C. to crystallize phosphoric acid hemihydrate crystals.

(b) This crystal suspension was transferred onto a perforated plate of a PTFE Buchner funnel, and the mother liquor was separated. The mass of the crystal at this time was about 280 g.

(c) Next, ultrapure water was sprayed from above the crystals on the Buchner funnel to wash and remove the raw material phosphoric acid retained on the crystal surfaces and crystal particles.

(d) The phosphoric acid obtained in (c) has a pore size of 0.1 μm.
Phosphoric acid was pumped at a rate of 0.16/min using a chemical circulation filtration device W [ChemiBoat PC-TTOO, manufactured by Kurabo Industries, Ltd.] equipped with a filter with a filtration area of 0.1.7 m2.
Repeatedly 0 times to remove suspended particles.

Fe in the phosphoric acid obtained by melting the phosphoric acid crystals obtained by this series of operations (1) and (3) and the phosphoric acid obtained in (d)
, Mn and Na contents were analyzed by atomic absorption spectrophotometry.

The results are shown in Table 2.

Table 2 Purification effects by crystallization, washing, and precision filtration (ppb
) Slimming Mad Yunoshichi E0 0q Jind Fe 180 60 20 20M
n 10 3 Not detected Not detected Na
250 80 40 30 Furthermore, when the number of suspended particles suspended in the high purity phosphoric acid obtained in (d) was measured, it was found that the number of suspended particles of 0.5 μm or more was
There were 45 pieces per cm3.

Example 2 (a) The raw material phosphoric acid used in Example 1 was placed in the crystallization container used in Example 1 and crystallized under the crystallization operating conditions shown in Example 1 to obtain phosphoric acid hemihydrate crystals. I got it.

(b) The slurry liquid in which phosphoric acid hemihydrate crystals were suspended in the crystallization flask was transferred onto a perforated plate of a PTFE Buchner funnel, and the mother liquor was separated.

(c) The crystals on the perforated plate were held together with the Buchner funnel in a constant temperature atmosphere, and a sweating operation was performed. The phosphoric acid hemihydrate crystal was melted and a sweating operation was performed until the amount of the dropped liquid was approximately 190, and the raw material phosphoric acid held on the crystal surface and between the crystal particles was dropped and removed.

(d) The phosphoric acid obtained in (c) was
Phosphoric acid was fed at a rate of 0.11/min using a chemical circulation device equipped with a filter with a filtration area of 0.17 m2, and suspended particles were filtered 30 times.

Fe in the phosphoric acid obtained by melting the phosphoric acid crystals obtained by this series of operations (b) and (c) and the phosphoric acid obtained in (d)
, Mn and Na contents were analyzed by atomic absorption spectrophotometry.

The results are shown in Table 3.

Table 3 Purification effects by crystallization, perspiration, and precision filtration (ppb
) Sabanami no Ki Sakuen Niri Sakuretsu F e 180 60 18 18
Mn 10 3 Not detected Not detected Na
250 80 35 30 Also, (
When the number of suspended fine particles suspended in the high purity phosphoric acid obtained in step d) was measured, the number of suspended fine particles of 0.5 μm or less was 40 per 1 Cm3.

Example 3 (A) The raw material phosphoric acid used in Example 1 was placed in the crystallization container used in Example 1, and crystallized under the crystallization operating conditions shown in Example 1 to obtain phosphoric acid hemihydrate crystals. Obtained.

(b) The slurry liquid in which phosphoric acid hemihydrate crystals were suspended in the crystallization flask was transferred onto a perforated plate of a PTFE Buchner funnel, and the mother liquor was separated.

(c) The crystals on the perforated plate were held together with the Buchner funnel in a constant temperature atmosphere, and a sweating operation was performed. Melt the phosphoric acid hemihydrate crystals, and the amount of liquid dropped is approximately Loot? The material was sweated until it became violent, and the raw material phosphoric acid retained on the crystal surface and between the crystal particles was removed dropwise.

(2) Next, ultrapure water is sprayed from above the crystals on the perforated plate to wash away the phosphoric acid remaining on the crystal surface and between the crystal particles.
The cleaning solution was removed dropwise.

(e) The phosphoric acid obtained in (d) was fed at a rate of 0.11/min using a chemical liquid circulation r-filtration device equipped with a filter with a pore size of 0.1 μm and a filtration area of 0.17 m2, and the process was repeated 30 times. The airborne particles were filtered out.

The contents of Fe, Mn, and Na in the phosphoric acid obtained by melting the phosphoric acid crystals obtained in the series of operations (b), (c), and (ii) and in the phosphoric acid obtained in (b) are calculated by atomic It was analyzed by spectrophotometry and the results are shown in Table 4.

Table 4 Purification effects by crystallization, perspiration, and precision filtration (ppb
) 0 engineering) -fff, Ren d Pack l Fe 60 20 Not detected Not detected Mn
1.0 3 Not detected Not detected N a
80 35 30 30 Also, when the number of suspended particles suspended in the high purity phosphoric acid obtained in (2) was measured, the number of suspended particles of 0.5 μm or more was 1.
There were 40 pieces per cm'.

Comparative Example The essential condition of the present invention is an atmosphere in which suspended particles are removed from the air phase and the number of particles of 0.3 μm or more is reduced to a range of substantially 0 to 100 per lft. In order to prove that
The Fe, Mn, and Na contents of the resulting phosphoric acids were compared.

In a laboratory configured to continuously introduce outside air directly, the same raw material phosphoric acid as in Example 1 was placed in a crystallization container, and purified and separated under the same crystallization operating conditions as in Example 1. We conducted an experiment.

When we measured the number of particles floating in the air phase in this laboratory, the number of particles larger than 0.3 μm was 1.00,000 particles per 1 ft'.

(a) Pour 8001 g of the raw material phosphoric acid into a PTFE separable flask as a crystallization container in the above atmosphere, insert a PTFE stirring blade, and stir the phosphoric acid into a 10 Q r
Rotate and stir at pm. The crystallization container containing this phosphoric acid was immersed in a constant temperature bath to cool the phosphoric acid. The temperature of phosphoric acid was cooled from 25°C to 20°C, and seed crystals with a particle size of 0.5
1 g of ~1.5 mm phosphoric acid hemihydrate crystals was charged. 14 3 hours after gradually lowering the temperature of phosphoric acid and adding seed crystals.
The temperature was lowered to °C to crystallize phosphoric acid hemihydrate crystals.

3 4 (b) This crystal suspension was transferred onto a perforated plate of a PTFE Buchner funnel, and the mother liquor was separated.

Melt the ice crystals and the amount of liquid dropped is about 1001? A sweating operation was applied, and the raw material phosphoric acid retained on the crystal surface and between the crystal particles was dropped and removed.

(iv) Next, ultrapure water was sprayed from above the crystals on the porous plate to wash and remove the raw material phosphoric acid held on the crystal surface and between the crystal particles.

(e) The phosphoric acid obtained in (2) was pumped at a rate of O, ], N/min using a chemical liquid circulation filtration device equipped with a filter with a pore size of 0.1 μm and a flow area of 0.17 m2. Suspended particles were filtered out repeatedly.

The content of Fe, Mn, and Na in the phosphoric acid obtained by melting the phosphoric acid crystals obtained by the series of operations (b), (c), and (d) and the phosphoric acid obtained in (e) is calculated by atomic amount. Analyzed by spectrophotometry. The results are shown in Table 5.

Table 5: Results of crystallization experiments conducted in normal atmosphere (ppb)
Mn 6 4 4 4Na
1.20 100 60 60 Also,
(When the number of suspended fine particles suspended in the high purity phosphoric acid obtained in 2) was measured, the number of suspended fine particles of 0.5 μm or more was 4000 per cm3.

[Effect of the invention] As explained above, the high purity phosphoric acid of the present invention contains Fe, M
Due to the small amount of n and Na elements mixed in, when used to remove a silicon nitride film in a semiconductor manufacturing process, it becomes a suitable electronic material that does not substantially contain impurities that degrade the electrical characteristics of fine particles.

Additionally, this high-purity phosphoric acid is characterized by a low content of impurities, making it suitable as a metal aluminum etching solution, an alumina etching solution for ceramics, and a phosphate glass raw material for optical fiber glass. .

Further, according to the method for producing high-purity phosphoric acid according to the present invention, there is an advantage that high-purity phosphoric acid that is not mixed with various metal elements can be easily purified and produced.

Claims (1)

[Claims] 1. When the concentration of H_3PO_4 is converted to 85% by weight, the impurity content is 20 ppb or less for Fe, 3 ppb or less for Mn, and 40 ppb or less for Na, and 0 contained in phosphoric acid. A high-purity phosphoric acid characterized in that the number of suspended particles having a particle size of .5 μm or more is 50 or less per ml. 2. Remove suspended particles from the air phase and reduce the number of particles of 0.3 μm or larger to substantially 0 to 10 per ft^3.
(a) In an atmosphere that has been purified to a temperature within the range of 0.000 to 0.000,
A crystallization step in which seed crystals are added while the temperature is maintained at a temperature lower than 0°C, and then the temperature is lowered to precipitate phosphoric acid hemihydrate crystals.(B) Washing the phosphoric acid hemihydrate crystals obtained in (B) and/or a step of purifying the phosphoric acid hemihydrate crystals by a sweating operation, and (c) then, after melting the purified phosphoric acid hemihydrate crystals,
A method for producing high-purity phosphoric acid, comprising the step of removing suspended fine particles with a particle size of 0.5 μm or more contained in phosphoric acid by microfiltration.