JP2001123232A - Method for refining gallium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method of refining of a gallium, by which the impurities like lead etc. difficult to remove, can be removed without using the recrystalliz ing method and the gallium having >=99.9999% purity and usable as a semi-con ductor raw material is obtained at a low cost and with high productivity. SOLUTION: After adding zinc to the gallium, the impurities like lead etc. is made to an azeotropic mixture with zinc by heating and holding to 420-910 deg.C under argon or nitrogen atmosphere while stirring and mixing. Successively, the impurity and zinc are vaporized and removed by heating to 800-1,000 deg.C while sucking gas to the vacuum and lastly, the zinc crystal grain and oxide, and film left in the gallium are filtrated and separated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying gallium using vacuum heating, and more particularly to a method for purifying gallium to purify gallium to a purity of 99.9999% or more, which can be used as a semiconductor raw material.

[0002]

2. Description of the Related Art Gallium is required to have a purity of 99.9999% or more for use in compound semiconductor crystals such as GaAs or GaP or liquid phase epitaxial growth such as GaP or GaAs. Gallium is recovered as a by-product from the buyer's solution for the production of alumina from bauxite or from the retort residue of zinc distillation of zinc blende or the sulfuric acid leaching residue of zinc roasting ore, and the recovered oxide After dissolving gallium in caustic soda solution,
Produced as 98-99% low purity gallium by electrowinning. This low-purity gallium is further purified by a combination of vacuum heating purification, acid washing, and recrystallization.
It is highly purified to 9.9999% or more.

On the other hand, as a scrap containing gallium, an end face cut portion of GaAs or GaP single crystal,
There are broken wafers, cutting waste, lapping waste, exhaust gas in the vapor phase epitaxial growth process, used gallium in the liquid phase epitaxial growth process, and damaged wafers after circuit formation. These gallium scraps are highly purified by vacuum purification, electrolytic purification, acid cleaning, and recrystallization purification steps alone or in combination, and used again as a compound semiconductor crystal or a raw material for liquid phase epitaxial growth.

Electrowinning or electrolytic refining is a method in which gallium oxide or gallium hydroxide is dissolved in an aqueous solution of caustic soda as an electrolytic solution, and gallium is deposited and collected on a cathode by electrolysis using platinum, carbon or stainless steel as an electrode. . The gallium concentration in the electrolyte is 30% or less,
Sodium hydroxide concentration is 30-50%, maximum 2000
Electrolyze at a current density of A / m ² .

The main purpose of electrowinning is to deposit gallium from gallium oxide or gallium hydroxide as a raw material, and its purity is limited to 99%. Electrorefining is performed with the aim of obtaining a higher purity of 99.99%. Hg, Al, Zn, Pb, etc. can be reduced by electrowinning or electrorefining, but it is difficult to precisely control the adhesion and entrainment of the electrolytic solution and the electrolysis conditions. The purity of the gallium obtained is 99.99%
Is the upper limit.

[0006] Vacuum heating purification is a method of evaporating and removing impurities having a higher vapor pressure than gallium by utilizing a difference in vapor pressure. It is possible to heat metallic gallium to a temperature of 1000 ° C. or higher at a degree of vacuum of 1.3 × 10 ⁻³ Pa or lower, and reduce impurities such as Hg and Zn having a high vapor pressure to 1 ppm or lower. However, in the case of impurities having a small vapor pressure difference from gallium, the impurities are easily mixed from the container because they are heated to a higher temperature, or loss due to evaporation of gallium is caused. Further, when the impurities form an intermetallic compound, it is difficult to make the value lower than several ppm.

[0007] Acid cleaning is a method in which gallium in a molten state is brought into contact with hydrochloric acid, nitric acid, or a mixed acid thereof to elute impurities having a high ionization tendency into acid, thereby increasing the purity. The acid diluted to 0.001 to 0.1 mol / dm ³ is brought into contact with gallium by stirring or the like to promote the elution of contained impurities. The stronger the stirring, the more the contact increases, so that the purification effect can be obtained in a short time. With this method, it is possible to reduce Ca, Zn, Cd, and the like.

However, with continued vigorous stirring, the acid solution becomes a black suspension. The black substance in the suspension is composed of gallium fine particles and a gallium oxide or hydroxide film formed on the surface thereof and is acid-soluble. Impurities are concentrated in the gallium oxide or hydroxide film on the surface of the gallium fine particles, and in order to obtain high-purity gallium,
The gallium particles need to be completely separated. Further, it is necessary to collect the separated gallium fine particles in order to improve the yield, which is a disadvantage in increasing the productivity.

[0009] Recrystallization is a method of concentrating impurities in a melt by utilizing the difference in segregation coefficient when crystallizing a crystal from a gallium melt to increase the purity of a solidified portion. Recrystallization techniques include directional solidification, zone melting, and single crystal growth. Unidirectional solidification is a method in which molten gallium contained in a vessel such as a boat is slowly cooled and solidified from one end to concentrate impurities in the melt. The cooling rate affects the segregation of impurities, and the lower the cooling rate, the higher the purification efficiency. However, if the cooling rate is reduced, the productivity is reduced and the cost is increased.

[0010] Zone melting is a method in which a large number of directional solidifications are continuously performed by a single operation, so that the low productivity of the directional solidification can be improved. When the number increases, the control becomes difficult, and the productivity has not been significantly improved. For this reason, recrystallization is used as a final purification step to reduce impurities that are difficult to remove by vacuum heating purification, electrolytic purification, and acid washing, but has a disadvantage of poor productivity. Principal elements to be purified by recrystallization include lead, indium and the like.

[0011] For low purity gallium of about 99.99% and scrap from liquid crystal epitaxial growth, the purity is generally increased to 99.9999% or more by vacuum heating purification, acid cleaning, and recrystallization to increase the purity. Gallium has been obtained.

[0012]

In the conventional method of purifying gallium, gallium has been highly purified by combining the above various methods according to the kind and amount of impurities contained in gallium. As described above, since a method of combining a number of purification steps optimal for the properties of impurities has been used, the conventional gallium purification method has many steps and is extremely complicated. In particular, impurities such as lead are difficult to remove by vacuum heating or acid cleaning, and generally have been removed by a recrystallization method, but the cost is high due to low productivity.

According to the present invention, gallium having a purity of at least 99.9999%, which can remove impurities such as lead without using a recrystallization method, has high productivity, and can be used as a semiconductor raw material, can be obtained at low cost. It is an object of the present invention to provide a method for purifying gallium that can be performed.

[0014]

In the method of purifying gallium according to the present invention, zinc is added to gallium, heated and maintained at 420 to 910 ° C. in an argon or nitrogen atmosphere, and then 800 to 1000 ° C. while being evacuated. The above-mentioned subject is solved by heating after heating and filtering. Zinc is thought to form an azeotrope with the impurities in gallium, making it possible to evaporate and remove high-boiling metals such as lead at lower temperatures than their original boiling point.

[0015] Gallium is put in a quartz container, and zinc is added thereto. Zinc is easy to handle in granular form, and the particle size is 10 μm to 5
mm is appropriate. The amount of zinc added depends on the amount of gallium charged and the impurity concentration, but is generally 50% of the total impurity amount.
~ 200 times better. If the amount is less than this range, the removal efficiency will be reduced, and it will be necessary to take a long time for removal or to increase the stirring intensity. On the other hand, if it exceeds this range, it takes a long time to remove zinc.

Next, the quartz container is set in an electric furnace, and the inside of the furnace is replaced with argon or nitrogen.
Heat to 0 ° C. and hold. Gallium and zinc melt, so
Mixing and stirring are carried out in order to efficiently bring the impurities into contact with zinc. Replacing the furnace with argon or nitrogen is
This is to prevent oxidation of zinc and gallium. In general, oxidation depends on the moisture in the atmosphere, so that dehumidified air may be used if the oxidation resistance of the furnace body and the heater is sufficient. It is appropriate to introduce argon or nitrogen at a rate of 500 to 1000 ml / min from the heating process to the heating and holding, but it is adjusted and controlled in consideration of the size of the furnace and the filling amount of gallium.

The heat holding temperature is set at 420 to 910 ° C. When the heat holding temperature is lower than 420 ° C., since zinc is a solid, the rate of diffusion reaction with impurities is low,
When the temperature is higher than 0 ° C., zinc is evaporated from gallium due to a high evaporation rate, and in any case, a purification effect cannot be expected. The heating and holding time is usually 1 to 5 hours, but it is necessary to control it according to the content of impurities and the charged amount of gallium.

As the stirring method, gas blowing stirring, impeller stirring and the like are appropriate, but the stirring method must not be so vigorous that gallium droplets are generated. The stirring time is preferably performed continuously from the heating process of the furnace to the end of the vacuum heating. If the stirring time is short, the probability of contact of the zinc with the impurities is reduced, and evaporation of zinc and the impurities is delayed by vacuum heating in the next step, so that a sufficient purification effect cannot be expected.

It is expected that zinc gradually dissolves in gallium as the temperature of the furnace rises, becomes a homogeneous melt by stirring, and becomes an azeotrope with lead in gallium. After the gallium to which zinc is added is heated and maintained at 420 to 910 ° C., the introduction of argon or nitrogen is stopped, and heating is performed at 800 to 1000 ° C. for 1 to 5 hours while the furnace is evacuated, so that lead evaporates simultaneously with zinc. The degree of vacuum is suitably 0.13 Pa, but is not limited thereto. When the degree of vacuum is increased, impurities are easily separated by evaporation, but the evaporation loss of gallium also increases. If the degree of vacuum is low, the removal of impurities is insufficient.

Gallium has a boiling point of 2403 ° C., whereas lead has a boiling point of 1750 ° C. and zinc has a boiling point of 907 ° C. When lead is evaporated and removed by ordinary vacuum heating, the loss of gallium evaporation increases.However, it is thought that an azeotropic mixture of lead and zinc is formed by adding zinc, and the evaporation proceeds almost at the boiling point of zinc. Can be Excess zinc can be removed by evaporation by vacuum heating and easily separated from gallium.

After the gallium is cooled to 30 to 80 ° C. in a furnace, it is suction-filtered with a filter cloth to remove residual zinc crystal grains and an oxide film floating on the gallium surface. As the filter cloth, a polyester or polypropylene non-woven cloth is used, and it is appropriate to perform filtration while controlling the filtration speed. As a vacuum pump for suction filtration, it is preferable to use a diaphragm pump to prevent contamination. However, the filter device is not limited to these as long as it can capture and separate the fine particles in gallium.

By the above-described operation, impurities such as lead, which have been usually utilized by the recrystallization method, can be removed by the vacuum heating purification method, so that an improvement in productivity can be realized.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Gallium (Ga 99.999% or more, Pb less than 10 ppm) is melted by heating to a temperature of 30 ° C. or more using an electric heater or an infrared lamp. Put gallium in a quartz container and add 1 kg of gallium
Of zinc (average particle size 0.1 mm). After the quartz container is placed in an externally heated vacuum heating furnace, a quartz impeller is inserted into gallium. The quartz impeller is rotated by an electric motor installed outside the furnace body via a vacuum bearing. The rotation speed is 6-1
0 rpm is suitable, but not limited thereto.

The pressure in the vacuum heating furnace was gradually reduced to 0.13 Pa by an oil rotary vacuum pump, and then 1000 ml / mi.
Nitrogen is introduced at about n, and gas replacement is performed. When the inside of the vacuum heating furnace becomes atmospheric pressure, the leak valve is opened and nitrogen is continuously flowed. Next, the vacuum heating furnace is heated to 420 to 910 ° C. for 10 minutes.
The temperature is raised at a rate of ° C./min, and the temperature is maintained for 2 hours. It must be arbitrarily changed in accordance with the temperature rising rate, the heating holding time, the impurity amount, and the gallium charged amount. Then close the leak valve,
The heating temperature is adjusted to 800 to 1000 ° C. at a rate of 10 ° C./min while the pressure inside the vacuum heating furnace is reduced to 0.13 Pa by an oil rotary vacuum pump, and heating is maintained for 2 hours. Zinc and lead become vapor and aggregate on the water-cooled cooling plate installed in the vacuum heating furnace.

After the heating is completed, the furnace is cooled, and after confirming that the gallium melt temperature has reached 50 ° C., the vacuum heating furnace is opened, the quartz container is taken out, and a polypropylene nonwoven fabric is adhered and fixed as a filter cloth. Using the prepared Buchner funnel, perform suction filtration.

[0026]

EXAMPLES [Example 1] Gallium (Ga 99.999%
As described above, Pb 5.7 ppm) uses an infrared lamp,
Heat and melt. 5 kg of gallium is put in a quartz container, and 2 g of zinc (average particle size: 0.1 mm) is further added. After the quartz container is placed in an externally heated vacuum heating furnace, a quartz impeller is inserted into gallium. The rotation speed of the quartz impeller is 6 rpm.

After the pressure in the vacuum heating furnace is slowly reduced to 0.13 Pa by an oil rotary vacuum pump, nitrogen is introduced at 1000 ml / min to perform gas replacement. When the inside of the vacuum heating furnace becomes atmospheric pressure, the leak valve is opened and nitrogen is continuously flowed.
Next, the temperature of the vacuum heating furnace is increased to 800 ° C. at a rate of 10 ° C./min, and heated and held for 2 hours.

Thereafter, the leak valve is closed, and the pressure in the vacuum heating furnace is reduced to 0.13 Pa by an oil rotary vacuum pump while reducing the pressure to 10 Pa.
Heat to 1000 ° C at a rate of ° C / min and maintain that temperature for 2 hours. Zinc and lead become vapor and aggregate on the water-cooled cooling plate installed in the vacuum heating furnace. After the heating was completed, the furnace was cooled, and after confirming that the gallium melt temperature reached 50 ° C., the vacuum heating furnace was opened, the quartz container was taken out, and a Buchner funnel with a polypropylene non-woven fabric bonded and fixed as a filter cloth was used. , And suction filtration was performed.

The concentration of Pb in the purified gallium collected by filtration was measured with a glow discharge mass spectrometer to find that it was 0.01 ppm.
Met. The gallium recovery was 99.5%.
Example 2 The operation was performed in the same manner as in Example 1 except that the heating in a nitrogen atmosphere before starting the vacuum heating was 450 ° C.

The concentration of Pb in the purified gallium collected by filtration was measured with a glow discharge mass spectrometer to find that it was 0.03 ppm.
Met. The gallium recovery was 99.6%.
Example 3 Except that the temperature during vacuum heating was set to 800 ° C.
The same operation was performed as in Example 2. The Pb concentration in the purified gallium collected by filtration was 0.02 ppm as measured by a glow discharge mass spectrometer. Gallium recovery is 99.8
%Met.

[0031]

According to the method for purifying gallium of the present invention, impurities such as lead, which have been generally removed by a recrystallization method, can be removed by a vacuum heating purification method. The productivity of gallium of 0.9999% or more is improved, and the cost can be reduced.

Claims (1)

[Claims] 1. Gallium which is characterized in that zinc is added to gallium, heated and maintained at 420 to 910 ° C. in an argon or nitrogen atmosphere, heated at 800 to 1000 ° C. while being evacuated, and then filtered. Purification method.