JPS63250428A - Method for purifying indium - Google Patents

Abstract

PURPOSE:To efficiently purify In by heating In to reduce In2O3 contained therein to In2O and sublimating or evaporating the same, then heating up the In2O further to remove residual impurities therefrom. CONSTITUTION:The metallic In is heated in a 1st heating temp. region to denature the In2O3 in the In by the reduction reaction to the In2O which is then sublimated or evaporated. The In is heated in the 2nd heating temp. region to remove the remaining In2O and residual impurity elements such as S and Si therefrom. An equally good practice is to remove the remaining trace oxides by providing the 3rd temp. region during the time when the above-mentioned 1st temp. region is shifted to the 2nd region and maintaining this temp. region for a short period. A vacuum or inert gaseous atmosphere is preferable if a vessel for storing the In melt is made of quartz glass and a vacuum, inert gaseous or reducing gaseous atmosphere is preferable if said vessel is made of a carbon system. The 1st temp. region is adequately 400- below 700 deg.C and the 2nd temp. region 700-1,100 deg.C. The purified In suitable as a raw material for compd. semiconductors, etc., is obtd. by the above-mentioned method.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is applicable to indium phosphide (Ir+P), indium gallium arsenide (InGaAs), and indium gallium arsenide phosphide (Ir+P), which are suitable as materials for semiconductor optical devices, for example.
The method for purifying indium, which is the raw material for m-v group compound semiconductors such as InGaAsP, is particularly concerned with heat-treating the metal in multiple temperature ranges to eliminate oxides and oxides mixed and dissolved in the metal. This invention relates to a method for efficiently removing impurities, etc.

"Conventional technology" In recent years, with the shift to long-wave technology in optical transmission systems,
．． 8) InP with a band gap in the t and ta bands,
Crystals in thin films of m-v group compound semiconductors such as InGaAs and InGaAsP are attracting attention, but when forming a thin film optical device using this type of semiconductor, it is necessary to reduce the carrier density of the thin film layer. For this purpose, the semiconductor must be manufactured after removing as much as possible residual impurity metals such as indium oxide, sulfur, and silicon present in the indium constituting the compound semiconductor to achieve high purity.

Also, semi-insulating InP, InGa with extremely high resistance value
In-based thin films such as As, InGaA, and sP are important as substrate materials for devices or device isolation thin films that electrically isolate between devices.In order to make this type of thin film high in resistance,
Ice is known in which transition metals such as iron and nickel are added to a thin film and the deep levels formed by these transition metals are utilized. , which prevents the thin film from increasing its resistance and makes it impossible to obtain desired characteristics.

Therefore, when producing the above-mentioned ■-v group compounds, it goes without saying that it is extremely important to establish a technology for refining indium, which is the raw material, to a high degree of purity. As a technology, conventionally J, A, Ad
amski et al. (Journal of Crystal
Growth, Vol. 64, p. 1, 1983), etc., the impurity-containing metal indium is
The residual impurities were removed by heating to 800° C. or higher in a vacuum atmosphere and keeping the heating temperature constant for several hours or more.

[Problem to be solved by the invention] The surface of commercially available metallic indium lumps before refining is covered with indium oxide produced by oxidation by oxygen in the air, and there is also some metallic indium inside the metallic indium. Indium oxide is generated or mixed during indium production, and such oxides are generally treated with hydrochloric acid,
It is removed by cleaning with an acid such as nitric acid, but
It cannot be completely removed, and even if it is completely defeated, the surface of the metal indium lump is often oxidized after cleaning and before the purification, so that it may be mixed into the metal indium lump. It is necessary to remove the oxides contained during the purification process.

However, metallic indium purified by the above-mentioned purification method can be determined by mass spectrometry of metallic indium after purification.
Alternatively, it has been confirmed that the electrical properties of a compound semiconductor manufactured using purified metallic indium as a raw material are effective in removing residual impurity metals other than indium oxide, such as sulfur and silicon. There was hardly any decrease in the amount of indium oxide floating on the metallic indium melt due to heating and melting.

For this reason, the technology aims to reduce and remove indium oxide and remove residual impurity metal by purifying the metal indium lump by holding it at a temperature of 800°C or higher in an atmosphere of reducing gas such as hydrogen gas. has been proposed, but
Even in this method, it is difficult to completely remove indium oxide present in large quantities on the surface of the heated and melted metal indium melt, and the quartz crucible used as a container for the indium melt is Si that reacts in a gas atmosphere and is liberated from the container by the reaction,
Since SiO is mixed into the metallic indium melt, a problem arises in that the effect of removing residual impurity metal is reduced. For this reason, attempts have been made to use a carbon container as the container, but these efforts have not been effective in removing the large amount of indium oxide present on the surface of the metallic indium melt.

For this reason, in conventional technology, a compound semiconductor polycrystal is manufactured using metallic indium mixed with indium oxide, and the crystal is grown by a liquid confinement pulling method, etc., while allowing some residual indium oxide. However, since indium oxide is insoluble, the presence of indium oxide in a compound semiconductor polycrystal reduces the single crystallization rate of the semiconductor, making it impossible to accommodate larger diameter single crystals. There was a point.

In view of the drawbacks of the prior art, an object of the present invention is to provide an indium purification method that can efficiently remove indium oxide along with residual impurity metals such as sulfur and silicon.

"Means to solve problems" First, the solution procedure that led to the present invention will be explained next.

Indium oxide is normally pressure trivalent indium oxide (1n
203), and such In20i,
Sublimes at temperatures above 850°C, but the rate of sublimation is slow;
Further, according to experiments conducted by the present inventors, it has been found that at temperatures higher than around 800° C., a kind of state change occurs in In2O3, and the rate of sublimation becomes extremely low.

Therefore, as explained in the "Problems to be Solved by the Invention" section, at a temperature of around 850°C, at which residual impurity metals can be removed, most of the In2O3 cannot be removed from the metallic indium even if held for a long time. do not have.

On the other hand, it is known that positive monovalent indium oxide (In20) has a lower melting point and higher volatility than positive trivalent indium oxide (In203), and according to the inventor's experiments, In20 It has been confirmed that sublimation occurs at temperatures of 560 to 700°C in vacuum.

Note that indium oxide includes positive divalent indium oxide (In
O) is also considered, but it can be ignored because it decomposes into a positive monovalent or positive trivalent oxide.

Therefore, in the present invention, in a first heating temperature range, the product of the positive trivalent indium present in the indium is transformed into a positive monovalent oxide by a reduction reaction, and the oxide is sublimed or evaporated. After that, a purification method is proposed in which residual impurity elements present in the indium are removed in a second heating temperature range.

In this case, the heating temperatures in the first heating temperature range and the second heating temperature range do not necessarily need to be constant, and may be varied.

Further, the transition from the first temperature range to the second temperature does not necessarily have to be done quickly; for example, while the temperature is raised from the first temperature range to the second temperature range, the third heating temperature By providing a temperature range and holding the temperature range for a short time, trace oxides that could not be removed in the first temperature range may be removed. After once cooling and solidifying the indium in the state,
The temperature may be raised to a second heating temperature range.

Further, the purification steps in the first and second temperature ranges may be performed in a vacuum atmosphere, an inert gas atmosphere, or a different atmosphere for each temperature range. When a quartz glass container is used as a storage container, when purification is performed in a reducing gas atmosphere, the container reacts in the reducing gas atmosphere, and Si released from the container due to the reaction
, SiO is mixed into the metallic indium melt, which reduces the effect of removing residual impurity metal, which is not preferable.

Although a quartz tube is normally used as a reaction tube, even if the quartz tube is used for purification in a reducing gas atmosphere, Si will not be introduced into the indium melt, unlike in the case of a storage container that comes into contact with the indium melt. , The contamination of SiO is slight and poses no practical problem.

"action" The effect of the present invention will be explained using indium as an example.

As mentioned above, the positive trivalent indium oxide present in the totally bent indium undergoes a kind of state change at temperatures higher than around 800°C.

Also, according to the inventor's experiments, In and In under reduced pressure
It has been confirmed that In20 is produced and sublimated from a mixture of 2O3 through a reduction reaction, and sublimation occurs at a heating temperature range of 565 to 700°C in vacuum.

Therefore, in the present invention, the first temperature range is set to 700°C in vacuum.
Below, the lower limit temperature range is set to a temperature around 400° C. at which sublimation begins under vacuum.

Incidentally, since the temperature range in which In20 is produced by the reduction reaction and the temperature range in which it is sublimated almost overlap, the reduction reaction and the sublimation step are performed simultaneously.

According to experiments, the indium oxide removal effect in such a temperature range is most efficient at 600° C. under vacuum, and the oxide can be removed to the point where it cannot be detected by oral administration.

Although the removal effect depends on the amount of indium melt in the storage container, it is necessary to maintain the temperature for at least one hour after raising the temperature.

In addition, when heated for a long time, the effect is recognized from temperatures around 400°C, but it was confirmed that In20 hardly sublimes at temperatures below 400°C.

Further, in the temperature range of 700° C. to 800° C., although indium oxide decreases, indium oxide remains even if heated for a long time. This is considered to be because the state of the positive trivalent indium oxide changes in parallel with the above reaction.

Therefore, if the first temperature range is 700° C. or higher, the effect of removing indium oxide is reduced and the object of the present invention cannot be smoothly achieved.

In addition, after sufficient heating at a temperature of 700℃ or less,
Heating temperature above °C, e.g. 700 °C to 800 °C (3rd
By raising the temperature to (temperature range) and heating for 10 minutes or more,
Of the In20 generated from In2O3, a trace amount of In20 dissolved in metal indium can be evaporated, making it possible to more effectively remove the oxide. This means that once In20 is generated, it is chemically stable, and once the transformation from In2O3 to In20 is completed, it becomes possible to efficiently sublimate indium oxide in a higher temperature range.

Further, after removing the oxide in the temperature range if (and the third temperature range), the second temperature range is heated to 700°C, preferably 800°C.
As is known, by setting the temperature to 00° C. or higher, residual impurity metals such as sulfur and silicon other than indium oxide can be removed.

However, if the temperature range exceeds 1100°C, the evaporation of metallic indium becomes noticeable and the loss is large, so it is not realistic.In addition, even in the second temperature range, a trace amount of In20 dissolved in metallic indium The evaporation of is carried out in a controlled manner.

If both the first and second temperature ranges are performed in the same atmosphere, there is no need to provide a third temperature range by directly transitioning from the first temperature range to the second temperature range. However, if a reducing atmosphere is used in the first temperature range and an inert atmosphere is used in the second temperature range (in this case, Si contamination can be prevented), or for other reasons, the second temperature range is
If it is required to completely remove indium oxide before processing in a temperature range, a third temperature range is set following the first temperature range to perform the pre-process of indium purification Things are also reasonable.

Embodiment FIGS. 1 and 2 show a heating furnace used in a method for purifying metallic indium according to an embodiment of the present invention, and the apparatus configuration of such a heating furnace will be briefly described.

Figure 1 shows a vertical heating furnace that performs heating in a vacuum atmosphere, and a quartz ampoule 2 that houses a crucible 4 for storing metallic indium.
The ampoule 2 is extended vertically, and a vacuum port 1 for evacuating the inside of the ampoule 2 is provided at the upper end thereof, and an electric furnace 3 is surrounded around the outside of the ampoule 2 corresponding to the stirrup in which the crucible 4 is accommodated. .

On the other hand, FIG. 2 shows a horizontal heating furnace that performs heating under an inert gas atmosphere, in which an electric furnace 3 is surrounded on the outside, and a quartz tube 7 that houses the crucible 4 extends horizontally. Quartz tube 7
An inert gas such as argon gas is flowed from one side of the crucible 4 to purify the metal indium stored in the crucible 4 in an inert gas atmosphere.

As the crucible 4, in addition to a crucible made of quartz glass or graphite, a crucible made of pBN, AIM, or the like can be used.

Next, an example of the present invention using such a heating furnace will be described in detail.

c: ISi Example) The first example is an example in which metallic indium is purified in a vacuum atmosphere using the vertical heating furnace shown in FIG. After that, put it into a quartz ampule 4, store the crucible 4 inside the quartz ampoule 2, and attach it to the vacuum opening 1 x 10
After evacuation to a vacuum state of 4 Pa, the temperature of metallic indium was raised to 200"C in an electric furnace 3 and melted. A grayish-white indium oxide with a diameter of 1 to 1.5 cm was deposited on the surface of the metallic indium melt 5. 6 gathered and floated.

Next, when the electric furnace 3 was heated to 600° C. and heated for 1 hour, indium oxide 6 was no longer observed. During this time, the vacuum port 1 of the quartz ampoule 2 and the electric furnace 3
Adhesion of black In20 was observed in the area between the two. This indicates that the indium oxide 6 floating on the surface of the metallic indium melt was removed and attached to the quartz ampoule 2.

Next, when the temperature of the electric furnace was raised to 800℃, it became 80℃.
It was observed that the amount of black In20 adhering to the portion of the quartz ampoule 2 between the vacuum 01 and the electric furnace 3 rapidly increased over a period of about 30 minutes from 10 minutes after the temperature reached 0°C. This indicates that the indium oxide dissolved in the metallic indium melt was removed.

Then, the heating temperature of 800° C. was maintained for an additional 5 hours to remove residual impurity metals other than the oxides.

(Second Example) The second example is an example in which metallic indium is purified under an inert gas using the horizontal heating furnace shown in FIG. The crucible 4 containing the lump is housed in a quartz tube 7, and the electric furnace 3 is heated while flowing argon gas as an inert gas from one side of the quartz tube 7.
When metallic indium was heated to 200°C and melted, it turned out to be gold.

Gray-white indium oxide 6 gathered and floated on the surface of the indium-containing melt 5 in a layer of 1.5 to 20 layers in diameter.

Next, when the electric furnace 3 was heated to eoo°C and heated for 1 hour, the indium oxide 8 became small in diameter to about 0.5 cs, and when heated for another 1 hour, the indium oxide 6 was observed. lost. During this time, adhesion of black In20 was observed on the downstream side of the argon gas in the quartz tube 7. It is thought that 1n20 was vaporized from the surface of the metallic indium melt and was blown to the downstream side of the gas by the argon gas.

Next, when the temperature of the electric furnace was raised to 800℃, it became 80℃.
10 minutes after the temperature reached 0°C, black In20 was applied to the part of the quartz tube 7 on the downstream side of the argon gas for about 30 minutes.
It was observed that the amount of adhesion increased rapidly.

This indicates that the indium oxide dissolved in the metallic indium melt was removed.

Then, as in the previous example, the heating temperature was further increased to 800°C for 55 minutes.
The sample was held for a period of time to remove the remaining impurity metals except for the oxides.

(Third Example) The third example is an example in which metallic indium is purified using the vertical heating furnace in the first purification process and the horizontal heating furnace in the second purification process. Similarly, crucible 4 containing a lump of metallic indium washed with hydrochloric acid is housed in quartz ampoule 2, and attached to vacuum outlet LX 1 (14
After evacuation to a vacuum state of Pa, the temperature of metallic indium was raised to 200°C in an electric furnace 3 and melted, and gray-white indium oxide 6 with a diameter of 1 to 1.5 cm was collected on the surface of the metallic indium solution 5. Floated.

Next, when the electric furnace 3 was heated to 800°C and heated for 1 hour, the indium oxide 6 was reduced to a diameter of 0.3 to 0.5C, and when heated for another 1 hour, the indium oxide 6 is no longer observed. During this time, the first
As in the embodiment, the vacuum port 1 and the electric furnace 3 in the quartz tube 2
Adhesion of black In20 was observed in the area between the two.

Here, the metal indium was cooled until it solidified, and the crucible 4 was transferred into a quartz tube 7, and while flowing argon gas as an inert gas from one side of the quartz tube 7, the temperature of the metal indium was raised to 800 ° C. in an electric furnace 3. However, the temperature of the electric furnace is 80
For about 30 minutes from 10 minutes after the temperature reached 0° C., black In20 was observed to adhere to the portion of the quartz tube 7 on the downstream side of the argon gas, as in the second embodiment. Then, the heating temperature of 800° C. was maintained for an additional 5 hours to remove residual impurity metals other than the oxides.

(Fourth Example) The fourth example is an example in which metallic indium is purified using the horizontal heating furnace in the first purification step and the vertical heating furnace in the second purification step. Similarly, a crucible 4 containing a lump of metallic indium washed with hydrochloric acid was placed in a quartz tube 7, and while flowing argon gas as an inert gas from one side of the quartz tube 7, 20% of metallic indium was heated in an electric furnace 3.
When the temperature was raised to 0°C and melted, metallic indium melt 5
Gray-white indium oxide 6 gathered and floated on the liquid surface in a layer with a diameter of about 2C.

Next, when the electric furnace 3 was heated to 600°C and heated for 1 hour, the indium oxide 6 was reduced to a diameter of about 0.5 cm, and when heated for another 1 hour, the indium oxide 8 was observed. lost. During this time, similarly to the second embodiment, a black I was placed on the downstream side of the argon gas in the quartz tube 7.
Adhesion of n20 was observed.

Here, the metal indium is cooled until it solidifies, and the crucible 4
Transfer it to the quartz ampoule 2 and attach it to the vacuum port 1.
It was evacuated to a vacuum state of X 10 (Pa).

When metal indium was heated to 800°C in the electric furnace 3, the temperature of the electric furnace was 800°C as in the first embodiment.
For about 30 minutes from 10 minutes after the temperature was reached, black In20 was observed to adhere to the portion of the quartz ampoule 2 between the vacuum outlet 1 and the electric furnace 3. Then, the heating temperature of 800° C. was maintained for an additional 5 hours to remove residual impurity metals other than the oxides.

When the metallic indium purified in each of the above Examples was analyzed by emission spectrometry, no sulfur or silicon was detected. Further, as described above, the indium oxide that was attached to the surface of the metal indium lump and mixed inside the metal indium lump was also removed from the metal indium.

Note that the heating temperatures in the first heating temperature range of 400°C or more and less than 700°C and the second heating temperature range of 700°C or more and 1100°C or less do not need to be constant, for example, 400°C or more and less than 700°C. It is possible to continue to gradually raise the temperature within a temperature range of less than 0.degree. C. over a period of one hour or more.

Similarly, it is possible to continue increasing the temperature within a temperature range of 700° C. or more and 1100° C. or less, for example, for a period of 10 minutes or more.

(First Comparative Example) In order to confirm the effect in the first temperature range, metallic indium was heated to 200°C and melted in an electric furnace 3 under the same conditions as the first example. After floating the indium compound θ on the surface of the melt 5, the electric furnace 3 was
When the temperature was raised to 0°C and heated for 2 hours, no decrease in indium oxide θ and no black In2O adhesion was observed on any part of the quartz ampule 2, so the heating time was further extended to 6 hours. Similarly, no change was observed in the indium oxide 6 floating on the surface of the metallic indium melt.

(Second Comparative Example) Next, in order to confirm the effect in the second temperature range, metal indium was heated to 200°C and melted in an electric furnace 3 under the same conditions as in the first example. After floating the indium oxide 6 on the surface of the melt 5, the electric furnace 3 was
The temperature was raised to 0°C and heated for 1 hour to remove the indium oxide 6 floating on the surface of the metallic indium melt.Then, the temperature of the electric furnace 3 was gradually raised to 1100°C. Approximately 10 minutes after reaching 1100℃, I
Since evaporation of n became noticeable, heating was discontinued at that point.

"Effects of the Invention" As described above, according to the present invention, it is possible to efficiently remove indium oxide adhering to the surface of the raw metal lump and mixed inside it, along with residual impurity metals such as sulfur and silicon. As a result, the single crystallization rate of the compound semiconductor can be improved, and the factors that inhibit the decrease in carrier density of thin film optical devices formed using such a semiconductor can be eliminated.
Adding transition metals such as iron and nickel to thin films can contribute to increasing the resistance of semi-insulating thin film elements.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are both schematic cross-sectional views of an apparatus used in a method for purifying metallic indium according to an embodiment of the present invention.
FIG. 1 shows an apparatus configuration when purification is performed in a vacuum, and FIG. 2 shows an apparatus configuration when purification is performed in an inert gas. l: Vacuum port 2: Quartz ampoule 3: Electric furnace 4:
Crucible 5: Metallic indium melt 6: Indium oxide 7: Quartz tube 8: Argon gas Figure 1 Figure 2

Claims (1)

[Claims] 1) In a method for purifying indium, which is to be a raw material for compound semiconductors, etc., in a first heating temperature range, the positive trivalent indium oxide present in indium is purified by a reduction reaction. Purification of indium, characterized in that after the oxide is transformed into a monovalent oxide and the oxide is sublimated or evaporated, residual impurity elements present in the indium are removed in a second heating temperature range. Method 2) During the transition from the first temperature range to the second temperature range, a third heating temperature range is provided and this temperature range is held for a short time, thereby removing the material in the first temperature range. 3) A method for purifying indium according to claim 1, in which a trace amount of oxide that has not been removed is removed. 3) When a quartz glass container is used as a storage container for the indium melt, the purification is performed in a vacuum atmosphere. or the indium purification method according to claim 1 or 2, which is carried out in an inert gas atmosphere 4) When a carbon-based container is used as the storage container for the indium melt, 5) The method for purifying indium according to any one of claims 1 to 3, wherein the purification is performed in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere. Indium purification method 6 according to any one of claims 1 to 4, wherein the purification steps in the first temperature range and the second temperature range are performed in different atmospheres. ) The first heating temperature range is a temperature range of 400°C or more and less than 700°C, and the second temperature range is 700°C or more and less than 110°C.
Claims 1 to 5 which are in the temperature range of 0°C or less
Method for purifying indium as described in any one of the preceding paragraphs