JPH0426728A - Manufacture of high purity in - Google Patents

Abstract

PURPOSE:To manufacture high purity In even including no elements hard to volatilize by subjecting In to vacuum baking, thereafter providing it with a temp. difference in the vertical direction, executing solidification from the lower part to the upper part, segregating included impurities on the surface of In and removing them. CONSTITUTION:In is housed in a boat, is subjected to heating treatment in vacuum at about 850 to 1000 deg.C for about 30min to 3hr and is subjected to vacuum baking. In this way, volatile elements such as oxides as well as Mg, Cu, Zn or the like are removed. After that, a temp. difference is provided by about >=10 deg.C/cm in the vertical direction of the boat in which the above In has been housed, and the In is cooled to about 250 deg.C at a certain cooling rate of about 5 to 150 deg.C/hr. Next, the In is furthermore cooled from the above temp. and is solidified from the lower part of the boat to its upper part. In this way, impurities such as the elements board to be volatilized such as Si, Fe, Cr, Al or the like included in the In are segregated in the vicinity of the surface of the In. Then, this segregated impurities are subjected to chemical etching by a water soln. including hydrochloric acid and H2O2 and are removed. In this way, the high purity In of about >=6N can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for purifying raw materials used for compound semiconductor crystal growth, and relates to a method for producing highly purified In.

(Prior art) Purity 99% is used as a raw material for crystal growth of high-purity InP.
．． 9999% In and P is commonly used. Furthermore, in order to increase the purity of the raw material In, vacuum baking or baking in a hydrogen atmosphere has been performed as a pretreatment. In this case of vacuum baking, usually I
Baking is performed at a vacuum level of 10-' Torr or higher and a baking temperature of 850° C. or lower for about 1 to 5 hours. This baking treatment is said to be effective in removing oxides and volatile elements.

(Problem to be solved by the invention) However, in the conventional vacuum baking method, SL.

A method for removing elements that are difficult to volatilize, such as Fe, C:r, and Aβ, has not been elucidated. Furthermore, these impurities could not be completely removed by baking treatment alone.

The present invention overcomes the drawbacks of the conventional vacuum baking method and removes SL, Fe, Cr, and Ag contained in high-purity In.
The purpose of the present invention is to provide a method for removing elements that are difficult to volatilize.

(Means for Solving the Problems) That is, the present invention provides that after vacuum baking In,
A temperature difference is created between the top and bottom of the boat containing n, and the temperature is cooled at a constant cooling rate to approximately 250°C, and the In is further cooled from this temperature to solidify from the bottom of the boat to the top of the boat. The present invention provides a method for producing high-purity In, which is characterized in that impurities contained therein are segregated near the surface of In, and then the segregated impurities are removed by chemical etching.

Next, embodiments of the present invention will be described with reference to the drawings.

Vacuum baking of In in the present invention is shown in Figures 1 and 2.
This can be carried out using the apparatus shown in the figure.

FIG. 1 is a side view (partially sectional view) of an apparatus for performing vacuum baking. In the figure, 1 is a vacuum apparatus, and one end of a quartz tube 2 is connected to the upper side surface of the vacuum apparatus. Inside this quartz tube 2, a PBN boat 3 is installed at a predetermined position, and In4 is housed in this.

Next, 5 is an electric furnace, which is installed on a pedestal 6 and is movable by casters 8.8 provided on the pedestal.
By moving this, it is possible to insert the quartz tube 2 into the electric furnace. As shown in the cross-sectional view of FIG. 2, the electric furnace 5 has a furnace core tube passing through its center.
Heaters 9 are provided above and below. This heater 9 is divided into multiple parts in the direction of penetration of the furnace core tube.

A method for purifying In using the above apparatus will be explained.

First, the inside of the vacuum device 1 is vacuumed (for example, vacuum degree I
After setting the electric furnace 5 to caster 8
．． 8 to the left, and the electric furnace is moved until the boat 3 is located at a predetermined position on the furnace core tube 10 of this electric furnace. Once the boat is in a predetermined position, heating begins.

FIG. 3 is an example of a temperature graph of this vacuum baking. As shown in Figure 3, first, the target temperature was 10
Raise the temperature to 00°C and hold at this temperature for 1 hour.

In the above example, the baking temperature is 1000°C for 1 hour, but in the present invention, the baking temperature is preferably 850 to 1000°C, and the holding time is preferably 30 minutes to 3 hours.

The electric furnace 5 is longer than the length of the boat 3 and can be heated uniformly in the lateral direction.

FIG. 4 is a diagram showing the temperature distribution of the boat portion containing In during vacuum baking holding. At this time, the temperatures T, T2 at the bottom and top of the boat are equal. Then, after a predetermined period of time, the In is cooled to around 250° C. at a constant cooling rate. The reason why the temperature is set at around 250° C. is that since the melting point of In is 156° C., impurities are segregated before reaching this temperature.

At this time, the power of the upper and lower divided heaters is adjusted so that there is a temperature gradient of 10° C./cm or more between the upper and lower parts of the boat part.

FIG. 5 is a diagram showing the temperature gradient at the top and bottom of the boat after cooling has started. Cooling is started in this state where there is a temperature gradient in the vertical direction of the boat.

FIG. 6 is a diagram showing the cooling process from around 250° C. (bottom of the boat).

First, relatively fast cooling, preferably between 5'C/hr and 15°C, until the temperature of the boat section reaches at least 250°C.
It is carried out at 0°C/hr. If the cooling rate is too fast, impurities will
This is because it remains inside or at the bottom, weakening the effect of the subsequent cooling step. From the above temperature, while maintaining scorching heat in the lateral direction and maintaining a constant temperature difference in the vertical direction of the boat, a constant solidification rate is usually 3 to 6 m.
In is gradually solidified from the bottom of the boat toward the top at a solidification rate of m/hr, preferably 2 to 3 mm/hr. This solidification method removes impurities that are difficult to volatilize.
It can be made to precipitate near the surface of n.

It is thought that the slower the solidification rate, the more impurities can be sufficiently segregated on the surface (the impurities contained in In include Zn, Si, F
e, Cu, S, etc., and these have a segregation coefficient of 1 in In.
Because it is smaller, when In solidifies, it is expelled to the outside). If the solidification rate is too high, impurities will be left inside the In and difficult to diffuse to the surface.

The impurities in In are removed by the above vacuum baking process.
Precipitates near the surface of n. After baking, the In-containing boat is chemically etched to create an In-containing boat.
Remove impurities adhering to the surface. Chemical etching can be carried out by conventional methods. There are no particular restrictions on the etching solution, but for example, 1 portion each of hydrochloric acid, hydrogen peroxide, and water.
: Mix at a ratio of 1:3 and immerse the entire boat into a container containing this liquid. The etching time varies depending on the size of the boat and is not particularly limited, but is usually about 30 minutes or more. After etching is completed, it is preferable to carry out water replacement over a period of about 2 hours while adding ultrasonic cleaning with deionized water.

Note that the etching solution is not limited, and in addition to hydrochloric acid-based solutions, nitric acid, aqua regia, sulfuric acid-based solutions, etc. can be used.

In which the purity has been increased in this way is used for the InP crystal component in the same manner as in the conventional case. In crystal is charged into a quartz ampoule together with red phosphorus (purity 99.9999%),
InP crystals are grown by a temperature gradient solidification method.

FIG. 7 is a diagram showing the temperature distribution for growing InP crystals by the temperature gradient solidification method using the quartz ampoule.

That is, the temperature of the boat part 3 is set to the melt temperature of 1062 degrees Celsius and the red phosphorus temperature of 545 degrees Celsius, and after synthesizing the InP melt, a constant temperature gradient (4~b) is set from the end of the boat to the heater power of the electric furnace. The adjustment electrically moves the temperature from one end of the boat to the other to solidify the crystals.

There are no particular restrictions on the boat for growing the InP crystal, and in addition to the PBN boat, a quartz boat (surface roughened to prevent In from getting wet on the boat) can be used.

Although the method of the present invention is suitable for In, it is also applicable to the purification of other metals such as Zn and Sn.

(Example) Next, the present invention will be explained in more detail based on examples.

Example 1 Raw material In(6N) (
Purity 99.9999% with impurities such as Mg and Aj! , S
(containing i, Fe, Cu, and Zn) was subjected to high purification treatment.

Approximately 1.5 kg of the above In raw material was placed in the PBN boat shown in Figure 1.
g, and the vacuum degree of vacuum device 1 is I.
After reaching X 10-7 Torr, the electric furnace 5 is moved and the boat is vacuum baked. As shown in FIG. 3, the heating was performed by first raising the temperature to a target temperature of 1000° C. over about 4 hours and maintaining this temperature for 1 hour. Cooling was started after 1 hour, and at this time the power of the upper and lower divided heaters was adjusted so that a temperature gradient of 10° C./cm or more was created between the upper and lower parts of the boat part, as shown in FIG. Cooling was started in this state where there was a temperature gradient in the vertical direction of the boat. Until the temperature of the boat reaches 250℃, the cooling rate is 125℃.
Cooling was performed at °C/hr. From around 250℃, In is gradually solidified from the bottom of the boat to the top at a solidification rate of 3 to 6 mm/hr while maintaining uniform heat in the lateral direction and a constant temperature difference in the vertical direction of the boat. It was. By such a solidification method, impurities that are difficult to volatilize were precipitated near the surface of In. After baking, In
Add chemical etching to the boat containing the I
Remove impurities attached to the surface of n. The etching solution is a mixture of hydrochloric acid, hydrogen peroxide, and water in a ratio of 1:1:3, and the boat is immersed in a container containing this solution. Etching time is approximately 30 minutes. After the etching was completed, water was replaced over a period of approximately 2 hours while ultrasonic cleaning was performed using deionized water. After replacing the water, the water is dried in a clean box through which purified nitrogen is circulated.

After sufficiently drying, place it in a quartz ampoule for growth.
Vacuum baking was performed at a temperature of about 00°C for about 30 minutes. Thereafter, as shown in Fig. 7, red phosphorus (purity 99.9999%) was put into this quartz ampoule, and I
It was sealed off at a vacuum level of 0-'Torr. Using this quartz ampoule, InP crystal was grown by the temperature gradient solidification method as shown in FIG.

A wafer is cut out from the center of the grown InP crystal ingot, and the wafer is subjected to mass spectrometry (85MS measurement).
The results are shown in Table 1. As a result, the concentration of impurity elements contained in the raw material In was significantly reduced, and this effect was recognized.

Table 1 (Note) The unit is ppmw, and other elements were below the detection sensitivity.

(Effect of the invention) According to the present invention, commercially available In (purity 99.9999%)
It is extremely effective for growing high-purity 1nP crystals.

[Brief explanation of drawings]

Figure 1 is a side (partial) view of an apparatus for vacuum baking In, Figure 2 is an enlarged sectional view of the electric furnace, and Figure 3 is the temperature process during vacuum baking. Figure 4 is a graph showing the temperature distribution of the In-containing boat section during vacuum baking retention, Figure 5 is a graph showing the temperature gradient at the top and bottom of the boat after cooling has started, and Figure 6 is a graph showing the temperature distribution of the boat containing In during vacuum baking. FIG. 7 is a diagram showing the cooling process from the vicinity of .degree.

Claims (1)

[Claims] After vacuum baking the In, a temperature difference is created in the vertical direction of the boat containing the In, and the temperature is kept at a constant cooling rate for about 25 minutes.
The In is cooled to 0°C and further cooled from this temperature to solidify the In from the bottom of the boat to the top of the boat, and the impurities contained in the In are segregated near the surface of the In. Then, the segregated impurities are removed by chemical etching. A method for producing high-purity In, the method comprising removing In.