JP2709272B2 - Measurement method of crystallization rate in sublimation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a crystallization rate in a sublimation method, and more particularly to a method for measuring a weight loss due to sublimation of a crystal raw material and a weight increase due to crystal precipitation as a weight transfer in a sealed tube.

[0002]

2. Description of the Related Art PVT (Physical Vapor Transporous) is used for purifying crystals and growing single crystals by a vapor phase method using a sealed tube.
t) method and CVT (Chemical Vapor Transport) method. In recent years, it is difficult to grow crystals by the melt method.
-Applied to the growth of Group VI compound semiconductor single crystals.

In the growth of ZnSe single crystals by the PVT method, large single crystals of about 10 mm square have been obtained (JOUR
NAL OF CRYSTAL GROWTH 94 (1989) P1-P5). In this method, 5 g of ZnSe polycrystal as a raw material and a ZnSe single crystal as a seed crystal are placed at both ends of a quartz sealed tube having a diameter of 20 mm and a length of 70 mm and sealed in a vacuum, and this quartz sealed tube is placed in an electric furnace. The polycrystalline material is set to about 1070 ° C. and the seed crystal is heated to about 1060 ° C. to grow a ZnSe single crystal on the seed crystal.

In the growth of ZnSe single crystal by the CVT method, a single crystal having a size of 14 × 14 × 20 mm has been obtained (JOURNAL OF CRYSTAL GROWTH 91 (1988) P639 to P646).
reference). This method uses a ZnSe powder of 10 g as a raw material, a ZnSe single crystal as a seed crystal, a diameter of 25 mm,
It is placed at both ends of a 50 mm long quartz sealed tube, and 5.4 mg of iodine is sealed in a vacuum with 5.4 mg of iodine per 1 cm ^{3 of the} inside volume of the sealed tube.
Then, the seed crystal is heated to about 840 to 845 ° C. to grow a ZnSe single crystal on the seed crystal.

[0005] The difference between the PVT method and the CVT method is that crystal growth in the PVT method proceeds according to the following reaction formula (I).
In the CVT method, since iodine is present in the quartz sealed tube, crystal growth proceeds according to the following reaction formula (II). ZnSe (s) → (←) Zn (g) + Se ₂ (g) (I) ZnSe (s) → (←) ZnI ₂ (g) + Se ₂ (g) (II)

When growing a single crystal by the PVT method or the CVT method, it is necessary to increase the growth rate as much as possible in consideration of productivity. However, when the growth rate exceeds a certain value, polycrystallization occurs (see the above-mentioned document). . Therefore, in order to maintain a high growth rate while avoiding polycrystallization, measurement of the growth rate is indispensable. However, in a method of growing a crystal in a sealed tube such as the PVT method or the CVT method, it has not been possible to measure the growth rate in the growth process. For this reason, it was not known whether the single crystal was growing or polycrystallized until the sealed tube was taken out after the growth was completed. Further, even in the case of refining a crystal raw material, it is impossible to estimate the end of the refining, so that the refining must be continued for an unnecessarily long time, and the productivity has been significantly impaired.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned drawbacks and to provide a measuring method capable of reliably measuring the crystallization rate in the sublimation method.

[0008]

The present invention has succeeded in solving the above-mentioned problems by employing the following constitutions. (1) A crystal raw material is vacuum-sealed at one end of a sealed tube, the sealed tube is inserted into a heating furnace, the crystal raw material is heated to a sublimation temperature, and a crystal deposition portion of the sealed tube is maintained at a crystallization temperature. In the method for measuring a crystallization rate during crystallization, a member serving as a first fulcrum is placed in the heating furnace, the sealed tube is placed on the member, and one end of the sealed tube is connected to the heating furnace. Extend out of the
A method for measuring a crystallization rate, wherein the extension is supported by a second fulcrum, and a change in weight applied to the second fulcrum is measured.

[0009]

According to the method for measuring the crystallization rate of the present invention, as shown in FIG. 1, a raw material is placed at the end of a tube with one end closed, and a sealed tube is formed with a sealing lid. , The intermediate portion of the tube is rotatably supported at a fulcrum 1 by inserting it into a heating furnace, the end of the tube extending outside the furnace is used as a fulcrum 2, supported by weight measuring means, and the raw material is heated and sublimated, and a sealing lid is provided. Crystals are deposited in the low temperature part on the side.
At this time, the weight applied to the fulcrum 2 changes due to the weight loss due to the sublimation of the raw material and the weight increase due to the crystal precipitation. Therefore, the change in the position of the center of gravity is measured, and the crystallization rate is calculated from the change.

Here, the distance between the two supporting points is L ₁ , the distance between the raw material and the crystal deposition position is L ₂ , and the raw material is W (g).
Assuming that only the sublimation occurs and the precipitate moves from the high temperature side to the low temperature side, the change in the weight on the fulcrum 2 is W × L ₂ / L ₁ (g)
Becomes Therefore, in order to improve the measurement sensitivity of the crystallization rate, the value of L ₁ / L ₂ may be reduced, and it is desirable that at least L ₁ / L ₂ be 1 or less. Note that the L ₁ / L ₂ = _1, is when the weight change is equal to the weight of the precipitated crystals.

The rate at which a crystal is purified or a single crystal is grown by the PVT or PCT method depends on the temperature of the entire sealed tube and the temperature difference between the crystal raw material side and the precipitated crystal side (the lowest temperature portion in the sealed tube) ( Hereinafter, referred to as ΔT). Therefore, in the method for purifying a crystal or the method for growing a single crystal of the present invention, the crystallization rate is optimized by raising or lowering the temperature of the entire sealed tube or adjusting ΔT based on the measured value of the crystallization rate. Perform control.

Further, as shown in FIG. 3, a thin tube is connected to the end of a sealed tube in which the crystal raw material is arranged, the constituent elements of the crystal are sealed in the end of the thin tube, and the heating temperature of the element is adjusted. The crystallization rate can be adjusted by controlling the vapor pressure of the element in the sealed tube. Therefore, this method can be used in combination with the above-mentioned crystallization rate optimization control method. Such a crystallization rate optimization control method
The use of the crystal growth method in the PVT method or the CVT method makes it possible to more reliably and efficiently grow a single crystal.

On the other hand, in the growth of a single crystal, it is important to minimize the number of nuclei generated when crystals are deposited at the end of the sealed tube. (It is ideal that the number of generated nuclei is 1.) In FIG. 4, the number of generated nuclei is suppressed by forming the sealing lid for forming the sealed tube into a conical shape. In FIG. 5, a seed crystal is arranged at the tip of the conical shape in FIG. 4 to facilitate the growth of a single crystal.

When crystal growth is performed using the above-mentioned conical encapsulation lid and keeping the crystallization rate (the rate of weight increase of the generated crystal) constant, the moving speed of the grown crystal surface becomes too fast in the initial stage of growth. Polycrystals are easily generated. Therefore, it is important to control the crystallization speed according to the conical shape so that the moving speed of the growing crystal surface is constant.

When a seed crystal is used, it is important to prevent the polycrystallization by removing the surface layer of the seed crystal by raising the temperature of the seed crystal to a temperature higher than the crystal raw material side before the start of growth to prevent subcrystallization. is there. Conventionally, the amount of removal of the surface layer could not be measured, so that the reproducibility of the removal of the surface layer and the single crystallization was poor. Since the removal amount of the layer can be measured easily and accurately, after removing the surface of the seed crystal by a predetermined amount, it is also easy to start the crystal growth by changing the temperature condition, and it Reproducibility has been improved.

One of the causes of a large variation in the growth rate when a single crystal or the like is grown by the PVT method or the CVT method is the polycrystalline composition of the raw material (ZnSe polycrystal).
And the ratio of Se). If the variation in the raw material composition is too large, the growth rate cannot be controlled to a predetermined rate only by controlling the temperature conditions.

Therefore, in the present invention, the polycrystalline raw material is preliminarily heated to a high temperature to be sublimated and sublimated, and the recrystallized polycrystalline raw material is used, or the polycrystal is previously pulverized into powder, and then the powder is placed in a vacuum. In a ZnSe crystal, 500 ° C. or more,
Heat for over 1 hour and use as raw material or ZnSe
In the crystal, ZnSe polycrystal synthesized by reacting hydrogen selenide and zinc vapor at a temperature of 500 ° C. or more is used as a raw material, thereby enabling crystal growth from a raw material with small composition variation and controlling the growth rate. It can be done more accurately. The above-described method is not limited to the purification of ZnSe crystals or the growth of single crystals, but may be used for ZnS, CdTe, CdS, etc.
It can be effectively applied to the growth of II-VI compound semiconductors.

[0018]

EXAMPLES As shown in Example 1 1, an inner diameter of 14 mm, filled with polycrystalline ZnSe starting material of from about 5g to the end of the quartz tube of the full-length 30 cm, 10 ^-6 the To
After evacuation to rr, the sealing lid was inserted, and vacuum sealing was performed so that the distance between the raw material and the sealing lid was 10 cm. The ZnSe polycrystalline raw material used was synthesized by heating and reacting Zn and Se in a quartz sealed tube having an inner surface coated with carbon, sliced into an appropriate size, and then etched with a boiling NaOH solution for 10 minutes. The sealed tube is, as shown in FIG.
It was inserted into a horizontal tubular electric furnace, and supported by a fulcrum 1 disposed inside a furnace core tube (inner diameter 30 mm) made of alumina of the electric furnace and a fulcrum 2 outside the electric furnace. As the fulcrum 1, as shown in FIG. 6, an alumina ring whose inside was machined to an acute angle was used. The fulcrum 2 was provided with an electronic balance capable of measuring a weight change with a measurement accuracy of 1 mmg.

Raise the temperature of the electric furnace to about 1020 ° C
The sublimation was carried out by heating to a temperature of about 1,000 ° C. at the surface of the sealing lid (the lowest temperature part in the sealed tube), and three purification experiments were performed to precipitate ZnSe crystals. The results are shown in FIG. .
In the temperature measurement, a thermocouple was used in which the inside of the furnace core tube was crawled so as not to touch the sealed tube. The weight of the purified product is twice the weight of the fulcrum 2 (multiplied by L ₁ / L ₂ = 2). FIG. 7 shows that the weight of the purified product increases in proportion to the purification time for each experiment. When the weight of the purified ZnSe finally taken out from the sealed tube was measured and compared with the measured value during the production, the measurement error was suppressed to 10% or less.

Example 2 A sealed tube filled with raw materials in the same manner as that prepared in Example 1 was placed in a furnace as shown in FIG. The distance L ₁ of the pivot 1 and the fulcrum 2 has close to 5 cm. In this case, an appropriate weight was attached to the fulcrum 2 in order to prevent the fulcrum 2 from rising from the balance of the weight of the sealed tube. Purification was carried out for 5 days by raising the temperature in the same manner as in Example 1. After 5 days, the amount of purified ZnSe removed from the sealed tube was 2.20 g. on the other hand,
Weight 0.5 measured during purification _{(L 1 / L 2 = 0.5} )
The weight of the purified product calculated by multiplying by 2.39 g was within 10% as in Example 1. In addition,
In Example 1, half the weight of the actually purified ZnSe was measured at the fulcrum 2, whereas in Example 2, twice the weight was measured, and the sensitivity was improved four times.

Example 3 In purifying a raw material by the method of Example 2, the purification rate was measured and calculated every day, and ΔT was adjusted so that the actual purification rate was maintained at 0.5 g / day. An attempt was made to control the temperature of the entire sealed tube up and down while keeping it constant. FIG. 9 shows the temperature on the side of the sealed tube lid. In order to keep ΔT constant,
The temperature on the raw material side and the temperature on the sealed tube lid side were raised and lowered by the same amount. As shown in FIG. 9, the results succeeded in maintaining the purification rate at approximately 0.5 g / day. If the temperature of the growth furnace is changed, the sealed tube expands and contracts.
When the temperature of the growth furnace was changed, the change in weight was calculated based on the weight after the temperature was stabilized (after 30 minutes). Therefore, the weight change for 30 minutes after the temperature was changed could not be measured, but this was not a problem since the measurement interval of the growth rate was one day.

[Example 4] When the raw material is purified by the method of Example 2, the purification rate is calculated every day, and the temperature on the raw material side is maintained such that the actual purification rate is maintained at 0.5 g / day. And the temperature on the side of the sealed tube was adjusted up and down. The results are shown in FIG. As is clear from the figure, the actual purification rate was successfully controlled at about 0.5 g / day. At this time, as in Example 3, the purification rate was calculated based on the weight 30 minutes after the temperature was changed.

Example 5 An inner diameter of 1.5 mm was placed on the raw material side of the sealed tube having an inner diameter of 14 mm shown in FIG.
A thin tube having a length of 50 mm was extended by 50 cm, and about 1 g of Zn was filled at the tip thereof. The other conditions were the same as in Example 1. A sealed tube prepared as shown in FIG. It was placed in the furnace so as to be 5 cm. Raise the temperature of the furnace, raise the temperature of the raw material to 1020 ° C, and raise the
Then, the temperature of Zn at the tip of the capillary was set to 500 ° C. Thereafter, as shown in FIG. 12, the purification rate was controlled to 0.5 g / day by raising and lowering the temperature of Zn.

Example 6 Instead of the sealed tube used in Example 4, as shown in FIG. 4, a single-crystal growth was attempted with a sealed tube lid having a conical shape. Crystal growth was performed for 2 weeks by controlling ΔT every 6 hours in the same manner as in Example 4 so that the growth rate during crystal growth was 0.5 g / day, and about 7 g of ZnSe crystal was obtained. . Table 1 shows the results of the same crystal growth performed 10 times. In 2 runs out of 10 runs, several grains were present at the tip of the conical shape, but one of them grew greatly to form a single crystal. In the fourth run, relatively large grains were obtained. However, in one run, ΔT is 5
Even when the temperature was increased to 0 ° C., the growth rate did not reach 0.5 g / day.

[0025]

[Table 1]

Example 7 In Example 6, instead of controlling the growth rate by controlling ΔT, the sealed tube with a thin tube shown in Example 5 was used. , And the crystal was grown 10 times by controlling the temperature of Zn during crystal growth to control the growth rate to 0.5 g / day. As a result, as shown in Table 2, almost the same results as in Example 6 could be obtained.

[0027]

[Table 2]

Example 8 In the growth of the single crystal of Example 6, as shown in FIG.
A single crystal was grown by disposing a ZnSe seed crystal at the tip of a conical sealed tube lid. The ZnSe seed crystal was obtained by cutting a (100) wafer having a thickness of 1 mm and a square of 5 mm from the single crystal ZnSe obtained in Example 6, polishing the surface with a diamond slurry having a particle size of 0.5 μm, and then polishing the surface with a boiling NaOH solution. One minute etched was used. The growth rate during crystal growth is 0.
Δ every 6 hours as in Example 6 so that 5 g / day
Crystal growth was performed over two weeks while controlling T. Table 3 shows the results of this crystal growth performed 10 times. Although the single crystal grew in 5 out of 10 runs, there were 2 runs in which the growth rate did not reach 0.5 g / day as in Example 6.

[0029]

[Table 3]

Embodiment 9 In Embodiments 6 and 8, the weight of the crystal growing per unit time (hereinafter referred to as the weight growth rate) was controlled to be constant. In a portion where the cross-sectional area of the portion is small, the amount of movement of the growth surface per unit time (hereinafter, referred to as growth speed) increases. Therefore, the sealed tube used in Example 8 is used, but while controlling the weight growth rate so that the growth rate is 1 mm / day along the solid line in FIG.
Crystal growth was performed over a week. The weight growth rate was controlled by changing ΔT. Table 4 shows the results of this crystal growth performed 10 times. A single crystal could be grown in 8 out of 10 runs, with polycrystals being formed only once and not growing once.

[0031]

[Table 4]

Example 10 In the crystal growth of Example 9, the temperature of the raw material side was set to 1020 ° C. and the temperature of the seed crystal side was set to 1040 ° C. before the crystal growth, and the seed crystal was 50 mg (about 80 μm thick). ), The temperature on the seed crystal side was lowered to 1000 ° C., and crystal growth was started. Thereafter, crystal growth was performed in the same manner as in Example 9. As shown in Table 5, as a result of performing this crystal growth 10 times, there was an example in which the crystal did not grow twice, but the remaining 8
In each case, a single crystal was obtained.

[0033]

[Table 5]

Example 11 In Examples 1 to 10, Zn and S were used as the starting ZnSe polycrystals.
In this example, a material obtained by sublimating and recrystallizing the above-mentioned ZnSe polycrystal by the method of Example 4 was used as a raw material.
Crystal growth was performed 10 times in the same manner as in Example 1. As a result, there was no case where the crystal did not grow, and the single crystal was successfully grown in all 10 times.

Example 12 A ZnSe polycrystal synthesized by heating and reacting Zn and Se was pulverized into a powder, and this powder was heated at 500 ° C. for 1 hour in a vacuum. Crystal growth was performed 10 times in the same manner as in 10. As a result, there was no case where the crystal did not grow, and the single crystal was successfully grown in all 10 times.

Example 13 Example 10 was carried out using a ZnSe polycrystal synthesized by reacting hydrogen selenide and zinc vapor at a temperature of 500 ° C. as a raw material.
Crystal growth was performed 10 times in the same manner as described above. As a result, there was no case where the crystal did not grow, and the single crystal was successfully grown in all 10 times.

[0037]

According to the present invention, by adopting the above structure, it is possible to measure the crystallization speed even in the process of crystal refining by the sublimation method or the growth of a single crystal. The control becomes easy, and the ZnSe single crystal can be grown with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a sectional view of a sealed tube used in Example 1.

FIG. 2 is a view in which the sealed tube of FIG. 1 is arranged in an alumina core tube of a horizontal tubular electric furnace.

FIG. 3 is a sectional view of a sealed tube used in Example 5.

FIG. 4 is a sectional view of a sealed tube used in Example 6, in which a sealed tube lid has a conical shape.

5 is a sectional view of a sealed tube used in Example 8, and FIG.
The seed crystal is arranged at the tip of the conical sealing lid of the sealing tube.

6A and 6B are a front view and a side view of an alumina ring whose inside is sharpened, which is used as a fulcrum 1 in a furnace core tube of an electric furnace.

FIG. 7 is a graph showing the relationship between the purification time and the increase in the weight of the purified product in Example 1.

FIG. 8 is a view in Example 2 in which a sealed tube is arranged in an alumina core tube of a horizontal tubular electric furnace.

FIG. 9 is a graph showing the relationship between the purification time and the increase in the weight of a purified product in Example 3.

FIG. 10 is a graph showing the relationship between the purification time and the increase in the weight of a purified product in Example 4.

FIG. 11 is a view in which a sealed tube used in Example 5 is arranged in an alumina core tube of a horizontal tubular electric furnace.

FIG. 12 is a graph showing the relationship between the purification time, the temperature of Zn, and the purification rate in Example 5.

FIG. 13 is a graph showing the relationship between the purification time, the weight of the purified product, and the target weight in Example 9.

Claims (1)

(57) [Claims] 1. A crystal material is vacuum-sealed at one end of a sealed tube, the sealed tube is inserted into a heating furnace, the crystal material is heated to a sublimation temperature, and a crystal deposition portion of the sealed tube is maintained at a crystallization temperature. In the method of measuring the crystallization rate when crystallization is performed, a member serving as a first fulcrum is placed in the heating furnace, the sealed tube is placed on the member, and one end of the sealed tube is A method for measuring a crystallization rate, comprising extending the heating furnace, supporting the extension at a second fulcrum, and measuring a change in weight applied to the second fulcrum.