JPH0676277B2 - Single crystal growth equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a technique for growing a compound semiconductor single crystal and an apparatus for producing a single crystal containing constituent elements having a high vapor pressure, for example, by a liquid sealed Czochralski method. The present invention relates to a technique effectively used for manufacturing a compound semiconductor single crystal.

[Prior Art] In the conventional single crystal growth technology, especially the liquid-encapsulated Czochralski method (LEC method), since the growth of the compound semiconductor single crystal has been performed in an open system, when the vapor pressure of one of the constituent elements is high. Can not prevent volatilization of this constituent element from the grown crystal and the melt, with a uniform composition,
It was difficult to grow a high quality crystal with a low defect density and excellent electrical characteristics. Therefore, it is called a vapor pressure control method for overcoming the defects of the crystal growth method and controlling the vapor pressure in the crystal growth atmosphere to prevent the vaporization of the high vapor pressure element and grow a high quality crystal. Crystal growth techniques have been proposed.

In this type of vapor pressure control method, it is considered essential to hermetically close the container, and for example, the crucible shaft and the pulling shaft should be B ₂
An invention relating to a method for pulling up a double melt seal in which a container is hermetically sealed by sealing with a glass having a low melting point such as O ₃ or a metal having a low melting point such as Ga has been proposed (JP-A-54).
-123585). In addition, instead of using a melt seal made of glass or a low melting point metal, it was sometimes grown in a sealed tube (ampule) made of quartz or the like.

However, in the former double melt sealing method, the equipment and operation are complicated, the productivity is low, and when cooled to room temperature, the shaft and the container come into close contact with each other due to the solidification of the glass or metal, resulting in repeated continuous operation. Cannot be used as a single crystal, there is contamination by impurities from glass or metal, and deposits that have peeled off or fallen from the seal of glass or metal enter the crystal growth part to cause polycrystal, etc. There are drawbacks such as a decrease in yield. On the other hand, when a sealed tube is used, it has a drawback that an expensive container such as quartz must be damaged each time it is used.

Therefore, the invention described in JP-A-59-182297 has been proposed in order to overcome the above-mentioned drawbacks and realize a vapor pressure control device excellent in practicality.

FIG. 2 shows an apparatus disclosed in Japanese Patent Laid-Open No. 59-182297, which has an inner diameter fitted around a pulling shaft 29 having a diameter of 20 mm.
A heat insulating cylinder 28 having a cylindrical portion 30 having a length of 22 mm and a length of 20 mm is attached to the crucible.
It is characterized in that it is installed so as to cover the upper part of 21 and has a gap between the two to prevent volatile elements from flowing out by convection.

[Problems to be Solved by the Invention] Although the invention of this prior application can overcome the problems of the double melt sealing method described above, it prevents volatile elements from flowing out of the container, Experiments by the inventors of the present application have revealed that there is a serious drawback regarding the vapor pressure control performance for growing crystals under a constant vapor pressure. That is, outflow of volatile elements cannot be sufficiently prevented only by the measures for preventing convection as described in the specification of JP-A-59-182297, and in order to prevent this, outflow due to diffusion is also required. It became clear that vapor pressure control cannot be implemented unless the device is designed to prevent it. Further, since there is no replenishment for the outflowing vapor in the above apparatus, the volatile element vapor pressure in the container gradually decreases with the passage of time during the growth of the crystal, usually several to several tens of hours. There is a problem that it is impossible in principle to maintain a constant vapor pressure during the required crystal growth.

This invention has been made in view of the above problems, in the case of growing a single crystal containing a high vapor pressure element by the pulling method, the volatility from the raw material melt and the single crystal during pulling An object of the present invention is to provide a single crystal production apparatus capable of preventing element volatilization, allowing repeated use of the apparatus, and capable of growing a high-quality crystal body with less impurities mixed therein with good reproducibility.

[Means for Solving the Problems] The present invention can control the vapor pressure to be substantially constant if the outflow amount of the volatile element in the growth of the compound semiconductor single crystal by the pulling method is 1 g or less per hour. Based on the demonstration that it is possible, cover the crucible with a semi-enclosed container,
This semi-enclosed container is provided with a cylindrical portion that fits with the pulling shaft, and the ratio A / L between the cross-sectional area A of the gap between the pulling shaft and the cylindrical portion and the length L of the cylindrical portion is 0.015 cm or less. To do so. Further, a reservoir for supplying a volatile element is provided around the crucible so that an amount of vapor corresponding to the amount of vapor flowing out from the gap around the pulling shaft is replenished.

[Operation] According to the means described above, in growing a compound semiconductor single crystal by the pulling method, the outflow of volatile components from the gap around the pulling shaft is suppressed to 0.1 g / hr or less, and the vapor pressure around the crucible is almost reduced. It is possible to achieve the above-mentioned object of providing a single crystal manufacturing apparatus which can be kept constant and by which a high quality crystal can be grown with good reproducibility.

[Example] In proposing the present invention, the present inventors investigated the outflow amount of As vapor, which is a volatile component, from the gap of the container for GaAs, which is a compound semiconductor single crystal. A schematic diagram of the apparatus used for the experiment is shown in FIG. In the apparatus shown in the figure, a semi-enclosed container 13 supported by a rotary shaft 12 is arranged in a high-pressure container 11, a cylindrical portion 13a is formed on an upper wall of the semi-enclosed container 13, and the cylindrical portion 13a is arranged from above. A shaft 14 is hung so as to penetrate through the heater, and a heater 15 is provided around the semi-enclosed container 13.
Has been placed.

In this apparatus, the inner diameter of the cylindrical portion 13a of the semi-hermetically sealed container 13 and the outer diameter of the shaft 14 are changed, metal As is housed in the container 13, and is heated by an external heater 15 to volatilize As and vaporize the vapor pressure. The outflow amount of As vapor to the outside of the container was examined under the condition of 1 atm, which is almost equal to the decomposition pressure during GaAs crystal growth.

Fig. 4 shows the ratio A / L (cm) of the length L of the cylindrical portion 13a to the clearance cross-sectional area A between the cylindrical portion 13a and the shaft 14 and the outflow amount of As vapor V _AS (g / hr) per hour. Shows the relationship with. From the figure, it was found that reducing the A / L has the effect of suppressing the outflow of As vapor. It is estimated that the outflow mechanism of As vapor is due to diffusion that A / L and V _AS have a nearly proportional relationship.

From the above experiment, if the vapor amount V _AS (g / hr) flowing out from the gap between the shaft and the cylindrical portion due to diffusion is 1 g / hr or less, the fluctuation of As vapor pressure in the semi-hermetic container hardly changes with time. However, when it is about 1 g / hr or more, the As vapor pressure decreases with the lapse of time for crystal growth, and it becomes impossible to control the vapor pressure to be constant. Further, even if the outflow amount is a little, it is possible to control the vapor pressure at a constant level as long as it can be satisfied by supplying As vapor from a reservoir or the like installed inside. It has been found that the vapor pressure of As can be easily kept constant during the crystal growth by actually using the reservoir if the vapor outflow rate V _AS is about 1 g / hr.

The present inventor proposes a single crystal pulling apparatus as shown in FIG. 1 based on the above demonstration.

Moreover, since the heater is provided around the cover member, by appropriately heating the cover member with this heater,
It is possible to prevent vapor such as As from being cooled by the cover member that has a low temperature and to be deposited on the inner wall surface, and it is possible to control the temperature distribution in the furnace more precisely and to control the temperature gradient in the sealant. Adjustment becomes easy.

In FIG. 1, 1 is a high-pressure container pressurized by an inert gas or nitrogen gas, 2 is a crucible which is arranged in the center of the high-pressure container 1 and which is supported by a rotating shaft 3. Ga, As is contained in the crucible 2. A raw material element such as and a sealant 4 such as B ₂ O ₃ are stored. Further, from above the high-pressure container 1, a pull-up shaft 5 is rotatably and vertically movable toward the inside of the crucible 2.

In this embodiment, a cover member 6 is provided around the crucible 2 and a heating heater 7 is arranged outside the cover member 6. On the bottom wall of the cover member 6, a cylindrical portion 6a that fits with the rotating shaft 3 that supports the crucible is formed. A cover member 8 is attached to the upper portion of the cover member 6, and the cover member 6 and the cover member 8 constitute a semi-hermetic container. A heat retaining heater 9 is arranged around the cover member 8, and the pulling shaft 5 is provided at the upper end of the cover member 8.
A cylindrical portion 8a that fits with is formed.

In this embodiment, the gap between the cylindrical portion 8a and the pulling shaft 5 and the gap between the rotating shaft 3 and the cylindrical portion 6a are the ratio A / of the sectional area A of the gap and the length L of the cylindrical portions 6a and 8a. It is designed so that each L is 0.06 cm or less. As a result, the pulling shaft 5
The amount of arsenic vapor flowing out of the gap between the rotating shaft 3 and the rotating shaft 3 is 0.5 g / hr or less, and the total amount of arsenic outflow is 1
It can be suppressed to g / hr, not only convection outflow,
Arsenic outflow due to diffusion can also be suppressed.

Further, in this embodiment, a conduit 6b whose lower end is closed is extended downward from a part of the bottom wall of the cover member 6, and an auxiliary heater 10 is arranged around the lower part of the conduit 6b. . Put a volatile element such as arsenic in this conduit 6b,
By heating with the auxiliary heater 10, a suitable amount of the vapor can be supplied into a space surrounded by the cover member 6 and the cover member 8 and serving as a crystal growth atmosphere. That is, a part of the conduit 6b and the auxiliary heater 10 form a reservoir as a vapor replenishing means.

By adjusting the temperature of the heater 10 that constitutes this reservoir, it is possible to generate and compensate the amount of vapor corresponding to the amount of arsenic vapor flowing out from the gap between the pulling shaft 5 and the rotating shaft 3. As a result, the arsenic vapor pressure around the crucible 2 can be kept constant during the crystal growth for a long time (tens of hours).

In this way, if the vapor pressure of arsenic is kept constant, it is possible to prevent the volatilization of arsenic from the surfaces of the raw material melt 16 and the growth crystal body 17 in the crucible as much as possible. Further, in this embodiment, the structure of the device is simple, the close contact between the shaft and the container, which has been a problem in the double melt sealing method, is avoided, and the device can be repeatedly used, resulting in a dramatic increase in productivity. In addition, the contamination due to the dropping of the sealing material from the melt sealing portion is prevented, and a high-quality single crystal can be manufactured with good reproducibility.

Next, a specific example of growing a GaAs single crystal using the single crystal pulling apparatus shown in FIG. 1 will be described.

First, the total amount of Ga and As having a purity of 7N is 4 kg as a raw material.
Then, 600 g of B ₂ O ₃ as a sealant was put therein.
The crucible used is made of pBN and has an inner diameter of 6 inches. Further, the ratio A / L of the clearance area between the pulling shaft 5 and the rotating shaft 3 to the length of the cylindrical portion is 0.05 cm, and the inside of the high-pressure container 1 is filled with 20 atm of argon gas, and arsenic of arsenic supplied by the reservoir The vapor pressure was 1 atm. Then, the pulling shaft 5 is rotated at a speed of 6 rpm, and the rotary shaft 3 of the crucible 2 is rotated at 30 rp.
While rotating in the opposite direction to the pulling shaft at a speed of m, 9 mm / hr
The pulling shaft 5 was raised at the speed of, and the crystal was grown for about 17 hours.

As a result, the diameter of the straight body part is 80 mm, the length is 150 mm, and the weight is about 3.4 kg.
A large-diameter GaAs single crystal was obtained. The surface of the crystals had a metallic luster, indicating no decomposition of As. Crystals grown in an open system without semi-sealing the container without controlling the vapor pressure have large surface decomposition, and when the wafer is cut by cutting perpendicular to the growth direction, Ga droplets due to decomposition are seen in the peripheral part. However, Ga droplets were not generated in the crystal grown by controlling the vapor pressure in the above example. The grown crystal had a high resistivity of 10 ⁷ Ωcm or more over the entire area and had good thermal stability.
Further, the shield part of the apparatus shown in FIG. 1 could be continuously used without being damaged through repeated growth experiments. Moreover, it was found that the single crystallization rate was 90% or more through the crystal growth of 20 times or more, and a high quality single crystal could be obtained with good reproducibility.

In addition, in the above-mentioned embodiment, the embodiment in which the clearance between both the pulling shaft 5 and the rotating shaft 3 is adjusted has been described.
In the case where the gap between the shaft and the semi-hermetic container is only between the pulling shaft 5 and the cover member 8 (for example, the cover member 6 is fixed to the rotating shaft 3 and the crucible and the semi-hermetic container are integrally rotated). In this case, by setting A / L to 0.1 cm or less, the outflow rate of volatile components can be suppressed to 1 g / hr or less. Further, by using the reservoir together, the vapor pressure can be controlled to be constant more easily.

Furthermore, by setting the outflow rate of the volatile component to be 0.1 g / hr or less, that is, the ratio of the gap cross-sectional area A to the length L is 0.015 or less, it becomes possible to control the vapor pressure without providing a reservoir.

The clearance cross-sectional area A is selected in a range that can prevent the outflow of volatile components due to convection, and the diameter of the pulling shaft of this embodiment is 2.5c.
In case of m, it is less than 5 cm ² . Also, the length L is selected within the range of 30 cm or less, which does not require a significant improvement of the apparatus, although the stroke of the lifting shaft of the present apparatus is 60 cm.

[Effects of the Invention] As described above, according to the present invention, the circumference of the crucible is covered with a semi-enclosed container, and the semi-enclosed container is provided with a cylindrical portion fitted with the pulling shaft. The ratio A / L between the cross-sectional area A of the gap and the length L of the cylindrical portion is set to 0.015 cm or less. Therefore, in growing the compound semiconductor single crystal by the pulling method, volatilization from the gap around the pulling axis is performed. It is possible to keep the vapor pressure around the crucible almost constant by suppressing the outflow of the sexual component to 0.1 g / hr or less, which has the effect of growing a high quality crystal with good reproducibility.

Furthermore, by providing a reservoir that supplies volatile elements around the crucible so that the amount of vapor that corresponds to the amount of vapor flowing out from the gap around the pulling shaft can be replenished, the vapor pressure around the crucible can be made even easier. It has an effect that it can be maintained and a high quality single crystal can be easily obtained.

Moreover, since the reservoir is provided with an independent heater, the volatile element such as As in the reservoir can be stably supplied by controlling this heater.

Although the case where the LEC method is applied has been described in the embodiments, the present invention can also be applied to a pulling method that does not use a sealant.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a single crystal growth apparatus according to the present invention, FIG. 2 is a sectional view showing an example of a conventional crystal pulling apparatus to which vapor pressure control is applied, and FIG. Prior to the proposal of the invention, a sectional view of an apparatus used to investigate the relationship between the clearance area of the pulling shaft and the outflow vapor amount, and FIG. 4 is a graph showing the relationship between the clearance area of the pulling shaft and the outflow vapor amount. . 1 ... High-pressure container, 2 ... Crucible, 3 ... Rotating shaft, 5 ...
Pull-up shafts 6, 8 ... Members constituting a semi-enclosed container, 7
...... Heater, 6a, 8a …… Cylindrical part, 6b, 10 …… Steam supply means (reservoir).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Osamu Oda Inventor Osamu Osamu 3-17-35, Shinzonan, Toda City, Saitama Prefecture, Japan Mining Co., Ltd. Electronic Materials and Parts Research Laboratories (56) Reference JP-A-59-182297 (JP, A) JP-A-62-207799 (JP, A) JP-A-61-158896 (JP, A) JP-B-61-27358 (JP, B2)

Claims (1)

[Claims] 1. A crucible containing a raw material is placed in a high-pressure vessel, heated and melted by a heater, a seed crystal is brought into contact with the surface of the raw material melt, and this is gradually pulled up to contain an element having a high vapor pressure. In a single crystal growth apparatus for growing a compound semiconductor single crystal, a substantially cylindrical cover member that surrounds the periphery of the crucible in the high-pressure container, and a cover member that is joined to the upper surface of the cover member and covers the upper portion of the crucible. A semi-hermetic container comprising a heater and heaters arranged around the cover member and the cover member, respectively, and a cylinder fitted with the pulling shaft at least at a portion where the crystal pulling shaft penetrates the cover member. Part is formed, and the cylindrical part and the cylindrical part are pulled up so that the flow rate of convection and diffusion of volatile elements from the gap between the cylindrical part and the pulling shaft is suppressed to 0.1 g / hr or less. The ratio of the clearance cross-sectional area with the shaft to the length of the cylindrical portion is set to 0.015 cm or less, and the cover member is composed of a bottomed cylindrical conduit and a heater mounted around the lower part of the conduit. A single crystal growth apparatus comprising a vapor replenishing means for replenishing an amount of vapor corresponding to the amount of volatile element vapor flowing out from the gap.