JP3938674B2 - Method for producing compound semiconductor single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a compound semiconductor single crystal by a liquid-sealed chiral porous method (hereinafter referred to as LEK method).
[0002]
[Prior art]
In general, III-V and II-VI compound semiconductors such as GaP, GaAs, InP, and CdTe have a high vapor pressure near the melting point, so that the raw material melt is made of B ₂ O ₃ (boron oxide) or the like. A single crystal is grown by a liquid sealing method covered with a liquid sealing agent layer. Currently, as this liquid sealing method, a liquid sealing Czochralski method (hereinafter referred to as LEC method), a LEK method, and the like are known.
[0003]
The LEC method is a method in which a crystal is pulled up while rotating as the crystal grows. It is industrialized because the crystal orientation can be controlled by seeding and it is easy to obtain a high-purity crystal. However, since it is difficult to control the diameter, it is difficult to obtain a uniform diameter, and since the temperature gradient in the melt during crystal growth is large, the thermal stress applied to the crystal increases and the dislocation density increases.
[0004]
On the other hand, in the LEK method, since the crystal is grown in a container containing the raw material melt without pulling up the crystal, the diameter of the grown crystal depends on the inner diameter of the crucible, and the diameter can be easily controlled. Further, since the temperature gradient in the melt during crystal growth is several degrees C / cm and is smaller by one digit or more than the LEC method, the thermal stress applied to the grown crystal is small. Therefore, it is possible to obtain a grown crystal having a low dislocation density as compared with the LEC method.
[0005]
Here, a conventional method of manufacturing a compound semiconductor by the LEK method will be specifically described with reference to FIG.
FIG. 2 is a schematic configuration diagram of a crystal growth apparatus used in the conventional LEK method. In this crystal growth apparatus 100, a cylindrical heater 2 is disposed in a sealed high-pressure vessel 1, and a crucible 3 is disposed in the center of the heater 2. The crucible 3 is rotatably supported by a support shaft 4 fixed to the lower end thereof. In the crucible 3, a raw material melt 5 such as InP is placed, and the upper surface of the raw material melt 5 is covered with a liquid sealant layer 6 such as B ₂ O ₃ .
[0006]
On the other hand, from above the crucible 3, a crystal pulling shaft 7 is suspended in the high-pressure vessel 1 so as to move up and down and rotate freely, and a seed crystal fixing jig (seed holder) provided at the tip of the crystal pulling shaft 7. ) 13 holds the seed crystal 14. A load cell 15 is connected to the crystal pulling shaft 7 so that the weight of the grown crystal can be observed.
[0007]
Further, a gas introduction pipe 8 for introducing a high-pressure inert gas is connected to the upper portion of the side wall of the high-pressure vessel 1 so that the pressure inside the high-pressure vessel 1 can be adjusted to a predetermined pressure.
[0008]
Conventionally, by using the crystal growth apparatus 100 described above, the crystal pulling shaft 7 is moved up and down to bring the seed crystal into contact with the surface of the raw material melt 5 in the crucible 3, and thereafter the shaft is rotated without moving up and down. The temperature of the heater 2 was gradually lowered while the single crystal was grown.
[0009]
In particular, when a single crystal is grown by a LEK method using a material that is difficult to grow a single crystal such as a II-VI group compound semiconductor, in order to reduce the dislocation density in the crystal, It was necessary to control the temperature gradient in the vertical direction to at least 20 ° C./cm or less. However, if the temperature gradient is reduced, the temperature on the liquid sealant 6 also becomes a high temperature of around 1000 ° C., so that the seed crystal 14 is decomposed and the tip melts and becomes tapered so that seeding cannot be performed.
[0010]
Accordingly, the present inventors have repeatedly studied on a method for producing a compound semiconductor by the LEK method, and proposed a technique capable of effectively preventing the seed crystal from being decomposed during crystal growth (Japanese Patent Laid-Open No. Hei 8-183690). Specifically, as shown in FIG. 1, the seed crystal 14 is covered with a fireproof cover 11, and a part or all of the fireproof cover is immersed in the liquid sealant. As a result, the inside of the refractory cover 11 is sealed, and the gas decomposed from the seed crystal 14 causes the internal pressure of the cover 11 to become the dissociation pressure of the seed crystal 11 relatively quickly. It will not progress. Therefore, it becomes possible to prevent the seed crystal from being decomposed for a long time, and it becomes possible to perform seeding easily.
[0011]
[Problems to be solved by the invention]
However, when crystal growth is performed by the prior application technique, there is a problem that crystallinity is slightly deteriorated due to stress from the seed crystal. That is, since the compound semiconductor crystal has a solid specific gravity smaller than that of the liquid, the volume expands when the crystal grows from the raw material melt. For this reason, if the seed crystal is attached to the upper part of the grown crystal for a long time, stress is applied to the grown crystal, which deteriorates the crystallinity.
[0012]
The present invention has been made in view of the above problems, and is a compound semiconductor single crystal in which a single crystal having excellent crystallinity can be obtained by reducing the dislocation density in the grown crystal and eliminating the stress from the seed crystal. It aims at providing the manufacturing method of a crystal | crystallization.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the present inventors have further studied the LEK method. As a result, in order to prevent the seed crystal from decomposing at the time of seeding, a method of covering the seed crystal with a refractory cover as in the prior application technique is effective. When this method is used, It has been found that if the shoulder is well formed, the crystallinity of the grown crystal does not deteriorate even if the seed crystal is decomposed thereafter. That is, it became clear that the “state of the seed crystal” affects the crystallinity of the grown crystal from the start of seeding until the shoulder of the grown crystal is formed. Therefore, the present inventors considered that if the seed crystal is completely decomposed and sublimated after the shoulder of the grown crystal is formed, stress from the seed crystal can be avoided.
[0014]
Regarding the influence of “stress from the seed crystal” on the crystallinity of the grown crystal, the stress due to the seed crystal increases remarkably when the body of the grown crystal becomes 1/5 or more of the whole. found. From this, the present inventors, in order to effectively avoid the deterioration of the crystallinity of the grown crystal due to the stress from the seed crystal, until 1/5 of the body portion of the grown crystal is formed. We thought that it was necessary to decompose and sublimate the seed crystals.
[0015]
The present invention has been completed based on the above knowledge, heating the inside of the high-pressure vessel as a high-pressure inert gas atmosphere, covering the raw material melt in the crucible placed in the high-pressure vessel with a liquid sealant, In the method for producing a compound semiconductor single crystal, in which a seed crystal whose surface is covered with a refractory cover is immersed in the raw material melt, and the temperature of the raw material melt is gradually decreased, the single crystal is grown. In the process of growing a crystal by immersing all or part of the cover in a liquid sealant, a smaller amount of gas than the amount of gas generated by decomposition of the seed crystal is caused to flow out of the cover. Is decomposed at a predetermined speed. That is, when the fireproof cover is provided, a gap is intentionally provided so that the inside of the cover is in a semi-sealed state.
[0016]
As a result, the inside of the refractory cover is in a semi-sealed state, and the seed crystal is decomposed to generate gas according to the amount of gas flowing out of the cover, so that the decomposition reaction of the seed crystal is not completely stopped. That is, the decomposition of the seed crystal proceeds gradually, eventually sublimating and the seed crystal disappears. Therefore, the growth crystal can avoid deterioration of crystallinity due to the stress from the seed crystal, so that a high-quality compound semiconductor single crystal can be obtained. Further, since the inside of the cover is in a semi-sealed state, decomposition of the seed crystal is suppressed, and seeding can be performed without causing dislocation in the crystal.
[0017]
Further, the seed crystal was decomposed and sublimated from the formation of the shoulder portion of the grown crystal to the formation of the 1/5 height portion of the body portion. In other words, the seed crystal is necessary until the shoulder portion of the grown crystal is formed, but is not particularly necessary after the shoulder portion is formed. Therefore, the seed crystal is decomposed and disappears after the shoulder portion is formed. In addition, since the stress from the seed crystal is large enough to affect the crystallinity of the grown crystal when the height of the grown crystal becomes 1/5 or more of the entire crystal, It was decomposed and sublimated.
Thereby, the compound semiconductor single crystal excellent in crystallinity can be manufactured with a high yield.
[0018]
Further, by determining the size of the seed crystal according to the amount of gas flowing out from the fireproof cover, it is possible to control so that the seed crystal is completely decomposed and sublimated in a desired time zone.
[0019]
In addition, you may utilize the clearance gap which arises by use of an O ring etc., when attaching a fireproof cover, without providing the said clearance gap. In addition, since the seed crystal is exposed to a high temperature atmosphere and decomposes before the single crystal is grown, the size (thickness) of the seed crystal is determined in consideration of the time (for example, 20 to 30 minutes). It should be.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing a schematic configuration of a crystal growth apparatus 100 used in the present embodiment, which has the same configuration as the crystal growth apparatus used in the prior art (Japanese Patent Laid-Open No. Hei 8-183690). .
Specifically, the crystal growth apparatus 100 of the present embodiment includes a sealed high-pressure vessel 1, a cylindrical heater 2 disposed in the high-pressure vessel 1, and a support shaft 4 at the center of the heater 2. The crucible 3 is rotatably supported, and the crystal pulling shaft 7 is vertically suspended above the crucible 3 and is suspended freely.
[0021]
In the crucible 3, a raw material melt 5 such as InP is placed, and the upper surface of the raw material melt 5 is covered with a liquid sealant 6 such as B ₂ O ₃ .
A load cell 15 is connected to the crystal pulling shaft 7 so that the weight of the grown crystal can be observed. The crystal pulling shaft 7 is provided with a fixing jig (seed holder) 13 for the seed crystal 14 at the tip thereof, thereby holding the seed crystal 14. Further, a pBN cover 11 is disposed so as to cover the seed crystal 14 and the seed chuck 13.
[0022]
A vent is provided between the pBN cover 11 and the lifting shaft 7 so that when the pBN cover 11 is immersed in the liquid sealant 6, the inside of the cover is in a semi-sealed state. . For example, if an O-ring is used for the joint portion of the pBN cover 11, the seed holder 13, and the lifting shaft 7, a gap is generated in the joint portion, so that the internal gas can flow out from this gap.
[0023]
As described above, in this embodiment, when the pBN cover 11 is immersed in the liquid sealant 6, the inside of the cover is not sealed but is semi-sealed, which is different from the prior art (Japanese Patent Laid-Open No. Hei 8-183690). . That is, if the inside of the cover is kept sealed when the fireproof cover 11 is immersed in the liquid sealant 6 as in the prior art, the seed crystal 14 remains without being decomposed for a long time. In particular, by making the inside of the cover semi-sealed, the decomposition gradually proceeds while suppressing the decomposition of the seed crystal 14. For example, the decomposition of the seed crystal 14 can be suppressed by adjusting the size of the gap so that a smaller amount of gas than the gas generated by the decomposition of the seed crystal flows out of the refractory cover 11.
[0024]
More specifically, the seed crystal 14 is not decomposed until the shoulder portion of the grown crystal 9 is completely grown, and then decomposed and sublimated until the body height of the grown crystal reaches 1/5. ing. For example, the decomposition reaction of the seed crystal 14 can be controlled as described above by adjusting the thickness of the seed crystal 14 and the gas flow rate leaking from the inside of the fireproof cover 11 to the outside.
[0025]
A gas introduction pipe 8 for introducing a high-pressure inert gas is connected to the upper part of the side wall of the high-pressure vessel 1 so that the pressure inside the high-pressure vessel 1 can be adjusted to a predetermined pressure.
[0026]
By using the crystal growth apparatus 100 described above, the crystal pulling shaft 7 is moved up and down to bring the seed crystal 14 into contact with the surface of the raw material melt 5 in the crucible 3, and the temperature of the heater 2 is gradually lowered to reduce the compound semiconductor. Single crystals can be grown.
[0027]
Hereinafter, a case where an InP compound semiconductor single crystal is grown will be described as an example of crystal growth using the crystal growth apparatus 100 described above.
First, an InP polycrystal as a compound semiconductor raw material is placed in a pBN-type crucible 3 having a thickness of 1 mm and an inner diameter of 80 mm so as to have a thickness of 50 mm, and B ₂ O ₃ as a liquid sealant is formed thereon with a thickness of 15 mm. I put it like that. Then, the high-pressure vessel 1 heated to above 1000 ° C. by heating by a heater 2, to melt the InP and _B 2 _{O 3.} At this time, in order to prevent volatilization of P (phosphorus), an inert gas 10 such as argon gas (Ar), for example, was introduced from the gas introduction tube 8 and the inside of the high-pressure vessel 1 was adjusted to 40 atm.
[0028]
Next, after adjusting the surface temperature of the InP raw material melt 5 to a temperature slightly higher than the melting point of InP (1062 ° C.), the crystal pulling shaft 7 is lowered to convert the seed crystal 14 having a crystal growth surface of (100) into InP. It was immersed in the raw material melt 5 and seeded. At this time, the axis lowering speed of the crystal pulling shaft 7 was set to 100 mm / h in the vicinity of the melt. At this time, the interface temperature between the Ar gas 10 and B ₂ O ₃ was 1040 ° C.
[0029]
At this time, InP decomposes and P gas is generated in the refractory cover 11, but when the InP dissociation pressure (about 10 atmospheres) at the interface temperature with B ₂ O ₃ is reached, the decomposition does not proceed further. However, in this embodiment, the inside of the refractory cover 11 is semi-sealed so that the P gas gradually leaks to the outside of the refractory cover 11, so that the decomposition of the seed crystal 14 proceeds gradually without being completely stopped. .
[0030]
In this example, a 2 mm square seed crystal was used so that the seed crystal 14 was completely decomposed and sublimated about 1 to 2 hours after the start of crystal growth. Further, the length of the seed crystal 14 is 10 mm longer than that of the fireproof cover 11 so that the tip of the seed crystal 14 contacts the surface of the raw material melt 5 when the fireproof cover 11 is immersed in the liquid sealant 6. I did it.
[0031]
When seeding was started, the seed crystal 14 had already been exposed to a high temperature atmosphere for about 20 minutes to 30 minutes and was slightly decomposed, but no tapering or the like was observed, and decomposition was progressing so as to affect seeding. It was confirmed that there was no.
After seeding, the shoulder of the grown crystal was formed in about 10 to 30 minutes. The average growth rate in the horizontal direction at this time is 50 to 200 mm / h. Even at this time when the shoulder portion of the crystal was grown, the seed crystal 14 remained sufficiently, and it was confirmed that the decomposition of the seed crystal was suppressed by the cover 11 made of pBN. As described above, in this embodiment, the seed crystal 14 was sufficiently left until the shoulder of the grown crystal was completely grown. Therefore, it is possible to suppress the occurrence of dislocations in the grown crystal accompanying the decomposition of the seed crystal. did it.
[0032]
Thereafter, a crystal having a height of 50 mm was grown in the vertical direction at a growth rate of 1 mm / h over 50 hours while gradually cooling the heater 2. On the way, it was confirmed that the seed crystal 14 was completely decomposed and sublimed about 1 to 2 hours after the start of crystal growth, that is, when the body of the grown crystal was grown about 1 to 2 mm. As a result, the grown crystal 9 was released from the seed crystal 14, and it was possible to prevent the crystallinity from deteriorating due to the stress from the seed crystal 14.
[0033]
Then, after the raw material melt 5 was completely crystallized, it was cooled for 6 hours to obtain an InP compound semiconductor single crystal having a height of 50 mm. The obtained InP compound semiconductor single crystal was a high-quality single crystal having a low dislocation density and excellent crystallinity.
[0034]
Next, using a seed crystal having a thickness of 4 mm square and growing the crystal in the same manner as in this example under other conditions, it took 4 to 6 hours for the seed crystal to completely decompose and sublimate. It cost. The height of the grown crystal at that time was 4 to 6 mm, but the quality of the obtained grown crystal was good, and even when the seed crystal was used, the influence of the stress on the grown crystal from the seed crystal was negligible. It was confirmed that.
[0035]
Further, as a result of examining the decomposition rate of the seed crystal by repeating experiments, the seed crystal is decomposed before the height of the grown crystal is about 10 mm, that is, before about 1/5 of the obtained grown crystal (50 mm in this embodiment) is grown. As a result, it was found that the stress applied to the grown crystal from the seed crystal does not adversely affect the crystallinity.
[0036]
As mentioned above, although this invention was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment. For example, the compound semiconductor single crystal to be grown is not limited to InP, and can be applied to the growth of III-V and II-VI compound semiconductor single crystals such as GaAs, GaP, CdTe, and the like.
[0037]
Moreover, the shape of the fireproof cover 11 does not need to be a cylindrical shape, and may be any shape that covers the seed crystal 14 and can suppress the decomposition thereof. In addition to pBN, the fireproof cover 11 may be made of a material that does not react with the melt at the crystal seeding temperature, such as Mo (molybdenum), W (tungsten), or Ta (tantalum).
[0038]
【The invention's effect】
According to the present invention, a seed crystal whose surface is covered with a refractory cover is immersed in a raw material melt covered with a liquid sealant, and the temperature of the raw material melt is gradually lowered to grow a single crystal. In the LEK (Liquid Sealing Cairo Porous) method to be performed, the amount of gas generated by decomposition of the seed crystal in the process of growing the crystal by immersing all or part of the refractory cover in the liquid sealant Since a smaller amount of gas is allowed to flow out of the cover, decomposition of the seed crystal during seeding can be suppressed, and the seed crystal can be gradually decomposed. Accordingly, the dislocation density of the grown crystal can be reduced, and deterioration of the crystallinity of the grown crystal due to stress from the seed crystal can be avoided, so that a high-quality compound semiconductor single crystal can be obtained with a high yield. There is an effect.
[0039]
The seed crystal is more effective if it is decomposed and sublimated after the shoulder portion of the grown crystal is formed until 1/5 of the body portion is formed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a crystal growth apparatus used in the LEK method of the present embodiment and the prior application (Japanese Patent Laid-Open No. Hei 8-183690).
FIG. 2 is a schematic configuration diagram of a crystal growth apparatus used in a conventional LEK method.
[Explanation of symbols]
1 High-pressure vessel 2 Heater 3 Crucible 4 Support shaft 5 Raw material melt 6 Liquid sealant (B ₂ O ₃ )
7 Crystal pulling shaft 8 Gas introduction tube 9 Growing crystal 10 Inert gas 11 pBN cover (fireproof cover)
13 Seed crystal holder (seed holder)
14 Seed crystal 100 Crystal growth equipment

Claims (2)

The inside of the high-pressure vessel is heated as a high-pressure inert gas atmosphere, the raw material melt in the crucible placed in the high-pressure vessel is covered with a liquid sealant, and the seed crystal whose surface is covered with a refractory cover is used as the raw material melt. In the method for producing a compound semiconductor single crystal, wherein the single crystal growth is performed by immersing in a single crystal and gradually lowering the temperature of the raw material melt.
In the process of growing a crystal by immersing all or part of the refractory cover in a liquid sealant, a gas smaller than the amount of gas generated by decomposition of the seed crystal is allowed to flow out of the cover. A method for producing a compound semiconductor single crystal, comprising decomposing and sublimating all seed crystals from the formation of the shoulder portion of the grown crystal to the formation of the 1/5 height portion of the body portion . 2. The method for producing a compound semiconductor single crystal according to claim 1, wherein the size of the seed crystal is determined in accordance with an amount of gas flowing out of the refractory cover.

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