JP6411952B2 - Method for producing pyrolytic boron nitride container - Google Patents

Description

  The present invention relates to a method for producing a pyrolytic boron nitride container, particularly a large crucible used for growing a III-V compound semiconductor single crystal, or an Al melting crucible used for vacuum deposition or molecular beam epitaxy (MBE). The present invention relates to a method for producing a pyrolytic boron nitride container and a pyrolytic boron nitride container that are optimal for the above.

  For raising III-V compound semiconductor single crystals, such as GaAs single crystals and InP single crystals, the horizontal Bridgman method (HB method), the horizontal temperature gradient solidification method (GF method), the liquid sealing pulling method (liquid sealing) Various methods such as Czochralski method (LEC method), vertical Bridgman method (VB method), and vertical temperature gradient solidification method (VGF method) are used.

  In order to prevent volatilization of the component elements, the LEC method is adopted, and conventionally, a quartz crucible or the like is used in this LEC method. In this case, since there is a problem that Si is mixed as an impurity in the crystal, a method of pulling up by doping Cr is usually adopted.

  However, when Cr is doped, the insulating property is lowered, so that it is not suitable as an IC substrate. Therefore, in order to obtain a non-doped semiconductor substrate, a high-purity group III-V compound is obtained, and even if it is mixed in a single crystal, it does not form an impurity level enough to act as a dopant. It has been proposed to use a “PBN” (sometimes called Pyrolytic Boron Nitride) container (Patent Document 1).

  Since this LEC method is grown in an environment with a high temperature gradient, it has the disadvantage that the dislocation density in the crystal is high. On the other hand, in the vertical boat method such as the VB method and the VGF method, a seed crystal is arranged in a PBN crucible, a raw material melt is brought into contact with the seed crystal, and a temperature is gradually decreased from the seed crystal side to grow a single crystal. This method is attracting attention as a substrate for electronic devices because it has a lower dislocation density than the LEC method.

In PBN crucibles used in these vertical boat methods, the inner wall surface of the crucible is coated with boron oxide (B ₂ O ₃ ) that is put together with the raw material so that the raw material melt is in direct contact and is difficult to wet. Is required. When the raw material and B ₂ O ₃ are put together and heated, B ₂ O ₃ having a low melting point melts and covers the inner wall surface of the crucible, and further heating causes the raw material to melt, so the raw material directly contacts the PBN crucible. Therefore, a single crystal with few defects can be obtained. However, when the PBN film is removed or peeled off from the inner wall surface of the PBN crucible, there is a high possibility that there is a portion that is not well covered with B ₂ O ₃ . As a result, a crystal boundary is generated starting from the place, and in the worst case, a critical problem arises in that a single crystal cannot be obtained by polycrystallization (Patent Document 2).

  Also, PBN containers are often made by forming a film on a carbon container mold material by a thermal CVD method, but carbon derived from the container mold material adheres to the surface after demolding. Therefore, it becomes a problem when a container is used in a process that dislikes carbon contamination (Patent Document 3).

JP-A-10-87306 JP 2003-146791 A JP 11-335195 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a PBN container that is unlikely to cause film removal and peeling, and is optimal for growing a single crystal, and a method for manufacturing the same.

  In order to solve the above-mentioned problems, the present invention provides a method for producing a pyrolytic boron nitride container, comprising the step of forming a film of pyrolytic boron nitride on a carbon container mold by a thermal CVD method. Removing the film from the container mold, obtaining a container-shaped molded body, oxidizing the container-shaped molded body to remove carbon adhering to the surface derived from the container mold, and thereafter A method for producing a pyrolytic boron nitride container comprising the step of subjecting the container-shaped molded body to a thinning process from the side in contact with the mold material to form a container is provided.

  When PBN is deposited on a carbon container mold, carbon derived from the container mold adheres. In this invention, in order to remove this carbon, after removing from a container mold material, a container-shaped molded object is oxidized. As a result, the carbon derived from the container mold material, for example, carbon adhering to the inner wall surface becomes carbon dioxide, and the carbon content is almost completely removed. Therefore, it is optimal for use in a process that dislikes carbon contamination.

In addition, this oxidation treatment also oxidizes the PBN on the surface layer to partially become B ₂ O ₃ . For example, if the oxidation conditions are about 800 ° C. to 1100 ° C. in air for about 3 hours, the oxide layer has a thickness of about 0.01 μm to 0.5 μm. Since this part is a mixture of PBN and B ₂ O ₃ , it becomes brittle and it is easy to remove the film locally. This portion can be removed by reducing the thickness, and a PBN container in which film removal and peeling do not occur can be obtained. Further, since the innermost film is formed in the initial stage of film formation, it is considered that the film formation atmosphere is not stable and there are many PBN defects. This surface layer is also removed by the above thinning process, and a PBN layer with few fresh defects is exposed on the surface.

  The thinning process is preferably performed by grinding or polishing or both.

If it is grinding and polishing, the layer containing B ₂ O _{3 on the} surface of the PBN container can be removed easily and reliably.

  In the thinning process, it is preferable to remove a surface layer having a thickness of 0.5 μm or more and 100 μm or less from the surface in contact with the container mold.

In the container subjected to such a thinning process, the layer containing B ₂ O ₃ is almost completely removed, and even when used for crystal growth, film removal and peeling are less likely to occur. It will be a thing.

It is preferable to perform the said thinning process about the corner part of the said container-shaped molded object.
It is considered that the corner portion connecting the surfaces of the PBN container is likely to be easily detached due to the PBN film quality easily due to the residual stress due to the anisotropy of the film. Therefore, reducing the thickness of the PBN layer that is originally brittle and partially B ₂ O _{3 at} this corner is more effective in exposing the PBN layer with few fresh defects.

  The present invention also relates to a pyrolytic boron nitride container in which a film is formed on a carbon container mold material by a thermal CVD method, removed from the container mold material, and then carbon attached to the surface is removed by oxidation treatment. In addition, a pyrolytic boron nitride container is provided, which is subjected to a thinning process from the side in contact with the container mold material.

In such a PBN container, there is no layer in which B ₂ O ₃ is mixed on the inner wall surface, and a fresh surface appears, and it is difficult for film removal and peeling to occur. It becomes the best one for etc.

  According to the present invention, it is possible to provide a high-quality PBN container that hardly causes film removal or peeling. The PBN container provided in the present invention is optimal for growing a single crystal, and by using this to grow a crystal, a single crystal with few crystal defects can be stably produced. Particularly, it is suitable for a large crucible used for growing a group III-V compound semiconductor single crystal, or an Al melting crucible used for vacuum deposition or molecular beam epitaxy (MBE). The PBN container provided by the present invention also has the advantage that cracks are unlikely to occur during use, and is also useful for cost reduction in semiconductor manufacturing and the like. Conventionally, high purity treated graphite has been used as a container mold material in order to avoid contamination of impurities in the PBN container. In the present invention, the thickness reduction treatment is performed after the oxidation treatment as described above, so that even if an untreated normal grade product is used as a container mold material, a container having the same quality as that of the conventional can be manufactured, and the cost of the container mold material can be reduced is there.

It is a schematic diagram of an external heating type low pressure CVD apparatus that can be used in the present invention. It is sectional explanatory drawing which showed a mode that the PBN container was removed from the container mold material made from carbon. It is sectional explanatory drawing which showed an example of the PBN container provided by this invention.

  Hereinafter, although an embodiment of the present invention is described in detail, the present invention is not limited to this.

  The present inventor has intensively studied, and when the PBN container is manufactured by a thermal CVD method using a carbon container mold material, the obtained PBN container-shaped molded body is oxidized and subjected to a thinning process. It has been found that a high-quality PBN container can be obtained, and a single crystal free of crystal defects can be obtained by crystal growth using this container.

  Hereinafter, description will be given with reference to the drawings.

In manufacturing the PBN container of the present invention, a known thermal CVD method can be used. The PBN film formation by thermal CVD is performed in an external heating type low pressure CVD apparatus 1 as shown in FIG. A container mold 4 made of carbon is arranged in a reaction chamber 2 equipped with a heater 3, a raw material supply unit 5 and an exhaust unit 6, and a compound containing N atoms such as NH ₃ (ammonia) and BCl ₃ (boron trichloride) Boron halide as a raw material is supplied as a raw material, and this is subjected to thermal CVD reaction at a high temperature of 1800 ° C. to 2000 ° C. to form a PBN film on the container mold 4. As the container mold material, various carbon materials such as graphite, C / C composite carbon, pyrolytic graphite and the like can be used, but it is preferable to use a graphite container mold material.

  The PBN film thus obtained is then removed from the container mold 4 as shown in FIG. 2 to obtain a container-shaped molded body 7. In this molded body, carbon derived from the container mold material is attached to the surface on the side in contact with the container mold material (inner side in FIG. 2). In the present invention, this is removed by oxidation treatment.

  There are no particular restrictions on the conditions for the oxidation treatment. For example, heating is performed in air at a temperature of 800 ° C. to 1100 ° C. for 1 to 10 hours, for example, about 3 hours. As a result, the carbon adhering to the container-shaped molded body is oxidized to carbon dioxide, and the carbon content is almost completely removed. During heating, the oxygen concentration in the surrounding atmosphere may be increased. By this oxidation treatment, the container obtained by the present invention has the carbon removed from the inner wall surface, so that it is optimal as a container used in a process that dislikes carbon contamination.

As a result of the oxidation treatment, the PBN on the surface layer is also oxidized and partially becomes B ₂ O ₃ . For example, when the oxidation treatment is performed under the above conditions, the oxide layer (a layer in which PBN and B ₂ O ₃ are mixed) has a thickness of about 0.01 μm to 0.5 μm, and the surface layer portion is easily removed. In the present invention, in order to remove the surface layer, the container-shaped formed body is subjected to a thinning process from the surface on the side in contact with the mold material, thereby completing the container.

  The method for reducing the thickness is not particularly limited, and any method can be used as long as the surface can be partially removed, and various conventional methods such as grinding, polishing, and etching can be used. However, in the present invention, it is preferable to perform the thinning process by grinding and / or polishing. This is because grinding and polishing are simple and low in cost, and the surface layer can be reliably removed with high accuracy. For example, grind using an NC lathe, or set the container on a rotary polishing machine, press the inner wall surface against the inner wall surface of the container using sandpaper, sponge with abrasive grains, or brush with abrasive grains, and rotate the container. While polishing. Both can be used together. At this time, the grinding and polishing amount may be obtained by actually measuring with an ultrasonic film thickness meter and a micrometer or by converting to a thickness from a difference in weight.

In the thinning process, it is preferable to remove a surface layer having a thickness of 0.5 μm or more and 100 μm or less from the surface in contact with the container mold. If the thickness is less than 0.5 μm, the partially broken B ₂ O ₃ PBN layer remains without being removed, and the film is peeled off in a relatively short usage time when used for crystal growth, causing crystal defects. There is a fear. On the other hand, if the thickness exceeds 100 μm, there is a high possibility that layer separation peculiar to the anisotropy of the PBN film will occur, which may also cause crystal defects. Further, since the removed film must be formed to be excessively thick, the cost is increased. In particular, the thinning process by polishing is not preferable because it takes a long time to polish and increases the cost. More preferably, the thickness to be removed is 1 μm or more and 50 μm or less. As a result, problems such as film removal can be suppressed without much cost, and the effects of the present invention can be maximized.

It is preferable to perform the said thinning process especially about the corner part of the said container-shaped molded object. Referring to FIG. 3, it is considered that the corner portion 8 is likely to be easily detached because the film quality tends to become brittle due to the residual stress due to the anisotropy of the PBN film. In particular, when the curvature is R20 mm or less at the bottom corner (R portion), the film is easily detached. Therefore, reducing the thickness of the PBN layer that is originally brittle and partially B ₂ O _{3 at} this corner is more effective in exposing the PBN layer with few fresh defects. In addition, although the said thinning processing amount may be made uniform over the whole inner wall surface, you may change variously for every location of a container-shaped molded object. For example, only the corner portion may be thinned, and the same effect can be obtained even if the grinding amount or the polishing amount is changed for each portion within the above-described thickness range. It can be appropriately changed based on the purpose, container shape and the like.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to these.

<Example 1-10, Comparative Example 1>
A cylindrical graphite container mold 4 having a diameter of 150 mmφ × 200 mmH and a corner portion R20 mm is set in the external heating low pressure CVD apparatus 1 shown in FIG. 1, and NH ₃ and BCl ₃ are placed in a vacuum of 2 Torr (267 Pa) for 1800. A PBN film was formed to a thickness of 1 mm on the container mold 4 by reacting at a temperature of 0 ° C. After cooling to room temperature, it was removed from the container mold 4 as shown in FIG. 2, and a container-shaped PBN molded body 7 having an inner diameter of 150 mm, a height of 200 mm, and a corner portion of R20 mm as shown in FIG.

The container-shaped molded body thus obtained was oxidized in the atmosphere at 850 ° C. for 3 hours to remove carbon adhering to the inner wall surface transferred from the graphite container mold. At this time, the thickness of the B ₂ O ₃ layer was about 0.05 μm. Further, the inner wall surface was polished and removed with a sandpaper of # 600 and various PBN containers were prepared (Examples 1 to 10).

  For comparison, a PBN container was produced by the same operation as above except that polishing removal was not performed (Comparative Example 1).

The following life test was performed on the PBN container thus obtained. 200 g of B ₂ O ₃ was put in the container, heated to 1100 ° C. and held for 1 hour, and then allowed to cool naturally. Thus B ₂ O ₃ is solidified again melted temporary this time B ₂ O ₃ is fell off from PBN container wall by heat shrinkage, the B ₂ O ₃ which has been partially adhered residual ethanol For 10 hours to complete removal. A series of these operations was repeated, and the number of times until a crack was generated in the container was determined and defined as life. In addition, every time a series of operations was completed, the state of membrane desorption and layer separation on the inner wall surface of the container was confirmed. The results of these examples are shown in Table 1.

  In Examples 1 to 10, depending on the polishing amount, there was an example in which membrane desorption or layer separation was observed in the first use, but all showed a life of 4 times or more. In addition, although the layer separation does not detach | desorb as a film | membrane, the layer separation has arisen and the state which is going to peel is shown. In particular, it has been found that when the polishing amount is 0.5 to 100 μm, especially 1 to 50 μm, the life is long and membrane detachment and layer separation are difficult to occur. On the other hand, in Comparative Example 1 in which the inner wall surface was not thinned, the cost of the expensive PBN container was three times.

<Examples 11-20, Comparative Example 2>
A container-shaped PBN compact was produced in the same manner as in Example 1-10, and then oxidized in the atmosphere at 1000 ° C. for 3 hours to remove carbon adhering to the inner wall surface by transfer from the graphite mold. Further, various corners of the inner wall surface were sanded and removed with a sandpaper of # 600 to produce various PBN containers (Examples 11 to 20).

  For comparison, a PBN container was produced by the same operation as above except that polishing removal was not performed (Comparative Example 2).

  The obtained PBN container was subjected to a life test in the same manner as in Example 1-10, and the state of membrane detachment and layer separation on the inner wall surface of the container was confirmed. The results are shown in Table 2.

  In Examples 11-20, depending on the polishing amount, there was an example in which membrane detachment or layer separation was observed in the first use, but all showed a life of 3 times or more. In particular, it has been found that when the polishing amount is 0.5 to 100 μm, especially 1 to 50 μm, the life is long and membrane detachment and layer separation are difficult to occur.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

DESCRIPTION OF SYMBOLS 1 ... External-heat type low pressure CVD apparatus, 2 ... Reaction chamber, 3 ... Heater, 4 ... Carbon container mold material, 5 ... Raw material supply part, 6 ... Exhaust part, 7 ... Container-shaped molded object, 8 ... Corner part

Claims (2)

A method of manufacturing a pyrolytic boron nitride container ,
Forming a film of pyrolytic boron nitride on a carbon container mold by a thermal CVD method ;
A step of obtaining a container-shaped molded body by removing the film-formed product from the container mold ,
Heating the container-shaped formed body at a temperature of 850 ° C. to 1100 ° C. for 1 to 10 hours, and removing the carbon adhering to the surface derived from the container mold material by oxidation treatment ;
Thereafter, a pyrolytic boron nitride comprising a step of forming a container by performing a thinning process for removing a surface layer having a thickness of not less than 0.5 μm and not more than 100 μm from the surface in contact with the mold material on the container-shaped molded body Container manufacturing method. The method for manufacturing a pyrolytic boron nitride container according to claim 1, wherein the thinning process is performed only on a corner portion of the container-shaped molded body.

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