DE102016006963A1 - A method of manufacturing a pyrolytic boron nitride container and pyrolytic boron nitride container - Google Patents

Abstract

The present invention provides a method of fabricating a pyrolytic boron nitride (PBN) container comprising the steps of: forming a layer of pyrolytic boron nitride on a carbon-made container mold by a thermal CVD method; Removing the pyrolytic boron nitride layer from the container mold to obtain a container shaped article; Performing an oxidation treatment on the container-shaped molding to remove adherent carbon on a surface of the container-shaped molding derived from the vessel mold; and then performing a thickness reduction treatment on the container-shaped molding from a side in contact with the container shape to form the pyrolytic boron nitride container. The present invention also provides such a PBN container. The PBN container of the present invention delaminates or peels only with difficulty and is suitable for growing a single crystal.

Description

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a pyrolytic boron nitride container and a pyrolytic boron nitride container. In particular, the present invention relates to a method of manufacturing a pyrolytic boron nitride container useful as a large sized crucible for use in pulling a single crystal of a III-V compound semiconductor or as a crucible for melting Al, which is for vacuum deposition or molecular beam epitaxy (US Pat. MBE), and a pyrolytic boron nitride container suitable for the above use.

DESCRIPTION OF RELATED TECHNIQUE

For pulling a III-V compound semiconductor single crystal, such as a GaAs single crystal or an InP single crystal, various methods have been used, for example, a Bridgman horizontal (HB) method, a Horizontal Gradient Freeze (HGF) method. Method), a Liquid Encapsulated Czochralski (LEC) method, a Vertical Bridgman (VB) method, a Vertical Gradient Freeze (VGF) method.

In order to avoid the vaporization of constituent elements, an LEC method is chosen, and in this LEC method, quartz crucibles were previously used. In this case, a problem arises in that Si impurities mix in a crystal, and consequently, the drawing is usually carried out with Cr doping.

However, Cr doping lowers the insulation and thereby makes the crystal unsuitable for IC substrates. Accordingly, in order to obtain a non-doped semiconductor substrate, there has been proposed the use of a pyrolytic boron nitride container (hereinafter referred to as "PBN") (Patent Literature 1) which gives a high-purity III-V compound and does not form an impurity level which acts as a dopant. even if it was mixed in the single crystal.

This LEC method may pull a crystal with a high temperature gradient and has the disadvantage that the dislocation density in the crystal is high. On the other hand, vertical boat methods such as a VB method in which a seed crystal is placed in a PBN crucible and brought into contact with a raw material melt to pull a single crystal, the temperature being slowly lowered from the seed side are slowly produced , gives a lower dislocation density compared to LEC methods. As a result, they are receiving increasing attention as a method of manufacturing a substrate for electron assembly.

In a PBN crucible used in these vertical boat methods, the inner wall of a crucible must be coated with boron oxide (B ₂ O ₃ ), which is fed with a raw material so as not to be wetted by direct contact with raw material melt. When the raw material and B ₂ O ₃ are fed together and heated, B ₂ O ₃ , which has a low melting point, melts and covers the inner wall of the crucible, and the raw material melts by further heating, and hence the raw material does not directly come along a PBN crucible in contact to produce a single crystal with few defects. When a PBN layer delaminates or peels off the inner wall of a PBN crucible, the likelihood of forming an area that is not properly covered with B ₂ O _{3 increases} . As a result, a crystal boundary is formed starting from the region, causing a fatal problem in polycrystallization, and in the worst case preventing a single crystal from being generated (Patent Document 2).

PNB containers are often made by forming a layer on a carbon-made container mold by a thermal CVD (Chemical Vapor Deposition) method. After removal of the mold, carbon derived from the container mold adheres to the surface of the PNB container. Consequently, a problem arises when the container is used for a process in which carbon contaminants are harmful (Patent Document 3).

Fonts of the prior art

patents

• Patent document 1: Japanese Laid-Open Publication No. Publ. H10-87306
• Patent document 2: Japanese Laid-Open Publication No. Publ. 2003-146791
• Patent 3: Japanese Laid-Open Publication No. Publ. H11-335195

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described problem. The object of the present invention is the provision of a PBN container. which is difficult to delaminate or peel and is capable of growing a single crystal, and a method for producing the same.

In order to solve the above problem, the present invention provides a method of manufacturing a pyrolytic boron nitride container, comprising the steps of:
Forming a layer of pyrolytic boron nitride on a carbon-made container mold by a thermal CVD method;
Removing the pyrolytic boron nitride layer from the container mold to obtain a container shaped article;
Performing an oxidation treatment on the container-shaped molding to remove adherent carbon on a surface of the container-shaped molding derived from the vessel mold; and then
Performing a thickness reduction treatment on the container shaped article from a side in contact with the container shape to form the pyrolytic boron nitride container.

When a layer of PBN is formed (attached) to a carbon-made container mold, carbon adheres to it from the container mold. In order to remove the carbon, in the present invention, a container-shaped blank is oxidized after being removed from the container mold. By this treatment, the carbon originating from the container mold and adhering, for example, to the inner wall, is almost completely eliminated by conversion into carbon dioxide. Thus, the present invention is ideal for use in a process in which carbon contaminants are detrimental.

This oxidation treatment also oxidizes PBN on the surface and partially converts it to B ₂ O ₃ . For example, when the oxidation conditions are set at 800 to 1100 C in the air for 3 hours, the oxidized layer will have a thickness of about 0.01 to 0.5 μm. Since PBN and B ₂ O ₃ are present together, this part is brittle and there is a risk that it partially delaminates. It is possible to remove this part by performing a starch reduction treatment to obtain a PBN container that does not delaminate or peel. Moreover, it is considered that the upper surface of the inside of the layer contains many PBN defects because it was formed during a first stage of forming the layer to which the atmosphere for forming a layer is not stable. This surface layer is also removed by the thickness reduction treatment, and a fresh PBN layer with few defects is on the surface.

Preferably, the thickness reduction treatment is carried out by grinding or polishing.

Both grinding and polishing can easily and uniformly remove the coexisting B ₂ O ₃ layer, which is a surface layer of the PBN container.

In the thickness reduction treatment on the container-shaped molding, it is preferable to remove a surface layer having a thickness of 0.5 μm or above and 100 μm or below from the side having contact with the container shape.

In a container subjected to such a thickness reduction treatment, the coexisting B ₂ O ₃ layer is almost completely removed, and hence the occurrence of delamination or peeling when used to grow a crystal is more reliably suppressed.

Preferably, the thickness reduction treatment is performed at a corner of the container-shaped molding.

It is believed that at the corner of a PBN container where the two surfaces meet, the nature of a PBN layer due to residual stress due to anisotropy of a layer tends to be brittle and is liable to segregate. Consequently, it is from the perspective of the Expose a fresh PNB layer with few defects more useful to perform the starch reduction treatment of the PBN layer in this corner, which is originally brittle and partially converted to B ₂ O ₃ .

The present invention also provides a pyrolytic boron nitride container manufactured as follows: forming a layer on a carbon-made container mold by a thermal CVD method, which is removed from the container mold, and then subjecting an oxidation treatment to carbon, adhered to a surface thereof, and subjecting a thickness reduction treatment to a side having contact with the container shape.

Such a PBN container exposes a fresh surface without involving a coextrusive B ₂ O ₃ layer on the inner wall, whereby the occurrence of delamination or peeling is difficult. Consequently, the PBN container of the present invention is ideally suited as a crucible for growing a single crystal and so on.

The present invention enables the provision of an improved PBN container which is difficult to delaminate or peel off. The PBN container provided by the present invention is ideal for growing a single crystal, and it is possible to stably grow a single crystal with few crystal defects by growing a crystal using the container. This is particularly suitable for a large-sized crucible used for pulling a III-V compound semiconductor single crystal, an Al melting crucible used for vacuum vapor deposition or molecular beam epitaxy (MBE), etc. The present invention PBN container also has the advantage that cracks are difficult to occur during use, and therefore it is useful for lowering the cost of manufacturing a semiconductor, etc. Previously, high purity treated graphite was used as a container mold to avoid mixing impurities in PBN containers. In the present invention, after the oxidation treatment, the starch reduction treatment is carried out as described above, and therefore it is possible to produce a container of the same quality as the earlier ones even if an untreated conventional form container mold is used, which has the advantage of that the costs for a container form are lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

Show it:

1 Fig. 12 is a schematic diagram of an external low-pressure CVD heater which can be used for the present invention;

2 an explanatory sectional drawing showing how a PBN container is removed from a carbon-made container shape;

3 an explanatory sectional view of an exemplary PBN container, which is provided by the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these.

The present inventors have found, after thorough investigation, that in producing a PBN container, a high-quality PBN container can be produced by performing a starch reduction treatment on the container-shaped PBN molding produced by a thermal CVD method after oxidation treatment a container made of carbon was prepared; and a single crystal can be generated without defects by pulling the crystal by using this PBN container.

The invention will be explained below with reference to the drawings.

In the production of a PBN container according to the present invention, any known thermal CVD method can be used. The formation of a PBN layer by a thermal CVD method is performed in a low-pressure external heating-CVD apparatus 1 performed, such as in 1 shown. In one with a heater 3 equipped reaction chamber 2 is a part for feeding raw material 5 , an exhaust part 6 and a container made of carbon 4 arranged. A compound containing N atom, such as NH ₃ (ammonia) and a boron halide such as BCl ₃ (boron trichloride) are supplied thereto as raw materials to form the container 4 by means of a thermal CVD reaction at high temperatures of 1800 to 2000 ° C to form a PBN layer. As a container mold, a container mold made of graphite is preferably used, although various carbon materials such as graphite, C / C carbon composites and pyrolytic graphite may be used.

The PBN layer you obtained will then be removed from the container 4 removed to a container-shaped fitting 7 , as in 2 shown to get. In this fitting, carbon derived from the container form adheres to the surface (inner side in FIG 2 ), which had contact with the container shape. This is removed by oxidation treatment in the present invention.

The conditions for the oxidation treatment are not particularly limited. For example, it is heated by heating at a temperature of 800 to 1100 ° C for 1 to 10 hours, for. B. carried out in the air for 3 hours. The carbon adhered to the container-shaped molding is oxidized by this treatment and converted into carbon dioxide, whereby it is almost completely removed. It is also possible to increase the concentration of oxygen in the surrounding atmosphere when heated. The container obtained by the present invention, in which carbon on the inner wall has been removed by oxidation treatment, is an ideal container for a process in which carbon contaminants are detrimental.

Due to the oxidation treatment, the surface PBN also partially oxidizes to B ₂ O ₃ . For example, an oxidation treatment having the above conditions forms an oxidized layer (a layer in which PBN and B ₂ O ₃ are present together) of a thickness of about 0.01 to 0.5 μm, which is liable to delaminate this surface part. In order to remove this surface, in the present invention, a starch reduction treatment is performed on the container-shaped molding on a side having contact with the container mold to complete the pyrolytic boron nitride container.

There are no particular limitations to the process of starch reduction treatment, and it is possible to use any method by which a part of the surface can be removed, including various conventional methods such as grinding, polishing, and etching. However, in the present invention, it is preferable to perform the thickness reduction treatment by grinding or polishing, or both. The surface layer can be easily and cheaply removed by grinding or polishing uniformly and accurately. For example, grinding may be done using an NC lathe; and polishing can be performed by pressing an abrasive paper, a sponge with abrasive grains or a brush with abrasive grains against the inner wall of a rotating container which has been clamped in a rotary polishing machine. Both can be used together. In this case, it is recommended that the amount of grinding or polishing be determined by measuring with an ultrasonic power meter or a micrometer, or by converting the weight difference into the thickness.

In the above starch reduction treatment, it is preferable to remove a surface layer having a thickness of 0.5 μm or above and 100 μm or below from the side having contact with the container shape. If the thickness is less than 0.5 μm, there is the possibility that the brittle PBN layer, which is partially converted to B ₂ O ₃ , will not be removed and will separate when pulling a crystal as a layer after a relatively short operation time, and thereby causes a crystal defect. On the other hand, if more than 100 μm is removed, the likelihood of forming a layer separation typical of anisotropy of a PBN layer is increased, which also causes a crystal defect. In addition, a thicker layer has to be formed for the layer thickness to be removed, thereby increasing the cost. In particular, in the thickness reduction treatment by polishing, a longer polishing time is required, which causes an unfavorable cost increase. More preferably, the starch to be removed is set to 1 μm or above and 50 μm or below. As a result, problems such as delamination can be suppressed without excessive cost, and the advantage of the present invention can be exhibited to the highest degree.

The above strength reduction treatment is particularly preferably performed at a corner of the container-shaped molding. This is based on 3 explained. At the corner 8th it is assumed that the layer tends to be particularly brittle and that due to residual stress due to anisotropy of a PBN layer there is a risk of separation (delamination or peeling). In particular, there is a risk of the layer separating when the rounding of the corner at the bottom ("R" part) is R 20 mm or less. Thus, the starch reduction treatment is on this PBN layer a corner that is initially brittle and partially converted to B ₂ O ₃ , more effective to expose a fresh PBN layer with few defects. It should be noted that the extent of the thickness reduction treatment may be uniform on the entire inner wall, but it may be different on each part of the container shaped fitting. For example, it is possible to perform the thickness reduction treatment only at the corner, or to change the amount of grinding or polishing on each part in the above thickness range to obtain the same advantage. It may be suitably changed on the basis of the purpose or the shape of the container.

EXAMPLE

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these.

<Examples 1 to 10, Comparative Example 1>

In the in 1 shown low-pressure CVD device with external heating 1 furnished with a cylindrical container shape 4 of graphite having a size of 150 mmφ x 200 mmH and a corner R of 20 mm, NH ₃ and BCl _{3 were} reacted at 1800 ° C under vacuum of 2 Torr (267 Pa) to form a PBN layer having a thickness of 1 mm at the container shape 4 train. This was cooled to room temperature and then from the container mold 4 as in 2 shown removed to a container-shaped PBN fitting 7 with an inside diameter of 150 mm, a height of 200 mm and the corner R of 20 mm, as in 3 shown to produce.

The container-shaped molding thus produced was subjected to an oxidation treatment at 850 ° C in the atmosphere for 3 hours to remove carbon which had been transferred from the graphite-made container mold and adhered to the inner wall. In this case, the thickness of the B ₂ O _3- converted layer was about 0.05 μm. In addition, each inner wall was polished to remove a predetermined thickness with a 600 grit abrasive paper to make a plurality of PBN containers (Examples 1 to 10).

For comparison, a PBN container was manufactured by the same procedure as above, except that the removal by polishing (thickness reduction treatment) was not performed (Comparative Example 1).

On PBN containers produced in this way, the following life tests were carried out. Into the containers, 200 g of B ₂ O _{3 was} fed and the temperature was raised to 1100 ° C and held there for 1 hour; then a natural cooling took place. In this process, the B ₂ O _{3 was} once melted and then solidified again, whereby the B ₂ O ₃ peeled off from the inner wall of the PBN container due to the thermal shrinkage; the partially remaining adherent B ₂ O ₃ was completely removed by immersion in ethanol for 10 hours. This series of operations was repeated to determine the repetition times until the container formed a crack, which was defined as the lifetime. In addition, the situation of layer separation or ply separation on the inner wall of the container was tested at both ends of the series of operations. The results from this example are shown in Table 1. [Table 1] Polishing thickness (μm) Lifetime (Male) Condition of the inner wall (layer separation) example 1 0.2 7 Layer separation at 2 times Example 2 0.5 10 Layer separation at 3 times Example 3 1 17 Layer separation at 6 times Example 4 3 18 Layer separation at 7 times Example 5 10 20 no layer separation Example 6 50 20 no layer separation Example 7 70 17 Layer separation at 7 times Example 8 100 16 Layer separation at 5 times Example 9 120 5 Layer separation at 1 time Example 10 150 4 Layer separation at 1 time Comparative Example 1 0 3 Layer separation at 1 time

In Examples 1 to 10, each lifetime was 4 times or more, although in some examples, film separation or pagination was found depending on the polishing strength of 1-time use. Incidentally, ply separation means a situation in which the ply created separation near peeling, but was not separated as a layer. It was found that, in particular, when the polishing strength was set to 0.5 to 100 μm, particularly 1 to 50 μm, a long life was attained and ply separation hardly occurred. On the other hand, in Comparative Example 1 where no thickness reduction treatment was performed on the inner wall, the life of the expensive PBN container was 3 times.

<Examples 11 to 20, Comparative Example 2>

Container-shaped PBN fittings were produced in the same manner as in Examples 1 to 10. Thereafter, the container-shaped PBN molded pieces were subjected to a 3-hour oxidation treatment at 1000 ° C in the atmosphere to remove carbon which had been transferred from the graphite molds and adhered to the inner walls. The corner of each inner wall was polished to remove a predetermined thickness with 600 grit abrasive paper to make several PBN containers (Examples 11 to 20).

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

Life tests were conducted on the thus prepared PBN containers, and the situation of layer separation or pore separation on the inner wall of the containers was tested in the same manner as in Examples 1 to 10. These results are shown in Table 2. [Table 2] Polishing thickness (μm) Lifetime (Male) Condition of the inner wall (layer separation) Example 11 0.2 5 Layer separation at 1 time Example 12 0N5 8th Layer separation at 3 times Example 13 1 11 Layer separation at 6 times Example 14 3 15 Layer separation at 6 times Example 15 10 18 no layer separation Example 16 50 18 no layer separation Example 17 70 15 Layer separation at 5 times Example 18 100 17 Layer separation at 3 times Example 19 120 4 Layer separation at 1 time Example 20 150 3 Layer separation at 1 time Comparative Example 2 0 2 Layer separation at 1 time

In Examples 11 to 20, each life was 3 times or more, although in some examples, film separation or ply separation was found depending on the polishing strength of 1-time use. It was found that, in particular, when the polishing strength was set to 0.5 to 100 μm, particularly 1 to 50 μm, a long life was attained and ply separation hardly occurred.

It should be noted that the present invention is not limited to the embodiment described above. The embodiment is merely an illustration, and all examples having substantially the same characteristics and showing the same functions and effects as the technical concepts described in the claims of the present invention are included in the technical scope of the present invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 10-87306 [0008]
• JP 2003-146791 [0008]
• JP 11-335195 [0008]

Claims (5)

A method of manufacturing a pyrolytic boron nitride container comprising the steps of: Forming a layer of pyrolytic boron nitride on a carbon-made container mold by a thermal CVD method; Removing the pyrolytic boron nitride layer from the container mold to obtain a container shaped article; Performing an oxidation treatment on the container-shaped molding to remove adherent carbon on a surface of the container-shaped molding derived from the vessel mold; and then Performing a thickness reduction treatment on the container shaped article from a side in contact with the container shape to form the pyrolytic boron nitride container. A method of manufacturing a pyrolytic boron nitride container according to claim 1, wherein the thickness reduction treatment is carried out in the form of grinding and / or polishing. A method of manufacturing a pyrolytic boron nitride container according to claim 1 or 2, wherein in the thickness reduction treatment on the container-shaped molding, a surface layer having a thickness of 0.5 μm or above and 100 μm or below is removed from the side in contact with the container mold would have. A method of manufacturing a pyrolytic boron nitride container according to any one of claims 1 to 3, wherein the thickness reduction treatment is performed at a corner of the container-shaped molding. Container of pyrolytic boron nitride, manufactured by: Forming a layer on a carbon-made container mold by a thermal CVD method, which is removed from the container mold, and then Subjecting to an oxidation treatment to remove carbon adhered to a surface thereof, and Subjecting a thickness reduction treatment from one side that had contact with the container shape.

Images