JPH0456766B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial application field) Pyrolytic boron nitride (hereinafter abbreviated as pBN) products,
Crucibles, boats, and other jigs for melting metals, alloys, and compounds, especially for use in molecular beam epitaxy (abbreviated as MBE) and liquid encapsulation Czochralski method (abbreviated as LEC method). Here, we will disclose the results of our research and development on the method for producing the pBN utensils, which are useful as such. pBN is a high-purity, high-quality boron nitride.
It is used in a wide range of fields such as the production of compound semiconductors and special alloys, and in particular, in the production of compound semiconductors such as GaAs, pBN's excellent corrosion resistance and high purity characteristics are utilized to the maximum extent possible. Therefore, it is considered an indispensable material for growing compound semiconductor single crystals with few impurities and excellent electrical properties. For example, in GaAs single crystal growth, pBN is used as a crucible in the above-mentioned LEC method, as a boat or other jig in the horizontal Bridgeman method (abbreviated as HB method), and is also used as a crucible on a GaAs single crystal wafer. Ga _1-X ,
pBN is also almost exclusively used as a metal melting crucible in the above-mentioned MBE method, which is a method for epitaxially growing mixed crystal compound semiconductors such as A _x ·As. Needless to say, pBN is widely used in US Patent No.
As disclosed in No. 3152006, a boron halide such as boron trichloride (BC ₃ ) and ammonia are used as raw materials at a temperature of 1450°C to 2300°C.
It is synthesized by the so-called chemical vapor deposition method (hereinafter abbreviated as CVD method), in which it is deposited in the form of a BN vapor deposited film on the surface of a suitable substrate under conditions of temperature and pressure of less than 50 torr. A pBN utensil can be obtained by appropriately selecting the substrate material and CVD conditions and separating the pBN vapor-deposited film deposited and synthesized on the surface of the substrate from the substrate. (Prior art) When the base material is inappropriate or the surface of the base material is rough, the base material and the pBN deposited film may be strongly bonded during pBN synthesis by the above-mentioned CVD method. This makes it difficult to bond and separate, making it impossible to obtain pBN utensils.
Due to the difference in thermal expansion between pBN deposited films, cracks may occur in pBN products during the cooling process after synthesis.
There is also the joy of having a product break. Even if the base material is successfully separated from the pBN deposited film, some fragments of the base material may remain attached to the surface of the pBN deposited film that was in direct contact with the rough surface of the base material. As a crucible, boat, or jig for melting compound semiconductors, etc.
When pBN utensils are actually used, they become a source of contamination such as impurities, so it is necessary to completely remove them. Conventionally, the remaining base material had to be scraped off along with part of the pBN equipment using sandpaper, or it had to be removed by chemical means such as acid treatment or oxidation treatment. These methods are very laborious and time consuming to manufacture. Furthermore, since it is difficult to confirm that the remaining base material has been completely removed, there are many drawbacks, such as the possibility that a small amount of base material may be mixed into the product. In order to facilitate the peeling of a deposit such as a pBN vapor deposited film from a substrate, it is proposed to provide a buffer layer on the substrate, which is made of a material that does not have any interaction with the deposit and has good peelability. No. 141829 and No. 57-111211 show that PG processing as a buffer layer is expensive, and powdered graphite and ZrSe powder only make it easier to peel off from the substrate, but do not cause deposits. It is unsuitable for manufacturing pBN utensils because the adhesive remains unavoidably. Furthermore, Japanese Patent Application Laid-open No. 109912/1983 describes the production of a pyrolytic boron nitride crucible with a multilayer structure in which a relatively thin inner wall is weakly bonded to a thick outer wall.
It has been described that by interrupting the deposition on the inner wall mandrel and through a cooling process below 1750°C, a weak bond is obtained with subsequent thick wall deposition on the outside. However, regarding this weak bond, there is no idea of using it to separate the mandrel together with the inner wall, but rather, there is no idea that the inner wall could be used to peel off the core metal together with the inner wall. It is an integral part of the thick outer wall for active use. (Problems to be Solved by the Invention) Therefore, it is an object of the present invention to provide an advantageous method for producing pBN utensils that does not have the above-mentioned drawbacks such as the introduction of contaminants in the prior art. (Means for solving the problem) The inventors conducted various studies to solve the above-mentioned drawbacks in conventional manufacturing, and as a result, they created a buffer between the graphite base material and the pBN vapor-deposited film. A pre-deposited layer serving as a layer is previously formed on the surface of the graphite substrate and this pre-deposited layer, in particular on top of this layer, is subsequently applied.
By forming a discontinuous layer in contact with the layer of pBN wares obtained by pBN precipitation synthesis,
This discontinuous layer simplifies the removal of flakes on pBN utensils together with the pre-deposited film on the graphite base plate, thus eliminating cracks and remaining parts of the graphite base material regardless of the surface condition of the graphite base material. It has been found that pBN utensils that do not generate any pBN can be easily obtained. Based on this knowledge, the present invention uses boron halide and ammonia as raw materials to precipitate and synthesize pBN on a graphite base material by chemical vapor deposition at a temperature of 1000°C or higher, and after cooling, the graphite base material is removed. do
In order to obtain pBN utensils, prior to the precipitation synthesis of the pBN, a layer with a thickness of 10 μm or more and 300 μm or less is placed on the surface of the graphite substrate to serve as a buffer zone between this and the pBN utensil to be made. A pre-deposited layer of pyrolytic boron nitride is pre-deposited, and then a layer is created on the surface of this pre-deposited layer.
A discontinuous boundary facing the pBN utensil is formed, and then pBN is successively precipitated and synthesized until the predetermined thickness of the pBN utensil is reached.While cooling, a pre-deposited layer is applied to the discontinuous interface along with the graphite base material to pBN. The gist of the present invention is a method for manufacturing pBN utensils, which is characterized by peeling and removal from the pBN utensils. In order to form the discontinuous boundary, 100% of the time is required for the formation of the pyrolytic boron nitride vapor deposited film after the preliminary vapor deposition layer is vapor-deposited on the graphite substrate and before the start of the synthesis of the pyrolytic boron nitride vapor-deposited film to obtain the pBN utensils. Maintaining the temperature and pressure by interrupting only the supply of raw materials for more than a minute, and at least maintaining the raw material ratio, temperature, deposition rate, and pressure during the deposition of pyrolytic boron nitride equipment on the surface of the preliminary deposition layer. Thickness with different conditions
Continuing the deposition of pyrolytic boron nitride over 5 μm or more is suitable as an embodiment. The pBN utensils obtained through the above procedure are isolated by the discontinuous boundary and the pre-deposited layer, and are precipitated and synthesized without direct contact with the graphite base material. Since the base material is peeled off and removed, even if the surface of the graphite base material is rough, there is no risk that some of the material will get mixed into the product. Under the thermal influence during this period, the predeposited layer becomes an effective buffer zone, and the strain is absorbed in this area, which has the advantage that it does not spread to the inside of the product. (Function) The reason why the thickness of the preliminary vapor deposition layer was defined as 10 μm or more and 300 μm or less is as follows. In other words, if the thickness of the pre-deposited layer is less than 10 μm, the thickness of the pre-deposited layer is not sufficient to serve as a buffer zone, and it becomes difficult to peel off the pre-deposited layer from the discontinuous boundary, requiring the introduction of a time-consuming process such as polishing. This is because, in some cases, a part of the graphite base material adhered to the pre-deposited layer may be mixed into the product. Further, the reason why the thickness is set to 300 μm or less is that even if the thickness of the pre-deposited layer is made larger than that, the effect as a buffer zone for suppressing the spread of cracks, etc., which is a concern to products and equipment, cannot be improved. There are no particular restrictions on the vapor deposition conditions when forming the preliminary vapor deposition layer on the surface of the graphite substrate, but they may be the same or different from those used in the precipitation synthesis by vapor deposition of the pBN utensil to be made. However, if you try to create a layer on the surface of this pre-deposited layer,
It is necessary to form a discontinuous boundary facing the pBN utensil, and for the formation of this discontinuous boundary, at least the pBN
Physical properties (orientation state of pBN layer, density,
(002) plane spacing) etc. In this way, the pre-deposited layer has a discontinuity with the pBN utensil, and at this discontinuous boundary, it becomes easy to peel off the pre-deposited layer together with the graphite base material from the pBN utensil. Depending on the difference in the above-mentioned physical properties, favorable results such as the pre-deposited layer spontaneously peeling off from the pBN utensil together with the graphite base material during the cooling process can be obtained. Here, it is sufficient that the thickness of the discontinuous boundary is 5 μm or more on the side of the pre-deposited layer in contact with the pBN utensil. Methods for effectively changing the physical properties of pBN at discontinuous boundaries include changing the ratio of boron halide and ammonia in the raw materials, changing the deposition temperature, changing the deposition rate, and changing the pressure during deposition. Any method of changing it is effective. (Example) Eight graphite plates of 5 cm width x 60 cm x 1 cm thickness were
8 on the top surface of the circular graphite plate (bottom plate) cm x 1 cm thick
A reaction chamber was formed by assembling it into a rectangular cylindrical shape. A hole with an inner diameter of 5 cm is made in the center of the bottom plate, and an outer tube with an outer diameter of 5 cm and an inner tube with an outer diameter of 2.5 cm, both of which are made of graphite and coated with pBN in advance, are fitted as a concentric double tube as a raw material gas introduction tube. On the other hand, a graphite substrate with a diameter of 5 cm and a length of 10 cm was suspended from the upper part of the reaction chamber. The surface roughness of the graphite base material is based on H _nax 100μm.
A 200μm one was also added. The entire reaction chamber was placed in a high-temperature resistance heating vacuum furnace, and stainless steel gas piping was connected to the raw material gas introduction tube so that BC ₃ gas could be supplied to the inner tube and NH ₃ gas could be supplied to the outer tube. Various pBN crucibles with a wall thickness of 1.5 mm were produced under various conditions shown in Table 1, under the conditions shown in Table 1, by heating to a predetermined temperature and under a predetermined pressure while evacuating the furnace to 10 ^-3 torr. The heating temperature and pressure are listed in Table 1 along with the deposition rate. The obtained crucible was analyzed for the amount of carbon in the crucible, and cracks in the appearance were observed, and the results are shown in Table 1.

【table】

【table】

[Table] (Effects of the invention) According to the method for manufacturing pBN utensils according to the present invention, the surface roughness of the graphite base material surface is irrelevant, there is no cracking, and there is no partial mixing of graphite base material components. It is possible to easily manufacture pyrolytic boron nitride ceramics without any waste.

Claims (1)

[Claims] 1. Using boron halide and ammonia as raw materials
Pyrolytic boron nitride is precipitated and synthesized on a graphite base material by chemical vapor deposition at a temperature of 1000°C or higher, and after cooling, the graphite base material is removed to obtain pyrolytic boron nitride utensils. Prior to the precipitation synthesis of the pyrolytic boron nitride, a layer of 10 μm or more and 300 μm in thickness is placed on the surface of the graphite base material to serve as a buffer zone between this and the pyrolytic boron nitride article to be made. A pre-deposited layer of pyrolytic boron nitride as shown below is pre-deposited, and then a discontinuous boundary is formed on the surface of the pre-deposited layer facing the pyrolytic boron nitride article to be made, and then subsequently: Pyrolytic boron nitride is precipitated and synthesized until it reaches a predetermined thickness for pyrolytic boron nitride utensils, and while cooling, a pre-deposited layer is added to the graphite base material at discontinuous boundaries from the pyrolytic boron nitride ware. A method for producing pyrolytic boron nitride utensils, characterized by removing flakes. 2 The formation of discontinuous boundaries occurs after the deposition of the pre-deposited layer.
The method according to claim 1, which is based on interruption of raw material supply for 10 minutes or more. 3. The formation of a discontinuous boundary is caused by the vapor deposition of pyrolytic boron nitride over a layer thickness of 5 μm or more on the surface of the pre-deposited layer, at least with a raw material ratio different from that during the vapor deposition of the pyrolytic boron nitride vessel. A method as claimed in claim 1. 4. The formation of a discontinuous boundary is due to the vapor deposition of pyrolytic boron nitride to a layer thickness of 5 μm or more on the surface of the pre-deposited layer at a temperature different from that during the vapor deposition of the pyrolytic boron nitride vessel. A method according to claim 1. 5. The formation of a discontinuous boundary is due to the vapor deposition of pyrolytic boron nitride to a layer thickness of 5 μm or more on the surface of the pre-deposited layer at a vapor deposition rate different from that during the vapor deposition of the pyrolytic boron nitride vessel. A method according to claim 1. 6. The formation of a discontinuous boundary is due to the vapor deposition of pyrolytic boron nitride to a layer thickness of 5 μm or more on the surface of the pre-deposited layer, at least at a pressure different from that during the vapor deposition of the pyrolytic boron nitride vessel. A method according to claim 1.