JPH0455159B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an improved boron nitride crucible and a method for manufacturing the same, particularly for molecular beam epitaxy (MBE).
The present invention relates to a crucible for melting metals and chemicals, and a method for manufacturing the same, for use in the Liquid Encapsulated Czyochralski (LEC) method, etc. [Prior art and its problems] Pyrolytic boron nitride (PBN) is a high-purity, high-quality boron nitride (BN) material that is used in a wide range of fields such as the production of compound semiconductors and special alloys. In particular, in the production of compound semiconductors such as GaAs, PBN's excellent corrosion resistance and high purity are utilized to the maximum extent possible, making it an indispensable material for growing compound semiconductor single crystals with few impurities and excellent electrical properties. It's summery. For example, in GaAs single crystal growth, PBN is used as a crucible in the LEC method and as a boat in the HB method (horizontal Bridgeman method). PBN is also used almost exclusively as a container (crucible) for melting metal in molecular beam epitaxy, which is a method for epitaxially growing mixed crystal compound semiconductors such as Ga _1-X Al _X As on GaAs single crystal wafers. It is used. PBN is boron trichloride (BCl ₃ ), as disclosed for example in U.S. Pat. No. 3,152,006.
The so-called chemical vapor deposition method (CVD method) uses boron halide and ammonia as gaseous raw materials, and deposits BN on the surface of a suitable substrate at a temperature of 1450℃ to 2300℃ and a pressure of less than 50T _prr . ) is synthesized by If you choose the base material and CVD conditions appropriately,
Separate the precipitated PBN film from the substrate and create free-standing PBN.
Goods can be obtained. The PBN obtained in this way has a structure in which the C-plane of hexagonal BN is highly oriented in the direction perpendicular to the film growth direction.
It has remarkable anisotropy in various physical properties. In terms of mechanical properties, the PBN film has good strength in the plane direction, but its strength in the film growth direction is not so strong, and therefore it tends to peel off into thin films in the film growth direction. However, the tendency of PBN to peel off has been a major cause of shortening the lifespan of PBN crucibles when used repeatedly. Below, we will explain the problems that conventionally occurred with crucibles for LEC and MBE. Compound semiconductor single crystal rods such as GaAs and InP are
These compounds or their raw materials are melted in a PBN crucible, the upper part of which is sealed with a melt of high-purity B ₂ O ₃ , and seed crystals of the compound are attached to the compound melt in the crucible, and gradually extracted from the melt. It is widely produced by the LEC method, which involves pulling single crystal rods of compounds.
After the single crystal has been pulled, the crucible is cooled to room temperature, and in order to be used again, it is necessary to remove the B ₂ O ₃ sealant that has cooled and solidified and adhered to the inner wall of the _crucible . _3During removal, some of the PBN layer
The phenomenon of peeling off from the inner wall of the crucible while remaining attached to B ₂ O ₃ frequently occurs. It is extremely rare that the PBN layer peels off uniformly over the entire inner surface of the crucible.
In many cases, only a certain part of the inner surface of the crucible peels off,
Moreover, the thickness of the part to be peeled off is also non-uniform. In extreme cases, localized peeling may extend to the outer wall of the crucible, leading to damage to the crucible. In addition, even if the peeling is not that deep, if the peeled part is left as is and reused, the interlayers of the BN layer in the laminated structure will come into contact with the melt, so trace impurities in the melt will be concentrated between the layers. This is undesirable as it may release impurities when used again or cause new flaking when removing B ₂ O _3. Therefore, if flaking occurs, remove the flaking at the deepest part of the flaking area. It is necessary to remove even the parts that did not occur. New deep peels may be introduced during this operation. For this reason, even if one peeling does not result in damage to the crucible, the thickness of the crucible becomes thinner each time crystals are grown, and the life of the crucible ends after several to ten times. In addition, when using PBN as a crucible for MBE and melting a metal such as aluminum that has good wettability with PBN, the crucible must be cooled down when the MBE equipment is stopped. The crucible is exposed to severe stress due to the significant difference in coefficient of thermal expansion between In particular, since the molten metal wets the crucible well, the cooled and solidified metal adheres very firmly to the inner wall of the crucible, which often leads to damage to the crucible. As a way to solve these problems, a multilayered wall structure crucible was proposed, consisting of a thick outermost wall to support the entire structure, and a thin middle wall and inner wall weakly connected to this (Japanese Patent Publication No. 17428/1983). , special public service 1977
-44154) and is commercially available. Such multi-wall structure crucibles have achieved a certain degree of success as metal melting crucibles such as MBE, but as stated in the technical information of Union Carbide Company in the United States, for example, the innermost wall may be damaged. If this happens, the metal inside the crucible will seep out to the outside of the inner wall, making it impossible to use it the next time. In addition, conventional multi-walled crucibles are manufactured by stopping the precipitation reaction every time each wall is deposited, lowering the temperature, and then returning the temperature to the precipitation temperature and restarting the precipitation reaction. However, it has the disadvantage that it is very labor intensive and time consuming to manufacture. In order to solve these drawbacks of conventional PBN crucibles, the inventors of the present application investigated the structure of the crucible and its manufacturing method, and as a result, they developed a BN crucible with a large number of individual walls each having a thickness within a certain range. We have found that the disadvantages of conventional PBN can be significantly improved by this structure, and we have also completed a method for easily producing a multi-walled PBN crucible. [Means for Solving the Problems] The gist of the present invention is as follows. (1) A multi-wall structure characterized by having at least five layers of individual walls each having a thickness of 5 to 100 μm bonded to each other, and having an overall wall thickness of 0.5 to 3 mm. A boron nitride crucible made of. (2) A boron nitride crucible, which has at least five layers of individual walls each having a thickness of 5 to 100 μm bonded to each other, and has a total wall thickness of 0.5 to 3 mm, is heated using boron halide. When manufacturing by chemical vapor deposition using gas and ammonia gas as raw materials, the first wall is
At a growth rate of 150 μm, and a second wall adjacent to this at a growth rate of 1.5 to 5 times that of the first wall,
A method for manufacturing a boron nitride crucible having a multi-walled structure, which is characterized by forming each wall in an alternating manner. The present invention will be explained in more detail below. In the multi-walled crucible of the first invention, the thickness of the individual walls must be in the range of 5 to 100 μm. If the thickness of the individual walls is less than 5 μm, the divisions between the individual walls will not be clear, and the effect of the multi-wall structure will not be obtained. Furthermore, when the thickness of the individual walls exceeds 100 μm, spontaneous lamination occurs between the walls due to stress between the walls, leading to undesirable results such as trapping of impurities. The entire crucible is composed of at least five layers of the above-mentioned individual walls bonded to each other, preferably weakly bonded to each other. If the number of layers is less than 5, the thickness of the entire crucible is too thin and sufficient strength cannot be obtained. Note that the number of layers of the walls constituting the crucible is determined from the thickness of each wall and the desired overall thickness of the crucible. The wall thickness of the entire crucible is 0.5 ~
It needs to be 3mm. If it is less than 0.5 mm, the overall strength will be insufficient, and if it exceeds 3 mm, spontaneous lamination will occur due to increased internal stress. Using such a multi-walled crucible of the present invention significantly extends the life span over conventional PBN crucibles. First, the behavior when used as a crucible for the LEC method will be explained. The crucible of the present invention has a large number of
Since the BN walls are bonded to each other, even if the BN layer peels off when B ₂ O ₃ is removed after crystal growth by the LEC method, the peeling is due to the bonding force intentionally introduced when making the BN crucible. Since the delamination is selectively initiated at weak interwall regions and the propagation of delamination occurs only between the walls where delamination is initiated, the thickness of the delamination film increases at the same time as it propagates, as observed in conventional PBN crucibles. This phenomenon of deepening and widening of peeling does not occur. Moreover, the thickness of each BN layer is 5
It has been found that when the thickness is set to ~100 μm, the layer on the innermost wall side of the crucible always peels off among the many mutually bonded BN layers, although the reason is not yet clear. Therefore, the peeling that occurs during B ₂ O ₃ removal always occurs at the innermost wall layer of the crucible, and the partially peeled layer can be removed without deep peeling.
The lifespan of the crucible is significantly longer than that of conventional crucibles, and it has the characteristics that there is little variation in the lifespan between crucibles. Furthermore, when the crucible of the present invention is used for metal melting such as MBE, the BN on the innermost wall of the multiple walls is subjected to tensile stress toward the inside of the crucible as it adheres to the metal during cooling. Because it is flexible and weakly bonded to its outer wall, the innermost wall with metal attached will not break, but will slightly separate from the outer wall and contract with the metal. Furthermore, even if the innermost wall is damaged and molten metal seeps between the walls, there are many BN walls outside that have the same characteristics as the innermost wall, so it is not possible to continue using it, unlike in the past. can. In this way, the use of the BN crucible of the present invention allows for more repeated use than before. Next, the second invention will be explained. The present invention particularly relates to a method for manufacturing a PBN crucible among multi-walled BN crucibles. First, the individual walls forming the multi-walled PBN crucible are formed by a CVD method using boron halide gas such as boron trichloride and ammonia gas as raw materials, at a pressure of 0.5 to 5 Torr. Preferably, the temperature is within the range of 1850 to 1950°C. If the pressure is less than 0.5 Torr, the decomposition of PBN becomes active, and if the pressure exceeds 5 Torr, fine particles of BN are generated as a by-product and incorporated into the PBN film, which is undesirable because the uniformity of the structure is impaired. Forms at temperatures below 1850°C. PBN has low strength and lacks practical strength as a crucible. Moreover, when the temperature exceeds 1950°C, a reaction occurs between the graphite of the base material and PEN, resulting in unfavorable results such as conversion of PBN to B ₄ C and an increase in the amount of carbon impurities in PBN. The most preferable pressure and temperature conditions are 0.75 to 3 Torr and 1900 to 1940°C. In order to weakly bond the individual walls formed under such conditions to each other, it is necessary to form adjacent walls at different film growth rates (evaporation rates). wall is 10~ per hour
A cycle of forming the second wall at a growth rate of 150 μm and a second wall adjacent thereto at a growth rate of 1.5 to 5 times that of the first wall is repeated. The reason for the 1.5 to 5 times difference in growth rate between the first wall and the second wall is that when the growth rate is less than 1.5 times different, the bonding force between the two walls becomes a single constant force. Since the growth rate is not much different from that of a continuous film formed, the purpose of the present invention, which is a multi-walled structure, is not achieved, and a difference in growth rate of more than five times causes the bond between the two walls to deteriorate. This is because spontaneous lamination occurs in pots where the force is too weak. Also, the growth rate of the wall is at most every hour.
Must be less than 750μm. This is 750 μm per hour
This is because the mechanical strength of a PBN film formed at a growth rate exceeding For this reason, the second
The growth rate of the first wall, which is formed at a growth rate of 1/1.5 to 1/5 of that of the first wall, is inevitably 150 μm or less per hour. Also, the first wall is that at least every hour
It is preferable to form at a growth rate of 10 μm or more.
This is to avoid unnecessary lengthening of the time required to complete one crucible. For example, as a condition that is good in terms of quality and is also preferable from the point of view of productivity, the first wall should be
150 μm, and a method of forming the second wall at a growth rate of 75 to 250 μm per hour. In order to produce one crucible, the first
Although it is necessary to repeatedly form the first and second walls alternately, there is no need to temporarily interrupt film formation when changing from the first to the second wall and from the second to the first wall. , can be changed continuously, so the crucible can be manufactured in the same time as a conventional crucible. One way to change the growth rate of the film on the first wall and the second wall is to change various factors that are said to affect the growth rate in regular CVD methods at predetermined intervals. That is, the concentration of the raw material gas introduced into the CVD reaction chamber,
Factors such as the flow rate of the gas flowing over the base material may be changed, and for example, the composition of the introduced gas, the flow rate, the pressure inside the CVD reaction chamber, etc. may be changed repeatedly at predetermined intervals. [Example] Examples 1 to 5 Using 8 graphite plates 5 cm wide x 60 cm long x 1 cm thick,
A reaction chamber having an octagonal cross section was formed on the top surface of a graphite plate (bottom plate) with a diameter of 20 cm. A hole with a diameter of 5 cm is made in the center of the bottom plate for gas introduction, and two graphite pipes (outer diameter 5 cm and 2.5 cm) coated with PBN in advance are connected coaxially as raw material gas introduction pipes. A graphite substrate measuring 5 cm and 6 cm in length was suspended. The entire reaction chamber was placed in a high-temperature resistance heating vacuum furnace, and stainless steel gas piping was connected to the inner and outer graphite pipes of the raw material gas introduction pipe so that BCl ₃ and NH ₃ gas could be supplied, respectively. While the furnace was evacuated to a level of 10 ^-3 Torr, it was heated to 1900° C. and under a pressure of 1 Torr, various PBN crucibles with an overall wall thickness of 1 mm were formed under the conditions shown in the table. The growth rate was controlled by changing the concentration of the raw material gas. A life test on the obtained crucible assuming single crystal growth by the LEC method was conducted using the following method. That is, 50 g of B ₂ O ₃ is placed in a crucible, heated to 1280° C. in an N ₂ atmosphere to melt the B ₂ O ₃ , and then cooled to room temperature. B ₂ O ₃ attached to the inner wall of the crucible is
The entire crucible is immersed in methanol and cleaned by ultrasonic cleaning for 20 to 40 minutes, which removes the residue that was attached to _{the B2O3} during the cooling contraction of _{the B2O3.}
Part of the inner wall of the PBN crucible peels off. This was repeated until the crucible was damaged. The number of times until failure of each crucible is shown in the table. A similar test was also conducted on a commercially available crucible (Comparative Example 5).

【table】

〔Effect of the invention〕

By using the crucible of the present invention, the life of the crucible in the MBE method and LEC method can be extended.
The manufacturing cost of compound semiconductors can be reduced. Furthermore, the manufacturing method of the present invention does not require interruption of vapor deposition, so that a high-performance crucible can be efficiently manufactured.

Claims (1)

[Claims] 1. At least five or more layers of individual walls each having a thickness of 5 to 100 μm are bonded to each other,
A boron nitride crucible having a multi-wall structure, characterized in that the total wall thickness is 0.5 to 3 mm. 2 At least five or more layers of individual walls each having a thickness of 5 to 100 μm are bonded to each other,
In addition, when manufacturing a boron nitride crucible with a total wall thickness of 0.5 to 3 mm by chemical vapor deposition using boron halide gas and ammonia gas as raw materials, the first wall is grown at a rate of 10 to 150 μm per hour. A nitriding method consisting of a multi-wall structure, characterized in that the second wall adjacent to this wall is formed at a growth rate of 1.5 to 5 times that of the first wall, alternately and repeatedly. How to make a boron crucible.