JPH0511073B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a boron nitride crucible with improved service life, particularly for melting metals and compounds used in molecular beam epitaxy (MBE), liquid-enclosed Czochralski (LEC), etc. Regarding the crucible. [Prior Art] 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). In addition, PBN is almost exclusively used 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.
Using boron halide and ammonia as gaseous raw materials, BN is deposited on the surface of a suitable substrate at a temperature of 1450°C to 2300°C and a pressure of less than 50 torr using the so-called chemical vapor deposition method (CVD method). be synthesized. 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, and therefore, for example,
When repeatedly used as a crucible in the LEC method, uneven layer delamination tends to occur when the sealant boron oxide (B ₂ O ₃ ) is removed, resulting in a short lifespan and a fixed lifespan. The drawback was that it was difficult to guarantee that. As a method to solve these drawbacks, a multi-wall structure crucible is proposed, which is composed of a large number of individual walls with thicknesses in a specific range with an intervening intermediate wall (Japanese Patent Application Laid-Open No. 61-285383). ). With such a multi-wall structure crucible, for example, when removing B ₂ O ₃ after crystal growth using the LEC method, exfoliation always occurs at the innermost wall layer of the crucible, and the partial exfoliation layer can be removed without deepening the exfoliation. Therefore, the lifespan of the crucible is greatly extended compared to conventional crucibles, and it has the advantage that there is little variation in the lifespan between crucibles. Furthermore, when manufacturing such a multi-walled crucible, the molar ratio of ammonia to boron halide in the raw material gas is varied and the formation is repeated alternately, which temporarily inhibits film formation. The advantage is that the crucible can be produced without any interruptions and without unnecessarily long periods of time. In such a multi-wall structure crucible, the thinner the individual walls, the longer the life will be. However, in the method described in Japanese Patent Application Laid-Open No. 61-285383, the thickness of the first wall is set to less than 20 μm. This has the disadvantage that the divisions between the individual walls are not clear and the effects of the multi-wall structure described above cannot be fully obtained. [Problems to be Solved by the Invention] As a result of various studies aimed at solving the above-mentioned drawbacks, the inventor of the present invention has found that a crucible manufactured by setting the flow rate of the raw material gas in the CVD reaction chamber to 50 m/s or higher is the first of its kind. It was discovered that the division between the walls becomes clear even when the wall thickness is less than 20 μm, and the present invention was completed. [Means for Solving the Problems] That is, the present invention provides a boron nitride crucible manufactured by a chemical vapor deposition method with a flow rate of raw material gas in a reaction chamber of 50 m/s or more, in which the thickness of one layer is 1 μm. A first wall having a thickness of at least 20 μm and a second wall having a thickness of 1/50 to 1/2 of the first wall,
This boron nitride crucible has a multi-wall structure in which the layers are alternately bonded to each other and have a total wall thickness of 0.5 to 3 mm. The present invention will be explained in more detail below. In the multi-wall structure crucible of the present invention, the thickness of the first wall is in the range of 1 μm or more and less than 20 μm. Thickness is 1μm
If it is less than 20 μm, the PBN film that makes up the wall will not have sufficient strength, so the life will be short when used for single crystal growth, and if it is more than 20 μm, the structure will be the same as a conventional multi-walled crucible, and the life extension effect will be reduced. It won't be enough. Next, the thickness of the second wall adjacent to the first wall is 1/50 to 1/2 that of the first wall. If the thickness is thinner than 1/50, the peelability of each layer will be poor, and the function as an intermediate wall will not be obtained sufficiently. Moreover, if it is thicker than 1/2, it is not preferable because it tends to cause lamination with the first wall. The total wall thickness of the crucible is 0.5 to 3 mm. If the wall thickness is less than 0.5 mm, the strength of the entire crucible will be insufficient, and if it exceeds 3 mm, internal stress will increase, resulting in spontaneous lamination, which is not preferable. The crucible of the present invention can have approximately 10 to 100 times more multi-walls than conventional crucibles because the individual walls are thinner. In the present invention, when forming individual walls,
It is important that the flow rate of the raw material gas in the CVD reaction chamber be 50 m/s or more. Flow velocity is 50m/s
If the thickness is less than 1, it is impossible to obtain a crucible with good peelability from layer to layer because the divisions between individual walls become unclear. The reason why the separation between the walls becomes clearer when the flow velocity is set to 50 m/s or more is presumed to be that the source gas conditions can be changed more quickly. Next, to explain the method for manufacturing the multi-wall structure crucible of the present invention, each wall forming the multi-wall structure PBN crucible is made of boron halide gas such as boron trichloride and ammonia gas as raw materials.
It is formed by CVD method, but the pressure at that time is
It is sufficient that the temperature is 5 torr or less and the temperature is 1850°C or higher. When the pressure exceeds 5 torr, fine particles of BN are produced as a by-product.
It tends to be incorporated into the PBN film and impair the uniformity of the tissue. Forms when the temperature is below 1850℃
PBN has low strength and tends to lack practical strength as a crucible. In order to weakly bond the walls formed under such conditions to each other, the first wall and the adjacent second wall (intermediate wall) may be mixed at different molar ratios of ammonia to boron halide. It can be vapor-deposited. That is, the molar ratio when forming the first wall may be 2 to 10, and the molar ratio of the second wall may be 1/3 or more and less than 2.
The flow rate of the raw material gas in the CVD reaction chamber is 50 m/s.
In order to adjust the amount above, the amount of introduced gas, the cross-sectional area of the space between the crucible graphite substrate and the CVD reaction chamber wall, and
This can be done by adjusting the temperature and pressure of the CVD reaction chamber. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. [Example Comparative Example] 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 was 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 were 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. The vacuum furnace
It was heated to 1900°C while evacuating to a level of 10 ^-3 torr. Next, under a pressure of 1 torr, the first wall was deposited with a molar ratio of ammonia to boron trichloride of 4, and the second wall was deposited with a molar ratio of 1 under the conditions shown in the table, and the total wall thickness was 1 mm. A PBN crucible was fabricated. A life test on the obtained crucible assuming single crystal growth by the LEC method was conducted using the following method. That is, put 50g of B ₂ O ₃ in the crucible and add N ₂
It is heated to 1280° C. in an atmosphere to melt B ₂ O ₃ and then cooled to room temperature. B ₂ O ₃ attached to the inner wall of the crucible
is removed by immersing the entire crucible in methanol and ultrasonic cleaning for 20 to 40 minutes, but at this time, the B ₂ O ₃ that was attached to the B ₂ O ₃ during cooling contraction was removed.
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. From the table, it can be seen that all of the examples of the present invention have a lifespan of 40 times or more, and have a longer lifespan than the comparative examples.

〔Effect of the invention〕

The boron nitride crucible having a multi-wall structure according to the present invention can significantly extend the service life in the MBE method and LEC method, thereby reducing the manufacturing cost of compound semiconductors.

Claims (1)

[Claims] 1 A boron nitride crucible manufactured by chemical vapor deposition with a flow rate of raw material gas in the reaction chamber of 50 m/s or more, and one layer of which has a thickness of 1 μm or more.
A first wall having a thickness of less than 30 μm and a second wall having a thickness of 1/50 to 1/2 of the first wall are bonded to each other and alternately stacked, and A boron nitride crucible having a multi-wall structure characterized by a wall thickness of 0.5 to 3 mm.