JPH01264995A - Production of compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To suppress the polycrystallization during the growth of the single crystal and to decrease the concn. of carbon in the crystal by adopting the constitution consisting in inserting the bottom end of a specific cylindrical body into a liquid sealing layer without directly inserting a sub-heater for local heating in order to suppress the polycrystallization into the liquid sealing layer at the time of pulling up the compound semiconductor single crystal by an LEC method. CONSTITUTION:A crystal raw material melt 4 housed in a crucible 3 heated by a heater 1 is covered by the liquid sealing layer 5 and the single crystal 6 grown by pulling up the same from the melt 4 is pulled up while heating the crystal 6 by the cylindrical sub-heater 7 provided on the outside circumference of the single crystal 6. The under-mentioned constitution is added in this method: At least either of the inside or outside surface of the sub-heater 7 is covered by the cylindrical body 8 which is made of pyrolytic boron nitride and projects downward from the bottom end of the sub-heater 7. The bottom end of the above-mentioned cylindrical body 8 is inserted into the liquid sealing layer 5 without bringing the sub-heater into contact with the liquid sealing layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a compound semiconductor single crystal, which involves pulling a single crystal from a crystal raw material melt coated with a liquid sealing layer.

[Prior Art] The liquid confinement drawing method (LEC method) is generally known as a method for growing single crystals of m-v group compound semiconductors such as GaAs and InP. This method uses, for example, GaA in a crucible.
A crystal raw material melt of s is poured in, a liquid sealing layer of B2 o3 is placed on the top surface to prevent the evaporation of the As element, and a seed crystal with a predetermined crystal orientation is poured from above through this liquid sealing layer. After contacting the melt, the seed crystal is pulled up to grow a single crystal with the same orientation as the seed crystal, but polycrystals are generated during crystal growth, resulting in a large amount of loss. It is known that the generation of polycrystals is related to the shape of the solid-liquid interface during crystal formation.If the interface periphery is concave downward, dislocations, which are one type of crystal defect, will propagate and the concave surface Polycrystals are generated when the particles are accumulated in some areas. In addition, the concave surface itself is also subjected to stress concentration and dislocations occur, causing polycrystalline formation.

On the other hand, when the shape of the interface periphery is downwardly convex,
The propagated dislocations are dispersed and annihilated to the side surfaces of the crystal, and are less subject to stress concentration, making it difficult to form polycrystals. Therefore, making the periphery of the solid-liquid interface downwardly convex is an effective means for suppressing polycrystallization, and many studies have been attempted in the prior art. One of the methods is to insert a sub-heater for local heating of the single crystal into the liquid sealing layer of B203, and heat the side surface of the crystal to suppress concavity of the periphery of the solid-liquid interface.

However, if the material of this subheater is carbon, which is highly versatile, the mixing of carbon into the crystal through the liquid sealing layer becomes noticeable, causing poor characteristics. Further, even if a carbon subheater coated with electrically neutral boron nitride (BN) or the like is used, elution of carbon due to deterioration of the coating layer cannot be completely prevented.

On the other hand, a method of using a high-frequency coil instead of a carbon sub-heater is also being considered, but since the coil material is made of copper, there is a problem of copper being mixed into the crystal.

[Problems to be Solved by the Invention] As mentioned above, in the conventional technology, a sub-heater for local heating of the single crystal is inserted into the liquid sealing layer, but since the heater is made of carbon, carbon gets mixed in and causes the single crystal to heat up. This causes poor characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a compound semiconductor single crystal, which can solve the problems of the prior art, suppress polycrystallization that occurs during the single crystal growth process, and reduce the carbon concentration of the single crystal. It is.

[Means for Solving the Problems] That is, the gist of the present invention is to cover a subheater located around a single crystal with a cylindrical body made of pyrolytic boron nitride and having a length that protrudes below the lower end of the subheater. The lower end of the cylindrical body is inserted into the liquid sealing layer without contacting the liquid sealing layer.

[Function] In the present invention, the subheater for local heating for suppressing polycrystals is not inserted directly into the liquid sealing layer, and the pyrolytic boron nitride protruding below the lower end of the subheater is provided on the outer periphery of the subheater. Since the lower end of the cylindrical body is inserted into the liquid sealing layer, the heat from the sub-heater can propagate inside the cylinder, form the liquid sealing layer, and heat the solid-liquid interface, which improves the characteristics of single crystal growth. It is possible to suppress the contamination of impurities that cause problems above, and reduce the carbon concentration of the single crystal.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a compound semiconductor single crystal manufacturing apparatus according to this embodiment.

In the figure, 1 is a heater, 2 is a susceptor, and a crucible 3 is installed in these. Crucible 3 is quartz or P
Made of BN (pyrolytic boron nitride). 4 is a crystal raw material melt, and 5 is a liquid sealing layer such as 8203, which covers the crystal raw material melt 4 and prevents loss of group V elements having high vapor pressure.

A single crystal 6 is pulled from the crystal raw material melt 4 by bringing a seed crystal (not shown) into contact with the crystal raw material melt 4 from above and pulling it up. In this embodiment, a cylindrical body 8 made of PBN is provided with a sub-heater 7 for local heating installed at one end, and the tip of this cylindrical body 8 is sealed with the liquid. It is inserted into the stop layer 5, and the insertion position of the tip is in the single crystal 5 near the crystal growth interface.
Make it a side. As a result, the heat from the sub-heater 7 for local heating is transmitted to the side surface of the single crystal 6 via the cylinder 8, suppressing downward concavity of the periphery of the solid-liquid interface and preventing polycrystallization. .

Furthermore, in this embodiment, the sub-heater 7 for local heating is not directly immersed in the liquid sealing layer 5 as described above, so that the incorporation of impurities that may cause problems with the characteristics of the single crystal 6 is suppressed.
The carbon concentration of the single crystal 6 can be reduced.

Table 1 shows the experimental results.

Table 1 Effect of reducing carbon concentration Regarding the effect of suppressing the generation of polycrystals, we were able to obtain the same results with this example as with the conventional type in which the sub-heater 7 for local heating is directly immersed in the liquid sealing layer 5. .

Incidentally, the cylindrical body 8 is made of PBN for the following reasons.

(1) The constituent elements boron (B) and nitrogen (
N) is electrically neutral, and even if it is mixed into the single crystal 6, it will not affect the characteristics.

(2) Shows anisotropy in thermal conductivity, as shown in Figure 2, which shows the thermal conductivity direction dependence of PBN. The thermal conductivity of PBH9 in the C direction (horizontal direction in Figure 1) is shown in Table 2. Street C
It is extremely low compared to the direction ↑′.

Therefore, it is possible to prevent the side surface of the single crystal 6 from being excessively heated by the sub-beater 7 for local heating via the cylindrical body 8, thereby preventing the characteristics from being adversely affected.

Table 2 Directional dependence of thermal conductivity of PBN [Effects of the invention] According to the present invention, the problems of the prior art are solved, polycrystalization that occurs in the process of single crystal growth is suppressed, and single crystal carbon This has the remarkable effect of reducing the concentration.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a compound semiconductor single crystal manufacturing apparatus showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the directional dependence of thermal conductivity of PBH. 2: Susceptor, 3: Crucible, 4: Crystal raw material melt, 5: Liquid sealing layer, 6: Single crystal, 7: Sub-heater for local heating, 8: Cylindrical body made of PBN. Ikki Takashi 1 N Otsu/λ ---''7C7O7

Claims (1)

[Claims] 1. A crystal raw material melt housed in a crucible heated by a heater is covered with a liquid sealing layer, and a single crystal pulled and grown from the crystal raw material melt is placed around the outer periphery of the cylindrical crystal. In a method for producing a compound semiconductor single crystal in which the single crystal is pulled up while being heated by a subheater, at least one of the inner surface or the outer surface of the subheater is covered with a cylindrical body made of pyrolytic boron nitride that protrudes below a lower end of the subheater; An apparatus for manufacturing a compound semiconductor single crystal, wherein the subheater inserts the lower end of the cylindrical body made of pyrolytic boron nitride into the liquid sealing layer without contacting the liquid sealing layer.