JPH0328397B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a single crystal pulling apparatus for pulling semiconductor single crystals using the liquid capsule Czyochralski method (hereinafter referred to as LEC method). [Prior art] In the LEC method, in the apparatus illustrated in Fig. 1,
The surface of the semiconductor raw material melt 1 is coated with B ₂ O ₃ as a sealant.
In this method, the seed crystal 3 is covered with the melt 2, the seed crystal 3 is immersed on the surface of the raw material melt 1, and the single crystal 4 is pulled up by pulling the seed crystal 3 up. In order to improve the quality of this single crystal, improve yield, and increase efficiency in subsequent steps, it is important to control the diameter of the single crystal and keep it constant. A method for controlling the diameter of this single crystal is to adjust the temperature of the raw material melt 1 by changing the power (output) of the crucible 6 of the apparatus and the heater 5 placed around the growing single crystal. , a method of varying the pulling speed V, etc. has been adopted. [Problems to be solved by the present invention] However, in the former method, the heat capacity of the heater 5, the crucible 6, etc. is large, and the heater 5 and the single crystal 4
Since the distance is large, the response speed is slow and fine control is not possible, and the conditions change depending on the remaining amount of the raw material melt 1, resulting in the disadvantage that the temperature at the solid-liquid interface cannot be kept constant. In the latter method, the temperature gradient near the solid-liquid interface changes with the speed, and the shape of the interface changes, so
There was a drawback that the properties of the single crystal changed as the pulling speed was changed, resulting in poor crystallinity. Furthermore, as a result of the large temperature gradient in the direction of the pulling axis in the B ₂ O ₃ melt 2, it is subjected to thermal distortion, which causes poor crystallinity. Conventionally, it has been difficult to alleviate this temperature gradient, resulting in the disadvantage that thermal strain increases the dislocation density of the single crystal. This is B ₂ O ₃ melt 2
This is because heat escapes to the axial direction and the temperature gradient in the axial direction is large, causing slipping of crystal planes due to thermal strain. [Means for Solving the Problems] The present invention has been made to solve the above-mentioned drawbacks, and by controlling the temperature distribution of the B ₂ O ₃ melt, the response of controlling the diameter of the single crystal is fast. The purpose of this project is to provide an apparatus that can easily produce a single crystal with uniform properties over the entire single crystal and a low dislocation density. _{, B2O3}
As a means for controlling the temperature distribution of the melt, an annular heater that is immersed in the B ₂ O ₃ melt to heat the melt, separate from the main heater, and a device that moves the heater relative to the crucible. The above objective is achieved by providing the following. The single crystal pulled by the present invention is, for example,
- Group compound semiconductors of the periodic table such as GaAs, GaP, InSb, InP, InAs, etc., such as ZnS, ZnSe,
− group compound semiconductors such as CdS and CdSe, Si, Ge
It is made of semiconductors such as group semiconductors such as or mixed crystals thereof. Hereinafter, the present invention will be explained by examples using the drawings. 2 and 3 are views showing an embodiment of the single crystal pulling apparatus of the present invention, and FIG. 2 is a longitudinal cross-sectional view of the apparatus;
FIG. 3 is a perspective view of the sealant heater. In the figure, the same reference numerals as in FIG. 1 indicate the same parts. In the figure, 7 is an annular heater for an auxiliary sealant installed separately from the main heater in the present invention, and is immersed in the B ₂ O ₃ melt 2. The annular heater 7 is made of carbon, for example, and is made of boron nitride (BN), pyrolytic boron nitride ( _pyrolytic boron nitride ₎ , etc., as shown in FIG. It is covered with a heater cover 8 made of a material such as PBN (abbreviated as PBN). Further, 9 is a thermocouple that measures the temperature near the interface between the B ₂ O ₃ melt 2 and the raw material melt 1. Then, the power of the main heater 5' is adjusted so that the temperature near the interface measured by the thermocouple 9 is constant. The main heater 5' corresponds to the heater 5 described in connection with the apparatus shown in FIG. Although not shown, the auxiliary annular heater 7 is provided with a device that moves up and down relative to the crucible 6, and after the B ₂ O ₃ is melted, the annular heater 7 moves the crucible 6 up and down. or lower the heater 7 to be immersed in the B ₂ O ₃ melt 2.
In addition, the position of the solid-liquid interface is determined by adjusting the position of the annular heater 7 and thermocouple 9 relative to the interface between the B ₂ O ₃ melt and the raw material melt during pulling, since the liquid level in the crucible 6 decreases as the crystal grows. The position is adjusted by moving these (7, 9) and the crucible 6 relatively upward or downward little by little so that the position does not change, thereby keeping the temperature distribution constant. That is, this is possible because the thickness of the B ₂ O ₃ melt 2 does not change and only the position in the axial direction shifts. Next, a method for pulling a single crystal using the above-mentioned single crystal pulling apparatus will be described. First, after melting the semiconductor raw material and B ₂ O ₃ in the crucible 6 , the crucible 6 or the annular heater 7 is moved to immerse the annular heater 7 in the B ₂ O ₃ melt 2 . Adjusting the power of the main heater 5' and the annular heater 7 to adjust the temperature distribution of the melts 1 and 2 to a predetermined temperature distribution, immersing the seed crystal 3 in the melt 1 and blending it, then pulling up the seed crystal 3, Pull up the single crystal 4. As the liquid level decreases, the annular heater 7 and thermocouple 9 are moved relative to the crucible 6. Fine control of the diameter during single crystal pulling is performed by the following method. Generally, when the power of the annular heater 7 relative to the sealant is changed, the temperature distribution within the B ₂ O ₃ melt 2 changes to
The figure shows an example qualitatively. In Figure 4, Figure A shows when the power is large, Figure B shows when the power is medium, and Figure C shows when the power is small. In the figure, the left end shows the annular heater 7 side, and the right end shows the single crystal 4 side. From FIG. 4, when the power of the annular heater 7 is increased, the temperature on the surface side of the single crystal 4 of the B ₂ O ₃ melt 2 increases, and the radiant heat from the annular heater 7 to the crystal also increases. The temperature gradient in the axial direction is also reduced. Therefore, when the diameter of the single crystal 4 increases, increasing the power of the annular heater 7 increases the temperature of the B ₂ O ₃ melt 2 and reduces the amount of heat escaping from the single crystal 4, increasing the diameter of the single crystal 4. becomes thinner. If the diameter of the single crystal 4 becomes thinner, the diameter can be increased by performing the reverse operation to the above. By controlling the power of the annular heater 7 to the sealant in this way and controlling the temperature distribution of the B ₂ O ₃ melt, the diameter of the single crystal 4 can be finely controlled. EXAMPLE GaAs semiconductor single crystals were manufactured by the LEC method using a B ₂ O ₃ melt using the single crystal pulling apparatus of the present invention shown in FIG. 2 and the conventional apparatus shown in FIG. 1, respectively. The temperature distribution of the B ₂ O ₃ melt and the raw material melt is as shown in FIG. It can be seen from FIG. 5 that the temperature gradient within the B ₂ O ₃ melt according to the present invention is smaller than that of the conventional example. These devices each have a diameter of 50 mm and a length of
A 100mm GaAs semiconductor single crystal was created. However, in the case of the present invention, the sealant heater 7
The diameter of the single crystal was controlled by controlling the temperature distribution of the B ₂ O ₃ melt. The variation in diameter of the obtained single crystal was ±3 mm in the case of the present invention, and ±7 mm in the conventional example. The distribution of dislocation density (×10 ⁴ /cm ² ) of the wafer taken from the front part of the single crystal is as shown in Figure 6 A and B, where Figure A is according to the present invention and Figure B is the one according to the present invention. indicates the conventional example. From FIG. 6, it can be seen that in the case of the present invention, the variation in dislocation density is smaller and lower than that of the conventional example. Table 1 shows the average dislocation densities of wafers taken from the front and back parts of each single crystal.

〔Effect of the invention〕

As described above, when pulling a single crystal by the liquid capsule Czyochralski method, the device of the present invention immerses it in a B ₂ O ₃ melt separately from the main heater.
By providing a heater that heats this melt and a device that moves the heater relative to the crucible, the temperature distribution of only the B ₂ O ₃ melt can be controlled independently, and the temperature distribution of the B 2 O 3 melt can be controlled independently. When the diameter of the crystal becomes thicker, increase the temperature of the B ₂ O ₃ melt and make the diameter thinner. When the diameter becomes thinner, lower the temperature of the B ₂ O ₃ melt and make the diameter thicker. Performs diameter control. This configuration has good responsiveness and allows the diameter of the single crystal to be controlled quickly and easily.
Therefore, it has the advantage of improving yield and efficiency in subsequent steps. Furthermore, according to the apparatus of the present invention, the temperature distribution of the B ₂ O ₃ melt can be controlled, and the temperature gradient near the solid-liquid interface can be controlled, and the shape of the solid-liquid interface during crystal growth can be adjusted to a downward convex shape. Since the shape can be controlled to an optimum shape, there is an advantage that a semiconductor single crystal having characteristics with a low dislocation density and little variation over the entire single crystal can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of a conventional single crystal pulling apparatus. 2 and 3 are views showing an embodiment of the single crystal pulling device of the present invention, FIG. 2 is a longitudinal sectional view of the device, and FIG. 3 is a perspective view showing an annular heater for the sealant. . Figure 4 A, B, and C are B ₂ O ₃ when the power of the encapsulant heater is changed, respectively.
FIG. 2 is a diagram qualitatively showing the temperature distribution within the melt. Fifth
The figure shows B ₂ O ₃ in an embodiment of the present invention and a conventional example.
FIG. 3 is a diagram showing the temperature distribution of the melt and the raw material melt.
FIGS. 6A and 6B are views showing the dislocation density distribution of wafers taken from the front part of single crystals obtained by the apparatus of the present invention and the conventional apparatus, respectively. 1... Raw material melt, 2... _B2O3 melt _, 3... Seed crystal, 4... Single crystal, 5... Heater, 5'...
Main heater, 6... Crucible, 7... Annular heater, 8... Heater cover, 9... Thermocouple.

Claims (1)

[Claims] 1. In an apparatus for pulling a single crystal using the liquid capsule Czyochralski method, as a means for controlling the temperature distribution of the B ₂ O ₃ melt, a device separate from the main heater is used.
A single crystal pulling apparatus comprising: an annular heater that is immersed in a B ₂ O ₃ melt to heat the melt; and a device that moves the heater relative to a crucible. 2. The single crystal pulling apparatus according to claim 1, wherein the annular heater is covered with boron nitride or pyrolytic boron nitride.