JP7800367B2 - Heater, single crystal manufacturing apparatus, single crystal manufacturing method - Google Patents

Description

The present invention relates to a heater for use in a single crystal manufacturing apparatus, a single crystal manufacturing apparatus equipped with the heater, and a single crystal manufacturing method using the heater.

Figure 1 is a perspective view showing the general shape of a conventional heater. As shown in Figure 1, a heater 90 used in a conventional single crystal manufacturing apparatus for pulling single crystals such as silicon single crystals has a general cylindrical shape and is provided with multiple through slits 91, 92 extending in the axial (vertical) direction of the cylinder and arranged circumferentially (equally spaced in the illustrated example). The through slit 91 extends axially from the upper end in the illustration and terminates at the lower end without opening at the lower end. On the other hand, the through slit 92 extends axially from the lower end in the illustration and terminates at the upper end without opening at the upper end. By arranging these through slits 91, 92 alternately in the circumferential direction, the heater 90 forms a long, serpentine current path. This configuration is suitable for the heater 90 to generate heat at a desired temperature through electrical resistance.

Japanese Patent Application Publication No. 04-357191

During single crystal production, it is desirable to maintain a constant melt temperature and ensure stable crystal growth. To achieve this, stabilizing heater output is essential. To stabilize heater output, the temperature of the heater or the components heated by the heater and near the heater is measured, and the heater output is controlled. A radiation thermometer is sometimes used to measure the temperature of the heater or the components heated by the heater from outside the chamber of the single crystal production equipment containing the heater, and the heater output is controlled by feeding back the measured temperature results. In this case, it is not easy to change the position of the measurement point for measuring the temperature of the heater or the components heated by the heater and near the heater, and the temperature measurement point used to control the heater output is fixed. Therefore, it is desirable to reduce the influence of a fixed temperature measurement point used to control the heater output and achieve stable control of the heater output.

However, even when measuring the temperature of conventional heaters, it was found that heater output could not be controlled appropriately depending on the heater's structure. For example, there are one-piece heaters and two-part heaters that are split axially in two. While the heater output could be controlled appropriately with the one-piece heater, it was sometimes impossible with the two-part heater. Conversely, even if the heater output could not be controlled appropriately with the one-piece heater, it was sometimes possible with the two-part heater.

The present invention therefore aims to provide a heater with improved output controllability, a single crystal manufacturing apparatus equipped with such a heater, and a single crystal manufacturing method using such a heater.

The gist and configuration of the present invention are as follows.
(1) A cylindrical heater used in a single crystal manufacturing apparatus,
A heater comprising a plurality of circumferential through slits extending in the circumferential direction.

(2) The heater described in (1) above has a serpentine shape consisting of a circumferentially extending portion that extends in the circumferential direction and an axially extending portion that extends in the axial direction, both separated by the circumferential through slit.

(3) A heater described in (1) or (2) above, having a structure that is plane-symmetrical with respect to a plane passing through the central axis of the cylinder.

(4) A single crystal manufacturing apparatus characterized by comprising the heater described in any one of (1) to (3) above.

(5) A method for producing a single crystal using the heater described in any one of (1) to (3) above.

The present invention provides a heater with improved output controllability, a single crystal manufacturing apparatus equipped with the heater, and a single crystal manufacturing method using the heater.

FIG. 1 is a perspective view showing a schematic shape of a conventional heater. 1 is a perspective view showing a schematic shape of a heater according to an embodiment of the present invention. FIG. 3 is a perspective view showing a schematic shape of a heater according to a modified example of the embodiment of FIG. 2 in which the heater has four electrodes. FIG. 1 is a cross-sectional view of a single crystal pulling furnace for explaining measurement of the temperature of a conventional integrated heater. FIG. 1 is a cross-sectional view of a single crystal pulling furnace for explaining measurement of the temperature of a conventional two-split heater. FIG. 10 is a schematic diagram for explaining measurement of the temperature of a conventional integrated heater. FIG. 10 is a schematic diagram for explaining measurement of the temperature of a conventional two-split heater. FIG. 2 is a cross-sectional view of a single crystal pulling furnace for explaining measurement of the temperature of the integrated heater of this embodiment. FIG. 2 is a cross-sectional view of a single crystal pulling furnace for explaining measurement of the temperature of a two-split heater according to the present embodiment. 5A and 5B are schematic diagrams for explaining measurement of the temperature of the integrated heater according to the embodiment. 5 is a schematic diagram for explaining measurement of the temperature of a two-split heater according to the present embodiment. FIG. FIG. 10 is a perspective view showing a schematic shape of a heater according to another embodiment of the present invention. FIG. 13 is a perspective view showing a schematic shape of a heater according to a modification of the embodiment of FIG. 12 in which the heater has four electrodes. FIG. 10 is a diagram showing test results of an example of the invention. FIG. 10 is a diagram showing test results of a comparative example.

Embodiments of the present invention will be described in detail below with reference to the drawings.

<Heater>
Fig. 2 is a perspective view showing a schematic shape of a heater according to one embodiment of the present invention. Heater 1 is used in an apparatus for producing single crystals such as silicon single crystals by the Czochralski method, and has a cylindrical shape as shown in Fig. 2. In the illustrated example, heater 1 has a structure that is plane-symmetrical with respect to a plane passing through the central axis of the cylinder, and a first axially penetrating (radially penetrating) slit 2 that extends axially from the upper end in the illustration through said plane divides most of the axial direction into two portions 1a and 1b, while portions 1a and 1b are connected at the lower end in the illustration.

The heater 1 also has multiple circumferential slits 3 (slits that extend circumferentially and penetrate radially) that extend circumferentially. In the illustrated example, there are first circumferential slits 3a that communicate with the first axial slit 2 and extend circumferentially on both sides from the communicating portion with the first axial slit 2, and second circumferential slits 3b that do not communicate with the first axial slit 2. In this example, the first circumferential slits 3a and the second circumferential slits 3b are arranged alternately at equal intervals in the axial direction. Each of the circumferential ends on one side of the multiple second circumferential slits 3b communicates with a second axial slit 4 that extends axially.

The heater 1 has a serpentine shape consisting of a circumferentially extending portion 5a that extends in the circumferential direction and an axially extending portion 5b that extends in the axial direction, which are partitioned by circumferentially extending slits 3 (in the illustrated example, partitioned by a first axially extending slit 2, a first circumferentially extending slit 3a, a second circumferentially extending slit 3b, and a second axially extending slit 4).

In the illustrated example, the extension length of the circumferentially extending portion 5a is longer than the extension length of the axially extending portion 5b. The circumferentially extending portion 5a at the illustrated lower end connects portions 1a and 1b without being separated by the first axially penetrating slit 2.

In the illustrated example, the two electrodes 6 extend axially and are connected to the circumferentially extending portion 5a at the upper end. This allows current to flow from the positive electrode to the negative electrode along the serpentine shape described above. Note that in the circumferentially extending portion 5a at the lower end, the current flows through a path that is approximately twice as long as the other circumferentially extending portions 5a.

Figure 3 is a perspective view showing the schematic shape of a heater in a modified version of the embodiment in Figure 2, where there are four electrodes. This modified version differs from the example in Figure 2 in that four electrodes are arranged at equal intervals in the circumferential direction at the illustrated lower end of the heater 1. As shown, the four electrodes 6 are connected to the circumferentially extending portion 5a of the illustrated lower end. One pair of opposing electrodes 6 are positive electrodes, and the other pair of opposing electrodes 6 are negative electrodes. With this configuration, current flows in two directions, from one positive electrode to two negative electrodes, in a serpentine shape.

The effects of the heater of this embodiment will be explained below in comparison with conventional heaters. Figure 4 is a cross-sectional view of a single crystal pulling furnace to explain the temperature measurement of a conventional integrated heater. Figure 5 is a cross-sectional view of a single crystal pulling furnace to explain the temperature measurement of a conventional two-piece heater. Figure 6 is a schematic diagram to explain the temperature measurement of a conventional integrated heater. Figure 7 is a schematic diagram to explain the temperature measurement of a conventional two-piece heater.

Through investigations, the inventors have discovered that the reason for the difference in responsiveness to heater output between the one-piece structure and the two-split structure divided into two in the axial direction is due to the following phenomenon.
As shown in FIG. 1 , a conventional heater has a through slit extending in the axial direction. Because current tends to travel the shortest path, current concentrates at the bends of the serpentine shape, resulting in a maximum amount of heat generated by Joule heat due to the current. Therefore, as shown in FIGS. 4 and 6 , in a one-piece heater, maximum heat-generating areas A appear alternately at the upper and lower ends of the heater in the horizontal direction in a cross-sectional view. These maximum heat-generating areas A are areas that most significantly reflect changes in heater power output. On the other hand, as shown in FIGS. 5 and 7 , in a two-part heater, maximum heat-generating areas A appear alternately at the upper and lower ends of the upper half and the lower half of the two-part heater in the cross-sectional view. That is, in a conventional heater with a through slit extending in the axial direction, the maximum heat-generating areas A appear aligned horizontally when projected vertically. As a result, for the same temperature measurement point, depending on the position, one may measure the maximum heat generation area A and the other may measure another area (for example, the area between the two maximum heat generation areas A) with the one-piece and two-piece types.In such cases, the response will differ between the one-piece and two-piece types because the measured temperature in relation to the heater output will be different.

Figure 8 is a cross-sectional view of a single crystal pulling furnace to explain the measurement of the temperature of the integrated heater of this embodiment. Figure 9 is a cross-sectional view of a single crystal pulling furnace to explain the measurement of the temperature of the two-piece heater of this embodiment. Figure 10 is a schematic diagram to explain the measurement of the temperature of the integrated heater of this embodiment. Figure 11 is a schematic diagram to explain the measurement of the temperature of the two-piece heater of this embodiment.

The heater 1 of this embodiment includes multiple circumferentially extending through-slits 3. Therefore, as shown in FIGS. 8 to 11 , whether the heater is an integrated heater or a two-piece heater, the meandering bends appear sequentially in the vertical direction, and the maximum heat generation portions A appear aligned vertically when projected horizontally. Therefore, when measuring the temperature from the horizontal direction, the maximum heat generation portion A can be the measurement target at any vertical position, whether the heater is an integrated heater or a two-piece heater. This prevents a difference in responsiveness to heater output between the integrated heater and the two-piece heater. Even if the maximum heat generation portion A cannot be the measurement target, the heater of the present invention allows a region near the maximum heat generation portion A to be the measurement target. Therefore, the difference in responsiveness to heater output between the integrated heater and the two-piece heater is smaller than that of conventional heaters.
As described above, the heater 1 of this embodiment can improve the controllability of the heater output when controlling the heater output by measuring the heater temperature from the horizontal direction of the pulling furnace. It can also observe changes in the thermal environment (such as thinning or oxide deposition) that occur significantly in the maximum heat-generating portion A. To ensure a good thermal environment, it is preferable to have a structure that is symmetrical with respect to a plane passing through the central axis of the cylinder, as in this embodiment.

Figure 12 is a perspective view showing the schematic shape of a heater according to another embodiment of the present invention. The heater 10 of the embodiment shown in Figure 12 is used in a manufacturing apparatus for single crystals such as silicon single crystals, and is cylindrical in shape as shown in Figure 12. In the embodiment of Figure 12, the first axial through slits 20 consist of a first axial through slit 20a extending axially from the upper end as shown and a first axial through slit 20b extending axially from the lower end as shown. The heater also has a first circumferential through slit 30a that communicates with the first axial through slit 20 (20a, 20b) and extends circumferentially on both sides from the communicating portion with the first axial through slit 20, and a second circumferential through slit 30b that does not communicate with the first axial through slit 20. The first circumferential through slits 30a are arranged in a staggered pattern. In this example, the first circumferential through slits 30a and the second circumferential through slits 30b are arranged alternately at equal intervals in the axial direction. Each of the circumferential ends on one side of the multiple second circumferential through slits 30b communicates with a second axial through slit 40 extending in the axial direction.

The heater 1 has a serpentine shape consisting of a circumferentially extending portion 50a and an axially extending portion 50b, which are separated by circumferential through slits 3 (30a, 30b) (in the illustrated example, separated by the first axial through slit 20, the first circumferential through slit 30a, the second circumferential through slit 30b, and the second axial through slit 40). The circumferentially extending portion 50a at the lower end in the illustration extends circumferentially without being separated by the first axial through slit 20.

In the illustrated example, the two electrodes 60 extend axially and are connected to the circumferentially extending portion 50a at the upper end shown. This allows current to flow from the positive electrode to the negative electrode along the serpentine shape described above.

Figure 13 is a perspective view showing the schematic shape of a heater in a modified version of the embodiment in Figure 12, where there are four electrodes. This modified version differs from the example in Figure 12 in that four electrodes are arranged at equal intervals in the circumferential direction at the illustrated lower end of the heater 1. As shown, the four electrodes 60 are connected to the circumferentially extending portion 50a of the illustrated lower end. One pair of opposing electrodes 6 are positive electrodes, and the other pair of opposing electrodes 6 are negative electrodes. With this configuration, current flows in two directions, from one positive electrode to two negative electrodes, in a serpentine shape.

12 and 13, the heater 10 is provided with a plurality of circumferential through slits 30 extending in the circumferential direction, so that the maximum heat generation portions A appear aligned vertically when projected horizontally. Therefore, when measuring the temperature from the horizontal direction, the maximum heat generation portion A can be the measurement target at any vertical position, whether it is an integrated type or a two-piece type, and therefore it is possible to prevent a difference in responsiveness to heater output between the integrated type and the two-piece type.
As described above, the heater 10 of the embodiment shown in Figures 12 and 13 can also improve the controllability of the output when controlling the heater output by measuring the heater temperature from the horizontal direction of the pulling furnace.

The heaters 1 and 10 shown in Figures 2, 3, 12, and 13 can be heaters made of high-purity carbon. Furthermore, these heaters 1 and 10 are preferably used to produce defect-free silicon single crystals. Here, "defect-free silicon single crystals" refer to crystals that are free of, or substantially free of, void defects caused by agglomeration of vacancies, known as COPs (crystal originated particles), and dislocation cluster defects caused by agglomeration of interstitial silicon.

<Single crystal manufacturing equipment>
An apparatus for producing a single crystal according to one embodiment of the present invention is used, for example, for producing a silicon single crystal by the Czochralski method, and includes a single crystal pulling furnace equipped with the heaters 1 and 10 of the above-described embodiments around a crucible. In this example, the apparatus for producing a single crystal may further include a measurement unit (such as a radiation thermometer) for measuring the temperature of the heater horizontally from outside the chamber in which the heater is housed. Other components of the single crystal pulling furnace may be similar to those of a conventional furnace, and therefore description thereof will be omitted. As an example, as shown in FIG. 4 and other figures, an apparatus for producing a single crystal 100 includes a crucible 102 for containing a silicon raw material such as polycrystalline silicon within a chamber 101. The crucible 102 is composed of a quartz crucible 102a and a carbon crucible 102b, with the quartz crucible 102a housed within the carbon crucible 102b. A heater 103 is disposed around the carbon crucible 102b, and a heat insulator 104 is disposed around the heater 103. The heater 103 heats the silicon raw material contained in the quartz crucible 102a to form a silicon melt M. A single crystal 106 is pulled up from the silicon melt M by a wire 105.

<Method of manufacturing single crystal>
The method for producing a single crystal according to one embodiment of the present invention is, for example, a method for producing a silicon single crystal by the Czochralski method, and is carried out using a single crystal pulling furnace equipped with the heaters 1 and 10 of the above-described embodiments around a crucible. Each step of the production method can be the same as in a normal method for producing a single crystal, and therefore a description thereof will be omitted.

The following describes examples of the present invention, but the present invention is not limited to these examples.

To verify the effectiveness of the present invention, a comparison was made between the heater power controllability of a conventional heater (comparison example) with the structure shown in Figure 1 and that of a heater (invention example) with the structure shown in Figure 2, using a pulling apparatus for producing 300 mm diameter single crystals by the Czochralski method. The effectiveness of the present invention was confirmed by evaluating whether applying the heater of the invention example to a pulling apparatus with poor heater power controllability using the heater of the comparison example. In this example, a numerical simulation using a heat transfer analysis model was conducted. The heaters of the invention example and the comparison example were modeled based on the heat generation distribution of the heaters. Only the modeled heaters differed between the invention example and the comparison example; all other components of the pulling apparatus and process conditions were the same. Conditions were imposed such that the heater temperature rose by 120 K when both the seed crystal position and the crucible position rose 55 mm in 55 minutes after the seed crystal was immersed in the melt.

Figure 14 shows the amount of change in heater power and the change in heater temperature over time in the example of the invention, and Figure 15 shows the amount of change in heater power and the change in heater temperature over time in the comparative example. As shown in Figures 14 and 15, the amount of change in heater power over time was large in the heat generation distribution of the comparative example, while the amount of change in heater power over time was small in the heat generation distribution of the example of the invention. This shows that the controllability of the heater power to increase the heater temperature by the same amount was more stable and better in the example of the invention than in the comparative example.

1, 10: heater,
2, 20: first axial through slit;
3, 30: circumferential through slits,
4, 40: second axial through slit;
5a, 50a: circumferentially extending portion,
5b, 50b: axially extending portion,
6, 60: Electrode

Claims (5)

A cylindrical heater used in a single crystal manufacturing apparatus,
A plurality of circumferential through slits extending in the circumferential direction are provided,
a first axial through slit consisting of a first upper end side axial through slit extending in the axial direction from the upper end of the heater and a first lower end side axial through slit extending in the axial direction from the lower end of the heater,
A heater, characterized in that all of the circumferential through slits communicate with either the first upper end side axial through slit or the first lower end side axial through slit . The heater described in claim 1 has a serpentine shape consisting of a circumferentially extending portion that extends in the circumferential direction and an axially extending portion that extends in the axial direction, both separated by the circumferential through slit. The heater described in claim 1 or 2 has a structure that is plane-symmetrical with respect to a plane passing through the central axis of the cylinder. A single crystal manufacturing apparatus comprising the heater according to claim 1 or 2. A method for producing a single crystal using the heater described in claim 1 or 2.