Method for manufacturing single crystal silicon

Abstract

To reduce the occurrence of dislocation in manufacturing monocrystalline silicon by pulling the monocrystalline silicon from a silicon melt to which a volatile dopant has been added.SOLUTION: A method of manufacturing monocrystalline silicon is provided, the method including pulling monocrystalline silicon out of a silicon melt by the Czochralski process, the silicon melt being stored in a crucible housed in a chamber, the silicon melt having a volatile dopant added thereto, in which a decompression rate ES for exhaust of a gas out of the chamber before the pulling of the monocrystalline silicon is within a range below at least until the pressure inside the chamber decreases from the atmospheric pressure to 80 kPa: 0 kPa / min<ES≤4.2 kPa / min.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silicon single crystal.

Background Art

[0002] Conventionally, in the production of a silicon single crystal in which a silicon single crystal is pulled up from a silicon melt by the Czochralski method, before pulling up the silicon single crystal, the inside of the chamber is depressurized using a vacuum pump, and then an inert gas such as argon gas is introduced to make the inside of the chamber an inert gas atmosphere. In addition, in order to reduce the resistance value of the silicon single crystal, a dopant is added to the silicon melt. As dopants capable of reducing the resistivity of the silicon single crystal, volatile dopants such as red phosphorus, arsenic, and antimony are known. On the other hand, it is known that a low-resistivity silicon single crystal is likely to have dislocations generated during pulling (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When dislocations occur during the pulling of a silicon single crystal, it is necessary to remelt the already grown silicon single crystal and perform pulling again. An object of the present invention is to provide a method for manufacturing a silicon single crystal that can reduce the occurrence of dislocations in a method for manufacturing a silicon single crystal in which a silicon single crystal is pulled up from a silicon melt added with a volatile dopant by the Czochralski method.

Means for Solving the Problems

[0005] The method for manufacturing a silicon single crystal according to the present invention is a method for manufacturing a silicon single crystal in which a silicon single crystal is pulled up from a silicon melt stored in a crucible stored in a chamber and to which a volatile dopant is added, by the Czochralski method. Before pulling up the silicon single crystal, the pressure reduction rate ES when exhausting gas from the chamber is within the following range until the pressure in the chamber decreases to at least 80 kPa from atmospheric pressure. 0 kPa / min < ES ≦ 4.2 kPa / min

[0006] In the above method for manufacturing a silicon single crystal, it is preferable that the pressure reduction rate ES is within the following range until the pressure in the chamber decreases to at least 80 kPa from atmospheric pressure. 2.0 kPa / min ≦ ES ≦ 4.2 kPa / min

[0007] In the above method for manufacturing a silicon single crystal, when the pressure in the chamber becomes lower than 80 kPa, it is preferable to make the pressure reduction rate ES faster than 4.2 kPa / min.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a silicon single crystal pulling apparatus 1 according to an embodiment of the present invention. The silicon single crystal pulling apparatus 1 is an apparatus for manufacturing a silicon single crystal SM using the Czochralski method. As shown in FIG. 1, the silicon single crystal pulling apparatus 1 includes a chamber 2, a crucible 3, a heater 4, a heat shield 5, a heat insulating material 6, and an exhaust device 7. Although not shown in FIG. 1, the silicon single crystal pulling apparatus 1 includes a drive unit for rotating and lifting the crucible 3, and a pulling unit for pulling up the silicon single crystal SM by immersing a seed crystal SC in a silicon melt M in the crucible 3 through a cable 13 and then rotating and pulling it up in a predetermined direction.

[0010] The chamber 2 includes a main chamber 10 for pulling up the silicon single crystal SM, and a pull chamber 11 connected to the upper part of the main chamber 10 and accommodating the pulled-up silicon single crystal SM. The pull chamber 11 is provided with a gas introduction part 12 for introducing an inert gas such as argon (Ar) gas into the chamber 2. The chamber 2 is also provided with a pressure gauge 14 for measuring the pressure inside the chamber 2.

[0011] The crucible 3 has a substantially bottomed cylindrical shape and can be stored in the main chamber 10. The silicon melt M is stored in the crucible 3. The heater 4 is arranged at a predetermined interval outside the crucible 3 and heats the silicon raw material and the silicon melt M in the crucible 3. The heat shield 5 is provided so as to surround the pulled-up silicon single crystal SM and blocks radiant heat from the heater 4 to the silicon single crystal SM.

[0012] The exhaust device 7 is a device for exhausting the gas in the chamber 2 and reducing the pressure in the chamber 2. The exhaust device 7 includes a piping part 16 and an exhaust pump 17 for exhausting the gas in the chamber 2 through the piping part 16. The piping section 16 includes a plurality of branch pipes 20, a first pipe 21 connected to the downstream side of the plurality of branch pipes 20 (the side opposite to the chamber 2 side), and a second pipe 22 that bypasses a part of the first pipe 21. One end of each of the plurality of branch pipes 20 is connected to the chamber 2. The other ends of the plurality of branch pipes 20 converge and are connected to the first pipe 21. In this embodiment, there are four branch pipes 20 (only two are shown in FIG. 1), which are arranged at equal intervals in the circumferential direction of the chamber 2. However, the number of branch pipes 20 is not limited to this. Alternatively, the first pipe 21 may be directly connected to the chamber 2 without providing the branch pipes 20.

[0013] A first valve 23 and a first flow rate adjustment valve 24 are provided in the first pipe 21. The first valve 23 is a valve mainly having the function of blocking the first pipe 21. In this embodiment, the first valve 23 is provided on the chamber 2 side of the first flow rate adjustment valve 24, but it is not limited to this.

[0014] The second pipe 22 is a pipe that branches from the first pipe 21 and is connected to the first pipe 21 again. The second pipe 22 branches from between the chamber 2 and the first valve 23 in the first pipe 21 and is connected to between the first valve 23 and the first flow rate adjustment valve 24 in the first pipe 21.

[0015] A second flow rate adjustment valve 25 and a second valve 26 are provided in the second pipe 22. In this embodiment, the second flow rate adjustment valve 25 is arranged on the upstream side (chamber 2 side) of the second valve 26, but it is not limited to this. The second valve 26 is a valve mainly having the function of blocking the second pipe 22.

[0016] As the first valve 23 and the second valve 26, valves having the function of blocking the pipe, such as ball valves, needle valves, gate valves, globe valves, etc., can be adopted.

[0017] The first flow rate adjustment valve 24 and the second flow rate adjustment valve 25 are valves that adjust the flow rate of the gas flowing through the pipes 21 and 22 by changing the opening degree. The flow rate adjustment valves 24 and 25 of the present embodiment are butterfly valves. The specifications of the butterfly valves are selected based on the inner diameters of the pipes 21 and 22, and the second flow rate adjustment valve 25 is suitable for adjusting a smaller flow rate than the first flow rate adjustment valve 24. Note that the flow rate adjustment valves 24 and 25 only need to be able to adjust the flow rate of the gas flowing through the pipes 21 and 22, and are not limited to butterfly valves. Valves such as needle valves, gate valves, globe valves, and ball valves can be adopted.

[0018] The second pipe 22 is formed such that the inner diameter of the second pipe 22 is smaller than the inner diameter of the first pipe 21. When the inner diameter of the first pipe 21 is D1 and the inner diameter of the second pipe 22 is D2, the first pipe 21 and the second pipe 22 are formed to satisfy the following mathematical formula (1). 1 / 5 ≦ D2 / D1 ≦ 3 / 5 ··· (1) The inner diameter of the first pipe 21 can be, for example, 100 mm, and the inner diameter of the second pipe 22 can be, for example, 50 mm.

[0019] The inner diameter of the second pipe 22 does not necessarily have to be smaller than the inner diameter of the first pipe 21 over the entire length of the second pipe 22. It is sufficient that at least the location where the second flow rate adjustment valve 25 is provided is smaller than the inner diameter of the first pipe 21.

[0020] 〔Method for manufacturing single crystal silicon〕 Next, a method for manufacturing a single crystal silicon using the single crystal silicon pulling apparatus 1 described above will be described. The present invention is suitable for manufacturing an n-type single crystal silicon having a very low electrical resistivity. When the n-type dopant (volatile dopant) is antimony (Sb), the electrical resistivity is 5 mΩ·cm or more and 20 mΩ·cm or less. When the n-type dopant is arsenic (As), the electrical resistivity is 1.2 mΩ·cm or more and 10 mΩ·cm or less. When the n-type dopant is red phosphorus (P), the electrical resistivity is 0.5 mΩ·cm or more and 5 mΩ·cm or less. The present invention is suitable for manufacturing an n-type single crystal silicon having such an electrical resistivity.

[0021] As shown in FIG. 2, the method for manufacturing a single crystal silicon includes a preparation step S1, a first evacuation step S2, a second evacuation step S3, a gas replacement step S4, a raw material melting step S5, a volatile dopant supply step S6, and a pulling-up step S7.

[0022] In the preparation step S1, polycrystalline silicon as a raw material for the single crystal silicon is prepared. After filling an appropriate amount of crushed polycrystalline silicon pieces into the crucible 3, the crucible 3 is accommodated in the main chamber 10.

[0023] The first evacuation step S2 is a step of evacuating the gas in the chamber 2 from the state of atmospheric pressure (101.325 kPa) to reduce the pressure in the chamber 2 before pulling up the single crystal silicon SM. From the viewpoint of production efficiency, it is preferable to evacuate quickly, but in the first evacuation step S2, the pressure reduction rate of the gas is intentionally slowed down. In the first evacuation step S2, the first valve 23 of the first pipe 21 is in a closed state, and the second valve 26 of the second pipe 22 is in an open state. Also, the first flow rate adjustment valve 24 of the first pipe 21 is in an open state. That is, the gas in the chamber 2 is exhausted through the second pipe 22.

[0024] In the first evacuation step S2, the pressure reduction rate ES of the gas is adjusted within the range shown by the following mathematical formula (2) by the second flow rate adjustment valve 25. 0 kPa / min < ES ≦ 4.2 kPa / min ··· (2) The adjustment of the pressure reduction rate ES by the second flow rate adjustment valve 25 is continued until at least the pressure in the chamber 2 reaches 80 kPa.

[0025] Here, the method for determining the above-described pressure reduction rate ES will be described. When the inventors grow a silicon single crystal SM using a volatile dopant, the volatile dopant evaporates from the surface of the silicon melt M during pulling, becomes amorphous, and adheres to the pipe portion 16. After the amorphous material rises, it adheres to the silicon single crystal SM and is considered to polycrystallize. In addition, in the silicon single crystal pulling apparatus 1 using a volatile dopant, amorphous material accumulated in the pipe portion 16 by repeating pulling. The inventors considered that by reducing the pressure reduction rate ES at the start of pulling (reducing the pressure reduction rate ES), it is possible to reduce the upward movement of the amorphous material and reduce the occurrence rate of dislocation formation, and conducted the following verification.

[0026] The pressure reduction rate ES in the first evacuation step S2 was determined by performing pulling of a plurality of silicon single crystals while changing the pressure reduction rate ES before pulling the silicon single crystal SM and verifying the presence or absence of dislocation formation. FIG. 3 is a graph showing the change in the pressure inside the chamber. The horizontal axis in FIG. 3 is time (min), and the vertical axis is the pressure (kPa) inside the chamber. As shown in FIG. 3, it was found that when the change in pressure at the start of evacuation is large, that is, the pressure reduction rate is fast (the pressure reduction rate is large), dislocation formation occurs, while when the change in pressure at the start of evacuation is small, that is, the pressure reduction rate is slow, dislocation formation does not occur. In other words, it was found that when the pressure inside the chamber is rapidly decreased, dislocation formation is likely to occur, and when the pressure inside the chamber is slowly decreased, dislocation formation does not occur.

[0027] From the verification results shown in FIG. 3, the boundary line for the occurrence or non-occurrence of dislocation formation was obtained, and it was found that dislocation formation can be reduced by making the pressure reduction rate the same as or slower than 4.2 kPa / min from this boundary line. In consideration of the time required for vacuum evacuation, since it is preferable to increase the pressure reduction rate, the pressure reduction rate ES is preferably adjusted within the range shown by the following mathematical formula (3). 2.0 kPa / min ≤ ES ≤ 4.2 kPa / min ··· (3) In this way, by adjusting the pressure reduction rate ES, the exhaust time can be shortened, and the production efficiency of the single crystal silicon SM can be improved.

[0028] The second exhaust step S3 is a step of gradually increasing the pressure reduction rate ES after the pressure in the chamber 2 reaches 80 kPa and exhausting until the pressure approaches 0 kPa. In the second exhaust step S3, first, the opening degree of the second flow rate adjustment valve 25 is gradually increased, and then the first valve 23 is opened. That is, it is switched so that the gas is exhausted through the first pipe 21. After the first valve 23 is opened, the second valve 26 may be closed. At this time, the pressure reduction rate ES can be finely adjusted by the first flow rate adjustment valve 24. In the second exhaust step S3, by exhausting through the first pipe 21 having a larger diameter than the second pipe 22, the exhaust can be performed quickly.

[0029] The gas replacement step S4 is a step of introducing an inert gas into the vacuum-exhausted chamber 2 to replace it with an inert gas atmosphere. The inert gas is introduced by the gas introduction unit 12. The raw material melting step S5 is a step of melting the polycrystalline silicon (silicon raw material) accommodated in the crucible 3 to form a silicon melt M. In the raw material melting step S5, while maintaining the inside of the chamber 2 in an inert gas atmosphere, the crucible 3 is rotated and the crucible 3 is heated by the heater 4, so that the polycrystalline silicon in the crucible 3 melts and a silicon melt M is generated.

[0030] In the volatile dopant supply step S6, a volatile dopant is added to the silicon melt M using a dopant supply device (not shown).

[0031] The pulling-up step S7 is a step of pulling up the single-crystal silicon SM while rotating it. In the pulling-up step S7, similar to the first evacuation step S2, the first valve 23 is closed, the second valve 26 is opened, and the pressure in the chamber 2 is adjusted to 60 ± 5 kPa using the second flow rate adjustment valve 25. In this way, by setting the pressure in the chamber 2 to a high pressure, evaporation of the volatile dopant can be suppressed.

[0032] According to the above embodiment, in the first evacuation step S2, by setting the pressure reduction rate ES to be the same as or slower than 4.2 kPa / min, the amorphous material derived from the volatile dopant adhering to the piping section 16 is less likely to fly up. As a result, it is possible to reduce the occurrence of dislocation caused by the adhesion of the amorphous material to the single-crystal silicon SM during pulling up.

[0033] Also, in the first evacuation step S2, by exhausting the gas through the second pipe 22 having a smaller diameter than the first pipe 21, the pipe resistance to the gas flowing through the pipe increases. As a result, it is possible to more easily slow down the pressure reduction rate ES.

[0034] Also, in the second evacuation step S3, by setting the pressure reduction rate ES to be faster than 4.2 kPa / min, it is possible to exhaust the gas quickly and improve the production efficiency of the single-crystal silicon SM.

Example

[0035] Next, examples and comparative examples of the present invention will be described. In the examples and comparative examples, the pulling up of the single-crystal silicon was performed multiple times, and a comparison was made of the dislocation generation rate with respect to the pressure reduction rate ES when exhausting the gas from the chamber before pulling up the single-crystal silicon. In both the examples and comparative examples, the target resistivity at the top of the straight body portion of the single-crystal silicon is 2.3 mΩ·cm. The conditions and results are shown in Table 1.

[0036]

Table 1

[0037] As shown in Table 1, it was found that in the examples where the pressure reduction rate ES was the same as or slower than 4.2 kPa, the generation rate of dislocation could be reduced to 38% compared to the comparative examples where the pressure reduction rate was faster than 4.2 kPa.

Explanation of symbols

[0038] 1... Silicon single crystal pulling apparatus, 2... Chamber, 3... Crucible, 4... Heater, 5... Heat shield, 6... Heat insulating material, 7... Exhaust apparatus, 12... Gas introduction part, 14... Pressure gauge, 16... Pipe part, 17... Exhaust pump, 21... First pipe, 22... Second pipe, 23... First valve, 24... First flow rate adjustment valve, 25... Second flow rate adjustment valve, 26... Second valve, ES... Pressure reduction rate, M... Silicon melt, SM... Silicon single crystal.

Claims

1. A method for manufacturing a silicon single crystal, which comprises pulling up a silicon single crystal from a silicon melt stored in a crucible stored in a chamber and added with a volatile dopant by the Czochralski method, wherein a decompression rate ES when exhausting gas from the chamber before pulling up the silicon single crystal is within the following range until the pressure in the chamber decreases to at least 80 kPa from atmospheric pressure. A method for manufacturing a silicon single crystal. 0 kPa / min < ES ≤ 4.2 kPa / min

2. In the method for manufacturing a silicon single crystal according to Claim 1, the decompression rate ES is within the following range until the pressure in the chamber decreases to at least 80 kPa from atmospheric pressure. A method for manufacturing a silicon single crystal. 2.0 kPa / min ≤ ES ≤ 4.2 kPa / min

3. In the method for manufacturing a silicon single crystal according to Claim 1 or Claim 2, when the pressure in the chamber becomes lower than 80 kPa, a method for manufacturing a silicon single crystal in which the decompression rate ES is made faster than 4.2 kPa / min.

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