Manufacturing process for silicon single crystal

Abstract

A manufacturing process for a silicon single crystal comprising the following steps: a melting step for producing a silicon melt containing a primary dopant; and a crystal pulling step that pulls the silicon single crystal out of the silicon melt, wherein the crystal pulling-up step comprises at least one additional doping step for adding a non-melted secondary dopant of the type having a conductivity opposite to that of the primary dopant into the silicon melt, a flow rate of Ar gas supplied to a drawing furnace during a first period in which the secondary dopant is not added is set as a first flow rate, and the flow rate of Ar gas supplied to the drawing-up furnace during a second period including a period in which the secondary dopant is added is set as a second flow rate that is greater than the first flow rate.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a manufacturing method for a silicon single crystal using the Czochralski (CZ) method, and more particularly to a method for supplying an additional dopant during a crystal pulling-up step. BACKGROUND OF THE INVENTION

[0002] A large number of silicon single crystals, which become substrate materials for semiconductor devices, are produced using the CZ process. The CZ process grows a large-diameter single crystal beneath a seed crystal by immersing the seed crystal in a silicon melt stored in a quartz crucible and gradually pulling the seed crystal upward while rotating the seed crystal and quartz crucible. According to the CZ process, a high-quality silicon single crystal can be produced in high yield.

[0003] Different dopants are used during the growth of silicon single crystals to adjust the electrical resistivity (hereinafter referred to simply as resistivity) of the single crystal. Typical dopants include boron (B), phosphorus (P), arsenic (As), and antimony (Sb). Typically, these dopants are introduced into a quartz crucible with a polycrystalline silicon source and melted together with the polycrystalline silicon by applying heat with a heater. Accordingly, a silicon melt containing a predetermined amount of dopant is created.

[0004] However, it is difficult to obtain a uniform resistivity in the pull-up axis direction because the dopant concentration in the silicon single crystal changes in the pull-up axis direction due to segregation. To solve this problem, a method in which a dopant is added midway through the pulling-up of a silicon single crystal is effective. For example, by adding a p-type dopant to the silicon melt midway through the pulling-up of an n-type silicon single crystal, a decrease in the resistivity of the silicon single crystal due to the influence of segregation of an n-type dopant can be suppressed. Such a method of adding an additional secondary dopant of the type with a conductivity opposite to that of the primary dopant is called counter doping.

[0005] Regarding the counter-doping technology, for example, Patent Literature 1 describes the addition of a dopant such that the supply rate of the dopant (e.g., p-type) that is the opposite type to the initially added type (e.g., n-type) satisfies a predetermined comparison expression. Furthermore, Patent Literature 2 describes a method for controlling the resistivity in the axial direction of the grown silicon single crystal by introducing a rod-shaped silicon crystal containing the secondary dopant into the raw material melt. RELATED PRIOR ARTPatent literature Patent Literature 1: Japanese Patent Laid-Open Publication JP H03-247585 A Patent Literature 2: Japanese Patent Laid-Open Publication JP 2016-216306 A

[0006] Czochralski processes in which the concentration of a dopant is controlled are known from US Pat. No. 5,129,986 A, CN 1 05 970 284 A, and DE11 2015 003 573 T5. CN 1 05 970 284 A and DE11 2015 003 573 T5 describe counter-doping with a second dopant whose conductivity is opposite to that of the first dopant. SUMMARY OF THE INVENTIONProblems to be solved by the invention

[0007] However, in counter-doping, in which a granular dopant is added to a silicon melt in a quartz crucible, a solid dopant is absorbed into a solid-liquid interface before the solid dopant is dissolved in the melt, causing dislocation in a silicon single crystal. This type of dislocation problem is particularly noticeable in the pulling-up of a silicon single crystal for IGBT, where the flow rate of Ar gas introduced into a pulling-up furnace is reduced to reduce the oxygen in the single crystal, and there is a need for improvement.

[0008] Therefore, the present invention provides a manufacturing method for a silicon single crystal that can prevent dislocation of the single crystal in a counter-doping process that adds a secondary dopant in the middle of pulling up the crystal. Means of solving the tasks

[0009] In order to solve the above problems, the silicon single crystal manufacturing method according to the present invention includes a melting step for producing a silicon melt containing a primary dopant and a crystal pulling-up step for pulling up the silicon single crystal from the silicon melt.The crystal pulling-up step includes at least one additional doping step of adding an unmelted secondary dopant of the type having a conductivity opposite to that of the primary dopant into the silicon melt, and the flow rate of Ar gas supplied to a pulling-up furnace during a first period in which the secondary dopant is not added is set as a first flow rate, and the flow rate of Ar gas supplied to the pulling-up furnace during a second period including a period in which the secondary dopant is added is set as a second flow rate greater than the first flow rate.

[0010] According to the present invention, it is possible to prevent dislocation of the silicon single crystal caused by the secondary dopant added into the silicon melt reaching the solid-liquid interface and being incorporated into the silicon single crystal in a non-molten state.

[0011] According to the invention, an increase in the second flow rate with respect to the first flow rate is preferably 40 l / min or more and 300 l / min or less in flow rate conversion at room temperature and atmospheric pressure. If it is less than 40 l / min, the effect is small, and if it is more than 300 l / min, the temperature of the melt surface may decrease and there is a risk of dislocation of the single crystal. Specifically, the increase in the second flow rate with respect to the first flow rate is preferably 80 l / min or more and 160 l / min or less. In addition, the second flow rate is preferably 120 l / min or more in flow rate conversion at room temperature and atmospheric pressure, preferably 1.5 times or more and 5 times or less of the first flow rate, and particularly preferably 2 times or more and 3 times or less.Accordingly, it is possible to prevent dislocation of the silicon single crystal caused by the unmelted secondary dopant being incorporated into the solid-liquid interface.

[0012] According to the invention, the additional doping step preferably increases the flow rate of Ar gas to the second flow rate before the start of the addition of the second dopant and returns the flow rate of Ar gas to the first flow rate after the addition of the secondary dopant ends. This makes it possible to further reduce the probability that the dopant added to the silicon melt is absorbed into the solid-liquid interface in a non-molten state.

[0013] According to the invention, it is preferable to set the pressure in the drawing furnace during the first period as a first pressure in the furnace, and to set the pressure in the drawing furnace during the second period as a second pressure in the furnace that is lower than the first pressure in the furnace. The probability of dislocation can be further reduced by changing the pressure in the furnace at the same time as the flow rate of Ar gas.

[0014] In the present invention, the amount of reduction of the second pressure in the furnace relative to the first pressure in the furnace is preferably 1 Torr (approximately 133.32 Pascals) or more and 10 Torr (approximately 1333.2 Pascals) or less. Generally, the first pressure in the furnace is often several tens of Torr (approximately multiples of 1333.2 Pascals), and if the amount of reduction of the second pressure in the furnace exceeds 10 Torr (approximately 1333.2 Pascals), the second pressure in the furnace becomes too low, and there is a risk of causing dislocation of the single crystal being pulled up. In addition, if the amount of reduction of the second pressure in the furnace is less than 1 Torr (approximately 133.32 Pascals), the second pressure in the furnace is not very different from the first pressure in the furnace, and thus it is difficult to obtain the effect of reducing the probability of dislocation.In contrast, when the amount of reduction of the second pressure in the furnace with respect to the first pressure in the furnace is 1 Torr (about 133.32 Pascals) or more and 10 Torr (about 1333.2 Pascals) or less, the probability of dislocation of the single crystal can be further reduced.

[0015] The silicon single crystal manufacturing method according to the present invention preferably disposes a substantially cylindrical heat-shielding member above the silicon melt to surround the silicon single crystal as it is pulled up from the silicon melt, and pulls up the silicon single crystal while controlling the flow rate of the Ar gas passing through a gap between the lower end of the heat-shielding member and the melt surface. When pulling up a silicon single crystal with a low oxygen concentration in the furnace in which the heat-shielding member is installed, the flow rate of the Ar gas flowing through the gap between the lower end of the heat-shielding member and the melt surface must be precisely controlled.According to the invention, by increasing the flow rate of Ar gas during counter-doping, the flow velocity of the Ar gas flowing from the center of the silicon single crystal toward an outer side near the melt surface of the silicon melt can be increased, preventing the unmelted dopant from approaching the solid-liquid interface. In particular, when the secondary dopant is added closer to the quartz crucible than to the lower end of the heat-shielding member, the flow velocity of the Ar gas passing through the gap between the lower end of the heat-shielding member and the melt surface and flowing from a central axis side of the silicon single crystal toward the outer side can be increased, which is effective in preventing the unmelted dopant from approaching the solid-liquid interface.

[0016] According to the invention, the oxygen concentration in the silicon single crystal is preferably 6×1017 atoms / cm 3 (ASTM F-121, 1979) or less and more preferably 4×10 17 atoms / cm 3(ASTM F-121, 1979) or less. In addition, the electrical resistivity of the silicon single crystal is preferably 10 Ω·cm or more and 1,000 Ω·cm or less, and more preferably 20 Ω·cm or more and 100 Ω·cm or less. Thus, when pulling up a silicon single crystal with a low oxygen concentration and a narrow resistivity range, it is necessary to reduce the flow rate of Ar gas in the furnace during the crystal pulling-up step. If counterdoping is performed under a condition that the flow rate of Ar gas is low, the probability of dislocation of the silicon single crystal increases. However, if the flow rate of Ar gas is increased only during a counterdoping step, as in the present invention, the probability of dislocation of the silicon single crystal can be reduced.

[0017] In addition, the silicon single crystal manufacturing method according to the present invention includes the melting step of producing the silicon melt containing the primary dopant and the crystal pulling-up step of pulling up the silicon single crystal from the silicon melt. The crystal pulling-up step includes at least one additional doping step of adding the unmelted secondary dopant of the type having a conductivity opposite to that of the primary dopant into the silicon melt. The pressure in the pulling-up furnace during the first period in which the secondary dopant is not added is set as the first pressure in the furnace, and the pressure in the pulling-up furnace during the second period, which includes the period in which the secondary dopant is added, is set as the second pressure in the furnace, which is lower than the first pressure in the furnace.

[0018] According to the invention, it is possible to prevent dislocation of the silicon single crystal caused by the secondary dopant added into the silicon melt reaching the solid-liquid interface in a non-molten state and being absorbed into the silicon single crystal.

[0019] According to the present invention, the amount of reduction of the second pressure in the furnace relative to the first pressure in the furnace is preferably 1 Torr (approximately 133.32 Pascals) or more and 10 Torr (approximately 1333.2 Pascals) or less. Generally, the first pressure in the furnace is often several tens of Torr (approximately multiples of 1333.2 Pascals), and if the amount of reduction of the second pressure in the furnace exceeds 10 Torr (approximately 1333.2 Pascals), the second pressure in the furnace becomes too low, and there is a risk of causing dislocation of the single crystal being pulled up. In addition, if the amount of reduction of the second pressure in the furnace is less than 1 Torr (approximately 133.32 Pascals), the second pressure in the furnace is not very different from the first pressure in the furnace, and thus, it is difficult to obtain the effect of reducing the probability of dislocation.In contrast, the probability of dislocation of the single crystal can be further reduced when the amount of reduction of the second pressure in the furnace with respect to the first pressure in the furnace is 1 Torr (about 133.32 Pascals) or more and 10 Torr (about 1333.2 Pascals) or less. Effect of the invention

[0020] The present invention provides a manufacturing method for the silicon single crystal which can prevent dislocation of the single crystal in the counter doping process which adds the secondary dopant in the middle of pulling up the crystal. BRIEF DESCRIPTION OF THE DRAWINGS [ Fig. 1] Fig. 1 is a cross-sectional view essentially illustrating the configuration of a single crystal manufacturing apparatus used in a method according to an embodiment of the present invention. [ Fig. 2] Fig. 2 is a flowchart describing a manufacturing method for a silicon single crystal according to the embodiment of the present invention. [ Fig. 3] Fig. 3 is a flowchart describing a step S16 of growing the part of the straight body, which includes a counter-doping step. [ Fig. 4] Fig. Figure 4 is a graph illustrating a relationship between a dopant addition period, a flow rate of Ar gas, and a pressure in a furnace. [ Fig. 5] Fig. Figure 5 is a graph illustrating a change in the resistivity of the silicon single crystal when counterdoping is performed twice. [ Fig. 6] Fig. 6 is a graph illustrating results in which the resistivity of the silicon single crystal was measured using the four-point probe method according to an embodiment. WAY TO IMPLEMENT THE INVENTION

[0021] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0022] Fig. 1 is a cross-sectional view essentially illustrating a configuration of a single crystal manufacturing apparatus used in a method according to an embodiment of the present invention.

[0023] As in Fig. 1, a single-crystal manufacturing apparatus 1 includes a chamber 10 constituting a pulling-up furnace for a silicon single crystal 2, a quartz crucible 12 installed inside the chamber 10, a graphite susceptor 13 supporting the quartz crucible 12, a shaft 14 supporting the susceptor 13 so that it can be lifted and rotated, a heater 15 arranged to surround the susceptor 13, a heat-shielding member 16 arranged above the quartz crucible 12, a single-crystal pulling-up wire 17 arranged above the quartz crucible 12 and on the same axis as the shaft 14, a wire winding mechanism 18 arranged on the top of the chamber 10, and a dopant supply device 20 that supplies a dopant source material 5 into the quartz crucible 12. and a controller 30 that controls various components.

[0024] The chamber 10 is configured with a main chamber 10a, an upper chamber 10b covering an upper opening of the main chamber 10a, and a slender cylindrical pulling chamber 10c connected to an upper opening of the upper chamber 10b. The quartz crucible 12, the susceptor 13, the heater 15, and the heat shield member 16 are provided in the main chamber 10a. The susceptor 13 is fixed to an upper end of a shaft 14, which is mounted to pass through the center of the bottom of the chamber 10 in the vertical direction. The shaft 14 is driven by a shaft drive mechanism 19 to rotate and raise it.

[0025] The heater 15 is used to melt a polycrystalline silicon source material filled in the quartz crucible 12 to produce a silicon melt 3. The heater 15 is a resistance heater made of carbon and is arranged to surround the quartz crucible 12 inside the susceptor 13. A thermal insulation material 11 is provided outside the heater 15. The thermal insulation material 11 is arranged along an inner wall of the main chamber 10a, thereby enhancing heat retention inside the main chamber 10a.

[0026] The heat-shielding member 16 is provided to prevent the heating of the silicon single crystal 2 by radiant heat from the heater 15 and the quartz crucible 12, and also to suppress temperature fluctuations in the silicon melt 3. The heat-shielding member 16 is a substantially cylindrical member with a diameter that decreases from the top toward the bottom, and is mounted to cover the top of the silicon melt 3 and surround the silicon single crystal 2 during growth. Graphite is preferred as the material for the heat-shielding member 16. An opening larger than the diameter of the silicon single crystal 2 is provided at the center of the heat-shielding member 16, thereby providing a pulling-up path for the silicon single crystal 2. As shown in the drawing, the silicon single crystal 2 is pulled upward through the opening.The diameter of the opening of the heat-shielding member 16 is smaller than an opening of the quartz crucible 12, and the lower end part of the heat-shielding member 16 is located toward an inner side of the quartz crucible 12, and thus the heat treatment member 16 does not interfere with the quartz crucible 12 even if an upper end of a rim of the quartz crucible 12 is raised above the lower end of the heat-shielding member 16.

[0027] Although the amount of melt in the quartz crucible 12 decreases during the growth of the silicon single crystal 2, the temperature fluctuation of the silicon melt 3 is suppressed by controlling the height of the quartz crucible 12 so as to keep a space (gap) between a melt surface and the heat shielding member 16 constant. In addition, the evaporation amount of dopant from the silicon melt 3 can be controlled by keeping a constant flow rate of Ar gas flowing near the melt surface (purge gas guide path). Accordingly, the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, and the like in the pull-up axis direction of the single crystal can be improved.

[0028] The wire 17, which is the pulling axis of the silicon single crystal 2, and the wire winding mechanism 18 that winds the wire 17 are provided above the quartz crucible 12. The wire winding mechanism 18 has a function of rotating the silicon single crystal 2 in addition to the wire 17. The wire winding mechanism 18 is arranged above the pulling chamber 10c, and the wire 17 extends downward from the wire winding mechanism 18, passes through the pulling chamber 10c, and a distal end of the wire 17 reaches the interior of the main chamber 10a. Fig. 1 shows a state in which the silicon single crystal 2 is suspended from the wire 17 in the middle of growth. During the pulling up of the single crystal, the single crystal grows by immersing a seed crystal in the silicon melt 3 and gradually pulling up the wire 17 while rotating the quartz crucible 12 and the seed crystal, respectively.

[0029] The top of the pulling chamber 10c is equipped with a gas inlet 10d for supplying Ar gas (purge gas) into the chamber 10, and the bottom of the main chamber 10a is equipped with a gas outlet port 10e for discharging Ar gas in the chamber 10. In this example, Ar gas means that the primary component of the gas (over 50 vol%) is argon and may include gas such as hydrogen and nitrogen.

[0030] An Ar gas supply source 31 is connected to the gas inlet 10d via a mass flow controller 32, and Ar gas from the Ar gas supply source 31 is introduced into the chamber 10 via the gas inlet 10d, and the amount of introduced Ar gas is controlled by the mass flow controller 32. In addition, Ar gas sealed in the chamber 10 is discharged to the outside of the chamber 10 via the gas outlet port 10e, and thus, it is possible to keep the interior of the chamber 10 clean by collecting SiO gas and CO gas present in the chamber 10. The Ar gas flowing from the gas inlet 10d toward the gas outlet port 10e passes the opening of the heat shielding member 16, flows along the melt surface from the center of the drawing-up furnace to the outside, and further flows downward and reaches the gas outlet port 10e.

[0031] A vacuum pump 33 is connected to the gas outlet port 10e via a pipe, and the chamber 10 is maintained in a state of stable reduced pressure by controlling the flow rate of Ar gas with a valve 34 while the Ar gas in the chamber 10 is exhausted with the vacuum pump 33. The pressure in the chamber 10 is measured with a pressure gauge, and the amount of Ar gas exhausted through the gas outlet port 10e is controlled so that the pressure in the chamber 10 remains stable.

[0032] The dopant supply device 20 includes a dopant supply tube 21 drawn from outside the chamber 10 into the interior of the chamber 10, a dopant funnel 22 disposed outside the chamber 10 and connected to an upper end of the dopant supply tube 21, and a sealing cap 23 sealing an opening 10f of the upper chamber 10b through which the dopant supply tube 21 passes.

[0033] The dopant supply pipe 21 is a conduit extending from a position where the dopant funnel 22 is located to immediately above the silicon melt 3 in the quartz crucible 12 by passing through the opening 10f of the upper chamber 10b. As the silicon single crystal 2 is pulled up, the dopant supply device 20 supplies additional dopant source material 5 into the silicon melt 3 in the quartz crucible 12. The dopant source material 5 withdrawn from the dopant funnel 22 is supplied to the silicon melt 3 by passing through the dopant supply pipe 21.

[0034] The dopant source material 5 supplied from the dopant supply device 20 is granular silicon containing a secondary dopant. Such a dopant source material 5 is produced by growing a silicon crystal containing a high concentration of secondary dopant using, for example, the CZ method, and then crushing the silicon crystal into small pieces. However, the dopant source material 5 used for counter-doping is not limited to silicon containing the secondary dopant and may be a dopant alone or a compound containing a dopant atom. Furthermore, the shape of the dopant source material 5 is not limited to granular and may also be a plate or rod shape.

[0035] Fig. 2 is a flowchart describing the manufacturing method of the silicon single crystal according to the embodiment of the present invention.

[0036] As in Fig. As shown in Figure 2, in the manufacture of the silicon single crystal 2, the quartz crucible 12 is first filled with a primary dopant as well as the polycrystalline silicon raw material (raw material filling step S11). The primary dopant in pulling up an n-type silicon single crystal is, for example, phosphorus (P), arsenic (As), or antimony (Sb), and the primary dopant in pulling up a p-type silicon single crystal is, for example, boron (B), aluminum (Al), gallium (Ga), or indium (In). Next, the polycrystalline silicon in the quartz crucible 12 is melted by heating with the heater 15, producing the silicon melt 3 containing the primary dopant (melting step S12).

[0037] Next, the seed crystal attached to the distal end of the wire 17 is lowered and brought into contact with the silicon melt 3 (step S13). Then, crystal pulling-up steps (S15 to S17) are performed, in which the single crystal grows by gradually pulling up the seed crystal while maintaining the state of contact with the silicon melt 3.

[0038] In the crystal pulling-up steps, a neck formation step S14, which forms a neck where the crystal diameter is thinned to achieve non-dislocation; a shoulder growth step S15, which forms a shoulder where the crystal diameter gradually increases; a straight body part growth step S16, which forms a part of the straight body maintained at a specific crystal diameter (for example, about 300 mm); and a tail growth step S17, which forms a tail where the crystal diameter gradually decreases, are performed in sequence, and finally, the single crystal is separated from the melt surface. The above steps complete a silicon single crystal ingot.

[0039] The step S16 of growing the straight body portion preferably includes at least one counter-doping step (additional doping step) in which a secondary dopant having a conductivity type opposite to the primary dopant contained in the silicon single crystal 2 is added. Accordingly, a change in the resistivity of the straight body portion of the silicon single crystal 2 in a crystal length direction can be suppressed.

[0040] The oxygen concentration in a silicon single crystal for IGBT is preferably 6×10 17 atoms / cm 3 (ASTM F-121, 1979) or less and more preferably 4×10 17 atoms / cm 3 (ASTM F-121, 1979) or less. In addition, the electrical resistivity of the silicon single crystal for IGBT is preferably 10 Ω cm or more and 1,000 Ω cm or less, and more preferably 20 Ω cm or more and 100 Ω cm or less.

[0041] Thus, when pulling up silicon single crystals for IGBTs with low oxygen concentration and a narrow resistivity range, slowing the flow rate of Ar gas flowing along the melt surface from a central axis side of the pulling-up furnace toward the outside is preferable. When additional doping is performed under such furnace conditions, the probability of dislocation of the silicon single crystal increases. However, the probability of dislocation of the silicon single crystal can be reduced by changing the furnace conditions during the counter-doping step according to the present invention.

[0042] Fig. 3 is a flowchart describing step S16 of growing the part of the straight body, including the counter doping step.

[0043] As in Fig. As shown in Figure 3, at the beginning of step S16 of growing the straight body part, the flow rate of the Ar gas and the pressure in the furnace are respectively adjusted to values ​​suitable for the growth of the silicon single crystal (step S21). For example, in a case of the silicon single crystal for IGBT, a low resistivity and a low interstitial oxygen concentration are desired. To grow such a silicon single crystal, the flow rate of Ar gas must be smaller than that for a silicon single crystal for a general semiconductor device. The flow rate of Ar gas required for the normal step S16 of growing the straight body part is defined as the first flow rate F1, and the pressure in the furnace is defined as the first pressure in the furnace P1.

[0044] The dopant concentration in the silicon single crystal increases as the crystal pull-up progresses, which may cause a deviation from a desired resistivity range. Therefore, in the middle of the step, when a timing for counterdoping is required, counterdoping is initiated (steps S22A, S23 to S25).

[0045] During counter-doping, the dopant source material 5 containing the secondary dopant is added to the silicon melt 3 (step S24). The secondary dopant is, for example, boron (B), aluminum (Al), gallium (Ga), or indium (In) when pulling up the n-type silicon single crystal, and the secondary dopant is, for example, phosphorus (P), arsenic (As), or antimony (Sb) when pulling up the p-type silicon single crystal.

[0046] During the dopant addition period, the Ar gas flow rate and the pressure in the furnace are each changed to values ​​suitable for counter-doping. The Ar gas flow rate F2 (second flow rate) during the dopant addition period (second period) is set to a value greater than the Ar gas flow rate F1 (first flow rate) during the normal crystal pulling period (first period) (F2 > F1). Furthermore, the pressure P2 in the furnace (second furnace pressure) during the counter-doping period is set to a value lower than the furnace pressure P1 (first furnace pressure) during the normal crystal pulling period (P2 < P1).The dopant addition period is, in a narrow sense, a period during which the dopant starting material 5 is actually added, but in a broader sense, it means a period of time necessary for the dopant added into the silicon melt to completely dissolve and thus the dislocation problem no longer occurs.

[0047] The increase in the Ar gas flow rate F2 relative to the Ar gas flow rate F1 is preferably 40 l / min or more and 300 l / min or less when converted to room temperature and atmospheric pressure. In addition, the Ar gas flow rate F2 is preferably 120 l / min or more when converted to room temperature and atmospheric pressure, and is preferably 1.5 times or more and 5 times or less of the Ar gas flow rate F1. Accordingly, it is possible to prevent dislocation of the silicon single crystal caused by the unmelted secondary dopant being incorporated into the solid-liquid interface.

[0048] The reduction in pressure P2 in the furnace relative to pressure P1 is preferably 1 Torr (approximately 133.32 Pascals) or more and 10 Torr (approximately 1333.2 Pascals) or less. The probability of dislocation can be further reduced by changing the pressure in the furnace at the same time as the Ar gas flow rate.

[0049] After the end of the counter-doping, the values ​​of the flow rate F1 of Ar gas and the pressure P1 in the furnace during the normal crystal pulling-up period (first period) are reset, and the growth of the straight body part is continued (steps S25, S26).

[0050] The counterdoping steps are repeated according to the required crystal length (steps S27Y, S22Y, S23 to S25). After the counterdoping is completed, the growth of the straight body continues, and at the point where counterdoping is required again, counterdoping is initiated. The number of counterdoping repetitions is predetermined, and counterdoping is repeated until the specified number of counterdopings is completed. During counterdoping, the Ar gas flow rate and the pressure in the furnace are changed each time to values ​​(F2, P2) appropriate for the counterdoping.In this way, it is possible to increase the yield of silicon single crystals with a small change in the resistivity in the pull-up axis direction by pulling up the silicon single crystal with the desired length while performing the counter doping the specified number of repetitions.

[0051] Fig. Figure 4 is a graph illustrating a relationship between the dopant addition period, the flow rate of Ar gas, and the pressure in the furnace.

[0052] As in Fig. As shown in Figure 4, during the dopant addition period, the pressure in the furnace is reduced and the flow rate of Ar gas is increased. For example, the flow rate of Ar gas during the dopant addition period (second period) is set to twice the flow rate of Ar gas during the normal pull-up period (first period) in which the dopant is not added. In addition, the pressure in the furnace during the dopant addition period (second period) is set to 80% of the pressure in the furnace during the normal pull-up period (first period).

[0053] When the flow rate of Ar gas introduced into the chamber 10 is increased, the flow velocity of the Ar gas flowing from the center of the chamber 10 toward the outside along the melt surface becomes fast, and thus the unmelted dopant floating near the melt surface can be prevented from approaching the solid-liquid interface between the silicon single crystal 2 and the silicon melt 3. Similarly, when the pressure in the furnace is increased, the flow velocity of the Ar gas flowing from the center of the chamber 10 toward the outside along the melt surface becomes fast, and thus the dopant can be prevented from approaching the solid-liquid interface.Accordingly, by temporarily changing the flow rate of Ar gas and the pressure in the furnace, it is possible to prevent dislocation of the single crystal caused by the dopant being incorporated into the solid-liquid interface between the silicon single crystal 2 and the silicon melt 3.

[0054] Fig. Figure 5 is a graph illustrating a change in resistivity in the silicon single crystal when counterdoping is performed twice, where the horizontal axis denotes the crystal length (relative value when the total length of the straight body part is defined as 1) and the vertical axis denotes the resistivity (relative value).

[0055] As in Fig. As shown in Figure 5, in the case where a silicon single crystal is doped with phosphorus alone as the primary dopant, the resistivity of the silicon single crystal is highest at the beginning of pulling up and only gradually decreases as pulling up proceeds, and consequently, the resistivity deviates from a standard when the crystal length exceeds about 0.44.

[0056] However, by performing a first counterdoping at a point where the crystal length is about 0.44 and a second counterdoping at a point where the crystal length is 0.63, the length of the single crystal in which the resistivity is within the standard can be made as long as possible.

[0057] As described above, the manufacturing method for the silicon single crystal according to the present embodiment includes a step in which the primary dopant of the silicon single crystal and the secondary dopant of opposite conductivity type are added into the silicon melt during the pulling-up step of the silicon single crystal, and the flow rate of Ar gas during the period of adding the secondary dopant is set higher than during the period in which the secondary dopant is not added, and the pressure in the furnace is lowered, and thus the dislocation of the single crystal can be prevented.

[0058] A preferred embodiment of the present invention has been described above, however, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible without departing from the scope of the present invention, and such modifications are of course covered by the scope of the present invention. EMBODIMENT (comparative example)

[0059] Counterdoping was performed without changing the Ar gas flow rate and the furnace pressure during the growth step of the straight body portion of the n-type silicon single crystal using phosphorus (P) as the primary dopant. During counterdoping, a change in resistivity was predicted due to the segregation of P, and boron (B), which served as the secondary dopant, was added just before the resistivity deviated from the standard. As a result, dislocation of the silicon single crystal occurred immediately after the addition of the secondary dopant. (Example)

[0060] Counterdoping was performed twice in the middle of the growth step of the straight body portion of the n-type silicon single crystal using phosphorus (P) as the primary dopant. During counterdoping, the Ar gas flow rate was increased to twice the normal rate, and after maintaining this increased Ar gas flow rate for 15 minutes, the Ar gas flow rate was returned to the normal rate (see Fig. 4). In addition, at the same time, the pressure in the furnace was set 5 Torr (approximately 666.6 Pascals) lower than the normal pressure, and after maintaining a state with this reduced pressure in the furnace for 15 minutes, the pressure in the furnace was returned to the normal pressure (see Fig. 4) It took 20 minutes to change the Ar gas flow rate and the pressure in the furnace (increase and decrease). The secondary dopant was added during a period that kept the conditions when the Ar gas flow rate was increased and the conditions when the pressure in the furnace was reduced constant. As a result, the silicon single crystal could be pulled up to completion without dislocation.

[0061] In order to examine the resistivity distribution in the crystal length direction of the thus obtained silicon single crystal, a sample was obtained by vertically dividing a crystal block near the dopant addition site, a grinding process was performed so that the sample thickness became 1.0 mm, and further, a donor-killing treatment (650°C, 40 minutes heat treatment) was performed for resistivity measurement.

[0062] The resistivity of the sample was then measured using the four-point probe method. The resistivity measurement spacing was 1 mm near the location where the secondary dopant was added and 5 mm everywhere else. The result of continuous resistivity measurements is shown in Fig. 6. As shown in the figure, the resistivity increases immediately after the addition of the dopant and maintains a resistivity consistent with segregation. The resistivity after the second addition of the secondary dopant was slightly lower than the target resistivity, but generally favorable results were obtained.

[0063] The pulling up of the silicon single crystal was performed four times, accompanied by the counterdoping described above, but dislocation did not occur in any of the silicon single crystals and favorable results were obtained. DESCRIPTION OF REFERENCE NUMBERS 1 single crystal production device 2 silicon single crystal 3 Silicon melt 5 Dopant (secondary dopant) 10 chambers 10a Main Chamber 10b upper chamber 10c drawing chamber 10d gas inlet 10e Gas outlet opening 10f opening 11 thermal insulation material 12 quartz crucibles 13 Susceptor 14 shaft 15 Heating 16 Heat shielding component 17 wire 18 Wire winding mechanism 19 Shaft drive mechanism 20 Dopant supply device 21 Dopant supply tube 22 dopant funnels 23 Sealing cap 30 Control 31 Ar gas supply source 32 mass flow controllers 33 Vacuum pump 34 Valve S11 Step of filling with starting material S12 Melting step S13 Step of contacting with the melt S14 Step of neck formation S15 Step of shoulder growth S16 Step of growth of the part of the straight body S17 Step of tail growth

Claims

[1] A method for producing a silicon single crystal comprising the following steps: a melting step for producing a silicon melt containing a primary dopant; and a crystal pulling step that pulls the silicon single crystal out of the silicon melt, wherein the crystal pulling-up step comprises at least one additional doping step for adding a non-melted secondary dopant of the type having a conductivity opposite to that of the primary dopant into the silicon melt, a flow rate of Ar gas supplied to a drawing furnace during a first period in which the secondary dopant is not added is set as a first flow rate, and the flow rate of Ar gas supplied to the drawing-up furnace during a second period including a period in which the secondary dopant is added is set as a second flow rate that is greater than the first flow rate. [2] The manufacturing method for a silicon single crystal according to claim 1, wherein an amount of increase of the second flow rate with respect to the first flow rate is 40 l / min or more and 300 l / min or less in a flow rate conversion at room temperature and atmospheric pressure. [3] The manufacturing method for a silicon single crystal according to any one of claims 1 and 2, wherein the second flow rate is 120 l / min or more in a flow rate conversion at room temperature and atmospheric pressure. [4] The manufacturing method for a silicon single crystal according to any one of claims 1 to 3, wherein the second flow rate is 1.5 times or more and 5 times or less of the first flow rate. [5] A manufacturing method for a silicon single crystal according to any one of claims 1 to 4, wherein the additional doping step comprises a dopant addition period during which a dopant source material is actually added, wherein the Ar gas flow rate is increased to the second flow rate before the start of the dopant addition period, and the Ar gas flow rate is returned to the first flow rate after the dopant addition period. [6] The manufacturing method for a silicon single crystal according to any one of claims 1 to 5, wherein a pressure in the pulling-up furnace during the first period is set as a first pressure in a furnace, and the pressure in the pulling-up furnace during the second period is set as a second pressure in a furnace which is lower than the first pressure in the furnace. [7] The manufacturing method for a silicon single crystal according to claim 6, wherein an amount of reduction of the second pressure in the furnace with respect to the first pressure in the furnace is 133.32 Pascals or more and 1333.2 Pascals or less. [8] A manufacturing method for a silicon single crystal according to any one of claims 1 to 7, wherein a cylindrical heat shielding member is arranged above the silicon melt so as to surround the silicon single crystal when it is pulled up from the silicon melt. [9] A manufacturing method for a silicon single crystal according to any one of claims 1 to 8, wherein the oxygen concentration in the silicon single crystal is 6×10 17 atoms / cm 3 (ASTM F-121, 1979) or less. [10] A manufacturing method for a silicon single crystal according to any one of claims 1 to 9, wherein the specific electrical resistance of the silicon single crystal is 10 Ω·cm or more and 1,000 Ω·cm or less. [11] A method for producing a silicon single crystal comprising the following steps: a melting step for producing a silicon melt containing a primary dopant; and a crystal pulling step that pulls the silicon single crystal out of the silicon melt, wherein the crystal pulling-up step comprises at least one additional doping step for adding a non-melted secondary dopant of the type having a conductivity opposite to that of the primary dopant into the silicon melt, a pressure in a drawing furnace during a first period in which the secondary dopant is not added is set as a first pressure in a furnace, and the pressure in the pull-up furnace during a second period, which includes a period in which the secondary dopant is added, is set as a second pressure in the furnace which is lower than the first pressure in the furnace. [12] The manufacturing method for a silicon single crystal according to claim 11, wherein an amount of reduction of the second pressure in the furnace with respect to the first pressure in the furnace is 133.32 Pascals or more and 1333.2 Pascals or less.

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