Method for manufacturing silicon single crystal, flow straightening member, and single crystal pulling device

The present invention relates to a manufacturing method of monocrystalline silicon, a flow regulator, and a monocrystal pull-up apparatus.

A method of manufacturing monocrystalline silicon according to Czochralski method has been typically known (see, for instance, Patent Literature 1).

A monocrystal pull-up apparatus of Patent Literature 1 includes: a tubular body coaxially surrounding monocrystalline silicon; and a gas flow regulator provided to a lower end of the tubular body and having a truncated cone-shaped surface extending downward. An opening is provided near a connector of the tubular body and the gas flow regulator. An inner diameter of the gas flow regulator is smaller than an inner diameter of the tubular body.

When monocrystalline silicon is manufactured by using a dopant in a form of antimony (Sb), under a reduced pressure of 100 mbar (about 10 kPa), most of downward inert gas flows along the truncated cone-shaped surface of the gas flow regulator from the opening to decrease the inert gas arriving at or near a crystallized part of a surface of a melt through an inside of the tubular body, thereby reducing evaporation of SiO and Sb 2 O 3 and increasing an oxygen concentration in silicon crystal.

Patent Literature(s)

Patent Literature 1: JP 5-238883 A

Problem(s) to be Solved by the Invention

However, reduction in evaporation of the dopant is not sufficient according to the method of Patent Literature 1.

An object of the invention is to provide a manufacturing method of monocrystalline silicon, a dopant flow regulator and a monocrystal pull-up apparatus, which are capable of reducing evaporation of a dopant.

Means for Solving the Problem(s)

An aspect of the invention provides a manufacturing method of monocrystalline silicon using a monocrystal pull-up apparatus including: a crucible; a crucible driver configured to raise, lower and rotate the crucible; a heater configured to heat the crucible to generate a dopant-added melt in which a dopant is added to a silicon melt; a pull-up portion configured to bring a seed crystal into contact with the dopant-added melt and subsequently pull up the seed crystal to grow monocrystalline silicon; a cylindrical heat shield provided above the crucible, surrounding the monocrystalline silicon; a chamber housing the crucible, the heater and the heat shield; and an intake provided on an upper side of the chamber and configured to introduce inert gas into the chamber, in which the manufacturing method includes; disposing a flow regulator under the heat shield, the flow regulator including an annular plate body surrounding the monocrystalline silicon; during growth of the monocrystalline silicon, simultaneously, controlling an internal pressure of the chamber to 20 kPa or more; keeping the flow regulator spaced from the dopant-added melt; and introducing the inert gas from above to between the monocrystalline silicon and the heat shield to divide the inert gas into a first flow gas flowing along a first flow path between the heat shield and the flow regulator to be away from the monocrystalline silicon and a second flow gas flowing along a second flow path between the flow regulator and a surface of the dopant-added melt to be away from the monocrystalline silicon.

According to the above arrangement, a partial pressure of the dopant being volatilized in the chamber is decreased by controlling the internal pressure of the chamber to 20 kPa or more that is higher than a typical pressure, so that the evaporation of the dopant from the surface of the dopant-added melt (hereinafter, also referred to as a dopant-added melt surface) can be reduced. Moreover, since the flow rate of the second flow gas is reduced by the flow regulator dividing the inert gas into the first flow gas flowing between the heat shield and the flow regulator and the second flow gas flowing between the flow regulator and the dopant-added melt surface, the evaporation of the dopant from the dopant-added melt surface can be reduced.

In the above aspect of the invention, it is preferable that the body of the flow regulator has an inner diameter smaller than an inner diameter at a lower end of the heat shield to form a gas receiver on the body, the gas receiver being located inside with respect to the lower end of the heat shield, and the inert gas is divided into the first flow gas flowing along an upper surface of the gas receiver to be introduced to the first flow path and the second flow gas flowing close to the monocrystalline silicon with respect to the gas receiver to be introduced to the second flow path.

According to the above arrangement, the flow rate of the first flow gas can be increased by forming the gas receiver located inside with respect to the lower end of the heat shield in the body. Consequently, since the flow rate of the second flow gas is decreased, the evaporation of the dopant from the dopant-added melt surface can be further reduced.

In the above aspect of the invention, it is preferable that the monocrystalline silicon grows while a height of the first flow path is kept higher than a height of the second flow path.

According to the above arrangement, the flow rate of the first flow gas can be increased by keeping the height of the first flow path higher than the height of the second flow path. Consequently, since the flow rate of the second flow gas is decreased, the evaporation of the dopant from the dopant-added melt surface can be further reduced.

In the above aspect of the invention, it is preferable that the flow regulator including an extension extending a diagonally-upward-and-outward direction from an outer edge of the body is provided to introduce the first flow gas in the diagonally-upward-and-outward direction.

According to the above arrangement, the first flow gas can be spaced by the extension from a vicinity of the dopant-added melt surface, so that the inert gas flowing over the dopant-added melt surface can be reduced. Consequently, the evaporation of the dopant from the dopant-added melt surface can be further reduced. Moreover, since an outer side of the entire flow regulator is bent upward, even when the amount of the dopant-added melt is reduced due to progress in the growth of the monocrystalline silicon, the pull-up operation of the monocrystalline silicon can be continued while the extension provided on the outer side of the flow regulator is kept in no contact with an inner surface of the crucible whose bottom side is shaped to have a diameter decreasing toward the bottom (e.g., a round bottom).

In the above aspect of the invention, it is preferable that the flow regulator is disposed with an upper end of the extension being positioned above the lower end of the heat shield to prevent, with the extension, radiant heat from at least one of the dopant-added melt, the crucible or the heater from reaching the monocrystalline silicon through the first flow path.

According to the above arrangement, by disposing the flow regulator with an upper end of the extension being positioned above the lower end of the heat shield, radiant heat from at least one of the dopant-added melt, the crucible or the heater can be prevented from reaching the monocrystalline silicon through the first flow path between the lower end of the heat shield and the body of the flow regulator. Consequently, the temperature gradient in the pull-up direction of the monocrystalline silicon can be increased.

In the above aspect of the invention, it is preferable that the flow regulator including a heat insulation material therein is disposed to prevent, with the heat insulation material, radiant heat from at least one of the dopant-added melt, the crucible or the heater from reaching the monocrystalline silicon.

According to the above arrangement, since the heat insulation material is provided inside the flow regulator, the radiant heat from at least one of the dopant-added melt, the crucible and the heater can be effectively prevented from reaching the monocrystalline silicon.

Another aspect of the invention provides a flow regulator attached to a monocrystal pull-up apparatus, the monocrystal pull-up apparatus including: a crucible; a crucible driver configured to raise, lower and rotate the crucible; a heater configured to heat the crucible to generate a dopant-added melt in which a dopant is added to a silicon melt; a pull-up portion configured to bring a seed crystal into contact with the dopant-added melt and subsequently pull up the seed crystal to grow monocrystalline silicon; a cylindrical heat shield provided above the crucible, surrounding the monocrystalline silicon; a chamber housing the crucible, the heater and the heat shield; and an intake provided on an upper side of the chamber and configured to introduce inert gas into the chamber, in which the flow regulator includes: a body in a form of an annular plate, provided under the heat shield and surrounding the monocrystalline silicon, the body forming a first flow path between the body and the heat shield and forming a second flow path between the body and a surface of the dopant-added melt; and an extension extending diagonally upward and outward from an outer edge of the body.

In the above aspect of the invention, it is preferable that at least one of the body or the extension includes a heat insulation material therein.

Still another aspect of the invention provides a monocrystal pull-up apparatus including: a crucible; a crucible driver configured to raise, lower and rotate the crucible; a heater configured to heat the crucible to generate a dopant-added melt in which a dopant is added to a silicon melt; a pull-up portion configured to bring a seed crystal into contact with the dopant-added melt and subsequently pull up the seed crystal to grow monocrystalline silicon; a cylindrical heat shield provided above the crucible, surrounding the monocrystalline silicon; a chamber housing the crucible, the heater and the heat shield; an intake provided on an upper side of the chamber and configured to introduce inert gas into the chamber; and the flow regulator according to the above aspect of the invention provided under the heat shield.

FIG. 1 is a cross-sectional view showing a monocrystal pull-up apparatus according to an exemplary embodiment of the invention.

FIG. 2 is an enlarged cross-sectional view showing a flow regulator of the monocrystal pull-up apparatus.

FIG. 3 is an enlarged cross-sectional view showing the flow regulator and the surroundings thereof at a bottom of a crucible when a dopant-added melt is reduced.

FIG. 4 illustrates a flow of an inert gas near a surface of the dopant-added melt when the flow regulator includes no extension.

FIG. 5 is a graph showing a relationship among presence or absence of the flow regulator, an internal pressure of a chamber, and an evaporation amount of a dopant (hereinafter, also referred to as a dopant evaporation amount) in Experiment 1 in Examples of the invention.

FIG. 6 is a graph showing a relationship between presence or absence of the flow regulator and electrical resistivity in Experiment 2 in Examples of the invention.

FIG. 7 is a graph showing a relationship among a shape of the flow regulator, a dopant evaporation amount, and a temperature gradient ratio in a pull-up direction of monocrystalline silicon in Experiment 3 in Examples of the invention.

Exemplary Embodiment(s)

A manufacturing method of monocrystalline silicon SM according to CZ method as an exemplary embodiment of the invention will be described below with reference to FIGS. 1 to 3 .

Firstly, a structure of a monocrystal pull-up apparatus 1 used in the manufacturing method of the monocrystalline silicon SM will be described.

As shown in FIG. 1 , the monocrystal pull-up apparatus 1 includes a chamber 21 , a crucible 22 disposed inside the chamber 21 , a crucible driver 23 , a heater 24 , a heat insulation cylinder 25 , a pull-up portion 26 , a flow regulation cylinder 27 , a heat shield 28 , and a flow regulator 29 .

An intake 21 A, from which inert gas (e.g., Ar gas) is introduced into the chamber 21 , is provided on an upper side of the chamber 21 . An exhaust outlet 21 B, through which gas inside the chamber 21 is discharged outward when a vacuum pump (not shown) is driven, is provided on a lower side of the chamber 21 .

A predetermined amount of inert gas is introduced from the intake 21 A into the chamber 21 . Then, the introduced inert gas is discharged from the exhaust outlet 21 B on the lower side of the chamber 21 , whereby the inert gas flows from the upper side to the lower side in the chamber 21 .

The crucible 22 is configured to melt polycrystalline silicon, which is a raw material of the monocrystalline silicon SM, into a silicon melt M.

The crucible driver 23 rotates the crucible 22 at a predetermined speed around a support shaft 23 A connected to a lower end of the crucible 22 while raising and lowering the crucible 22 at a predetermined speed.

The heater 24 , which is disposed outside the crucible 22 , is configured to heat the crucible 22 to generate a dopant-added melt MD in which a dopant is added to the silicon melt M.

The heat insulation cylinder 25 is disposed to surround the crucible 22 and the heater 24 .

The pull-up portion 26 includes: a pull-up driver 26 A; and a pull-up cable 26 B having a first end connected to the pull-up driver 26 A. The pull-up driver 26 A is configured to vertically move and rotate the pull-up cable 26 B at a predetermined speed. A seed holder 26 C holding a seed crystal or a doping device (not shown) is attached to a second end of the pull-up cable 26 B. The doping device is configured to dope the silicon melt M with a dopant in the crucible 22 to generate the dopant-added melt MD.

The flow regulation cylinder 27 , which is in a form of a cylinder surrounding the monocrystalline silicon SM, is configured to guide downward the inert gas flowing from the upper side.

The heat shield 28 , which is provided above the crucible 22 , is formed in a truncated cone surrounding a lower side of the flow regulation cylinder 27 and the monocrystalline silicon SM. A lower end of the heat shield 28 is connected to a lower end of the flow regulation cylinder 27 . The heat shield 28 blocks radiant heat that the heater 24 radiates upward.

The flow regulator 29 includes: an annular plate body 29 A; an extension 29 B extending diagonally upward and outward from an outer edge of the body 29 A; and a projection 29 C projecting upward from an inner edge of the body 29 A. An inner diameter D 2 of the body 29 A is smaller than an inner diameter D 1 at a lower end of the heat shield 28 . A heat insulation material 29 D is placed inside the body 29 A and the extension 29 B.

The flow regulator 29 is spaced below from the heat shield 28 through a support 30 and surrounds the monocrystalline silicon SM. The support 30 in a form of a stick connects the heat shield 28 to the flow regulator 29 at two to four positions substantially equidistant in a circumferential direction of the monocrystalline silicon SM. The flow regulator 29 and the heat shield 28 are coaxially disposed, thereby forming an annular gas receiver 29 E at an inner side with respect to the lower end of the heat shield 28 . Herein, the gas receiver 29 E is a part of an inner region of the body 29 A, specifically a region defined from an inner circumferential surface of the body 29 A to an intersection of an extension line of an inner surface of the flow regulation cylinder 27 shown by a dotted line in FIG. 2 and an upper surface of the body 29 A. Moreover, the upper surface of the body 29 A and an upper surface of the extension 29 B of the flow regulator 29 are respectively provided in parallel to a bottom surface 28 A and an outer circumferential surface 28 B of the heat shield 28 , thereby forming a first flow path R 1 between the flow regulator 29 and the heat shield 28 . Moreover, a second flow path R 2 is formed between the flow regulator 29 and a surface of the dopant-added melt MD. Further, the flow regulator 29 is provided such that an upper end of the extension 29 B is located higher than the bottom surface 28 A of the heat shield 28 .

Next, a manufacturing method of the monocrystalline silicon SM will be described.

In the exemplary embodiment, the monocrystalline silicon SM including a straight body having a diameter set at 200 mm is manufactured. However, the monocrystalline silicon SM may be manufactured such that the diameter of the straight body is set at 150 mm, 300 mm, 450 mm or the like.

An electrical resistivity of the monocrystalline silicon SM is preferably in a range from 1.2 mΩ·cm to 5.0 mΩ·cm when the dopant is arsenic. The electrical resistivity is preferably in a range from 0.5 mΩ·cm to 2.0 mΩ·cm when the dopant is red phosphorus. The electrical resistivity is preferably in a range from 10 mΩ·cm to 30 mΩ·cm when the dopant is antimony.

Firstly, properties required in the monocrystalline silicon SM are set in the monocrystal pull-up apparatus 1 . The required properties are exemplified by the electrical resistivity, a flow rate of inert gas (which is a pull-up condition for satisfying an oxygen concentration), an internal pressure of the chamber 21 , a rotation speed of each of the crucible 22 and the monocrystalline silicon SM, and heating conditions of the heater 24 .

Next, the heater 24 is controlled on a basis of the set value to heat the crucible 22 , thereby melting polycrystalline silicon (silicon material) and the dopant in the crucible 22 to generate the dopant-added melt MD. Subsequently, inert gas is introduced at a predetermined flow rate from the intake 21 A into the chamber 21 and the internal pressure of the chamber 21 is maintained at 20 kPa or more. The internal pressure of the chamber 21 is preferably 80 kPa or less.

Next, the pull-up cable 26 B is lowered to immerse the seed crystal into the dopant-added melt MD. While the crucible 22 and the pull-up cable 26 B are rotated in a predetermined direction, the monocrystalline silicon SM is pulled up to grow.

During the growth of the monocrystalline silicon SM, as shown in FIG. 2 , an inert gas G flowing downward is divided by the flow regulator 29 into a first flow gas G 1 and a second flow gas G 2 .

At this time, since the inert gas G is introduced into the first flow path R 1 by the gas receiver 29 E to increase a flow rate of the first flow gas G 1 , a flow rate of the second flow gas G 2 can be decreased. Evaporation of the dopant can be thus reduced by controlling the internal pressure of the chamber 21 to 20 kPa or more, which is higher than a typical pressure, to decrease a partial pressure of the dopant and by decreasing the flow rate of the second flow gas G 2 .

The speed of raising the crucible 22 is controlled in accordance with a lowering speed of a liquid surface of the dopant-added melt MD such that a height H 1 of the first flow path R 1 is kept higher than a height H 2 of the second flow path R 2 . With this arrangement, the flow rate of the first flow gas G 1 can be increased and the flow rate of the second flow gas G 2 can be decreased.

The first flow gas G 1 is further introduced diagonally upward and outward by the extension 29 B, and is unlikely to flow into a region P near the surface of the dopant-added melt MD-surface, the region P being encircled by a dotted line in FIG. 2 . With this arrangement, evaporation of the dopant can be reduced. As described above, the monocrystalline silicon SM having a desired electrical resistivity can be manufactured by reducing the evaporation of the dopant.

Since an outer side of the entire flow regulator 29 is bent upward, even when the amount of the dopant-added melt MD is reduced due to progress in the growth of the monocrystalline silicon SM as shown in FIG. 3 , the monocrystalline silicon SM can be kept being pulled up while the extension 29 B provided on the outer side of the flow regulator 29 is kept in no contact with an inner surface of the crucible 22 whose diameter at a bottom portion is reduced toward the bottom (e.g., a round bottom).

Further, since the upper end of the extension 29 B is positioned above the bottom surface 28 A of the heat shield 28 , the extension 29 B can prevent radiant heat from at least one of the dopant-added melt MD, the crucible 22 and the heater 24 from reaching the monocrystalline silicon SM through the first flow path R 1 , so that a temperature gradient in a pull-up direction of the monocrystalline silicon SM can be increased. Furthermore, since the heat insulation material 29 D inside the flow regulator 29 can more effectively block the radiant heat, the temperature gradient in the pull-up direction of the monocrystalline silicon SM can be further increased.

Modification(s)

The invention is not limited to the above exemplary embodiment but any improvement and design change are possible without departing from the scope of the present disclosure. Moreover, the specific procedure and configuration for implementing the invention may be any procedures and configurations without departing from the scope of the present disclosure.

For instance, in some embodiments, the flow regulation cylinder 27 is not provided. As long as the internal pressure of the chamber 21 is controlled to 20 kPa or more, the monocrystalline silicon SM can be manufactured in the same manner as in the above exemplary embodiment with the reduced evaporation of the dopant.

Moreover, for instance, in some embodiments, the inner diameter D 2 of the body 29 A is equal to or more than the inner diameter D 1 at the lower end of the heat shield 28 . For instance, in some embodiments, the height H 1 of the first flow path R 1 is equal to or less than the height H 2 of the second flow path R 2 .

Further, for instance, in some embodiments, the extension 29 B is not provided to the flow regulator 29 as shown in FIG. 4 . When the extension 29 B is provided, for instance, in some embodiments, the body 29 A and the extension 29 B are respectively not in parallel to the bottom surface 28 A of the heat shield 28 and the outer circumferential surface 28 B of the heat shield 28 . In some embodiments, the upper end of the extension 29 B is positioned at the same height as that of the lower end of the heat shield 28 , or is positioned at a lower height than the lower end of the heat shield 28 . For instance, in some embodiments, the heat insulation material 29 D is not provided inside the flow regulator 29 .

Next, the invention will be described more in detail by Examples, however, is by no means limited to the Examples.

Experiment 1: Research of Relationship between Presence or Absence of Flow regulator and Internal Pressure of Chamber, and Dopant Evaporation Amount

EXPERIMENT EXAMPLE 1

A monocrystal pull-up apparatus was prepared without the flow regulator 29 , which was the only difference from the monocrystal pull-up apparatus 1 shown in FIG. 1 . The inner diameter D 1 at the lower end of the heat shield 28 was set at 280 mm.

The internal pressure of the chamber 21 was set at 80 kPa. Monocrystalline silicon SM having the following properties was manufactured under the following manufacturing conditions. An evaporation amount of the dopant at this time was measured.

A concentration of the dopant incorporated into the monocrystalline silicon SM was calculated on a basis of an electrical resistivity of the monocrystalline silicon SM at this time. The evaporation amount of the dopant from the dopant-added melt MD was measured on a basis of this concentration of the dopant incorporated. The thus calculated evaporation amount increased as the electrical resistivity of the monocrystalline silicon SM became higher with respect to a desired value.

<Manufacturing Conditions>

Flow rate of inert gas: 150 L/min

Distance (constant during the manufacturing) between the lower end of the heat shield 28 and the surface of the dopant-added melt MD: 10 mm

<Properties of Monocrystalline Silicon>

Dopant: red phosphorus

Electrical resistivity: from 0.6 mΩ·cm to 1.2 mΩ·cm

Diameter of the straight body: 200 mm.

EXPERIMENT EXAMPLE 2

A monocrystal pull-up apparatus 1 was prepared by providing the flow regulator 29 as shown in FIG. 1 to the monocrystal pull-up apparatus used in Experiment Example 1. Components of the monocrystal pull-up apparatus 1 were configured as follows.

<Structures of Components of Monocrystal Pull-Up Apparatus>

Inner diameter D 2 of the body 29 A of the flow regulator 29 : 250 mm

Height H 1 of the first flow path R 1 : 10 mm

Width of the gas receiver 29 E: 15 mm

The internal pressure of the chamber 21 was set at 10 kPa. Monocrystalline silicon having the same properties as in Experiment Example 1 was manufactured under the following manufacturing conditions. The evaporation amount of the dopant at this time was measured.

<Manufacturing Conditions>

Flow rate of inert gas: 150 L/min

Height H 2 (constant during the manufacturing) of the second flow path R 2 : 12.5 mm

EXPERIMENT EXAMPLES 3 TO 5

Monocrystalline silicon in each of Experiment Examples 3 to 5, having the same properties as in Experiment Example 1, was manufactured with the same arrangement and conditions as in Experiment Example 2, except that the internal pressure of the chamber 21 was changed to 20 kPa (Experiment Example 3), 40 kPa (Experiment Example 4) and 80 kPa (Experiment Example 5). The evaporation amount of the dopant at this time was measured.

Evaluation

FIG. 5 shows dopant evaporation amount ratios in Experiment Examples 2 to 5 provided that the dopant evaporation amount in Experiment Example 1 is defined as 100%.

It has been found from comparison between Experiment Example 1 and Experiment Example 2 that the dopant evaporation amount was reduced by providing the flow regulator 29 but the decreased amount was not sufficient.

In comparison among Experiment Examples 2 to 5, it has been found that the dopant evaporation amount in Experiment Example 3 was reduced at the larger amount than that in Experiment Example 2, and that the larger dopant evaporation amount was reduced as the internal pressure of the chamber 21 was increased from the results of Experiment Examples 4 and 5.

In view of the above, it has been found that evaporation of the dopant is reducible by providing the flow regulator 29 in the monocrystal pull-up apparatus 1 and by controlling the internal pressure of the chamber 21 to 20 kPa or more (and 80 kPa or less) during the growth of the monocrystalline silicon.

Experiment 2: Research of Relationship between Presence or Absence of Flow Regulator and Electrical Resistivity

Pieces of monocrystalline silicon were prepared under the same conditions as in Experiment Examples 1 and 5. An electrical resistivity of a straight body of each of the pieces of monocrystalline silicon was measured at each of solidification rates. The measurement results are shown in FIG. 6 . It should be noted that the solidification rate of the straight body is 0% at an upper end and 100% at a lower end.

It was observed that the overall electrical resistivity in Experiment Example 5 was lower than that in Experiment Example 1. This is considered to be because the evaporation of the dopant was more reduced in Experiment Example 5 than in Experiment Example 1 as described in Experiment 1.

Experiment 3: Research of Relationship Among Shape of Flow Regulator, Dopant Evaporation Amount, and Temperature Gradient Ratio in Pull-Up Direction of Monocrystalline Silicon

EXPERIMENT EXAMPLE 6

The same monocrystal pull-up apparatus as in Experiment Example 5 was prepared except that the flow regulator 29 shown in FIG. 1 was replaced by a flow regulator consisting of the body 29 A shown in FIG. 4 . Monocrystalline silicon having the same properties as in Experiment Example 5 was manufactured with the same arrangement and conditions as in Experiment Example 5. The evaporation amount of the dopant at this time was measured. Moreover, the temperature gradient in the pull-up direction in the monocrystalline silicon was examined.

Evaluation

Monocrystalline silicon was manufactured under the same conditions as in Experiment Example 5. The evaporation amount of the dopant and the temperature gradient in the pull-up direction in the monocrystalline silicon were examined.

FIG. 7 shows the dopant evaporation amount ratio (shown by a bar graph) in Experiment Example 5 provided that the dopant evaporation amount in Experiment Example 6 is defined as 100%, and a temperature gradient ratio (shown by a line graph) in Experiment Example 5 provided that the temperature gradient in Experiment Example 6 is defined as 100%. In order to obtain the temperature gradient ratio, a relationship between a temperature and a distance from an interfacial surface between the dopant-added melt MD and the monocrystalline silicon SM at an axial core of the monocrystalline silicon SM is obtained using heat conduction analysis software (simulation). An inclination of the graph showing the relationship is defined as a temperature gradient.

The dopant evaporation amount in Experiment Example 5 was decreased to about 70% of the dopant evaporation amount in Experiment Example 6. It has been found from the above that the extension 29 B provided to the flow regulator 29 can guide the first flow gas G 1 diagonally upward and outward to reduce the evaporation of the dopant.

The temperature gradient in Experiment Example 5 was increased to about 110% of the temperature gradient in Experiment Example 6. It has been found from the above that the extension 29 B provided to the flow regulator 29 can prevent radiant heat from at least one of the dopant-added melt MD, the crucible 22 or the heater 24 from reaching the monocrystalline silicon through the first flow path R 1 .