JP5413354B2 - Silicon single crystal pulling apparatus and silicon single crystal manufacturing method - Google Patents

Description

  The present invention relates to a silicon single crystal pulling apparatus using the Czochralski method, and more particularly to a heat insulating structure of a silicon raw material and a seed crystal. The present invention also relates to a method for producing a silicon single crystal by the Czochralski method, and to a method for heating a silicon raw material and a seed crystal.

  The Czochralski method (CZ method) is well known as one method for producing silicon single crystals for semiconductor devices. In the CZ method, a silicon raw material filled in a crucible is heated and melted, a seed crystal is immersed in the obtained silicon melt, and the seed crystal is gradually pulled to grow a single crystal. In the pulling process, first the neck part is formed by the dash method to reduce the diameter to eliminate dislocations, the shoulder part to increase the crystal diameter, the body part to grow a single crystal with a constant diameter, and the crystal diameter is reduced. The tail portions are sequentially formed.

  With the recent increase in diameter of silicon single crystals, the size of the crucible to be used has increased, and the amount of raw material used per time has increased. Therefore, the heater power must be increased in order to melt all the raw materials in the crucible, particularly the raw material in the central part of the crucible. However, when the heater power is increased, the amount of heat that the quartz crucible receives from the heater increases, the melting of the inner surface of the quartz crucible (cristobalite conversion) is promoted, and single crystal dislocation occurs in the process of subsequent single crystal growth, There is a problem that the product yield decreases.

  Therefore, Patent Document 1 describes the amount of heat that the quartz crucible receives from the heater by melting the silicon single crystal material in a state where the radiation heat shielding plate is suspended in the radiation screen when melting the silicon material in the crucible. A method for reducing the cristobalite formation on the inner surface of the quartz crucible has been proposed. After the polycrystalline silicon is melted, the radiant heat shield plate is raised into the pull chamber, the radiant heat shield plate and its supporting member are taken out, and an operation for changing to the seed crystal is performed. Thereafter, the pulling shaft is lowered to grow a single crystal.

  In addition, due to the recent increase in the weight of silicon single crystals, the necking process using the conventional dash method has a neck diameter that is too thin to withstand the weight of the single crystal, and the neck portion breaks and the single crystal falls. Is a problem.

  Therefore, in Patent Document 2, the seed crystal is brought into contact with the silicon melt in a single crystal pulling method in which the seed crystal is grown by immersing the seed crystal in the melt in the crucible and then pulling the seed crystal. After that, a method has been proposed in which the seed crystal is immersed in the silicon melt while heating the vicinity of the interface between the seed crystal and the silicon melt using auxiliary heating means, and the single crystal is pulled up without forming a neck. According to this method, even a large-weight single crystal can be safely pulled up, and by using a general ordinary seed crystal, there is no need to generate new costs for the seed crystal, and the single crystal suspension It is possible to reduce the required process time by eliminating dislocations at the lower part at high speed.

  In Patent Document 3, the gap between the heat shielding member provided above the crucible and the surface of the silicon melt is widened to increase the heat flow from the heater or increase the heater power. A method has been proposed in which the temperature of the seed crystal is increased, the temperature difference between the seed crystal and the silicon melt is reduced, and dislocations introduced into the seed crystal due to thermal stress are reduced. Further, Patent Document 3 proposes a method of adjusting the temperature of the seed crystal by attaching a heat reflecting plate to the seed chuck. According to this method, the radiant heat from the heater or silicon melt can be concentrated on the seed crystal, and the minimum diameter of the single crystal in the necking step can be made larger than before.

  In Patent Document 4, a thermal insulator is disposed at a general partition position between the main chamber portion and the pull chamber portion over a period from the start of the pulling operation until the grown silicon single crystal ingot enters the pull chamber portion. A method of manufacturing a silicon single crystal that is pulled up is disclosed. The heat insulator has a cross-sectional shape that has an insertion part of the seed crystal pulling wire 11a for suspending the seed crystal and can block at least a part of the internal space cross section of the pull chamber part.

JP 2004-292288 A Japanese Patent No. 3065076 Japanese Patent No. 4184725 Japanese Patent Laid-Open No. 11-012092

  However, in the method described in Patent Document 1, in order to grow a single crystal after the dissolution of the silicon raw material, the pulling shaft is raised, the radiant heat shielding plate and its supporting member are taken out, and the operation of changing to the seed crystal is performed. It needs to be done and is very cumbersome. Moreover, the operation | work which replaces the radiation heat shielding board heated with high temperature with the silicon raw material and its supporting member is very dangerous.

  Further, in the method described in Patent Document 2, auxiliary heating means for heating the seed crystal must be newly prepared. In addition, since the seed crystal is immersed in the silicon melt while heating the vicinity of the interface between the seed crystal and the silicon melt using the auxiliary heating means, there is a risk that the auxiliary heating means may come into contact with the silicon melt, and its position control There is also a problem that is very difficult.

  In the method described in Patent Document 3, since the heat reflecting plate is attached to the seed chuck, the heat reflecting plate can be used only when the seed crystal is heated. Further, since the heat reflecting plate approaches the melt surface together with the seed crystal, the silicon melt is easily contaminated when a metal material capable of efficiently reflecting radiant heat (infrared rays) is used as the material of the heat reflecting plate. There is also a problem.

  Furthermore, although the method described in Patent Document 4 can efficiently heat the single crystal ingot being pulled, there is a problem that it is difficult to efficiently heat the seed crystal.

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a silicon single crystal pulling apparatus and silicon capable of efficiently performing melting of a silicon raw material and heating of a seed crystal with a simple configuration. The object is to provide a method for producing a single crystal.

  In order to solve the above-described problems, a silicon single crystal pulling apparatus according to the present invention includes a crucible for holding a silicon melt, a heater provided around the crucible, a top of the crucible, and a seed crystal at the tip. A first lifting shaft attached; a heat shielding member having a substantially inverted frustoconical cylindrical portion disposed above the crucible; a substantially disk-like heat shielding plate having a hollow portion; and the crucible A second pulling shaft provided at an upper end and having the heat shielding plate attached to a tip thereof, the heat shielding plate covering the upper side of the silicon melt and the heat insulation as viewed from the silicon melt. The heat retention position is a position that overlaps the heat shield member in the vertical direction, and the position control of the heat shield plate is performed in the first position. Pull up one The elevation control axis, characterized in that is carried out independently.

  According to the present invention, since the position control of the heat shield plate is performed separately from the position control of the seed crystal, the heat shield plate is installed at the heat retaining position between the time of melting the silicon raw material and the seed crystal landing liquid. I can leave. In addition, since the second pulling shaft is controlled independently of the first pulling shaft that raises and lowers the seed crystal, the retracted position of the heat shield plate can be set above the heat retaining position, and the retracted position and the heat retaining position can be set. It is easy to move between. Therefore, the silicon raw material can be efficiently heated using the heat shielding plate when the silicon raw material is melted, and the seed crystal can be efficiently heated using the same heat shielding plate when the seed crystal is deposited.

  In this invention, it is preferable that the said hollow part of the said heat-shielding board has a magnitude | size which can let the said seed crystal suspended by the said 1st raising shaft pass. According to this configuration, when the seed crystal is deposited, the seed crystal can be reliably deposited without interfering with the heat shielding plate. Further, when the heat shield plate is moved to the retracted position after the seed crystal is deposited, interference between the heat shield plate and the first pulling shaft can be avoided, and the heat shield plate can be easily moved in the vertical direction. be able to.

  In this invention, it is preferable that the area of the main surface of the said heat shielding board is 60% or more of the cross-sectional area of the silicon single crystal pulled up. According to this configuration, the silicon raw material and the seed crystal before landing can be efficiently heated.

  In the present invention, the thermal shielding plate preferably has a thermal conductivity of 0.1 to 0.5 W / m · K in a temperature range of 300 to 1500 ° C. According to this configuration, the heat insulating function of the heat shielding plate can be effectively exhibited, and the silicon raw material and the seed crystal can be efficiently heated.

  In the present invention, it is preferable that the heat shielding plate is obtained by coating the surface of the basic structure of the carbon composite with graphite. According to this configuration, it is possible to provide a heat shielding plate that is lightweight and excellent in heat insulation and durability without contaminating the silicon single crystal.

In addition, in order to solve the above-described problems, a method for producing a silicon single crystal according to the present invention includes a method in which a heat shielding member having a cylindrical portion having a substantially inverted truncated cone shape is disposed above a crucible holding a silicon melt. A method for pulling up a single crystal, in which a substantially disc-shaped heat shielding plate having a hollow portion is held at a heat retaining position that overlaps the heat shielding member with respect to the vertical direction and covers the quartz crucible. A melting step of melting the silicon raw material in the quartz crucible in a state, and passing the seed crystal prepared above the heat shield plate through the hollow part while maintaining the position of the heat shield plate at the heat retaining position And a landing step for landing on the silicon melt in the crucible, and a retracting step for moving the position of the heat shielding plate to a retracted position above the heat retaining position as viewed from the silicon melt. And before A shoulder forming step of growing while gradually increasing the diameter of the single crystal, a body forming step of growing while maintaining the diameter of the single crystal constant, and the silicon melt by gradually reducing the diameter of the single crystal. And a tail formation step of separating from the tail.

  In the method for producing a silicon single crystal according to the present invention, after the seed crystal is deposited and before the shoulder formation step, the diameter of the seed crystal is 6 mm or more while the heat shielding plate is placed in the heat retaining position. It is preferable to further include a necking step of adjusting so as to be.

  According to the present invention, it is possible to provide a silicon single crystal pulling apparatus and a silicon single crystal manufacturing method capable of efficiently performing melting of a silicon raw material and heating of a seed crystal with a simple configuration.

FIG. 1 is a schematic side sectional view showing the configuration of a silicon single crystal pulling apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view showing an example of the configuration of the heat shielding plate 22 and the seed chuck 17. FIG. 3 is a flowchart showing a manufacturing process of a silicon single crystal according to a preferred embodiment of the present invention. 4A to 4F are cross-sectional views schematically showing a manufacturing process of a silicon single crystal.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic side sectional view showing the configuration of a silicon single crystal pulling apparatus according to a first embodiment of the present invention.

  As shown in FIG. 1, the silicon single crystal pulling apparatus 10 according to the present embodiment includes a chamber 11, a support shaft 12 that passes through the center of the bottom of the chamber 11 and is provided in the vertical direction, and an upper end portion of the support shaft 12. A fixed graphite susceptor 13, a quartz crucible 14 accommodated in the graphite susceptor 13, a heater 15 provided around the graphite susceptor 13, and a support shaft drive mechanism 16 for moving the support shaft 12 up and down and rotating. From the seed chuck 17 for holding the seed crystal 1, the wire (first wire) 18 for suspending the seed chuck 17, the wire winding mechanism 19 for winding the wire 18, the heater 15 and the quartz crucible 14 Prevents silicon single crystal ingot from being heated by radiation heat and suppresses temperature fluctuation of silicon melt 2 That a substantially inverted truncated cone shape of the heat shield member 20, and a control unit 21 that controls each unit.

  The silicon single crystal pulling apparatus 10 according to the present embodiment includes a heat shielding plate 22 that covers the opening of the heat shielding member 20 and a pair of wires (second wires) 23 that suspend the heat shielding plate 22. ing. Since the wire 18 is provided at the center of the apparatus, the heat shielding plate 22 whose central axis coincides with the wire 18 cannot be suspended by a single wire. Moreover, the heat shielding plate 22 needs to maintain a horizontal state. For these reasons, two wires are used for the heat shielding plate 22. The wire winding mechanism 19 is used not only for winding the single crystal pulling wire 18 but also for winding the wire 23. The raising / lowering operation of the heat shielding plate 22 is performed by the vertical movement of the wire 23. The heat shielding plate 22 has a circular hollow portion, and when the seed crystal 1 is positioned below the heat shielding plate 22, the wire 18 for pulling up the seed crystal 1 passes through the hollow portion. Therefore, the raising / lowering operation of the heat shielding plate 22 can be performed independently of the seed crystal 1.

  A gas introduction port 24 for introducing Ar gas as a carrier gas into the chamber 11 is provided at the upper part of the chamber 11. A gas outlet 27 is provided. Ar gas is introduced into the chamber 11 from the gas introduction port 24 through the gas pipe 25, and the introduction amount is controlled by the conductance valve 26. In addition, Ar gas in the sealed chamber 11 is discharged from the gas discharge port 27 via the exhaust gas pipe 28 to the outside. A conductance valve 29 and a vacuum pump 30 are provided in the middle of the exhaust gas pipe 28, and the pressure inside the chamber 11 is reduced by controlling the flow rate with the conductance valve 29 while sucking the Ar gas in the chamber 11 with the vacuum pump 30. The state is maintained.

  The heat shielding member 20 is a substantially inverted truncated cone-shaped cylindrical member provided above the quartz crucible 14 and around the pulling passage of the silicon single crystal. The heat shielding member 20 serves to insulate the seed crystal 1 and the silicon single crystal obtained by growing the seed crystal 1 from radiant heat generated in high-temperature portions such as the quartz crucible 14, the silicon melt 2, and the heater 15. Further, the heat shielding member 20 prevents impurities (for example, silicon oxide) generated in the chamber 11 from adhering to the silicon single crystal and inhibiting its growth.

  Further, the heat shielding member 20 plays a role of guiding Ar gas supplied from above the chamber 11 to the center of the surface of the silicon melt 2 and further passing the melt surface to the peripheral portion of the melt surface. And Ar gas is discharged | emitted from the gas exhaust port 27 provided in the bottom part of the chamber 11 with SiO gas evaporated from the melt. For this reason, the gas flow rate on the liquid surface can be stabilized, and oxygen evaporated from the silicon melt 2 can be kept in a stable state. The gas flow rate on the liquid surface can be adjusted by the width of the gap G between the lower end of the heat shielding member 20 and the surface of the silicon melt 2. The width of the gap G can be adjusted by raising or lowering the support shaft 12 and changing the vertical position of the quartz crucible 14.

  FIG. 2 is a schematic perspective view showing an example of the configuration of the heat shielding plate 22 and the seed chuck 17.

  As shown in FIG. 2, the heat shielding plate 22 is a disc-shaped (donut-shaped) heat insulating member having a hollow portion 22a. In order for the heat shielding plate 22 to function effectively as a heat insulating member, it is preferable to have a low thermal conductivity of 5 to 10 W / m · K in a temperature range of 300 to 1500 ° C. Although not particularly limited, it is preferable that the heat shielding plate 22 according to the present embodiment is obtained by coating the surface of the basic structure of the carbon composite with graphite. According to this configuration, it is possible to provide a heat shielding plate that is lightweight and excellent in heat insulation and durability without contaminating the silicon single crystal.

The area of the main surface of the heat shielding plate 22 is preferably 60% or more of the cross-sectional area of the pulled silicon single crystal. This is because if it is less than 60%, the heat insulating property is insufficient. On the other hand, the area of the main surface of the heat shielding plate 22 is preferably large enough not to interfere with the heat shielding member 20. Further, the diameter R ₁ of the heat shielding plate 22 is more preferably equal to or smaller than the minimum diameter R ₂ of the opening 20 a of the heat shielding member 20. It is preferable that the thickness _{D 1} of the heat shielding plate 22 is 20～250Mm. The thickness D ₁ of the heat shielding plate 22 is thin and heat insulation and durability becomes insufficient than 20 mm, when the thickness is larger than 250mm is contrary to the more insulation effect is not obtained, it controls increases weight This is because it becomes difficult and disadvantageous in terms of cost.

The diameter R ₃ (or maximum width) of the seed crystal 1 is preferably 5 mm or more. If the seed crystal 1 having a diameter R ₃ of less than 5 mm, because it is difficult to support the single crystal of 12 inch diameter weighing more than 300 kg. Greater than the maximum diameter _{R 4} seed crystal 1 of the seed chuck 17, for example, about 10 mm. The diameter R ₅ of the hollow portion 22 a of the heat shielding plate 22 is preferably larger than the diameter R ₄ of the seed chuck 17 so that the seed crystal 1 attached to the seed chuck 17 can pass therethrough. In this case, it is preferable that at least one of the hollow portion 22a of the seed chuck 17 and the heat shielding plate 22 has a tapered surface. In the illustrated configuration, tapered surfaces are formed on both the seed chuck 17 and the hollow portion 22 a of the heat shielding plate 22. According to this configuration, when the seed crystal moves in the vertical direction (particularly in the descending direction) through the hollow portion 22a, the seed chuck 17 is caught by the corner portion of the hollow portion 22a, and the heat shield plate 22 becomes the seed chuck 17. Can be prevented.

  The heat shielding plate 22 according to the present embodiment approaches the silicon melt 2 in the quartz crucible 14 and covers the upper part thereof between the start of melting of the silicon raw material and the necking step, thereby opening the opening 20a of the heat shielding member 20. And the silicon melt 2 and the seed crystal 1 are efficiently heated. Thereby, the heat load applied to the quartz crucible 14 can be reduced by suppressing the heater power, and the heat shock due to the temperature difference from the silicon melt 2 when the seed crystal 1 is deposited can be suppressed. Hereinafter, the silicon single crystal manufacturing method according to the present embodiment using the heat shielding plate 22 will be described in detail.

  FIG. 3 is a flowchart showing a manufacturing process of a silicon single crystal according to a preferred embodiment of the present invention. FIGS. 4A to 4F are cross-sectional views schematically showing the manufacturing process of the silicon single crystal.

  As shown in FIGS. 3 and 4A, in the manufacture of a silicon single crystal, first, a polycrystalline silicon fragment as a raw material is prepared and filled in a quartz crucible 14 housed in a graphite susceptor 13 in a chamber 11. (Step S11). Next, as shown in FIG. 4A, the heat shield plate 22 is lowered and installed at a heat retaining position above the quartz crucible 14 (step S12). At this time, the seed chuck 17 and the seed crystal 1 attached to the tip of the wire 18 are in a retreat position sufficiently higher than the quartz crucible 14 and are separated from the silicon raw material before melting.

  The heat shield position of the heat shield plate 22 is a position overlapping the heat shield member 14 in the vertical direction, and the heat shield plate 22 enters the inside of a substantially inverted truncated cone shape cylinder. The heat insulation position of the heat shielding plate 22 is preferably 100 to 600 mm high from the melt surface when the silicon raw material is melted. This is because if it is lower than 100 mm, the seed crystal may come into contact with the melt, and if it is higher than 600 mm, the heat insulating property is insufficient.

  Next, as shown in FIG. 4B, melting of the silicon raw material is started while the heat shielding plate 22 is maintained at the heat retaining position. At the time of melting the silicon raw material, the inside of the chamber 11 is made an Ar gas atmosphere under reduced pressure, and then the polycrystalline silicon in the quartz crucible 14 is heated and melted by the heater 15 (step S13). At this time, the seed crystal 1 is maintained in the retracted position. As described above, when the maximum diameter of the silicon single crystal is 400 mm or more, it takes a long time to melt the silicon raw material, and if the heater power is increased to melt in a short time, the state of the quartz crucible 14 is adversely affected. There's a problem. However, if the heat shielding plate 22 serving as a lid is disposed above the silicon raw material and the quartz crucible 14 is covered, the silicon raw material can be efficiently heated without applying an excessive heat load to the quartz crucible 14. .

  Next, as shown in FIG. 4 (c), the seed crystal 1 is lowered near the liquid surface of the silicon melt 2 while keeping the heat shielding plate 22 in the heat retaining position, and then the seed crystal is not deposited. 1 is kept at that position for a predetermined time and preheated (step S14). At this time, since the seed crystal 1 is sufficiently heated in a substantially closed space between the heat shielding plate 22 and the silicon melt 2, the temperature difference between the seed crystal 1 and the silicon melt 2 is sufficiently large. Can be made smaller.

  Next, as shown in FIG. 4D, the seed crystal 1 is further lowered to land on the silicon melt 2 (step S15). At this time, since the temperature difference between the seed crystal 1 and the silicon melt 2 is sufficiently small, it is possible to prevent the occurrence of dislocation due to the thermal shock during the landing. Further, the seed crystal 1 is adjusted to the silicon melt 2 while adjusting the temperature until the silicon melt 2 is stabilized at about 1500 ° C. The temperature adjustment period at this time is about 3 to 6 hours. Thus, the temperature adjustment of the silicon melt 2 is completed.

  Next, the pulling of the silicon single crystal is started. In pulling up the silicon single crystal by the CZ method, the silicon single crystal is grown on the lower end of the seed crystal 1 by slowly pulling up the seed crystal 1 while rotating the support shaft 12 and the wire 18 in opposite directions.

  In the present embodiment, seed drawing (dash neck) by the dash method is not performed, and a neck portion having a minimum diameter of 6 mm or more is formed (step S16). Conventionally, in the necking process, in order to eliminate dislocations originally contained in the seed crystal and slip dislocations generated in the seed crystal due to thermal shock at the time of landing, narrowing down until the minimum diameter of the seed crystal is about 3 to 5 mm. It was out. However, in this embodiment, since the liquid is deposited after the temperature difference between the seed crystal and the silicon melt is minimized, the occurrence of dislocation due to thermal shock can be prevented, and the seed squeezing can be made unnecessary. Accordingly, it is possible to form a thick neck portion that does not include dislocations, and to realize a thickness of the neck portion that can withstand a large weight single crystal.

  Next, as shown in FIG. 4E, the heat shielding plate 22 is raised to the retracted position, and the opening 20a of the heat shielding member 20 is opened (step S17). If the heat shielding plate 22 is disposed at the heat retaining position, it will interfere with the pulling of the silicon single crystal. Therefore, the heat shielding plate 22 is pulled upward to secure a silicon single crystal pulling passage. Thereafter, the pulling speed of the seed crystal 1 and the temperature of the silicon melt 2 are adjusted to enlarge the diameter of the neck portion, and the process proceeds to the growth of the shoulder portion (step S18).

  When the shoulder portion reaches a predetermined diameter, the process shifts to body part growth as shown in FIG. 4 (f) (step S19). In order to increase the wafer yield, the diameter of the body must be constant. During single crystal growth, the heater output, pulling speed, and crucible The ascending speed is controlled. In particular, as the silicon single crystal grows, the silicon melt 2 decreases and the liquid level decreases. Therefore, the liquid level during silicon single crystal growth is kept constant by raising the crucible as the liquid level decreases. And the diameter of the single crystal being grown is adjusted to be constant.

  Next, after growing the silicon single crystal until the body part reaches a predetermined length, the thermal balance between the silicon melt and the silicon single crystal existing at the crystal growth interface is disrupted, and a sudden thermal shock is applied to the crystal. In order to prevent quality abnormalities such as slip dislocation and abnormal oxygen precipitation from occurring, the diameter is gradually reduced to form a conical tail, and the silicon single crystal is separated from the silicon melt 2 ( Step S20). Thus, a silicon single crystal ingot is completed.

  As described above, according to the present embodiment, the heat shielding plate 22 that is the opening 20a of the heat shielding member 20 and covers the upper portion of the silicon melt is provided, and the position control of the heat shielding plate 22 is performed at the position of the seed crystal 1. Since it is performed independently from the control, the heat shielding plate 22 can be installed at a predetermined heat retaining position from the start of melting of the silicon raw material to the necking step. Therefore, the silicon raw material can be efficiently heated using the heat shielding plate 22 when the silicon raw material is melted, and the seed crystal 1 can be efficiently heated using the same heat shielding plate 22 when the seed crystal 1 is deposited. And a thick neck portion without dislocation can be formed reliably.

  As described above, the present invention has been described based on its preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, they are also included in the present invention.

  For example, in the above-described embodiment, the heat shielding plate 22 is disposed at the heat retaining position from the start of melting of the silicon raw material to the end of necking. What is necessary is just to arrange | position the board 22 in a heat retention position. That is, the heat shielding plate 22 may be moved to the retracted position before starting necking, and after the seed crystal is sufficiently heated using the heat shielding plate 22, the seed crystal may be moved to the retracted position.

  In the above embodiment, the winding mechanism 19 common to the first wire 18 and the second wire 23 is used. However, a separate winding mechanism may be prepared for each wire. Moreover, although the wire is used as the pulling shaft of the seed crystal or the heat shielding plate, the pulling may be performed using a pulling rod.

Example 1
In order to pull up a silicon single crystal using the silicon single crystal pulling apparatus 10 shown in FIG. 1, and to form a gap G (see FIG. 1) and a body portion set to form a dislocation-free neck portion. A ratio with the set gap G (hereinafter referred to as GAP ratio) was obtained. As shown in FIG. 1, the gap G is a gap between the lower end of the heat shielding member 20 and the surface of the silicon melt 2. By adjusting the width of the gap G, the amount of heat given to the seed crystal can be increased, and dislocation of the seed crystal can be achieved.

  The pulling of the silicon single crystal was performed both when the heat shield plate was used and when the heat shield plate was not used. In the Example using a heat shielding board, the silicon single crystal was pulled up according to the manufacturing process shown in FIG. The diameter of the neck portion was 6 mm, and the heat shielding plate was arranged at a height of 245 mm from the liquid level. The cross-sectional area of the heat shielding plate was the same as the target diameter (wafer diameter) of the single crystal to be pulled up, and the thickness of the heat shielding plate was 75 mm. On the other hand, in the comparative example not using the heat shielding plate, the silicon single crystal was pulled according to the conventional general manufacturing process. The results are shown in Table 1.

  As shown in Table 1, the GAP ratio is smaller when the heat shield plate is present than when there is no heat shield plate, and this tendency is the same in all the target diameters of the single crystal of 200 mm, 300 mm, and 400 mm. . From this result, it can be seen that the presence of the heat shielding plate increases the heating effect of the seed crystal, and the seed crystal can be heated sufficiently without widening the gap G between the heat shielding member and the liquid surface of the silicon melt. It was.

  It was also found that the GAP ratio increases as the target diameter of the single crystal increases. From this, it was found that the larger the target diameter of the single crystal, the more the heat shielding plate is required, and the greater the effect of the heat shielding plate.

(Example 2)
The relationship between the distance from the surface of the silicon melt to the heat shielding plate and the GAP ratio was determined. The target diameter of the single crystal was 300 mm, and the structure of the heat shielding plate and the pulling conditions were the same as in Example 1. The results are shown in Table 2.

  As shown in Table 2, it was found that the GAP ratio increases as the distance from the liquid surface to the heat shielding plate increases. From this, the desired effect was obtained if the distance from the liquid surface was in the range of 100 to 600 mm. However, when the distance from the liquid surface to the heat shield plate is 700 mm, the effect of providing the heat shield plate is not completely absent, but the maximum value of the GAP ratio is 3.0 or more, and the desired effect It was found that could not be obtained.

(Example 3)
The relationship between the diameter ratio of the heat shielding plate to the target diameter of the single crystal and the GAP ratio was determined. The target maximum diameter of the single crystal was 300 mm, and the structure of the heat shield plate and the pulling conditions were the same as in Example 1. The results are shown in Table 3.

  As shown in Table 3, the GAP ratio increases as the diameter ratio decreases (that is, as the diameter of the heat shield plate decreases). If the diameter ratio is in the range of 60 to 100 (%), a desired effect is obtained. It was. However, when the diameter ratio is 50 (%), the effect of providing the heat shielding plate is not completely eliminated, but the maximum GAP ratio is 3.0 or more, and the heat shielding plate is provided. It has been found that the desired effect cannot be obtained.

Example 4
The relationship between the thickness of the heat shielding plate and the GAP ratio was determined. The target diameter of the single crystal was 300 mm, and the structure of the heat shielding plate and the pulling conditions were the same as in Example 1. The results are shown in Table 2. The results are shown in Table 4.

  As shown in Table 4, the GAP ratio increased as the thickness of the heat shielding plate increased, and a desired effect was obtained if it was within the range of 20 to 300 mm. However, when the thickness of the heat shielding plate is 10 mm, the effect of providing the heat shielding plate is not completely absent, but the maximum value of the GAP ratio is 3.0 or more, and a desired effect cannot be obtained. I understood that.

DESCRIPTION OF SYMBOLS 1 Seed crystal 2 Silicon melt 10 Silicon single crystal pulling apparatus 11 Chamber 12 Support shaft 13 Graphite susceptor 14 Quartz crucible 15 Heater 16 Support shaft drive mechanism 17 Seed chuck 18 Wire 19 Mechanism 20 Heat shield member 20a Heat shield member opening 21 Control device 22 Heat shielding plate 22a Heat shielding plate hollow 23 Wire 24 Gas inlet 25 Gas pipe 26 Conductance valve 27 Gas outlet 28 Exhaust pipe 29 Conductance valve 30 Vacuum pump

Claims (7)

A crucible for holding a silicon melt;
A heater provided around the crucible;
A first pulling shaft provided above the crucible and having a seed crystal attached to the tip;
A heat shielding member having a substantially inverted frustoconical cylindrical portion disposed above the crucible;
A substantially disc-shaped heat shield plate having a hollow portion;
A second lifting shaft provided above the crucible and having the heat shielding plate attached to the tip;
The heat shielding plate is configured to be movable between a heat retaining position that covers the top of the silicon melt and a retracted position that is above the heat retaining position as viewed from the silicon melt,
The heat retaining position is a position overlapping the heat shielding member with respect to the vertical direction,
The position control of the said heat shielding board is performed independently of the raising / lowering control of a said 1st pulling axis | shaft, The silicon single crystal pulling apparatus characterized by the above-mentioned.   2. The silicon single crystal pulling apparatus according to claim 1, wherein the hollow portion of the heat shielding plate has a size that allows the seed crystal to pass therethrough.   3. The silicon single crystal pulling apparatus according to claim 1, wherein an area of a main surface of the heat shielding plate is 60% or more of a cross-sectional area of the silicon single crystal to be pulled.   4. The silicon according to claim 1, wherein the heat shielding plate has a thermal conductivity of 0.1 to 0.5 W / m · K in a temperature range of 300 to 1500 ° C. 5. Single crystal pulling device.   5. The silicon single crystal pulling apparatus according to claim 1, wherein the heat shielding plate is obtained by coating the surface of a basic structure of a carbon composite with graphite. 6. A method for producing a silicon single crystal in which a silicon single crystal is pulled up in a state where a heat shielding member having a cylindrical portion having a substantially inverted truncated cone shape is disposed above a crucible holding a silicon melt,
The silicon raw material in the quartz crucible is melted in a state in which a substantially disk-shaped heat shielding plate having a hollow portion is held at a heat retaining position that overlaps the heat shielding member in the vertical direction and covers the top of the quartz crucible. Melting process to
While maintaining the position of the heat shield plate at the heat retaining position, the seed crystal prepared above the heat shield plate is caused to pass through the hollow portion and descend to be deposited on the silicon melt in the crucible. Liquid landing process;
A retracting step of moving the position of the heat shield plate to a retracted position above the heat retaining position when viewed from the silicon melt;
Shoulder forming step of growing while gradually increasing the diameter of the single crystal;
A body forming step for growing the single crystal while maintaining a constant diameter;
And a tail forming step of gradually reducing the diameter of the single crystal and separating it from the silicon melt. The method further comprises a necking step of adjusting the diameter of the seed crystal to be 6 mm or more while the heat shielding plate is disposed at the heat retaining position after the liquid deposition step and before the shoulder formation step. A method for producing a silicon single crystal according to claim 6.

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