Device for the production of single crystals

Abstract

Apparatus (1, 1') for producing a single crystal (4) according to a Czochralski process, wherein the apparatus (1, 1') comprises: a main chamber (2) adapted to accommodate a crucible (6, 7) adapted to accommodate a raw material melt (5), and a (8) heater adapted for heating the raw material melt (5); a drawing chamber (3) which is continuously provided on an upper section of the main chamber (2) and adapted to accommodate a single crystal (4) drawn from the raw material melt (5); a cooling cylinder (12) extending from a ceiling section of the main chamber (2) towards a surface of the raw material melt (5) to surround the single crystal (4); and an auxiliary cooling cylinder (19) which is inserted into the interior of the cooling cylinder (12), wherein the device (1, 1') also includes a diameter enlargement element (20) adapted to fit into the auxiliary cooling cylinder (19), the auxiliary cooling cylinder (19) has at least one slot (SL) passing through it in an axial direction, and the auxiliary cooling cylinder (19) is adapted to come into close contact with the cooling cylinder (12) by pressing the diameter enlargement element (20) into the auxiliary cooling cylinder (19) to increase the diameter of the auxiliary cooling cylinder (19).

Description

TECHNICAL AREA

[0001] The present invention relates to a device for producing a single crystal according to the Czochralski process (hereinafter abbreviated as CZ process). STATE OF THE ART

[0002] The following describes a conventional device for producing a single crystal using the Czochralski method, using the growth of a silicon single crystal as an example.

[0003] Fig. Figure 8 shows an example of a conventional apparatus for producing a single crystal.

[0004] In a single-crystal growing apparatus 101, used for the production of a silicon single crystal by a CZ process, crucibles 106, 107 and a heater 108 are generally arranged in a main chamber 102 in which a single crystal 104 is grown. The crucibles 106, 107 hold a raw material melt 105 and can move up and down. The heater 108 is arranged to surround the crucibles 106, 107. A pull chamber 103 for receiving and removing the grown single crystal 104 is continuously provided at an upper part of the main chamber 102. When the single crystal 104 is produced using such a device 101 for the production of a single crystal, a seed crystal 116 is immersed in the raw material melt 105 and carefully pulled upwards while being rotated to allow the single crystal 104 to grow in the form of a rod.Meanwhile, crucibles 106, 107 are raised according to the crystal growth in order to keep the melt surface at a constant height so that the desired diameter and crystal quality are achieved.

[0005] Furthermore, in the growth of the single crystal 104, the seed crystal 116, attached to a seed holder 117, is immersed in the raw material melt 105. A wire 115 is then carefully wound onto the wire while the seed crystal 116 is rotated in a desired direction by a pulling mechanism (not shown) to grow the single crystal 104 from an end section of the seed crystal 116. To eliminate dislocations that occur when the seed crystal 116 comes into contact with the melt, the crystal is initially thinned to a diameter of about 3 to 5 mm at an early stage of growth. After the dislocations are eliminated, the diameter is enlarged to the desired diameter to grow the single crystal 104 of the required quality. Alternatively, if a large-diameter crystal is to be grown, the following procedure is proposed.For example, the seed crystal 116 to be used is shaped so that it has an end section with a sharply pointed tip or a rounded end, such that the shaped end section of the seed crystal 116 comes into contact with the silicon melt. First, the tip of the seed crystal 116 is carefully brought into contact with the silicon melt. Then, the seed crystal 116 is lowered at such a low speed that the end section of the seed crystal 116 melts until a desired thickness is reached. Subsequently, the seed crystal 116 is slowly raised to grow a silicon single-crystal ingot with the desired diameter without constriction (see patent specification 1).

[0006] In these cases, the drawing speed for a section with a constant diameter and an unchanged single crystal 104 diameter, although dependent on the diameter of the single crystal 104 being drawn, is approximately 0.4 to 2.0 mm / min and is extremely slow. If drawing is forced at a high speed, the single crystal 104 deforms during growth, so that a columnar product with a constant diameter can no longer be obtained. Otherwise, problems arise, for example: sliding dislocations are created in the single crystal 104, or the single crystal 104 cannot be extracted from the melt as a product. Therefore, the increase in the crystal growth rate is limited.

[0007] To improve productivity and reduce costs in the aforementioned production of single crystal 104 using the CZ process, increasing the growth rate of the single crystal 104 is an important approach. Accordingly, various improvements have been implemented to achieve this increase in the growth rate of the single crystal 104.

[0008] It is known that the growth rate of the single crystal 104 is determined by the thermal equilibrium of the single crystal 104 during growth and can be increased by efficiently dissipating the heat emitted from a surface of the single crystal 104. In this case, increasing the cooling effect on the single crystal 104 enables even more efficient production of the single crystal 104. Furthermore, it is known that the cooling rate of the single crystal 104 influences the crystal quality. For example, ingrown defects that form in the silicon single crystal during its growth can be controlled by the ratio between a temperature gradient in the crystal and the growth rate of the single crystal, and a defect-free single crystal 104 can be grown by controlling this ratio (see patent specification 2).Intensifying the cooling effect on the single crystal 104 during growth is therefore important for producing defect-free crystals and also for improving productivity by increasing the growth rate of the single crystal 104. DE 11 2013 001 054 T5 discloses a method for producing a silicon single-crystal wafer, wherein, under a growth condition that achieves V / G ≥ 1.05 × (V / G)crt, where V is a growth rate in the growth of the silicon single-crystal ingot, G is a temperature gradient near a crystal growth interface, and (V / G)crt is a value of V / G when a dominant point defect changes from a vacancy to interstitial Si, a silicon single-crystal ingot with an oxygen concentration of 7 × 10⁻⁵ is produced. 17atoms / cm³ (ASTM '79) or less is grown, and a silicon single-crystal wafer enclosing a region where defects are dominant and where FPDs are not detected by preferential etching is produced from the grown silicon single-crystal ingot. DE 11 2008 003 609 T5 discloses a device for producing a single crystal, growing the single crystal according to the Czochralski method, comprising at least: a main chamber in which a crucible for holding a raw material melt and a heater for heating the raw material melt are arranged; a drawing chamber in which the grown single crystal is pulled and held, the drawing chamber being continuously provided above the main chamber;and a cooling cylinder extending at least from a ceiling of the main chamber to a surface of the raw material melt such that it surrounds the single crystal during drawing, the cooling cylinder being forcibly cooled with a coolant; the device further comprising at least one auxiliary cooling cylinder fitted into an interior of the cooling cylinder, and the auxiliary cooling cylinder having a gap extending in an axial direction and reaching to the surface of the raw material melt. QUOTE LIST PATENT LITERATURE Patent specification 1: JP H10-203898 A Patent specification 2: JP H11-157996 A Patent specification 3: JP S57-40119 B2 Patent Document 4: JP S64-65086 A Patent specification 5: WO 01 / 57293 A1 Patent specification 6: JP H06-199590 A Patent specification 7: JP 2009-161416 A SUMMARY OF THE INVENTIONAL PROBLEM

[0009] To efficiently cool the single crystal 104 in the CZ method, an effective method exists in which the radiant heat of the single crystal 104 is absorbed in a forced-cooled object, such as a chamber, without the crystal being directly exposed to the radiation of the heater 108. One device structure capable of achieving this is the screen structure (see patent specification 3). However, in this structure, the shape of the screen, to prevent contact with the upper ends of the crucibles 106, 107 due to their upward movement, necessitates an upper part of the screen with a smaller inner diameter. Consequently, the screen structure has a flaw that hinders the cooling of the crystal. Although an inert gas can flow during crystal growing to prevent contamination by an oxidizing gas, such a screen structure also presents the problem that a cooling effect on the single crystal 104 cannot be expected.

[0010] Against this background, a setup is proposed comprising a gas flow guide cylinder 114 for guiding the inert gas and a heat shield ring for protecting the gas guide cylinder 114 from direct radiation from the heater 108 and the molten raw material 105 (see patent specification 4). With this method, the cooling effect of the inert gas on the single crystal 104 is expected. However, considering that the radiant heat of the single crystal 104 is absorbed in a cooling chamber, a high cooling capacity cannot be assumed.

[0011] Subsequently, a method is proposed to solve the problems of the screen and the gas flow guide cylinder 114 and to achieve efficient cooling, in which a water-cooled cooling cylinder 112 is arranged around the crystal (see patent specification 5). In this method, an outer surface of the cooling cylinder 112 is protected by a cooling cylinder protective material, such as a graphite protective cover, etc., thereby enabling the heat of the single crystal 104 to be efficiently dissipated from the interior of the cooling cylinder 112. However, since the cooling cylinder 112 does not extend close to the melting surface for safety reasons, the cooling effect on the single crystal 104 is somewhat reduced in an area not covered by the cooling cylinder 112.

[0012] Furthermore, patent specification 6 discloses a method in which a graphite element inserted into the cooling cylinder 112 is extended. However, this method cannot achieve a sufficient cooling effect because the cooling cylinder and the extended graphite element are exposed to external heat. Moreover, contact between the cooling cylinder 112 and the graphite element is difficult. Consequently, heat cannot be efficiently conducted from the graphite element to the cooling cylinder 112.

[0013] Fig. Figure 9 shows another exemplary conventional apparatus for producing a single crystal.

[0014] This example is characterized by the fact that, unlike the example in Fig.8 further comprises an auxiliary cooling cylinder 119. Patent specification 7 discloses, for example, a method in which the auxiliary cooling cylinder 119, to be installed in the cooling cylinder 112, is provided with a slot extending axially and the auxiliary cooling cylinder 119 extends towards the surface of the raw material melt 105. In this method, the heat generated by the single crystal 104 is conducted through the auxiliary cooling cylinder 119 to the cooling cylinder 112, which enables an improvement in the drawing speed of the single crystal 104. In addition, the outer diameter of the auxiliary cooling cylinder 119 is equal to the inner diameter of the cooling cylinder 112, so that the two parts can come into close contact with each other.

[0015] Newer devices for producing a single crystal, however, have larger dimensions. In order for the auxiliary cooling cylinder 119 to be smoothly inserted into the cooling cylinder 112 in such a device, it is now necessary to provide a predetermined gap between the two parts during installation; in other words, the outer diameter of the auxiliary cooling cylinder 119 must be smaller than the inner diameter of the cooling cylinder 112. In this case, due to dimensional tolerances, the cooling cylinder 112 cannot fully seal against the auxiliary cooling cylinder 119. This leads to the problem of reduced thermal conductivity from the auxiliary cooling cylinder 119 to the cooling cylinder 112.

[0016] The present invention was made to solve the problems mentioned above. One objective of the present invention is to provide a device for producing a single crystal that can increase the growth rate of the single crystal by efficiently cooling the single crystal during growth. SOLUTION TO THE PROBLEM

[0017] To achieve this goal, the present invention provides a device for producing a single crystal according to a Czochralski method, wherein the device comprises: a main chamber designed to hold a crucible adapted to hold a molten raw material, and a heater adapted for heating the raw material melt; a drawing chamber which is continuously provided at an upper part of the main chamber and adapted to accommodate a single crystal drawn from the raw material melt; a cooling cylinder extending from a ceiling section of the main chamber towards a surface of the raw material melt to surround the single crystal; and an auxiliary cooling cylinder which is installed inside the cooling cylinder, wherein The device also includes an element for increasing the diameter, which is adapted to fit into the auxiliary cooling cylinder. the auxiliary cooling cylinder has at least one slot passing through it in an axial direction, and The auxiliary cooling cylinder is adapted to come into close contact with the cooling cylinder by pressing the diameter enlargement element into the auxiliary cooling cylinder to increase the diameter of the auxiliary cooling cylinder.

[0018] Since the auxiliary cooling cylinder in such a device for single crystal production has an axially oriented slot, its diameter increases when the diameter-enlarging element is pressed into it. Furthermore, this increased diameter brings the auxiliary cooling cylinder into close contact with the cooling cylinder, which surrounds one of its outer surfaces. This efficiently conducts heat from the pulled single crystal to the cooling cylinder. Consequently, the growing single crystal is cooled efficiently, resulting in a higher single crystal growth rate (crystal pulling rate) and improved productivity.

[0019] Preferably, the diameter enlargement element has a wedge shape and is adapted to increase the diameter of the auxiliary cooling cylinder by being partially or completely inserted and pressed into the at least one slot of the auxiliary cooling cylinder.

[0020] The wedge-shaped diameter enlarger element, as described above, can increase the diameter of the auxiliary cooling cylinder. In this respect, the wedge angle of the diameter enlarger element is preferably 45° or less, taking into account: a force vector acting in the direction that increases the diameter of the auxiliary cooling cylinder; and a force (restoring force) to decrease the diameter of the auxiliary cooling cylinder due to the reaction to the force described above. To reduce the required compressive force exerted by the diameter enlarger element on the auxiliary cooling cylinder, and thus to facilitate insertion of the diameter enlarger element into the auxiliary cooling cylinder, the wedge angle is preferably 5° or more and 20° or less.

[0021] Furthermore, the slot provided in the auxiliary cooling cylinder, which penetrates it axially, has a width of preferably 1% or more and 70% or less of the diameter of the auxiliary cooling cylinder, so that the wedge function comes into play. Taking into account the thrust force exerted by the wedge and the effect of the increased diameter of the auxiliary cooling cylinder, the width is preferably 5% or more and 20% or less of the diameter.

[0022] One method for inserting the diameter enlarger element into the auxiliary cooling cylinder involves a worker manually inserting the element, as the auxiliary cooling cylinder becomes easily deformable by creating a slot. However, if a material that is difficult to deform is used for the auxiliary cooling cylinder, a method can also be employed in which a tool, such as a hammer, is used to strike the diameter enlarger element, thereby increasing the diameter of the auxiliary cooling cylinder and bringing it securely and firmly into close contact with the cooling cylinder.

[0023] The longer and thicker the auxiliary cooling cylinder, the greater its heat capacity. However, the greater the distance between the cooling cylinder and an inner surface of the auxiliary cooling cylinder where the heat of the pulled single crystal is absorbed, the less effective the cooling of the single crystal becomes. Therefore, the auxiliary cooling cylinder extends downwards from the cooling cylinder over a length of preferably 250 mm or less, and the auxiliary cooling cylinder has a wall thickness of preferably 60 mm or less.

[0024] Furthermore, the effect of increasing the diameter of the auxiliary cooling cylinder is greater the longer the diameter-enlarging element is (the length in the axial direction). However, considering the strength of the diameter-enlarging element during sliding, its length is preferably 10% or more and 60% or less than the length of the auxiliary cooling cylinder. The diameter-enlarging element has a wall thickness of preferably 60 mm or less than that of the auxiliary cooling cylinder. In this case, if the slot provided in the auxiliary cooling cylinder and penetrating it axially has a large width, a cuboid corresponding to the width of the slot in the auxiliary cooling cylinder can, for example, be connected to a wedge tip of the diameter-enlarging element.

[0025] Preferably, the auxiliary cooling cylinder has a tapered shape such that an inner diameter is smaller on a lower side, the diameter enlargement element has a tapered shape such that an outer diameter is smaller on a lower side, and the diameter enlargement element is adapted to increase the diameter of the auxiliary cooling cylinder by being inserted and pressed into the interior of the auxiliary cooling cylinder.

[0026] If both the auxiliary cooling cylinder and the diameter enlarger element have a tapered shape as described above, pressing the diameter enlarger element into the interior of the auxiliary cooling cylinder causes the diameter enlarger element to enlarge the auxiliary cooling cylinder from the inside, thereby achieving the desired diameter enlargement. In this respect, the diameter enlarger element has a tapered angle of preferably 45° or less, taking into account: the vector of the force acting in the direction in which the diameter of the auxiliary cooling cylinder is increased; and the force (restoring force) required to decrease the diameter of the auxiliary cooling cylinder due to the reaction against the force described above.To reduce the required pressure force on the auxiliary cooling cylinder through the diameter enlargement element and to facilitate the insertion of the diameter enlargement element into the auxiliary cooling cylinder, the tapering angle is preferably 5° or more and 20° or less.

[0027] One method for inserting the diameter enlarger element into the auxiliary cooling cylinder can be a manual insertion by a worker. This is because the auxiliary cooling cylinder, with its axially oriented slot, is easily deformable, and the division of the auxiliary cooling cylinder can further facilitate the diameter enlargement. Alternatively, a method can be used to strike the diameter enlarger element with a tool, such as a hammer, to increase the diameter of the auxiliary cooling cylinder and bring it securely and firmly into close contact with the cooling cylinder.

[0028] Furthermore, the extent to which the diameter enlarger element is inserted depends on the gap (difference) between the inner diameter of the cooling cylinder and the outer diameter of the auxiliary cooling cylinder. For example, if the cooling cylinder has an inner diameter of 430 mm, the diameter enlarger element is preferably inserted at a distance of 20 mm or less, taking into account the mechanical strength of the graphite element. Additionally, the inner diameter of a tapered upper section in the auxiliary cooling cylinder and the outer diameter of a tapered lower section in the diameter enlarger element preferably differ by 20 mm or more and 70 mm or less, respectively, so that the diameter enlarger element comes into contact with the inside of the auxiliary cooling cylinder to enhance the diameter enlargement effect.

[0029] The material of the auxiliary cooling cylinder preferably consists of graphite, carbon composite material, stainless steel, molybdenum and tungsten.

[0030] These improve the thermal conductivity from the auxiliary cooling cylinder to the cooling cylinder, thereby successfully improving the speed of crystal cooling.

[0031] The material of the diameter enlargement element preferably consists of any of graphite, carbon composite material, stainless steel, molybdenum and tungsten.

[0032] These improve the thermal conductivity from the diameter enlargement element to the auxiliary cooling cylinder, thereby successfully improving the rate of crystal cooling. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0033] As described above, the present invention makes it possible to provide a device for the production of a single crystal which can increase the growth rate of the single crystal by efficiently cooling the single crystal during growth. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a cross-sectional view showing an example of a device for producing a single crystal according to the present invention. Fig. Figure 2 is a perspective view showing examples of an auxiliary cooling cylinder and a diameter enlargement element. Fig. Figure 3 is a perspective view showing a state in which the diameter enlargement element is inserted into the auxiliary cooling cylinder. Fig. Figure 4 is a cross-sectional view showing another example of the device according to the invention for producing a single crystal. Fig.Figure 5 is a perspective view showing examples of part of an auxiliary cooling cylinder and a diameter enlargement element. Fig. Figure 6 is a perspective view showing a state in which the diameter enlargement element is inserted into the auxiliary cooling cylinder. Fig. Figure 7 is a cross-sectional view showing a state in which the diameter enlargement element is inserted into the auxiliary cooling cylinder. Fig. Figure 8 is a cross-sectional view showing an example of a conventional apparatus for producing a single crystal. Fig. Figure 9 is a cross-sectional view showing another example of a conventional apparatus for producing a single crystal. DESCRIPTION OF THE EXECUTION FORMS

[0034] As previously mentioned, in single-crystal production using the CZ method, efficient cooling of the single crystal during growth is an effective means of increasing productivity and reducing costs to boost the growth rate. For this purpose, structures have been proposed in which a cooling cylinder surrounding the single crystal during growth is integrated into a main chamber.

[0035] In such a structure for cooling a growing single crystal with a cooling cylinder, the cooling cylinder is prevented from coming into contact with the molten raw material. To this end, the cooling cylinder is not extended to near the liquid surface of the molten raw material; instead, an auxiliary cooling cylinder is inserted inside the cooling cylinder, and the auxiliary cooling cylinder is extended towards the liquid surface of the molten raw material. In this case, the heat generated by the growing single crystal is conducted to the cooling cylinder via the auxiliary cooling cylinder. However, with the recent increase in the size of single crystal growing equipment, the outer diameter of the auxiliary cooling cylinder is chosen to be smaller than the inner diameter of the cooling cylinder to allow for easy insertion of the auxiliary cooling cylinder inside the cooling cylinder.This makes it increasingly difficult to bring the two into close contact, leading to the problem that the efficiency of heat conduction from the auxiliary cooling cylinder to the cooling cylinder is reduced.

[0036] The present inventors have seriously addressed these problems and have discovered a slot provided in an auxiliary cooling cylinder that penetrates it axially. In particular, providing this slot in the auxiliary cooling cylinder allows for an increase in the cylinder's diameter. Even if, for example, a predetermined gap is provided between a cooling cylinder and an auxiliary cooling cylinder to facilitate insertion of the latter, the diameter of the auxiliary cooling cylinder is increased after insertion, bringing the auxiliary cooling cylinder into close contact with the cooling cylinder and successfully improving the thermal conductivity between the auxiliary and cooling cylinders.

[0037] Furthermore, the inventors have thoroughly investigated measures for increasing the diameter of the auxiliary cooling cylinder. In particular, measures where an auxiliary cooling cylinder is provided with a slot that penetrates it axially, and the diameter of the auxiliary cooling cylinder is increased by thermal expansion, involve dimensional tolerances in the inner diameters of cooling cylinders and the outer diameters of auxiliary cooling cylinders, and there are numerous types of gaps between two cylinders. Therefore, with these measures, the diameter of the auxiliary cooling cylinder cannot be increased sufficiently to allow it to be brought into safe, close contact with a cooling cylinder.

[0038] Accordingly, the present inventors have seriously investigated measures for increasing the diameter of the auxiliary cooling cylinder and have consequently determined that an auxiliary cooling cylinder can be safely brought into close contact with a cooling cylinder by: additionally providing a diameter enlargement element, which is inserted into the auxiliary cooling cylinder, and pressing the diameter enlargement element in to increase the diameter of the auxiliary cooling cylinder. This finding has led to the completion of the present invention.

[0039] Specifically, the present invention relates to a device for producing a single crystal according to a Czochralski method, wherein the device comprises the following: a main chamber adapted to accommodate a crucible adapted to hold a molten raw material, and a heater adapted for heating the raw material melt; a drawing chamber which is continuously provided at an upper part of the main chamber and adapted to accommodate a single crystal drawn from the raw material melt; a cooling cylinder extending from a ceiling section of the main chamber towards a surface of the raw material melt to surround the single crystal; and an auxiliary cooling cylinder which is inserted into the interior of the cooling cylinder, wherein The device also includes a diameter enlargement element adapted to fit into the auxiliary cooling cylinder, the auxiliary cooling cylinder has a slot that extends through in the axial direction, and The auxiliary cooling cylinder is adapted to come into close contact with the cooling cylinder by pressing the diameter enlargement element into the auxiliary cooling cylinder to increase the diameter of the auxiliary cooling cylinder.

[0040] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings, although the present invention is not limited thereto. Reference numerals are summarized in the following table: 1, 1', 101 Device for producing a single crystal 2, 102 Main Chamber 3, 103 Draw chamber 4,104 single crystal 5,105 Raw material melting 6, 7, 106, 107 crucibles 8, 108 Heating 9, 109 Heat-insulating element 10, 110 Gas outlet 11, 111 Gas inlet 12, 112 cooling cylinders 13, 113 Coolant inlet 14, 114 Gas flow guide cylinder 15, 115 Drawing wire 16, 116 Seed crystal 17, 117 Germination holders 18, 118 Crucible axis 19, 119 Auxiliary cooling cylinders 19(A), 19(B), 19(C), 19(D) four parts of the auxiliary cooling cylinder 20 Diameter enlargement element AX axis SL slot F Fitting section θ1' angle at the lowest end of the fitting section θ1 Tapering angle (wedge angle) θ2' Tapering angle between the inner surface and the outer surface of the diameter enlargement element θ2 Taper angle between the inner surface and the outer surface of the auxiliary cooling cylinder

[0041] Fig. Figure 1 shows an example of a device for producing a single crystal according to the present invention.

[0042] In a device 1 for producing a single crystal, a quartz crucible 6 is adapted to hold a raw material melt (e.g., silicon melt) 5. A heater 8 is configured to heat and melt a crystalline raw material (e.g., polycrystalline silicon) to form a raw material melt 5 and also to maintain the raw material melt 5 at a suitable temperature. A seed holder 17 for attaching a seed crystal 16 is connected to the tip of a pull wire 15.

[0043] The quartz crucible 6 is installed while being held by a graphite crucible 7. The graphite crucible 7 is supported by a crucible pivot (support axis) 18, which is adapted to rotate and move vertically around the center point of the lower part of the graphite crucible 7. A drawing chamber 3 is provided at the upper part of the main chamber 2. The drawing chamber 3 is equipped with an opening door for removing a single crystal (e.g., a silicon single crystal) 4 drawn from the raw material melt 5.

[0044] The drawing chamber 3 is equipped with a gas inlet 11 for introducing an atmospheric gas (e.g., argon gas). The main chamber 2 is equipped at its lower part with a gas outlet 10 for releasing the introduced atmospheric gas. While an atmospheric gas is introduced through the gas inlet 11, the seed crystal 16 is immersed in the raw material melt 5. The drawing wire 15 is wound onto the wire while being rotated to draw the single crystal 4.

[0045] The quartz crucible 6 and the graphite crucible 7 can be moved upwards / downwards in the axial direction of crystal growth by means of the crucible rotation axis 18. The quartz crucible 6 and the graphite crucible 7 are raised to compensate for the lowered liquid surface of the raw material melt 5, which crystallizes and is thus reduced during crystal growth. In addition, a heat-insulating element 9 surrounds the outer sides of the heater 8 (the sides facing the crucibles 6 and 7) to protect the main chamber 2 from the direct radiant heat of the heater 8 and also to prevent heat loss from the molten raw material melt 5.

[0046] To improve the growth rate of the single crystal 4, it must also be cooled rapidly. A cooling cylinder 12 is provided for this purpose. The cooling cylinder 12 is made of, for example, a metal and coaxially surrounds the grown single crystal 4. The cooling cylinder 12 also has a hollow internal structure. A coolant (e.g., water, etc.) introduced through a coolant inlet 13 circulates within the cavity of the cooling cylinder 12 to cool it and is then discharged to the outside.

[0047] A gas flow guide cylinder 14 coaxially surrounds the drawn single crystal 4 and extends downwards from a lower end of the cooling cylinder 12 into the cooling cylinder 12. The gas flow guide cylinder 14 guides an inert gas introduced from the gas inlet 11 and is designed to shield the radiant heat from the heater 8 and the raw material melt 5, thereby improving the cooling effect on the single crystal 4. Furthermore, the gas flow guide cylinder 14 is positioned below the lower end section of the cooling cylinder 12, thus also preventing the cooling cylinder 12 from coming into contact with the raw material melt 5 and causing a phreatic explosion.

[0048] An auxiliary cooling cylinder 19 is adapted to fit inside the cooling cylinder 12. One of the functions of the auxiliary cooling cylinder 19 is to absorb the radiant heat emanating from the pulled single crystal 4 and transfer the absorbed heat to the cooling cylinder 12. For this purpose, the auxiliary cooling cylinder 19 coaxially surrounds the pulled single crystal 4 and extends further downwards than the lower end of the cooling cylinder 12. Since the auxiliary cooling cylinder 19 can also enclose a lower part of the single crystal 4 in this case, it is possible to efficiently conduct the heat from the single crystal 4 through the auxiliary cooling cylinder 19 to the cooling cylinder 12.

[0049] In this case, to maximize the cooling effect on the single crystal 4, it is important to bring the auxiliary cooling cylinder 19 into close contact with the cooling cylinder 12 so that heat is efficiently transferred from the auxiliary cooling cylinder 19 to the cooling cylinder 12. For this purpose, the present invention employs a diameter-enlarging element 20 adapted to fit inside the auxiliary cooling cylinder 19. The diameter-enlarging element 20 is inserted into the auxiliary cooling cylinder 19 to increase its diameter, so that the enlarged auxiliary cooling cylinder 19 comes into close contact with the cooling cylinder 12. Specific examples of increasing the diameter of the auxiliary cooling cylinder 19 are described below.

[0050] Fig.Figure 2 shows examples of the auxiliary cooling cylinder and the diameter enlarger element. The auxiliary cooling cylinder 19 has a cylindrical shape with an axis AX at its center. The axis AX essentially corresponds to a crystal growth axis in the growth of the single crystal.

[0051] The auxiliary cooling cylinder 19 has a slot SL that penetrates it axially. The slot SL has an upper portion that is V-shaped to form a fitting section F. The slot SL facilitates the adjustment of the auxiliary cooling cylinder 19. Furthermore, the fitting section F is designed to fit into the diameter-enlarging element 20, thereby increasing the diameter of the auxiliary cooling cylinder 19. In this example, the fitting section F has the shape of an inverted triangle, and an angle θ1' at its lower end (one apex of the inverted triangle) is set, for example, to 5° or more and 20° or less.

[0052] The wedge-shaped diameter enlarger element 20 is configured to fit into part or all of the fitting section F. As a specific example, the diameter enlarger element 20 has the shape of an inverted triangle such that its width narrows towards the bottom. The bottom end (the apex of the inverted triangle) has a taper angle (wedge angle) θ1, which is preferably identical to the angle θ1' of the fitting section F, e.g., 5° or more and 20° or less.

[0053] When the auxiliary cooling cylinder 19 and the diameter enlarger element 20 are used as described above to fit and push the diameter enlarger element 20 into the auxiliary cooling cylinder 19, the pressure for pushing the diameter enlarger element 20 is converted into a force to increase the diameter of the auxiliary cooling cylinder 19, thereby increasing the diameter of the auxiliary cooling cylinder 19, as shown in Fig. 3 shown. Consequently, the auxiliary cooling cylinder 19 will certainly come into close contact with the cooling cylinder 12 (see Fig. 1) It should be noted that the auxiliary cooling cylinder 19 and the diameter enlargement element 20 are preferably made of a material with excellent heat resistance, high thermal conductivity, and high emissivity. The material is preferably, for example, any of graphite, carbon composite (CC material), stainless steel, molybdenum, and tungsten.

[0054] Fig. Figure 4 shows another example of the device according to the invention for producing a single crystal.

[0055] The apparatus 1' shown in this figure for producing a single crystal is the same as the apparatus 1 for producing a single crystal in Fig. 1, except that the auxiliary cooling cylinder 19 and the diameter enlargement element 20 are in comparison to the device 1 for producing a single crystal in Fig. 1 are different. Therefore, the auxiliary cooling cylinder 19 and the diameter enlargement element 20 are described below. The other components are designated with the same symbols as in Fig. Marked as 1, and they will not be discussed in more detail.

[0056] Fig. Figure 5 shows examples of part of the auxiliary cooling cylinder and the diameter enlargement element. Fig. 6 and Fig.Figure 7 shows states in which the diameter enlargement element is inserted into the auxiliary cooling cylinder.

[0057] The auxiliary cooling cylinder 19 has four slots SL that penetrate it axially. These four slots SL divide the auxiliary cooling cylinder 19 into four parts A, B, C, and D. In other words, when these four parts A, B, C, and D are combined, the auxiliary cooling cylinder 19 forms a cylindrical shape with the axis AX as its center point. Note that the in Fig. 5 auxiliary cooling cylinders shown 19 in one of the four parts A, B, C and D in Fig. 6 corresponds.

[0058] As in Fig.As shown in Figure 7, the auxiliary cooling cylinder 19 has a tapered shape such that an upper part of it has a sloping inner surface and that the inner diameter is smaller on one lower side, i.e., the cross-sectional width narrows towards the upper end. Simultaneously, the diameter-enlarging element 20 has a ring shape that fits into the auxiliary cooling cylinder 19. Furthermore, the diameter-enlarging element 20 has a tapered shape such that a lower section of it has a sloping outer surface and that the outer diameter is smaller on one lower side, i.e., the cross-sectional width narrows towards the lower end.

[0059] Assuming that an angle between the inner and outer surfaces of the auxiliary cooling cylinder 19 is represented by a taper angle θ2, the taper angle θ2 is set, for example, to 5° or more and 20° or less. Assuming that an angle formed between the inner and outer surfaces of the diameter enlargement element 20 is represented by a taper angle θ2', the taper angle θ2' is preferably set to be identical to the taper angle θ2 of the auxiliary cooling cylinder 19, for example, to 5° or more and 20° or less.

[0060] When such an auxiliary cooling cylinder 19 and a diameter enlarger element 20 are used to insert and push the diameter enlarger element 20 into the auxiliary cooling cylinder 19, the pressure for pushing the diameter enlarger element 20 is converted into a force to increase the diameter of the auxiliary cooling cylinder 19, thereby increasing the diameter of the auxiliary cooling cylinder 19, as shown in the Fig. 6 and Fig. 7 shown. As a result, the auxiliary cooling cylinder 19 comes into close contact with the cooling cylinder 12 (see Fig. 4) It should be noted that the auxiliary cooling cylinder 19 and the diameter enlargement element 20 are preferably made of a material with excellent heat resistance and high thermal conductivity and emissivity. The material is preferably, for example, any of graphite, carbon composite (CC material), stainless steel, molybdenum, and tungsten.

[0061] As described above, the auxiliary cooling cylinder 19 in the devices according to the invention for producing a single crystal has the slot(s) SL that penetrate it in the axial direction. Accordingly, the diameter of the auxiliary cooling cylinder 19 is increased when the diameter-enlarging element 20 is inserted into the auxiliary cooling cylinder 19. Furthermore, The diameter of the auxiliary cooling cylinder 19 is increased so that it comes into close contact with the cooling cylinder 12, which surrounds the outer surface of the auxiliary cooling cylinder 19. This allows the heat from the grown single crystal 4 to be efficiently transferred from the auxiliary cooling cylinder 19 to the cooling cylinder 12. In this way, the single crystal 4 is efficiently cooled during growth, and this efficient cooling makes it possible to increase the growth rate of the single crystal 4 (crystal pulling rate) and improve productivity. EXAMPLES

[0062] The present invention is described in detail below with reference to examples of the present invention. However, the present invention is not limited to these examples. (Example 1)

[0063] In Example 1, single crystals 4 were grown by using the apparatus 1 for the production of a single crystal, as in Fig. Figure 1 was shown, installed under the following conditions. A crystal growing rate for producing the single crystal 4 with the desired quality was verified.

[0064] The single crystals 4 to be grown were silicon single crystals. These silicon crystals, which had a diameter of 12 inches (300 mm), were grown using the Czochralski method (MCZ method) with the aid of a magnetic field. The quartz glass crucible 6 had a diameter of 32 inches (800 mm). The specified inner diameter of the cooling cylinder 12 was 430 mm. The specified outer diameter of the auxiliary cooling cylinder 19 was 429.5 mm, and its length was 350 mm. The tolerances for the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19 were ±0.4 mm and ±0.1 mm, respectively.

[0065] The auxiliary cooling cylinder 19 used had the slot SL, which penetrated it in the axial direction, as in Fig.Figure 2 shows that the slot SL had an upper portion cut into a V-shape to form the fitting section F. Furthermore, the diameter-enlarging element 20 used had a wedge shape that fit into part or all of the fitting section F. Specifically, the diameter-enlarging element 20 had the shape of an inverted triangle, the width of which narrows towards the lower end, and the taper angle θ1 at the lower end was set to 10°. Similarly, the fitting section F of the auxiliary cooling cylinder 19 also had the shape of an inverted triangle, and the angle θ1' at the lower end was set to 10°.

[0066] In such a device 1 for producing a single crystal, immediately after the insertion of the auxiliary cooling cylinder 19, the gap (difference) between the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19 was 0.8 mm. After the diameter enlarger element 20 was inserted into the auxiliary cooling cylinder 19 and pressed in, the auxiliary cooling cylinder 19 was enlarged to the desired diameter such that the gap between the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19 was 0 mm. In other words, the auxiliary cooling cylinder 19 fit snugly against the cooling cylinder 12 without a gap. It should be noted that a graphite material was used for the auxiliary cooling cylinder 19 and the diameter enlarger element 20, which has the same thermal conductivity as metals and a higher emissivity than metals.

[0067] While the cooling cylinder 12 and the auxiliary cooling cylinder 19 were in close contact due to the diameter-enlarging element 20, the single crystals 4 were grown and a growth rate was determined at which all crystals were defect-free. Since the range of growth rates required to obtain a defect-free crystal is quite narrow, the suitable growth rate for obtaining a completely defect-free single crystal 4 can be easily determined by: dividing each grown single crystal 4 into samples and then checking whether the samples are defect-free or not. In Example 1, selective etching was used to check whether such samples were defect-free crystals or not in order to determine a growth rate at which all crystals were defect-free. (Comparative example 1)

[0068] In comparative example 1, the Fig.The apparatus 101 shown in Figure 8 is used to produce a single crystal in order to determine a growth rate at which the entire single crystal 104 is a defect-free crystal. More precisely, in Comparative Example 1, the growth rate was evaluated using the apparatus 101 to produce a single crystal without an additional cooling cylinder.

[0069] Note that in Comparative Example 1, the single crystals 104 were produced under the same conditions as in Example 1 and the evaluation was carried out as in Example 1, with the exception that the apparatus for producing a single crystal was as in Example 1. Fig. 8 was shown, used.

[0070] Furthermore, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117 and 118 correspond to in Fig.8 each of the main chamber 2, the drawing chamber 3, the single crystal 4, the raw material melt 5, the quartz crucible 6, the graphite crucible 7, the heater 8, the heat-insulating element 9, the gas outlet 10, the gas inlet 11, the cooling cylinder 12, the coolant inlet 13, the gas flow guide cylinder 14, the drawing wire 15, the seed crystal 16, the seed crystal holder 17 and the crucible rotation axis 18 in Fig. 1. (Comparative example 2)

[0071] In comparative example 2, the Fig. The apparatus 101 shown in Figure 9 is used to produce a single crystal in order to determine a growth rate at which the entire single crystal 104 is a defect-free crystal. More precisely, in Comparative Example 2, the growth rate was evaluated using the apparatus 101 to produce a single crystal with an auxiliary cooling cylinder, but without a diameter enlarger element.

[0072] Note that in comparative example 2, the single crystals 104 were prepared under the same conditions as in example 1, and the evaluation was carried out as in example 1, with the exception that the Fig. The device shown in Figure 9 was used to produce a single crystal.

[0073] Furthermore, in Fig. 9 the same components as in Fig. 8 with the same characters as in Fig. Marked 8. Furthermore, 119 corresponds to... Fig. 9 the auxiliary cooling cylinder 19 in Fig. 1.

[0074] Table 1 shows the crystal pull rates (growth rates) at which all pulled single crystals in Example 1, Comparison Example 1 and Comparison Example 2 were defect-free crystals. [Table 1] Comparison of crystal growth rates between Example 1, Comparison Example 1 and Comparison Example 2 configuration Crystal drawing speed No auxiliary cooling cylinder (comparative example 1) 1,000 Auxiliary cooling cylinders only (comparative example 2) 1,058 Auxiliary cooling cylinder + diameter enlargement element (Example 1) 1,105

[0075] As can be seen from Table 1, the growth rate in Example 1 was approximately 10.5% higher than in Comparison Example 1, which did not use an auxiliary cooling cylinder. Furthermore, the growth rate in Example 1 was approximately 4.4% higher than in Comparison Example 2, which used the auxiliary cooling cylinder but not the diameter enlarger element. (Example 2)

[0076] In Example 2, single crystals 4 were prepared using the method described in Fig. A crystal growing rate for producing the single crystal 4 with the desired quality was verified using the apparatus 1' shown in section 4 under the following conditions.

[0077] The single crystals 4 to be grown were silicon single crystals. The single crystals were produced under the same conditions as in Example 1, and the evaluation was carried out as in Example 1, except that the auxiliary cooling cylinder 19 and the diameter enlarger element 20 were used as in Example 1. Fig. Figure 5 shows the components used. In particular, the specified value of the inner diameter of the cooling cylinder 12 was 430 mm, the specified value of the outer diameter of the auxiliary cooling cylinder 19 was 429.5 mm, and the length was 350 mm. Furthermore, tolerances of ±0.4 mm and ±0.1 mm were used for the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19, respectively.

[0078] The auxiliary cooling cylinder 19 used had four slots SL penetrating it in an axial direction, as shown in Fig. Figure 6 shows that the auxiliary cooling cylinder 19 was divided into four parts A, B, C and D by these four slots SL. As shown in Fig.As shown in Figure 7, the auxiliary cooling cylinder 19 used had a tapered shape such that the upper part had an inclined inner surface and that the width of the cross-sectional shape narrowed towards the upper end. At the same time, the diameter enlargement element 20 used had a ring shape that was fitted into the interior of the auxiliary cooling cylinder 19, as shown in Figure 7. Fig. 7 shown. In addition, the diameter enlargement element 20 used had such a tapered shape that the lower section had an inclined outer surface and that the width of the cross-sectional shape was narrowed towards the lower end.

[0079] Furthermore, both the tapering angle θ2 between the inner surface and the outer surface of the auxiliary cooling cylinder 19 and the tapering angle θ2' between the inner surface and the outer surface of the diameter enlargement element 20 were set to 10°.

[0080] In such a device 1' for producing a single crystal, immediately after the insertion of the auxiliary cooling cylinder 19, the gap (difference) between the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19 was 0.8 mm. After the diameter enlarger element 20 was inserted into the auxiliary cooling cylinder 19 and pushed in, the four parts of the auxiliary cooling cylinder 19 moved in their respective diameter directions. This enlarged the auxiliary cooling cylinder 19 to the desired diameter, so that the gap between the inner diameter of the cooling cylinder 12 and the outer diameter of the auxiliary cooling cylinder 19 became 0 mm. In other words, the auxiliary cooling cylinder 19 fits snugly and without gaps against the cooling cylinder 12.

[0081] Table 2 shows the crystal growth rates at which all grown single crystals in Example 2, Comparison Example 1 and Comparison Example 2 were defect-free crystals. [Table 2] Comparison of crystal growth rates between Example 2, Comparison Example 1 and Comparison Example 2 configuration Crystal drawing speed No auxiliary cooling cylinder (comparative example 1) 1,000 Auxiliary cooling cylinders only (comparative example 2) 1,058 Auxiliary cooling cylinder + diameter enlargement element (Example 2) 1,102

[0082] As can be seen from Table 2, the growth rate in Example 2 was approximately 10.2% higher than in Comparison Example 1, which did not use an auxiliary cooling cylinder. Furthermore, the growth rate in Example 2 was approximately 4.1% higher than in Comparison Example 2, which used the auxiliary cooling cylinder but not the diameter enlarger element. Therefore, a higher growth rate was also achieved in Example 2 than in Example 1.

[0083] As can be seen from the results above, in both examples 1 and 2 the growth rate of the single crystal 4 was successfully increased compared to the reference examples 1 and 2. This shows that the devices 1, 1' according to the invention for producing a single crystal are able to efficiently cool the single crystal 4 during growth and increase the growth rate of the single crystal 4.

[0084] As described above, the present invention enables the outer diameter of the auxiliary cooling cylinder 19 to be increased by inserting and pressing the diameter enlarger element 20 into the auxiliary cooling cylinder 19. This satisfactorily increases the degree of contact between the auxiliary cooling cylinder 19 and the cooling cylinder 12, thus enabling efficient cooling of the single crystal 4 during growth. In other words, the growth rate of the single crystal 4 can be increased by efficiently cooling the single crystal 4 during its growth.

[0085] It should be noted that the present invention is not limited to the embodiments described above, but is defined in the claims.

Claims

[1] Apparatus (1, 1') for producing a single crystal (4) according to a Czochralski process, wherein the apparatus (1, 1') comprises: a main chamber (2) adapted to accommodate a crucible (6, 7) adapted to accommodate a raw material melt (5), and a (8) heater adapted for heating the raw material melt (5); a drawing chamber (3) which is continuously provided on an upper section of the main chamber (2) and adapted to accommodate a single crystal (4) drawn from the raw material melt (5); a cooling cylinder (12) extending from a ceiling section of the main chamber (2) towards a surface of the raw material melt (5) to surround the single crystal (4); and an auxiliary cooling cylinder (19) which is inserted into the interior of the cooling cylinder (12), wherein the device (1, 1') also includes a diameter enlargement element (20) adapted to fit into the auxiliary cooling cylinder (19), the auxiliary cooling cylinder (19) has at least one slot (SL) passing through it in an axial direction, and the auxiliary cooling cylinder (19) is adapted to come into close contact with the cooling cylinder (12) by pressing the diameter enlargement element (20) into the auxiliary cooling cylinder (19) to increase the diameter of the auxiliary cooling cylinder (19). [2] Device (1, 1') for producing a single crystal (4) according to claim 1, wherein the diameter enlargement element (20) has a wedge shape and is adapted to increase the diameter of the auxiliary cooling cylinder (19) by being partially or completely inserted and pressed into the at least one slot (SL) of the auxiliary cooling cylinder (19). [3] Device (1, 1') for producing a single crystal (4) according to claim 1, wherein the auxiliary cooling cylinder (19) is tapered so that the inner diameter is smaller on one lower side, the diameter enlargement element (20) has such a tapered shape that an outer diameter on a lower side is smaller, and, the diameter enlargement element (20) is configured to increase the diameter of the auxiliary cooling cylinder (19) by inserting and pressing the diameter enlargement element (20) into the interior of the auxiliary cooling cylinder (19). [4] Device (1, 1') for producing a single crystal (4) according to any one of claims 1 to 3, wherein a material of the auxiliary cooling cylinder (19) consists of any of graphite, carbon composite material, stainless steel, molybdenum and tungsten. [5] Device (1, 1') for producing a single crystal (4) according to any one of claims 1 to 4, wherein a material of the diameter enlargement element (20) consists of any of graphite, carbon composite, stainless steel, molybdenum and tungsten.

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