JP2020037499A - Heat shield member, apparatus for pulling single crystal and method for manufacturing single crystal - Google Patents

Abstract

To provide: a heat shield member capable of expanding the pulling speed margin of a single crystal having a defect-free crystal obtained when pulling the single crystal by the Czochralski method; an apparatus for pulling a single crystal using the same; and a method for manufacturing a silicon single crystal.SOLUTION: A heat shield member 20 comprises: a cylindrical part 22 surrounding a single crystal 3 pulled from a melt; and an annular swollen part 23 projected inside in the radial direction from a lower end portion of the cylindrical part and including an annular heat insulator H and a wall material 21 surrounding the heat insulator H. The wall material 21 includes an inner side wall part 23c for covering the inner peripheral surface of the heat insulator H; a cavity part V is provided between the inner side wall part 23c and the inner peripheral surface of the heat insulator H; a recessed part 30 is formed on the outer surface of the inner side wall part 23c facing the outer peripheral surface of the single crystal 3; and the outer surface of the inner side wall part 23c has a downward inclined surface 30a.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a heat shielding member used for pulling a single crystal by the Czochralski method (CZ method), a single crystal pulling apparatus using the same, and a method for manufacturing a single crystal.

  Many silicon single crystals used as substrate materials for semiconductor devices are manufactured by the CZ method. In the CZ method, a seed crystal is immersed in a silicon melt contained in a quartz crucible, and the seed crystal is gradually pulled up while rotating the seed crystal and the quartz crucible, thereby growing a large single crystal at the lower end of the seed crystal. According to the CZ method, a high-quality silicon single crystal ingot can be manufactured with a high yield.

  It is known that the type and distribution of defects contained in a silicon single crystal grown by the CZ method depend on the ratio V / G between the crystal pulling speed V and the temperature gradient G in the crystal in the crystal pulling direction.

  FIG. 11 is a diagram showing a general relationship between V / G and types and distributions of crystal defects. As shown in the figure, when V / G is large, vacancies become excessive and voids, which are aggregates thereof, are generated. A void is a crystal defect generally called COP (Crystal Originated Particle). On the other hand, when V / G is small, interstitial silicon atoms become excessive and dislocation clusters as aggregates thereof are generated. In order to grow a silicon single crystal that does not contain Grown-in defects such as COPs and dislocation clusters, strict control of V / G is required.

  Even a silicon single crystal that does not include a COP and dislocation clusters does not necessarily have the same crystal quality, and includes a plurality of regions that behave differently when heat-treated. Specifically, between the region in which the COP occurs and the region in which the dislocation cluster occurs, there are three regions of the OSF region, the Pv region, and the Pi region in ascending order of V / G.

  The OSF region contains plate-like oxygen precipitates (OSF nuclei) in an as-grown state (a state in which no heat treatment is performed after single crystal growth), and is performed at a high temperature (generally 1000 to 1200 ° C.). This is an area where OSF (Oxidation induced Stacking Fault) occurs when heat treatment is performed. The Pv region is a region that contains oxygen precipitation nuclei in an as-grown state and is likely to generate oxygen precipitates when subjected to two-stage heat treatment at low and high temperatures (for example, 800 ° C. and 1000 ° C.). The Pi region is a region that contains almost no oxygen precipitate nuclei in an as-grown state and hardly generates oxygen precipitates even when heat treatment is performed. In order to grow a high-quality silicon single crystal in which the Pv region and the Pi region are separately formed, more strict control of V / G is required.

  V / G in the crystal pulling direction of the single crystal largely depends on the pulling speed V of the single crystal. Therefore, the control of V / G in the crystal pulling direction is performed by adjusting the crystal pulling speed V. On the other hand, since the crystal pulling speed V is the same at any position in the radial direction of the single crystal orthogonal to the crystal pulling direction, to control the V / G in the radial direction of the single crystal, It is necessary to adjust the temperature gradient G, and an appropriate high-temperature region (hot zone) is constructed in the chamber so that the difference between the temperature gradient G at the central portion of the single crystal and the temperature gradient G at the outer peripheral portion falls within a predetermined range. There is a need to. The temperature gradient G in the radial direction of the single crystal is controlled by a heat shielding member provided above the silicon melt, so that an appropriate hot zone can be constructed near the solid-liquid interface.

  In order to obtain a defect-free silicon single crystal, for example, Patent Document 1 discloses a cylindrical portion surrounding a silicon single crystal rod and blocking radiant heat from a heater, a bulging portion provided at a lower portion of the cylindrical portion, and a bulging portion. And a ring-shaped heat storage member provided inside the unit.

  Further, Patent Document 2 includes a cone-shaped heat radiation control unit formed below the heat shielding member, and a plurality of heat radiation plates arranged on the heat radiation control unit. Each of the plurality of heat radiating plates is pivotally supported by the heat shielding member, and the angle can be changed by rotating each of the plurality of heat radiating plates. It describes that the heat radiation plate is made to fall down when the straight body of the crystal rod is formed.

  Patent Document 3 discloses a cylindrical portion surrounding a silicon single crystal rod, a bulging portion provided at a lower end portion of the cylindrical portion, and a ring surrounding an outer peripheral surface of the single crystal rod while being inserted into the cylindrical portion. Heat insulating member, comprising a support member for supporting the heat insulating cover above the bulging portion, the heat shielding member configured to be able to change the radial distribution of the temperature gradient by moving the heat insulating cover in the vertical direction. Has been described.

JP 2004-107132 A JP 2000-7496A JP 2006-69803 A

  As described above, V / G can be controlled by precisely controlling the crystal pulling speed V, whereby a defect-free silicon single crystal can be manufactured. However, since there is a limit in precise control of the crystal pulling speed V, it is required to expand the allowable range (pulling speed margin) of the crystal pulling speed at which a defect-free silicon single crystal can be pulled.

  The diameter control of the silicon single crystal 3 is mainly performed by adjusting the crystal pulling speed V, and the crystal pulling speed V is appropriately changed in order to suppress the diameter variation. During the crystal pulling process, about 0.015 mm / min. Speed fluctuation has occurred. That is, since the fluctuation of the crystal pulling speed V cannot be completely eliminated, it is desirable that the defect-free crystal can be pulled even if a speed fluctuation of about 0.015 mm / min occurs.

  Accordingly, an object of the present invention is to provide a heat shielding member capable of expanding a margin of a pulling speed at which a defect-free crystal can be obtained, a single crystal pulling apparatus using the same, and a method of manufacturing a single crystal.

    The inventor of the present application has conducted intensive studies on the structure of the heat shielding member capable of increasing the lifting speed margin, and as a result, has increased only the opening diameter of the internal heat insulating material without changing the opening diameter of the heat shielding member. By providing a cavity inside the tip of the bulging part and providing a concave part on the inner peripheral surface of the bulging part of the heat shielding member to form a downward inclined surface, the temperature gradient in the radial direction of the single crystal Was found to be close to the ideal temperature gradient, thereby increasing the lifting speed margin.

  The present invention is based on such technical knowledge, and the heat shielding member according to the present invention is used for a single crystal pulling apparatus by a Czochralski method, and surrounds a single crystal pulled from a melt. A cylindrical tubular portion to be formed, and an annular bulged portion projecting radially inward from a lower end portion of the tubular portion, wherein the bulged portion has an annular heat insulating material and a wall material surrounding the heat insulating material. The wall material has an inner side wall portion that covers an inner peripheral surface of the heat insulating material, and a cavity is provided between the inner side wall portion and the inner peripheral surface of the heat insulating material. A recess is formed on the outer surface of the inner side wall facing the outer peripheral surface of the single crystal, and the outer surface of the inner side wall has a downwardly inclined surface.

  According to the present invention, the temperature gradient in the radial direction of the single crystal can be made closer to the ideal temperature gradient, and the radial distribution of crystal defects can be flattened. Therefore, the manufacturing speed of defect-free crystals can be increased by increasing the margin of the pulling speed at which defect-free crystals can be obtained.

  In the present invention, it is preferable that the outer surface of the inner side wall portion further includes an upwardly inclined surface disposed below the downwardly inclined surface. According to this configuration, it is possible to make the temperature gradient in the crystal closer to the ideal high temperature gradient and further flatten the radial distribution of crystal defects.

  In the present invention, the height of the downward inclined surface is preferably larger than the height of the upward inclined surface. According to this, it is possible to further increase the pulling speed margin and increase the production yield of defect-free crystals.

  In the present invention, it is preferable that a cross-sectional shape of the concave portion is substantially V-shaped, and the downward inclined surface and the upward inclined surface are flat surfaces. Further, the cross-sectional shape of the concave portion may be substantially C-shaped, and it is also preferable that the downward inclined surface and the upward inclined surface are curved surfaces. In either case, the temperature gradient in the crystal can be made closer to the ideal high temperature gradient to further flatten the radial distribution of crystal defects.

  In the present invention, the wall material may further include an upper wall portion covering an upper surface of the heat insulating material, a bottom wall portion covering a bottom surface of the heat insulating material, and an outer side wall portion covering an outer peripheral surface of the heat insulating material. preferable. As described above, in the structure in which the periphery of the heat insulating material is surrounded by the wall material, by providing a cavity between the inner side wall portion and the inner peripheral surface of the heat insulating material, the outer surface of the inner side wall portion faces downward. The effect of improving the lifting speed margin by providing the inclined surface can be enhanced.

  In addition, the single crystal pulling apparatus according to the present invention includes a chamber, a crucible that supports the melt in the chamber, a heater that heats the melt, a crucible driving mechanism that rotates and raises and lowers the crucible, A single crystal pulling mechanism for pulling the single crystal from the liquid; and a heat according to the present invention as described above, which is provided above the melt and surrounds the single crystal pulled from the melt and shields radiant heat from the heater. And a shielding member. According to the present invention, the temperature gradient in the crystal can be made closer to the ideal temperature gradient, whereby the pulling speed margin for obtaining a defect-free crystal can be increased, and the production yield of the defect-free crystal can be increased.

  Furthermore, the method for producing a single crystal according to the present invention is a method for producing a single crystal by the Czochralski method of pulling a single crystal from a melt in a crucible, and using the heat shielding member according to the present invention described above. Surrounding the single crystal pulled from the substrate. According to the present invention, the temperature gradient in the crystal can be made closer to the ideal temperature gradient, whereby the pulling speed margin for obtaining a defect-free crystal can be increased, and the production yield of the defect-free crystal can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the heat-shielding member which can enlarge the pulling speed margin which can obtain a defect-free crystal, a single crystal pulling apparatus using the same, and a single crystal manufacturing method can be provided.

FIG. 1 is a schematic side sectional view showing a configuration of a single crystal pulling apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating the steps of manufacturing the silicon single crystal according to the present embodiment. FIG. 3 is a schematic sectional view showing the shape of a silicon single crystal ingot. FIG. 4 is a graph showing an example of the ideal temperature gradient G _ideal . FIG. 5 is a schematic sectional view showing the configuration of the heat shielding member in detail. 6A to 6E are schematic cross-sectional views showing variations of the shape of the bulging portion of the heat shielding member. FIGS. 7A to 7D are diagrams for comparing a lifting speed margin obtained when the heat shielding member 20 according to the present embodiment is used with a conventional heat shielding member, and FIG. (B) shows the conventional crystal defect distribution, (c) shows the structure of the heat shielding member according to the present embodiment, and (d) shows the crystal defect distribution according to the present embodiment. FIG. 8 is a diagram illustrating the shape of the concave portion of the bulging portion of the heat shielding member according to Examples 3 to 6, and particularly illustrating a difference in the position of the vertex (point C) of the inclination of the concave portion. FIG. 9 is a graph showing the results of heat transfer calculation (point defect simulation) of Examples 3 to 6. FIG. 10 is a graph showing a difference in a lifting speed margin in Examples 3 to 6 due to a difference in the shape of the concave portion of the bulging portion of the heat shielding member. FIG. 11 is a diagram showing a general relationship between V / G and types and distributions of crystal defects.

  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 a configuration of a single crystal pulling apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, a single crystal pulling apparatus 1 includes a water-cooled chamber 10, a quartz crucible 11 for holding a silicon melt 2 in the chamber 10, a graphite crucible 12 for holding the quartz crucible 11, and a graphite crucible. A rotary shaft 13 for supporting the rotary shaft 12, a shaft drive mechanism 14 for rotating and raising and lowering the rotary shaft 13, a heater 15 disposed around the graphite crucible 12, and an outer surface of the heater 15 along the inner surface of the chamber 10. A heat insulating member 20 disposed above the quartz crucible 11, a single crystal pulling wire 18 disposed above the quartz crucible 11 and coaxially with the rotating shaft 13. , A wire winding mechanism 19 disposed above the chamber 10.

  The chamber 10 includes a main chamber 10a and an elongated cylindrical pull chamber 10b connected to an upper opening of the main chamber 10a. The quartz crucible 11, the graphite crucible 12, the heater 15, and the heat shielding member 20 are It is provided in the chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the chamber 10, and an atmosphere gas in the chamber 10 is provided below the main chamber 10a. Is provided with a gas outlet 10d for discharging gas. In addition, an observation window 10e is provided on the upper portion of the main chamber 10a, and the growth state of the silicon single crystal 3 can be observed from the observation window 10e.

  The quartz crucible 11 is a quartz glass container having a cylindrical side wall and a curved bottom. The graphite crucible 12 is held in close contact with the outer surface of the quartz crucible 11 so as to enclose the quartz crucible 11 in order to maintain the shape of the quartz crucible 11 softened by heating. The quartz crucible 11 and the graphite crucible 12 constitute a double structure crucible for supporting the silicon melt in the chamber 10.

  The graphite crucible 12 is fixed to the upper end of the rotating shaft 13, and the lower end of the rotating shaft 13 passes through the bottom of the chamber 10 and is connected to a shaft drive mechanism 14 provided outside the chamber 10. The graphite crucible 12, the rotating shaft 13 and the shaft driving mechanism 14 constitute a rotating mechanism and a lifting mechanism of the quartz crucible 11.

  The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 to generate the silicon melt 2 and to maintain the molten state of the silicon melt 2. The heater 15 is a resistance heating heater made of carbon, and is provided so as to surround the quartz crucible 11 in the graphite crucible 12. A heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby enhancing the heat retention in the chamber 10.

  The heat shielding member 20 suppresses the temperature fluctuation of the silicon melt 2 to form an appropriate hot zone near the crystal growth interface, and also prevents the silicon single crystal 3 from being heated by radiant heat from the heater 15 and the quartz crucible 11. It is provided for. The heat shield member 20 is a substantially cylindrical member made of graphite, and is provided so as to cover a region above the silicon melt 2 excluding a pulling path of the silicon single crystal 3.

  The diameter of the opening 20 a at the lower end of the heat shielding member 20 is larger than the diameter of the silicon single crystal 3, thereby securing a pulling path of the silicon single crystal 3. Further, the outer diameter of the lower end of the heat shielding member 20 is smaller than the diameter of the quartz crucible 11, and the lower end of the heat shielding member 20 is located inside the quartz crucible 11. The heat shielding member 20 does not interfere with the quartz crucible 11 even if it is raised above the lower end of the quartz crucible.

  Although the amount of the melt in the quartz crucible 11 decreases with the growth of the silicon single crystal 3, the silicon crucible 11 is raised by raising the quartz crucible 11 so that the gap between the melt surface and the heat shielding member 20 becomes constant. The temperature fluctuation of the liquid 2 can be suppressed, and the evaporation amount of the dopant from the silicon melt 2 can be controlled by keeping the flow velocity of the gas flowing near the melt surface constant. Therefore, it is possible to improve the stability of the silicon single crystal 3 such as the crystal defect distribution, the oxygen concentration distribution, and the resistivity distribution in the pulling axis direction.

  Above the quartz crucible 11, a wire 18 as a pulling shaft of the silicon single crystal 3 and a wire winding mechanism 19 for winding the wire 18 are provided. The wire winding mechanism 19 has a function of rotating the silicon single crystal 3 together with the wire 18. The wire take-up mechanism 19 is disposed above the pull chamber 10b, the wire 18 extends downward from the wire take-up mechanism 19 through the inside of the pull chamber 10b, and the tip of the wire 18 is located inside the main chamber 10a. It has reached space. FIG. 1 shows a state in which the silicon single crystal 3 being grown is suspended on the wire 18. When pulling up the silicon single crystal 3, the silicon single crystal 3 is grown by gradually pulling up the wire 18 while rotating the quartz crucible 11 and the silicon single crystal 3 respectively.

  FIG. 2 is a flowchart illustrating the steps of manufacturing the silicon single crystal according to the present embodiment. FIG. 3 is a schematic sectional view showing the shape of a silicon single crystal ingot.

  As shown in FIG. 2, the manufacturing process of the silicon single crystal 3 according to the present embodiment includes a raw material melting step S11 in which a silicon raw material in a quartz crucible 11 is heated by a heater 15 to generate a silicon melt 2; The seed crystal attached to the tip of the silicon melt 2 to drop the seed crystal onto the silicon melt 2 and gradually pull up the seed crystal while maintaining the contact state with the silicon melt 2 to grow a single crystal Crystal growing step (S13 to S16).

  In the crystal growing step, a necking step S13 for forming a neck 3a having a narrowed crystal diameter for eliminating dislocations, and a shoulder growing step S14 for forming a shoulder 3b having a crystal diameter gradually increased with crystal growth. And a body part growing step S15 for forming a body part 3c maintained at a specified crystal diameter of 450 mm or more, and a tail part growing step S16 for forming a tail part 3d having a crystal diameter gradually reduced as the crystal grows. Will be implemented.

  Thereafter, a cooling step S17 of separating and cooling the silicon single crystal 3 from the melt surface is performed. Thus, a silicon single crystal ingot 3 having a neck 3a, a shoulder 3b, a body 3c and a tail 3d as shown in FIG. 3 is completed.

  As shown in FIG. 11, the type and distribution of the crystal defects contained in the silicon single crystal 3 depend on the ratio V / G between the crystal pulling speed V and the temperature gradient G in the crystal. When V / G is large, vacancies become excessive and voids (COP), which are aggregates of vacancies, are generated. On the other hand, when V / G is small, interstitial silicon atoms become excessive and dislocation clusters, which are aggregates of interstitial silicon, are generated. Further, between the region where COP occurs and the region where dislocation clusters occur, there are three regions of OSF region, Pv region, and Pi region in order of V / G in descending order. In order to say that the silicon single crystal 3 is a defect-free crystal, it is necessary that the silicon single crystal 3 does not include a Grown-in defect such as a COP or a dislocation cluster and that an OSF ring does not occur after the evaluation heat treatment. It is necessary that the entire surface be a defect-free crystal.

  In order to grow a defect-free crystal at a high yield by controlling the crystal pulling speed V, it is preferable that the pulling speed margin is as wide as possible. The pulling speed margin is specifically Vmgn shown in FIG. 11, and refers to an allowable width of the crystal pulling speed V that allows an arbitrary region in the silicon single crystal 3 to be a Pv region or a Pi region. Usually, the pulling speed margin Vmgn correlates with the width of V / G from the Pv-OSF boundary to the Pi-dislocation cluster boundary. That is, as the V / G width from the Pv-OSF boundary (lower limit) to the Pi-dislocation cluster boundary (upper limit) increases, the pulling speed margin Vmgn increases, and conversely, the P-dislocation shifts from the Pv-OSF boundary (lower limit). As the width of V / G up to the cluster boundary (upper limit) becomes smaller, the pulling speed margin Vmgn becomes smaller.

The pulling speed margin Vmgn for obtaining a defect-free crystal can be increased by flattening the radial distribution of crystal defects. The criticality (V / G) _cri for realizing the flattening of the radial distribution of crystal defects can be theoretically obtained from the condition that the concentration of vacancies is equal to the concentration of interstitial silicon. ).
(V / G) _cri = 6.68 × 10 ⁻⁴ σ _mean +0.159 (1)

Here, σ _mean is the stress at an arbitrary position in the crystal. As is clear from the above equation (1), (V / G) _{cri at} which the interstitial silicon concentration and the vacancy concentration become equal depends on the stress in the crystal. The (V / G) _cri can be obtained from the stress distribution in the crystal by heat transfer calculation or the like. Further, since the pulling speed V is constant in the radial direction, the ideal temperature gradient G _ideal for realizing the flattening of the radial distribution of crystal defects can be obtained from the above equation (1) as the following equation (2). .
G _ideal = V / (6.68 × 10 ⁻⁴ σ _mean +0.159) (2)

FIG. 4 is a graph showing an example of the ideal temperature gradient G _ideal , in which the horizontal axis represents the position (relative value) of the single crystal in the radial direction and the vertical axis represents the temperature gradient (° C./mm). As shown, the ideal temperature gradient G _ideal is highest at the center of the single crystal and gradually decreases toward the outermost periphery. If such an ideal temperature gradient G _ideal can be realized, it is possible to maximize the lifting speed margin.

In order to increase the pulling speed margin by bringing the temperature gradient G closer to the ideal temperature gradient G _ideal , the following heat shielding member 20 is used in the single crystal pulling apparatus 1 according to the present embodiment.

  FIG. 5 is a schematic sectional view showing the configuration of the heat shielding member 20 in detail.

  As shown in FIG. 5, the heat shielding member 20 is a structure in which a heat insulating material H is housed inside a housing formed of a graphite wall material 21, and is a circle pulled up from the silicon melt 2. A cylindrical tubular portion 22 surrounding the outer peripheral surface of the columnar silicon single crystal 3 is provided, and an annular bulging portion 23 that projects radially inward from the lower end of the tubular portion 22. The cylindrical portion 22 has an inner wall portion 22a and an outer wall portion 22b, and a heat insulating material H is provided between these wall materials 21. The bulging portion 23 has an upper wall portion 23a, a bottom wall portion 23b, an inner side wall portion 23c, and an outer side wall portion 23d, and a heat insulating material is provided in a space surrounded by these wall materials 21. H is provided.

The opening diameter (opening radius r _h ) of the annular heat insulating material H in the bulging portion 23 is sufficiently larger than the opening diameter (opening radius r _s ) of the heat shielding member 20. A cavity V is provided between the portion 23c and the heat insulating material H. By providing the hollow portion V inside the tip of the bulging portion 23, the temperature gradient G in the radial direction of the silicon single crystal 3 can be made closer to the ideal temperature gradient G _ideal to increase the pulling speed margin. Further, through the aperture radius r _s of the heat shield member 20 is made smaller than the opening radius r _h insulation H, by narrowing the gap 17a between the silicon single crystal 3 and the heat shield member 20 in the gap 17a The flow rate of the inert gas can be maintained, and thereby deformation such as bending of the crystal can be suppressed.

  When the outer peripheral surface of the inner side wall portion 23c is not a surface shape along the inner peripheral surface of the heat insulating material H, that is, when the outer peripheral surface shape of the inner side wall portion 23c and the inner peripheral surface shape of the heat insulating material H are different, the hollow It can be recognized that the part V is provided. When the outer peripheral surface of the inner side wall portion 23c has a surface shape along the inner peripheral surface of the heat insulator H, that is, the outer peripheral surface shape of the inner side wall portion 23c and the inner peripheral surface shape of the heat insulator H are the same, Even when these surfaces are arranged in parallel at a certain distance (for example, 5 mm or more), it can be recognized that the cavity V is provided instead of the gap generated due to the dimensional tolerance.

The aperture radius r _s of the heat shield member 20, the shortest distance from the center axis of the heat shield member 20 which coincides with the crystal pulling axis 3z to the outer surface of the inner side wall portion 23c. Further, the opening radius r _h of the insulating material H, the shortest distance from the center axis of the heat shield member 20 to an inner side surface of the heat insulating material H. The difference between the opening radius r _h of the opening radius r _s and the heat insulating material H of the heat shield member 20 is at least 15 mm, preferably from the viewpoint of the enlargement of the pulling rate margin is 25mm or more, and particularly not less 70mm or more preferable. Also from the viewpoint of preventing dislocation and an increase in single crystal 3 of the heat load on the quartz crucible 11, the difference between the opening radius r _h of the opening radius r _s and the heat insulating material H of the heat shield member 20 is less than 200mm Is preferable, and it is particularly preferable that it is 150 mm or less.

In conventional heat shielding member 20, wall material 21 covering the heat insulating material H is merely the outer wall member for preventing the falling of the heat insulating material H, the heat insulating material H without changing the aperture radius r _s of the heat shield member 20 the idea that only the larger aperture radius r _h of did not exist until now. However, by increasing the opening diameter of the heat insulating material H and providing the cavity V inside the tip of the bulging portion 23 as in the present embodiment, the temperature gradient G in the crystal in the radial direction is made closer to the ideal temperature gradient G _ideal . Thus, the lifting speed margin can be increased.

  In the present embodiment, a substantially V-shaped concave portion 30 is formed in a sectional view on the outer surface of the inner side wall portion 23c which is the inner peripheral surface of the bulging portion 23 of the heat shielding member 20. Thus, the outer surface of the inner side wall 23c has a downward inclined surface 30a provided above the inner side wall 23c and an upward inclined surface 30b provided below the inner side wall 23c. Here, the downward inclined surface refers to an inclined surface whose normal to the direction of the silicon single crystal 3 is downward. In addition, the upward inclined surface refers to an inclined surface in which the direction of the normal to the direction of the silicon single crystal 3 is upward.

As described above, when the tip portion of the bulging portion 23 is hollowed, the tip portion is likely to be heated to a high temperature, and further, the concave portion 30 is formed on the inner peripheral surface of the bulging portion 23 of the heat shielding member 20 to face downward. When the inclined surface 30a is provided, the area of the inner side wall 23c seen from the center of the single crystal 3 increases, so that the heat input to the silicon single crystal 3 can be increased, and the radial direction of the silicon single crystal 3 can be increased. Can be made closer to the ideal temperature gradient G _ideal . Therefore, the radial distribution of crystal defects can be flattened, and the crystal pulling speed margin can be increased.

  The depth d of the concave portion 30 provided on the inner peripheral surface of the bulging portion 23 of the heat shielding member 20 is preferably 10 mm to 30 mm. If the depth of the concave portion 30 is less than 10 mm, the effect of providing the concave portion 30 cannot be obtained, and if the depth of the concave portion 30 is deeper than 30 mm, the effect of providing the concave portion 30 becomes weak. is there.

In the present embodiment, the height h ₁ of the downward slope surface 30a is preferably greater than the height h ₂ of the upward inclined surface 30b. In this way, by making the downward inclined surface 30a relatively wide, the temperature gradient G in the radial direction of the silicon single crystal 3 can be made closer to the ideal temperature gradient G _ideal .

  In the present embodiment, the cross-sectional shape of the concave portion 30 is substantially V-shaped, and the downward inclined surface 30a and the upward inclined surface 30b are both flat surfaces, but the cross-sectional shape of the concave portion 30 is substantially C-shaped. Is also good. Further, in the present embodiment, the thickness of the inner side wall portion 23c is substantially constant, but the thickness of the inner side wall portion 23c may change along the height direction.

  FIGS. 6A to 6E are schematic cross-sectional views showing variations of the shape of the bulging portion 23 of the heat shielding member 20.

  In the heat shielding member 20 shown in FIGS. 6A and 6B, the cross-sectional shape of the concave portion 30 formed in the inner peripheral surface of the bulging portion 23 is substantially V-shaped, and the downward inclined surface 30 a and the upward The inclined surface 30b forms a flat surface.

Among them, heat-shielding member 20 shown in FIG. 6 (a) is the same as FIG. 5 (a), the case where the height h ₁ of the downward slope surface 30a is larger than the height h ₂ of the upward inclined surface 30b It is. Therefore, the inclination angle theta ₁ downward inclined surface 30a with respect to the vertical plane is smaller than the inclination angle theta ₂ of the downward slope surface 30b.

Figure 6 heat shield member 20 (b) is a case where the height _{h 1} of the downward slope surface 30a is smaller than the height _{h 2} of the upward inclined surface 30b. Therefore, the inclination angle theta ₁ downward inclined surface 30a with respect to the vertical plane is greater than the inclination angle theta ₂ of the downward slope surface 30b.

Although not shown, the height h ₂ of height h ₁ and the upward inclined surface 30b of the downwardly inclined surface 30a may be the same. In this case, the inclination angle theta ₁ downward inclined surface 30a with respect to the vertical plane is the same as the inclination angle theta ₂ of the downward slope surface 30b.

  In the heat shielding member 20 shown in FIGS. 6C and 6D, the cross-sectional shape of the concave portion 30 formed on the inner peripheral surface of the bulging portion 23 is substantially C-shaped, and the downward inclined surface 30a and the upward inclined surface 30a are formed. The inclined surface 30b forms a curved surface.

Among them, heat-shielding member 20 in FIG. 6 (c) is a case where the height _{h 1} of the downward slope surface 30a is larger than the height _{h 2} of the upward inclined surface 30b. The heat shield member 20 in FIG. 6 (d) is a case where the height _{h 1} of the downward slope surface 30a is smaller than the height _{h 2} of the upward inclined surface 30b. Although not shown, the height h ₂ of height h ₁ and the upward inclined surface 30b of the downwardly inclined surface 30a may be the same.

  In the heat shielding member 20 shown in FIG. 6E, the thickness of the inner side wall portion 23c constituting the inner peripheral surface of the bulging portion 23 is not constant, and the concave portion 30 is provided on the outer surface of the inner side wall portion 23c. In contrast, the point is that the inner surface of the inner side wall portion 23c is a flat surface (vertical surface). Also in this case, the inner surface of the inner side wall portion 23c is not in contact with the heat insulating material H, so that a cavity V is provided between the inner side wall portion 23c and the heat insulating material H.

  FIGS. 7A to 7D are diagrams for comparing a lifting speed margin obtained when the heat shielding member 20 according to the present embodiment is used with a conventional heat shielding member, and FIG. (B) shows the conventional crystal defect distribution, (c) shows the structure of the heat shielding member according to the present embodiment, and (d) shows the crystal defect distribution according to the present embodiment.

  When the conventional heat shielding member shown in FIG. 7A is used, the radial distribution of crystal defects varies largely in the plane as shown in FIG. 7B, so that the pulling speed margin Vmgn becomes narrow. . However, when the heat shielding member according to the present embodiment shown in FIG. 7C is used, the radial distribution of crystal defects is flattened as shown in FIG. However, the pulling speed margin Vmgn can be made wider than before.

  As described above, the single crystal pulling apparatus 1 according to the present embodiment includes the heat shielding member 20 surrounding the silicon single crystal 3 pulled up from the silicon melt 2, and the tip of the bulging portion 23 of the heat shielding member 20. Since the hollow portion V is provided inside the portion and the concave portion 30 including the downward inclined surface 30a is formed on the inner peripheral surface of the bulging portion 23, the temperature gradient in the radial direction of the single crystal is reduced to the optimum temperature gradient distribution. Can be approached. Therefore, the manufacturing yield of defect-free crystals can be increased by increasing the pulling speed margin Vmgn.

  As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that they are included in the range.

  For example, in the above embodiment, the heat radiating member used for pulling a silicon single crystal has been described as an example, but the application of the heat radiating member according to the present invention is not limited to pulling a silicon single crystal. It can be used for pulling crystals.

  The influence of the shape of the bulging portion of the heat shielding member on the lifting speed margin was examined. First, the lifting speed margin when using the heat shielding member according to the comparative example in which the inner peripheral surface of the bulging portion was a vertical surface and no cavity was formed inside the bulging portion was evaluated by point defect simulation. Then, the lifting speed margin of the comparative example was set as a reference value ("1").

  Next, a heat shield according to the first embodiment having the same structure as that of the comparative example except that a hollow portion is provided inside the distal end portion of the bulging portion and a substantially V-shaped concave portion is formed on the inner peripheral surface of the bulging portion. The lifting speed margin when the member was used was evaluated by a point defect simulation. As a result, as shown in Table 1, the lifting speed margin of Example 1 in which the substantially V-shaped concave portion was formed was 1.33 times that of the comparative example, which was a better result than the comparative example.

  Next, a heat shield according to the second embodiment having the same structure as that of the comparative example except that a hollow portion is provided inside the distal end portion of the bulging portion and a substantially C-shaped concave portion is formed on the inner peripheral surface of the bulging portion. The lifting speed margin when the member was used was evaluated by a point defect simulation. As a result, as shown in Table 1, the lifting speed margin of Example 2 in which the substantially C-shaped concave portion was formed was 1.25 times, which was a better result than the comparative example.

  The influence of the difference in the shape of the substantially V-shaped recess formed on the inner peripheral surface of the bulging portion of the heat shielding member on the temperature of the single crystal was examined. More specifically, the radiant heat received by the single crystal when the coordinates of the apex (point C) of the slope for forming the downward slope and the downward slope on the inner peripheral surface of the bulging portion of the heat shielding member are changed, respectively. Was evaluated. The origin (point O) of the coordinates of point C is the lower end of the bulging portion of the heat shielding member.

  FIG. 8 is a diagram illustrating the shape of the concave portion of the bulging portion of the heat shielding member according to Examples 3 to 6, and particularly illustrating a difference in the position of the vertex (point C) of the inclination of the concave portion.

As shown in FIG. 8, the third embodiment, when than the height h ₁ of the downward slope surface greater towards the height h ₂ of the upward inclined surface, the fourth embodiment, the depth of the recess than Example 3 If the d is deeper as 15 mm, example 5, when more of the height h ₂ of the upward sloping surface than the height h ₁ of the downward inclined surface is small, example 6, a concave portion than in example 5 Is deeper by about 15 mm.

  FIG. 9 is a graph showing the results of heat transfer calculations (point defect simulations) of Examples 3 to 6, in which the vertical axis represents the amount of radiant heat received by the crystal outer peripheral surface 150 mm above the melt surface. .) Is a relative value when the heat input is 1.

  As shown in FIG. 9, when a substantially V-shaped concave portion was provided on the inner peripheral surface of the bulging portion of the heat shielding member, the amount of radiant heat increased as compared with the comparative example (Ref.) In which the concave portion was not provided. . In particular, Example 6> Example 4, Example 5> Example 3, and it can be seen that the amount of radiant heat increases by making the height of the downward inclined surface larger than the height of the upward inclined surface. Thus, it was found that the amount of heat input to the single crystal can be increased by changing the shape of the inner peripheral surface of the bulging portion of the heat shielding member.

  Next, the pulling speed margins of Examples 3 to 6 were calculated from the results of the heat transfer calculation. As a result, as shown in FIG. 10, the pulling speed margin was improved as compared with the comparative example (Ref.). In particular, Example 6> Example 4, Example 5> Example 3, and it can be seen that the lifting speed margin increases by making the height of the downward inclined surface larger than the height of the upward inclined surface.

Reference Signs List 1 single crystal pulling device 2 silicon melt 3 silicon single crystal 3a neck 3b shoulder 3c body 3d tail 3z crystal pulling shaft 10 chamber 10a main chamber 10b pull chamber 10c gas inlet 10d gas outlet 10e viewing window 11 quartz Crucible 12 Graphite crucible 13 Rotary shaft 14 Shaft drive mechanism 15 Heater 16 Insulating material 17a Gap 18 between silicon single crystal and heat shield member 18 Wire 19 Wire take-up mechanism 20 Heat shield member 20a Opening of heat shield member 21 Heat shield member The wall material 22 of the tubular portion 22a The inner wall portion 22b of the tubular portion The outer wall portion 23 of the tubular portion The bulging portion 23a The upper wall portion 23b of the bulging portion The bottom wall portion 23c of the bulging portion The inner side wall portion 23d of the bulging portion The bulging portion Outer side wall 30 Recess 30a Downward inclined surface 30b Upward inclined surface H Cavity

Claims (8)

A heat shielding member used in a single crystal pulling apparatus by the Czochralski method,
A cylindrical tubular portion surrounding the single crystal pulled up from the melt,
An annular bulge protruding radially inward from the lower end of the cylindrical portion,
The bulging portion has an annular heat insulating material and a wall material surrounding the heat insulating material,
The wall material has an inner side wall portion covering an inner peripheral surface of the heat insulating material,
A cavity is provided between the inner side wall and the inner peripheral surface of the heat insulating material,
A heat shielding member, wherein a concave portion is formed on the outer surface of the inner side wall portion facing the outer peripheral surface of the single crystal, and the outer surface of the inner side wall portion has a downward inclined surface.   The heat shielding member according to claim 1, wherein the outer surface of the inner side wall further includes an upwardly inclined surface disposed below the downwardly inclined surface.   The heat shielding member according to claim 2, wherein the height of the downward inclined surface is larger than the height of the upward inclined surface.   The heat shielding member according to claim 2, wherein a cross-sectional shape of the concave portion is substantially V-shaped, and the downward inclined surface and the upward inclined surface are flat surfaces.   The heat shielding member according to claim 2, wherein a cross-sectional shape of the concave portion is substantially C-shaped, and the downward inclined surface and the upward inclined surface are curved surfaces.   The wall material further includes an upper wall portion covering an upper surface of the heat insulating material, a bottom wall portion covering a bottom surface of the heat insulating material, and an outer side wall portion covering an outer peripheral surface of the heat insulating material. The heat shielding member according to any one of the above.   A chamber, a crucible for supporting the melt in the chamber, a heater for heating the melt, a crucible drive mechanism for rotating and lifting the crucible, and a single crystal pulling mechanism for pulling the single crystal from the melt And a heat shielding member according to any one of claims 1 to 6, which is provided above the melt and surrounds the single crystal pulled up from the melt to shield radiant heat from the heater. A single crystal pulling apparatus comprising:   A method for producing a single crystal by a Czochralski method of pulling a single crystal from a melt in a crucible, wherein the single crystal pulled from the melt using the heat shielding member according to any one of claims 1 to 6. A method for producing a single crystal, comprising surrounding a crystal.

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