JP2023079428A - Single crystal pulling apparatus - Google Patents

Abstract

To provide a single crystal pulling apparatus capable of suppressing the deformation of a lower heater.SOLUTION: A single crystal pulling apparatus includes: a graphite crucible 4 for holding a quartz crucible 3 for storing a raw material melt 11; a pedestal 5 for elevatably holding the graphite crucible 4; and a lower heater 9 arranged in the lower part of the graphite crucible 4. The lower heater 9 is constituted of: an electrode clamp connected and fixed to an electrode 10 extending from the lower part of the single crystal pulling apparatus 1; and a heating part having an annular member surrounding the central shaft of the pedestal 5 connected and fixed to the electrode clamp and having a heater pattern formed in the annular member, and the electrode clamp consists of a material having a coefficient of thermal expansion smaller than that of the material of the heating part.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an apparatus for pulling a silicon single crystal used, for example, as a semiconductor substrate, and more particularly, to an apparatus for pulling a single crystal having a lower heater for heating the bottom of a crucible containing raw material melt.

Semiconductors such as silicon and gallium arsenide are composed of single crystals and are used for memory devices of small to large computers, and there is a demand for large-capacity, low-cost, and high-quality storage devices.

The Czochralski method, which is the main method of manufacturing silicon single crystals, melts the silicon raw material in a quartz crucible to form a melt (raw material melt), brings the seed crystal into contact with it, and pulls it up while rotating it. This is a manufacturing method for obtaining a single crystal. At present, the magnetic field application CZ method (MCZ method), in which a magnetic field is applied to the melt to suppress convection, is mainly used for manufacturing large crystals with a diameter of 300 mm or more.

In a general silicon single crystal pulling apparatus, a raw material melt is stored inside a quartz crucible, and the quartz crucible is held by a graphite crucible. Furthermore, the graphite crucible is held by a pedestal that can be raised and lowered in the vertical direction. A resistance heating heater made of graphite is used for melting the polysilicon raw material and keeping the temperature of the raw material melt. In general, a cylindrical heater placed on the side of the graphite crucible is used. A heater may be used.

Heater materials used in silicon single crystal pulling equipment include isotropic graphite material (CIP material) formed by cold isostatic pressing (CIP) and carbon fiber reinforced carbon composite material (C/ C composite material). Compared to isotropic graphite, carbon fiber reinforced carbon composites have higher strength, higher thermal conductivity, and a lower coefficient of thermal expansion (thermal expansion coefficient), so they have superior properties as heater materials. In general, the coefficient of linear thermal expansion of isotropic graphite material is about 5 × 10 ^-6 /K, whereas the carbon fiber reinforced carbon composite material has a coefficient of linear thermal expansion of 1 × 10 ^-6 /K in the direction parallel to the laminated surface. is less than However, carbon fiber reinforced carbon composite materials are much more expensive than isotropic graphite materials, and are difficult to process into complicated shapes. Therefore, isotropic graphite materials are generally used for heaters.

Here, a conventional lower heater is shown in FIG. As shown in FIG. 5, the lower heater 99 has a structure comprising an annular heating portion 991 and two electrode clamps 992 extending from the heating portion 991 . The central axis of the pedestal passes through the ring of the heat generating portion 991 . Holes are formed at the tips of the two electrode clamps 992, and are connected and fixed to electrodes extending from the lower part of the single crystal pulling device through the holes. The inside of the furnace is heated by being heated.

In the structure of FIG. 5, the ends of the two electrode clamps are fixed by connecting them to the electrodes, so that the lower heater, which has reached a high temperature, cannot freely thermally expand, generating thermal stress. Graphite material has the property that strain remains even after the stress is removed, and once deformation due to thermal stress occurs in a high temperature state, the deformation cannot be completely restored even in a cold state. Creep deformation also progresses when stress is continuously applied at high temperature. Due to these factors, the lower heater gradually deforms with use. As the deformation progresses, the dimensions do not match, making it impossible to connect the lower heater to the electrode connection portion, and the lower heater becomes unusable in a shorter time than the original service life, resulting in an increase in cost.

At the bottom of the graphite crucible facing the lower heater, molded carbon fiber insulation is often placed in order to reduce power consumption during operation, which tends to cause the lower heater to become hot. Also, in order to precisely control the heating range of the lower heater, the heat generating portion may be limited to the vicinity of the center of the bottom of the crucible. In this case, since there are spatial restrictions on the placement of the lower heater, it is difficult to increase the surface area of the heat-generating part compared to a cylindrical heater placed facing the side of the graphite crucible. increases, the lower heater tends to reach a high temperature. When the temperature of the lower heater rises due to these factors, a larger thermal stress is generated, and deformation progresses more easily.

As a prior art related to heater deformation, Patent Document 1 discloses a CZ crystal manufacturing apparatus characterized by supporting a graphite heater with a heater support made up of a heat-resistant member and an electrical insulating member.
Further, Patent Document 2 discloses a graphite heater characterized by grooves formed along the longitudinal direction of the resistance heating portion.

JP-A-10-167876 JP 2014-062004 A

Patent Literature 1 aims at suppressing vertical deformation due to the weight of the heater, and cannot cope with horizontal deformation caused by thermal expansion as described above. In addition, there is also the problem that the heat generated by the heater tends to diffuse through the heater support, so it cannot be said to be a desirable solution.
In Patent Document 2, since the number of resistance heating portions can be reduced and the thickness of each resistance heating portion can be increased, the strength of the heater can be increased against deflection due to increased weight. However, since the magnitude of thermal stress generated by inhibition of thermal expansion in the horizontal direction is the same regardless of the presence or absence of the grooves, even the technique of Patent Document 2 cannot prevent the deformation of the lower heater described above. it is conceivable that.

In this way, the actual situation is that there are few prior arts that attempt to solve the deformation of the lower heater in the horizontal direction. It is thought that this is a new problem that has arisen in recent years due to the increase in the size of the lifting equipment and the progress in the control of the heating distribution and the structure of the furnace with enhanced heat insulation for power saving. be done.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a single crystal pulling apparatus capable of suppressing deformation of the lower heater.

In order to achieve the above object, the present invention provides a graphite crucible holding a quartz crucible for storing raw material melt, a pedestal holding the graphite crucible so that it can be raised and lowered, and a lower heater arranged below the graphite crucible. A single crystal pulling apparatus comprising:
The lower heater is
an electrode clamp connected and fixed to an electrode extending from the bottom of the single crystal pulling apparatus;
a heat-generating portion having an annular member surrounding the central axis of the pedestal connected and fixed to the electrode clamp, and a heater pattern formed in the annular member;
The single crystal pulling apparatus is provided, wherein the electrode clamp is made of a material having a smaller thermal expansion coefficient than the material of the heat generating portion.

With such a single crystal pulling apparatus of the present invention, the thermal expansion of the electrode clamp can be reduced compared to the case where the electrode clamp is also formed of the same material as the heat generating portion, and the thermal stress of the entire lower heater can be reduced. can be mitigated. As a result, the deformation of the lower heater can be prevented, so that the service life of the lower heater can be extended and the cost can be reduced.
Moreover, since the use of more expensive materials with a low coefficient of thermal expansion can be minimized by confining it to the electrode clamp, an increase in material costs can also be minimized.

Here, the annular member of the heat generating portion may be flat.
Alternatively, the annular member of the heat generating portion may be cylindrical.
Alternatively, the annular member of the heating portion may have a cylindrical portion and a flat plate-like ring portion located on the side opposite to the side of the cylindrical portion connected and fixed to the electrode clamp.

Even if the annular member of the heating portion is a lower heater having these forms, the relationship between the materials of the heating portion and the electrode clamp can be made as described above, and the effect of preventing deformation of the lower heater can be obtained. can.

Further, the heat generating portion may be connected and fixed to the electrode clamp with a bolt.

With such a structure, the heat-generating part and the electrode clamp can be firmly connected, so that it is possible to prevent heat generation due to contact resistance at the connecting part.

Further, the material of the electrode clamp can be a carbon fiber reinforced carbon composite material.

By forming the electrode clamp, which can be easily processed, from a carbon fiber-reinforced carbon composite material in this way, it is possible to efficiently prevent deformation of the lower heater while suppressing the manufacturing cost of the lower heater.

Further, the material of the heat generating portion can be an isotropic graphite material.

By using the isotropic graphite as the material for the heat generating portion having the heater pattern, it is relatively easy to process and the heater pattern can be easily formed.

According to the single crystal pulling apparatus of the present invention, the thermal expansion of the electrode clamp is alleviated while suppressing an increase in material cost, so that the thermal stress generated in the entire lower heater can be alleviated. As a result, deformation that progresses with use of the lower heater can be suppressed, and the life of the lower heater can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the single-crystal pulling apparatus of this invention. FIG. 2 is a structural diagram showing an example of a first form of structure of a lower heater; FIG. 4 is a structural diagram showing an example of a second embodiment of the structure of the lower heater; FIG. 4 is a structural diagram showing an example of a third embodiment of the structure of the lower heater; FIG. 10 is a top view showing an example of a conventional lower heater;

The present invention will be described in more detail below, but the present invention is not limited to these.
FIG. 1 shows an example of a single crystal pulling apparatus (hereinafter also referred to as a pulling apparatus) of the present invention. This single crystal pulling apparatus 1 includes a quartz crucible 3 on the central axis of a pulling furnace 2, a graphite crucible 4 holding the quartz crucible 3, and a pedestal 5 holding the graphite crucible 4 vertically and rotatably. I have more. A wire 7 having a seed crystal 6 held at its tip is suspended above the quartz crucible 3 so as to be able to move up and down.
The cylindrical heater 8 and the lower heater 9 are each connected and fixed to an electrode 10 extending from the lower part of the pulling device 1 (more specifically, the pulling furnace 2), and are supplied with power from a power supply (not shown). By doing so, resistance heating is performed. A raw material contained in the quartz crucible 3 (here, polysilicon raw material is taken as an example to pull up a silicon single crystal) is heated by a cylindrical heater 8 and a lower heater 9 to form a raw material melt 11. be. Furthermore, a magnetic field generator 12 having a superconducting coil is provided around the pulling furnace 2, and a magnetic field is applied to the raw material melt 11 by energizing the superconducting coil, thereby suppressing melt convection.
In this state, the seed crystal 6 is gently brought into contact with the raw material melt 11 and then raised, thereby growing the silicon single crystal 13 while pulling it up.

(first form)
FIG. 2 shows an example of the structure of the lower heater 9 according to the invention. FIG. 2 is a top view. The lower heater 9 mainly consists of a heating portion 91 and an electrode clamp 92 .
First, the heat generating portion 91 will be described. The heat generating portion 91 has an annular member 91A, which has a flat plate shape in the example shown in FIG. In order to heat the bottom of the graphite crucible 4, a hole H1 is provided in the center of the annular member 91A, and the central axis of the pedestal 5 is placed through the hole H1. A heater pattern 91B is formed on the annular member 91A. The heater pattern 91B is designed by forming linear or curved slits in the horizontal direction so as to have appropriate heater resistance and heat generation distribution. In FIG. 2, the heater pattern 91B is formed by zigzag (alternately) forming linear slits from the inner peripheral side and the outer peripheral side of the annular member 91A.

The electrode clamp 92 is a structure for connecting the heating portion 91 and the electrode 10 . Here, two linear flat plate-like electrode clamps 92 are arranged so as to face each other across a hole H1 of an annular member 91A of the heating portion 91 . For the connection with the electrodes 10, for example, as shown in FIG. Various methods can be used, such as connecting and fixing the electrode clamp 92 by sandwiching it with a bolt.

On the other hand, the other end of each electrode clamp 92 and the annular member 91A of the heat generating portion 91 are connected (fastened) by, for example, bolts 93. In this case, the heat generating portion 91 must be firmly fixed to the electrode clamp 92. and heat generation due to contact resistance can be suppressed. Moreover, it is also possible to fix with an adhesive without using a fastening part such as a bolt, or to fasten by combining the fastening part and an adhesive. When bolts 93 are used for fastening as shown in FIG. 2, shear stress is applied when thermal expansion occurs. As for the material of the bolt 93 , it is desirable to use the same material as that of the heating portion 91 or the electrode clamp 92 in order to match the thermal expansion coefficient with that of the heating portion 91 or the electrode clamp 92 .

In FIG. 2, the number of the electrode clamps 92 and the number of electrodes 10 connected and fixed thereto is two, but in order to be suitably used in a three-phase AC power supply, the number may be three, or the number may be four or more. good. Moreover, the shape of the electrode clamp 92 is preferably designed to have a cross-sectional area larger than that of the heat generating portion 91 in order to concentrate heat generation on the heat generating portion 91 .

In the prior art, the electrode clamp was often integrally formed of the same material as the heating portion (see FIG. 5). However, according to the present invention, the electrode clamp 92 is made of a material having a smaller thermal expansion coefficient than the material of the heat generating portion 91 . By using a material for the electrode clamp 92 whose thermal expansion coefficient is smaller than that of the heat generating portion 91, the thermal stress applied to the heat generating portion 91 can be reduced. In comparison, deformation of the lower heater 9 can be suppressed.
By using a relatively expensive material with a lower coefficient of thermal expansion only for the electrode clamp 92 portion, it is possible to prevent the cost of the lower heater 9 from increasing while achieving the excellent effect of preventing deformation as described above. is.
For example, an isotropic graphite material that is advantageous in terms of processing and cost can be used for the heat generating part 91, and a carbon fiber reinforced carbon composite material or the like that has a smaller thermal expansion coefficient and is less likely to deform can be selected for the electrode clamp 92. can be done. Naturally, the material of the heat generating portion 91 and the material of the electrode clamp 92 are not limited to this combination, and any combination of the material of the electrode clamp 92 having a smaller coefficient of thermal expansion may be used.

By the way, when a carbon fiber reinforced carbon composite material is used as the material of the lower heater for the whole heater including the heating part and the electrode clamps, the coefficient of linear thermal expansion is less than 1/5 of the isotropic graphite material. However, since the carbon fiber reinforced carbon composite material is an expensive material, an increase in parts procurement costs is unavoidable. In addition, since it is more difficult to process intricately and precisely than isotropic graphite materials, it may not be possible to manufacture depending on the shape, and even if it is possible to manufacture it, the cost will increase further, so it is not a desirable solution. do not have. In particular, a heat-generating portion with a heater pattern tends to have a complicated shape.
Therefore, considering feasibility and cost, it is extremely effective to use different materials for the heating portion 91 and the electrode clamp 92 as in the present invention.

When using a carbon fiber reinforced carbon composite material for the electrode clamp 92, if the electrode clamp 92 is manufactured so that the thickness direction (vertical direction) of the electrode clamp 92 and the stacking direction of the carbon fiber reinforced carbon composite material match, The horizontal thermal expansion coefficient, which is a problem, can be reduced.

Further, it is more desirable that the electrodes 10 connected to the electrode clamps 92 of the lower heater 9 can move up and down in the vertical direction. In the manufacturing process of the silicon single crystal 13 , the graphite crucible 4 is operated while its vertical position is finely adjusted by the pedestal 5 . If the electrode 10 on which the lower heater 9 is placed can move up and down in accordance with the graphite crucible 4, heat can be transferred to the graphite crucible 4 more efficiently, which is advantageous for controlling the heat distribution in the furnace.

(Second form)
FIG. 3 shows an example of another construction of the lower heater according to the invention. The drawing on the left side of FIG. 3 is a top view. The drawing on the right side is a cross-sectional view taken along line AA of the top view, but for reference, the inner peripheral surface of a cylindrical annular member is shown as a partial side view for the hole for the pedestal in the central portion. ing.
The heat generating portion 191 of the lower heater 19 (heat generating portion 191, electrode clamp 192) has a cylindrical annular member 191A in which a heater pattern 191B is formed by upper and lower slits. It is arranged so that the central axis of the pedestal 5 passes through the central hole of the annular member 191A.
This shape is effective when heating a narrower area near the center of the graphite crucible 4 .

(Third form)
FIG. 4 shows yet another structural example of the lower heater according to the invention. The drawing on the left side of FIG. 4 is a top view. The drawing on the right side is a cross-sectional view taken along the line BB of the top view, but for reference, the inner peripheral surface of the cylindrical portion is shown as a partial side view of the hole for the pedestal in the central portion.
An annular member 291A of the heat generating portion 291 of the lower heater 29 (heat generating portion 291, electrode clamp 292) has a cylindrical portion 291C and a plate-like ring portion 291D on which a heater pattern 291B is formed. The central axis of the pedestal 5 is arranged to pass through the central hole of the cylindrical portion 291C and the central hole of the ring portion 291D. One end (lower end) of the cylindrical portion 291C is connected and fixed to the electrode clamp 292, and the ring portion 291D is positioned at the other end (upper end) of the cylindrical portion 291C.
Vertical slits are formed in the cylindrical portion 291C, and horizontal slits are formed in the ring portion 291D, thereby forming a three-dimensional heater pattern 291B between the cylindrical portion 291C and the ring portion 291D. It is

As described above, the shape of the second embodiment shown in FIG. 3 is effective when heating a narrower range near the center of the graphite crucible 4, but the surface area of the heating portion is less than that of the first embodiment shown in FIG. tend to be smaller. Therefore, in order to prevent the temperature of the lower heater from becoming excessively high, a third mode as shown in FIG. 4 can be employed. As shown in FIG. 4, the cylindrical portion 291C may be integrally formed with a flat plate-like ring portion 291D positioned at the upper end thereof. Alternatively, a separate cylindrical member and a plate-like ring-shaped member may be combined and integrated by bonding or the like.

It should be noted that the configuration of the electrode clamps 192, 292 is basically the same as that of the electrode clamp 92 in the case of the first embodiment shown in FIG. 2 in both the second embodiment and the third embodiment. However, since the length of the electrode clamp is longer in FIGS. 3 and 4 than in FIG. 2, the effect of suppressing deformation obtained by using a material with a small thermal expansion coefficient for the electrode clamp is higher than in FIG. becomes. Also, the method of connecting the heating portion and the electrode clamp is the same as in the case of FIG.

In manufacturing a silicon single crystal using such a single crystal pulling apparatus 1 of the present invention, the lower heater is used at an appropriate power and height position for each process.
For example, in the melting process of polysilicon raw material, it is desirable that the lower heaters 9, 19, 29 are used with electric power equal to or higher than that of the cylindrical heater 8. If the melting process is performed under the condition that the electric power of the lower heater is significantly lower than that of the cylindrical heater, the polysilicon raw material is preferentially melted from the position near the side of the quartz crucible, and unmelted portions tend to occur near the center. . In such a state, the unmelted raw materials become unbalanced, so that the raw materials rotate in the melt and come into contact with the graphite member existing directly above the melt, or the raw materials located on the lower side surface melt first. As a result, when the lower central portion is melted, the material positioned above may drop into the melt and the melt may scatter. Moreover, it takes a long time to complete the melting, which causes a decrease in productivity. For the same reason as above, it is desirable that the height position of the lower heater be as close to the graphite crucible as possible during melting.
In the pulling step after melting, the power and height position are appropriately determined according to the quality of the crystal to be pulled. For example, when manufacturing a single crystal with a low oxygen concentration, it is desirable to use a low power to melt the quartz crucible and suppress natural convection from the bottom of the crucible. If so, it is desirable to use a somewhat high power.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.
(Example 1)
Using the single crystal pulling apparatus of the present invention shown in FIG. 1, a polysilicon melt of 400 kg was formed in a quartz crucible with a diameter of 32 inches (800 mm), and a silicon single crystal with a diameter of 300 mm was pulled.
A lower heater having the structure shown in FIG. 2 was used, the heating portion was made of isotropic graphite material, and the electrode clamp was made of carbon fiber reinforced carbon composite material.
The heat-generating part was a plate-shaped annular member with an inner diameter of 240 mm, an outer diameter of 620 mm, and a thickness of 25 mm, and the electrode clamp was made up of two linear members with a length of 240 mm and a thickness of 30 mm. In addition, the bolts for fastening the heating part and the electrode clamp were made of isotropic graphite. The power of the lower heater was used while being changed to an appropriate value for each process.
The pulling of the silicon single crystal was repeated under the above conditions until the cumulative energization time of the lower heater reached about 800 hours. After that, when the shortest distance between the circumferences of the two holes (hole H2 for the electrode bolt) provided in the electrode clamp for connection with the electrode was measured during cold operation, the distance was 2 compared to before the lower heater was used. .1 mm contracted.

(Comparative example 1)
The lower heater used had a structure in which the heating part and the electrode clamp shown in FIG. 5 were integrally formed, and was made of isotropic graphite. A silicon single crystal was pulled repeatedly under the same conditions as in Example 1 using a single crystal pulling apparatus having the same configuration as in Example 1 except for the above. The shortest distance between the circumferences of the two holes in the electrode clamp was measured after the lower heater had been used until the cumulative energization time reached about 800 hours, and it was found to have shrunk by 4.8 mm compared to before the lower heater was used.

The shrinkage amount of the lower heater of Example 1 is about 44% of that of Comparative Example 1, and the electrode clamping as in Example 1 is preferable to using the isotropic graphite material for the entire lower heater as in Comparative Example. The use of a carbon fiber reinforced carbon composite material with a lower coefficient of thermal expansion in the lower heater suppresses the deformation of the lower heater. Since the carbon fiber reinforced carbon composite material is used only for the electrode clamp, the increase in cost is also suppressed.

In addition, this invention is not limited to the said embodiment. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present invention and produces similar effects is the present invention. It is included in the technical scope of the invention.

DESCRIPTION OF SYMBOLS 1... Single-crystal pulling apparatus of this invention, 2... Pulling furnace, 3... Quartz crucible,
4... graphite crucible, 5... pedestal, 6... seed crystal, 7... wire,
8... cylindrical heater, 9, 19, 29... lower heater, 10... electrode,
DESCRIPTION OF SYMBOLS 11... Raw material melt, 12... Magnetic field generator, 13... Silicon single crystal,
91, 191, 291... heat generating portion, 91A, 191A, 291A... annular member,
91B, 191B, 291B ... heater pattern,
92, 192, 292... electrode clamps, 93... bolts,
291C... Cylindrical part, 291D... Ring part,
H1... hole for pedestal, H2... hole for electrode bolt.

Claims (7)

A single crystal pulling apparatus comprising a graphite crucible holding a quartz crucible for storing a raw material melt, a pedestal holding the graphite crucible so that it can be raised and lowered, and a lower heater arranged below the graphite crucible,
The lower heater is
an electrode clamp connected and fixed to an electrode extending from the bottom of the single crystal pulling apparatus;
a heat-generating portion having an annular member surrounding the central axis of the pedestal connected and fixed to the electrode clamp, and a heater pattern formed in the annular member;
A single crystal pulling apparatus, wherein the electrode clamp is made of a material having a thermal expansion coefficient smaller than that of the material of the heat generating portion. 2. The apparatus for pulling a single crystal according to claim 1, wherein the annular member of said heating portion is flat. 2. The apparatus for pulling a single crystal according to claim 1, wherein the annular member of said heating portion is cylindrical. The annular member of the heating portion has a cylindrical portion and a flat plate-like ring portion located on the side opposite to the side of the cylindrical portion connected and fixed to the electrode clamp. Item 1. The apparatus for pulling a single crystal according to item 1. 5. The apparatus for pulling a single crystal according to claim 1, wherein the heating portion is connected and fixed to the electrode clamp with a bolt. 6. The apparatus for pulling a single crystal according to claim 1, wherein the material of said electrode clamp is a carbon fiber reinforced carbon composite material. 7. The apparatus for pulling a single crystal according to claim 1, wherein a material of said heat generating portion is an isotropic graphite material.

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