JP7264043B2 - Single crystal growth method and single crystal growth apparatus - Google Patents

Description

The present invention relates to a single crystal growing method and a single crystal growing apparatus for growing a single crystal by the Czochralski method.

A method called the Czochralski method (hereinafter referred to as the CZ method) is known as a method for producing single crystals such as silicon single crystals. In the CZ method, a single crystal is produced by placing a seed crystal on the liquid surface of a silicon melt in a crucible and lifting the seed crystal upward.

The type and distribution of crystal defects contained in the silicon single crystal manufactured by the CZ method are determined by the growth rate (pulling rate) V of the silicon single crystal and the crystal growth in the direction of the pulling axis near the crystal growth interface from the melting point to 1300 ° C. It is known to depend on the ratio V/G to the temperature gradient G.
When V/G is large, vacancies become excessive, and void defects, which are aggregates thereof, occur. A void defect 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 are generated due to their aggregates. Therefore, V/G must be strictly controlled in order to produce single crystals that do not contain COPs or dislocation clusters. At present, by controlling the crystal pulling speed V, silicon single crystals for 300 mm wafers free of COPs and dislocation clusters are mass-produced.

However, even a silicon wafer containing no COPs and dislocation clusters cut out from a silicon single crystal pulled by controlling V/G does not necessarily have a homogeneous surface on its entire surface and behaves differently when heat-treated. contains the region of For example, between the region where COPs occur and the region where dislocation clusters occur, there are three regions, the OSF region, the Pv region, and the Pi region, in descending order of V/G.

The OSF region contains OSF nuclei in an as-grown state, and when thermally oxidized at a high temperature of 1000 to 1200° C. for 1 to 10 hours, an OSF (Oxidation induced Stacking Fault) occurs. This is the area where The Pv region is a region in which oxygen precipitate nuclei are included in the as-grown state, and oxygen precipitates are likely to occur when two-step heat treatment at low temperature and high temperature is performed. The Pi region is a region that contains almost no oxygen precipitate nuclei in the as-grown state and is less likely to generate oxygen precipitates even when subjected to heat treatment.

As a method for producing a silicon single crystal with few crystal defects, for example, in Patent Document 1, a manufacturing apparatus having a cooling unit installed so as to surround the silicon crystal and a heating unit above it is used, and the crystal solidification temperature is set to 1300 to the crystal temperature. It is described that the cooling gradient to °C is set to 2 °C/mm or more, and then the crystal is pulled under the conditions that the holding area at the crystal temperature is 1200 °C or more and the solidification temperature or less is 200 mm or more. According to the method for producing a silicon single crystal described in Patent Document 1, it is possible to produce a CZ silicon single crystal having extremely few COP defects or dislocation defects and excellent device characteristics such as oxide film withstand voltage characteristics and PN junction leakage current characteristics. is possible.

Also, in Patent Document 2, while the ingot is growing, the temperature of the ingot should be adjusted so as not to cool any part of the ingot below the temperature T _A (e.g., 1050° C.) at which the agglomeration of intrinsic point defects in the ingot occurs. is described to grow single crystal silicon ingots substantially free of agglomerated intrinsic point defects by adjusting the . In this method, sufficient time is given for the single crystal to stay at a temperature higher than the temperature _TA at which the agglomeration reaction occurs, and the interstitial silicon atoms and vacancies are annihilated or outwardly diffused, at least to a certain extent. A monocrystalline silicon ingot having a diameter portion substantially free of agglomerated intrinsic point defects is grown.

JP-A-11-43396 Japanese Patent Publication No. 2003-517412

By the way, the diameter of the crystal is increasing, but as the diameter increases, the central portion of the crystal becomes more difficult to cool than the outer peripheral portion of the crystal, and the temperature gradient G in the crystal in the direction of the pulling axis becomes smaller. The distribution of the temperature gradient G within the cross section of the silicon single crystal perpendicular to the pulling axis direction tends to be uneven. As a result, the allowable range of V/G that allows the entire surface of the silicon single crystal cross section perpendicular to the pulling axis direction to be the Pv region or the Pi region becomes extremely narrow, and the control of the crystal pulling speed V suddenly becomes difficult. There is a problem of becoming

Therefore, an object of the present invention is to provide a permissible range (hereinafter referred to as "PvPi margin") of the crystal pulling speed V that allows the entire surface in the cross section of the silicon single crystal perpendicular to the pulling axis direction to become the Pv region or the Pi region. It is possible to increase the production yield of large-diameter silicon single crystals with a diameter of 300 mm or more that do not contain COPs and dislocation clusters, thereby improving the productivity of large-diameter silicon wafers that do not contain COPs and dislocation clusters and have a diameter of 300 mm or more. An object of the present invention is to provide a single crystal growth method and a single crystal growth apparatus capable of achieving this.

The present invention is suitable for producing large-diameter silicon single crystals with a diameter of 300 mm or more that do not contain COPs and dislocation clusters. This has the effect of increasing the production yield of silicon single crystals containing no clusters. Hereinafter, a silicon single crystal containing no COPs and dislocation clusters will be referred to as a defect-free silicon single crystal, and a silicon wafer containing no COPs and dislocation clusters will be referred to as a defect-free wafer.

A single crystal growing method of the present invention is a single crystal growing method for growing a silicon single crystal comprising a shoulder portion, a body portion and a tail portion by the Czochralski method, wherein the body portion of the silicon single crystal is pulled up. A pulling step, and during the pulling step, a cooling body installed to surround the silicon single crystal and promoting cooling of the silicon single crystal from the outer peripheral side of the silicon single crystal is moved up and down to perform the cooling. It is characterized by having a cooling body raising/lowering step for changing the distance between the lower end of the body and the liquid surface of the silicon melt.

In the cooling body raising/lowering step, it is preferable that the cooling body is lowered from a position at the start of pulling up the body (body starting position).

In the cooling body raising/lowering step, it is preferable that the cooling body is lowered from a position at the start of pulling up of the body portion and then raised.

In the single crystal growing method, in the pulling step, the body portion is pulled up in order of the top region, the middle region, and the bottom region. is smaller than the distance at the start of pulling up the body portion and the distance at the end of pulling up the body portion (preset end position of the body portion). .

In the single crystal growing method, in the cooling body elevating step, the cooling body is lowered at a lifting rate of the body portion of 20% to 30%, and the cooling body is raised at a lifting rate of the body portion of 70% to 90%. It is preferable to let
Here, the pulling rate of the body portion is defined as a position in the longitudinal direction of the crystal defined as 100% for the length of the body portion set in advance in the production of the single crystal and 0% for the start position of the body portion. is. Normally, when the single crystal is grown normally without troubles in the apparatus and without dislocations in the single crystal, the length of the grown body portion is the same as the preset length of the body portion. .

A single crystal growth apparatus of the present invention is a single crystal growth apparatus for growing a silicon single crystal comprising a shoulder portion, a body portion and a tail portion by the Czochralski method, comprising: a crucible for holding a silicon melt; a cooling body installed so as to surround a silicon single crystal, capable of moving up and down, and promoting cooling of the silicon single crystal from the outer peripheral side; and a controller controlling at least the cooling body, wherein the controller comprises and a cooling body control unit for moving the cooling body up and down to change the distance between the lower end of the cooling body and the liquid surface of the silicon melt.

In the above-described single crystal growth apparatus, if the body portion is pulled up in order of the top region, the middle region, and the bottom region, the cooling body control unit controls the cooling body and the silicon during the pulling of the middle region. The cooling body is moved up and down so that the distance from the liquid surface of the melt is smaller than the distance at the start of pulling up the body part and the distance at the end of pulling up the body part. is preferably controlled.

In the above-described single crystal growth apparatus, if the diameter of the silicon single crystal to be grown is D, the cooling body control unit controls the difference Hd between the highest position and the lowest position of the cooling body to be 0.1×D. It is preferable that the cooling body is moved up and down so as to satisfy <Hd.

In the above single crystal growth apparatus, the cooling body control unit lowers the cooling body at a lifting rate of the body portion of 20% to 30%, and raises the cooling body at a lifting rate of the body portion of 70% to 90%. It is preferable to raise and lower the cooling body so as to

In the single crystal growth apparatus, it is preferable that the cooling body is vertically divided into two, and that only the lower cooling body is moved up and down.

1 is a schematic cross-sectional view of a single crystal growth apparatus according to an embodiment of the present invention; FIG. FIG. 2 is an enlarged cross-sectional view of a single crystal growth apparatus around a silicon single crystal to be grown; It is a figure which shows the general relationship between V/G, and the kind and distribution of a crystal defect. It is a flow chart which shows the process of the single crystal growth method concerning the embodiment of the present invention. FIG. 6 is a schematic diagram for explaining the relationship between the pulling rate of the body portion and the distance between the second cooling body and the liquid surface of the silicon melt in a comparative example. FIG. 5 is a schematic diagram for explaining the relationship between the pulling rate of the body portion and the distance between the second cooling body and the liquid surface of the silicon melt in the example.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[Single crystal growth device]
FIG. 1 is a schematic cross-sectional view of a single crystal growth apparatus 1 according to an embodiment of the invention.
A single crystal growth apparatus 1 is an apparatus for pulling and growing a silicon single crystal S by the Czochralski method. As shown in FIG. 1, a single crystal growth apparatus 1 includes a water-cooled chamber 2 forming an outer shell, a crucible 3 arranged in the center of the chamber 2, a rotating shaft 4 supporting the crucible 3, a rotating It comprises a shaft driving mechanism 5 for rotating and raising and lowering the shaft 4 , a heater 6 , a heat shield 7 arranged above the crucible 3 , and a control device 8 .
Further, the single crystal growth apparatus 1 is installed so as to surround the silicon single crystal S to be grown, and has a cylindrical cooling body 12 ( water cooling body).

The chamber 2 is composed of a main chamber 10 and a cylindrical pull chamber 11 connected to an upper opening 10A of the main chamber 10 . The crucible 3 , heater 6 , thermal shield 7 and cooling body 12 are arranged inside the main chamber 10 .

The crucible 3 is a container in which the silicon melt M is stored and has a circular shape when viewed from above in the vertical direction. The crucible 3 has a double structure composed of an inner quartz crucible 3A and an outer graphite crucible 3B. The crucible 3 is fixed to the upper end of a vertically extending rotating shaft 4 that can rotate and move up and down. A lower end of the rotating shaft 4 is connected to a shaft driving mechanism 5 provided outside the chamber 2 through the bottom of the chamber 2 .

The heater 6 is a heating device that heats the silicon melt M in the crucible 3 . The heater 6 has a cylindrical shape and is arranged on the outer peripheral side of the crucible 3 . The heater 6 is a so-called carbon heater of a resistance heating type. A heat insulator 9 is provided outside the heater 6 along the inner surface of the chamber 2 .

Above the crucible 3, there are provided a wire 16, which is a shaft for pulling the silicon single crystal, and a wire winding mechanism 17 for winding the wire 16. As shown in FIG. The wire winding mechanism 17 has a function of rotating the silicon single crystal S together with the wire 16 .
The wire winding mechanism 17 is controlled by the controller 8 . A wire winding mechanism 17 is arranged above the pull chamber 11 . The wire 16 extends downward through the inside of the pull chamber 11 from the wire winding mechanism 17 , and the tip of the wire 16 reaches the internal space of the main chamber 10 .
FIG. 1 shows a state in which a silicon single crystal S in the middle of growth is suspended from a wire 16 . When the silicon single crystal S is pulled, the wire 16 is gradually pulled up while rotating the crucible 3 and the silicon single crystal S, respectively, to grow the silicon single crystal S.

The thermal shield 7 has a tubular shape and surrounds the silicon single crystal S being grown above the silicon melt M in the crucible 3 .
The heat shield 7 suppresses temperature fluctuations of the silicon melt M to form an appropriate thermal environment in the vicinity of the crystal growth interface, and prevents heating of the silicon single crystal S by radiant heat from the heater 6 and the crucible 3. is provided in The heat shield 7 is a substantially cylindrical member made of graphite, and is provided so as to cover the region above the silicon melt M except for the pulling path of the silicon single crystal S.

A gas introduction port 14 is provided in the pull chamber 11 . A gas inlet 14 introduces an inert gas such as argon gas into the chamber 2 . An exhaust port 15 is provided at the bottom of the main chamber 10 . The exhaust port 15 sucks and exhausts the gas in the chamber 2 by driving a vacuum pump (not shown). The inert gas introduced into the chamber 2 through the gas inlet 14 descends between the silicon single crystal S being grown and the thermal shield 7 . Next, the inert gas passes through the gap between the lower end of the heat shield 7 and the surface of the silicon melt M, and then flows outside the heat shield 7 and further outside the crucible 3 . After that, the inert gas descends outside the crucible 3 and is discharged from the exhaust port 15 .

The cooling body 12 forcibly cools the silicon single crystal S with a coolant such as water that is circulated inside. The cooling body 12 is made of, for example, a metal with good thermal conductivity such as copper, and the inner surface side thereof is blackened to increase heat absorption efficiency, and the outer surface side thereof can be chrome-plated.

The cooling body 12 promotes cooling of the silicon single crystal S during growth, thereby playing a role of controlling the intra-crystal temperature gradient G in the direction of the pulling axis of the single crystal central portion and the single crystal outer peripheral portion. Since the cooling body 12 absorbs heat from the outer peripheral portion of the silicon single crystal S, the portion where the silicon single crystal S and the cooling body 12 face each other is closer to the cooling body than the central portion of the silicon single crystal S. Strongly influenced by 12. On the other hand, in the portion where the silicon single crystal S and the cooling body 12 do not face each other, the central portion of the silicon single crystal S is affected by the cooling body 12 relatively more strongly than the outer peripheral portion of the silicon single crystal S. Therefore, by moving the cooling body 12 away from or closer to the vicinity of the crystal growth interface, it is possible to change the radial distribution of the crystal temperature gradient G in the pulling axis direction in the vicinity of the crystal growth interface.

The cooling body 12 is arranged on the outer peripheral side of the silicon single crystal S to be grown so as to surround the pulling path of the silicon single crystal S.
The cooling body 12 is composed of a first cooling body 12A connected to the upper opening 10A of the main chamber 10, and a second cooling body 12B arranged below the first cooling body 12A and movable up and down. That is, the cooling body 12 of this embodiment is vertically divided into two, and only the lower second cooling body 12B is configured to move up and down.

By dividing the cooling body 12 into two in the vertical direction and only the lower second cooling body 12B is configured to move up and down, even a lifting mechanism with a low lifting load capacity (for example, a lifting mechanism with a small motor) can operate the second cooling body. 12B can be lifted and lowered, the lifting mechanism can be made compact. In addition, the lower second cooling body 12B is arranged near the crystal growth interface from the melting point to 1300° C., which strongly affects the type and distribution of crystal defects in the silicon single crystal. Therefore, moving only the second cooling body 12B up and down to move it away from or closer to the crystal growth interface will affect the distribution of the temperature gradient G in the cross section of the silicon single crystal perpendicular to the pulling axis direction (radial direction within the crystal). is effective in controlling the defect distribution in the cross section (radial direction within the crystal).
The distance between the silicon single crystal S to be grown and the cooling body 12 is preferably small, and is appropriately determined in consideration of the diameter margin of the silicon single crystal S.

FIG. 2 is an enlarged cross-sectional view of the periphery of the silicon single crystal S to be grown. As shown in FIG. 2, where D is the diameter of the silicon single crystal S grown by the single crystal growth apparatus 1 and ID is the inner diameter of the first cooling body 12A and the second cooling body 12B, the first cooling body 12A and the second cooling body 12B have ID. The second cooling body 12B is formed to have an inner diameter ID of 1.05×D or more and 1.3×D or less. For example, the diameter D of the silicon single crystal S to be grown can be set to 310 mm, and the inner diameter ID of the cooling body 12 can be set to 350 mm. Note that the inner diameters of the first cooling body 12A and the second cooling body 12B do not need to be the same.

The second cooling body 12B can be vertically moved by an elevating mechanism (not shown). The elevating mechanism of the second cooling body 12B is controlled by the cooling body control section 8A of the control device 8. As shown in FIG.
The second cooling body 12B can move up and down between a position (upper end) that is as close as possible to the first cooling body 12A and a position (lower end) that is as close as possible to the liquid surface MA of the silicon melt M. By raising and lowering the second cooling body 12B, the portion of the silicon single crystal S to be cooled can be changed.
The elevating mechanism for the second cooling body 12B can be composed of, for example, a mechanism consisting of a rack, a pinion, and a motor, or a direct-acting cylinder.

The controller 8 raises the crucible 3 by controlling the shaft driving mechanism 5 so that the distance G1 (gap) between the liquid surface MA of the silicon melt M and the lower end of the heat shield 7 is constant. That is, even if the amount of the silicon melt M in the crucible 3 decreases as the silicon single crystal S grows, the distance G1 is kept constant.
As a result, the temperature fluctuation of the silicon melt M can be suppressed, and the amount of evaporation of the dopant from the silicon melt M can be controlled by keeping the flow velocity of the inert gas flowing near the liquid surface MA constant. Therefore, the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the direction of the pulling axis of the silicon single crystal S can be improved.

Assuming that the height of the first cooling body 12A is H1, the first cooling body 12A is formed so that 0.9×D<H1<1.5×D. Similarly, when the height of the second cooling body 12B is H2, the second cooling body 12B is formed so that 0.9×D<H2<1.5×D.
The height H2 of the second cooling body 12B is preferably smaller than the height H1 of the first cooling body 12A.
Further, the first cooling body 12A and the second cooling body 12B are preferably formed so that 2×G1<ST<4×G1, where ST is the vertical stroke of the second cooling body 12B. . In other words, first cooling body 12A and second cooling body 12B are such that when second cooling body 12B is at the highest position, the distance between the lower end of second cooling body 12B and liquid surface MA is greater than 2×G1. It is formed to be larger than 4×G1.

Specifically, when the gap G1 is 80 mm and the diameter of the grown silicon single crystal S is 310 mm, the height of the first cooling body 12A and the second cooling body 12B is preferably about 350 mm. The inner diameters of the first cooling body 12A and the second cooling body 12B are preferably about 350 mm, and the stroke ST of the second cooling body 12B is preferably about 200 mm.

[Relationship between the ratio V/G of the crystal pulling speed V and the temperature gradient G in the crystal and the crystal quality]
Next, the relationship between the crystal quality and the ratio V/G between the crystal pulling speed V and the temperature gradient G in the crystal will be described.
The type and distribution of crystal defects contained in the silicon single crystal S depend on the ratio V/G between the crystal pulling speed V and the temperature gradient G within the crystal. V/G must be controlled.

FIG. 3 is a vertical cross-sectional view of a silicon single crystal S, showing a general relationship between V/G and types and distributions of crystal defects.
As shown in FIG. 3, when V/G is large, vacancies become excessive and void defects (COP), which are aggregates of vacancies, occur. On the other hand, when V/G is small, interstitial silicon atoms become excessive, and dislocation clusters are generated due to aggregates of interstitial silicon. Furthermore, between the region where COPs occur and the region where dislocation clusters occur, there are three regions, the OSF region, the Pv region, and the Pi region, in descending order of V/G. In order to say that the silicon single crystal is a defect-free crystal, it is necessary that the entire surface in the cross section of the silicon single crystal perpendicular to the pulling axis direction is a defect-free region. Here, the term “defect-free region” refers to a region that does not contain grown-in defect COPs and dislocation clusters. Among defect-free crystals, single crystals in which OSF rings do not occur after the evaluation heat treatment and are composed only of Pv regions or Pi regions are regarded as more perfect defect-free crystals. The present invention is effective not only for manufacturing defect-free crystals, but also for manufacturing more perfect defect-free crystals composed only of Pv regions or Pi regions.

In order to control the crystal pulling speed V and grow a defect-free crystal with a high yield, the PvPi margin (pulling speed margin) is used as an index, and the thermal environment surrounding the single crystal during pulling is adjusted so as to make the PvPi margin as wide as possible. is preferably controlled.
Here, the PvPi margin broadly refers to the permissible width of the crystal pulling speed V that allows any region in the silicon single crystal S to be the Pv region or the Pi region. It means the minimum value of the PvPi margin (PvPi in-plane margin) in the cross section of the silicon single crystal perpendicular to the direction. Since the temperature gradient G in the crystal usually does not change significantly, the PvPi margin is approximately proportional to the width of V/G from the Pv-OSF boundary to the Pi-dislocation cluster boundary in FIG.

The diameter control of the silicon single crystal S is mainly performed by adjusting the pulling speed V, and the crystal pulling speed V is appropriately changed in order to suppress the diameter fluctuation. Speed fluctuation is occurring. That is, since the fluctuation of the pull-up speed V cannot be completely eliminated, a pull-up speed margin is required to allow a speed fluctuation of about 0.015 mm/min.

The width of the PvPi margin is affected by the residence time in the temperature range of 600±200° C. in addition to the temperature gradient near the melting point, and the shorter the residence time in the temperature range, the wider the PvPi margin. Therefore, in the present embodiment, the silicon single crystal S is quenched to shorten the residence time in the temperature range of 600±200° C., and the distribution of the temperature gradient G in the crystal in the pulling-axis direction near the melting point is made uniform, so that PvPi To improve the manufacturing yield of defect-free crystals by enlarging the in-plane margin.

The silicon single crystal S pulled up from the silicon melt M is cooled while the temperature decreases as the distance from the liquid surface MA of the silicon melt M increases. When the silicon single crystal S quickly passes through the temperature range of 600±200° C., it is possible to suppress aggregation of vacancies and widen the PvPi margin. How short the residence time in the temperature range of 600±200° C. is and how wide the PvPi margin is can be obtained from point defect numerical analysis that analyzes the diffusion and pair annihilation of vacancies and interstitial silicon. As described above, if the PvPi margin is widened, the control of the crystal pulling speed V becomes easier, so that it becomes possible to stably grow a defect-free crystal.

[Effect of Embodiment]
The single crystal growth apparatus 1 of this embodiment shortens the residence time in the temperature range of 600±200° C. by the first cooling body 12A. Furthermore, by moving the second cooling body 12B to optimize the in-furnace thermal environment surrounding the crystal, particularly the thermal environment near the crystal growth interface, the crystal in the cross section of the silicon single crystal orthogonal to the pulling axis direction is The distribution of the internal temperature gradient G can be made uniform, the PvPi margin can be expanded, and the production yield of defect-free crystals can be increased.

When the thermal environment near the crystal growth interface changes due to the movement of the second cooling body 12B, the shape of the crystal growth interface also changes. is complicated. Therefore, means such as experiments or numerical simulations are effective in making the temperature gradient G in the crystal uniform.
A single crystal growth method including a specific control method for the second cooling body 12B will be described below.

FIG. 4 is a flow chart showing the single crystal growth method according to this embodiment. 5 and 6 are schematic diagrams for explaining the relationship between the pulling rate of the body portion of the silicon single crystal S and the position of the second cooling body 12B.
Here, the pulling rate of the body portion is the position in the longitudinal direction of the crystal defined as 100% for the length of the body portion set in advance in manufacturing the single crystal and 0% for the start position of the body portion. be. Normally, when the single crystal is grown normally without troubles in the apparatus and without dislocations in the single crystal, the length of the grown body portion is the same as the preset length of the body portion. .

As shown in FIG. 4, the single crystal growth method of the present embodiment comprises a raw material melting step P1 in which a silicon raw material in a crucible 3 is heated and melted by a heater 6 to generate a silicon melt M; A liquid contacting step P2 in which a seed crystal attached to the tip portion is lowered and brought into contact with the silicon melt M, and a single crystal is grown by gradually pulling up the seed crystal while maintaining a contact state with the silicon melt M. and a pulling step (P3 to P5).

In the pulling step, a shoulder portion pulling step P3 for forming a shoulder portion S1, which is an expanded diameter portion in which the crystal diameter gradually increases with crystal growth, and a body portion, which is a constant diameter portion maintained at a specified crystal diameter of 300 mm or more. A body portion pulling step P4A for forming S2 and a tail portion pulling step P5 for forming a tail portion S3, which is a diameter-reduced portion whose crystal diameter gradually decreases along with crystal growth, are sequentially performed.
In addition, in the single crystal growth method of the present embodiment, the second cooling body 12B is moved up and down during the execution of the body portion pulling step P4A so that the lower end of the second cooling body 12B and the liquid surface MA of the silicon melt M are separated from each other. It has a cooling body lifting process P4B that changes the distance.

In the present invention, as shown in FIGS. 5 and 6, for the body portion S2, top region R1 (raising rate 0% to 33%), middle region R2 (raising rate 33% to 67%) and the bottom region R3 (67% to 100% pull-up). The three regions substantially evenly divide the body portion S2 into three. In the body portion lifting step P4A, the body portion S2 is lifted in order of the top region R1, the middle region R2, and the bottom region R3.

As described above, in the single crystal growth method of the present embodiment, the second cooling body 12B is vertically moved. Specifically, the cooling body control unit 8A of the control device 8 determines that the distance G2 during the lifting of the middle region R2 is the same as when the body portion S2 starts to be lifted (the lifting rate of the body portion S2 is 0%, see FIGS. 5 and 6). ) and the distance G2 at the end of lifting the body portion S2 (the lifting rate of the body portion S2 is 100%). A distance G2 is the distance between the lower end of the second cooling body 12B and the liquid surface MA of the silicon melt M. As shown in FIG.
That is, in the single crystal growth method of the present embodiment, during the pulling of the body portion S2, the second cooling body 12B is temporarily moved to the liquid surface MA of the silicon melt M (between the silicon single crystal S and the silicon melt M). (solid-liquid interface).

In addition, the cooling body control unit 8A of the control device 8 raises and lowers the second cooling body 12B so that the difference Hd between the highest position and the lowest position of the second cooling body 12B satisfies 0.1×D<Hd. Let

Next, using the schematic diagrams shown in FIGS. 5 and 6, the details of the elevation control of the second cooling body 12B will be described. FIG. 5 shows a comparative example, and FIG. 6 shows an example. In the comparative example shown in FIG. 5, the distance G2 (see FIG. 2) between the lower end of the second cooling body 12B and the liquid surface MA of the silicon melt M is constant, and in the example shown in FIG. 6, the distance G2 is varied. ing.

5 and 6, the upper part is a vertical cross-sectional view of the silicon single crystal S, and a diagram for explaining the relationship between V/G and the type and distribution of crystal defects is shown in the top region R1, the middle region R2, and the bottom region. Each of the regions R3 is shown.
The lower part shows a graph for explaining the position of the second cooling body 12B. In the graph, the horizontal axis is the pulling rate of the body portion S2, and the vertical axis is the distance G2 between the lower end of the second cooling body 12B and the liquid surface MA of the silicon melt M.

As shown in FIG. 5, when the distance G2 is constant, the in-plane distribution of crystal defects cannot be maintained constant. That is, the in-plane distribution of crystal defects is different in the top region R1, the middle region R2, and the bottom region R3 of the body portion S2 of the silicon single crystal S, and a desired PvPi margin can be secured in the middle region R2 of the body portion S2. However, the desired PvPi margin cannot be secured in the top region R1 and the bottom region R3 of the body portion S2.

The PvPi region between the OSF region and the dislocation cluster region in the top region R1 in FIG. 5 is shifted in the direction of higher V/G in the crystal periphery than in the crystal center. Therefore, in order to obtain a defect distribution similar to that of the middle region R2 and secure a desired PvPi margin, the second cooling body 12B is moved up and down so that the crystal within the cross section of the silicon single crystal orthogonal to the pulling axis direction is It is necessary to make the distribution of the temperature gradient G uniform.

In contrast, in the method for pulling the silicon single crystal S of the present embodiment, as shown in FIG. 6, the second cooling body 12B is moved up and down so that the distance G2 changes.
Specifically, the PvPi region in the top region R1 of the conventional example shown in FIG. 2. Raise the cooling body 12B away from the crystal growth interface. In addition, in order to make the PvPi region in the bottom region R3 of the conventional example have the same distribution as that in the middle region R2, the second cooling body 12B is raised so as to relax the cooling of the central part of the crystal and away from the crystal growth interface.

That is, the cooling body control section 8A of the control device 8 controls the second cooling body 12B so that the second cooling body 12B is closest to the liquid surface MA during the lifting of the middle region R2.
More specifically, the cooling body control unit 8A of the present embodiment controls the second cooling body so that the distance G2 is about 220 mm from the time when the body part S2 starts to be pulled up (the body part start position) to the time when the top region R1 is being pulled up. 12B.

Next, at the timing when the body portion S2 is lifted by about 20%, the second cooling body 12B is lowered so that the distance G2 is 212 mm from the position (distance G2=220 mm) when the body portion S2 starts to be lifted.
After that, the distance G2 is kept at 212 mm in the middle region R2, and the second cooling body 12B is raised so that the distance G2 becomes 252 mm at the timing when the body portion S2 is raised by about 80%. After that, the distance G2 is kept at 252 mm until the body part S2 is pulled up.

The timing for lowering the second cooling body 12B is preferably a raising rate of 20% to 30% (20% or more and 30% or less). The timing of raising the second cooling body 12B is preferably a raising rate of 70% to 90% (70% or more and 90% or less).

By controlling the second cooling body 12B in this way, the intra-crystal temperature gradient G is optimized, and the top region R1 of the body portion S2 is reduced as shown in the vertical cross-sectional view of the silicon single crystal S in the upper part of FIG. to the bottom region R3, the in-plane distribution of crystal defects can be kept constant, and the production yield of defect-free crystals can be increased.

In addition, the cooling body 12 is vertically divided into two parts, and only the lower second cooling body 12B is moved up and down, so that the lifting device can be made compact.

The method of controlling the second cooling body 12B described above is an example, and the distance G2 during the lifting of the middle region R2 is the distance G2 at the start of lifting the body portion S2 and the distance G2 at the end of lifting the body portion S2. It is not limited to this as long as the second cooling body 12B is moved up and down so as to be smaller than G2. For example, the distance G2 at the start of pulling up may be greater than the distance G2 at the end of pulling up.

Also, regarding how much the cooling body is raised and lowered, the relationship between the defect distribution and the distance G2 as shown in the upper part of FIG. 5 or FIG. 0% to 100%) and can be determined based on the relationship. Further, in understanding the relationship between the defect distribution and the distance G2 as shown in the upper part of FIG. 5 or FIG. 6 or the relationship between the PvPi margin and the distance G2, single crystal pulling experiments or It can be grasped by defect simulation by computer.

Further, in the above-described embodiment, the cooling body 12 is vertically divided into two parts, but a single cooling body 12 may be moved up and down.
In that case, the lower limit of the elevation range of the cooling body 12 can be a position where the lower end of the cooling body 12 is at the same height as the lower end of the heat shield 7, and the upper limit of the elevation range of the cooling body 12 is the cooling body 12 can be positioned at the same height as the upper opening 10A of the main chamber 10. As shown in FIG.
If the lower end of the cooling body 12 is located below the lower end of the heat shield 7, it is the same as changing the distance G1 (gap) between the liquid surface MA of the silicon melt M and the lower end of the heat shield 7. Since the effect occurs, it rather makes the production of defect-free single crystals difficult. If the lower end of the cooling body 12 is located above the upper opening 10A, the cooling body 12 will be stored in the pull chamber 11 and the effect of raising and lowering the cooling body 12 will not be obtained.

DESCRIPTION OF SYMBOLS 1... Pulling apparatus, 2... Chamber, 3... Crucible, 4... Rotating shaft, 5... Shaft driving mechanism, 6... Heater, 7... Thermal shield, 8... Control device, 12... Cooling body, S... Silicon single crystal, S2... Body part.

Claims (5)

A single crystal growing method for growing a silicon single crystal comprising a shoulder portion, a body portion, and a tail portion by the Czochralski method,
a pulling step of pulling up the body portion of the silicon single crystal;
During the pulling step, a cooling body which is installed to surround the silicon single crystal and promotes cooling of the silicon single crystal is moved up and down from the outer peripheral side of the silicon single crystal so that the lower end of the cooling body Having a cooling body lifting process for changing the distance from the liquid surface of the silicon melt,
In the lifting step, when a predetermined length of the body portion is set to 100% and a training start position of the body portion is set to 0% to define a lifting rate of the body portion, the body portion is set to the lifting rate is raised in order of three regions: a top region of 0% to 33%, a middle region of 33% to 67%, and a bottom region of 67% to 100%,
In the cooling body lifting step, the distance during lifting of the middle region is smaller than the distance at the start of lifting the body and the distance at the end of lifting the body, and The cooling body is raised and lowered so that a difference Hd between the highest position and the lowest position of the cooling body, where D is the diameter of the silicon single crystal, satisfies 0.1×D<Hd. Single crystal growth method. In the cooling body raising/lowering step, the cooling body is lowered at a lifting rate of the body portion of 20% to 30%, and the cooling body is raised at a lifting rate of the body portion of 70% to 90%. Item 1. The method for growing a single crystal according to item 1 . A single crystal growth apparatus for growing a silicon single crystal comprising a shoulder portion, a body portion, and a tail portion by the Czochralski method,
a crucible holding a silicon melt;
a cooling body, which is installed so as to surround the silicon single crystal, is movable up and down, and promotes cooling of the silicon single crystal from the outer peripheral side;
a control device that controls at least the cooling body,
The control device has a cooling body control unit that moves the cooling body up and down to change the distance between the lower end of the cooling body and the liquid surface of the silicon melt,
When the length of the body portion set in advance is 100% and the raising rate of the body portion is defined as 0%, the raising rate of the body portion is set to 0% to 33%. % top area, middle area between 33% and 67%, and bottom area between 67% and 100%.
The cooling body control unit controls the distance during lifting of the middle region to be smaller than the distance at the start of lifting the body portion and the distance at the end of lifting the body portion, and The cooling body is raised and lowered so that a difference Hd between the highest position and the lowest position of the cooling body, where D is the diameter of the silicon single crystal, satisfies 0.1×D<Hd. Single crystal growth equipment. The cooling body control unit lowers the cooling body at a raising rate of the body portion of 20% to 30% and raises the cooling body at a raising rate of the body portion of 70% to 90%. 4. The single crystal growth apparatus according to claim 3 , wherein the single crystal growth apparatus is raised and lowered. 5. The single crystal growth apparatus according to claim 3 , wherein said cooling body is vertically divided into two parts, and only the lower cooling body is moved up and down.

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