JP4785764B2 - Single crystal manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a single crystal that is pulled up while growing the single crystal by the Czochralski method (hereinafter referred to as “CZ method”).

  The CZ method is widely used for the growth of silicon single crystals. In this method, the seed crystal is brought into contact with the surface of the silicon melt contained in the crucible, the crucible is rotated, and the seed crystal is pulled upward while rotating in the opposite direction. In this way, a single crystal is formed.

  As shown in FIG. 4, in the pulling method using the conventional CZ method, first, raw material polysilicon is loaded into a quartz glass crucible 51 and heated by a heater 52 to obtain a silicon melt M. Thereafter, the silicon single crystal C is pulled by bringing the seed crystal P attached to the pulling wire 50 into contact with the silicon melt M. For the purpose of reducing the cost, a recharging method is often used in which a single crystal is pulled up, then raw material polysilicon is added to the remaining melt, and the single crystal is pulled up again.

  In general, prior to the start of pulling, after the temperature of the silicon melt M is stabilized, as shown in FIG. 5, necking is performed in which the seed crystal P is brought into contact with the silicon melt M to dissolve the tip of the seed crystal P. Necking is an indispensable process for removing dislocations generated in a silicon single crystal due to thermal shock generated by contact between the seed crystal P and the silicon melt M. The neck portion P1 is formed by this necking. The neck portion P1 is generally required to have a diameter of 3 to 4 mm and a length of 30 to 40 mm or more.

  In addition, as a process after the start of pulling, after necking is completed, a crown process for expanding the crystal to the diameter of the straight body part, a straight body process for growing a single crystal as a product, and a single crystal diameter after the straight body process are gradually reduced. The tail process is performed.

By the way, in this CZ method, as the pulling of the single crystal proceeds, the liquid level of the silicon melt decreases. Therefore, if the control of keeping the liquid level constant is not performed, the amount of evaporation of oxygen from the silicon melt There is a problem that the oxygen concentration in the axial direction of the obtained single crystal changes.
For this reason, Patent Document 1 discloses a method of keeping the position of the molten liquid surface constant by measuring the liquid surface of the silicon melt and raising the crucible at a constant speed with respect to the single crystal pulling speed. .
Japanese Patent No. 2735960

  By the way, in the furnace where the single crystal pulling step is performed, a predetermined gas flow (for example, Ar gas) is usually formed from the upper side to the lower side, and the SiO gas evaporated from the liquid surface of the silicon melt does not stay. It is made like that. In addition, the predetermined gas flow formed in the furnace is rectified by a radiation shield above the crucible having upper and lower openings formed so as to surround the periphery of the single crystal.

  However, as in the method disclosed in Patent Document 1, the flow rate of the gas on the melt surface changes by simply measuring the liquid surface position and adjusting the crucible position to keep the liquid surface position constant. As a result, fluctuations in the amount of evaporation of the SiO gas occur, and there is a problem that the oxygen concentration around the crystal becomes nonuniform. In addition, when the flow rate of the gas on the melt surface is lowered, there is a problem that the foreign matter on the melt surface cannot be moved away from the crystal, and the crystal is easily dislocated.

  In addition, the frequency of occurrence of defects in these technical problems is increased when a plurality of crystals are pulled up using the same quartz crucible by the recharge method or when the heater temperature rises for remelting crystals that have undergone dislocation during pulling. When the crucible deformation is accelerated, it is particularly remarkable in that the crucible diameter is 30 inches or more and the degree of deformation is large. In addition, in order to adjust the oxygen concentration of the crystal, it frequently occurred when the amount of inert gas introduced into the puller was changed or when the inner diameter of the radiation shield was changed.

  The present invention has been made under the circumstances as described above. In a method for producing a single crystal in which a plurality of silicon single crystals are pulled using the same quartz crucible by a recharge method, the radiation shield and the melt surface are provided. A single crystal with a uniform oxygen concentration over the entire length can be stably manufactured by controlling the gap size between them within a predetermined range and controlling the flow rate of the gas flowing between the radiation shield and the single crystal. An object of the present invention is to provide a method for producing a single crystal.

In order to solve the above-described problems, a method for producing a single crystal according to the present invention is a method for producing a single crystal in which a plurality of silicon single crystals are pulled using the same quartz crucible by a recharging method. Between the silicon melt surface and the lower end of the radiation shield provided above the melt surface, the fluctuation of the first gap is controlled within ± 1 mm from And a gas flow rate flowing downward through the second gap, which is formed between the radiation shield and the single crystal and is closest to the silicon melt surface, is formed in the furnace body. The correlation between the setting of the second gap and the gas supply amount is measured in advance, and the measurement result is used for the control of the flow velocity, or a flow velocity measurement means for measuring the flow velocity is provided, and the measurement result is Used to control the flow rate, characterized in that controlled to be less than 1 m / sec or more 15 m / sec.

The flow rate is preferably controlled to be 8.5 m / sec or more and 15 m / sec or less. Further, in controlling the fluctuation of the first gap, the liquid level height of the silicon melt is measured, the dimension of the first gap is calculated based on the measured liquid level height, and the calculation is performed. It is desirable to adjust the height position of the crucible or the radiation shield based on the dimension of the first gap .

Thus, by controlling the fluctuation of the first gap within ± 1 mm, the evaporation amount of the SiO gas from the silicon melt M is made substantially constant, and the single crystal C having a uniform axial oxygen concentration distribution is obtained. Obtainable.
In addition, by controlling the flow rate of the gas flowing through the second gap to be 1 m / sec or more and 15 m / sec or less, it is possible to suppress the evaporation effect of SiO gas and improve the oxygen concentration around the crystal. Furthermore, the foreign matter on the surface of the melt can be kept away from the crystal, and dislocation of the crystal can be prevented.

  According to the present invention, in the method for producing a single crystal in which a plurality of silicon single crystals are pulled using the same quartz crucible by the recharge method, the gap dimension between the radiation shield and the melt surface is controlled within a predetermined range, In addition, by controlling the flow rate of the gas flowing between the radiation shield and the single crystal, it is possible to obtain a single crystal manufacturing method capable of stably manufacturing a single crystal having a uniform oxygen concentration over the entire length. .

Embodiments of a method for producing a single crystal according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a single crystal pulling apparatus 1 in which a method for producing a single crystal according to the present invention is implemented.
This single crystal pulling apparatus 1 includes a furnace body 2 formed by superposing a pull chamber 2b on a cylindrical main chamber 2a, a crucible 3 provided in the furnace body 2, and a semiconductor loaded in the crucible 3. A heater 4 for melting the raw material (raw material polysilicon) M and a pulling mechanism 5 for pulling up the single crystal C to be grown are provided. The crucible 3 has a double structure, and is composed of a quartz glass crucible 3a on the inside and a graphite crucible 3b on the outside.
The pulling mechanism 5 has a winding mechanism 5a driven by a motor and a pulling wire 5b wound up by the winding mechanism 5a, and a seed crystal P is attached to the tip of the wire 5b.

In addition, an inert gas supply means 20 for supplying an inert gas G (for example, Ar gas) at a predetermined flow rate is provided in the furnace body 2 to adjust the atmosphere in the chamber. The inert gas supply means 20 provides a pull chamber. A gas flow by the inert gas G is formed from the upper side to the lower side of 2b. The supply amount of the inert gas G by the inert gas supply means 20 is controlled by the arithmetic control device 8b of the computer 8.
Further, in the main chamber 2a, an upper portion and a lower portion are formed so as to surround the periphery of the single crystal C above and in the vicinity of the crucible 3, and extra radiant heat from the heater 4 or the like is applied to the growing single crystal C. A radiation shield 6 is provided for shielding and rectifying the gas flow in the furnace. The gap d1 (first gap) formed between the lower end of the radiation shield 6 and the melt surface is controlled so as to maintain a predetermined distance according to the desired characteristics of the single crystal to be grown.

As shown in FIG. 1, an electric coil 13 for applying a magnetic field is installed outside the main chamber 2a, and an MCZ method (Magnetic field) is used to grow a single crystal by applying a cusp magnetic field in the silicon melt of the crucible 3. applied CZ method) is used.
According to this MCZ method, convection on the melt surface is suppressed, and the impurity concentration distribution in the radial direction can be made uniform. Moreover, the effect that the deterioration of the inner surface of the quartz glass crucible 3a can be prevented by suppressing the convection.

Further, a liquid level position detection device 14 for detecting the height position of the liquid level M1 of the silicon melt M is provided outside the furnace body 2.
The liquid surface position detection device 14 includes a laser light oscillator 15 that oscillates coherent detection light, an imaging device, for example, a CCD camera 16, and an image processing device 17 that processes an image captured by the CCD camera 16. .

The laser light oscillator 15 is disposed above the main chamber 2b, oscillates green laser light (wavelength 490 to 550 nm) in response to a command signal from the computer 8, and irradiates a predetermined spot on the melt surface M1 with the green laser light. It is made like that.
The CCD camera 16 is focused on a predetermined spot on the melt surface M1 irradiated with the green laser light by the laser light oscillator 15, picks up an image of the predetermined spot, and the picked-up image is an image processing device 17. To be output.
Further, the image processing device 17 processes the image signal input from the CCD camera 16, detects the height position of the silicon melt liquid surface M1, and outputs it to the arithmetic control device 8b of the computer 8. Yes.

As shown in FIG. 1, the single crystal pulling apparatus 1 includes a heater control unit 9 that controls the amount of power supplied to the heater 4 that controls the temperature of the silicon melt M, a motor 10 that rotates the crucible 3, and a motor. And a motor control unit 10a for controlling the number of rotations of ten.
Also, an elevating device 11 that controls the height of the crucible 3, an elevating device control unit 11 a that controls the elevating device 11, and a wire reel rotating device control unit 12 that controls the pulling speed and the number of rotations of the grown crystal. Yes. Furthermore, an electric coil control unit 13 a that controls the operation of the magnetic field applying electric coil 13 is provided. Each of these controllers 9, 10a, 11a, 12, 13a is connected to an arithmetic control device 8b of the computer 8.

  In the single crystal pulling apparatus 1 configured as described above, the raw material polysilicon M is first loaded into the quartz glass crucible 3a, and the flow shown in FIG. 2 is performed based on the program stored in the storage device 8a of the computer 8. The crystal growth process is started.

First, the inert gas supply means 20 is controlled by the arithmetic and control unit 8b, and the inside of the furnace body 2 is brought into a predetermined atmosphere. And the heater control part 9 is operated by the instruction | command of the arithmetic control apparatus 8b, the heater 4 is heated, and, thereby, the raw material polysilicon M of the quartz glass crucible 3a is fuse | melted (step S1 of FIG. 2).
Further, the motor control unit 10a and the lifting device control unit 11a are operated by a command from the arithmetic control device 8b, and the crucible 3 is rotated at a predetermined rotational speed at a predetermined height position.

Next, the electric coil control unit 13a is operated according to a command from the arithmetic control device 8b, and a predetermined current is caused to flow through the magnetic field applying electric coil 13. As a result, a magnetic field having a predetermined strength is applied to the melt M (step S2 in FIG. 2).
Then, in response to a command from the arithmetic control device 8b, the wire reel rotating device control unit 12 is operated, the winding mechanism 5a is operated, and the wire 5b is lowered. Then, the seed crystal P attached to the wire 5b is brought into contact with the silicon melt M, and necking for melting the tip of the seed crystal P is performed to form the neck portion P1 (step S3 in FIG. 2).

Here, the height position of the melt surface M1 with respect to a predetermined reference value is measured by operating the liquid surface position detection device 14, and a gap d1 between the melt surface M1 and the lower end of the radiation shield 6 is determined based on this measurement. The gap control process for controlling the distance is started (step S4 in FIG. 2).
This gap control process is continued until the end of the pulling process.

  When the neck portion P1 is formed, the pulling conditions are adjusted with parameters such as the power supplied to the heater 4 and the pulling speed (usually a speed of several millimeters per minute) according to the command of the arithmetic control device 8b, and the crown process (FIG. 2) Step S5) and the straight body process (Step S6 in FIG. 5) are continuously performed.

  In this straight body process, the arithmetic and control unit 8b controls the inert gas supply means 20, and is formed between the radiation shield 6 and the single crystal C (straight body part), and the gap closest to the silicon melt surface M1. The flow rate of the inert gas G flowing through d2 (second gap: 22 mm, for example) is set to 1 m / sec or more and 15 m / sec or less (step S7 in FIG. 5). This is because when the flow rate of the gas G flowing through the gap d2 is less than 1 m / sec, the effect of moving the foreign matter on the surface of the melt away from the crystal is lost, and the crystal is likely to dislocation. On the other hand, when the flow rate of the gas G is higher than 15 m / sec, the effect of SiO evaporation from the melt surface near the crystal is increased, and a low-oxygen concentration melt is taken into the crystal periphery. This is because the concentration decreases and the in-plane distribution of oxygen deteriorates.

This flow rate control is realized by measuring the correlation between the setting of the gap d2 in the furnace body 2 and the gas supply amount in advance and using the measurement result for the control of the inert gas supply means 20. Alternatively, a flow rate measuring unit (not shown) may be provided, and the measurement result may be fed back to the control of the inert gas supply unit 20.
When the straight body process is completed, a tail process (step S8 in FIG. 2) for reducing the body diameter is performed, and the single crystal C is pulled up to the pull chamber 2b.

  As described above, the gap control process is performed during the pulling process. In the gap control process, as shown in the flow of FIG. 3, first, the height position of the melt surface M1 is detected by the liquid surface position detecting device 14, and the arithmetic control device 8b of the computer 8 is in the pulling process. The height position data of the changing liquid level M1 is input (step S31 in FIG. 3).

In the arithmetic and control unit 8b, the measurement dimension of the gap d1 is calculated based on the lower end position of the radiation shield 6 fixed in the chamber 2b and the height position of the melt surface M1 input from the image processing unit 17.
Then, it is determined whether or not the variation in the measurement dimension of the gap d1 is within ± 1 mm (step S32 in FIG. 3). If not satisfied, the lifting device control unit 11a is controlled so as to satisfy the condition to lift the lifting device. 11, the height position of the crucible 3 is adjusted (step S33 in FIG. 3).
As described above, during the pulling process, control is performed so as to satisfy the condition of step S32, and the single crystal pulling process proceeds (step S34 in FIG. 3).

  The setting of the desired gap dimension d1 varies depending on the crystal characteristics to be grown. However, for example, when growing a crystal in the front V-rich region, the pulling speed is fast, so that it is set to 20 to 30 mm. In the case of growing a crystal in which the entire crystal plane is a neutral region, the thickness is set to 40 to 80 mm. In either case, the fluctuation of the gap d1 during the pulling process is suppressed within ± 1 mm, thereby suppressing variations in the oxygen concentration distribution.

As described above, in the embodiment according to the present invention, the height position of the liquid level M1 of the silicon melt M is measured during the pulling process of the single crystal C, and the liquid level M1 and the radiation shield are measured based on the measured values. 6 The gap d1 with the lower end is controlled to have a predetermined dimension. Thereby, the evaporation amount of SiO gas from the silicon melt M is made substantially constant, and a single crystal C having a uniform oxygen concentration distribution in the axial direction can be obtained.
Furthermore, at the time of forming the straight body portion, the flow rate of the inert gas G formed between the radiation shield 6 and the single crystal C (straight body portion) and flowing through the gap d2 closest to the melt surface M1 is: It is controlled to be 1 m / sec or more and 15 m / sec or less. Thereby, the evaporation effect of SiO gas can be suppressed and the oxygen concentration of the crystal periphery can be improved. Furthermore, foreign matter on the surface of the melt can be kept away from the crystal, and dislocation of the crystal can be prevented.
Therefore, according to the method of the present invention, it is possible to stably obtain a single crystal C having a uniform oxygen concentration distribution over the entire length.

In addition, according to the embodiment of the present invention, one crucible 3 is used for pulling a single crystal a plurality of times, and when the crucible 3 changes with time, or crystals that have undergone dislocation in the course of pulling are remelted. When the crucible deformation is accelerated as the heater temperature rises, the height position of the liquid level M1 can always be measured even when the crucible diameter is 30 inches or more and the degree of deformation is large. Can be suppressed within. Therefore, the evaporation amount of the SiO gas from the silicon melt M can be made substantially constant, and the single crystal C having a uniform oxygen concentration distribution in the axial direction can be stably obtained.
In addition, since the gas flow rate in the gap d2 formed between the radiation shield 6 and the single crystal C can be controlled regardless of the crucible deformation, the SiO gas evaporation effect is suppressed and the oxygen concentration around the crystal is improved. The foreign matter on the liquid surface can be kept away from the crystal to prevent dislocation of the crystal.

In the above-described embodiment, an example is shown in which the gap d1 between the height position of the melt surface M1 and the lower end of the radiation shield 6 is controlled to a predetermined dimension. Without limitation, a means for moving the radiation shield 6 up and down may be provided, and the gap d1 may be controlled by moving the radiation shield 6 up and down.
Moreover, in the said embodiment, although it was set as the structure measured by the optical method using a laser beam as a structure of the liquid level position detection apparatus 14 which measures the height position of the melt surface M1, it is limited to this structure. Instead, the liquid surface position may be detected by another known technique.

Then, the manufacturing method of the single crystal which concerns on this invention is further demonstrated based on an Example. In this example, the effect was verified by actually performing an experiment using the single crystal pulling apparatus having the configuration described in the above embodiment.
[Example 1]
In Example 1, the single crystal manufacturing method according to the present invention is used for pulling up, and measuring the fluctuation of the gap size after a plurality of pulling steps and the in-plane distribution of oxygen concentration in the crystal plane at the lower part of the straight body part. did. As pulling conditions, initial charge amount: 140 kg, number of pulling crystals: 4, crystal diameter: 206 mm, magnetic field method: cusp magnetic field, magnetic field strength (crucible wall): 400 Gauss, furnace Ar gas flow rate: 100 L / min, furnace pressure : 50 Torr, crucible rotation speed: 8 rpm, crystal rotation speed: 13 rpm, gap setting value between melt and radiation shield lower end (gap d1 in the embodiment): 30 mm, gap setting value between single crystal and radiation shield ( The gap d2) in the embodiment was 22 mm, and the flow rate of the inert gas in the gap between the single crystal and the radiation shield (gap d2 in the embodiment) was 8.5 m / sec.

As experimental results, the change in gap size is shown in the graph of FIG. 6, and the oxygen concentration in-plane distribution is shown in the graph of FIG. The in-plane distribution of the oxygen concentration was measured from the center to the radius of 90 mm at a pitch of 5 mm after processing the crystal wafer. ((In-plane maximum value−In-plane minimum value) / In-plane minimum value) · 100 (%).
As shown in FIG. 6, the gap size variation was suppressed to within ± 1 mm. Further, the oxygen concentration in-plane distribution was 4% or less in all lots as shown in FIG.

[Comparative Example 1]
In Comparative Example 1, the gap was adjusted only once before growing the single crystal. Other conditions are the same as in the first embodiment.
As experimental results, the change in gap size is shown in the graph of FIG. 8, and the oxygen concentration in-plane distribution is shown in the graph of FIG.
As shown in FIG. 8, the variation of the gap dimension was expanded to a maximum of about 5 mm during single crystal growth. In addition, it was confirmed that the in-plane distribution of oxygen concentration exceeded 4% as shown in FIG.

[Comparative Example 2]
In Comparative Example 2, the flow rate of the inert gas in the gap between the single crystal and the radiation shield (gap d2 in the embodiment) was set to 16 m / sec. Other conditions are the same as in the first embodiment.
As an experimental result, the oxygen concentration in-plane distribution is shown in the graph of FIG. As shown in FIG. 10, the oxygen concentration in-plane distribution was concentrated in the vicinity of 2%, but the generation of lots exceeding 4% was confirmed. From this result, if the flow rate of the inert gas in the gap between the single crystal and the radiation shield (gap d2 in the embodiment) is 15 m / sec, the oxygen concentration in-plane distribution is 4% or less in almost all lots. It was considered to be suppressed.
From the experimental results of the above examples, according to the present invention, the oxygen concentration of a plurality of single crystals continuously produced using one crucible is made uniform, and a single crystal having desired characteristics is stably produced. Confirmed that you can.

  The present invention relates to a method for producing a single crystal by pulling the single crystal by the Czochralski method, and is suitably used in the semiconductor manufacturing industry and the like.

FIG. 1 is a block diagram schematically showing a configuration of a single crystal pulling apparatus in which a method for producing a single crystal according to the present invention is implemented. FIG. 2 is a flow showing the steps of the method for producing a single crystal according to the present invention. FIG. 3 is a flow of the gap control process in the flow of FIG. FIG. 4 is a diagram for explaining a pulling method using the conventional CZ method. FIG. 5 is a diagram for explaining formation of a neck portion in a pulling method using a conventional CZ method. FIG. 6 is a graph showing the results of Example 1. FIG. 7 is another graph showing the results of Example 1. FIG. 8 is a graph showing the results of Comparative Example 1. FIG. 9 is another graph showing the results of Comparative Example 1. FIG. 10 is a graph showing the results of Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Furnace body 2a Main chamber 2b Pull chamber 3 Crucible 3a Quartz glass crucible 3b Graphite crucible 4 Heater 5 Pulling mechanism 6 Radiation shield 8 Computer 8a Storage device 8b Arithmetic storage device 13 Electric coil for magnetic field 14 Liquid surface position Detection device 15 Laser light oscillator 16 CCD camera 17 Image processing device C Single crystal M Raw material polysilicon, silicon melt P seed crystal P1 Neck portion

Claims (4)

In a method for producing a single crystal by pulling a plurality of silicon single crystals using the same quartz crucible by a recharge method,
From the start to the end of pulling the single crystal,
Controlling the fluctuation of the first gap formed between the silicon melt surface and the lower end of the radiation shield provided above the melt surface within ± 1 mm;
Forming a gas flow from the top to the bottom of the furnace body;
The flow rate of the gas formed between the radiation shield and the single crystal and flowing through the second gap closest to the silicon melt surface is set as the second gap setting and the gas supply amount in the furnace body. Is measured in advance, and the measurement result is used for controlling the flow velocity, or a flow velocity measuring means for measuring the flow velocity is provided, and the measurement result is used for controlling the flow velocity. A method for producing a single crystal, which is controlled to be equal to or less than sec. The method for producing a single crystal according to claim 1, wherein the flow velocity is controlled to be 8.5 m / sec or more and 15 m / sec or less. In controlling the variation of the first gap,
Measuring the liquid level height of the silicon melt, and calculating the dimension of the first gap based on the measured liquid level height;
Method for producing a single crystal according to claim 1 or 2, characterized in that for adjusting the height position of the crucible based on the dimension of the first gap the calculated. In controlling the variation of the first gap,
Measuring the liquid level height of the silicon melt, and calculating the dimension of the first gap based on the measured liquid level height;
Method for producing a single crystal according to claim 1 or 2, characterized in that for adjusting the height position of the radiation shield on the basis of the dimension of the first gap the calculated.

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