JPH0826882A - Device for pulling up single crystal - Google Patents

Abstract

PURPOSE:To provide a device for pulling up single crystal capable of avoiding occurrence of an accident during pulling by starting an alarm from difference between a calculated value and a measured value based on information from a controlling means in terms of an electric current of a motor for pulling up device for pulling up single crystal. CONSTITUTION:This modified device for pulling up single crystal is equipped with a calculating means 12 for operating an electric current value which should be sent to a motor 18 for pulling up single crystal from an information of pulling speed sent from a controlling means 11 for regulating the pulling of single crystal and from an information on the size of the single crystal 19, an electric current value measuring means 13 for measuring an electric current value actually flowing to the motor 18 for pulling up the single crystal, a subtracting means 14 for obtaining difference between the operated electric current value and the actually measured electric current value made from the these means, and an alarm means 15 for sending an alarm depending upon the output value of the subtracting means 14. A device provided with a pulling condition changing means for changing the pulling condition of the single crystal depending upon the output value of the subtracting means 14 is preferable instead of the alarm means 15 or besides it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal pulling apparatus for growing a silicon single crystal used as a semiconductor material, for example.

[0002]

2. Description of the Related Art There are various methods for growing a single crystal, one of which is the Czochralski method (hereinafter referred to as the CZ method). FIG. 8 is a sectional view schematically showing a single crystal pulling apparatus used in the conventional CZ method.
Indicates a crucible.

The crucible 31 comprises a bottomed cylindrical quartz inner layer holding container 31a and a bottomed cylindrical graphite outer layer holding container 31b fitted to the outside of the inner layer holding container 31a. The crucible 31 is supported by a support shaft 39 that rotates at a predetermined speed in the direction of the arrow in the figure. A resistance heating type heater 32 is provided outside the crucible 31.
Are arranged concentrically, and the crucible 31 is filled with a melt 33 of the single crystal raw material melted by the heater 32. A pulling shaft 34 made of a pulling rod, a wire, or the like is hung on the center axis of the crucible 31. The seed crystal 35 attached to the tip of the pulling shaft 34 via a seed chuck 34a is melted 33
The melt 33 is solidified by growing the single crystal 36 by bringing the melted liquid 33 into contact with the surface and rotating the pulling shaft 34 in the same axis as the supporting shaft 39 in the same direction or in the opposite direction at a predetermined speed. .

By the way, when the semiconductor single crystal 36 is pulled by this pulling method, in order to adjust the electric resistivity and electric conductivity type of the single crystal 36, the melt 33 is pulled before the pulling.
Impurities are often added to the inside. However, in the ordinary CZ method, a single crystal 36 having a uniform electric resistivity in the growth axis direction of the single crystal 36 cannot be obtained due to a so-called segregation phenomenon occurring between the single crystal 36 and the melt 33. There was a problem.

The segregation phenomenon means that the single crystal 3 at the interface between the single crystal 36 and the molten liquid 33 during solidification of the single crystal 36.
Although the impurity concentration of 6 and the impurity concentration of the melt 33 do not match, the effective segregation coefficient Ke (impurity concentration of the single crystal 36 / impurity concentration of the melt 33) is often smaller than 1. In this case, since the single crystal 36 grows and the impurity concentration of the melt 33 gradually increases due to the segregation phenomenon, the impurity concentration of the single crystal 36 also gradually increases, and the electrical resistivity decreases. Therefore, some of the single crystals 36 grown by the above method do not meet the standard regarding the electrical resistivity, and the yield is reduced.

Therefore, a melt layer method has been developed as a single crystal pulling method for preventing a decrease in the yield of the electrical resistivity due to the occurrence of the above-mentioned segregation phenomenon and for raising the yield related to the electrical resistivity.

FIG. 9 is a sectional view schematically showing a single crystal pulling apparatus used in the melt layer method. The basic characteristic of this fusion layer method is that the crucible 3 having the same structure as in FIG.
In FIG. 1, the single crystal raw material is melted by the heater 32, the molten layer 33 is formed in the upper layer and the solid layer 38 is formed in the lower layer, and the solid layer 38 is gradually eluted as the single crystal 36 grows. , To keep the impurity concentration of the molten layer 33 constant. The structure of the apparatus is the same as that of the apparatus used in the CZ method, and the pulling method of the single crystal 36 is almost the same as the pulling method by the CZ method except for the above steps.

In the melt layer method, two different methods have been proposed as a method for keeping the impurity concentration of the melt layer 33 constant, that is, a constant melt layer thickness method and a melt layer thickness changing method.
According to this method of constant melting layer thickness, the solid layer 38 containing no impurities is melted as the single crystal 36 is pulled, the volume of the melting layer 33 is kept constant, and impurities are continuously added to the melting layer 33. There is a method of keeping the impurity concentration of the melted layer 33 constant by using the method described in JP-B-34-8242, JP-B-62
-880 and Japanese Utility Model Publication No. 3-7405 disclose the above-mentioned method. Further, the solid layer 38 is made to contain impurities in advance, the molten layer 33 is not added with impurities, and the impurities are not added. A method of keeping the volume of the molten layer 33 constant while melting the solid layer 38 containing a with the pulling of the single crystal 36 and keeping the impurity concentration of the molten layer 33 substantially constant is
JP-B-62-880 and JP-A-63-25298.
No. 9 publication.

The melt layer thickness changing method is a method of intentionally changing the volume of the melt layer 33 to keep the impurity concentration of the melt layer 33 constant without adding impurities during the pulling of the single crystal 36. , JP 61-205691, JP 61-205692, JP 61-2.
It is disclosed in Japanese Patent No. 15285 and Japanese Patent Publication No. 3-79320.

In the above two melt layer methods,
The thickness of the molten layer 33 is controlled by the heater 32 as a heating element.
Length and power, position and depth of crucible 31 and heater 32
This is performed by appropriately selecting the shape and material of the heat retaining cylinder 42 that is provided around the outside of the crucible 31 and that promotes heat transfer in the lower portion of the crucible 31.

As described above, in the fusion layer method, the impurity concentration of the fusion layer 33 can be kept substantially constant, so that there is an advantage that the yield relating to the electrical resistivity can be improved. However, since the single crystal 36 is pulled up under the condition that the solid layer 38 is formed below the crucible 31, the solid layer 38 below the crucible 31 is formed into the single crystal 36.
Growing during the pulling up of the solid layer 3 as shown in FIG.
In some cases, the solid layer 38 grows toward the single crystal 36 side from the normal interface 45 between the melted layer 33 and the molten layer 33 to form the convex solid layer 46. The solid layer 46 may be fixed to the single crystal 36 depending on pulling conditions,
Further, since the solid layer 46 is fixed to the lower portion of the crucible 31 via the solid layer 38, if the pulling is continued while the single crystal 36 and the solid layer 46 are fixed, the single crystal pulling device may be damaged or the single crystal pulling device may be damaged. There is a risk that an accident such as dropping of the single crystal 36 may occur due to breakage of the neck portion of the crystal 36.

On the other hand, Japanese Patent Laid-Open No. 5-4890 discloses a method for detecting the occurrence of sticking between the single crystal and the solid layer by measuring the torque fluctuation of the single crystal pulling motor.

[0013]

However, in the single crystal pulling apparatus described in JP-A-5-4890, since a wire such as stainless steel is used as the pulling shaft, a single crystal and a solid layer are formed. Even if the sticking occurs, the wire portion is easily twisted and the torque fluctuation of the single crystal pulling motor is alleviated. For this reason, it is actually difficult to accurately detect the sticking between the single crystal and the solid layer due to the torque fluctuation, and the present situation is that the management is visually performed.

By the way, if the time until the fixed state between the single crystal 36 and the solid layer 46 is found and the processing such as stopping the pulling is carried out within about 5 minutes from the time when the fixed state occurs, the single crystal is said. It is said that it is possible to prevent the pulling device from being damaged and the single crystal 36 from falling during pulling, but since the single crystal pulling device is managed by a small number of operators during actual operation, There is a high possibility that the discovery of adhesion between the single crystal 36 and the solid layer 46 will be delayed. If the discovery of the adhesion between the single crystal 36 and the solid layer 46 is delayed and the pulling is continued as described above, the pulling of the single crystal 36 becomes impossible, and the single crystal 36 raises the crucible 31. Damage to the single crystal pulling device or damage to the neck of the single crystal 36
There was a problem such as a fall accident.

The present invention has been made in view of the above problems, and automatically detects the adhesion between the single crystal being pulled and the solid layer under the crucible and gives an alarm, and / or stops the pulling of the single crystal. It is an object of the present invention to provide a single crystal pulling apparatus which is provided with means for preventing damage to the apparatus and a single crystal falling accident.

[0016]

In order to achieve the above object, a single crystal pulling apparatus according to the present invention is provided with information about a pulling rate sent from a control means for controlling a single crystal pulling, and information sent from the control means. A computing means for computing a current value to be passed through the single crystal pulling motor based on the information about the size of the single crystal thus obtained, and a current value measuring means for measuring the current value actually flowing through the single crystal pulling motor. And subtracting means for obtaining the difference between the current value measured by the current value measuring means and the current value calculated by the calculating means, and alarm means for issuing an alarm according to the output value of the subtracting means. It is characterized by being. (1) Further, in order to achieve the above object, the single crystal pulling apparatus according to the present invention is provided with the information about the pulling speed sent from the control means for controlling the single crystal pulling and the single crystal sent from the control means. Computation means for computing the current value to flow to the single crystal pulling motor from the information on the size of the crystal, current value measuring means for measuring the current value actually flowing in the single crystal pulling motor, and the current Subtracting means for obtaining the difference between the current value measured by the value measuring means and the current value calculated by the calculating means, and pulling for changing the pulling condition of the single crystal according to the output value sent from the subtracting means It is characterized in that it is provided with condition changing means. (2) Further, in order to achieve the above-mentioned object, the single crystal pulling apparatus according to the present invention is provided with the information about the pulling rate sent from the control means for controlling the single crystal pulling, and the single crystal sent from the control means. Computation means for computing the current value to flow to the single crystal pulling motor from the information on the size of the crystal, current value measuring means for measuring the current value actually flowing in the single crystal pulling motor, and the current Subtracting means for obtaining the difference between the current value measured by the value measuring means and the current value calculated by the calculating means, alarm means for issuing an alarm according to the output value of the subtracting means, and the subtracting means. It is characterized in that it is provided with a pulling condition changing means for changing the pulling condition of the single crystal in accordance with the output value coming (3).

[0017]

The present inventors have studied the situation in which the solid layer formed in the lower part of the crucible grows and adheres to the single crystal during the pulling of the single crystal.

When the single crystal and the solid layer under the crucible adhere to each other, the weight obtained by adding the weight of the pulled single crystal, the weight of the crucible, the weight of the melt, and the amount of the solid layer under the crucible at the time when the adhesion occurs. It becomes a load on the lifting motor. From this, after the occurrence of sticking, the load applied to the single crystal pulling motor rapidly increases, and the current value flowing in the single crystal pulling motor sharply increases above a predetermined value. Therefore, the inventors have found that the adhesion between the single crystal and the solid layer under the crucible can be detected by monitoring the value of the current flowing through the single crystal pulling motor, and have completed the present invention.

That is, according to the single crystal pulling apparatus (1) of the present invention, the difference between the current value that should normally flow in the single crystal pulling motor and the current value that actually flows in the single crystal pulling motor. Is determined, and it is determined whether or not a sticking state has occurred according to the difference, and an alarm is issued when the sticking state is determined.

Further, according to the single crystal pulling apparatus (2) of the present invention, the difference between the current value to be passed through the single crystal pulling motor and the current value actually flowing through the single crystal pulling motor is determined. It is determined whether or not a sticking state has occurred according to the difference, and if the sticking state is determined, the subsequent pulling conditions for the single crystal are changed.

Further, according to the single crystal pulling apparatus (3) of the present invention, the difference between the current value that should flow in the single crystal pulling motor and the current value that actually flows in the single crystal pulling motor is It is determined whether or not a fixed state has occurred according to the difference, and if the fixed state is determined, an alarm is issued and subsequent pulling conditions for the single crystal are changed.

[0022]

Embodiments of the single crystal pulling apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a system configuration diagram schematically showing a single crystal pulling apparatus according to the first embodiment. In the figure, 19 indicates a single crystal, and the length, diameter, etc. of the single crystal 19 are measured by a non-contact type measuring means (not shown), and these pieces of information are input to the control means 11. ing. The control means 11 is connected to a driving device 16 for driving the single crystal pulling motor 18, and is also connected to the computing means 12, and the single crystal pulling motor 18 is connected via the driving means 16.
In addition to controlling the number of revolutions, the information from the single crystal 19 is sent to the calculating means 12. Single crystal pulling motor 1
A current value measuring means 13 for detecting the current value actually flowing in the single crystal pulling motor 18 is connected to 8, and the current value as an analog amount measured by the current value measuring means 13 is an A / D converter. It is adapted to be converted into a digital quantity at 17 and inputted to the subtracting means 14. In the calculation means 12, the single crystal 19 sent from the control means 11
From the information on the pulling speed of the single crystal 19 and the information on the size of the single crystal 19, the calculated current value to be passed to the normal single crystal pulling motor 18 when the single crystal 19 is not fixed is calculated. ing. In the subtracting means 14 to which the current value from the A / D converter 17 and the calculated value from the calculating means 12 are input, these values are subtracted and it is judged whether or not the single crystal 19 is stuck. When it is determined that the single crystal 19 is stuck, an alarm signal is issued to the alarm means 15.
The CPU 20 is configured to include these control means 11, calculation means 12 and subtraction means 14.

In the single crystal pulling apparatus constructed as described above, the operation of the CPU 20 will be described with reference to the flow chart shown in FIG.

First, in step 1, the diameter and length of the single crystal 19 being pulled (hereinafter referred to as the size of the single crystal).
The measurement data of is input to the control means 11 from the measurement means. Next, at step 2, electric signals for temperature adjustment of the heater and speed adjustment of the pulling motor based on the measurement data are transmitted from the control means 11 to the driving device 16 and the driving device 16 is controlled. Next, the electric signal for speed adjustment of the motor in step 2 is also output to the calculating means 12, and the current value which will flow to the single crystal pulling motor from the motor speed adjusting data and the single crystal weight data is given to the calculating means 12. Is calculated (S3). Next, the current value actually flowing in the single crystal pulling motor 18 is measured by the current value measuring means 13, the current value as an analog value is converted into a digital signal in the A / D converter 17, and the subtracting means 14 is used. Is input to (S4). here,
The subtraction means 14 calculates the difference between the current value that is supposed to flow through the motor 18 and that is input in step 3 and the current value that is actually flowing measured in step 4 (S5).
It is determined whether the data is within a predetermined value (S
6). When it is determined that the data is within the predetermined value, the process returns to step 1, while when it is determined that the data is not within the predetermined value, the single crystal 19 and the solid layer below the crucible are fixed. A judgment is made and an alarm signal is output to the alarm means 15 (S7).

A case in which a single crystal is pulled by the melt layer method using the single crystal pulling apparatus having the above structure will be described below.

First, a crucible 3 in which a quartz outer layer holding container 31b (FIG. 9) is fitted with a quartz inner layer holding container 11a.
1, the single crystal raw material is polycrystalline single crystal silicon (lamp 3
5 kg, granules 30 kg), then 0.6 g of phosphorus-silicon alloy as an N-type dopant was added, and the inside of the chamber was made to have an argon atmosphere of 10 Torr, and the heater 3 was used.
2 is supplied with 102 kw of electric power to melt all the raw materials, and then the heater power is set to 86 kw to keep the molten state of all the raw materials for about 1 hour. After that, set the heater power to 7
The solid layer 38 is grown under the molten layer at 4 kW to stabilize it. Next, the seed crystal 35 is immersed in the molten layer 33, and the crucible 31 and the pulling shaft 34 are respectively set to 1 rpm and 10 rpm.
The single crystal 36 having a single crystal diameter of 6 inches and a length of 1.2 m is pulled by rotating at a rotation speed of rpm. The single crystal 36
In order to detect the sticking between the solid layer 38 and the solid layer 38, the heater position and the pulling speed are adjusted to the conditions where the sticking occurs, and the single crystal 36 is pulled up.
The rotation directions of the pull-up shaft 34 and the pull-up shaft 34 are opposite to each other.

FIG. 3 shows the results obtained by pulling up the single crystal 36 under the above conditions and measuring the time from the occurrence of sticking to the occurrence of an alarm.
The vertical axis represents the time (s) from the occurrence of sticking until the alarm is issued. In addition, this experiment was performed 5 times, and the time at which the sticking occurred was visually determined, and the time at which the rotation direction and the rotation speed of the single crystal 36 and the rotation direction and the rotation speed of the crucible 31 coincided with each other was set as the time at which the sticking occurred. .

As is apparent from FIG. 3, in the single crystal pulling apparatus according to this example, an alarm was issued within 10 seconds after the time when visual fixation occurred. As described above, if the time until the adhered state between the single crystal 36 and the solid layer 38 is found and the processing such as stopping the pulling is performed within about 5 minutes from the time when the sticking occurs, the pulling is performed. Since it is possible to prevent the device from being damaged and the single crystal 36 from falling during pulling, it can be said that the above-mentioned treatment is sufficiently quickly performed within 10 seconds. Therefore, according to the single crystal pulling apparatus according to the present embodiment, the automatic sticking detection can be performed and the rapid processing can be performed, so that the sticking between the single crystal 36 and the solid layer 38 below the crucible occurs. It is possible to prevent damage to the single crystal pulling device due to the single crystal 36 lifting the crucible 31 and accidents such as dropping of the single crystal 36 due to damage to the neck portion of the single crystal 36.

FIG. 4 shows a single crystal pulling apparatus according to the embodiment, which is different from the embodiment shown in FIG. 1 in that pulling condition changing means 21 is provided. The pulling condition changing means 21 receives the electric signal from the subtracting means 14 and changes the pulling condition of the single crystal 19.

FIG. 5 is a flow chart showing the operation of the CPU 20 shown in FIG. 4, which differs from the flow chart shown in FIG. 2 in step 7 and subsequent steps, and when it is determined in step 7 that sticking has occurred, this sticking occurs. Is output from the subtracting means 14 to the pulling condition changing means 21, and the pulling condition changing means 21 sends a control signal for stopping the crystal pulling motor 18 or stopping the supply of electric power to the heater 32. To be done. Therefore, in the single crystal pulling apparatus according to the embodiment shown in FIGS. 4 and 5, breakage of the apparatus is automatically prevented.

FIG. 6 shows a single crystal pulling apparatus according to still another embodiment, which is different from the embodiment shown in FIG. 4 in that the alarm means 15 is connected to the subtracting means 14.

FIG. 7 is a flowchart showing the operation of the CPU 20 shown in FIG. 6, which is different from the flowchart shown in FIG. 5 in step 7. In this embodiment, an alarm signal is output from the subtracting means 14 to the alarm means 15 in step 7. Therefore, in the single crystal pulling apparatus according to the embodiment shown in FIGS. 6 and 7, an alarm signal is issued, and the crystal pulling motor is automatically stopped to prevent the apparatus from being damaged.

[0034]

As described above in detail, in the single crystal pulling apparatus (1) according to the present invention, the information about the pulling speed sent from the control means for controlling the single crystal pulling, and the control means. Calculation means for calculating the current value that should flow to the single crystal pulling motor from the information about the size of the single crystal that is sent, and current value measurement for measuring the current value that is actually flowing in the single crystal pulling motor Means, subtracting means for obtaining a difference between the current value measured by the current value measuring means and the current value calculated by the calculating means, and alarm means for issuing an alarm according to the output value of the subtracting means Therefore, when sticking between the single crystal and the solid layer below the crucible occurs, for example, an alarm can be issued within 10 seconds, the sticking can be detected early, and the single crystal lifts the crucible. It is possible to avoid the occurrence of accidents such as single crystal pulling equipment damage due to damage to the single crystal pulling equipment and single crystal falling due to damage to the neck portion of the single crystal, and in a production line where a small number of operators manage a large number of pulling furnaces. Will be easier to operate.

Further, in the single crystal pulling apparatus (2) according to the present invention, the information about the pulling rate sent from the control means for controlling the single crystal pulling and the single crystal sent from the control means. And a current value measuring means for measuring the current value actually flowing in the single crystal pulling motor, and the current value. Subtracting means for obtaining the difference between the current value measured by the measuring means and the current value calculated by the calculating means, and pulling condition for changing the pulling condition of the single crystal according to the output value sent from the subtracting means Since the changing means is provided, when sticking between the single crystal and the solid layer below the crucible occurs, the pulling condition can be changed within, for example, 10 seconds, and the single crystal changes the crucible. It is possible to automatically avoid the occurrence of accidents such as damage to the single crystal pulling device due to lifting and single crystal falling due to damage to the neck of the single crystal, and a small number of operators manage a large number of pulling furnaces. It becomes easy to operate in the operating line.

Further, in the single crystal pulling apparatus (3) according to the present invention, the information about the pulling rate sent from the control means for controlling the single crystal pulling, and the single crystal sent from the control means. And a current value measuring means for measuring the current value actually flowing in the single crystal pulling motor, and the current value. Subtracting means for obtaining the difference between the current value measured by the measuring means and the current value calculated by the calculating means, alarm means for issuing an alarm in accordance with the output value of the subtracting means, and the subtracting means. Since the pulling condition changing means for changing the pulling condition of the single crystal according to the output value of the single crystal is provided, when sticking between the single crystal and the solid layer under the crucible occurs, for example, 10 seconds or more. Since changing the pulling conditions and issuing an alarm, it is possible to detect the sticking earlier, and at the same time, the single crystal pulling device is damaged by the single crystal lifting the crucible, and the single crystal falls due to damage to the neck portion of the single crystal. It is possible to automatically avoid the occurrence of accidents such as, and it becomes easy to operate in an operation line in which a small number of operators manage a large number of lifting furnaces.

[Brief description of drawings]

FIG. 01 is a system configuration diagram showing a single crystal pulling apparatus according to an example.

FIG. 2 is a flowchart showing an operation of the CPU 20 shown in FIG.

FIG. 03 is a graph showing the results of measuring the time from the occurrence of sticking to the occurrence of an alarm in the single crystal pulling apparatus according to Example 1.

FIG. 04 is a system configuration diagram showing a single crystal pulling apparatus according to another embodiment.

FIG. 05 is a flowchart showing an operation of the CPU 20 shown in FIG.

FIG. 06 is a system configuration diagram showing a single crystal pulling apparatus according to still another embodiment.

7 is a flowchart showing the operation of the CPU 20 shown in FIG.

FIG. 08 is a cross-sectional view schematically showing a single crystal pulling apparatus used in a conventional CZ method.

FIG. 9 is a cross-sectional view schematically showing a single crystal pulling apparatus used in a conventional melt layer method.

FIG. 10 is a schematic cross-sectional view showing a state in which a solid layer and a molten layer are fixed to each other.

[Explanation of symbols]

 11 Control Means 12 Computing Means 13 Current Value Measuring Means 14 Subtracting Means 15 Alarm Means

Front page continuation (72) Inventor Teruo Izumi 4-533 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Masahiko Okui 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd.

Claims (3)

[Claims] 1. A current to be passed to a single crystal pulling motor from information about the pulling rate sent from the control means for controlling the pulling of the single crystal and information about the size of the single crystal sent from the control means. A calculation means for calculating a value, a current value measurement means for measuring a current value actually flowing in the single crystal pulling motor, a current value measured by the current value measurement means, and a calculation value by the calculation means A single crystal pulling apparatus comprising: subtraction means for obtaining a difference from a current value; and alarm means for issuing an alarm according to an output value of the subtraction means. 2. A current to be passed to a single crystal pulling motor from information about the pulling rate sent from the control means for controlling the pulling of the single crystal and information about the size of the single crystal sent from the control means. A calculation means for calculating a value, a current value measurement means for measuring a current value actually flowing in the single crystal pulling motor, a current value measured by the current value measurement means, and a calculation value by the calculation means A single crystal pulling apparatus comprising: a subtracting unit for obtaining a difference from a current value; and a pulling condition changing unit for changing a pulling condition of the single crystal according to an output value sent from the subtracting unit. . 3. A current to be passed to a single crystal pulling motor from information about the pulling speed sent from the control means for controlling the pulling of the single crystal and information about the size of the single crystal sent from the control means. A calculation means for calculating a value, a current value measurement means for measuring a current value actually flowing in the single crystal pulling motor, a current value measured by the current value measurement means, and a calculation value by the calculation means Subtracting means for obtaining the difference from the current value, alarm means for issuing an alarm according to the output value of the subtracting means, and pulling condition for changing the pulling condition of the single crystal according to the output value sent from the subtracting means A single crystal pulling apparatus comprising: a changing unit.