JP2007254178A - Method for growing single crystal and single crystal growing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a single crystal to optimally control a top portion of a crystal into a desired shape in the growth of a single crystal by a floating zone melt method (FZ method). <P>SOLUTION: The method includes: a crystal diameter detection step of detecting a crystal diameter at the solid-liquid interface in the crystal side; a crystal diameter change rate calculation step (ST310) of calculating a crystal diameter change rate as a change rate of the crystal diameter per unit time; a crystal diameter change rate comparing step of comparing the change rate in the crystal diameter to a preliminarily determined range of the change rate in the crystal diameter; and a material feed speed commanding step of keeping the material feed speed (ST313) if the change rate of the crystal diameter exceeds the upper limit of the determined range (ST312) and of increasing the material feed speed (ST315) when the change rate is lower than the lower limit of the determined range (ST314). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a single crystal growth method and a single crystal growth apparatus. Specifically, the present invention relates to automatic control when a crystal top portion is formed in a desired shape in single crystal growth by a floating zone melting method (FZ method).

Conventionally, a floating zone melting method (floating zone method, FZ method) is known as a method for growing a semiconductor single crystal. A single crystal growth apparatus 10 for growing a single crystal by the floating zone melting method is shown in FIG.
The single crystal growing apparatus 10 includes a material feeding mechanism 11 that is disposed on the upper shaft side and supplies the material 600 downward at a predetermined speed, and a crystal that is disposed on the lower shaft side and pulls down the crystal 500 that is crystallized at a predetermined speed. A pulling mechanism 12 and a heating coil 13 for heating the tip of the material 600 are provided. Then, while the material 600 is melted by the heating coil 13, the material feed speed by the material feed mechanism 11 and the crystal pulling speed by the crystal pulling mechanism 12 are controlled to predetermined speeds, respectively, so that the semiconductor single crystal 500 having a predetermined shape is formed. To manufacture.

  Here, in growing the top portion 510 corresponding to the tip portion of the semiconductor single crystal 500, it is necessary to arrange the shape so as to smoothly increase from the diameter of the seed crystal to the target diameter (the diameter of the straight body portion). Therefore, the voltage applied to the heating coil 13, the material feed rate, and the crystal pulling rate must be appropriately controlled.

In Patent Document 1, the above-described applied voltage and each speed (material feed speed, crystal It is disclosed that the top portion 510 is formed in a desired shape by controlling the pulling-down speed.
In particular, it is disclosed that the voltage applied to the heating coil 13 is controlled in accordance with the increase or decrease of the zone length L. When the zone is too long, there is a problem that the zone is cut, and when the zone is too short, there is a problem that crystals are disturbed due to a steep temperature gradient. Therefore, the zone length L is controlled to an appropriate length. As a result, the crystal shape can be indirectly controlled. In measuring the material diameter Pd, the crystal diameter Sd, and the zone length L, a CCD camera 14 is installed in the vicinity of the heating coil 13, and the material diameter Pd, crystal diameter Sd, and zone length L are taken from an image captured by the CCD camera 14. Is required.

JP-A-9-77588

Certainly, if appropriate control based on the material diameter Pd, the crystal diameter Sd, and the zone length L is executed, the shape of the grown single crystal can be formed into a desired shape.
However, the heating coil 13 needs to be replaced depending on the type of single crystal to be grown. However, if the heating coil 13 is replaced, the relative position of the heating coil 13 with respect to the CCD camera 14 changes. When the distance between the heating coil 13 and the solid-liquid interface is detected as the zone length L, if the relative position between the CCD camera 14 and the heating coil 13 changes, the detected zone length L differs. Therefore, if the control is performed with the same setting before and after the heating coil 13 is replaced, a single crystal having a desired shape cannot be obtained. Although it is conceivable to make an adjustment for accurately detecting the zone length L every time the heating coil 13 is replaced, it takes too much time and cost to make a fine adjustment each time the coil is replaced. Not realistic.

  An object of the present invention is to provide a single crystal growth method and a single crystal growth apparatus that can be optimally controlled regardless of coil replacement.

  The method for growing a single crystal according to the present invention includes a material feeding mechanism that feeds a material downward, a heating unit that heats a lower end portion of the material to melt the material, and a coaxial line with the material feeding mechanism. A crystal pulling mechanism for pulling down a crystal grown using a molten material as a raw material, and a single crystal growing method for growing a single crystal by a floating zone melting method using a single crystal growing apparatus, the heating means A crystal diameter detection step for detecting a crystal diameter at a crystal-side solid-liquid interface, which is a solid-liquid interface between a melted portion where the material is melted by heating by the crystal and a crystal where the melted portion is crystallized, and material feed by the material feed mechanism A material feed rate control step for controlling a speed, wherein the material feed rate control step calculates a crystal diameter change rate that is a change amount per unit time of the crystal diameter; and Crystal diameter change A crystal diameter change rate comparison step for comparing the crystal diameter change rate calculated in the calculation step with a preset range of the crystal diameter change rate, and the material according to a comparison result in the crystal diameter change rate comparison step A material feed speed commanding step for commanding a material feed speed of the feed mechanism.

  In such a configuration, first, a material is set in the material feeding mechanism, and a seed crystal is set in the crystal pulling mechanism. Then, while the material is fed downward by the material feeding mechanism, the lower end portion of the material is melted by the heating means, and the melted material is adhered to the seed crystal. Then, the seed crystal grows using the molten material as a raw material, and the single crystal is grown, so that the crystal is pulled downward by the crystal pulling mechanism according to the growth of the single crystal.

  Here, it is necessary to grow the single crystal into a desired shape. In particular, the top part of the single crystal must be grown smoothly from the seed crystal diameter to the target diameter (straight body part diameter), and the crystal should be grown with the diameter kept constant in the straight body part. I must. In this respect, if the material feed rate is too fast, the crystal will be too thick, and conversely if the material feed rate is too slow, the crystal will be too thin. It is important for control.

  In the configuration of the present invention, first, the crystal diameter is detected in the crystal diameter detection step. Based on the crystal diameter detected in the crystal diameter detection step, the crystal diameter change rate which is the amount of change per unit time of the crystal diameter is calculated in the crystal diameter change rate calculation step. The range of the crystal diameter change rate for making the single crystal into a predetermined shape is set as the set range, and the crystal diameter change rate calculated in the crystal diameter change rate calculating step is the set range in the crystal diameter change rate comparing step. To be compared. And according to the comparison result in the crystal diameter change rate comparison process, the material feed speed is commanded by the material feed speed command process. For example, when the crystal diameter change rate is out of the set range, the material feed speed is increased, decelerated, or maintained so that the crystal diameter change rate falls within the set range. For example, if the crystal diameter change rate is larger than the set range, it means that the crystal is overweight earlier than planned, so that the material feed rate can be maintained as it is without increasing or decelerated. Take as an example. Alternatively, when the crystal diameter change rate is smaller than the set range, it means that the crystal is not thicker than planned, and therefore the material feed speed is increased as an example. As described above, the crystal can be formed into a desired shape by adjusting the material supply rate by controlling the material feed rate so that the crystal diameter change rate falls within the set range.

According to such a configuration, since the material feed speed is controlled based on the change in the crystal diameter, the material feed speed can be appropriately controlled by accurately detecting the crystal diameter.
Conventionally, the zone length, which is the distance between the solid-liquid interface on the crystal side and the heating means (for example, heating coil), is measured, and control of various control targets including the material feed speed is performed so that this zone length is within a predetermined range. Had gone. However, the heating means is exchanged depending on the type and size of the single crystal to be grown, and when the heating means is exchanged, the attachment position of the heating means is shifted. For example, an error of about 1 mm occurs due to the play of the mounting hole, and if an error of the heating means due to individual differences in products or changes in diameter is included, a deviation of about 2 mm occurs in some cases. Thus, when the attachment position of the heating means is different, an error occurs when measuring the zone length, which is the distance between the crystal-side solid-liquid interface and the heating means. As described above, it is impossible to grow a single crystal into a desired shape by the control based on the zone length measured with an error. Further, if the zone length is accurately measured, there is a trouble that the mounting error of the heating means must be calibrated every time the heating means (for example, a heating coil) is replaced.

  In this regard, in the present invention, when the material feed rate is controlled based on the crystal diameter, the crystal diameter can be accurately detected regardless of the attachment error of the heating means. A single crystal can be grown into a desired shape by controlling the material feed rate so that the crystal diameter change rate falls within a predetermined setting range based on the crystal diameter that can be accurately detected in this way. Further, since the exchange of the heating means does not affect the detection of the crystal diameter, an appropriate heating means can be used according to the type and size of the crystal. In addition, compared to the case where the crystal shape is indirectly controlled by controlling the zone length to a predetermined length as in the prior art, in the present invention, the change rate of the crystal diameter is set within a predetermined range. Therefore, the control goal of controlling the crystal shape can be achieved directly and reliably.

  In the present invention, the setting range of the crystal diameter change rate is a set range having an upper limit value and a lower limit value as threshold values, and the material feed speed command step includes the crystal diameter change rate in the crystal diameter change rate comparison step and If the crystal diameter change rate is below the lower limit value of the set range by comparison with the set range, the material feed speed is increased, and if the crystal diameter change rate exceeds the upper limit value of the set range, It is preferable to maintain the material feed speed.

In such a configuration, the crystal diameter change rate is compared with the lower limit value of the setting range in the crystal diameter change rate comparison step.
If the crystal diameter change rate is below the lower limit of the setting range, the material feed speed is increased. The fact that the crystal diameter change rate is below the lower limit of the setting range means that the crystal is thinner than planned, so changing the crystal diameter by increasing the material feed rate by increasing the material feed rate The rate can be within the set range. Further, the crystal diameter change rate is compared with the upper limit value of the setting range. If the crystal diameter change rate exceeds the upper limit value of the setting range, the material feed speed is maintained without increasing. If the crystal diameter change rate exceeds the upper limit of the setting range, it means that the crystal is too thick than planned, and the material supply amount is excessive, so without increasing the material feed rate. Maintain the material feed rate. Thereby, the thickness of the crystal can be suppressed and the change rate of the crystal diameter can be within the set range.
In this way, the crystal can be grown into a desired shape by adjusting the material feed rate according to the comparison between the crystal diameter change rate and the set range.

  In the present invention, the crystal diameter detection step detects the crystal diameter at regular time intervals, and the crystal diameter change rate calculation step calculates an average value for the nearest predetermined number of crystal diameters detected at regular time intervals. It is preferable to calculate the difference between the average value for the predetermined number in the past and the crystal diameter change rate.

In such a configuration, the crystal diameter is detected at regular intervals by the crystal diameter detection step. For example, detecting the crystal diameter at intervals of 2 seconds is an example. The crystal diameter change rate calculating step calculates an average value of past predetermined number data based on the crystal diameter data, and further calculates an average value of the latest predetermined number data.
For example, an average value of 10 crystal diameter data in the latest 20 seconds is calculated, and an average value of 10 crystal diameter data in 20 seconds from 100 seconds to 80 seconds before is calculated as an example. . Then, in the crystal diameter change rate calculating step, the difference between the latest average value and the past average value is calculated to obtain the crystal diameter change rate.
According to such a configuration, since the crystal diameter change rate is calculated based on an average value of a predetermined number instead of single data, it greatly affects the detection error of the crystal diameter in a single crystal diameter detection process. The control can be stabilized without being subjected to the above.

  In the present invention, the material feed rate control includes a material diameter detection step of detecting a material diameter at a material-side solid-liquid interface, which is a solid-liquid interface between the melted portion where the material is melted by heating by the heating means and the material. The process includes a supply balance calculation step for calculating a difference between a material supply amount based on the material feed speed and the material diameter and a crystallization amount based on the crystal pulling speed and the crystal diameter as a supply balance, and a preset supply balance setting range. A supply balance comparison step that compares the supply balance with respect to the supply balance comparison step, wherein the material feed speed command step commands the material feed speed of the material feed mechanism according to a comparison result in the supply balance comparison step. preferable.

  In such a configuration, when the material is fed to the heating means by the material feeding mechanism and the crystal is pulled down by the crystal pulling mechanism, the supply balance between the material supply amount and the crystal pulling amount is calculated by the supply balance calculating step. That is, the material diameter is detected by the material diameter detection process, and the crystal diameter is detected by the crystal diameter detection process. The supply balance calculation step calculates the material supply amount based on the material feed speed and the material diameter by the material feed mechanism, calculates the crystallization amount based on the crystal pulling speed and the crystal diameter by the crystal pulling mechanism, The difference between the material supply amount and the crystallization amount is calculated. For example, when the material feed speed is Zp, the material diameter is Pd, the crystal pulling speed is Re, and the crystal diameter is Sd, the supply balance is calculated by the following equation.

  The calculated supply balance is compared with a preset setting range in the supply balance comparison step. Then, according to the comparison result in the supply balance comparison process, the material feed speed is commanded by the material feed speed command process. For example, when the supply balance is below a predetermined lower limit, the material supply amount is too small compared to the crystallization amount, so the material feed speed is increased so that the supply balance falls within the set range. . Then, a single crystal can be grown while maintaining a balance between the material supply amount and the crystallization amount.

  In the present invention, the setting range of the supply balance is a setting range having a lower limit value as a threshold value, and the material feed speed command step is performed by comparing the supply balance and the setting range in the supply balance comparison step. It is preferable to increase the material feed speed when it is below the lower limit value of the setting range, and to maintain the material feed speed when the supply balance is equal to or higher than the lower limit value.

In such a configuration, the supply balance is compared with the lower limit value of the setting range in the supply balance comparison step. If the supply balance is below the lower limit value of the setting range, the material supply amount is too small compared to the crystallization amount. Therefore, the material feed speed is increased so that the supply balance falls within the setting range. Then, a single crystal can be grown while maintaining a balance between the material supply amount and the crystallization amount. Further, when the supply balance is equal to or higher than the lower limit value of the setting range, it means that the material supply amount is sufficient, and the material feed speed is maintained without increasing.
In this way, by controlling the material feed rate so that the supply balance falls within the set range, for example, it is possible to appropriately grow single crystals while avoiding inconveniences such as the melting part being cut.

  In the present invention, in the material feed rate command step, first, a material feed rate is determined based on the comparison result in the crystal diameter change rate comparison step, and the crystal diameter change rate is within a set range of the crystal diameter change rate. In this case, it is preferable to further determine the material feed speed based on the comparison result in the supply balance comparison unit.

In such a configuration, the material feed rate is subjected to control based on the crystal diameter change rate and control based on the supply balance. First, the material feed rate is adjusted so that the crystal diameter change rate is within the set range, and when the crystal diameter change rate is within the set range, the supply balance is further controlled to be within the set range. Is done. If the crystal diameter change rate deviates from the set range, the shape of the single crystal deviates from the schedule, so that the crystal diameter change rate is preferentially executed within the set range.
However, even if the change rate of the crystal diameter is within the set range, the crystal does not grow unless the supply balance is appropriate. Therefore, the growth of the single crystal can be appropriately advanced by setting the supply balance within the set range. .

  In the present invention, a material diameter detecting step for detecting a material diameter at a material-side solid-liquid interface, which is a solid-liquid interface between the melted portion where the material is melted by heating by the heating means and the material, and application to the heating means An applied voltage control step for controlling a voltage, and the material includes a tapered portion that gradually increases in diameter from a tip portion, and a straight body portion having a constant diameter, and the applied voltage control step When the material melted by the heating means is a tapered portion, the applied voltage is set to a value that correlates with the material diameter, and when the material melted by the heating means is a straight body portion, It is preferable that the applied voltage is a value correlated with the crystal diameter, and the target voltage is maintained when the applied voltage reaches a preset target voltage.

  In such a configuration, the heating temperature of the heating means is appropriately changed according to the amount of material to be melted and the amount of crystallization. First, when the taper portion of the material is melted by the heating means, the amount of the material melted by the heating means varies depending on the material diameter, so the heating temperature is correlated with the material diameter. And when the part melted by the heating means shifts from the taper part of the material diameter to the straight body part having a constant diameter, the amount of the material melted by the heating means varies depending on the amount of crystallization, so the heating temperature is the crystal The value correlates with the diameter. As described above, by appropriately controlling the heating temperature of the heating means, it is possible to supply a melted material as a crystallization raw material to the crystal, and it is possible to appropriately grow a single crystal.

  In the present invention, a crystal pulling rate control step for controlling the crystal pulling rate by the crystal pulling mechanism is provided, and the crystal pulling rate according to the crystal diameter is preset, and the crystal pulling rate control step is the crystal size detecting step. It is preferable to determine the crystal pulling speed based on the crystal diameter detected in (1).

In such a configuration, the crystal pulling speed by the crystal pulling mechanism is set in advance, and in the crystal pulling speed control step, the crystal pulling speed is controlled according to the predetermined set speed.
When it is desired to grow a single crystal into a desired shape, it is desirable from the viewpoint of stably growing a crystal having a desired shape that the crystal pulling rate is increased gradually and smoothly at a predetermined set speed. And in controlling a crystal | crystallization to a predetermined shape, it can respond by control of a raw material feed rate.

  The single crystal growing apparatus of the present invention is disposed on a coaxial line with a material feeding mechanism for feeding the material downward, a heating means for heating the lower end of the material to melt the material, and the material feeding mechanism. A crystal pulling mechanism that pulls down a crystal grown using a molten material as a raw material, and a crystal growth device that includes a molten portion in which the material is melted by heating by the heating means, and a crystal in which the molten portion is crystallized. A crystal diameter detecting means for detecting a crystal diameter at a crystal-side solid-liquid interface that is a solid-liquid interface of the material, and a material feed speed control unit that controls a material feed speed by the material feed mechanism, and the material feed speed control unit Is a crystal diameter change rate calculation unit that calculates a crystal diameter change rate that is a change amount per unit time of the crystal diameter, and the crystal diameter change rate that is calculated by the crystal diameter change rate calculation unit is preset. Crystal diameter change A crystal diameter change rate comparison unit that compares with a set range of the rate, and a material feed speed command unit that commands a material feed speed of the material feed mechanism according to a comparison result in the crystal diameter change rate comparison unit. Features.

According to such a configuration, the same effects as those of the above-described invention can be achieved.
That is, since the material feed speed is controlled based on the crystal diameter, the crystal diameter can be accurately detected regardless of the attachment error of the heating means. The single crystal can be grown into a desired shape by controlling the material feed so that the crystal diameter change rate falls within a predetermined setting range based on the crystal diameter that can be accurately detected.

  In the present invention, the crystal diameter detecting means picks up an image of a crystal-side solid-liquid interface that is a solid-liquid interface between a melted portion where a material is melted by heating by the heating means and a crystal where the melted portion is crystallized. And a crystal diameter calculator that calculates the crystal diameter at the solid-liquid interface based on the imaging data imaged by the imaging means.

  In such a configuration, the crystal-side solid-liquid interface is imaged by the imaging means, and the crystal diameter at the solid-liquid interface is calculated by the crystal diameter calculation unit based on this imaging data. Thereafter, various control objects including the material feed speed are controlled based on the crystal diameter. According to such a configuration, since the imaging data can be continuously acquired by the imaging means, the crystal diameter can be sampled at a minute time interval (for example, every 2 seconds).

  When providing a material diameter detecting means for detecting the material diameter, the material diameter detecting means includes an imaging means for imaging the solid-liquid interface between the melted part and the material, and a material diameter calculation for calculating the material diameter based on the imaging data. It is mentioned as an example that it is provided with a part. The crystal diameter detecting means and the material diameter detecting means can share one imaging means.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be illustrated and described with reference to reference numerals attached to respective elements in the drawings.
(First embodiment)
1st Embodiment which concerns on the single-crystal growth apparatus of this invention is described.
First, a semiconductor single crystal 500 grown by the single crystal growth apparatus 100 of the present invention will be described.
FIG. 1 is a diagram showing the shape of a semiconductor single crystal 500 grown by the single crystal growing apparatus 100.
FIG. 2 is a diagram showing a state in which the seed crystal 540 and the material 600 before melting are set in the crystal pulling mechanism 120 and the material feeding mechanism 110, respectively.

  As shown in FIG. 1, the semiconductor single crystal 500 includes a top portion 510 that gradually increases in diameter from the tip portion and becomes thicker, and a straight body portion 520 that grows with a substantially constant diameter when the target diameter is reached. , And a bottom portion 530 whose diameter is abruptly reduced and the end portion is cut from the straight body portion 520. As shown in FIG. 2, the material 600 includes a tapered portion 610 that gradually increases in diameter from the distal end portion, and a straight body portion 620 having a constant diameter.

Then, the material 600 is heated to a molten state with the tip of the material 600 inserted between the heating coils 130, and the material 600 melted by the material feeding mechanism 110 is sent downward to adhere to the seed crystal 540. Then, the seed crystal 540 grows using the molten material 600 as a raw material, and the single crystal 500 is grown. The feed rate of the material 600 and the pulling rate of the crystal 500 are appropriately controlled to grow the single crystal 500 having the shape shown in FIG. In particular, it is necessary to arrange the shape so that the top portion 510 of the single crystal 500 smoothly increases from the diameter of the seed crystal 540 to the target diameter (the diameter of the straight body portion 520). For this reason, the voltage applied to the heating coil 130, the material feed rate, and the crystal pulling rate must be appropriately controlled.
Hereinafter, in the description of the present embodiment, automatic control for forming the top portion 510 of the single crystal 500 will be described.

The single crystal growth apparatus 100 of the present invention will be described.
FIG. 3 is a diagram showing a configuration of the single crystal growing apparatus 100.

  The single crystal growing apparatus 100 includes a material feeding mechanism 110 that is disposed on the upper shaft side and supplies the material 600 downward at a predetermined speed, and a crystal that is disposed on the lower shaft side and pulls down the crystal 500 that is crystallized at a predetermined speed. A pulling mechanism 120, a heating coil (heating means) 130 for heating the front end portion of the material 600, a CCD camera (imaging means) 140 for imaging with a solid-liquid interface between the material side and the crystal side in view, and a CCD camera 140 And a control unit 200 that controls the applied voltage to the heating coil 130 and the driving speed of the material pulling mechanism 110 and the crystal pulling mechanism 120 based on the imaging data from.

The material feeding mechanism 110 and the crystal pulling mechanism 120 are arranged coaxially.
The material feeding mechanism 110 has a holding unit 111 that holds the material 600 on the lower end side, and feeds the material 600 from top to bottom.
The crystal pulling mechanism 120 has a holding portion 121 that holds the crystal 500 on the upper end side, and pulls down the crystal 500 from top to bottom.
The heating coil 130 is disposed between the material feeding mechanism 110 and the crystal pulling mechanism 120, and its position is fixed.
The heating coil 130 heats the front end of the raw material 600 fed downward by the raw material feed mechanism 110 in a state of surrounding the front end of the raw material 600 to melt the front end of the raw material 600.

  The CCD camera 140 is disposed in the vicinity of the heating coil 130. Then, the CCD camera 140 includes from the front end (lower end) of the material 600 to the front end (upper end) of the crystal 500 in the visual field, with the melted portion melted by the heating coil 130 as the center.

  The control unit 200 includes an image processing unit 210 that processes imaging data of the CCD camera 140, a diameter calculation unit 220 that calculates a material diameter and a crystal diameter based on the imaging data, and a voltage that controls an applied voltage to the heating coil 130. A control unit 230, a crystal pulling speed control unit 240 that controls the driving speed of the crystal pulling mechanism 120, and a material feed speed control unit 300 that controls the driving speed of the material feeding mechanism 110 are provided.

The image processing unit 210 takes in the image data from the CCD camera 140 and outputs it to the diameter calculation unit 220.
The diameter calculation unit 220 calculates the diameter (diameter) of the material 600 at the solid-liquid interface based on the imaging data, and calculates the diameter (diameter) of the crystal 500 at the solid-liquid interface based on the imaging data. And a crystal diameter calculation unit 222.
The material diameter calculator 221 and the crystal diameter calculator 222 calculate the material diameter and the crystal diameter at a predetermined time interval (for example, every 2 seconds). Note that the method of calculating the material diameter and the crystal diameter in the material diameter calculation unit 221 and the crystal diameter calculation unit 222 is not particularly limited, and can be realized by, for example, performing edge detection from imaging data.

  Here, the CCD camera 140 and the material diameter calculation unit 221 constitute material diameter detection means, and the material diameter detection process is executed. The CCD camera 140 and the crystal diameter calculation unit 222 constitute a crystal diameter detection unit, and a crystal diameter detection process is executed.

  The voltage control unit 230 controls the voltage applied to the heating coil 130 based on the material diameter and the crystal diameter (heating temperature control process). Since the amount of melting of the material 600 is changed by controlling the voltage applied to the heating coil 130, the amount of the raw material supplied to the crystal 500 is changed. For example, if the volume per unit length of the material 600 is small, such as the tip of the tapered portion 610 of the material 600, the heating temperature may be low, while the volume per length as in the straight body 620. When the temperature increases, the heating temperature is raised and the material 600 is sufficiently melted.

FIG. 4 is a diagram illustrating an example of a voltage applied to the heating coil 130.
The voltage controller 230 controls the voltage applied to the heating coil 130 in two stages. The material 600 includes a taper portion 610 that gradually increases in diameter from the tip and a straight body portion 620 having a constant diameter. When the material 600 fed between the heating coils 130 is the taper portion 610. The voltage controller 230 applies a voltage value determined based on the material diameter to the heating coil 130. When the material 600 sent between the heating coils 130 moves from the taper portion 610 to the straight body portion 620, the voltage control unit 230 next sets a voltage value determined based on the crystal diameter, not the material diameter. Apply to heating coil 130. When the applied voltage value reaches a preset target value, the target value is kept.

  In other words, the diameter of the straight body 620 of the material 600 is preset as a constant value in the voltage control unit 230, and when the material diameter calculated by the material diameter calculation unit 221 is equal to or less than the constant value, it is based on the material diameter. When a voltage value is applied to the heating coil 130 and the material diameter exceeds a fixed value, a voltage value based on the crystal diameter is applied to the heating coil 130.

In determining the voltage value based on the material diameter or the crystal diameter, an equation of a linear function using the material diameter or the crystal diameter as a parameter is set in advance, and the voltage value can be determined based on this equation. Take as an example.
A specific procedure for controlling the voltage to the heating coil 130 by the voltage controller 230 will be described later.

The crystal pulling speed controller 240 controls the driving speed of the crystal pulling mechanism 120 based on the crystal diameter calculated by the crystal diameter calculator 222 (crystal pulling speed control step). In the crystal pulling speed control unit 240, the relationship between the crystal diameter and the pulling speed is set in advance, and the pulling speed is determined according to the crystal diameter calculated by the crystal diameter calculating unit 222.
FIG. 5 is a diagram illustrating an example of a change in the crystal pulling rate.
The crystal diameter reduction speed control unit increases the crystal reduction speed step by step to the target speed in four stages.
That is, in the crystal pulling speed control unit 240, three stages of crystal diameter values are set as set values, and pulling speeds corresponding to the respective set values are set. Then, when the crystal diameter reaches each set value, the pulling speed is increased stepwise. A specific procedure for controlling the crystal pulling mechanism 120 by the crystal pulling speed control unit 240 will be described later.

In the taper portion 610 of the material 600, the material feed speed control unit 300 controls the driving speed of the material feed mechanism 110 based on a preset value, and after the material diameter reaches a fixed value, the crystal diameter is adjusted. The driving speed of the material feeding mechanism 110 is controlled based on the rate of change and the supply balance of the material 600 (material feeding speed control step).
FIG. 6 is a diagram illustrating a configuration of the material feed speed control unit 300.
The material feed speed control unit 300 determines the driving speed of the material feed mechanism 110 based on the change rate of the crystal diameter, and based on the balance between the supply amount of the material 600 and the crystallization amount. A supply balance determination unit 350 that determines the drive speed of the material feed mechanism 110, and a material feed speed command unit that commands the drive speed to the material feed mechanism 110 based on the determination by the crystal diameter change rate determination unit 310 and the supply balance determination unit 350. 380.

  The crystal diameter change rate determination unit 310 includes a crystal diameter storage unit 320 that temporarily stores the crystal diameter calculated by the crystal diameter calculation unit 222, and a crystal diameter change rate based on the change of the crystal diameter at a certain time interval. A crystal diameter change rate calculating unit 330 to calculate, and a crystal diameter change rate comparing unit 340 for comparing the set threshold value with the crystal diameter change rate.

The crystal diameter storage unit 320 sequentially stores the crystal diameter values calculated by the crystal diameter calculation unit 222.
Here, the crystal diameter calculation unit 222 calculates the crystal diameter every 2 seconds, and the crystal diameter storage unit 320 stores the value of the crystal diameter for 100 seconds.
That is, the crystal diameter storage unit 320 stores 50 pieces of crystal diameter data from the oldest crystal diameter value to the latest crystal diameter value.
FIG. 7 shows an example of crystal diameter data stored in the crystal diameter storage unit 320.

  The crystal diameter change rate calculating unit 330 calculates the change rate of the crystal diameter at regular time intervals (crystal diameter change rate calculating step). In growing the single crystal 500 into a desired shape, the top portion 510 is gradually thickened from the seed crystal 540 at the tip toward the straight body portion 520, and the straight body portion 520 must maintain a constant diameter. I must. In order to grow the single crystal 500 in a desired shape in this way, the change rate of the crystal diameter, which is the degree of weight of the crystal 500, is set within a predetermined range so that the crystal 500 does not become too thick or too thin. . Here, the difference between the average value of the crystal diameter data in the latest 20 seconds and the average value of the crystal diameter data in 20 seconds from 80 seconds to 100 seconds ago is defined as the crystal diameter change rate. That is, the crystal diameter change rate calculation unit 330 calculates the average value of the crystal diameter data for the latest 10 as the new crystal diameter average value, and further calculates the average of the 10 crystal diameter data from 80 seconds to 100 seconds ago. The value is calculated as an average value of past crystal diameters. Then, the difference between the new crystal diameter average value and the past crystal diameter average value is obtained and used as the crystal diameter change rate.

The crystal diameter change rate comparison unit 340 compares the crystal diameter change rate with respect to a set range in which the upper limit value and lower limit value of the crystal diameter change rate set in advance according to the crystal diameter value are set as threshold values (crystal diameter Change rate comparison process).
FIG. 8 shows a setting range of the crystal diameter change rate.
A predetermined range of the crystal diameter change rate is set in correlation with the crystal diameter. Then, the crystal diameter change rate comparison unit 340 compares the crystal diameter change rate calculated by the crystal diameter change rate calculation unit 330 with the upper limit value and the lower limit value of the setting range, and the comparison result is sent to the material feed speed command unit 380. Output.

  The supply balance determination unit 350 includes a supply balance calculation unit 360 that calculates a supply balance that is the difference between the supply amount of the material 600 and the crystallization amount, and a supply balance comparison unit 370 that compares the set threshold value with the supply balance. .

The supply balance calculation unit 360 calculates a supply balance based on the material diameter Pd, the material feed speed Zp, the crystal diameter Sd, and the crystal pulling speed Re (supply balance calculation step).
Supply balance is sought in relation supply amount of the material 600 and (~Pd ² × Zp) and crystallization amount (~Sd ² × Re), represented by the following equation.

The supply balance comparison unit 370 compares the supply balance with a set range having a lower limit value of the supply balance that is set in advance according to the value of the crystal diameter as a threshold (supply balance comparison process).
FIG. 9 shows a setting range of supply balance. Then, the supply balance comparison unit 370 compares the supply balance calculated by the supply balance calculation unit 360 with the set range, and outputs the comparison result to the material feed speed command unit 380.

The material feed speed command unit 380 controls the driving speed of the material feed mechanism 110 based on a preset value in the taper portion of the material 600, and after the material diameter reaches a constant value, the crystal diameter change rate. Based on the comparison results in the comparison unit 340 and the supply balance comparison unit 370, the drive speed of the material feed mechanism 110 is controlled (material feed speed command step).
When the material 600 fed between the heating coils 130 is the taper portion 610, the material feed speed command unit 380 keeps the material feed speed to a predetermined value.
When the material diameter exceeds the fixed value and the material 600 fed between the heating coils 130 becomes the straight body 620, the material feed speed command unit 380 includes the crystal diameter change rate comparison unit 340 and the supply balance comparison unit 370. The driving speed of the material feeding mechanism 110 is controlled based on the comparison result in.

At this time, the material feed speed command unit 380 first controls the driving speed of the material feed mechanism 110 based on the comparison result in the crystal diameter change rate comparison unit 340.
FIG. 10 is a diagram illustrating an example of the relationship between the crystal diameter change rate and the setting range.
When the crystal diameter change rate is below the lower limit value of the setting range according to the comparison result in the crystal diameter change rate comparison unit 340 (reference numeral 344 in FIG. 10), the material feed speed command unit 380 sets the material feed speed. Raise.
Here, the fact that the crystal diameter change rate is below the lower limit value of the setting range means that the crystal 500 is not as fat as desired and is too thin. The supply amount is increased to thicken the crystal 500.

In addition, the material feed speed command unit 380 determines that the material feed rate command unit 380 has a material feed rate when the crystal diameter change rate exceeds the upper limit of the set range (reference numeral 345 in FIG. 10). Keep without increasing speed.
Here, the fact that the crystal diameter change rate exceeds the upper limit value of the setting range means that the crystal 500 is too thicker than planned, so the material feed speed is increased for a while without increasing the supply amount of the material 600. Keep it.

Then, when the crystal diameter change rate is within the set range, the material feed speed command unit 380 next controls the driving speed of the material feed mechanism 110 based on the comparison result in the supply balance comparison unit 370.
FIG. 11 is a diagram illustrating an example of the relationship between the supply balance and the setting range.
The material feed speed command unit 380 keeps the material feed speed when the supply balance is higher than the lower limit value based on the comparison result in the supply balance comparison unit 370. The fact that the supply balance is higher than the lower limit means that the supply amount of the material 600 is sufficient with respect to the crystallization amount, so the material feed speed is kept. On the other hand, when the supply balance is below the lower limit (reference numeral 372 in FIG. 11), the material feed speed is increased. The fact that the supply balance is below the lower limit means that the supply amount of the material 600 is insufficient with respect to the crystallization amount, so the material feed speed is increased.
Here, FIG. 12 is a diagram illustrating an example of a change in the material feed speed when the above control is performed.

The operation (single crystal growth method) of the first embodiment having such a configuration will be described.
When growing the single crystal 500 using the single crystal growing apparatus 100, the heating coil 130 is replaced according to the type and size of the crystal 500 to be grown, and the CCD camera 140 is set in the vicinity of the heating coil 130.
Then, the seed crystal 540 is set in the holding unit 121 of the crystal pulling mechanism 120, and the material 600 is set in the holding unit 111 of the material feeding mechanism 110 (see FIG. 2).
In this state, the growth of the single crystal 500 is started.
First, the material feeding speed and the crystal pulling speed by the material feeding speed controller 300 and the crystal pulling speed controller 240 are set to a predetermined driving speed.
Moreover, the voltage application to the heating coil 130 by the voltage controller 230 is set to a predetermined applied voltage.
In this state, the melting of the material and the growth of the crystal are started manually, for example, and automatic control by the control unit 200 is started when the material diameter and the crystal diameter can be imaged by the CCD camera 140. For example, automatic control by the control unit 200 is started when the crystal length reaches 40 mm.

Further, imaging by the CCD camera 140 is started, and imaging data is sent from the image processing unit 210 to the diameter calculating unit 220. The material diameter Pd and the crystal diameter Sd are calculated by the material diameter calculator 221 and the crystal diameter calculator 222 every predetermined time (2 seconds) based on the imaging data. The calculated material diameter Pd and crystal diameter Sd are output to the voltage controller 230, the crystal pulling speed controller 240, and the material feed speed controller 300. The voltage control unit 230 controls the voltage applied to the heating coil 130, the crystal pulling speed control unit 240 drives the crystal pulling mechanism 120, and the material feeding speed control unit 300 drives the material feeding mechanism 110. Executed.
Hereinafter, each control operation will be described with reference to FIGS.

First, voltage control applied to the heating coil 130 by the voltage controller 230 will be described.
FIG. 13 is a flowchart showing a procedure for controlling the voltage applied to the heating coil 130 by the voltage controller 230.
FIG. 4 is a diagram illustrating an example of a voltage applied to the heating coil 130.
In the voltage control of the heating coil 130, first, in ST100, the material diameter calculated by the material diameter calculation unit 221 is read. In ST101, the calculated material diameter is compared with a constant value set in the voltage control unit 230.
As described above, this fixed value is the diameter of the straight body portion 620 of the material 600.
When the value of the material diameter does not reach the constant value (ST101: NO), a voltage value based on the material diameter is applied to the heating coil 130. That is, a voltage value is calculated by multiplying the material diameter by a predetermined coefficient in ST102, and a voltage is applied to the heating coil 130 in ST103. Since the material diameter is calculated every 2 seconds, the process returns to ST100 and repeats ST100 to ST103 until the material diameter reaches a constant value.

  In ST101, when the value of the material diameter has reached a constant value (ST101: YES), the applied voltage value is controlled based on the crystal diameter, and the applied voltage value is increased to the target value. That is, when the material 600 fed between the heating coils 130 by the material feeding by the material feeding mechanism 110 moves from the tapered portion 610 to the straight body portion 620 and the material diameter reaches a constant value (ST101: YES), in ST110, the crystal The crystal diameter calculated by the diameter calculator 222 is read. In ST111, a voltage value is calculated by multiplying the crystal diameter by a predetermined coefficient, and a voltage is applied to the heating coil 130 in ST112.

  Since the crystal diameter is controlled to gradually increase at the top portion 510 of the single crystal 500 to be grown, when the voltage of the heating coil 130 having a positive correlation with the crystal diameter is controlled, the applied voltage value is gradually increased. To rise. The voltage value that gradually increases is compared with a preset target value (ST113), and when the voltage value does not reach the target value (ST113: NO), the voltage based on the crystal diameter is repeated by repeating ST110 to ST113. A value is applied to the heating coil 130.

When the applied voltage value reaches the target value in ST113 (ST113: YES), the target voltage value is kept and the target voltage value is applied to the heating coil 130.
The application of the target voltage value is continued until the end condition (ST121) is satisfied, and the process ends when the end condition is satisfied. An example of the termination condition is that the length of the single crystal 500 to be grown reaches a design value.

Next, control of the crystal pulling speed by the crystal pulling speed control unit 240 will be described.
FIG. 14 is a flowchart showing a procedure for controlling the crystal pulling speed by the crystal pulling speed controller 240.
FIG. 5 is a diagram illustrating an example of a change in the crystal pulling rate.
In controlling the crystal pulling speed, first, in ST200, the crystal diameter calculated by the crystal diameter calculating unit 222 is read.
The crystal pulling speed is controlled so as to increase in four steps according to the change in crystal diameter. The crystal pulling speed control unit 240 has three crystal diameter setting values (first setting value to third setting). Value) and a lowering speed (first speed to target speed) according to the crystal diameter are preset. Note that the crystal pulling speed is merely set to increase in four steps as an example, and the speed setting can be freely set according to the manufacturing conditions.
The read crystal diameter is compared with the first set value (ST201). If the crystal diameter does not reach the first set value (ST201: NO), crystal pulling is executed at the first speed (ST202).

ST200 to ST202 are repeated until the crystal diameter reaches the first set value. When the crystal diameter reaches the first set value (ST201: YES), the crystal pulling rate is increased by one step and the crystal is pulled down at the second rate. Execute (ST211). Then, while reading the crystal diameter calculated by the crystal diameter calculator 222 until the crystal diameter reaches the second set value (ST212), crystal pulling is executed at the second speed (ST210 to ST212).
When the crystal diameter reaches the second set value (ST210: YES), the crystal pulling speed is increased by one step and the crystal pulling is executed at the third speed. Then, while reading the crystal diameter calculated by the crystal diameter calculator 222 until the crystal diameter reaches the third set value (ST222), the crystal pulling is executed at the third speed (ST220 to ST222).
When the crystal diameter reaches the third set value (ST220: YES), the crystal pulling speed is increased by one step and the crystal pulling is executed at the target speed (ST230).
Here, the third set value is set to a value slightly smaller than the target value of the crystal diameter. The target value of the crystal diameter is the diameter of the straight body 520 of the single crystal 500 to be grown.
The crystal pulling is executed at the target speed until the end condition is satisfied, and the process ends when the end condition is satisfied.
An example of the termination condition is that the length of the single crystal 500 to be grown reaches a design value.

Next, control of the material feed speed by the material feed speed control unit 300 will be described.
FIG. 15 is a flowchart illustrating a procedure of material feed speed control by the material feed speed control unit 300.
FIG. 12 is a diagram illustrating an example of a change in the material feed speed.
In controlling the material feed speed, first, when the material 600 fed between the heating coils 130 is the tapered portion 610, the material feed speed is kept at a preset value.
That is, when the material diameter calculated by the material diameter calculation unit 221 is read (ST300) and the material diameter is equal to or smaller than a fixed value and the taper portion 610 of the material 600 (ST301: NO), the material feed speed is set to the set value. It is kept with. When the material diameter reaches a constant value and the material 600 becomes the straight body 620 (ST301: YES), thereafter, the material feed rate is controlled based on the crystal diameter change rate and the supply balance.
In ST310, the crystal diameter change rate calculating unit 330 calculates the crystal diameter change rate (crystal diameter change rate calculating step).

Here, as described above, the crystal diameter change rate is a change in crystal diameter at a constant time interval, and is calculated based on the crystal diameter stored in the crystal diameter storage unit 320. In ST311, the calculated crystal diameter change rate is compared with the set range (FIG. 8) in the crystal diameter change rate comparison unit 340 (crystal diameter change rate comparison step). First, in ST312, when the crystal diameter change rate is compared with the upper limit of the setting range and the crystal diameter change rate exceeds the upper limit (ST312: NO, see reference numeral 345 in FIG. 10), the material feed speed Is kept without raising (material feed speed command process). In ST312, when the crystal diameter change rate is equal to or lower than the upper limit of the set range (ST312: YES), in ST314, the crystal diameter change rate is compared with the lower limit value of the set range.
In ST314, when the crystal diameter change rate is below the lower limit value of the setting range (ST314: NO, see reference numeral 344 in FIG. 10), the material feed speed is increased (material feed speed command process).

In ST314, when the crystal diameter change rate is equal to or higher than the lower limit value of the setting range (ST314: YES), that is, when the crystal diameter change rate is within the setting range (ST312 and ST314: YES),
When the material feed speed is controlled based on the supply balance, the supply balance calculation unit 360 calculates the supply balance (ST320, supply balance calculation step).
As described above, the supply balance is a value obtained in relation to the supply amount (˜Pd ² × Zp) of the material 600 and the crystallization amount (˜Sd ² × Re).
The calculated supply balance is compared with the lower limit value of the setting range in the supply balance comparison unit 370 (ST321, supply balance comparison process).
If the supply balance is below the lower limit (ST322: NO), the material feed speed is increased (material feed speed command process).
On the other hand, when the supply balance is equal to or greater than the lower limit value and within the set range (ST322: YES), the material feed speed is kept (material feed speed command process).

In this way, control of the material feed rate based on the crystal diameter change rate and the supply balance is executed (ST310 to ST330), and when the end condition is satisfied (ST340), the control is ended.
An example of the termination condition is that the length of the single crystal 500 to be grown reaches a design value.

  In this way, by controlling the material feed speed so as to keep the crystal diameter change rate and the supply balance within the set range, as shown in FIG. 16, the single crystal 500 has a desired shape even though the surface is slightly waved. Be nurtured.

According to such 1st Embodiment, there can exist the following effects.
(1) Since the material pulling speed, the crystal pulling speed, and the voltage applied to the heating coil 130 are controlled based on the change in the crystal diameter and the material diameter, it is optimal by accurately detecting the crystal diameter and the material diameter. Automatic control of single crystal growth can be performed. By executing automatic control based on the crystal diameter and material diameter that can be accurately detected, the single crystal 500 can be stably grown into a desired shape.

(2) Compared to the case where the shape of the crystal 500 is indirectly controlled by controlling the zone length to a predetermined length as in the prior art, in this embodiment, the material feed rate is controlled to change the crystal diameter. Since the rate is set within a predetermined range, the control target of controlling the shape of the crystal 500 can be directly and reliably achieved.

(3) When automatic control is executed based on the crystal diameter and the material diameter, the mounting error of the heating coil 130 is not related to the control performance. Since the replacement of the heating coil 130 does not affect the detection of the crystal diameter and the material diameter, the heating coil 130 can be replaced with an appropriate heating coil 130 according to the type and size of the crystal 500.

(4) The crystal diameter change rate calculation unit 330 calculates the difference between the latest average value and the past average value to obtain the crystal diameter change rate. Since the crystal diameter change rate is calculated based on an average value of a predetermined number instead of single data, the control can be stabilized without being greatly affected by the detection error of the crystal diameter at a time. .

(5) Since the supply balance is calculated by the supply balance calculation unit 360 and the material feed speed is controlled so that the supply balance falls within the set range according to the comparison result in the supply balance comparison unit 370, the material supply amount and crystallization The single crystal 500 can be grown while maintaining a balance with the amount. For example, it is possible to appropriately grow the single crystal 500 while avoiding inconvenience such as the melting part being cut.

(6) The material feed rate is subjected to control based on the crystal diameter change rate and control based on the supply balance, and therefore, it preferentially executes the crystal diameter change rate within the set range. Can be controlled to a predetermined shape. Furthermore, even if the crystal diameter change rate is within the set range, the crystal 500 cannot be grown unless the supply balance is appropriate. However, the growth of the single crystal 500 can be appropriately advanced by setting the supply balance within the set range. it can.

(7) Since the voltage applied to the heating coil 130 is appropriately controlled according to the material diameter or the crystal diameter, the melted material 600 as a crystallization raw material can be appropriately supplied to the crystal 500, and single crystal growth Can proceed stably.

(8) The crystal pulling speed by the crystal pulling mechanism 120 is set in advance, and the crystal pulling speed is increased stepwise and smoothly at a predetermined setting speed. Can be trained. And in controlling a crystal | crystallization to a predetermined shape, it can respond by control of a raw material feed rate.

Next, Experimental Examples 1 and 2 will be described with reference to FIGS.
In Experimental Examples 1 and 2, the position of the heating coil is different.
That is, in the experimental example 1 shown in FIGS. 18 and 19, the position of the heating coil is 76.98 mm, and in the experimental example 2 shown in FIGS. 20 and 21, the position of the heating coil is 74.80 mm.
Note that the position of the heating coil 130 is represented by the distance from the upper end of the imaging region to the upper surface of the heating coil 130 on the imaging screen by the CCD camera 140.

Here, in Experimental Example 1 and Experimental Example 2, since the crystal grows using the taper portion of the material as a raw material until the crystal length is about 100 mm, the material feeding speed is a predetermined set value.
When the crystal diameter reaches 130 mm, the formation of the top portion of the single crystal is finished, and the crystal diameter is continuously controlled in the straight body portion of the single crystal.
18 to 20, the data for forming the top portion of the crystal are extracted and shown.

  In FIG. 18, when the position of the heating coil is 76.98 cm and a single crystal is grown, the horizontal axis indicates the crystal length, and the vertical axis indicates the change between the crystal diameter and the crystal diameter change rate. The deformation of the crystal can be read by the fluctuation of the crystal diameter change rate. The crystal diameter change rate is stable in the range of the crystal length of 100 mm to 200 mm, and the crystal is stably expanded at a constant rate. It turns out that the top part is formed. FIG. 19 shows changes in the crystal diameter change rate and the material feed rate. It can be seen that the material feed rate is gradually increased while the crystal diameter change rate is kept stable.

Next, FIG. 20 shows changes in crystal diameter and crystal diameter change rate when a single crystal is grown with the position of the heating coil being 74.8 cm.
The position of the heating coil is different from Experimental Example 1, but also in Experimental Example 2, the crystal diameter change rate is stable in the crystal length range of 100 mm to 200 mm, and the crystal is stably expanded at a constant rate. However, it turns out that the top part is formed. Similarly, as shown in FIG. 21, it can be seen that the material feed rate is gradually increased while the crystal diameter change rate is kept stable.
As described above, as can be seen from Experimental Example 1 and Experimental Example 2, according to the single crystal growth method and the single crystal growth apparatus of the present invention, regardless of the position of the heating coil, the crystal diameter change rate is stabilized, A single crystal can be grown into a desired shape.

The present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
Although the heating means is a heating coil, it is of course not limited as long as the material is heated and melted.
As the means for detecting the material diameter and the crystal diameter, an example in which the CCD camera and its imaging data processing means are used has been shown, but the means for detecting the diameter is not particularly limited.
Although Formula 2 was shown as a formula for obtaining the supply balance, there is no particular limitation as long as it represents a balance between the supply amount of the material and the crystallization amount. The supply balance setting range may be set as appropriate.
Although the material feed speed is kept when the crystal diameter change rate exceeds the upper limit value of the setting range, for example, the material feed speed may be reduced.

  The present invention can be used for single crystal growth by a floating zone melting method.

The figure which shows the shape of the semiconductor single crystal grown with a single crystal growth apparatus. The figure which shows the state which set the seed crystal and the raw material before melting to the crystal pulling-down mechanism and the raw material feeding mechanism, respectively. The figure which shows the structure of a single crystal growth apparatus. The figure which shows an example of the voltage applied to a heating coil. The figure which shows an example of the change of a crystal pulling speed. The figure which shows the structure of a raw material feed speed control part. The figure which shows an example of the crystal diameter data memorize | stored in a crystal diameter memory | storage part. The figure which shows the setting range of a crystal diameter change rate. The figure which shows the setting range of supply balance. The figure which shows an example of the relationship between a crystal diameter change rate and a setting range. The figure which shows an example of the relationship between a supply balance and a setting range. The figure which shows an example of a raw material feed speed. The flowchart which shows the procedure of the applied voltage control to the heating coil by a voltage control part. The flowchart which shows the procedure of the crystal pulling speed control by a crystal pulling speed control part. The flowchart which shows the procedure of the material feed speed control by a material feed speed control part. The figure which expands and shows the surface of a single crystal. The figure which shows the conventional single crystal growth apparatus. FIG. 3 is a graph showing changes in crystal diameter and crystal diameter change rate in Experimental Example 1; The figure which shows the change of a crystal diameter change rate and a raw material feed rate in Experimental example 1. FIG. In Experimental example 2, the figure which shows the change of a crystal diameter and a crystal diameter change rate. In Experimental example 2, the figure which shows the change of a crystal diameter change rate and a raw material feed rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single crystal growing apparatus, 11 ... Material feeding mechanism, 12 ... Crystal pulling mechanism, 13 ... Heating coil, 14 ... CCD camera, 100 ... Single crystal growing apparatus, 110 ... Material feeding mechanism, 111 ... Holding part, 120 ... Crystal Pull-down mechanism, 121 ... holding unit, 130 ... heating coil, 140 ... CCD camera, 200 ... control unit, 210 ... image processing unit, 220 ... diameter calculation unit, 221 ... material diameter calculation unit, 222 ... crystal diameter calculation unit, 230 DESCRIPTION OF SYMBOLS ... Voltage control part 240 ... Crystal pulling-down speed control part 300 ... Material feed speed control part 310 ... Crystal diameter change rate judgment part 320 ... Crystal diameter storage part 330 ... Crystal diameter change rate calculation part 340 ... Crystal diameter Change rate comparison unit 350 ... Supply balance determination unit 360 ... Supply balance calculation unit 370 ... Supply balance comparison unit 380 ... Material feed speed command unit 500 ... Crystal, 510 ... Top Department, 520 ... straight body, 530 ... bottom section, 540 ... seed crystal, 600 ... material, 610 ... tapered portion, 620 ... straight body.

Claims (10)

A material feed mechanism that feeds the material downward, a heating means that heats the lower end of the material to melt the material, and a crystal that is grown on the melted material disposed on the same axis as the material feed mechanism A single crystal growth method for growing a single crystal by a floating zone melting method using a single crystal growth apparatus equipped with a crystal pulling mechanism for lowering
A crystal diameter detecting step of detecting a crystal diameter at a crystal-side solid-liquid interface, which is a solid-liquid interface between a melted portion where the material is melted by heating by the heating means and a crystal where the melted portion is crystallized;
A material feed speed control step for controlling a material feed speed by the material feed mechanism, and the material feed speed control step comprises:
A crystal diameter change rate calculating step of calculating a crystal diameter change rate that is a change amount per unit time of the crystal diameter;
A crystal diameter change rate comparison step for comparing the crystal diameter change rate calculated in the crystal diameter change rate calculation step with a preset range of the crystal diameter change rate;
A material feed speed commanding step for commanding a material feed rate of the material feed mechanism according to a comparison result in the crystal diameter change rate comparison step. The method for growing a single crystal according to claim 1,
The setting range of the crystal diameter change rate is a setting range having an upper limit value and a lower limit value as threshold values,
The material feed speed command process includes:
If the crystal diameter change rate is lower than the lower limit value of the setting range by comparing the crystal diameter change rate and the setting range in the crystal diameter change rate comparison step, increase the material feed speed,
A single crystal growth method characterized by maintaining a material feed rate when the crystal diameter change rate exceeds an upper limit of a set range. In the method for growing a single crystal according to claim 1 or claim 2,
In the crystal diameter detection step, the crystal diameter is detected at regular intervals,
The crystal diameter change rate calculating step calculates a difference between an average value of the most recent predetermined number of crystal diameters detected at fixed time intervals and an average value of the past predetermined number as a crystal diameter change rate. A single crystal growth method characterized. In the method for growing a single crystal according to any one of claims 1 to 3,
A material diameter detecting step of detecting a material diameter at a material-side solid-liquid interface, which is a solid-liquid interface between the melted portion where the material is melted by heating by the heating means and the material,
The material feed speed control step includes:
A supply balance calculation step of calculating a difference between a material supply amount based on the material feed speed and the material diameter and a crystallization amount based on the crystal pulling speed and the crystal diameter as a supply balance;
A supply balance comparison step for comparing the supply balance with respect to a preset supply balance setting range,
The material feed speed command process includes:
A single crystal growth method characterized by instructing a material feed speed of the material feed mechanism according to a comparison result in the supply balance comparison step. The method for growing a single crystal according to claim 4,
The setting range of the supply balance is a setting range having a lower limit value as a threshold,
The material feed speed command process includes:
If the supply balance is below the lower limit value of the setting range by comparing the supply balance and the setting range in the supply balance comparison step, increase the material feed speed,
A material growth rate is maintained when the supply balance is greater than or equal to the lower limit value. The method for growing a single crystal according to claim 5,
The material feed speed command process includes:
First, the material feed speed is determined based on the comparison result in the crystal diameter change rate comparison step,
When the crystal diameter change rate is within a set range of the crystal diameter change rate, a material feed rate is further determined based on a comparison result in the supply balance comparison unit. In the method for growing a single crystal according to any one of claims 1 to 6,
A material diameter detecting step of detecting a material diameter at a material-side solid-liquid interface that is a solid-liquid interface between the melted portion where the material is melted by heating by the heating means and the material;
An applied voltage control step for controlling an applied voltage to the heating means,
The material has a tapered portion that gradually increases in diameter from the tip portion, and a straight body portion having a constant diameter,
The applied voltage control step includes
When the material melted by the heating means is a tapered portion, the applied voltage is a value correlated with the material diameter,
When the material melted by the heating means is a straight body part, the applied voltage is a value correlated with the crystal diameter,
A method for growing a single crystal, comprising maintaining the target voltage when the applied voltage reaches a preset target voltage. In the method for growing a single crystal according to any one of claims 1 to 7,
A crystal pulling rate control step for controlling the crystal pulling rate by the crystal pulling mechanism,
The crystal pulling speed according to the crystal diameter is preset,
The crystal pulling speed control step determines the crystal pulling speed based on the crystal diameter detected in the crystal diameter detecting step. A material feed mechanism that feeds the material downward, a heating means that heats the lower end of the material to melt the material, and a crystal that is grown on the melted material disposed on the same axis as the material feed mechanism In a single crystal growth apparatus equipped with a crystal pulling mechanism that pulls down
A crystal diameter detecting means for detecting a crystal diameter at a crystal-side solid-liquid interface that is a solid-liquid interface between a melted portion where the material is melted by heating by the heating means and a crystal where the melted portion is crystallized;
A material feed speed control unit that controls a material feed speed by the material feed mechanism, and the material feed speed control unit includes:
A crystal diameter change rate calculating unit for calculating a crystal diameter change rate that is a change amount per unit time of the crystal diameter;
A crystal diameter change rate comparison unit that compares the crystal diameter change rate calculated by the crystal diameter change rate calculation unit with a preset range of the crystal diameter change rate;
A material feed rate command unit that commands a material feed rate of the material feed mechanism according to a comparison result in the crystal diameter change rate comparison unit. In the single crystal growth apparatus according to claim 9,
The crystal diameter detecting means includes
Imaging means for imaging a crystal-side solid-liquid interface that is a solid-liquid interface between a melted portion where the material is melted by heating by the heating means and a crystal where the melted portion is crystallized;
A single crystal growth apparatus, comprising: a crystal diameter calculation unit that calculates a crystal diameter at a solid-liquid interface based on imaging data imaged by the imaging means.

Images