JP4035924B2 - Single crystal diameter control method and crystal growth apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single crystal diameter control method and a crystal growth apparatus, and more particularly, for growing a single crystal such as a silicon single crystal used as a semiconductor material while controlling the diameter of the single crystal. The present invention relates to a method for controlling the diameter of a single crystal and a crystal growth apparatus.
[0002]
[Prior art]
There are various methods for growing a single crystal. Among the most typical Czochralski method (hereinafter referred to as CZ method), for example, on the surface of a silicon (hereinafter referred to as Si) melt. A Si single crystal having a cylindrical shape is grown by bringing the seed crystal into contact and pulling it up while controlling the pulling rate. Since the Si single crystal to be pulled is later finished into a cylindrical ingot by grinding the outer peripheral portion, the product yield decreases when the diameter of the pulled Si single crystal in the horizontal section varies. Considering the product yield in this way, it is desirable that the single crystal to be pulled up maintains the same diameter value over the entire straight body.
[0003]
For this reason, diameter control is conventionally performed in pulling a single crystal, and as a diameter control method in the CZ method, the deviation between the measured value of the single crystal diameter and the target diameter value is fed back to the pulling speed to assist. In particular, a method for adjusting the heater temperature has been proposed. Japanese Laid-Open Patent Publication No. 4-219388 discloses a control method in which a feedback control system is designed and only a pulling speed is set as an operation amount.
[0004]
JP-A-4-108687 discloses the weight of a single crystal being pulled up every predetermined time, calculates the single crystal outer diameter from the amount of change in the single crystal weight, and calculates the calculated single crystal outer diameter. Discloses a method for controlling the diameter of a single crystal by controlling the temperature of a heater, which is a heating means, in accordance with the deviation between the target diameter value and the target diameter value.
[0005]
[Problems to be solved by the invention]
However, in the single crystal diameter control method using the pulling speed of the single crystal as described above as the manipulated variable, the pulling speed is adjusted to control the single crystal diameter, and therefore the pulling speed is changed as the single crystal is pulled. In other words, the thermal conditions that greatly affect crystal growth or crystal defects must be changed. Therefore, even if single crystals having the same diameter are obtained, the thermal conditions of the single crystal growth process are changed in accordance with the fluctuation of the pulling rate, so that crystal defects are likely to occur, and high quality single crystals are obtained. There was a problem that it was difficult.
[0006]
On the other hand, in the method of controlling the diameter of the single crystal by controlling the temperature of the heater as the heating means, after the heater temperature is changed, the effect appears and the diameter starts to change. Since there is a so-called dead time, there is a problem that the response is poor, the diameter control performance of the single crystal is poor, and it is not practical.
[0007]
The present invention has been made in view of the above problems, and a single crystal diameter control method capable of efficiently producing a high-quality single crystal with few crystal defects while accurately controlling the diameter of the single crystal. And it aims at providing a crystal growth device.
[0008]
[Means for solving the problems and effects thereof]
In order to achieve the above object, the method (1) for controlling the diameter of a single crystal according to the present invention fixes the pulling rate constant so that the crystal defect quality is stabilized over the entire straight body in the silicon single crystal manufacturing process. A single crystal diameter control method for growing a single crystal while maintaining a target diameter when pulling up,
When setting the operation amount of the heating means temperature disposed around the crucible for melting the crystal raw material,
The response of the single crystal diameter value when the heating means is changed stepwise is preliminarily obtained to assume a transfer function of a first-order lag system, and the measured value of the single crystal diameter and the stored target diameter value In addition to the main loop that calculates the manipulated variable by feeding back the deviation from
The amount of influence over time of the width of the fusion ring that is brighter than the surrounding that appears near the interface between the single crystal and the melt is determined in advance, and the width of the fusion ring that is continuously detected. The diameter of the single crystal is controlled to the target diameter by calculating the amount of operation of the temperature of the heating means by a minor loop that feeds back the amount of operation obtained from the change over time of the material. It is characterized by that.
In addition, the method (2) for controlling the diameter of a single crystal according to the present invention changes the response characteristic of the single crystal diameter value when the heating means temperature is changed stepwise, and the heating means temperature is changed stepwise. It is characterized in that it is obtained by performing a step response test for examining the response of the single crystal diameter value in the case of the above.
[0009]
When pulling and growing a single crystal from the melt, the height Hk of the interface 22 between the single crystal 20 and the melt 13 is higher than the height Hy of the melt surface, as shown in FIG. As a result, a ring-shaped portion (hereinafter referred to as a fusion ring) 21 having a higher luminance than the surrounding having a meniscus angle (inclination angle) θ is formed between the interface end and the melt surface. The fusion ring 21 is inclined with respect to the melt surface, and the radiated light from the inner wall surface of the quartz crucible is easily reflected, so that it appears bright and bright compared to other portions of the melt surface. It is possible to obtain the fusion ring width W by imaging the fusion ring 21 and performing image processing.
The fusion ring width W widens before the diameter of the single crystal 20 increases, and narrows before the diameter of the single crystal 20 decreases. The time-dependent variation information of the fusion ring width W is used as prior information of the variation of the single crystal diameter. Can do.
[0010]
According to the method for controlling the single crystal diameter, in addition to the deviation between the actual measured value of the single crystal diameter and the target diameter value, based on the temporal information of the fusion ring width as the preceding information of the fluctuation of the single crystal diameter, Since the temperature of the heating means is set, it is possible to solve the so-called response delay problem that the response time from the setting of the temperature of the heating means, which has been a problem in the past, until the diameter of the single crystal fluctuates is large. .
In other words, it is possible to accurately predict the future value of the single crystal diameter using the fluctuation information of the fusion ring width before the actual measurement value of the single crystal diameter is known, thereby solving the response delay problem. Can do. In addition, since the pulling speed is not used to control the diameter of the single crystal, it is possible to pull the single crystal stably with the pulling speed almost constant, and a high-quality single crystal with few crystal defects can be obtained.
[0011]
A single crystal growth apparatus (1) according to the present invention comprises a crucible for melting a crystal raw material,
Heating means disposed around the crucible;
Lifting and lowering means for pulling up the silicon single crystal while growing it from the melt in the crucible;
Measuring means for measuring the diameter of the single crystal to be grown;
Detection means for detecting the width of the fusion ring having a higher brightness than the surroundings appearing in the vicinity of the interface between the single crystal and the melt ;
A temperature calculating means for calculating a set temperature of the heating means based on a deviation between an actual measurement value of the single crystal diameter and a target diameter value, and information over time of the width of the fusion ring having the high brightness;
Control means for controlling the amount of power supplied to the heating means based on the calculated set temperature,
The temperature calculation / control means stores the measured value of the single crystal diameter detected by the detection means from the amount of influence that the time-dependent variation of the width of the fusion ring obtained in advance has on the single crystal diameter. In addition to the main loop for calculating the manipulated variable of the heating means temperature by feeding back the deviation from the target diameter value, the variation over time of the fusion ring width determined in advance affects the single crystal diameter. From the influence amount, it has a function of inserting and feeding back a minor loop for adding the operation amount of the heating means temperature to be operated according to the width of the fusion ring detected by the detection means. It is said.
In the single crystal growth apparatus (2) according to the present invention, in the single crystal growth apparatus (1), the temperature calculation / control unit includes a change over time in the width of the fusion ring in the single crystal diameter. As the influence amount exerted, the response characteristic obtained by carrying out a step response test for examining a response of the single crystal diameter value when the heating means temperature is changed stepwise is stored. Yes.
[0012]
According to the crystal growth apparatus described above, the width of the fusion ring formed in the vicinity of the interface between the melt and the growing single crystal is detected, and the time-dependent information of the fusion ring width that is the preceding information of the fluctuation of the single crystal diameter The single crystal can be pulled up while controlling the amount of power supplied to the heating means based on the above, until the diameter of the single crystal fluctuates after setting the temperature of the heating means, which has been a problem in the past Efficiently produce high-quality single crystals with few crystal defects, while solving the so-called response delay problem of large response time, and enabling stable single crystal pulling with a substantially constant pulling speed. Can do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a single crystal diameter control method and a crystal growth apparatus according to the present invention will be described below with reference to the drawings.
FIG. 2 is a cross-sectional view schematically showing the crystal growth apparatus according to the embodiment, in which 11 denotes a furnace body. A quartz crucible 12a having a bottomed cylindrical shape is disposed in a substantially central portion in the furnace body 11, and the quartz crucible 12a is filled with a melt 13 obtained by melting a raw material for single crystal. ing. The quartz crucible 12a is held by a graphite susceptor 12b, and the crucible 12 is constituted by the quartz crucible 12a and the graphite susceptor 12b. A rotating shaft 14 is attached to the lower portion of the graphite susceptor 12b, and a crucible rotating means and a crucible lifting / lowering means (both not shown) are connected to the lower portion of the rotating shaft 14, and the crucible 12 is rotated by these crucible rotating / lifting means. Is rotated at a predetermined speed and is driven in the vertical direction. Further, a cylindrical heater 15a is disposed on the outer periphery of the graphite susceptor 12b, and a power supply means 15b is connected to the heater 15a. The heating means 15 includes the heater 15a and the power supply means 15b. Has been. And the temperature of the heater 15a is adjusted by changing the electric power supply amount from the electric power supply means 15b, and the temperature of the melt 13 in the crucible 12 is adjusted. Further, a heat retaining cylinder 15 c is disposed between the heater 15 a and the furnace body 11.
[0014]
A hollow cylindrical casing 11 a is formed above the furnace body 11, a wire 17 is suspended on the same axis as the rotating shaft 14 of the crucible 12 in the casing 11 a, and a seed holder 17 a is disposed at the lower end of the wire 17. The seed crystal 17b is attached to the seed holder 17a. A wire pulling device 19 is disposed on the upper portion of the casing 11a via a wire rotating device 18. The wire rotating device 18 and the wire pulling device 19 include motors 18a and 19a, respectively, and the wire 17 rotates when the motor 18a is driven. When the motor 19a is driven, the wire 17 moves in the vertical direction. The lifting / lowering means 16 includes the wire 17, the wire rotating device 18, the wire pulling device 19 and the like.
[0015]
An observation window 11b is formed on the top of the furnace body 11, and a two-dimensional CCD camera 31 is disposed at a predetermined position facing the single crystal 20 with the observation window 11b interposed therebetween. The CCD camera 31 is connected to the image processing unit 32. It is connected. The CCD camera 31 and the image processing unit 32 are included in the measurement / detection means 30 so that the CCD camera 31 images the luminance distribution in the vicinity of the fusion ring 21 formed around the single crystal 20. It has become.
[0016]
Then, as shown in FIG. 3, this luminance signal is processed in the image processing unit 32, the distance between two luminance intensities at a predetermined threshold value L is calculated, and the width W of the fusion ring 21 is continuously increased. It is to be detected. The measuring / detecting means 30 is configured such that the threshold value is corrected in accordance with a change in the maximum level of the luminance signal so that the width W is prevented from being affected by the luminance intensity. It has become. The measuring / detecting means 30 can also measure the diameter D of the single crystal 20.
[0017]
The measurement / detection means 30 is connected to a temperature calculation / control means 33. The temperature calculation / control means 33 takes in the actual values of the fusion ring width and the single crystal diameter, the actual measurement value of the single crystal diameter and the target. The operation value of the heater temperature is calculated by comparing with the diameter value, and in addition to that, the actual value of the fusion ring width W is compared with the actual measurement value of the fusion ring width W a predetermined time before the operation amount of the heater temperature. And an output unit that outputs a control signal for the amount of supplied power required based on the calculated operation amount of the heater temperature to the power supply means 15b.
[0018]
The temperature calculation / control unit 33 is connected to the power supply unit 15b and is also connected to the motor 19a, and the amount of supplied power required according to the fluctuation state of the fusion ring width W calculated by the temperature calculation / control unit 33. The pulling speed information is output to the heating means 15 and the lifting / lowering means 16.
[0019]
If this apparatus constructed using such, for example, a single crystal 20 is grown to a predetermined target diameter D _S, then it is possible grow target diameter D _S single crystal 20 while maintaining a first quartz crucible 12a The raw material for Si single crystal is filled therein, and the crucible 12 is heated to a predetermined temperature by the heating means 15 to form the melt 13. Next, the crucible 12 is rotated at a predetermined speed, and the seed crystal 17 b is brought into contact with the surface of the melt 13. Then, the wire 17 is pulled up while rotating at a predetermined speed, and the single crystal 20 formed by the solidification of the melt 13 is grown.
[0020]
By then measuring and detecting means 30, after the shoulder is formed single crystal 20 was confirmed to be grown to a predetermined target diameter D _S, to set and fix the pull rate to a predetermined value. Next, while continuously detecting the width W of the fusion ring 21, the amount of power supplied by the power supply means 15b is adjusted according to the fluctuation state of the fusion ring width W, so that the diameter D of the single crystal 20 is a predetermined target diameter D. Control to be maintained at _S. In order to prevent the upper surface level of the melt 13 from being lowered and the diameter D of the single crystal 20 from fluctuating as the single crystal 20 is pulled up, the upper surface level of the melt 13 is always constant using the crucible lifting / lowering means. Control to maintain the height.
[0021]
FIG. 4 is a block diagram for explaining the function of the temperature calculation / control unit 33. The temperature calculation / control unit 33 adds the deviation between the measured value of the single crystal diameter and the stored target diameter value as an addition point 1. In addition to the main loop that calculates the amount of operation of the heater temperature by feeding back to the heater, the heater to be operated is determined based on the amount of influence that the change over time in the fusion ring width has on the single crystal diameter. It has a function of adding the manipulated variable of temperature to the addition point 2. That is, a minor loop for calculating the heater temperature manipulated variable from the fluctuation amount of the fusion ring width W is inserted into the main loop and fed back to the addition point 2.
[0022]
As the influence of the heater temperature on the diameter of the single crystal 20, a transfer function of a first order lag system with a dead time is assumed. The time constant and dead time of the process are obtained by performing a step response test for examining the response of the single crystal diameter value when the heater temperature is changed stepwise. Based on the response characteristics thus obtained, for example, an improved limit sensitivity method (a so-called method for adjusting PID control parameters in relation to a proportional gain and a limit period when the oscillation state is exceeded by exceeding the stability limit by proportional control). In the limit sensitivity method, controllers C ₁ and C ₂ are designed by a parameter adjustment method using a multiplier factor determined in advance from the standardized wasted time obtained by dividing the wasted time by the limit period and the type of transfer characteristic. .
[0023]
FIG. 5 is a diagram showing the results obtained by computer simulation, showing the response characteristics when a step-like change is given as a disturbance, and the response characteristics of a simple feedback control system ( Compared to curve A), the control system response characteristics (curve B) using information on fluctuations in the fusion ring width over time has yielded superior characteristics and uses information on fluctuations in the fusion ring width over time. By doing so, it became possible to control the single crystal diameter excellent in disturbance suppression, and the diameter control characteristics were greatly improved.
[0024]
As is apparent from the above description, according to the method for controlling the single crystal diameter according to the embodiment, in addition to the deviation between the measured value of the single crystal diameter and the target diameter value, the vicinity of the interface between the single crystal 20 and the melt 13 Since the temperature of the heating means 15 is set on the basis of the time-lapse information of the fusion ring width W appearing in FIG. 1, until the diameter of the single crystal 20 fluctuates after setting the temperature of the heating means 15 which has been a problem in the past. The so-called response delay problem that the response time is long can be solved.
In addition, since the pulling speed is not used for controlling the single crystal diameter, it is possible to pull the single crystal 20 stably with a substantially constant pulling speed, and it is possible to obtain a high quality single crystal 20 with few crystal defects.
[0025]
Also, according to the crystal growth apparatus according to the embodiment, the width W of the fusion ring 21 formed in the vicinity of the interface between the melt 13 and the growing single crystal 20 is detected, and this is the preceding information on the fluctuation of the single crystal diameter. Since the single crystal 20 can be pulled up while controlling the amount of electric power supplied to the heating means 15 based on the information of the fusion ring width W over time, the temperature of the heating means 15 that has been a problem in the past is set. While solving the so-called response delay problem that the response time until the diameter of the single crystal 20 fluctuates is large, it is possible to pull the single crystal 20 stably with a substantially constant pulling speed, and high quality with few crystal defects The single crystal 20 can be efficiently manufactured.
[0026]
In the above-described embodiment, the case where the two-dimensional CCD camera 31 is used as the measurement / detection unit 30 has been described. However, scanning may be performed using a one-dimensional CCD camera.
[0027]
In the above-described embodiment, the case where the Si single crystal is grown has been described. However, the present invention can be similarly applied to the case where a single crystal other than Si is grown using the CZ method.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the vicinity of an interface between a pulled single crystal and a melt.
FIG. 2 is a cross-sectional view schematically showing a crystal growth apparatus according to an embodiment of the present invention.
FIG. 3 is a curve diagram schematically showing the relationship between the luminance distribution in the vicinity of the fusion ring detected by the detection means of the crystal growth apparatus according to the embodiment and the width of the fusion ring.
FIG. 4 is a block diagram illustrating functions of a temperature calculation / control unit according to the embodiment.
FIG. 5 is a diagram showing response characteristic results according to an example and a comparative example when a disturbance obtained by simulation by a computer is applied.
[Explanation of symbols]
12 Crucible 13 Melt 15 Heating means 16 Lifting means 20 Single crystal 21 Fusion ring 30 Measuring / detecting means 33 Temperature calculation / control means

Claims (4)

A single crystal diameter control method that grows a single crystal while maintaining the target diameter when pulling up with a fixed pulling speed fixed so that the crystal defect quality is stabilized over the entire straight body in the silicon single crystal manufacturing process. There,
When setting the operation amount of the heating means temperature disposed around the crucible for melting the crystal raw material,
The response of the single crystal diameter value when the heating means temperature is changed stepwise is obtained in advance, assuming a transfer function of a first-order lag system, and the measured value of the single crystal diameter and the stored target In addition to the main loop that calculates the manipulated variable by feeding back the deviation from the diameter value,
The amount of influence that the time-dependent variation of the width of the fusion ring having higher brightness than the surrounding that appears in the vicinity of the interface between the single crystal and the melt has on the single crystal diameter is obtained in advance, and the fusion ring is continuously detected. The diameter of the single crystal is set to the target diameter by calculating the amount of operation of the heating means temperature by a minor loop that is fed back by adding the amount of operation obtained from the variation of the width of the material over time. A method of controlling the diameter of a single crystal, characterized by controlling. A step response test was conducted to examine the response characteristics of the single crystal diameter value when the heating means temperature was changed stepwise, and the response of the single crystal diameter value when the heating means temperature was changed stepwise. The method for controlling the single crystal diameter according to claim 1, wherein the single crystal diameter is obtained by: A crucible for melting the crystal raw material;
Heating means disposed around the crucible;
Lifting and lowering means for pulling up the silicon single crystal while growing it from the melt in the crucible;
Measuring means for measuring the diameter of the single crystal to be grown;
Detection means for detecting the width of the fusion ring having a higher brightness than the surroundings appearing in the vicinity of the interface between the single crystal and the melt ;
A temperature calculating means for calculating a set temperature of the heating means based on a deviation between an actual measurement value of the single crystal diameter and a target diameter value, and information over time of the width of the fusion ring having the high brightness;
Control means for controlling the amount of power supplied to the heating means based on the calculated set temperature,
The temperature calculation / control means stores the actual value of the single crystal diameter detected by the detection means from the amount of influence that the temporal variation of the width of the fusion ring obtained in advance has on the single crystal diameter. In addition to the main loop for calculating the operation amount of the heating means temperature by feeding back the deviation from the target diameter value, the change over time of the fusion ring width obtained in advance is the single crystal diameter It has a function of inserting and feeding back a minor loop for adding the operation amount of the heating means temperature to be operated by the width of the fusion ring detected by the detection means from the influence amount on the detection means. A crystal growth apparatus characterized by the above. The temperature calculation / control means includes a response of the single crystal diameter value when the temperature of the heating means is changed in steps as an influence amount on the single crystal diameter due to a change in the width of the fusion ring over time. 4. The single crystal growth apparatus according to claim 3, wherein the response characteristic obtained by performing a step response test is stored.

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