JPH078754B2 - Single crystal manufacturing method - Google Patents

Description

The present invention relates to a method for producing a single crystal, and particularly to a method for producing a single crystal by the Czochralski method.

(Prior Art) Conventionally, a pulling method called Czochralski method is known as a method for producing an oxide single crystal such as LiTaO ₃ or LiNbO ₃ . This Czochralski method is a method in which the crystal raw material contained in the melting crucible is heated and melted by a heating means such as a high-frequency coil provided around the melting crucible, and then the seed crystal is brought into contact with the raw material melt surface to gradually melt temperature. It is a method of growing a single crystal by lowering the seed crystal while pulling it while rotating the seed crystal.

In the Czochralski method, the diameter of the seed crystal is usually continuously increased to form a shoulder, and the shoulder is formed.After the shoulder reaches a predetermined diameter, the crystal diameter is controlled to be a constant diameter. While pulling up the seed crystal, the straight body part is formed.

The diameter control at this time becomes a very important problem in the Czochralski method.

The conventional manufacturing method by the Czochralski method will be described below.

As shown in FIG. 3, after the seed crystal 3 is brought into contact with the surface of the raw material melt 2 housed in the melting crucible 1, the seed crystal 3 is pulled up while rotating to grow a single crystal 4. At this time, the weight of the single crystal 4 is detected by the weight detector 11, and deviation information between the weight measurement value signal from the weight detector 11 and the reference weight signal generator 12 and the pull-up distance detector 13 are detected. The pulling distance information of the single crystal is output to the PID control circuit 14. Then, based on these pieces of information, the control signal output from the PID control circuit 14 and the preset heating program signal from the program signal generator 15 are added and output to the high frequency output controller 16.

Then, the melt temperature is changed by controlling the high-frequency power supplied from the high-frequency oscillator 17 to the high-frequency coil 5 based on the signal information output from the high-frequency output controller 16, thereby controlling the diameter of the single crystal.

In such a manufacturing method, the program signal generator
The more accurate the program signal from 15 is, the more accurate the diameter control can be expected, but the program signal differs depending on the structure, material, etc. of the pulling furnace. Since thermal characteristics such as thermal conductivity change due to conversion and the like, in order to set an optimum program signal, it is necessary to try growing several times in advance. In order to improve this point, it has been considered to add a correction circuit for the program signal (Japanese Patent Laid-Open No. 56-59692).

(Problems to be Solved by the Invention) However, in any of the diameter control methods according to the above-mentioned conventional methods, for example, when the weight deviation deviates in the positive direction with time as shown in FIG. 4 (a), PID control circuit 14
The control signal from is in the direction of increasing the power while fluctuating as shown in FIG. 4 (b), and the total output signal which is the sum of the program signal and the control signal is shown in FIG. 4 (c). Therefore, the heating control with fluctuation is performed,
A sudden temperature change is given to the raw material melt, and the fluctuation of the control signal causes the temperature fluctuation to be several times larger than that of the case of using only the program signal.

As described above, the conventional method is a method of controlling the diameter of a single crystal by performing an operation of adding a correction value obtained from a control signal to a heating program. There is a problem that it is not possible to grow crystals with high quality and high yield, because it causes fluctuations, deteriorates the quality of the grown single crystal, and requires several times of growth to set an optimum program signal. . These problems occur when the growth rate of an oxide single crystal, such as Li ₂ B ₄ O ₇ or YAG, is extremely slow and bubbles are easily generated due to temperature fluctuations. Will result in.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a single crystal manufacturing method capable of significantly reducing the time required to set a program signal and growing a single crystal with high quality and high yield. To do.

[Structure of the Invention] (Means for Solving the Problems) In the method for producing a single crystal of the present invention, the single crystal is housed in a melting crucible.
The seed crystal is brought into contact with the melt surface of the Li ₂ B ₄ O ₇ or YAG raw material,
In the method for producing a single crystal in which the seed crystal is gradually pulled up while changing the raw material melt temperature based on a preset heating program, the weight of the single crystal grown every unit time is detected, The diameter of the grown single crystal is calculated from the weight change information of the single crystal, and the time gradient of the preset heating program is automatically corrected based on the time-dependent change information of the calculated diameter value of the single crystal. However, it is characterized in that the fluctuation of the crystal diameter of the single crystal is controlled within ± 0.5 mm.

(Operation) The method of the present invention calculates the diameter value of a single crystal from the weight increase amount of the single crystal per unit time, and preset Li ₂ B ₄ O ₇ or By automatically correcting the time gradient of the heating program of the YAG raw material melt, the tube required for setting the program signal can be significantly shortened, and single crystals can be grown with high quality and high yield.

(Example) Hereinafter, one example of the method of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a single crystal production apparatus to which the method of the present invention is applied. The seed crystal 23 brought into contact with the melt surface of the raw material melt 22 contained in the melting crucible 21 is pulled up while rotating. The single crystal 24 is grown. The weight of the single crystal 24 grown at this time is detected by the weight detector 31, the weight value signal is converted into a digital signal by the A / D converter 32, and the digital signal is input to the microcomputer 33. The output signal from the microcomputer 33 is converted into an analog signal by the D / A converter 34,
The high frequency output controller 35 is input to the high frequency output controller 35.
The high frequency power supplied to the high frequency coil 25 is controlled by the high frequency oscillator 36 based on the signal information from.

In the microcomputer 33, a melting crucible diameter, a reference diameter of a single crystal to be grown, a melt specific gravity, a crystal specific gravity, a crystal growth parameter such as a pulling rate and a time gradient, an operation time, and a heating program in which an operation amount is set are input. Has been done.

FIG. 1 shows an example of the operation of the microcomputer 33. For example, when the single crystal diameter gradually increases as shown in FIG. 2 (a), the weight of the single crystal detected per unit time is The single crystal diameter is calculated from the single crystal growth parameter programmed in the microcomputer 33 by the increase amount, and the growth control signal, that is, the main growth control signal according to the fluctuation state of the single crystal diameter within the predetermined time from the single crystal diameter data for each unit time. In the example, the control signal of the high frequency oscillator 36 is calculated. The predetermined time is updated every unit time.

The control signal occurs in the form of a time gradient of heating power and controls the time gradient of a predetermined heating program. As a result, an output signal as shown in FIG. 2B is obtained, and in this case, the time gradient of the heating power becomes smaller.

With the crystal growth method described above, extremely high quality,
Crystals can be grown with a high yield, and there is no need to set a new heating program even if the growth conditions change due to deterioration of the furnace material.

The method of the present invention, oxide single crystal, especially large thermal response delay,
In addition, it is effective for crystals in which bubbles are likely to occur due to temperature fluctuations.

Further, by setting the reference diameter of the single crystal so as to change with time, the method of the present invention can be applied in the shoulder forming step after seeding.

The method of the present invention is a piezoelectric substrate material for surface acoustic wave devices.
A specific example applied to the method for growing a Li ₂ B ₄ O ₇ single crystal will be described.

In the production of Li ₂ B ₄ O ₇ which is an oxide single crystal, especially when it is used as a piezoelectric substrate material for a surface acoustic wave device, it is required to produce a high quality single crystal without bubbles. On the other hand, Li ₂ B
_Since the raw material melt of ₄ O ₇ has a low thermal conductivity and a high viscosity, if the temperature of the raw material melt fluctuates during the growth of the single crystal, bubbles easily enter the crystal. Therefore, in controlling the diameter of the single crystal by the conventional method, a large temperature fluctuation is given to the raw material melt, and it is very difficult to obtain a high quality single crystal without bubbles.

Now, in this specific example method, the melting crucible 21 made of platinum is mixed with Li ₂ B ₄ O.
₇ Put the raw material powder and heat it to 950 ℃
And then contact the seed crystal 23 with the raw material melt 22
After the 23 is well matched with the raw material melt, the seed crystal 23 is gradually pulled while rotating. Then, the raw material melt 22 at a predetermined speed
The shoulder portion 24a of the single crystal 24 is formed by lowering the temperature of. The single crystal diameter is calculated by the microcomputer 33 from the crystal weight detected by the weight detector 31 per unit time and can be monitored on the display. When the single crystal diameter reached 80 mmφ, the automatic diameter control program of the present invention was activated.

This automatic diameter control program controls the diameter by lowering the melt temperature based on the sum of the preset time gradient (ΔT / Δt) _o and the control signal (ΔT / Δt) _t calculated by the microcomputer 33. There is. The fluctuation of the crystal diameter of the single crystal thus grown can be controlled within ± 0.5 mm, and a high quality crystal without bubbles can be grown.

[Effects of the Invention] As described above, according to the method for producing a single crystal of the present invention, the fluctuation range of the control signal for heating the melting crucible becomes about 1/10, and the temperature fluctuation of the raw material melt is greatly reduced. It can be suppressed to within ± 0.5 ° C, and it becomes possible to grow a single crystal with high quality without bubbles and fluctuation of crystal diameter within ± 0.5 mm.

Furthermore, even if there is a large change in the growth conditions, such as a change in the furnace structure or the conversion of refractories, it is not necessary to set a new heating program and the crystal growth yield is improved by about 50%.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of a single crystal growth apparatus used in one embodiment of the method of the present invention, and FIG. 2 is a diagram for explaining the control operation according to the method of the present invention. FIG. 4 is a diagram showing a change, FIG. 3B is a diagram showing an output signal, FIG. 3 is a diagram showing a configuration of a single crystal growing apparatus used in a conventional method, and FIG. 4 is a diagram for explaining a control operation by the conventional method. In the figure, (a) is a diagram showing changes in weight deviation, (b) is a diagram showing control signals generated by the PID control circuit, (c) is a diagram.
FIG. 6 is a diagram showing an output signal including a correction value. 21 …… Melting crucible 22 …… Raw material melt 23 …… Seed crystal 24 …… Single crystal 25 …… High frequency coil 31 …… Weight detector 32 …… A / D converter 33 …… Microcomputer 34 …… D / A converter 35 …… High frequency output controller 36 …… High frequency oscillator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Omi 72 Horikawa-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Horikawa-cho factory (56) References JP-A-60-65788 (JP, A) Special Kai 58-145692 (JP, A) JP 59-102896 (JP, A) JP 52-104473 (JP, A)

Claims (1)

[Claims] 1. Li ₂ B ₄ O ₇ or YAG contained in a melting crucible
A method for producing a single crystal in which a seed crystal is brought into contact with a melt surface of a raw material, and a single crystal is grown by gradually pulling up the seed crystal while changing the raw material melt temperature based on a preset heating program, Detect the weight of the single crystal grown for each time, calculate the diameter of the single crystal grown by weight change information of this single crystal, based on the time-dependent change information of the calculated diameter value of the single crystal Automatically corrects the time gradient of the preset heating program and adjusts the crystal diameter fluctuation of single crystal by ± 0.5 m
A method for producing a single crystal, characterized by controlling within m.