JP2811826B2 - Single crystal growing apparatus and single crystal growing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high quality YAG (Y ₃ Al ₅ O ₁₂ ) single crystal or Nd: YA
The present invention relates to a fully automatic growth apparatus and a single crystal growth method for G (YAG doped with Nd ₂ O ₃ ) single crystals.

[Conventional technology]

Conventionally, a single crystal of Nd: YAG is grown by a pulling method (Czochralski method). In the gravimetric method, in order to grow a long crystal having a required diameter, a voltage proportional to the weight of the pulled crystal is generated by a load cell,
This voltage is converted into a signal that matches the input conditions of the computing device (such as a personal computer) and input to the computing device. The arithmetic device compares the weight signal with a reference weight value previously input to the arithmetic device, controls the high-frequency power based on this difference, corrects the crystal diameter, and grows the crystal. When inputting the output voltage of the load cell to the computing device, a signal converter and an A / D converter are connected to the output side of the load cell. Conventionally, however, there is only one signal converter and the maximum output voltage of the load cell is A / D. The signal converter is set to have the maximum input voltage of the D converter. That is, the maximum input voltage of the signal converter is the maximum output voltage of the load cell.

[Problems to be solved by the invention]

Since the growth temperature of the Nd: YAG single crystal is high (1970 ° C.) and the growth time is very long (300H), even a slight change in the material or configuration of the heat-retaining refractory contributes to the temperature history. Moreover, Nd: YAG single crystals are very sensitive. For this reason, the composition of the refractory becomes more complicated in order to maintain more stability, and the crystal monitoring window becomes very small, making it difficult to see the growth state.

Automatic growth under such circumstances becomes difficult by an optical method using a CCD camera or the like, and a weight type using a load cell is generally used. In the weight formula based on the weight signal, since the magnitude of the weight signal is directly caused by the crystal diameter, if the reading accuracy of the weight signal is poor, a crystal with many irregularities is grown and a reading error of the weight signal occurs. In addition, a large temperature change is caused to grow a crystal having a large unevenness in crystal diameter, and as a result, crystal growth may not be possible.
For this reason, the improvement of the reading accuracy of the weight signal and the study of the breeding method have been problems.

An object of the present invention is to solve this problem and provide an apparatus and a method for growing a high-quality single crystal.

[Means for solving the problem]

The single crystal growing apparatus of the present invention measures the weight of a single crystal grown from a melt of a single crystal raw material in a crucible heated by the high frequency coil and a crucible heated by the high frequency coil provided with a vacuum thermocouple for measuring supplied power. A load cell, a signal conversion circuit that converts an output voltage of the load cell into a signal that matches an input condition of an A / D converter, and an analog controller that controls the supplied power so that an output signal of the vacuum thermocouple approaches a predetermined value M. A single crystal growing apparatus comprising: a crystal system control unit that obtains an increasing rate of the weight of the single crystal body from an output signal of the signal conversion circuit and changes the M according to a predetermined program. the maximum read range is 10-15%, respectively grown scheduled crystal weight value V _S,
The first signal converter, the second signal converter, and the third signal converter, which are the maximum measurable weight values of V _S and the load cell, are connected in parallel.

Further, the method for growing a single crystal of the present invention includes a high-frequency coil provided with a vacuum thermocouple for measuring supplied power, and a weight of a single-crystal body grown from a melt of a single-crystal raw material in a crucible heated by the high-frequency coil. A load cell to be measured, a signal conversion circuit for converting an output voltage of the load cell into a signal that matches an input condition of an A / D converter, and controlling the supplied power so that an output signal of the vacuum thermocouple approaches a predetermined value M. An analog controller and crystal system control means for changing the M in accordance with a predetermined program by determining an increasing speed of the weight of the single crystal body from an output signal of the signal conversion circuit, wherein the signal conversion circuit has a maximum readable capacity. A first signal converter, a second signal converter, and a third signal converter whose ranges are respectively 10 to 15% of the crystal weight value V _{S to} be grown, the maximum measurable weight value of V _S and the load cell. Are connected in parallel, a target crystal diameter D ₀ and a crystal length L ₀ are set in advance, and the maximum input power of the first signal converter is set.
V _M10 , the maximum input voltage V _{M11 of} the second signal converter, and the maximum input voltage V _M12 of the third signal converter are input to a computing device, and the weight of the growing crystal is calculated at appropriate time intervals. when, during the period from the start of development until the time T ₁ that the grown crystal diameter D ₁ is D ₀ ≦ D _1, when the input voltage V ₁₀ of the first signal converter is V ₁₀ ≦ V _M10 V ₁₀ voltage to calculate the weight value based on the second input voltage V ₁₁ of the signal converter to calculate the weight value based on the time of V _10> V _M10, the length of T ₁ after growing crystal L is L = until reaching the L ₀ is V ₁₁ calculates the weight value based on V ₁₁ when V ₁₁ ≦ V _M11, V ₁₁ is the input of the third signal converter when V _11> V _M11 Voltage
Calculates a weight value based on V _12, and is that performing crystal size controlled by changing the predetermined value M by pre-determined program based on the weight increasing rate.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the single crystal growing apparatus of the present invention.

This embodiment will be described together with the background to the invention.

The present inventors have studied a crystal growth apparatus and a weight detection method to improve the accuracy of the crystal weight signal, and have analyzed in detail the relationship between the change in the diameter of the grown single crystal and the crystal weight, and the high-frequency power, and Various studies were performed. As a result, one load cell is installed in a normal crystal growing apparatus, and an output signal of this load cell is output to an arithmetic unit, a recorder, or the like via a signal converter. In general, the weight detection range of the load cell is adjusted so that the maximum weight value of the installed apparatus capable of growing crystals is detected. For this reason, in actual crystal growth, it is normal to use the detection range of the load cell within about 1/2 to 2/3. For this reason, it became clear that the detection accuracy of the weight signal, that is, the weight detection accuracy of the arithmetic device was reduced. This decrease in weight detection accuracy leads to a decrease in control of crystal growth, resulting in high quality N
d: YAG development was difficult to draw. Also, in order to increase the accuracy of the weight detection, the weight detection range of the load cell may be adjusted so as to be the growth expected crystal weight for each growth,
Adjustment is difficult because the load cell itself is a precision machine and is installed on top of the device.

The present inventors have paid their attention to a signal converter on the output side of the load cell in order to improve the weight detection accuracy under a certain condition of the load cell, and have conducted research. As a result, it has been found that by converting a signal from the load cell, the weight signal can be read with high resolution and a high-quality Nd: YAG single crystal can be grown by performing an amount of conversion corresponding to the growth process. In the method of growing a crystal, after dipping a seed crystal in a solution, the crystal is pulled up while rotating at a certain speed, and the crystal is gradually thickened. Thereafter, after reaching the desired diameter, the high-frequency power is controlled so that the diameter reaches the desired length until the diameter reaches the desired length, and the pulling is performed. In the case of shoulder making, the larger the crystal diameter, the greater the effect on the subsequent crystal quality, and the weight change is very small, and the amount is Nd: Y
Many experiments revealed that the AG single crystal accounts for 10 to 15% of the weight of the crystal to be grown. As a result, the single first signal converter 10 is used to increase the sensitivity of the shoulder forming portion.
The maximum input of this converter is 10
Set to ~ 15%. On the other hand, a second signal converter 11 was separately installed so that the expected crystal weight became the maximum input of the converter in order to improve the reading accuracy of the grown crystal weight. Further, a third signal converter 12 is provided so that a maximum crystal can be supplied to a load cell so that the crystal can be grown even when a crystal larger than the expected crystal is required due to various troubles or experimental changes during the crystal growth. And the same as the maximum output signal. Next, a method of reading the crystal weight during the crystal growth will be described in detail with reference to the flowchart shown in FIG.

FIG. 2 is a flow chart for explaining one embodiment of the method for growing a single crystal of the present invention. First, before starting the growth, a target crystal diameter (D ₀ ) and a crystal length are determined in step 14. (L ₀ ), the maximum input voltage (V _M10 ) of the first signal converter ₁₀ , the maximum input voltage (V _M11 ) of the second signal converter 11, and the maximum input voltage (V _M11 ) of the third signal converter 12. Maximum input voltage (V
_M12 ) into the computer (5). Next, in step 15, the raw material in the crucible is melted, and then seeding and pulling are started, and the input voltage of the first signal converter 10 (V
₁₀ ) Detect and convert to weight. The accumulated time from the start of pulling in step 16 is measured, and the crystal length during growth (L)
Is calculated. The crystal diameter during growth (D ₁ ) is calculated from the weight value converted in step 17. In step 18, the amount of weight increase determined in advance is compared with the weight during growing, and an amount corresponding to the difference is added to the analog controller (8) to control the current flowing through the high-frequency coil, thereby controlling the diameter of the crystal diameter during growing. Is performed. Next, in step 19, it is determined whether or not the time (T ₁ ) when D ₁ has reached D ₀ is set. If T ₁ is not set, the process proceeds to step 20, where D ₁ is D ₀ ≦ D ₁ In the case of, V ₁₀ ≦ V _M10 is determined in step 21, and if V ₁₀ ≦ V _M10 , V ₁₀ is detected in step 22 and converted into weight, and
Proceed to 6 to continue the training. If V ₁₀ ≦ V _M10 , V ₁₁ is detected in step 23 and converted into weight, and the process proceeds to step 16. If D ₀ ≦ D _{1 in} step 20, the current time (T ₁ ) is set in step 24. When it is determined _{V 11 ≦ V M11 V 11 ≦} V M11 in step 26 when in step 25 is not a L = L _0, and detects the V ₁₁ was converted to weight in step 27, the process proceeds to step 16. When V ₁₁ ≦ V _M11 is not satisfied, V ₁₂ is detected in step 28 and converted into weight, and the process proceeds to step 16. Also in step 19
If T ₁ is set, the routine proceeds to step 25, and, when at step 25 of L = L ₀ disconnected from solution crystal during the growth, development is completed.

As described above, by separately detecting the weight of the grown crystal in the shoulder forming portion and the straight body portion and growing the crystal, it is possible to detect the weight with high precision, particularly in the shoulder forming portion where the weight increase rate is low. As a result, an ideal shoulder can be formed and a high-quality single crystal can be grown. Further, even if the weight of the grown crystal becomes larger than expected in the growing process, it is possible to grow the crystal. If a plurality of weight signals are detected at the same time, the failure of the signal converter and the failure of the load cell can be found, and the signal line can be detected. Noise correction from is also possible.

Next, a specific description will be given using numerical values. Using the single crystal growing apparatus shown in FIG. 1, the target crystal diameter of the single crystal (D ₀ ) =
The length (L ₀ ) of the φ32 crystal is set to 200 mm, the maximum input voltage (V _M11 ) of the second signal converter 11 is 75 mV, and the output voltage is 10 V,
The output voltage was set to 10 V when the maximum input voltage (V _M10 ) of the first signal converter 10 was 15 mV, and the output voltage was set to 10 V when the maximum input voltage (V ₁₂ ) of the third signal converter 12 was 150 mV.
At this time, the load detectable range of the load cell is 1.5 kg and the output voltage is 150 mV. These pieces of information are input to the personal computer 5. Also, first to third signal converters
FIG. 3 shows the input / output equivalence of 10 to 11.

Next, 2100 g of Nd: YAG single crystal raw material (high purity Al ₂ O ₃ , Y ₂ O ₃ doped with 0.8 at% Nd, weighed and mixed in appropriate amounts, respectively) were placed in an Ir crucible 1 of 85φ × 100 ^h × 1.7 ^t. In addition, a heat insulating refractory was installed and provided at the center of the high frequency coil 3. According to a command from the personal computer 5, power is applied to the high-frequency coil 3 by the analog controller 8 and the high-frequency oscillator 9 via the D / A conversion circuit 7, and the raw material 1 in the Ir crucible is melted. ) Was used as a seed crystal <111>, immersed in the melt, and confirmed to be under the optimal temperature condition. At a pulling speed of 1 mm / hr, the rotation speed is
20 rpm. Set the program of the target diameter (D _X ) so that the fattening result of the growth result becomes about 30 mm after the start of pulling up, and set the signal 4 from the load cell or the vacuum thermocouple 13
The output of high-frequency power is controlled by a personal computer using signals from the PC. The input value of the first signal converter 10 immediately after the start of pulling was 4.2 mV (42 g). 29 hours (T ₁ ) after the pulling was started, D ₁ reached 30φ and the shoulder was controlled. At this time, the signal detector 10 was 11 mV (110 g). Thereafter, the diameter control of the straight body portion shown in FIG. 4 was started using the detection signal (V _1L ) of the second signal converter 11. After 180 hours,
Since the pulled length reached 180 mm, the crystal was cut off and the growth was completed. At this time, the output value of the second signal converter 11 was 72 mV (720 g). Confirmation of weight signal is 3rd
In the part with the shoulders shown in the figure, the first to third signal converters 10, 11, 12 directly compare the respective detected values by the second and third signal converters 11, 12 in the straight body. The grown crystal has a very smooth shoulder with no corners. Further, when a rod (4φ × 10 mm) cut from the crystal is measured for birefringence by phase difference, 4n = 1 × 10 ^-7 or less is obtained. Thus, a high-quality Nd: YAG single crystal with very little optical distortion was obtained.

〔The invention's effect〕

As described above, since the single crystal growing apparatus of the present invention has the first to third signal converters having different maximum readable ranges, during the growth of the shoulder making portion and the straight body portion and at the growth end point. It is possible to perform high-quality single crystal growth with good reproducibility by controlling the crystal diameter of the grown crystal according to a predetermined program using this single crystal growth apparatus. There is an effect that becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the single crystal growing apparatus of the present invention, FIG. 2 is a flowchart for explaining a method of reading a crystal weight during growing in the single crystal growing method of the present invention,
FIG. 3 is a diagram showing the relationship between the input voltage and the output voltage of the first to third signal converters, and FIG. 4 is a diagram for explaining each part of the crystal for growing the crystal. 1 is an Ir crucible, 2 is a Nd: YAG single crystal,
3 is a high-frequency coil, 4 is a load cell, 5 is a personal computer, 6 is an A / D converter, 7 is a D / A converter, 8 is an analog controller, 9 is a high-frequency oscillator, and 10, 11, and 12 are first to first, respectively. The third signal converter, 13 is a vacuum thermocouple.

Claims (2)

(57) [Claims] 1. A high-frequency coil provided with a vacuum thermocouple for measuring supplied power, a load cell for measuring the weight of a single crystal grown from a melt of a single crystal raw material in a crucible heated by the high-frequency coil, A signal conversion circuit that converts the output voltage of the load cell to a signal that matches the input conditions of the A / D converter,
An analog controller that controls the supply power so that the output signal of the vacuum thermocouple approaches a predetermined value M, and a rate of increase in the weight of the single crystal body is obtained from an output signal of the signal conversion circuit, according to a predetermined program. in single crystal growing apparatus comprising a crystal system control means for changing the M, the signal conversion circuit, 10-15% of the maximum read range, each grown scheduled crystal weight value V _S, the maximum V _S and the load cell A first signal transducer that is a measurable weight value, a second
A single crystal growing apparatus, wherein the signal converter and the third signal converter are connected in parallel. 2. A high-frequency coil provided with a vacuum thermocouple for measuring supplied power, a load cell for measuring the weight of a single crystal grown from a melt of a single crystal raw material in a crucible heated by the high-frequency coil, A signal conversion circuit that converts the output voltage of the load cell to a signal that matches the input conditions of the A / D converter,
An analog controller that controls the supply power so that the output signal of the vacuum thermocouple approaches a predetermined value M, and a rate of increase in the weight of the single crystal body is obtained from an output signal of the signal conversion circuit, according to a predetermined program. It includes a crystal system control means for changing the M, the signal conversion circuit 10 maximum scan range of each grown scheduled crystal weight value V _S
To 15%, V _S and a first signal converter is the maximum measurable weight value of the load cell, a single crystal growing apparatus in which the second signal converter, and a third signal converter connected in parallel with,
The target crystal diameter D ₀ and the crystal length L ₀ are set in advance, and the maximum input voltage V _M10 of the first signal converter, the maximum input voltage V _{M11 of} the second signal converter, and the third signal conversion When the maximum input voltage V _{12 of} the vessel is input to the computing device and the weight of the growing crystal is calculated at appropriate time intervals, the growing crystal diameter D ₁ after starting the growing is D ₀ ≦ D ₁ . between times T ₁ comprising the input voltage V ₁₀ of the first signal converter calculates the weight value based on a voltage of V ₁₀ when V ₁₀ ≦ V _M10, second when V _10> V _M10 the input voltage V ₁₁ of the signal converter to calculate the weight value based on the, V ₁₁ until length L of the T ₁ after growing crystals reaches the L = L ₀ is V ₁₁ ≦ V _M11
Group to calculate the weight value based on V _11, V ₁₁ calculates the weight value based on the input voltage V ₁₂ of the third signal converter when V _11> V _M11, and the weight gain rate when the And controlling the crystal diameter by changing a predetermined value M according to a program determined in advance.