JPS5848518B2 - Automatic crystal diameter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the growth of a single crystal by the so-called rotary pulling method, and in particular, it controls the growth of a single crystal by feeding back changes in the weight of the melt in a crucible to the temperature of the melt. The present invention relates to a device for automatically controlling the diameter of.

One of the methods for growing single crystals from a melt is to immerse a seed crystal in a crystallization melt and pull it up while rotating, which is well known as the so-called rotational pulling method (or simply the pulling method). It is being

In the growth of single crystals by the rotational pulling method, controlling the diameter of the crystal during growth to a constant level is one of the extremely important requirements for improving crystal quality and reducing costs.

Generally known methods for detecting the diameter of a growing crystal include optical measurement using an infrared camera and the force method, which is calculated from changes in the weight of the crucible containing the melt.
The former method may cause erroneous measurements due to reflected light from objects other than the object or clouds on the observation window, so the latter method is more advantageous in this respect.

The crystal diameter is usually controlled by the pulling speed, melt temperature, or a combination thereof, but since varying the crystal pulling speed will impair the quality of the crystal, the pulling speed should be kept constant. , it is more desirable to control the crystal diameter by manipulating the melt temperature.

FIG. 1 schematically shows an example of a conventional method for controlling the crystal diameter by detecting a change in the weight of the melt and feeding it back to the temperature of the melt.

As the single crystal 1 is rotated and pulled up at a constant speed, the amount of the crystal melt 2 decreases, and therefore the weight of the crucible 3 containing the melt 2 decreases over time.

The weight is converted into an electric signal ■ by the weight sensor 10, and this electric signal ■ is a reference signal corresponding to the ideal crystal weight change programmed in the setting device 20 in advance.
.

The deviation e (""vo - v) is inputted to the control device 30 as an operation signal.

The control signal, {E, is further applied to an output controller 40 for controlling the output to the high frequency coil 4, which is controlled by the program signal E throughout the pulling cycle by the programmer 50. The control signal {E will be fed back to this program output system.

In this way, the high frequency output is adjusted and the temperature of the melt 2 is controlled so that the deviation e becomes zero, that is, a predetermined crystal diameter is maintained.

Conventionally, a so-called PID operation type control device 30 has been used, but the PID operation type device is very expensive and requires a large number of capacitance elements and dead time, especially in the crystal growth process. In the case of a process with many disturbances, it is difficult to set the PID constant, and a long setting time is required for equipment installation and maintenance.

The present invention has been made in order to improve the above-mentioned conventional drawbacks, and aims to provide a device that automatically controls crystal diameter with high precision using a relatively simple control system.

FIG. 2 is a block diagram for explaining the automatic crystal diameter control device according to the present invention.

FIG. 4 shows an example of the circuit.

The difference between the control device of the present invention and conventional control devices lies in the structure of the control device 30.

That is, in the control device 30, the operating signal e generated in the same manner as before is first time-differentiated by the differential controller 31, and then the differential signal stone is intermittently multi-position controlled by the intermittent pedestal 32 at regular time intervals. It is transmitted to the vessel 33.

The multi-position controller 33 outputs a control signal JE that changes discontinuously in a stepwise manner with respect to the value of the input signal π, and feeds it back to the programmed signal E.

The differential operation by the differential controller 31 has the effect of increasing the proportional sensitivity without imparting excessive vibration to the system, and can also shorten the settling time.

Intermittent operation of the control signal by the intermittent controller 32 is effective for correcting dead time.

Furthermore, discontinuous operation using the multi-position controller 33 provides more stable and reliable control against noise caused by external disturbances.

The multi-position controller used in the present invention is one that controls so-called 3-position operation or 4-position operation, that is, it outputs one of three or more predetermined values depending on the magnitude of the input signal. In this case, it is desirable that the output (operated amount) be zero, especially when the absolute value of the input signal is smaller than a certain specific value.

This is because feedback is stopped when the crystal diameter is within a predetermined error range with respect to the target value, which is effective in protecting the program control system from noise caused by disturbances such as floating fields and vibrations of the crucible.

A multi-position controller can be manufactured extremely easily by combining one or more commercially available inexpensive molded comparators.

For example, FIG. 3 is a diagram showing one configuration example of a 5-position controller, FIG. 3a is a circuit diagram when two comparators are used, and FIG.
Figure b is a graph showing the relationship between the input to this circuit and the output JE.

Depending on the magnitude relationship between the input signal and the set voltages X1 and X2 of the comparators 331 and 332, one of five voltage values O, ±■1, ±■2 is output.

From an economical point of view, a three-position controller that can be configured with only one comparator is desirable as a multi-position controller used in the present invention, but if more precise control is also taken into consideration,
5-position controller is most desirable 0 Voltage value in Figure 3b X1 t X2 + Vt t and ■
2 is set to be optimal for the crystal pulling process, but for large deviation differential values, 7 is set in order to give a larger operation amount to reduce the deviation differential value in an accelerated manner. It is effective to set ① to be larger than twice 1.

The differential controller and the intermittent leg controller used in the present invention each determine the amount of change in the control amount based on the differential operation and the differential value, and perform intermittent operation that gives the amount of change in control once every several tens of seconds to several minutes. Any of various known devices, circuits, parts, etc. may be used.

Furthermore, it is also possible to add a low-pass filter, etc. to the feedback control system of the present invention in addition to the differential leg mechanism, intermittent controller, and multi-position controller, which are essential structural requirements of the present invention. be.

Next, as an example of the present invention, a case of growing a LiNbO3 single crystal will be described in detail.

Li20 and N are placed in a platinum crucible with an internal volume of 80φ x 80mm.
The weight ratio of b205 is 48.7:51.

The total of Li2CO3 and Nb205 is I
Kp is loaded and heated to a temperature higher than its melting point in the atmosphere to melt it.

Next, the melt temperature is set to the optimum temperature, a LiNb03 single crystal seed crystal is immersed in the melt, and pulling is started at a speed of 5 MM/H while rotating at 15 RPM, and at the same time a temperature control program is started.

In this case, the intermittent controller has an on time and an off time of 10 each.
seconds, and 50 seconds.

The multi-position controller was a 5-position controller as shown in FIG. 3, and two comparators 4115104 manufactured by Burr-Brown were used, and the outputs (1) and (2) were set to 3 and 10μ, respectively.

As described above, for the target value of crystal diameter 50φ, ±
Control within 1φ was achieved.

According to the present invention, as is clear from the above embodiments, by performing the differential operation intermittently and discontinuously, P
Compared to ID operation, the crystal diameter can be automatically controlled with high precision using a cheaper control device and more easily.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an example of a conventional method for automatically controlling the diameter of a pulled crystal in a rotational pulling method, and FIG. 2 is a diagram for explaining a control device according to the present invention. , and FIG. 3 are circuit diagrams and graphs of a five-position controller which is an embodiment of the multi-position controller used in the present invention, and FIG. 4 is an example of a control circuit diagram of the present invention. 1... Crystal being pulled, 2... Melt of crystal material, 3... Crucible, 4... High frequency output coil, 10... ...Weight sensor, 20...
...Target value setter, 30...Control device, 31
... Differential controller, 32 ... Intermittent controller, 33 ... Multi-position controller, 40 ... High frequency output controller, 50 ... ...Output program device, 331...Comparator, 332...Comparator.

Claims (1)

[Scope of Claims] 1. A method that converts the weight of a crucible containing a melt of a crystal raw material into an electrical signal, and feeds back the electrical signal to a system that programmatically controls the temperature of the melt, thereby controlling the crystal during rotational pulling growth. In a device for automatically controlling the diameter of A controller and a multi-position controller that performs discontinuous operation,
1. An automatic crystal diameter control device comprising a multi-position controller whose output is approximately zero when the absolute value of an input signal is smaller than a certain characteristic value. 2. The multi-position controller is a 5-position controller, and the signal human force envelope absolute value is compared with certain characteristic values Xi, X2, and dt de! When L-1<XI, the output is 0, when XI≦1, the output is Vl, when X2≦lit, the output is ■2,
The automatic crystal diameter control device according to claim 1, wherein the output voltage value is set so that V2)2V1. 3. Automatic crystal diameter control device according to claim 1, wherein the multi-position controller includes one or more comparators.