CS248696B1 - Apparatus for automatically controlling the melt crystal single crystal mass growth rate - Google Patents

Abstract

Device for automatic control of the mass growth rate of single crystals during pulling from the melt, enabling automated growing of defect-free single crystals, consisting of a weighing head, a current source, a deflection sensor circuit, a pulling rod and a crystal diameter regulator, where the goal is achieved in that the weighing head is formed by a coil (1) of an electromagnet for compensating the mass of the crystal and a pulling rod (3), terminated by a core (2) of the electromagnet, in its extension there is placed the middle electrode of the deflection sensor (4), hit by a differential capacitive sensor, which is connected to a high-frequency voltage source from a stable oscillator and further by a detection circuit, the output of which is connected to the electromagnet current source via a regulator (28) and the crystal diameter regulator (28) is connected via a measuring resistor (21) of the electromagnet current via a filter element (22) simultaneously with the output of the compensation integrator (24) to the input of the comparator (23), the input of the compensation integrator The integrator (24) is connected via a reed relay (25) to the output of the comparator (23) and the output (26) of the reed relay (25) is connected to a timer (27), while the comparator (23) is further connected to a temperature controller (28) in the furnace, including a crystal growth program controller, or a drawing speed controller.

Description

(54) Apparatus for automatically controlling the single crystal growth rate during melt drawing

Apparatus for automatically controlling the mass growth rate of single crystals during melt drawing, allowing automated cultivation of low-quality single crystals, consisting of a weighing head, current source, displacement sensor circuit, rod rod and crystal diameter regulator where the target is achieved by (1) a crystal mass compensation solenoid and a draw bar (3), terminated by a solenoid core (2), with an elongated displacement center electrode (4) displaced by a differential capacitance sensor connected to a high-frequency stable voltage oscillator source; a detection circuit, the output of which is connected via a regulator (28) to the electromagnet current source and the crystal diameter regulator (28) is connected via the electromagnet current measuring resistor (21) via a filter element (22) simultaneously with the output of the compensating integrator (24) to the comparator input (23), the input of the compensating integrator (24) is connected via the reed relay (25) to the comparator (23) output and the reed (26) of the reed relay (25) is connected to the timer (27); 23) is further connected to a temperature regulator (28), including a crystal growth program regulator or a drawing rate regulator.

248 696

- i 248 698

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for automatically controlling the single crystal growth rate during melt drawing.

Single-crystal drawing from melt is used in various modifications at present> most often for industrial preparation of various single-crystal types, such as semiconducting substances (silicon, gallium arsenide, gallium phosphide, germanium) or aluminum oxide-like substances (sapphire, ruby, aluminum yttrium garnets, gadolinium galito, rare aluminates

In soils with perevskite structure, niobates, tantallates, germanates, tungstates. ··). The growth generally proceeds in such a way that a single crystal seed of the material in the form of an oriented rod mounted on a drawing device rotating about its axis at equilibrium temperature touches the melt of the starting material, mostly in the crucible, and then withdraws at the optimum for the material while decreasing temperature of the melt. This leads to a gradual growth of the crystals to the desired diameter, which must then be kept as constant as possible. Growth often takes place in a space with a defined protective atmosphere or in a vacuum. If cultivation is carried out on a device with manual crystal growth control and manual control of melt temperature and drawing rate as a means of controlling crystal growth rate, the grown crystals have a number of structural defects, optical defects and irregular shape, since crystal observation cannot be detected changes in crystal growth and respond in time to interventions in temperature and drawing speed. In addition, manual cultivation requires very careful operation and a higher number of workers.

248 «

For this reason, various types of cultivation equipment equipped with different systems have been developed in recent years, which allow automatic control of the crystal growth rate, thus reducing the labor required and substantially increasing the overall efficiency of the crystal preparation.

The devices are constructed in particular on the following approaches: optical crystal diameter sensing, sensing a drop in the level of the melt in the crucible, an X-ray measurement of the crystal diameter, sensing the weight loss of the melt in the crucible, and sensing the weight gain of the crystal. The measured values are processed in electronic controllers and, when compared to the programmed values, the differential signal is used to control the melt temperature or the drawing speed, sometimes both. Individual principles have their advantages and disadvantages, differ in sensitivity and some are specifically suitable for certain types of single crystals ·

The present invention relates to an apparatus based on the principle of sensing the crystal weight gain. The devices described so far have been based on a different method and design of crystal weight sensing. For example, various types of strain gauges on which the crystal weight acts are used. This method is more structurally complicated, requires a thermostatic element of the sensitive element and its sensitivity is lower than the device described herein. Another method is structurally based on the mintrra principle, where the rotating crystal is suspended by a coiled spring that ee stretches the increasing weight of the crystal, its elongation sensed e.g. by an inductive sensor is used as an input signal to the growth regulator. The disadvantage of such a device is that the growth does not take place in a constant position, but as the spring stretches, the crystal moves downwards against the pulling direction, and the lower sensitivity of the displacement transducers relative to the sensors operating at one point.

248

These difficulties and drawbacks are substantially eliminated by a device for automatically controlling the mass growth rate of single crystals during melt drawing, consisting of a weighing head, a power source, a displacement sensor circuit, a draw bar, and a crystal diameter regulator. from a solenoid coil to compensate for the mass of the crystal and a tension rod terminated by an electro magnet core, in the extension of which the central electrode of the displacement sensor consisting of a differential capacitive sensor is connected, connected to a high-frequency voltage source from a stable oscillator; the regulator is connected to the electromagnet current source and the crystal diameter regulator is connected via the filter resistance of the electromagnet current through the filter circuit simultaneously with the compensator integrator output to the comparator input, compensator input The reed integrator is connected to the comparator output via a reed relay, and the reed relay coil is connected to a timing switch, wherein a furnace temperature controller, including a growth program, and optionally a drawing rate controller, are connected to the comparator.

In the following, in conjunction with the accompanying drawings, the invention is described in more detail as a specific embodiment.

Fig. 1 schematically illustrates the construction of the device; and Fig. 2 is a schematic diagram of the control elements.

FIG. 1 shows the drawing rod J, at its upper end the electromagnet core 2 and in the extension of the drawing rod J the displacement sensor 6. Further shown is a solenoid coil J, a support body 8, a carrier plate 6 of a carrier 6, an outer tube χ, a bearing J, a glass tube 11. and the top of the furnace 10.

FIG. 2 shows a measuring resistor 21, a filter member 22 a comparator 20, an integrator 24, a relay 26, a coil 26, a timer 27, and a controller 28.

The operation of this device is described below.

The weight of the drawn crystal growing on the lower portion of the draw bar J, including its weight, is compensated by the electromagnet force, where the electromagnet core 2 mounted on the draw bar J has a smaller diameter than the inner diameter of the glass tube 11.

AND

- 248 t 248 898 electromagnet. The solenoid coil 1 is mounted on the support body 8. The capacitive displacement sensor 4 located above the electromagnet is designed such that its central electrode, fixed in the extension of the draw bar, limits its maximum vertical movement. The draw bar 2 is coaxially fixed with respect to the outside

the tube 2 by means of the foils fixed in the retainers 6 and is fixed by means of bearings 2 in the support body 8 and allows the transmission of rotation which is further transmitted by the carriers 6 and the foils. / sealed by means of O-rings and seals, so as to ensure the leakproofness of the growing apparatus, - the clearing allows the cultivation of single crystals in both vacuum and protective atmosphere. The solenoid coil 2 is supplied by a current source through a measuring resistor 21 and the source is controlled by a modified voltage from a displacement sensor 4 having a static sensitivity of 10 m.

Thus, a constant vertical position of the drawbar 2 is maintained. The signal corresponding to the weight of the grown crystal is taken as a voltage from the measuring resistor 21. The signal after the disturbing voltage is applied in the filter element 22 is connected to the comparator input 23. 24. The output of comparator 23 is connected to the input of integrator 24 via reed relay 24. When the reed relay 25 98 is closed, the negative feedback loop closes, the output voltage from integrator 24 compensates for the voltage applied to comparator input 24. By periodically switching the reed relay 22 through the coil 26 and the timer 27, the crystal weight control is performed to control the weight gain.

A comparator 28, optionally a crystal growth programmer and a furnace temperature regulator are connected to the comparator.

Claims (1)

SUBJECT OF THE INVENTION 248 696 Apparatus for automatically controlling the mass growth rate of single crystals during melt drawing, comprising a weighing head, a current source, a displacement sensor circuit, a draw bar and a crystal diameter regulator, characterized in that the weighing head is formed by a solenoid coil (1) a pulling rod (3) terminated by a solenoid core (2) in its extension by the central electrode of the displacement sensor (4) consisting of a differential capacitive sensor connected to a high-frequency voltage source from a stable oscillator and a detection circuit (28) only with the electromagnet current source, the crystal diameter regulator (28) is connected via the electromagnet current measuring resistor (21) via the filter element (22) simultaneously with the compensator integrator output (24) to the comparator input (23), the compensator integrator input (24) is via a reed relay (25) connected to the output of the comparator (23) and a coil (26) of the reed relay (25) is connected to a timer (27), the comparator (23) being further connected to an oven temperature controller (28) including a crystal growth program regulator, or a drawing rate regulator.