RU1798396C - Method for automated growing crystals from melt - Google Patents

Abstract

Usage: the invention relates to a technique for growing crystals by melt-drawing by the Czochralski method and can be used to obtain crystals of various cross-sectional shapes. SUMMARY OF THE INVENTION: the method improves the accuracy of maintaining the geometric parameter of the cross section of the crystal. In this case, a plate is introduced parallel to the surface of the melt into the melt, the temperature of this plate Tp is measured, two additional signals are generated, the first of which is proportional to the rate of temperature change. Tp, and the second the signal is the second derivative of this temperature and is summed by the feedback signals of the T and V channels, and the deviation is compensated by the sum signal. 1 ill.

Description

The invention relates to a technique for growing crystals by extrusion from a melt by the Chukhralsky method in an automatic mode and can be used to produce high-quality crystals with a round, square, and other cross-sectional shapes: gadolini, terbium, calcium, lithium niobate, and lithium tantalate, germanate and bismuth silicate, langasite and others.

The aim of the invention is to increase the accuracy of maintaining the geometric parameter of the cross section of the crystal.

Typically, when using a two-channel control system, the controller structure looks as follows:

where Am and Am are the deviations of the mass and its derivative from the given values, respectively,

U is a control vector consisting of T and V components,

Ki I J1 J2 - tuning matrix

factors related to the weight sensor.

In the proposed method, the structure of the regulator in the general case is as follows:

 Am

U Kix | . J + K2X Am

/

tn

Tn

(2)

 HO 00 CL

ABOUT

about

U Kix (

Am am

ABOUT)

where Tp and Tp are the first and second derivatives of the plate temperature,

"2. I J3 g / 14 I - tuning matrix

coefficients related to the temperature sensor.

As can be seen from the proposed control law (2) ,. the deviation Am. of the rate of temperature Tn is stabilized, which leads to a constant not only cross-sectional area, but also its shape.

The drawing shows a diagram of an implementation of a method for growing crystals from a melt in an automatic mode.

A plate 3 with a thermocouple 4 is lowered into the melt 1, which is placed in the crucible 2, parallel to the surface of the melt 1, after which the seed 5 is fed to the surface of the melt 1, the rotation drives b and the movement 7 of the upper rod 8 are turned on, a wire 9 and then a wire are formed t growing crystal 10 in automatic mode. The vertical movement of the plate 3 is carried out in accordance with the decrease in the level of the melt 1 by means of the displacement drive 11. The motor of the displacement and rotation drives 7.11 is controlled from the computer 12 using the interface modules 13, 14, 15. The crystal 10 is weighed with using the weight sensor 16. The signals from the weight sensor 16 and the thermocouple 4 are fed to analog-to-digital converters 17 and 18, also connected to the computer 12. The computer 12 is controlled by the crystal form 10: via the V-channel using the interface module 13 , on the T-channel using digital-to-analog will convert eat 19. From the digital-to-analog converter 19, the signal is supplied to the electric energy source 20, by means of which the heater 21 is supplied

The proposed method for growing crystals from a melt in an automatic mode is implemented as follows.

Example. Gadolinium molybdate crystals of 0 ° orientation were grown by the Czochralski method from a platinum crucible having the following dimensions: diameter - 50 mm, height - 50 mm, wall thickness - 3 mm. The heat zone was in the form of sintered alumina tubes, and a platinum conical screen was also used. The melt was at a temperature of 1160 ° C. A platinum plate with a diameter of 30 mm and a thickness of 1 mm to a depth of 2 mm from the surface of the melt was lowered into the melt. The temperature Tg of the wafer was measured using a Pt-PtRh-10 thermocouple. After seeding and shaping of the ribbon, the cultivation was carried out automatically. In this case, the movement of the plate during crystal growth

in such a way that the distance between the plate and the surface of the melt is kept constant. The cultivation was carried out at a drawing speed of 5 mm / h and a rotation speed of 100 rpm, the maximum angle of crystal growth was 130 °. To control the technological process of growth, a personal computer such as IBM PC / AT was used with an interface device made in the UME standard. Two-channel (T- and V-) control was implemented, supplemented by components with respect to the derivatives of the plate. Calculation and summation of control components Ui and U2

Ui-kix

 Am am

/ Tp

Tp

; U Ui + u2

made by computer.

Twelve crystals of good quality gadolini molybdate were obtained with a constant square cross-section (30 mm square side) 60-80 mm long.

PRI me R 2. The crystals of lithium niobate were grown by the Czochralski method from a platinum crucible having the following dimensions: diameter - 120 mm, height - 120 mm, wall thickness - 3 mm.

The heat zone was made in the form of sintered alumina pipes, and a platinum screen was used as the active screen. The melt was at a temperature of 1270 ° C. A platinum plate with a diameter of 80 mm and a thickness of 1 mm to a depth of 4 mm from the melt surface was lowered into the melt; the plate temperature was measured using a Pt-PtRh-10 thermocouple. After seeding and shaping of the ribbon, the cultivation was carried out automatically. In this case, the movement of the plate was carried out in accordance with a decrease in the level of the melt in the crucible so that the distance of the plate from the surface of the melt was kept constant. Cultivation was carried out at a rotation speed of 10 rpm, the maximum angle during the formation of the forward and reverse cones was 65 °. To control the growth process, a personal computer of the type IBM PC / AT was used with a VME interface device. Two-channel control was implemented, supplemented by

components according to temperature derivatives, as in Example 1. 3 crystals of lithium niobate with a diameter of 80 mm and a length of 130 mm of good quality were grown. The accuracy of maintaining the diameter was 0.2%.

Using the proposed method for growing crystals from a melt in an automatic mode, in comparison with existing methods, stabilization of the interphase boundary with respect to the surface of the melt provides crystals with predetermined shapes and geometric cross-sectional parameters.

Claims (1)

Formula for Acquisition A method of growing crystals from a melt in an automatic mode, consisting of seeding and growing stages, including measuring the mass and length of the crystal, determining the geometric parameter of the cross-section of the crystal from the measured values and controlling it by changing the melt temperature and / or the rate of drawing the crystal, different the fact that, in order to improve the quality of the grown crystals by increasing the accuracy of maintaining their geometric cross-sectional parameter, at the stage of seeding under an etched crystal is introduced into the melt with a plate whose plane is parallel to the surface of the melt, while the distance between the plate and the surface of the melt is maintained constant at the growing stage, the temperature of the plate is measured, its first and second derivatives are determined, and the value of the geometric parameter of the crystal cross section is further adjusted with respect to the first and second derivatives of the plate temperature and simultaneously with respect to the melt temperature and the drawing speed of the crystal.