Apparatus for growing monocrystals from melt

FIELD: crystal growing.

SUBSTANCE: crystal growing apparatus comprises double-section chamber, seed holder fixed on rod, crucible, furnace provided with heater assembled on U-shaped lamellas following the crucible outline, centering ring with closed parts of lamellas attached to it, and water-cooled annular current leads. According to invention, furnace is constructed in the form of two heaters similar in shape, mass, and size, which are mirror reflection of each other; closed parts of U-shaped lamellas are attached to centering ring being moved apart to 90°; rod with seed holder is disposed inside upper heater; free ends of lamellas are connected through conducting adapters to current leads with alternation of current charge signs as follows: "++--"; crucible is supported by insulated supports disposed between heater lamellas; conducting adapters are made from refractory material having resistivity lower than that of lamellas; and ends of adapters connected with lamellas are positioned at the same distance from axis of heater.

EFFECT: enabled growing large-size monocrystals and increased their structural perfection due to lack of supercooling of melt and increased service time of units.

6 cl, 2 dwg

 

The invention relates to a device for growing single crystals from the melt to the seed crystal and can be used in the technology of growing crystals, such as sapphire method of Amoz.

A device for growing monocrystalline ribbons sapphire, which includes a camera located inside the crucible, thermal unit, the shaper, structurally mounted on the stem.

Thermal unit made in the form of cylindrical graphite heater, the inner surface of which is coated with a layer of silicon carbide, and screens.

The crucible to melt coated on the external side with a layer of tungsten. The crucible is mounted on a pedestal and placed inside a graphite heater. Screens placed above the crucible (See. A. St. USSR №1213781, M CL 30 In 15/34, publ. 23.04.1991 year).

The device has the following disadvantages.

The material of the heater - graphite with a deposited layer of silicon carbide, chemically reacts with corrosive oxides of aluminum at high temperatures, which dramatically reduces the life of the heater and pollutes the carbon of the growing crystal. The heater cannot be repaired in the event of a breakdown. The device does not allow you to grow a high quality bulk single crystals.

A device for growing bulk single crystals, including the camera, two melting heat is the body and two-piece crucible. In the upper section of the melted source material using one heater located around the upper section of the crucible, and the cultivation is carried out on the lower section of the crucible using a different heater installed under the bottom section of the crucible (See. A. St. No. 661966, M CL 30 In 15/02, publ. 30.03.80 year).

The device does not provide a growing bulk single crystals because of the impossibility of creating in the melt directional heat dissipation through the center of the melt when rassasyvanii single crystal.

A device for growing single crystals from a melt containing crucible, heater, which is installed inside the crucible, and the system heat shields, one of which has the shape of a truncated cone or cylinder and fitted around the crystal in the border region between the surface of the melt and the crystal, another heat shield prevents the passage of heat radiation from the side surface of the crystal in the upper part of the chamber (See. U.S. patent No. 6338757, M CL 30 In 35/00, publ. 15.01.2002,).

The device has the following disadvantages.

System heat shields sophisticated and conservative. To control the temperature gradient is not possible.

A device for growing single crystals from the melt to the seed crystal, comprising a cylindrical chamber with a lid, heat the node, the crucible to melt structurally, ukreplennyj on the rod. The camera is made of two sections, thermal unit is installed in the lower section of the chamber and consists of a heater, built from the curved shape of the crucible U-shaped blades, closed circular water-cooled current leads are made with holes, in which are secured the free ends of the blades, and U-shaped curved ends of the slats mounted on the centering their ring. The current leads are installed on insulators, centering the heater, and the findings are located on the lateral surface of the cylinder in different horizontal planes. The current leads are either coaxial or one above the other. The slats are made of the same length and configuration and assembled in a circle. Centering ring, tightening curved U-shaped ends of the slats, is not involved in the electric circuit (See. RF patent №2222644, M CL 30 In 15/00, 15/34, publ. BI 03, 2004) the Device is taken as the closest analogue. The essence of the device is similar in design thermal unit in which all the elements, namely: the heater, the current leads, insulators, made compactly and represent a single whole.

Thermal unit design has several advantages.

The heater is assembled from strips, mounted on the closed annular current and centring ring at the same time performs the function of a thermal shaper has the ability to change fo the mu profile of grown crystals. The heater is simple in operation, can be easily assembled and disassembled when changing profile of the single crystal, as change forms radial isotherm is achieved by removing or adding the desired number of slats in sections.

Thermal unit design significantly increases its service life and is ergonomic.

The known device significantly improves the quality of farmed in the traditional way of single crystals, when the growing process is carried out at the outlet of the heat of crystallization or a reduction in the speed of growing or reducing the power to the heater in the area of the melt, thereby reducing its temperature. Both have a negative impact on the process or reducing its productivity, or increasing the supercooling of the melt at the crystallization front, causing the formation of structural defects (small angle boundaries, polycrystalline structure).

The technical result of the claimed invention is the possibility of growing large-size single crystals by the method of Amoz, improved structural perfection due to the absence of supercooling of the melt, increasing the lifetime of the nodes.

The technical result is achieved in that a device for growing single crystals, including two cameras, structurally fixed on the rod, the crucible, thermal unit with heater, collected from the curved shape of the crucible U-shaped strips, centering ring, which is fixed to the closed side of the blades, the water-cooled ring current, thermal unit is designed as two identical shape, weight and dimensions of the heaters, which are mirror images of each other, with the closed part of the U-shaped slats mounted on centring ring deployed on 90°and stem with structuralism located inside of the upper heater, the free ends of the lamellas through conductive adapter is connected to the current leads with alternating signs current load plus plus minus minus, the crucible is installed on insulated bearings situated between the lamellae of the heater with the same sign of the current load, and a conductive adapter is made of refractory material with a resistance lower than the resistance of the slats at the ends of the adapters connected to the blades, are located at the same distance from the axis of the heater; the slats are made of rare refractory metals and their alloys, such as tungsten, molybdenum, bolted; the slats are made of graphite, Silit; current leads are located in the sections of the camera, and the current leads of the upper heater and the lower heater current leads are located at the same distance from PL is Scoti connector top and lower sections of the chamber.

Growing crystals from the melt by the method of Amoz eliminates the occurrence of supercooling of the melt as the heat of crystallization assign by increasing the axial temperature gradient in the area of the growing crystal from its minimum value. Axial gradient regulate the temperature of a thermal zone above the melt throughout the reaction volume, which is a rod with structuralism and the grown crystal in the reduction and at the same time maintaining the same melt temperature throughout the volume of the crucible, resulting in heat always goes through the center of the melt in the direction of crystal growth, which excludes the occurrence of supercooling of the melt.

The essence of the claimed device is a new design thermal unit containing two identical shape, weight, dimensions and design of the heater is installed in mirror image to each other and form a single thermal area in which on the one side the stem with structuralism and the grown single crystal and the crucible with the melt. The design of the heaters and their relative positions allow a fundamentally different way to grow the single crystal. This novelty consists in the implementation of cultivation not of "supercooled" melt, as in the prototype, but from an overheated the go".

Another advantage of the claimed design of the device is a new implementation of the heaters.

The novelty lies in the scan at 90° closed sections bent U-shaped ends of the slats. This allows to significantly reduce the diameter of the ring, which is fixed to the U-shaped ends of the blades and, consequently, reduce the unheated area of the crucible. One of the conditions of the process of growing single crystals by the method of Amoz is the elimination of local overheating of the melt and maintaining a uniform temperature in the entire volume of the melt.

The above design features aimed at ensuring this requirement.

Connecting the slats to the load current with alternating signs load plus plus minus minus (++--) allows you to move the support crucible from the rod in the center of the crucible and place them between the slats with the same sign evenly spaced around the periphery of the crucible with the melt closer to the heater. This is especially important when growing large single crystals of crucibles large diameter, as at a temperature of 2000°With the bottom of the crucible tungsten deformed.

In the claimed design summary and uniformly distributed area supports significantly more than one Central crucible. This increases the service life of the crucible and the whole device.

In the claimed mouth is oiste water-cooled current leads are coaxial, either one above the other. And in one and in another embodiment, a vertically arranged parts (branches) of the lamellae have different lengths. The minimum difference in the amount equal to the distance between opposite-pole tires current.

The difference in the length of the branches lamellae leads to a different value of resistance, and if certain dimensions of the device, this difference becomes significant, and thus leads to non-uniform temperature characteristics of thermal field. To address this proposed free ends of the lamellas to connect with current via adapters are made of conductive material with a lower resistance than the material of the slats.

To ensure uniformity of the temperature field all points of connection of the ends of the slats with the adapters are located at the same distance from the axis of the heater. This condition can be accomplished by regulating the length of the adapter, the further conductive bus from the center of the heater, the longer the adapter. Impedance adapter in this case can be neglected.

The use of low-adapter allows you to eliminate the deformation lamellae directly from the annular water-cooled current leads, thus increasing their lifespan.

The presence of the adapter allows you to adjust the diameter of the heater, and therefore, provides the opportunity to use the ti is whether different diameters.

The device schematically represented in the drawings.

Figure 1 shows the AA - axial slit, figure 2 - view of CENTURIES - horizontal.

The device consists of two chambers (not shown), shaft with structuralism 1, the crucible 2, the upper heater 3, the lower heater 4, the current leads 5, 6 (inner and outer, respectively, for the heaters 3 and 4), branches 7 slats heaters 3, 4, closed U-shaped parts 8 are rotated by 90° and fixed respectively on the centering ring 9. The vertical sections of the branches 7 are connected through the adapter 10 with water-cooled current leads 5, 6. The crucible 2 is installed on the supports 11, which are located between the blades closer to the walls of the crucible 2 and pillar 12 in the bottom center of the crucible. All supports are made elektroizolyatsionnymi from the camera.

Figure 1 shows the melt 13, the seed crystal 14, the grown crystal 15.

To control the temperature of the upper heater 3 is installed thermocouple 17.

The device operates as follows.

In the bottom section of the camera set lower heater 4, which put the crucible 2 with the charge and in the upper section of the camera set the heater 3, within which is placed a rod with structuralism 1 and the seed crystal 14. The chamber vacuum and begin heating the mixture fed to the upper heater 3 30-50% of its capacity, the need for the Oh for complete melting of the charge. Then the temperature of the upper heater 3 according to the testimony EMF of thermocouple stabilize and the remaining power is served on the lower heater 4. After melting of the charge and stabilize the temperature in thermal region, formed by two heaters 3, 4, begin the process. After the persecution begin razresevanje single crystal.

The process of razresevanja to a given diameter and the subsequent growth of the crystal is carried out by controlled lowering the temperature of the upper heater to full sample of the melt, while the power supplied to the lower heater, remain unchanged during the whole process of cultivation.

After growing the resulting crystal is cooled in refrigerated conditions to prevent thermal stresses in the crystal. To do this, gradually reduce the load of the lower heater to obtain the temperature in the lower section of the camera is equal to the temperature in the upper section.

Thus, the claimed device for growing single crystals from the melt by the method of Amoz allows the process of growing single crystals from the "overheated" melts, which excludes any structural defects associated with the effect of hypothermia on the phase boundary "melt-crystal". The device provides a substantial increase date the core nodes slats heaters crucible. In addition, thermal unit design allows you to grow bulk single crystals of different diameters without changing the whole setup in General.

1. Device for growing single crystals, including two cameras, structurally attached to the rod, the crucible, thermal unit with heater, collected from the curved shape of the crucible U-shaped strips, centering ring, which is fixed to the closed side of the blades, the water-cooled ring current, characterized in that thermal unit is designed as two identical shape, weight and dimensions of the heaters, which are mirror images of each other, with the closed part of the U-shaped slats mounted on centring ring deployed on 90°and stem with structuralism located inside of the upper heater, the free ends of the lamellas through conductive adapter is connected to the current leads with alternating signs current load plus plus minus minus", the crucible is installed on insulated bearings situated between the lamellae of the heater with the same sign of the current load, and a conductive adapter is made of refractory material with a resistance lower than the resistance of the slats at the ends of the adapters connected to the blades, are located on the same distance the AI from the axis of the heater.

2. The device according to claim 1, characterized in that the slats are made of rare refractory metals and their alloys.

3. The device according to claim 2, characterized in that the slats are made of tungsten, molybdenum.

4. The device according to claim 2, characterized in that the slats are made of bolted.

5. The device according to claim 1, characterized in that the slats are made of graphite, Silit.

6. Device according to any one of claims 1 to 3, characterized in that the current leads are located in the sections of the camera, and the current leads of the upper heater and the lower heater current leads are located at the same distance from the plane of the upper connector and the lower section of the chamber.



 

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3 ex

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2 cl, 4 ex, 1 tbl

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1 ex, 1 tbl, 1 dwg

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1 ex, 1 tbl, 1 dwg

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