RU2222645C1 - Device for monocrystals growing from melt - Google Patents

Abstract

FIELD: production of monocrystals. SUBSTANCE: the invention presents a device used for the bulky volumetric profiled monocrystals growing from a melts, for example, sapphire by the Chokhralsky and Kiropulos methods. The device for growing monocrystals from melt with a seed crystal includes a cylindrical chamber with a cover, a king-pot for a melt, a seed-holder mounted on a rod with a capability of rotation and vertical motion. The chamber is made two-sectional and with the mechanism of a vertical motion of the sections. The thermal assembly is mounted between the upper and lower sections of the chamber and is made in the form of a hollow water-cooled cylinder with located inside it: a heater assembled out of the U-shaped lamels, bent following the form of the inner surface of the king-pot, and the closed-circuit ring-type water-cooled current conductors. The cylinder surface is fixed to an additional rod, which is supplied with the mechanism to relocate the cylinder in vertical direction and around the rod. The inner side of the cylinder in its lower part has ledges, on which insulators are placed. The current conductors have pinholes, in which the free ends of lamels are fixed, and the bent U-shaped ends of the lamels are fixed on the ring centering them; current conductors are installed on the insulators centering the heater, and their leads are located on the side surface of the cylinder in the different horizontal planes. The heater is mounted inside the king-pot and dimensions of the king-pot and the heater meet the ratio d≤2d_h-d_kp. The invention allows to increase perfection of the structure and to ensure homogeneity of dimensions along the full length of a monocrystal, to increase productivity due to increase of the sizes of loading, to decrease power consumption, consumption of initial material due to complete sampling a melt during a monocrystal growing and to increase the service life of the wolframic king-pots and the heater. EFFECT: increased monocrystals structure perfection and homogeneity of dimensions along the full their length, decreased power and materials consumption, increased service life of king-pots and the heater. 6 cl, 3 dwg

Description

 The invention relates to devices for growing single crystals from melts on a seed crystal and can be used in technology for growing crystals, for example, sapphire, according to the methods of Czochralski, Kyropoulos.

 The technical problem solved by the invention is the creation of a device for growing large-sized bulk profiled single crystals from a melt in a uniform thermal field, simplifying the design and operation of the thermal unit and heater, in particular, as well as ensuring the stability of growing regimes of bulk single crystals of various profiles and sizes and increasing structural perfection crystals.

 A device is known for growing single-crystal sapphire ribbons, including a chamber, a crucible located inside the chamber, a heat unit, a former, a seed holder mounted on a rod.

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

 The melt crucible is coated on the outside with a tungsten layer. The crucible is mounted on a pedestal and placed inside a graphite heater. Screens are placed above the crucible (see ed. St. USSR 1213781, publ. 04/23/1991, C 30 V 15/34).

 The device has the following disadvantages.

 The heater material - graphite with a sprayed layer of silicon carbide, chemically reacts with aggressive aluminum oxides at high temperatures, which dramatically reduces the heater's life and contaminates the growing crystal with carbon. The heater cannot be restored in the event of a breakdown. The thermal unit cannot provide the creation of rectangular radial isotherms necessary for obtaining high-quality volumetric profiled single crystals.

 The device cannot be used for growing large crystals.

 A device for growing profiled crystals of refractory compounds is known, including a chamber, a crucible with a former installed in it and a heat assembly containing a graphite heater coaxial with a gap in the form of a cup with a front hole at the level of the end of the former and with an increasing hole cross section to the bottom, and a screen in the form of a hollow cylinder mounted above the crucible using rods mounted on the upper insulation block. The heater is connected to a current source (see ed. St. USSR 1592414, publ. 15.09.90, C 30 V 15/34).

 The device is designed to produce sapphire tubes and cannot be used to grow high-quality bulk single crystals.

 A device for growing bulk single crystals, including a chamber, two melting heaters and a two-section crucible. In the upper section, the starting material is melted using one heater located around the upper section of the crucible, and cultivation is carried out from the lower section of the crucible using another heater installed under the lower section of the crucible (see ed. St. 661966, publ. 30.03.80, C 30 B 15/02). The device is taken as a prototype.

 The device cannot be used for growing bulk shaped single crystals, due to the impossibility of creating radial isotherms of different geometries in the melt.

 The technical result of the claimed invention is the ability to grow large-sized single crystals of a given shape and structural perfection due to the constancy of the shape of the radial isotherm and small temperature gradients in the melt, as well as the ease of operation and ergonomics of the thermal unit and heater, in particular.

The technical result is achieved by the fact that in the device for growing single crystals from a melt on a seed crystal, including a cylindrical chamber with a lid, a heat unit, a melt crucible, a seed holder mounted on a rod with the possibility of rotation and vertical movement, according to the invention, the camera is made of two sections and with a mechanism of vertical displacement of sections, a thermal unit is installed between the upper and lower sections of the chamber and is made in the form of a hollow water-cooled cylinder, with inside and a heater assembled from U-shaped lamellas curved in shape of the inner surface of the crucible and closed ring water-cooled current leads, the cylinder is mounted on an additional rod located on the outer surface of the cylinder and equipped with a mechanism for moving the cylinder vertically and around the rod, the inner side of the cylinder in the lower its parts are made with protrusions on which insulators are placed, current leads are made with holes in which the free ends of the lamellas are fixed, and the U-shaped curved ends of the lamellas akrepleny centering on their ring current leads mounted on the insulators, centering the heater, and their terminals are located on the lateral surface of the cylinder in different horizontal planes, a heater installed inside the crucible, the dimensions of the crucible and the heater meet the relation d _KP ≤2d _heating. -d _crucible .

 The current leads are either coaxial or one above the other.

 The lamellas are made of the same length and configuration and are assembled in a circle or in sections, the number of lamellas in the heater and holes in the current leads is a multiple of 12. To create radial isotherms of polygonal shapes, the length of the lamella sections and their location correspond to the lengths of the sides of the polygon.

 The diameter of the hollow cylinder is equal to the diameters of the sections of the chamber.

 A centering ring that pulls together the curved U-shaped ends of the lamellas is not involved in the electrical circuit.

 The essence of the claimed device lies in the new design of the thermal unit, all of whose elements, namely: the heater, current leads, insulators, a bearing cylinder are compact and are a single unit.

 New in the design of the device is the installation of a heater inside the crucible and compliance with the stated ratio of the diameters of the crucible, heater and the diameter of the grown crystal. The crucible in this case is both a melt holder and a shield for the heater. It provides the possibility of lowering the temperature on the heater and on the crucible, increasing the weight and diameter of the crystal, the absence of local overheating of the melt, and, consequently, the appearance of bubbles in it. This has a positive effect on the structure of the grown single crystal and the energy consumption per unit of output.

 The design of the heating unit also has a number of advantages.

 The heater, assembled from lamellas mounted on closed ring current leads and a centering ring, simultaneously performs the functions of a thermal former, has the ability to change the shape of radial isotherms and determine the shape of the profile of grown crystals. The heater is easy to operate, can be easily assembled and disassembled when changing the profile of a single crystal, because changing the shape of the radial isotherms is achieved by removing or adding the required number of lamellas in sections. The initial number of lamellas and the number of holes in the cable leads is a multiple of 12.

 A hollow water-cooled cylinder also performs several functions. He, forming the middle section of the chamber, at the same time is the holder of current leads with lamellas of the heater and also creates a symmetric thermal field relative to the vertical axis of the chamber by centering the heater both due to insulators resting on the internal protrusions of the cylinder, and due to the possibility of horizontal movement of the lamellas of the heater in the holes of the ring current leads. The symmetry of the thermal field increases the perfection of the shapes and structure of the crystal.

 In addition, the implementation of the cylinder with the possibility of vertical movement and movement around the axis of the rod, on which the cylinder is fixed, provides easy access to the heater and the ability to replace the elements of the thermal unit, as well as to the cavities of the upper and lower sections of the chamber.

 In general, the design of the thermal unit significantly increases its service life, is ergonomic and does not require the expense of expensive graphite, which pollutes the single crystal and cannot be restored.

 The location of the heater inside the crucible allows you to grow large-sized single crystals. The ability to obtain not only round, but also polygonal forms of radial isotherms by changing the number of lamellas and their location in current leads allows, in combination with other essential features, to grow large-sized bulk shaped sapphire single crystals with a high degree of structural perfection and a given size along the entire length of the single crystal.

 The stated ratio of the diameters of the crystal, crucible and heater provides the highest productivity of the device and full sampling of the melt, since in this case the necessary condition is met so that the temperature on the crucible is greater than or equal to the melting temperature of the initial components of the melt.

 The device is schematically depicted in figure 1.

 The device includes an upper 1 and lower 2 chamber sections made with a vertical movement mechanism (not shown in FIG. 1), with a cover 3, a grass holder 4, a crucible 5 made, for example, of tungsten and mounted in the lower chamber section 2, the upper rod 6 for attaching the seed holder 4, the lower rod 7 for attaching the crucible 5. The rods 6 and 7 are made with rotation. Between the upper section 1 and the lower section 2 of the chamber, a thermal unit is installed in the form of a hollow water-cooled cylinder 8. Inside the cylinder 8 there is a heater 9 assembled from U-shaped slats 10 curved in shape of the inner surface of the crucible and made of refractory metals and alloys, for example, tungsten , and closed ring water-cooled current leads 11, 12. Current leads 11, 12, located one above the other or coaxially (not shown), have holes 13 in which the upper ends of the U-shaped slats are fixed 10. The lower curved U-shaped to seedlings lamellae 10 are fixed centering of ring 14, not participating in the heater circuit 9.

 The cylinder 8 is mounted on an additional rod 15, which is located on the outer side of the cylinder 8 and is equipped with a movement mechanism (not shown in FIG. 2) of the cylinder 8 vertically and around the rod 15. On the inner surface of the hollow cylinder 8, protrusions are made 16.

 The current leads 11, 12 are installed on the protrusions 16 in the insulators 17, which center both the current leads 11, 12 and the heater 9.

 On the lateral surface of the cylinder 8 in different horizontal planes are placed the conclusions 18, 19 of the current leads 11, 12. The heater 9 is installed inside the crucible 5.

 A device for growing single crystals from melts on a seed crystal works as follows.

Collect the heat assembly. To do this, in a water-cooled cylinder 8, mounted on a rod 15 and rotated 90 ^° relative to the vertical axis of the chamber (see Fig. 2), water-cooled current leads 11, 12 are mounted on centering insulators 17.

 To grow profiled bulk single crystals, for example, of a rectangular shape (Fig. 3 (a, b, c)), U-shaped lamellas 10 are assembled in sections 13, the length of which corresponds to the lengths of the sides of a given rectangle, in the holes 13 of the ring current leads 11, 12. The upper ends of the lamellas 10 are fixed in the holes 13 of the current leads 11, 12, and the lower curved U-shaped ends are on the centering ring 14, which is not included in the electric circuit of the heater.

The thermal assembly thus assembled is turned 90 ^° and aligned with the vertical axis of the chamber, and hermetically connected to the lower section 2 of the chamber. In this case, the heater enters the crucible with its lamellas 5. The charge is loaded into the crucible with the heater. A crystal in the form of a tetrahedral prism is installed on the upper rod 6, one of the side faces of which is oriented in accordance with the sections of the lamellae 10, creating a rectangular radial isotherm for the growth of a rectangular crystal with a natural facet.

 The upper section 1 of the chamber is hermetically connected to the thermal unit, the heater 9 is turned on, and the process of growing single crystals by the Czochralski method is carried out to obtain crystals of a rectangular shape.

 Round sapphire single crystals with a diameter of up to 200 mm and a square shape with a size of 150x150 mm of a perfect structure without size deviations along the entire length of the single crystals were grown.

 The device allows you to get the following positive effect.

 1. The possibility of growing large profiled single crystals.

 2. Improve the perfection of the structure and ensure uniformity of size along the entire length of the single crystal.

 3. Increase productivity by increasing download sizes.

 4. Reduce energy intensity.

 5. To reduce the consumption of the starting material due to the complete sampling of the melt during the growth of a single crystal.

 6. Increase the life of the tungsten crucibles and heater.

Claims (6)

1. A device for growing single crystals from a melt on a seed crystal, including a cylindrical chamber with a lid, a thermal unit, a melt crucible, a seed holder mounted on a rod rotatably, characterized in that the chamber is made of two sections and with a mechanism for vertical movement of sections, a thermal unit installed between the upper and lower sections of the chamber and made in the form of a hollow water-cooled cylinder with a heater placed inside it, assembled from t curved on the inner surface for U-shaped lamellas, and closed ring water-cooled current leads, the cylinder is mounted on an additional rod located on the outer surface of the cylinder and equipped with a mechanism for moving the cylinder vertically and around the rod, the inner side of the cylinder in its lower part is made with protrusions on which insulators are placed , the current leads are made with holes in which the free ends of the lamellas are fixed, and the U-shaped curved ends of the lamellas are fixed on the centering ring, the current leads are installed on insulators, cent heaters, and their conclusions are located on the lateral surface of the cylinder in different horizontal planes, the heater is installed inside the crucible, while the dimensions of the crucible and heater correspond to the ratio d of the _crystal ≤ 2d of the _heater -d of the _crucible . 2. The device according to claim 1, characterized in that the current leads are located coaxially or one above the other. 3. The device according to any one of claims 1 and 2, characterized in that the lamellas are made of the same length and configuration. 4. The device according to any one of claims 1 to 3, characterized in that the number of slats in the heater and the hole in the current leads is a multiple of 12. 5. The device according to any one of claims 1 to 4, characterized in that to create radial isotherms of polygonal shapes, the lamellas are assembled in sections whose length and location correspond to the sides of the polygon. 6. The device according to any one of claims 1 to 5, characterized in that the diameter of the hollow cylinder is equal to the diameters of the sections of the chamber.

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