RU2534103C1 - Device for growth of monocrystals from melt by vertical pulling technique - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: device comprises chamber 1 to accommodate crucible 2 for melt, at least one main heater 4 for melting of initial material in crucible 2. There is an extra heater 9 arranged above the melt in the area of solid-melt interface and shaped to ring-like disc. Part-through radial cut-outs are made at inner and/or outer lateral sides of said disc. Besides, at least one heat-insulation shield 7 is arranged between lateral sides of the main heater 4 and chamber 1. Part-through radial cut-outs of inner and outer lateral sides of top heater 9 alternate so that radial cut-outs of one lateral side are located between radial cut-outs of the other lateral side.

EFFECT: ingots of increased diameter with smooth cylindrical surface, dislocation-free monocrystals with dislocation density of 200 cm^-2 suitable for production of solid-state, particularly, germanium plates of at least 100 mm diameter and at least 160 mcm depth.

9 cl, 4 dwg

Description

The invention relates to a device for growing single crystals from a melt by the Czochralski method, in particular, to a device for growing single crystals of germanium. Semiconductor materials, including germanium-based materials, are extremely promising for use in microelectronics, optoelectronics, solar energy and IR optics.

The technology for producing semiconductor, in particular, germanium wafers includes the stages of growing single crystals and manufacturing polished wafers from single crystals, and the dimensions and quality of the wafers obtained are largely determined by the size and quality of the grown single crystals.

The objective of the invention is to provide a device for growing single crystals from a melt by the Czochralski method, in particular, for growing single crystals of germanium, providing a more uniform temperature distribution in the region of the crystallization front to obtain dislocation-free crystals of large diameters.

A wide range of technical solutions is known in the art for improving the thermal assembly of devices for growing single crystals from a melt by the Czochralski method.

A device is known for growing crystals from a melt by the Czochralski method, including a crucible, upper, lower, and side heaters, a heat-insulating shielding element configured to separate the incoming purge gas stream into a first partial stream and a second partial stream so that the first partial stream is directed through the region melt, and the second partial flow is directed along the channel inside the heat-insulating shielding element, bypassing the space in the crucible located above th melt before exiting it from the "hot zone" (RF Patent №2456386, S30V 15/14, publ. 20.07.2012).

The disadvantage of this device is that with this design of the "hot zone" the temperature gradients in the single crystal are large, which, in turn, does not provide the necessary conditions for obtaining a single crystal with a perfect structure.

A device is known for growing a single crystal by the Czochralski method using a platinum heater having a flat ring shape located on a crucible and having a certain ratio of the thickness of the heater to the thickness of the walls of the crucible and a certain ratio of the diameter of the drawn crystal to the inner diameter of the heater with a total thickness of the heater of about 0.25 mm. The heat generated by the ring heater of this geometry improves the symmetry of the radial temperature distribution on the surface of the melt and improves the straightness of the side of the grown crystal (Japanese patent No. JP 58050956, C30 15/14, publ. 11/14/1983).

A flat ring-shaped platinum heater does not have the necessary temperature effect on the grown part of the crystal; therefore, the crystal structure is not perfect.

A device is known for growing silicon single crystals from a melt, comprising a chamber with holes for evacuating a gas stream, in which a melt crucible is located in a stand on the rod, an upper gas guide screen forming a gas stream above the melt, and a heater, the device being provided with a lower gas guide an annular screen with a central hole for moving the stand mounted above the heater, openings for evacuating the gas flow are made in the chamber body between the upper and the lower gas guide screens, and the space between the housing, the lower gas guide ring screen, the heater and the rod is filled with backfill (RF patent 2241079, C30B 15/00, 15/14, publ. 11/27/2004).

In this device, improvements are aimed at organizing gas flows for the removal of silicon monoxide from the growth zone of silicon single crystals and are not intended to form a temperature field in the grown crystal, which ensures the perfect structure of the single crystal.

A device for growing a single crystal is known, in which a main heater is used to obtain and heat the melt, placed around the crucible, and an upper heater for annealing and slowing down the cooling rate of the ingot immediately after its crystallization, made in the form of a tubular element provided with longitudinal slots running parallel to the axis of the tubular the upper heater (US patent No. 6503322, C30B 15/14, NPKl. 117/204, publ. 07.01.2003).

However, the design of the upper heater used in this technical solution is not able to ensure uniform temperature distribution in the region of the crystallization front. This device is intended for annealing crystals after the growth process according to the Czochralski method.

The closest technical solution to the claimed invention is a device for growing single crystals from a melt by the Czochralski method according to US patent No. 5137699, containing a crucible for placing a melt, from which a single crystal is grown, lower and side heaters to maintain a predetermined temperature of the crucible with the melt and an additional independently controlled upper a heater placed above the melt in the zone where the curing of the single crystal occurs. Although the upper independently adjustable heater, made in the form of an annular disk placed above the melt, known from this technical solution, improves the quality of the grown single crystals, it still does not allow a sufficiently uniform temperature distribution in the region of the crystallization front and, therefore, does not provide dislocation-free crystals of large diameters (US patent No. 5137699, C30B 15/14, NPKl. 422/246, publ. 11.08.1992).

The objective of the invention is to provide a device for growing single crystals from a melt by the Czochralski method, in particular, for growing single crystals of germanium, providing a more uniform temperature distribution in the region of the crystallization front to obtain dislocation-free crystals of large diameters.

The invention consists in the following.

A device for growing single crystals from a melt by the Czochralski method, contains a chamber in which are placed:

melt crucible,

at least one main heating element for melting the starting material in a crucible,

an additional upper heating element located above the melt in the region of the crystallization front and having the shape of an annular disk, on the inner and / or external lateral sides of which non-through radial slots are made, and at least one heat-insulating shielding element located between the lateral sides, at least one main heating element and a chamber.

The non-through radial slots of the inner side and the outer side of the upper heating element can be arranged alternately so that the radial slots of one side are located between the radial slots of the other side of the upper heating element.

The angle between the directions of the radial slots of the inner and outer sides of the upper heating element is from 40 ° to 15 °, preferably 20 °.

The radial slots of the inner side and the outer side of the upper heating element may be located at different or equal distances from each other.

The inner diameter of the annular upper heating element is larger than the diameter of the grown single crystal, the outer diameter is smaller than the inner diameter of the crucible, and the depth of the slots of the inner and outer sides of the upper heating element in the radial direction is from 1/2 to 3/4 of the difference between the outer and inner diameters of the upper heating element.

In one preferred embodiment, the radial slots of the inner side and the outer side of the upper heating element have the same depth in the radial direction.

The width of the radial slots of the inner side and the outer side of the upper heating element is 2-6 mm.

The upper heating element is movably mounted on vertically extending holders connected to the current leads.

The device may further comprise a backfill placed between the heat-insulating shielding element and the side of the chamber.

The technical result of the claimed invention is the provision of the manufacture of ingots of increased diameter with a smooth cylindrical side surface, the production of practically dislocation-free single crystals having a dislocation density of less than 200 cm ^-2 and a uniform distribution in the volume of alloying impurities suitable for producing semiconductor, in particular germanium, wafers with a diameter not less than 100 mm and a thickness of less than 160 microns.

The invention is illustrated by drawings.

Various embodiments of the claimed invention will be described in more detail with reference to the following drawings, which are given as examples of implementation of the invention.

Figure 1 is a view in cross section of the claimed device for growing single crystals from the melt.

Figure 2 is a sectional view of another embodiment of the inventive device for growing single crystals from a melt.

Figure 3 is a top view of an additional upper heater placed above the melt, according to the claimed invention.

Figure 4 is a cross section of the heater along the line aa, as shown in figure 3.

Figure 1 shows a device for growing single crystals from a melt by the Czochralski method according to the claimed invention, comprising a chamber 1 in which a crucible 2 for a charge and / or melt is placed. The crucible is mounted on the support 3 of the crucible, which can provide rotation of the crucible and the movement of the crucible in the vertical direction. At least one main heating element 4 is located near the crucible, which provides heat to heat and melt the raw material charge and maintain the temperature of the crucible during the drawing of the crystal. In the exemplary embodiments shown in FIGS. 1 and 2, the main heater 4 is a lower heater and has a section with vertical side walls that are located near the side walls of the crucible and rest on the conductive support 5 of the main heater, mounted on the current leads. The crucible base passes through the central hole of the support 5 of the main heater. If necessary, the device may use two or more main heaters located near the bottom and / or side surfaces of the crucible. Between the vertical side of the heating element 4 and the side wall forming the side 6 of the chamber 1, at least one heat-insulating shielding element 7, mainly two or three heat-insulating shielding elements 7. is installed. In contrast to FIG. 1, in the example shown figure 2, heat-insulating shielding elements 7 are placed on additional supporting racks. The heat-insulating shielding elements 7 can be made of graphite or a carbon-containing composite material based on carbon fiber, and it is possible to make all heat-insulating shielding elements from the same high-temperature heat-insulating material or using combinations of different materials. Based on the upper edge of at least one heat-insulating shielding element, an upper protective ring screen 8 can be installed.

Above the upper surface of the melt in the region of the crystallization front, there is an upper additional heating element 9, which according to the claimed invention is made in the form of an annular disk. The inner diameter of the annular upper heating element is larger than the diameter of the grown single crystal, which allows the crystal to be pulled out of the melt without contact with the upper heater, and the outer diameter of the annular upper heater is smaller than the inner diameter of the crucible, which ensures free rotation of the crucible in the horizontal direction and movement of the crucible in the vertical direction.

A distinctive feature of the claimed invention is the implementation of an annular disk-shaped upper additional heater with blind through radial cuts.

As shown in more detail in FIGS. 3 and 4, the upper heater is in the form of an annular disk having an upper annular flat surface or side 10, a lower annular flat surface or side 11, an inner side surface or side 12 corresponding to a side surface of a central hole of the upper disk additional heater, and the outer side surface or side 13 of the annular upper heater corresponding to the outer diameter of the disk, the distance between the upper and lower tseobraznymi flat surfaces 10 and 11 defines the height of the upper heater and the distance between the inner and outer sides 12 and 13, is an annular surface corresponding to the inner and outer diameters of the heater disc, forms a width of the upper heater.

The radial slots 14 are cutouts in the body of the heater, which start from the inner annular lateral side 12 and extend to the outer annular lateral side 13 of the heater and / or from the outer annular lateral side 13 and extend to the inner annular lateral side 12. The direction in which the slot corresponds to the direction of the radii of a circle whose diameter corresponds to the outer diameter of the disk having a center coinciding with the center of the body of the ring-shaped disk of the upper heater. Radial slots are not through, that is, they do not pass through from the outer side surface of the disk along the width of the disk of the upper heater, but have a depth that is from 1/2 to 3/4 of the width of the ring disk of the upper heater, that is, from the difference in its external and inner diameters. In a specific exemplary embodiment, the slots have a depth in the radial direction of 20-30 mm, for example 25 mm, and a width of 2-6 mm, in particular 4 mm. As a rule, radial slots extend along the entire height of the upper heater from the upper annular surface to the lower annular surface of the upper heater and have the form of a narrow rectangular cut. The possibility of making cuts in the form of cuts having a different geometric shape in the cross section, for example, triangular, in the form of a circle, oval, trapezoid, cuts having walls of curved shape, as well as any combination of these geometric shapes, is not excluded.

Such radial slots 14 may extend from the inner side 12 or from the outer side 13, and may be formed on both sides of the annular disk of the upper heater. Moreover, although this is not shown in the figures, different sections of the upper heater may have a different combination and different geometric shapes of the slots located on their inner and / or outer sides.

The radial slots of the inner side and / or the outer side of the upper heating element are spaced a predetermined distance from each other, in particular, as shown in the embodiment of FIG. 3, are spaced at equal intervals and at the same distance from each other. It is also possible to place adjacent slots at different distances with different intervals between them.

In a preferred embodiment, the radial slots of the inner side and the outer side of the upper heating element are arranged alternately, so that the radial slots of one side are located between the radial slots of the other side of the additional upper heating element. The angle between the radial lines passing through the centers of adjacent slots of the inner side and the slots of the outer side, that is, between the center lines of the radial slots, can be from 40 ° to 15 °, preferably 20 °.

The slots of the inner side and the outer side of the upper heating element can have the same depth or different depth in the radial direction depending on the required geometry of the upper additional heating element and depending on its desired resistance.

The upper heating element 9 is movably mounted on vertically extending holders connected to the current leads, at least two diametrically opposite slots made on the upper surface of the heating element have a shape that provides mounting means for connecting the upper heating element 9 with vertical holders. The upper heater 9 may be made of graphite or composite graphitized materials. The number and dimensions of the slots 14 in the body of the additional upper heater are selected so that its electrical resistance provides the necessary heat energy over the melt in the region of the crystallization front during the growth of single crystals. In this case, for example, with the growth of single crystals of germanium, the temperature on the additional heater will be 800-850 ° C.

In the upper part of the chamber there is also a device for pulling a single crystal from a melt containing a seed rod 15 vertically movable and rotatable around its vertical axis with a single crystal seed mounted on it.

Further, the operation of the claimed device for growing single crystals from a melt by the Czochralski method will be illustrated by the example of growing single crystals of germanium, which does not exclude the possibility of growing silicon single crystals and single crystals of other semiconductor materials based on elements of groups III-VI of the periodic system of elements. The raw material mixture to obtain a single crystal containing polycrystalline zone-purified germanium or recycled material from previously grown single crystals of this brand is loaded into the crucible 3, the device chamber 1 is evacuated, and the raw material charge is heated and melted in the crucible using the main lower heater 4. After the charge is melted, the temperature is set at which crystallization occurs on a single-crystal seed dropped into the melt, called the seed temperature, which in this embodiment is 937 ° C. When pulling the seed in the vertical direction using the rod 15 of the device for drawing a single crystal, the conical part of the single crystal is first grown to the required diameter when controlling the temperature on the main heater. Further, by controlling the temperature on the lower main heater and on the additional upper heater located above the melt, which according to the claimed invention is made in the form of an annular disk with non-through radial cuts, the cylindrical part of the single crystal is grown. At the end of the growth of the cylindrical part of the single crystal, an inverse cone is formed to exclude a sharp temperature drop when the single crystal is separated from the melt. After the cultivation process is completed, a step-by-step disconnection of the power supply to the heaters is performed.

Thus, in the process of growing the cylindrical part of the crystal, using an additional upper heater 9 in the form of a ring having the above construction and placed above the melt, a more uniform temperature distribution is provided in the region of the crystallization front, and a germanium single crystal is grown from the melt in a temperature field that provides a temperature gradient of about 60 ° / cm in the crystal in the region of the crystallization front. The temperature on the main heater lies in the range of 1000-1100 ° С, and on the additional upper heater located above the melt, the temperature is 800-850 ° С. This makes it possible to obtain low-dislocation germanium crystals of large diameters, in particular, single crystals with a dislocation density of less than 200 cm ^-2 and a uniform distribution of dopants in the bulk of the single crystal, which are suitable for producing semiconductor, in particular, germanium wafers with a diameter of at least 100 mm and a thickness of less than 160 microns.

The presence of maximum values of heat fluxes from the surface of the ingots in the region of the crystallization front and their sharp decrease (~ 2 times) at a distance of the crystal radius from the phase boundary requires active heat exposure in this region in order to reduce the amount of heat sinks and the resulting elevated temperature gradients and thermoelastic stresses in the crystal. In this regard, in the claimed invention, in the area of the crystallization front, an additional upper heater is used having the structure according to the invention, which makes it possible to precisely control the temperature, for example, using a thermocouple, in the region of maximum heat sinks from the surface of the drawn crystal and provides a constant heat flow from the front crystallization. At the same time, the grown single crystals maintain a constant diameter of the ingots and have a more even cylindrical side surface, which is an important parameter from the point of view of subsequent calibration, processing and cutting of the ingots to obtain single crystal plates with a diameter of 100 mm or more. The claimed device allows to obtain single crystals with high structural perfection, corresponding to the requirements for the subsequent manufacture of ultrafine wafers from them with a thickness of up to 160 microns.

Claims (8)

1. A device for growing single crystals from a melt by the Czochralski method, comprising a chamber in which are placed: a melt crucible, at least one main heating element for melting the starting material in the crucible, an additional upper heating element located above the melt in the region of the crystallization front and at least one heat-insulating shielding element located between the sides of at least one main heating element and the chamber, characterized in that inside and / or on the outer side sides of the additional upper heating element, non-through radial slots are made, which are arranged alternately, so that the radial slots of one side are located between the radial slots of the other side of the upper heating element. 2. The device according to claim 1, characterized in that the angle between the directions of the radial slots of the inner and outer sides of the upper heating element is from 40 ° to 15 °, preferably 20 °. 4. The device according to claim 1 or 2, characterized in that the radial slots of the inner side and the outer side of the upper heating element are located at the same distance from each other. 5. The device according to claim 1, characterized in that the inner diameter of the annular upper heating element is larger than the diameter of the grown single crystal, and the outer diameter is smaller than the inner diameter of the crucible, and the depth of the slots of the inner and outer sides of the upper heating element in the radial direction is from 1/2 up to 3/4 of the difference between the outer and inner diameters of the upper heating element. 6. The device according to claim 1, characterized in that the radial slots of the inner side and the outer side of the upper heating element have the same depth in the radial direction. 7. The device according to claim 1, characterized in that the radial slots of the inner side and the outer side of the upper heating element have a width of 2-6 mm 8. The device according to claim 1, characterized in that the upper heating element is movable mounted on vertically extending holders associated with current leads. 9. The device according to claim 1, characterized in that it further comprises a backfill, and the backfill is placed between the heat-insulating shielding element and the side of the camera.

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