KR19990008776A - Graphite support vessel having low concentration of calcium impurities and process using the vessel for production of single crystal silicon - Google Patents

Abstract

A new graphite support container (eg susceptor) has been disclosed that is used in the Czochralski type crystal puller to produce single crystal silicon and to support a silica sand container (eg crucible). The concentrations of alkaline earth metals and alkali metal impurities, particularly calcium, in graphite support vessels (e.g. susceptors) may be determined by the silica sand container (e.g., supported by the support vessel in the production of single crystal silicon in a Czochralski-type crystal puller. Substantially affects non-uniformity of the crucible). Advantageously, the use of graphite support vessels of sufficiently low calcium concentration, preferably not more than about 1 ppm by weight, results from the relatively higher capacity filling that even the silicone melt requires for heating of the relatively higher temperature support vessels. It is allowed for the production of single crystal silicon without substantially non-uniform devitrification of the vitreous silica sand container holding the molten silicon produced. The reduction in the local crystallization degree of the glassy silica container is allowed for improved silicon crystal properties including lowered potential for loss of the overall structure of the silica sand container and improved zero-defect growth.

Description

Graphite support vessel having low concentration of calcium impurities and process using the vessel for production of single crystal silicon

The present invention relates generally to the production of single crystal silicon, and more particularly to a new graphite susceptor used to support a silica sand crucible in the growth of single crystal silicon ingots by the Czochralski method. The invention also relates to a process for preparing single crystal silicon using a novel susceptor.

Most of the single crystal silicon used in the manufacture of microelectronic circuits is prepared by the Czochralski process. In this process, monocrystalline silicon ingots are produced by melting polycrystalline silicon in a crucible, dipping crystal nuclei into molten silicon, and withdrawing nuclei crystals and growing single crystal ingots to initiate single crystal growth. Polycrystalline silicon is typically melted in glassy silica sand (SiO ₂ ) crucibles or other siliceous containers. Vitreous silica is an amorphous form of silica sand, and crucibles made of vitreous silica are generally referred to as quartz crucibles or fused quartz crucibles. Silica sand also exists in the change of crystallization form, including alpha and beta of quartz, tridymite and cristobalite.

However, some problems exist with the performance of silica sand containers at the high temperatures required to melt polycrystalline silicon. For example, vitreous silica sand is less viscous with increasing temperature and softens sufficiently to flow below the applied strength at temperatures above about 1815K. Thus, silica sand containers are prone to loss of the overall structure, including sagging and / or other deformations in the production of single crystal silicon. Graphite support containers such as susceptors or crucibles are typically used to support silica sand crucibles, liners or other containers in which polycrystalline silicon is melted. The surface of the graphite support container and / or the silica sand container in contact with them may be coated, for example with SiC, TiC, NbC, TaC or ZrC (Japan 7089789A), free carbon. In addition, the inner and / or outer surface of the silica sand container may comprise a homogeneous layer of crystalline silica sand (US Pat. No. 4,429,009, US Pat. No. 5,053,359) or devitrification to form uniformly, such as a layer devitrified in situ. It is coated with a promoter (Europe 0753605A).

Another problem associated with the high temperature performance of silica sand containers is the local deformation of the glassy silica sand for crystallization formation (e.g. beta-cristobarite), referred to as non-uniform breakthrough. The cristobarite group formed on the inner surface of the silica sand container is released into the silicon melt and interlocks into the growth crystals, causing defects therein. Expanding heterogeneous cristobarite growth also causes loss of the overall structure of the silica sand container and includes deformation and flex, bulging and other distortions in the shape of the silica sand container. Non-uniformity of silica sand is a flux that enhances the purity of the silica sand and the nuclei of the crystallized silica sand (eg cristobarite) and transforms the crystallized silica into other formations (eg cristobarite to tridymite). It is repeatedly affected by the degree of contamination on the surface of the silica sand with the surface contamination acting. Fused quartz products are therefore approached to minimize the degree of non-uniform devitrification, including improving the surface cleaning and purity of the silica sand container. For example, Japanese Patent No. 52/038873 discloses the use of xenon lamps to radiate an internal crucible surface to remove metal contaminants that are electrostatically attached to the silica sand surface. JP 60/137892 discloses the removal of alkali metals from a silica sand crucible using electrolysis.

Despite the aforementioned approach, there is a problem that the adverse effects of non-uniform devitrification and the overall structural and zero-defect crystal growth of the silica sand container remain. Since the rate of localization, non-uniformity, and devitrification increase dramatically with increasing temperature, this problem arises in the production of larger diameter single crystal silicon ingots filled with larger polycrystalline silicon in larger capacity silica sand containers. It is sensitive as an industrial movement. The higher temperatures required for such devices increase the substantial uneven devitrification potential and cause deformation of the silica sand container and ultimately reduce the zero-defect growth of single crystal silicon ingots.

It is an object of the present invention to prepare single crystal silicon of better properties, and also to prepare single crystals from larger fillings, especially when the degree of localization of non-uniform breakthrough of silica sand containers is reduced, thereby improving the overall structure of the container and Increase the zero-defect growth of silicon crystal growth therein. It is also an object of the present invention to achieve monocrystalline silicon with improved properties in cost in an effective way to minimize the adverse effects present in commercial production methods.

In short, the present invention therefore relates to a process for producing monocrystalline silicon ingots from polycrystalline silicon. According to the process, polycrystalline silicon is loaded into the silica sand container. The silica sand container is a siliceous container that may or may not be treated. The container is supported by a graphite support container adapted to receive a silica sand container in a manner such that the container is positioned in the graphite support container and the outer surface of the container is in contact with at least some area of the inner surface of the support container. The contact area between the inner surface of the support container and the outer surface of the container is defined as the interface area. Graphite support vessels are more suitable for use in Czochralski type crystal pullers and may also be treated or untreated graphite support vessels.

According to one embodiment of this process, the calcium concentration in the graphite support vessel is clearly low to prevent substantial uneven devitrification of the silica sand container in the interface region during the continuous process step. In certain processes, the calcium concentration inside the graphite support container does not exceed about 1 ppm by weight. The calcium concentration in the graphite support container does not exceed about 0.7 ppm, about 0.2 ppm by weight, and does not exceed about 0.1 ppm in order to improve the excellentness.

According to another embodiment of the process, the cumulative concentration of alkaline earth metal and alkali metal in the graphite support vessel does not exceed about 1 ppm by weight. It is preferable that the cumulative concentration of the metal selected from the group consisting of calcium, magnesium, strontium, lithium, sodium and potassium in the graphite support container does not exceed about 0.7 ppm by weight.

In one of the foregoing embodiments of the process, the support container, container and polycrystalline silicon are heated to melt the polycrystalline silicon and form a silicon melt. The graphite support vessel is subjected to a temperature of at least about 1550 ° C., preferably at least 1575 ° C., for at least 2 hours, preferably at least 4 hours, in an area where the inner surface of the corner portion of the support container contacts the outer surface of the corner portion of the silica sand container. Can be heated to obtain. Monocrystalline silicon ingots are drawn from molten silicon.

The invention also relates to a graphite support container, such as a susceptor or crucible, used to support a silica sand container in the production of single crystal silicon ingots from a silicon melt formed in the container. The support container includes a body made of graphite.

Clearly, according to one graphite support container embodiment, the calcium concentration in the graphite body does not exceed 1 ppm by weight. The calcium concentration in the graphite body does not exceed about 0.7 ppm, about 0.2 ppm by weight, and does not exceed about 0.1 ppm in order to improve the excellentness.

According to another embodiment of the graphite support container, the cumulative concentration of alkaline earth metal and alkali metal in the graphite body does not exceed about 1 ppm by weight. The cumulative concentration of the metal selected from the group consisting of calcium, magnesium, strontium, lithium, sodium and potassium in the graphite body preferably does not exceed about 0.7 ppm by weight. More preferably, the calcium concentration in the graphite body cannot exceed 0.2 ppm by weight.

For one of the foregoing embodiments of the graphite support container, the graphite body has an inner surface defining an open cavity, the shape of which is in the form of silicon melt in the silica sand container and in the production of single crystal silicon from the melt. It has been adapted to receive a silica sand container as at least a portion of the inner surface of the body in contact with the outer surface of the silica sand container to support the container. The body is suitably designed for use in Czochralski-type crystal impressions. The body may consist essentially of graphite, or optionally, the coating may be at least a portion of the interior surface of the body.

Other features and objects of the invention will be apparent to those skilled in the art and will be pointed out below.

1 is a cross-sectional view of an empty Czochralski crucible.

2 is a cross-sectional view of an empty susceptor suitable for use in supporting the crucible of FIG. 1.

FIG. 3 is a schematic of a Czochralski-type crystal puller including a cross-sectional view of the crucible of FIG. 1 supported and positioned by the susceptor of FIG. 2 for forms typically used in a batch process.

4 is a schematic view of a Czochralski-type crystal puller including a cross-section of an inner crucible and an outer crucible with an external crucible supported and positioned by a susceptor for forms typically used in a continuous process.

5 is a schematic block diagram illustrating a process for producing a graphite support container.

FIG. 6 shows the zero-potential of single crystal silicon during various neck attempts using a silica sand crucible supported by a graphite susceptor having a calcium concentration ranging from 0.1 ppm to 0.2 ppm or from 0.8 ppm to 1.7 ppm. Plot showing growth.

※ Explanation of code about main part of drawing ※

1, 10: crucible 12, 32: inner surface

14, 34: outer surface 17, 37: centerline

18, 38: corner 19, 39: wall

24: open cavity 30: graphite susceptor

46: base 50: CZ crystal raise

52: bearing rack

The invention will be described in more detail below with reference to the drawings, wherein like reference numerals are used to designate like numerals in the several figures.

According to the invention, the concentrations of alkaline earth metals and alkali metal impurities, especially calcium, which appear on the surface and volume of the graphite support vessel (eg susceptor) are supported when producing single crystal silicon in a Czochralski crystal lifter. It substantially affects the degree and occurrence of non-uniform devitrification phenomenon of the silica sand container (for example, crucible) supported by the container. Without being bound by this theory, using a support container with low concentrations of alkaline earth metals and alkali metal impurities reduces the degree of diffusion from the support container to the outer surface of the silica sand container, and thus locally crystallizes the nucleation site. Reduce the degree of non-deviality of the silica sand container. Single crystal silicon can be produced using a graphite support vessel that effectively has a low calcium concentration and is preferably 0.7 ppm or less by weight even at high-capacity filling, without substantial non-uniform devitrification of the silica sand container of glass. Reducing the local crystallization degree of the glass silica sand container allows for improved silicon crystal properties, including improved structural integrity of the silica sand container and improved zero-defect growth.

As used herein, the word container refers to a crucible, liner or other pool of molten silicon that can be formed for use in preparing single crystal silicon ingots in a Czochralski-type crystal puller. It means to include a container. The word support container means to include a susceptor, crucible or other receptacle used to support the container. The word polycrystalline silicon is meant to include polycrystalline silicon that is not limited in shape, form or method of manufacture, and also, for example, chunk polycrystalline silicon and fluidized bed typically prepared by a Siemens type process. By granular polycrystalline silicon typically prepared by the reaction process is meant.

The polycrystalline silicon is loaded into a silica sand container suitable for use in bonding with the graphite support container of the present invention to prepare single crystal silicon by the Czochralski method. The silica sand container may be an untreated glass silica sand container consisting essentially of silica, or optionally at least some area of the inner and / or outer surface of the silica sand container may be handled according to various methods currently known or later in the art. It may be a treated silica sand container comprising a glass silica sand container having an inner and outer surface to be developed. For example, such treatment methods include forming an outer coating (eg, SiN) on the surface or growing such a coating in the situ on the surface. It is generally desirable to uniformly apply a devitrification facilitator to uniformly form a layer of devitrified silica at the surface or to promote the formation of such a uniformly slit layer. The use and formation of uniformly devitrified layers on the surface of the silica sand container is distinguished from the non-uniform devitrification sought to be avoided by the present invention with respect to the degree of control during the devitrification process and the non-local nature of the uniform and consequently devitrified silica layers. do. Regardless of whether the container is treated or untreated, the volume of the silica sand container is preferably substantially free of alkaline earth metals, alkali metals and other impurities, and the surface of the silica sand container is preferably substantially on or inside of it. It is free of unevenly distributed alkaline earth metals and alkali metal impurities. Silica sand containers of suitable properties are commercially available from a variety of sources including, for example, General Electric, Cults Product Department (Cleveland, Ohio).

Although the special external structure of the silica sand container is not very precise, the container will generally be in the form of a cup and will have an internal and external surface that exhibits at least partially closed structure that may not contain or contain liquids such as molten silicon. Can be. Referring to FIG. 1, a sample silica sand container is an untreated silica sand crucible 10. The crucible 10 generally has an inner surface 12, an outer surface 14, a centerline 15 and an upper edge 16. The inner surface 12 defines an open cavity 24 in which polycrystalline silicon is loaded. The crucible 10 comprises a bottom 17, a corner 18 and a side or wall 19, hereinafter referred to as the bottom 17, the corner 18 and the wall 19 of the crucible 10. . As in the illustrated embodiment, the wall 19 is substantially vertical and the floor 17 is substantially horizontal. More precisely, the wall 19 defines a substantially vertical circumferential surface comprising an upper portion 19a, a middle portion 19b and a bottom portion 19c, and each of the upper portion, the middle portion and the bottom portion 19a, 19b. And 19c) comprises about one third of the total surface area of the wall 19. Suitable divisions between the top, middle and bottom portions 19a, 19b and 19c are generally shown as phantom lines 21. The bottom 17 is a parabola and also has a slope where the horizontal component is substantially larger than the vertical component. The corner 18 is a curved annular border region at the vicinity of the intersection of the wall 19 and the floor 17. The corner 18 has a radius of curvature smaller than the radius of curvature of the floor 17 and the change in curvature radius generally intersects the floor 17. The corner 18 has a top and a bottom that are each half including about half of the total surface area of the corner 18, the top half closer to the wall 19 and the bottom half closer to the bottom 17. The centerline 15 of the crucible 10 is substantially parallel to the wall 19 and intersects the geometric center point of the bottom 17.

The graphite support vessel is supported in the formation of silicon melt therein and in the production of single crystal silicon from molten silicon. The graphite support vessel may or may not be treated. Untreated graphite support vessels consist essentially of carbon in the formation of graphite. The treated graphite support vessel comprises a core vessel consisting essentially of graphite and at least a portion of the inner and / or outer surface of the core vessel has an outer surface according to various methods now known in the art and will be developed later. For example, such treatment methods include growing by forming a coating of SiC, TiC, NbC, TaC, ZrC, BN or carbon glass on the surface or by coating on the surface of the core container.

When the particular form of the graphite support container is not extremely critical, the support container is generally cupped and placed in the graphite support container having at least a portion of the inner surface of the support container in contact with at least a portion of the outer surface of the silica sand container. It has an internal and an external structure defining a structure adapted to receive a container. The area in contact between the inner surface of the support container and the outer surface of the container defines the interface area. The support container is preferably further adjusted for use in the Czochralski type crystal puller. Referring to FIG. 2, a representative graphite support container is an unprocessed graphite susceptor 30. The susceptor 30 has an inner surface 32, an outer surface 34, a centerline 35 and an upper edge 36. The inner surface 32 of the susceptor 30 defines an open cavity 44 and includes a bottom portion 37, a corner portion 38 and a side wall 39, hereinafter the bottom of the susceptor 30 ( 37), core 38 and wall 39, respectively. In the illustrated embodiment, the susceptor bottom 37 is substantially horizontal and the susceptor wall 39 is substantially vertical. More particularly, bottom 37 is parabolic and has a slope that is substantially greater in the horizontal component than in the vertical component. The susceptor wall 39 defines a circumferential region and includes an upper portion 39a, a middle portion 39b, and a bottom portion 39c, each of which has a top portion, a middle portion and a bottom portion 39a, 39b, and 39c. About one third of the total surface area of (39). Suitable divisions between the top, middle and bottom portions 39a, 39b and 39c are generally shown by phantom lines 41. The susceptor wall 39 is tapered slightly open to the true vertical, and the diameter of the wall 39 at the upper edge 36 of the susceptor 30 is at a low point in the wall 39, for example, At the bottom 39b of the wall 39, it is slightly larger than the diameter of the measured wall 39. The finely open tapered wall 39 facilitates the receipt of other silica sand containers into the silica sand crucible 10 or into the open cavity. The susceptor corner 38 is a curved annular border region near the intersection of the wall 39 and the floor 37. Corner 38 intersects wall 39 where the curve of corner 38 stops, generally illustrated by line 42. The corner 38 has a radius of curvature smaller than the radius of curvature of the floor 37 and generally intersects the floor 37 where the curvature changes. The corner 38 has a top and a bottom that are each half including about half of the total surface area of the corner 38, the top half closer to the wall 39 and the bottom half closer to the bottom 37. The centerline 35 of the susceptor 30 is substantially parallel to the wall 39 and intersects the center point in the form of the bottom 37. The susceptor 30 further includes a base 46 located below the bottom 37 of the inner surface 32. The base 46 is adapted to connect to the movable pedestal 52 of the Czochralski type crystal puller.

3 shows a crucible 10 supported and positioned by a susceptor 30 in a Czochralski-type crystal puller 50 having a base 46 of susceptor 30 attached to a movable bearing base 52. ) Is shown. This structure is typical for producing single crystals using a batch Czochralski type process. The areas of the inner surface 32 of the susceptor 30, defined as the bottom 37, the corner 38, and the bottom 39b of the wall 39, correspond to the corresponding portions 17, 18 and 19b of the crucible 10. ) In contact with The interface area for this container support container system is defined as the contact area between the crucible and the susceptor. In the general case, however, the extent and specific location of the interfacial region depends on the particular design for the silica sand container and the graphite support container. Such designs are generally based on consideration of structural support and thermal deformation. In addition, the contact region defining the interface region will change with time during the crystal growth process with respect to the batch process. Referring to FIG. 3, after the silicon melting is formed in the silica sand crucible 10, the molten silicon 48 under the melting surface 58 is removed from the walls 19, the corners 18 and the bottom of the crucible 10 ( 17) exert a static force on the force of gravity. Since the heat treated silica sand container softens at the melting point, the static / gravity force is activated to push the softened silica sand container against the graphite support vessel. However, in the batch process, the degree of molten silicon decreases when the silicon ingot is formed, and thus, when the silicon ingot is formed, the hydrostatic pressure applied to the wall 19, the corner 18, and the bottom 17 is When the crystal is pulled down, the upper portions 19a and 39a of the walls 19 and 39 are released to each other, and also the contact between the outer surface 14 of the crucible wall 19 and the support container wall 39. The amount of decreases. Thus, in general, it defines a subregion of the interface region based on the contact time between the silica sand container and the wall of the support vessel: (1) a non-contact region substantially positioned on the initial melting line (ie molten silicon 48) On the initial level of the surface 58); (2) an instantaneous contact area located substantially below the initial melting line except substantially above the final melting line; And (3) the hydrostatic pressure and / or the weight of the silica sand container pushes the softened container against the support container during the entire crystal pulling process. For the container / support container system illustrated in FIGS. 1 to 4, the non-contact area is the height 19a, 39a of the container and support container wall, respectively, as the highest of the interface area between the graphite susceptor and the wall of the silica sand container illustrated therein. It is correlated as 1/3. The instantaneous contact area is correlated with the top-half of the bottom third and corner components of the wall. 1 to 4, for example, the instantaneous contact area may comprise wall portions 19b, 19c, 39b, 39c and upper half 18, 38 of the corner. The continuous contact area is generally correlated with the bottoms 17, 37 and the bottom half 18, 38 of the corner.

The crucible 10 and the susceptor 30 are typical in FIGS. 1, 2 and 3, respectively. The form of the silica sand container and the graphite support container may vary substantially from the illustrated embodiment and is still within the scope of the present invention. One of the designs selected for the silica sand container and the graphite support container is shown in FIG. 4. In such a design, an inner crucible 10 'and an outer crucible (located and supported in the graphite support container (susceptor, 30') are shown. The dual container system comprising 10) is arranged in a typical way for the preparation of single crystal silicon using a continuous Czochralski type process.

Regardless of whether the graphite support vessel is treated or not, and also regardless of the particular form of the support vessel, calcium, magnesium, which appears as an accumulated concentration of alkali metals and / or alkaline earth metals, in particular as impurities in and on the surface of the graphite support vessel , Strontium, lithium, sodium and potassium are generally low enough to prevent substantial non-uniform devitrification of the silica sand container at the interface region when the polycrystalline silicon is melted and the monocrystalline silicon ingot is drawn from the molten silicon. As used herein, the term substantially non-uniformity is a clear commercial reduction in the overall structure of the silica sand container (e.g., cusping, fluxing, pitting, bulking ( bulging, bowing and / or other variations) and / or mean local crystallization of vitreous silica that apparently commercially decreases within the zero-potential length during growth of single crystal silicon ingots from silicon melt formed in the silica sand container. The reduction within the zero-potential length is preferably at most 10%, particularly preferably at most 5%, more preferably at most 1% and most preferably at most 0.5%. A reduction of more than 0.5% within the zero-potential length is currently clearly considered commercially, but a smaller decrease will be apparent in the future. Substantial non-uniformity is characterized by a number of observable shapes, such as excess deformation of the white powder accompanied by obvious fitting, cusping and / or fluxing. Fluxing is related to the local softening of the silica sand container and is evidenced by the glossy shape or visible glow on the outer surface of the silica sand container. Fluxing is particularly relevant to indicators of harmful non-uniformity. The cumulative concentrations of alkali metals and / or alkaline earth metals, especially calcium, magnesium, strontium, lithium, sodium and potassium, appearing in the graphite support vessel are preferably low enough to avoid fluxing areas of about 1 cm 2 or more. More preferably, the cumulative concentration is very low to be fluxed to about 0.5 cm 2 or less.

In general, the concentration of the above-mentioned impurities in the untreated graphite support container used as the untreated silica sand container, particularly calcium, is preferably about 1.0 ppm or more with respect to the weight of the graphite material in which the graphite support container is formed (e.g. See Example 1). The concentration of the above-mentioned impurities shown in such a graphite support container is about 0.7 ppm or less, 0.5 ppm or less, 0.2 ppm or less and most preferably 0.1 ppm or less by weight in order to improve the excellentness. As described above, when either the inner surface of the support container or the outer surface of the silica sand container is treated so that at least one surface is a treated surface in the interface region, a higher concentration of alkali metal and alkaline earth metal impurities, in particular calcium, Can tolerate without substantial non-uniformity. Accurate top concentrations are limits of alkali and / or alkaline earth metal impurities to substantially avoid, and uneven devitrification, cleaning of surfaces of silica sand containers and / or graphite support containers, special crucibles, regardless of whether the silica sand containers and / or graphite support containers have been treated. Various dependences may be placed on factors including the heat-zone temperature profile (temperature and time) used for size and fill size. Nevertheless, single crystal silicon of improved properties can be obtained with induction and the concentration limits described above are lower. Once polycrystalline silicon is loaded into a suitable silica sand container / graphite support system, the crucible can be placed in a conventional CZ silicon crystal growth apparatus and the polycrystalline silicon can be formed until a pool of molten silica sand is formed in the silica sand container. It may be heat treated to melt polycrystalline silicon. The heat treatment profile is not very critical and also depends in general on the size and shape of the loading (ie chunk, granular or mixed loading) crucibles, the shape and size of the crystal growth phase, and the like. In a typical arrangement, referring to the crucible / susceptor system illustrated in FIGS. 3 and 4, the bearing 52 supporting the base 46 of the susceptor 30 is the bottom 17 of the crucible 10. It is located as if it is near the top of the heater 54. The crucible 10 is gradually lowered into the space inner surface of the heater 54. The speed at which the crucible 10 is lowered closer to the heater 54 and the values of other factors affecting the melting of the polycrystalline silicon, such as heater power, crucible rotation and system pressure, are generally known in the art.

Usually, the temperature of the contact area between the crucible 10 and the susceptor 30 at the corners 18, 38 is about 18 (about 46 cm) diameter crucibles filled with about 60 kg polycrystalline silicon during melting in the range of about 4 hours. It is preferably at least about 1550 ° C. for an 18 (about 46 cm) diameter crucible filled with about 70 kg polycrystalline silicon, optionally over a melting period ranging from about 4 hours to 6 hours. Higher temperatures, preferably at least about 1575 ° C., at least about 1600 ° C. or at least about 1625 ° C., are also 18/60 kg or less for the effect of shorter melting periods without the effect of defects on the overall structure of the silica sand container or graphite support container. Can be used for 18 / 70kg systems. The advantages of the present invention are particularly evident using silica sand container diameters and / or larger fill sizes. For example, the temperature of the hot flux corner region may be in a 32 (about 56 cm) diameter crucible filled with about 100 kg polycrystalline silicon for a melting period of about 7 hours to 10 hours or filled with a melting period of about 10 hours and 120 kg or more. It is preferably about 1600 ° C or higher. However, even higher temperatures are used as 22/120 kg systems, at or above about 1675 ° C. or above about 1700 ° C. for the effect of proportionally shorter melting periods (eg, in the range of about 6 hours to about 8 hours). do. For larger silica sand containers, as with a 24 (about 61 cm) diameter crucible filled with about 140 kg of polycrystalline silicon, the corner temperature is preferably at least 1650 ° C and may also be at least 1675 ° C or at least 1700 ° C. . Melting periods for a 24/140 kg system can vary in temperature, but are typically in the range of about 10 hours to about 12 hours at 1650 ° C. and from about 8 hours to about 10 hours in the temperature range of about 1675 ° C. to about 1700 ° C. . As in another example, a 32 (about 81 cm) diameter crucible filled with an amount of polycrystalline silicon in the range of about 160 kg to about 200 kg has a corner at a temperature of at least about 1650 ° C, more preferably at least about 1675 ° C or 1700 ° C. Can be heated at a temperature. Such higher temperatures are desirable to allow for commercially relevant melting periods for 32 / 160-200 kg systems, for example in the range of about 12 hours to about 15 hours. The combination of the above-mentioned silica sand container diameter, filling size and melting period, and in particular, such parameters as changing temperature, is cited as a representative advantage of the present invention and is not intended to limit it as the scope of the present invention. Those skilled in the art will appreciate that the low impurity support vessels described above, generally allow the use of silica sand containers heated at high temperatures without adversely affecting crystal growth in combination with known systems. The possibility of using higher temperatures is to express improved productivity through larger packing sizes and / or reduced melting periods.

When heated, polycrystalline silicon is exposed to a purge gas to eject undesirable gases such as SiO (g) and CO (g) resulting from the reaction of SiO (g) with hot graphite. The purge gas is an inert gas such as argon and flows in a speed range of about 10 l / min to about 300 l / min, depending on the size and shape of the crystal drawer.

When the silicon melt is formed, the single crystal silicon ingot is drawn from the molten silicon according to the Czochralski type process. 3 and 4, a single crystal silicon ingot 55 is drawn in a Czochralski-type crystal puller 50 from a silicon melt formed in a silica sand crucible 10 supported by a graphite susceptor 30. Special methods and conditions for drawing single crystal silicon ingots are known in the art. The high temperatures established during melt formation are generally maintained while the single crystal silicon melt is drawn. Advantageously, when the high purity graphite support vessel (eg susceptor, 30) of the present invention is used to support a silica sand container (eg crucible, 10), the partial temperature of the graphite support vessel is the highest heat. At about 1500 ° C. or higher in the production of monocrystalline silicon ingots from them (typically for a period of at least about 4 hours or at least about 5 hours) without being susceptible to flux and causing uneven devitrification of the silica sand container at the interface region, if necessary , Have the highest temperature (eg, the corner area of the support container) that can be maintained at about 1525 ° C., 1550 ° C., 1575 ° C., 1600 ° C., 1625 ° C., 1650 ° C., 1675 ° C., or 1700 ° C. or higher. When the temperature of the graphite support vessel (e.g. susceptor 30) is changed during the formation and crystal drawing of the silicon melt and can also vary locally for different periods of time, between different regions of the support vessel, The average temperature at the particular location of the acceptor is generally higher temperature for larger crucible diameters with a larger filling capacity of polycrystalline silicon. Usually, the upper concentration limit of alkali and alkaline earth metal impurities in the graphite support vessel will decrease as part or all of the following parameters: crucible size (eg diameter), fill size (eg weight), its Support vessel temperature at corner radius, and time at a temperature of about 1500 ° C. or more. The concentration and temperature values mentioned above are representatively considered and are merely exemplary. Usually, the most predetermined concentrations of alkali and alkaline earth metals for any system or batch are substantially non-uniformly devitrified in the silica sand container at the interface region when polycrystalline silicon is melted and single crystal silicon ingots are drawn from the molten silicon, as described above. Concentration is low enough to prevent.

High purity graphite support vessels with alkaline earth metal and alkali metal impurities, in particular calcium impurities, can be prepared in the same manner as the usual method, such support vessels currently being made at concentrations suitable for use in the present invention. Particular attention was paid to the selection of binder raw materials and fillers with low concentrations of impurities, with special emphasis on the purification steps to ensure low levels of alkali and alkaline earth metal impurities that were satisfactory. A detailed description of the manufacturing process for producing graphite can be found in the 1983 JEC press, in particular pp. 22-58, Tey. Ishikawa and Tie. Nagaoki (English editor Ai C. Lewis) was recently released on Carbon Technology. In brief, referring to FIG. 5, the fill material (eg pixelated petroleum coke) is ground to a relatively uniform particle size, sieved and mixed and then binder (eg coal tar) in the kneading process. Pitch). After mixing the filler and the binder raw material, the resultant mixture is formed into a predetermined shape (for example, an ingot) by a molding or extraction process. The raw material formed is then baked in the carbonization process, and the carbonized raw material output is either directly or graphitized to the next step when it is penetrated and rebaked to increase density and / or hot refining process, usually Such purification processes are prone to halogen gas at temperatures of about 2500 ° C. for extended periods of time, including either baked carbon and / or graphitized carbon. Alkali and alkaline earth metal impurities are removed during the graphitization step and / or through a refining process in which the impurities are removed using a high temperature purification process. Stock graphite is then processed to form the graphite support vessel of the present invention. Commercial production of graphite support vessels (eg, UCAR, Clarksburg, WVa) can achieve the degree of purity required for the graphite support vessels of the present invention.

The example below illustrates the principles and advantages of the invention.

example

Example 1: Production of single crystal silicon using a graphite susceptor with varying concentrations of calcium.

In some tests, single crystal silicon ingots are produced from silicon metal formed in an untreated vitreous silica sand crucible. The silica sand crucible is supported by a graphite susceptor having a varying concentration of calcium (in the range from about 0.1 ppm to about 1.8 ppm). Multiple neck attempts to draw silicon ingots have been recorded.

The following monocrystalline silicon production, the properties of the glassy quartz crucibles used in each operation, were observed with particular attention to the degree of devitrification, fitting, cuping and fluxing of the crucible wall. Crucibles used as susceptors with high concentrations of calcium (in the range 0.8 ppm to 1.7 ppm) were observed to have weight loss due to the apparent amount of fitting, cuping and fluxing of the crucible wall. In contrast, silica sand crucibles used as graphite susceptors with low concentrations of calcium (in the range from about 0.1 ppm to about 0.2 ppm) were observed to have light weight devitrification, with a minimum amount of cuffing, fluxing and fitting of the crucible wall.

The presence of dislocations in the single crystal ingot result was also determined. The results are summarized in FIG. 6 and also the zero-potential growth of single crystal silicon is made using a graphite susceptor with varying concentrations of calcium and using a number of neck attempts. One of the high calcium composition (range from 0.8 ppm to about 1.7 ppm) or the low calcium composition (range from about 0.1 ppm to about 0.2 ppm) was grouped in FIG. 6. The data in FIG. 6 shows that during the operation in which silicon crystals are drawn as a small number of nexuses, the zero-potential growth results in 100% when using a low calcium composition susceptor, but with a high calcium composition susceptor Only at 60%. When all data are taken into account, regardless of the number of neck attempts required to initiate crystal growth, zero-potential growth results in 72% of cases using a low calcium composition susceptor, but using a high calcium composition susceptor Only 40% of the time. As such, the use of low calcium composition susceptors adversely affects the extent to which zero-potential growth of single crystal silicon is achieved.

It is intended to inform those skilled in the art as to the description and principles, and the practical application of the invention. Those skilled in the art can apply and adapt the present invention in many forms. Accordingly, the particular embodiments of the invention disclosed are not intended to be exhaustive or exhaustive of the invention.

The present invention relates to the production of single crystal silicon, and more particularly, to a graphite susceptor used to support a silica sand crucible in the growth of an ingot of single crystal silicon by the Czochralski method. The present invention thus reduces the deformation of the silica sand container and reduces the zero-defect growth of single crystal silicon ingots.

Claims (20)

Forming a pool of molten silicon in a silica sand container having an outer surface, Supporting a silica sand container having a graphite support container having an inner surface that is at least a portion of the support container in contact with an outer surface of the silica sand container; In addition, in the process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski method including a method of drawing a single crystal silicon ingot from molten silicon, the calcium concentration in the graphite support container does not exceed 1 ppm by weight. A process for producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski method. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the calcium concentration in the graphite support container does not exceed 0.7 ppm by weight. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the calcium concentration in the graphite support container does not exceed 0.2 ppm by weight. A process for producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the calcium concentration in the graphite support container does not exceed 0.1 ppm by weight. The Czochralski according to claim 1, wherein the graphite support container is heated to obtain a temperature of 1550 ° C or more for at least 2 hours in an area where the inner surface of the corner portion of the support container contacts the outer surface of the corner portion of the silica sand container. Process for producing monocrystalline silicon ingots from polycrystalline silicon according to the mold method. The Czochralski according to claim 1, wherein the graphite support container is heated to obtain a temperature of 1575 ° C or higher for at least 4 hours in an area where the inner surface of the corner portion of the support container contacts the outer surface of the corner portion of the silica sand container. Process for producing monocrystalline silicon ingots from polycrystalline silicon according to the mold method. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the graphite support container is an untreated graphite support container. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the graphite support container is a graphite susceptor. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 1, wherein the silica sand container is a treated silica sand container. Forming a pool of molten silicon in a silica sand container having an outer surface, Supporting a silica sand container having a graphite support container having an inner surface that is at least a portion of the support container in contact with an outer surface of the silica sand container; In addition, in the process of producing a single crystal silicon ingot from polycrystalline silicon according to a Czochralski-type method including a method of drawing a single crystal silicon ingot from molten silicon, the cumulative concentration of alkali earth metal and alkali metal in the graphite support container is determined by weight. A process for producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski method, characterized in that it does not exceed 1 ppm. The method according to claim 10, wherein the cumulative concentration of the metal selected from the group consisting of calcium, magnesium, strontium, lithium, sodium and potassium in the graphite support container does not exceed 0.7 ppm by weight. Process for producing monocrystalline silicon ingots from polycrystalline silicon. The process of producing a single crystal silicon ingot from polycrystalline silicon according to the Czochralski type method according to claim 10, wherein the concentration of calcium in the graphite support container does not exceed 0.2 ppm by weight. It is possible to accommodate a silica sand container consisting essentially of graphite and having at least a portion of the inner surface of the body in contact with the outer surface of the silica sand container to support the silica sand container during silicon melt formation of the silica sand container and when producing single crystal silicon from the melt. A graphite support container for supporting a silica sand container in production of single crystal silicon from a silicon melt formed in a silica sand container according to a Czochralski-type rice method comprising a body having an inner surface defining an open cavity therein, wherein the calcium concentration in the body is weight A graphite support container for supporting a silica sand container in production of single crystal silicon from a silicon melt formed in the silica sand container according to the Czochralski rice method, characterized in that it does not exceed 1 ppm. 14. A support container according to claim 13, wherein the calcium concentration in the graphite body does not exceed 0.7 ppm by weight. 14. A support container according to claim 13, wherein the calcium concentration in the graphite body does not exceed 0.2 ppm by weight. 14. A support container according to claim 13, wherein the calcium concentration in the graphite body does not exceed 0.1 ppm by weight. 14. The support container of claim 13, further comprising a coating covering at least a portion of the inner surface of the graphite body. It is possible to accommodate a silica sand container consisting essentially of graphite and having at least a portion of the inner surface of the body in contact with the outer surface of the silica sand container to support the silica sand container during silicon melt formation of the silica sand container and when producing single crystal silicon from the melt. A graphite support container for supporting a silica sand container in the production of single crystal silicon from a silicon melt formed in a silica sand container according to a Czochralski-type rice method comprising a body having an inner surface defining an open cavity therein, the alkaline earth metal in the graphite body and The cumulative concentration of alkali metals does not exceed 1 ppm by weight, and the black silica supporting the silica sand container in the production of single crystal silicon from the silicon melt formed in the silica sand container according to the Czochralski-type rice method is characterized by the above-mentioned. Soft case container. 19. The support container of claim 18, wherein the cumulative concentration of a metal selected from the group consisting of calcium, magnesium, strontium, lithium, sodium, and potassium in the graphite body does not exceed 0.7 ppm by weight. 19. The support container of claim 18, wherein the calcium concentration in the graphite body does not exceed 0.2 ppm by weight.