JPH1129395A - Graphite-supporting container having calcium impurity in low concentration and its use in production of single crystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce high-quality single crystal silicon from large charge amount by keeping calcium concentration of a graphite-supporting vessel for housing a silica container for producing a single crystal silicon ingot so as not to exceed a specific value. SOLUTION: A polycrystalline silicon is charged into a silica container (crucible) 10 in order to produce single crystal silicon ingot and at least a part of inner surface 32 of a graphite susceptor 30 is brought into contact with the outer surface 14 of the silica container 10 to support the silica container 10. The polycrystalline silicon is melted by heating the silica container 10 and polycrystalline silicon at least about 1,575 deg.C for at least 4 hr to form melted silicon 48 and single crystalline silicon ingot 55 is pulled up from the melted silicon 48. In this time, the calcium concentration in the graphite susceptor 30 for supporting the silica container 10 is kept to about <=1 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to the production of single crystal silicon, and more particularly to a novel graphite susceptor used to support a silica crucible during the growth of a single crystal silicon ingot by the Czochralski method. susceptors). The present invention also relates to a method for producing single crystal silicon using the novel susceptor.

[0002]

2. Description of the Related Art Most of single crystal silicon used for manufacturing microelectronic circuits is manufactured by the Czochralski (CZ) method. In this method, the polycrystalline silicon is melted in a crucible, the seed crystal is immersed in the molten silicon, the seed crystal is pulled up, the single crystal growth is started, and the single crystal silicon ingot is grown. Manufactured. Polycrystalline silicon is generally a vitreous silica (SiO ₂ ) crucible, or other silica-lined container.
melted during s). Vitreous silica is an amorphous form of silica, and crucibles made of vitreous silica are commonly referred to as quarts cruibles or fused quarts cruibles. Silica also exists in various crystalline forms, including the α and β forms of quartz, tridymite and cristobalite.

However, there are several problems with the performance of silica containers at the high temperatures required to melt polycrystalline silicon. For example, vitreous silica becomes less viscous with increasing temperature, about 1815 K
Softens sufficiently to flow under stresses applied at temperatures above Thus, silica containers are susceptible to loss of structural integrity, including sagging and / or other deformations during single crystal silicon production. Thus, a graphite support vessel such as a susceptor or crucible is commonly used to support a silica crucible, liner or other container in which the polycrystalline silicon is melted.

[0004] The surface of the graphite container and / or the silica container in contact therewith is, for example, Si
C, TiC, NbC, TaC or ZrC (JP708
9789A), or glasseous carbon
(U.S. Pat. No. 5,476,679 to Lewis et al.). Further, the inner surface of the silica container and / or
Alternatively, the outer surface can include a homogeneous layer of crystalline silica (Pastor et al., US Pat. No. 4,429,099; Loxl).
Ey et al., U.S. Pat. No. 5,053,359) or can be coated with a devitrification accelerator to form a homogeneous devitrification layer in situ (EP 0 735 605 A).

Another problem associated with the high temperature performance of silica containers is the local transformation of vitreous silica to a crystalline form (eg, β-crystalborite), which is called heterogeneous devitrification. Crystabolite island (Crystabolite island) formed on the inner surface of the silica container
s) is released into the silicon melt and incorporated into the growing crystal, thereby creating defects therein. Excessive heterogeneous growth of crystallites also results in a loss of structural integrity of the silica container, including bending, blistering, and other distortions and deformations of the shape of the silica container. Heterogeneous devitrification of silica is affected by the purity of the silica and the level of contamination of the silica surface, which promotes the nucleation of crystalline silica (eg, crystallites) and converts crystalline silica to other forms. It has been reported to act as a flux to transform (eg, from cristavorite to tridymite). Fused Quarts Product
s , General Electric Company General Catalog 7700, p
See pages 17-18 (January 1987). Therefore, methods of minimizing the degree of heterogeneous devitrification include improving the purity and surface cleanliness of the silica container. For example, Japanese Patent Publication No. 52/038883 discloses the use of a xenon lamp that irradiates the inner surface of a crucible to remove metallic contaminants that are electrostatically attached to the silica surface. Japanese publication No. 60/137892,
Disclosed is the removal of alkali metals from silica crucibles using electrolysis.

[0006] Despite the above methods, heterogeneous devitrification and its adverse effects on the structural integrity and zero defect crystal growth of silica containers remain problems. In a larger capacity silica container, the rate of local heterogeneous devitrification increases dramatically with increasing temperature,
This problem is becoming particularly acute as the industry shifts to producing larger diameter single crystal silicon ingots with higher polycrystalline silicon loadings. The higher temperatures required in such applications increase the likelihood of substantial heterogeneous devitrification, cause deformation of the silica container, and ultimately reduce zero defect growth of the single crystal silicon ingot.

[0007]

Accordingly, it is an object of the present invention to produce higher quality single crystal silicon, and in particular to reduce the degree of local heterogeneous devitrification of silica containers, The objective is to produce single crystal silicon from a larger load while improving the structural integrity of the container and increasing the zero defect growth of silicon crystal growth therein. It is a further object of the present invention to obtain such improved quality single crystal silicon in a cost-effective manner with minimal impact on existing commercial manufacturing methods.

[0008]

SUMMARY OF THE INVENTION Accordingly, in brief,
The present invention relates to a method for producing a single crystal silicon ingot from polycrystalline silicon. According to the method of the present invention, polycrystalline silicon is loaded into a silica container. The silica container may be a treated or untreated silica container. The container is housed in a graphite support vessel and the graphite support vessel adapted to receive the silica container in a manner such that the outer surface of the container contacts at least a portion of the inner surface of the support vessel, such that the container is Supported. The area of contact between the inner surface of the support container and the outer surface of the container defines an interface area. The graphite support vessel is further adapted for use in a Czochralski crystal puller and may be a treated or untreated graphite support vessel, such as a treated or untreated graphite susceptor.

According to one embodiment of the method of the present invention, the concentration of calcium present in the graphite support vessel prevents substantial heterogeneous devitrification of the silica container in the interfacial region during the subsequent process steps. Low enough to be used. In a preferred method, the concentration of calcium in the graphite support vessel does not exceed about 1 ppm by weight. The concentration of calcium in the graphite support vessel preferably does not exceed about 0.7 ppm by weight, more preferably about 0.2 ppm.
Does not exceed ppm by weight, particularly preferably does not exceed about 0.1 ppm by weight.

According to another embodiment of the method of the present invention, the cumulative concentration of alkaline earth metals and alkali metals present in the graphite support vessel does not exceed about 1 ppm by weight.
Preferably, the cumulative concentration of a metal selected from the group consisting of calcium, magnesium, strontium, lithium, sodium and potassium, present in the graphite support vessel, does not exceed about 0.7 ppm by weight. Preferably, the calcium concentration in the graphite support vessel of an embodiment of the method of the present invention does not exceed about 0.2 ppm by weight.

In any of the foregoing embodiments of the method of the present invention, the support vessel, container and polycrystalline silicon are heated to melt the polycrystalline silicon and form a silicon melt. The graphite support vessel is provided for at least about 2 hours in a region where the inner surface of the corner portion of the support container is in contact with the outer surface of the corner portion of the silica container.
Heating can be performed to achieve a temperature of at least about 1550 ° C., preferably at least about 1575 ° C., preferably for a time of at least about 4 hours. A single crystal silicon ingot is withdrawn from the molten silicon.

The present invention also provides a graphite support vessel, such as a susceptor or crucible, used to nest a silica container during the manufacture of a single crystal silicon ingot from the silicon melt formed in the container. Also concerns. The support vessel has a body consisting essentially of graphite.

Importantly, according to one graphite support embodiment, the concentration of calcium present in the graphite body does not exceed about 1 ppm by weight. The concentration of calcium present in the graphite body preferably does not exceed about 0.7 ppm by weight, more preferably about 0.2 ppm.
Does not exceed ppm by weight, particularly preferably does not exceed about 0.1 ppm by weight.

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

[0015] For any of the foregoing embodiments of the graphite support vessel, the graphite body has an interior surface defining an open cavity such that the shape of the cavity is such as to nest the silica container. Wherein at least a portion of the inner surface of the graphite body contacts the outer surface of the silica container to support the silica container during silicon melt formation in the silica container and during production of single crystal silicon from the melt. I have. The body is designed to be adapted for use in a Czochralski crystal puller. The body may consist essentially of graphite, or the coating may be on at least a part of the inner surface.

[0016] Other features and objects of the invention will be in part apparent to those skilled in the art and in part pointed out below.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail hereinafter with reference to the drawings, in which the same items are provided with the same reference numbers in more than one drawing.

In accordance with the present invention, the concentration of alkaline earth metal and alkali metal impurities, especially calcium, present in the bulk or on the surface of a graphite support vessel (eg, a susceptor) is determined by a Czochralski crystal puller. Substantially affects the presence and degree of heterogeneous devitrification of the silica container (eg, crucible) supported by the support vessel during the production of single crystal silicon therein. Without being bound by theory, by using a support vessel having a low concentration of alkaline earth metal and alkali metal impurities, the extent of diffusion of impurities from the support vessel to the outer surface of the silica container is reduced, thereby Reduce the number of nucleation sites for local crystallization,
The degree of heterogeneous devitrification on the silica container is reduced. By using a graphite support vessel having a sufficiently low calcium concentration, preferably about 0.7 ppm by weight or less, even from high volumes of charge material,
Without substantial heterogeneous devitrification of the vitreous silica container,
Single crystal silicon can be manufactured. Reducing the degree of local crystallization of the vitreous silica container improves the structural integrity of the silica container and allows for improved silicon crystal quality, including improved zero defect growth.

As used herein, the term "container" can form a pool of molten silicon for use in manufacturing a single crystal silicon ingot with a Czochralski crystal puller. Means a crucible, liner, or other container. "Support container
The term (support vessel) means a susceptor, crucible, or other receptors used to support a container. The term "polycrystalline silicon" means polycrystalline silicon that has no limitations with respect to shape, morphology or method of manufacture, e.g., "chunk" polycrystalline silicon, generally manufactured by a Siemens-type method, and Includes "granular" polycrystalline silicon produced by the bed reaction process.

To produce single crystal silicon by the Czochralski method, polycrystalline silicon is loaded into a silica container suitable for use with the graphite support of the present invention. The silica container may be an untreated vitreous silica container consisting essentially of silica, or at least a portion of the inner and / or outer surface of the silica container is a method currently known in the art or developed in the future. A treated silica container comprising a vitreous silica container having an inner surface and an outer surface that has been treated by the various methods described.
Such treatment methods currently include, for example, forming an external coating (eg, SiN) on a surface, or growing such a coating in situ on a surface. It is generally preferred to form a homogeneous layer of devitrified silica on the surface, or to uniformly apply a devitrification promoting agent that promotes the formation of such a homogeneous devitrified layer.

The formation and use of a homogenous devitrification layer on the surface of a silica container can be achieved by the present invention in terms of the degree of control of the degree of devitrification and the homogeneity and delocalization of the resulting devitrified silica layer. Distinguished from the heterogeneous devitrification sought to be prevented. Preferably, regardless of whether the container is treated or untreated, the bulk of the silica container is substantially free of alkaline earth metals, alkali metals and other impurities, and the surface of the silica container is Preferably, it is substantially free of non-uniformly distributed alkaline earth metals and alkali metal impurities on its outer and inner surfaces. Suitable quality silica containers are available, for example, from General Electric Co., Quartz Products
It is commercially available from various sellers, including the Department (Cleveland, Ohio).

Although the specific geometry of the silica container is not limited, the container is generally cup-shaped and has an outer surface defining an at least partially closed structure capable of containing or retaining a liquid, such as molten silicon, and Has an inner surface. Referring to FIG. 1, an exemplary silica container is an untreated silica crucible 10. Crucible 1
The 0 generally has an inner surface 12, an outer surface 14, a centerline 15, and an upper end 16. Inner surface 12 defines an open cavity 24 into which polycrystalline silicon is loaded. Crucible 10
It includes a bottom portion 17, a corner portion 18, and a side or wall portion 19, which are hereinafter referred to respectively as crucible 1
0, referred to as the bottom 17, corner 18, and wall 19. In the embodiment shown, wall 19 is substantially vertical and bottom 17 is substantially horizontal. More precisely, the wall 19 comprises an upper part 19a, an intermediate part 19
b, and a substantially vertical peripheral region including the bottom portion 19c, the top portion, the middle portion, the bottom portion, 19a,
9b and 19c each occupy about 1/3 of the total surface area of the wall 19. Top, middle, bottom, 19a, 19b,
The approximate division of 19c is shown generally by non-solid line 21.

The bottom 17 is parabolic with a slope having a horizontal component substantially greater than a vertical component. The corner 18 is a curved annular boundary area near the intersection of the wall 19 and the bottom 17. Generally, as shown by line 22,
The corner 18 intersects the wall 19 at the end of the curve of the corner 18. The corner 18 has a radius of curvature smaller than the radius of curvature of the bottom 17 and generally intersects the bottom 17 where the radius of curvature changes. Corner 18 has an upper half and a lower half, each occupying about half of the total surface area of corner 18, with the upper half closer to wall 19 and the lower half closer to bottom 17. The center line 15 of the crucible 10 is substantially parallel to the wall 19 and intersects the geometric center point of the bottom 17.

[0024] The graphite support vessel supports the silica container during the formation of the silicon melt in the silica container and during the production of single crystal silicon from molten silicon. The graphite support vessel may be an untreated or a treated graphite support vessel. The untreated graphite support vessel consists essentially of carbon in graphite form. The treated graphite support vessel is a core vessel
sel), the heart vessel consists essentially of graphite, has an inner surface and an outer surface, at least a portion of the inner and / or outer surface of the heart vessel is currently known in the art. (E.g., coating) by various methods, or later developed. Such processing methods are currently available, for example, on surfaces with SiC, Ti
It involves forming a coating of C, NbC, TaC, ZrC, BN, or glassy carbon, or growing such a coating in situ on the surface of the heart vessel.

Although the specific geometry of the graphite support vessel is not limited, the support vessel is generally cup-shaped,
An inner surface defining a structure adapted to receive the silica container such that at least a portion of the inner surface of the support container contacts at least a portion of the outer surface of the container to load the silica container into the graphite support container. And has an outer surface. The area of contact between the inner surface of the support vessel and the outer surface of the container defines an interface area. The support vessel is
It is preferably further adapted for use in a Czochralski crystal puller. Referring to FIG. 2, an exemplary graphite support vessel is an untreated graphite susceptor 30.

The susceptor 30 has an inner surface 32 and an outer surface 3
4, having a centerline 35, and an upper end 36. The inner surface 32 of the susceptor 30 defines an open cavity 44 and the bottom portion 3
7, corner portion 38 and side or wall portion 39
, Each of which is hereinafter referred to as susceptor 30
, Are referred to as the bottom 37, corner 30, and wall 39.
In the embodiment shown, the susceptor bottom 37
Are substantially horizontal and the susceptor wall 39 is substantially vertical. More specifically, the bottom 37 is approximately parabolic and has a slope with a horizontal component that is substantially greater than the vertical component. The susceptor wall 39 defines a peripheral area that includes a top portion 39a, a middle portion 39b, and a bottom portion 39c, and includes a top portion, a middle portion, a bottom portion, 39a, 39c.
b and 39c each occupy about 1/3 of the total surface area of the wall 39. Top part, middle part, bottom part, 39a, 39b,
The approximate division of 39c is shown generally by non-solid line 41.

The wall 39 at the upper end 36 of the susceptor 30
Is slightly larger than the diameter of the wall 39 measured at a lower position of the wall 39, for example, at the bottom portion 39b of the wall 39, with respect to true vertical. Opened slightly conical. The slightly conical opening wall 39 facilitates the storage of the silica crucible 10 or other silica container in the open cavity 44. The corner 38 of the susceptor
A curved annular boundary region near the intersection of the wall 39 and the bottom 37. The corner 38 intersects the wall 39 where the curvature of the corner 38 ends, generally as indicated by line 42. The corner 38 has a radius of curvature that is smaller than the radius of curvature of the bottom 37 and generally intersects the bottom 37 where the radius of curvature changes. Corner 38 has an upper half and a lower half, each occupying about half of the total surface area of corner 38, with the upper half closer to wall 39 and the lower half closer to bottom 37. The center line 35 of the susceptor 30 is substantially parallel to the wall 39 and intersects the geometric center of the bottom 37. The base 46 is adapted to couple to a movable pedestal 52 of a Czochralski crystal puller.

FIG. 3 shows the crucible 10 positioned within and supported by the susceptor 30 in a Czochralski crystal puller 50, with the base 46 of the susceptor 30 mounted on a movable pedestal 52. . This arrangement is typical for producing single crystal silicon using the batch Czochralski method. Bottom 3
7, a portion of the inner surface 32 of the susceptor 30 defined by the corner 38 and the bottom portion 39b of the wall 39 is in contact with the outer surface 14 of the corresponding portion 17, 18 and 19b of the crucible 10. The interface area of the container-support vessel system is defined by this area of contact between the crucible and the susceptor. However, in general, the extent and specific location of the interfacial area will depend on the particular design of the silica container and the graphite support container. Such designs are generally compatible with structural support and heat transfer considerations.
derations). Furthermore, the contact area defining the interface area changes with time during the crystal growth process, for a batch process.

Referring to FIG. 3, after the silicon melt is formed in the silica crucible 10, molten silicon 48 below the melt surface 58 is applied to the walls 19, corners 18 and bottom 17 of the crucible 10 by hydrostatic force. (Gravity) work. As the heated silica container softens at the melting temperature, hydrostatic / gravitational forces act to force the softened silica container against the graphite support container. However, in the batch method, as the silicon ingot is formed, the water level of the molten silicon decreases, and thus, as the single crystal ingot is raised, the walls 19, corners 18,
And the hydrostatic pressure acting on the bottom 17 is reduced, whereby the upper portions 19a, 39a of the walls 19, 39 separate from one another, so that as the crystal is pulled up, the outer surface 14 of the crucible wall 19 and the support vessel wall 39 The amount of contact with the inner surface 32 is reduced. Thus, it is generally possible to define a small area of the interface area based on the contact time between the silica container wall and the support container wall: (1) substantially above the initial melt line (ie, A non-contact area located above the initial water level of the surface 58); (2) a temporary contact area located substantially below the initial melt line but substantially above the final melt line. And (3)
A continuous contact area where the hydrostatic pressure and / or the weight of the silica container is substantially located at the point where the hydrostatic pressure and / or the weight of the silica container presses the softened container against the support container during the entire crystal pulling process.

With respect to the container / support vessel system shown in FIGS. 1-4, the non-contact areas are the walls of the silica container and the graphite susceptor, shown as the upper portions 19a and 39a of the container and support vessel walls, respectively. It roughly corresponds to the upper third of the interface area with the wall. The temporary contact area generally corresponds to the lower 2/3 of the wall and the upper half of the corner component. For example, in FIGS. 1-4, the temporary contact area comprises the wall portions 19b, 19c, 39
b, 39c, and the upper half of corners 18, 38. The continuous contact area is generally at the bottom 17, 37,
And the lower half of corners 18, 38.

The dimensions of the crucible 10 and susceptor 30 shown in FIGS. 1, 2 and 3 are exemplary.
The geometries of the silica container and the graphite support vessel may differ substantially from the illustrated embodiment and still fall within the scope of the present invention. One alternative design for the silica container and the graphite support container is shown in FIG. In this design, a dual container system comprising an internal crucible 10 'and an external crucible 10 "located in and supported by a graphite support vessel (susceptor 30') is a continuous Czochralski process. Used to produce single crystal silicon.

Regardless of whether the graphite support vessel has been treated or untreated, and regardless of the particular geometry of the support vessel, alkali metals and / or impurities present in the bulk of the graphite support vessel and on its surface as impurities. Alternatively, the cumulative concentration of the alkaline earth metals, especially calcium, magnesium, strontium, lithium, sodium and potassium, is generally that of the silica container in the interfacial area while the polycrystalline silicon melts and the single crystal silicon ingot is pulled up from the molten silicon. Concentration must be low enough to prevent substantial heterogeneous devitrification of the

As used herein, “substantially heterogeneous devitrification” means localized crystallization of vitreous silica, which results in the structural integrity of the silica container (eg,
Cusping, fluxin
g), commercially significant reduction in pitting, blistering, bowing, and / or other deformations) and / or zero discs in the growth of single crystal silicon ingots from silicon melts formed in silica containers. This results in a commercially significant decrease in location length. The reduction in zero dislocation length is preferably less than about 10%, more preferably less than about 5%, even more preferably less than about 1%, and most preferably less than about 0.5%. At present, a reduction in zero dislocation length of more than 0.5% is considered commercially significant, but in the future a smaller reduction will be significant. Would.

[0034] Substantial heterogeneous devitrification is generally indicated by several observable features, such as excessive formation of a white powder with significant pitting, cuffing and / or fluxing. Fluxing is associated with local softening of the silica container and is manifested by a visually shiny or shiny appearance of the outer surface of the silica container. Fluxing is an indicator particularly related to disadvantageous heterogeneous devitrification. Thus, the cumulative concentration of alkali metals and / or alkaline earth metals, especially calcium, magnesium, strontium, lithium, sodium and potassium present in the graphite support vessel is about 1 cm.
Preferably, it is low enough to prevent fluxing of more than ^two areas. Cumulative concentration is about 0.5c
More preferably, less than m ² is low enough to be fluxed.

Generally, the concentration of said impurities, especially calcium, in the untreated graphite support vessel used with the untreated silica container is about 1.0 ppm or about 1.0 ppm, based on the weight of the graphite material making up the graphite support vessel. The following is preferable (for example, see Example 1). The concentration of said impurities present in such a graphite support vessel is preferably less than about 0.7 ppm by weight, more preferably less than about 0.5 ppm by weight, even more preferably less than about 0.2 ppm by weight, most preferably Less than about 0.1 ppm by weight.

As mentioned above, when either the inner surface of the support vessel or the outer surface of the silica container is treated, such that at least one surface of the interfacial region is the treated surface, substantial heterogeneous loss occurs. Without transparency, higher concentrations of alkali and alkaline earth metals, especially Ca impurities, are acceptable. The exact upper concentration of alkali metal and / or alkaline earth metal impurities that prevent substantial heterogeneous devitrification depends on the cleanliness of the silica container and / or graphite support vessel surface, specific crucible dimensions and loadings. It will vary depending on factors including the hot zone temperature distribution used (temperature and time), whether the silica container and / or graphite support vessel is being processed, and the like. Nevertheless, improved quality single crystal silicon can be obtained according to the above-mentioned indicators and preferred concentration limits.

[0037] Once the polycrystalline silicon is loaded into a suitable silica container / graphite support system, the crucible is placed in a conventional CZ silicon crystal growth apparatus until a pool of molten silicon is formed in the silica container. The polycrystalline silicon is heated to melt the polycrystalline silicon. The heating profile is not limited, but generally depends on the type of loading (ie, chunk loading, granular loading, or mixed loading), the size and design of the crucible, the size and type of crystal grower, etc. And change. In a typical arrangement,
Referring to the crucible / susceptor system shown in FIGS. 3 and 4, a pedestal 52 supporting the base 46 of the susceptor 30 is positioned such that the bottom 17 of the crucible 10 is near the top of the heater 54. The crucible 10 is gradually lowered into the space inside the heater 54. Crucible 10
The rate at which is gradually lowered in proximity to heater 54, and other factors that affect the melting of polycrystalline silicon, such as heater power, crucible rotation and system pressure, are generally known in the art.

Typically, the temperature of the area of contact between crucible 10 and susceptor 30 at corners 18, 38 is about 18 inches (about 46 cm) in diameter loaded with about 60 kg of polycrystalline silicon during a melting period of about 4 hours. As for the crucible,
At least about 1500 ° C., or from about 4 hours to
During a melting period of about 6 hours, the temperature is at least about 1550 ° C. for an 18 inch diameter crucible loaded with about 70 kg of polycrystalline silicon. Higher temperatures (preferably at least about 1575 ° C., at least about 16
00 ° C., or at least about 1625 ° C.) can be used in such 18 inch / 60 kg or 18 inch / 70 kg systems without detrimentally affecting the structural integrity of the silica container or graphite support container. Short melting periods can be achieved. The advantages of the present invention are particularly pronounced when using larger diameter silica containers and / or higher loadings.

For example, during a melting period of about 7 to about 10 hours, about 100 kg of polycrystalline silicon is loaded with a diameter of 22 kg.
For an inch (about 56 cm) crucible, or for a similar crucible using a larger charge of 120 kg and a melting time of about 10 hours, the temperature of the high heat-fluxing corner region is preferably at least 1600 ° C. However, even higher temperatures (at least about 1675 ° C.
Or at least about 1700 ° C.) can be used in such a 22 inch / 120 kg system to achieve proportionately shorter melting times (eg, about 6 to about 8 hours). Large silica container, for example, about 140kg
24 inch diameter (approximately 61
cm), the corner temperature is preferably at least about 1650 ° C., and at least about 1675 ° C.
° C or at least about 1700 ° C. The melting period of such a 24 inch / 140 kg system varies with temperature, but generally ranges from about 10 hours to about 12 hours at about 1650 ° C, and from about 1675 ° C to about 17 hours.
At a temperature of 00 ° C., it is from about 8 hours to about 10 hours.
As another example, a 32 inch (about 81 cm) diameter crucible loaded with polycrystalline silicon in an amount of about 160 kg to about 200 kg may be at least about 1650 ° C., more preferably at least about 1675 ° C. or at least about 1700 ° C. Can be heated to corner temperature. For such a commercially reasonable 32 inch / 160-200 kg system,
These higher temperatures are preferred so that the melting time is for example about 12 to about 15 hours.

The silica container diameters, loadings and melting times described above, and in particular, the combination of such parameters with various temperatures, are cited as being illustrative of the advantages of the present invention. Is not intended to limit the scope of the invention. One of ordinary skill in the art will readily appreciate that the use of a low-impurity support vessel as described above generally allows the silica container to be heated to higher temperatures without the deleterious effects on crystal growth associated with known systems. There will be. The ability to use higher temperatures means that higher loadings and / or reduced melting times can increase productivity.

In order to flush out undesired gases such as CO (g) and SiO (g) generated from the reaction of SiO (g) with hot graphite, polycrystalline silicon is generally purged during heating with a purge gas. Exposure to
The purge gas is generally an inert gas, such as argon, and generally flows at a rate of about 10 L / min to 300 L / min, depending on the type and size of the crystal puller.

Once the silicon melt is formed, the single crystal silicon ingot is pulled up from the molten silicon by the Czochralski method. Referring to FIGS. 3 and 4, a single crystal silicon ingot 55 is provided in a Czochralski crystal puller 50 by a silica crucible 1 supported by a graphite susceptor 30.
0 from the silicon melt formed. Specific methods and conditions for pulling single crystal silicon ingots are known in the art. While the single crystal silicon melt is raised, the elevated temperature set during melt formation is generally maintained.

Advantageously, when the high purity graphite support vessel (eg, susceptor 30) of the present invention is used to support a silica container (eg, crucible 10), it is subjected to the highest heat fluxing and highest. A portion of a graphite support vessel having a temperature (eg, generally,
The temperature in the corner region of the support vessel) during the growth of the single crystal silicon ingot therefrom (generally, at least about 4 hours or at least about 5 hours) will cause substantial heterogeneous devitrification of the silica container in the interface area. About 1500 ° C. or higher, or if necessary, about 1525 ° C., 1550 ° C., 1575 ° C., 16 ° C.
00 ° C, 1625 ° C, 1650 ° C, 1675 ° C, 170
It can be maintained at 0 ° C. or higher. Graphite support container (eg, susceptor 30)
Although the temperature of the susceptor varies during the formation of the silicon melt and crystal pulling, and may vary locally between different portions of the support vessel for a period of time, the time average temperature at a particular location of the susceptor is generally Higher for larger diameter crucibles with larger loading capacity of polycrystalline silicon.

In general, the upper limit of the concentration of alkali and alkaline earth metal impurities in a graphite support vessel decreases as any or all of the following parameters increase: crucible size (eg, diameter), loading (eg, Weight), temperature of the support vessel at the corner roundness, time at a temperature above about 1500 ° C. The above concentration and temperature values are to be considered merely exemplary and suggestive; in general, for any system or geometry, the most preferred concentrations of alkali and alkaline earth metals are as described above. Thus, the concentration is low enough to prevent substantial heterogeneous devitrification of the silica container in the interfacial region while the polycrystalline silicon is melted and the single crystal silicon ingot is pulled up from the molten silicon.

High purity graphite support vessels having alkaline earth metal and alkali metal impurities, especially calcium impurities, present in concentrations suitable for use in the present invention can be used to provide fillers and fillers having lower concentrations of such impurities. Special attention is paid to the choice of binder raw materials and such support vessels are now being constructed, with particular emphasis on the purification steps to ensure a sufficiently low concentration of alkali or alkaline earth metal impurities. It can be manufactured by the same general method. A detailed description of the graphite production method can be found in T. Ishikawa & T. Nagaoki (English Editor ICLewi
s) Recent Carbon Technology , especially pp. 22-58, JEC Press,
1983.

Briefly, with reference to FIG. 5, the filler material (eg, calcined petroleum coke) is comminuted, sieved, blended to a relatively uniform particle size, and then combined in a kneading step. Agent (eg, coal tar pitch)
Mix with. After mixing the filler material and the binder material, the resulting mixture is formed into the desired shape (eg, an ingot), generally by a molding or extrusion process.
Next, the formed material is baked in a carbonization step,
The resulting carbonized material is graphitized as such or following an impregnation and re-baking step to increase its density and / or following a high temperature purification step. Typically, such purification steps reduce the baked and / or graphitized carbon to about 250
Including prolonged exposure to halogen gas at a temperature of 0 ° C. Alkali and alkaline earth metal impurities are removed during the graphitization step and / or by a purification process in which the impurities are removed using a high temperature purification method.
Next, the graphite material is machined to form the graphite support container of the present invention. Manufacturers of graphite support vessels (eg, UCAR, Clarksburg, WVa)
The purity levels required for the graphite support vessels of the present invention can be achieved.

The following examples illustrate the principles and benefits of the present invention.

[0048]

EXAMPLES Example 1 Production of Single Crystal Silicon Using Graphite Susceptors with Various Concentrations of Calcium In some experimental runs, a single crystal silicon ingot was prepared from a silicon melt formed in an untreated vitreous silica crucible. Manufactured. Silica crucibles were supported by graphite susceptors having various concentrations of calcium (about 0.1 ppm to about 1.8 ppm). The number of neck attempts to pick up the silicon ingot was recorded.

Following the production of single crystal silicon, the quality of the vitreous quartz crucible used in each run was observed with particular attention to the level of devitrification, pitting, casping and fluxing of the crucible wall. Crucibles used with susceptors having high concentrations of calcium (0.8 ppm to about 1.7 ppm) have been observed to have severe devitrification, with a considerable amount of pitting, casping and fluxing of the crucible walls Was done. In contrast, silica crucibles used with graphite susceptors having low concentrations of calcium (about 0.1 ppm to about 0.2 ppm), with minimal amount of crucible wall cusping, pitting and fluxing, It was observed to have at most a slight devitrification.

The presence or absence of dislocation (dislocation) in the obtained single crystal ingot was also determined. The results are summarized in FIG. 6, which illustrates whether zero dislocation growth of single crystal silicon was obtained using graphite susceptors with various concentrations of calcium using various numbers of neck trials. FIG. 6 shows that the high calcium content (about 0.8 ppm-
About 1.7ppm) or low calcium content (about 0.1ppm ~
(Approximately 0.2 ppm). The data in FIG. 6 show that for runs where the silicon crystal was taken in a low number of neck attempts, zero dislocation growth was achieved 100% with the low calcium content susceptor and the high calcium content It shows that only 60% was achieved with the quantity susceptor. Regardless of the number of neck attempts required to initiate crystal growth, considering all data, at 72% of the cases with low calcium content susceptors,
Zero dislocation was achieved, but only at 40% with a high calcium content susceptor. Thus, it is clear that the use of a low calcium content susceptor significantly affects the degree to which zero dislocation growth of single crystal silicon is achieved.

In view of the foregoing detailed description and examples of the present invention, it is understood that several objects of the present invention have been attained. The description and examples set forth herein are:
It is intended to inform those skilled in the art about the present invention, its principles, and its practical application. Those skilled in the art can adapt and apply the invention in a number of forms to best suit the needs of a particular application. Accordingly, the specific embodiments of the invention described above are not exhaustive or limiting of the invention.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of an empty graphite susceptor suitable for use to support the crucible of FIG.

FIG. 3 includes a cross-sectional view of the crucible of FIG. 1 disposed in and supported by the susceptor of FIG.
1 is a schematic view of a Czochralski-type crystal pulling device having a shape generally used in a batch method.

FIG. 4 includes a cross-sectional view of an internal crucible and an external crucible, wherein the external crucible is disposed within and supported by the susceptor, a Czochralski crystal puller of a shape commonly used in a continuous process. Schematic diagram.

FIG. 5 is a schematic block diagram showing a manufacturing process of a graphite support container.

FIG. 6 shows a single crystal during various runs of various numbers of neck trials using silica crucibles supported by graphite susceptors having calcium concentrations of 0.1 ppm to 0.2 ppm, or 0.8 ppm to 1.7 ppm. Plot showing whether zero dislocation growth of silicon has been achieved.

[Explanation of symbols]

10 Crucible 10 'Internal crucible 10 "External crucible 12 Inner surface 14 Outer surface 15 Centerline 16 Top end 17 Bottom part 18 ..Corner portion 19 ... Wall portion 19a ... Top portion 19b ... Intermediate portion 19c ... Bottom portion 21 ... Non-solid line 22 ... Line 30 ... Susceptor 30 '... Susceptor 32 ... inner surface 34 ... outer surface 35 ... center line 36 ... upper end 37 ... bottom part 38 ... corner part 39 ... wall part 39a ... upper part 39b ...・ Intermediate part 39C ・ ・ ・ Bottom part 41 ・ ・ ・ Non-solid line 42 ・ ・ ・ Line 44 ・ ・ ・ Open cavity 46 ・ ・ ・ Base 48 ・ ・ ・ Molten silicon 50 ・ ・ ・ Crystal take-off device 52 ・ ・ ・ Movable pedestal 54 ... heater 55 ... single crystal silicon Down ingot 58 ... melt surface

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Richard El Hansen United States 44117 Cleveland, Ohio 21800 tungsten boulevard

Claims (5)

[Claims] 1. A method for producing a single crystal silicon ingot from polycrystalline silicon by a Czochralski type method, comprising forming a pool of molten silicon in a silica container having an outer surface; Contacting at least a portion of the inner surface with the outer surface of the silica container to support the silica container by a graphite support container having the inner surface; and lifting the single crystal silicon ingot from the molten silicon; Calcium concentration of about 1 ppm by weight
The method characterized by not exceeding. 2. In a region where the inner surface of the corner portion of the support container contacts the outer surface of the corner portion of the silica container, the graphite support container is heated to a temperature of at least about 1575 ° C. for a period of at least about 4 hours. The method according to claim 1, wherein is obtained. 3. A method for producing a single crystal silicon ingot from polycrystalline silicon by a Czochralski type method, comprising forming a pool of molten silicon in a silica container having an outer surface; Contacting at least a portion of the inner surface with the outer surface of the silica container to support the silica container by a graphite support container having the inner surface; and lifting the single crystal silicon ingot from the molten silicon; Wherein the cumulative concentration of alkaline earth metal and alkali metal present in the slag does not exceed about 1 ppm by weight. 4. A graphite support for supporting a silica container during the production of single crystal silicon from a silicon melt formed in the silica container by a Czochralski-type process, the support being essentially graphite. A body having an inner surface defining an open cavity capable of nesting the silica container, wherein at least a portion of the inner surface of the body is in contact with the outer surface of the silica container, A body for supporting a silica container during formation of the silicon melt in and production of single crystal silicon from the melt, wherein the concentration of calcium present in the body does not exceed about 1 ppm by weight. Graphite support container. 5. A graphite support for supporting a silica container during the production of single crystal silicon from a silicon melt formed in the silica container by a Czochralski-type process, the support being essentially graphite. A body having an inner surface defining an open cavity capable of nesting the silica container, wherein at least a portion of the inner surface of the body is in contact with the outer surface of the silica container, A body supporting a silica container during the formation of a silicon melt in the melt and the production of single crystal silicon from the melt, wherein the cumulative concentration of alkaline earth metal and alkali metal present in the graphite body is about 1%. A graphite support container characterized by not exceeding ppm by weight.