JP7172844B2 - Silica glass crucible for pulling silicon single crystal and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a quartz glass crucible used for pulling a silicon single crystal by the Czochralski method (CZ method) and a method for producing the same.

A silica glass crucible is used for pulling a silicon single crystal by the CZ method. In the CZ method, a polycrystalline silicon raw material is heated in a quartz glass crucible to form a silicon melt, a seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled up while rotating the crucible. grow a large single crystal at the bottom of the According to the CZ method, it is possible to grow single crystals with a large diameter and improve the productivity of silicon single crystals.

Regarding quartz glass crucibles, Patent Document 1, for example, describes a quartz glass crucible having a three-layer structure in which the outer layer of the crucible is an Al-added quartz layer, the intermediate layer is a natural or synthetic quartz layer, and the inner layer is a transparent quartz layer. Further, in Patent Document 2, at least the inner layer of the corner portion is a transparent synthetic layer, the intermediate layer is a transparent or opaque natural layer or natural synthetic mixed layer, and the outer layer is an opaque natural layer. A crucible structure with decreasing thickness is described.

Further, in Patent Document 3, a semi-fused silica layer is provided on the surface of the outer surface layer, the center line average roughness (Ra) of the semi-fused silica layer is 50 to 200 μm, and the preferred layer thickness of the semi-fused silica layer is A quartz glass crucible is described which is 0.5 to 2.0 mm. Furthermore, in Patent Document 4, a quartz glass crucible having an outermost layer in which unmelted or semi-fused silica powder is unevenly distributed is manufactured, and solid silica powder is sprayed on the outer surface at a spray pressure of 0.1 to 5 MPa, It describes a method for optimally controlling silica powder that separates from the outermost layer of the crucible without grinding, by spraying high-pressure water at a spray pressure of 24 to 40 MPa, followed by hydrofluoric acid aqueous solution treatment.

JP-A-2000-247778 International publication 2004/106247 pamphlet JP 2009-84114 A JP 2010-202515 A

According to the conventional quartz glass crucible having an Al-added layer on the outer layer of the crucible, the strength of the crucible can be improved by crystallizing the outer surface of the crucible. However, if the aluminum concentration is high, there is a problem that the crystal layer foams and exfoliates, reducing the strength of the crucible.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a silica glass crucible capable of quickly crystallizing the outer surface of the crucible to increase the strength of the crucible and suppressing foaming and exfoliation of the crystal layer, and a method of manufacturing the same. It is in.

In order to solve the above-mentioned problems, the quartz glass crucible for pulling a silicon single crystal according to the present invention comprises a transparent layer made of silica glass containing no air bubbles, and silica glass provided outside the transparent layer and containing a large number of air bubbles. A bubble layer and an outer half-molten layer formed by sintering raw silica powder in a semi-molten state provided outside the bubble layer, wherein the bubble layer is an inner bubble layer made of silica glass to which aluminum is not added. and an Al-added outer bubble layer made of silica glass to which aluminum is added, provided outside the inner bubble layer, and at least part of the outer semi-molten layer in contact with the Al-added outer bubble layer is made of aluminum is added, and the average concentration of aluminum contained in the Al-added semi-molten layer is 30 ppm or more and 95 ppm or less.

According to the present invention, the strength of the crucible can be increased by crystallizing the entire outer surface of the crucible during the step of pulling the silicon single crystal. In particular, the existence of the aluminum-added semi-molten layer on the outer surface of the crucible can speed up the initial crystallization of the outer surface of the crucible. can be made As a result, a slight gap can be formed between the crucible and the carbon susceptor, and the gas in the quartz glass generated with the crystallization of the crucible can be discharged from this gap, and the crystal layer on the outer surface of the crucible can be discharged. It is possible to prevent a decrease in strength of the crucible and generation of particles due to foaming and peeling.

In the present invention, the thickness of the Al-added semi-molten layer is preferably 5 μm or more and 500 μm or less. If the thickness of the Al-added semi-molten layer is less than 5 μm, the effect as a crystal nucleus is weak, so initial crystallization is slow and the crucible cannot stand on its own. This leads to foaming and peeling of the crystal layer. On the other hand, when the thickness of the Al-added semi-molten layer is larger than 500 μm, the difference in thermal expansion coefficient between the excessively thick Al-added semi-molten layer and the glass layer causes external peeling during the silicon single crystal pulling process. Deformation of the crucible may make it impossible to continue the crystal pulling process. However, if the thickness of the Al-added semi-molten layer is 5 μm or more and 500 μm or less, the outer surface of the crucible can be crystallized early, and the crystallized outer surface of the crucible can be prevented from foaming and peeling.

A quartz glass crucible according to the present invention has a cylindrical side wall, a curved bottom, and a corner positioned between the side wall and the bottom and having a larger curvature than the bottom. It is preferable that the added outer bubble layer and the Al-added semi-molten layer are provided at least on the side wall portion. Thus, when the Al-added outer bubble layer and the Al-added semi-molten layer are provided at least on the side wall of the crucible, the strength of the side wall of the crucible can be increased and the crucible can stand on its own. can suppress deformation of the side wall portion of the

It is preferable that the bubble layer on the side wall portion has a two-layer structure of the inner bubble layer and the Al-added outer bubble layer, and the bubble layer on the bottom portion has a single-layer structure of the inner bubble layer. In this case, the lower end portion of the Al-added outer cell layer has a tapered shape, and the thickness reduction rate of the lower end portion is preferably 0.5 mm/mm or less, and preferably 0.2 mm/mm. is more preferred. If the rate of decrease in the thickness of the lower end portion of the Al-added outer bubble layer is moderate, it is possible to prevent cracks from occurring due to concentration of stress at the interface between the Al-added layer and the Al-free layer.

It is preferable that the bubble content rate of the Al-added outer bubble layer in the side wall portion is higher than the bubble content rate of the inner bubble layer. According to this, it is possible to increase the strength of the crucible as well as the heat insulating property, and it is possible to suppress the increase in temperature of the inner surface of the crucible.

In the present invention, the aluminum concentration in the surface layer portion of the Al-added semi-molten layer is 100 ppm or more, and the aluminum concentration in the deep layer portion of the Al-added semi-molten layer, which is deeper than the surface layer portion, is higher than the aluminum concentration in the surface layer portion. is preferably low. When the concentration of aluminum in the surface layer portion of the Al-added semi-molten layer is higher than that in the deep layer portion, the effect of promoting crystallization by the Al-added semi-molten layer can be enhanced. Since the Al-added semi-molten layer is formed by cooling the raw material silica powder to which Al is added in a semi-molten state, the Al concentration increases as it approaches the surface where the original shape is maintained. On the other hand, excess raw silica powder adhering to the surface of the Al-added semi-molten layer is removed by washing with high-pressure water, and the aluminum concentration on the surface of the Al-added semi-molten layer changes depending on the degree of washing at this time. Note that the aluminum concentration distribution in the Al-added semi-molten layer is microscopically uneven, and in particular, a portion with a high Al concentration is unevenly distributed in a mesh-like manner within a region of 1 mm ³ in the Al-added semi-molten layer. It is preferable that a high-concentration region where the Al concentration is higher than 60 ppm and a low-concentration region where the Al concentration is lower than 25 ppm are mixed.

In conventional quartz glass crucibles, the semi-molten layer on the outer surface is not formed, or even if it is formed, the thickness thereof is very thin, so that the initial crystallization of the outer surface of the crucible does not occur. In contrast, in the present invention, for example, by weakening the current flowing through the arc electrode in the second half of the arc melting process, the temperature gradient during heating of the raw material silica powder is moderated, and the rate of progress of vitrification is slowed down. The arc is then continued in that low current state. Arc melting time is longer than usual. As a result, the thickness and shape of the quartz glass are almost the same as in the normal case, but the outer surface semi-molten layer is formed thicker than normal. In particular, in the present invention, by forming an outer surface semi-molten layer having a high aluminum concentration, it is possible to promote crystallization of the outer surface of the crucible while preventing foaming and peeling of the crystal layer.

Further, the method of manufacturing a silica glass crucible for pulling a silicon single crystal according to the present invention includes a step of filling the inner surface of a rotating mold with Al-added silica powder and Al-free silica powder in order to form a deposited layer of silica powder. a transparent layer made of silica glass containing no bubbles by heating and melting the deposited layer of silica powder from the inside of the mold and adjusting the depressurizing force of the deposited layer from the inner surface side of the mold; , a bubble layer made of silica glass containing a large number of bubbles provided outside the transparent layer, and an outer semi-molten layer provided outside the bubble layer and formed by sintering raw silica powder in a semi-molten state. forming a quartz glass crucible; and adjusting the thickness of the outer semi-molten layer of the quartz glass crucible taken out of the mold to 5 μm or more and 500 μm or less. The average concentration is 30 ppm or more and 95 ppm or less.

ADVANTAGE OF THE INVENTION According to the present invention, there is provided a quartz glass crucible capable of not only crystallizing the entire outer surface of the crucible during the process of pulling a silicon single crystal, but also preventing the crystal layer from foaming and peeling, thereby increasing the strength of the crucible. can be manufactured.

In the present invention, the deposited layer of silica powder is preferably formed by depositing Al-added natural silica powder , Al-free natural silica powder and synthetic silica powder in this order. Thereby, a highly pure transparent layer can be formed on the inner surface of the crucible, and contamination of the silicon melt in the crucible can be prevented.

ADVANTAGE OF THE INVENTION According to this invention, the quartz-glass crucible which can crystallize the outer surface of a crucible, and can raise the intensity|strength of a crucible, and its manufacturing method can be provided, preventing foaming peeling of a crystal layer.

FIG. 1 is a schematic side sectional view showing the structure of a quartz glass crucible according to an embodiment of the invention. FIG. 2 is a schematic cross-sectional view showing an enlarged structure of a portion (X portion) of the side wall portion of the quartz glass crucible of FIG. FIG. 3 is a schematic diagram for explaining the state of the quartz glass crucible during crystal pulling. FIG. 4 is a schematic diagram for explaining the method for manufacturing a quartz glass crucible according to this embodiment. FIG. 5 is a schematic diagram for explaining the manufacturing method of the quartz glass crucible according to the present embodiment together with FIG. FIG. 6 is a schematic diagram for explaining the manufacturing method of the quartz glass crucible according to the present embodiment together with FIGS. 4 and 5. FIG.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic side sectional view showing the structure of a quartz glass crucible according to an embodiment of the invention. FIG. 2 is a schematic cross-sectional view showing an enlarged structure of a portion (X portion) of the side wall portion of the silica glass crucible of FIG.

As shown in FIGS. 1 and 2, this silica glass crucible 1 is a silica glass container for supporting silicon melt, and includes a cylindrical side wall portion 10a, a gently curved bottom portion 10b, It has a corner portion 10c located between the side wall portion 10a and the bottom portion 10b and having a larger curvature than the bottom portion 10b.

The diameter (aperture) of the quartz glass crucible 1 is 24 inches (approximately 600 mm) or more, preferably 32 inches (approximately 800 mm) or more. This is because such a large-diameter crucible is used for pulling a semiconductor silicon single crystal ingot having a diameter of 200 mm or more, and is required to be resistant to deformation even when used for a long period of time.

The thickness of the crucible varies slightly depending on its location, but the thickness of the side wall portion 10a of a crucible of 24 inches or more is 8 mm or more, and the thickness of the side wall portion 10a of a large crucible of 32 inches or more is 10 mm or more to 40 inches (about 1000 mm). ), the wall thickness of the side wall portion 10a of the above large crucible is preferably 13 mm or more. This is because a large-capacity crucible must be thick enough not to be deformed by pressure from a large amount of silicon melt.

The quartz glass crucible 1 according to the present embodiment includes a transparent layer 11 (bubble-free layer) made of silica glass containing no air bubbles, and a bubble layer made of silica glass provided outside the transparent layer 11 and containing a large number of minute air bubbles. 12 (opaque layer), and an outer semi-molten layer 13 provided outside the bubble layer 12 and formed by cooling raw silica powder in an unmelted or semi-molten state.

The transparent layer 11 is a layer forming the inner surface 10i of the crucible that comes into contact with the silicon melt, and is provided to prevent the single crystallization rate from decreasing due to air bubbles in the quartz glass. The transparent layer 11 preferably has a thickness of 0.5 to 10 mm. thickness. Similar to the bubble layer 12, the transparent layer 11 is preferably provided over the entire crucible from the side wall portion 10a to the bottom portion 10b of the crucible. It is also possible to omit the formation of

The fact that the transparent layer 11 does not contain air bubbles means that the air bubble content and air bubble size are such that the single crystallization rate does not decrease due to the air bubbles. If there are bubbles near the inner surface of the crucible, the inner surface of the crucible will be melted away, making it impossible to confine the bubbles in the quartz glass, and the bubbles in the quartz glass will burst due to thermal expansion during crystal pulling. This is because the crucible fragment (quartz piece) may be peeled off by doing so. If the crucible fragments released into the melt are transported by the melt convection to the growth interface of the single crystal and incorporated into the single crystal, they cause dislocations in the single crystal. In addition, when the bubbles released into the melt due to the melting of the inner surface of the crucible float to the solid-liquid interface and are incorporated into the single crystal, they cause pinholes. The bubble content in the transparent layer 11 is preferably 0.1 vol % or less, and the average diameter of the bubbles is preferably 100 μm or less.

The bubble content and bubble diameter of the transparent layer 11 can be non-destructively measured using optical detection means. The optical detection means includes a light receiving device for receiving transmitted light or reflected light of the light irradiated to the crucible. The light-emitting means for the irradiation light may be built in the light-receiving device, or an external light-emitting means may be used. Preferably, the optical detection means is one that can be rotated along the inner surface of the crucible. As irradiation light, visible light, ultraviolet light, infrared light, X-rays, laser light, or the like can be used. A digital camera including an optical lens and an imaging device can be used as the light receiving device. The result of measurement by the optical detection means is taken into an image processing device, and the bubble content per unit volume is calculated.

In order to detect bubbles existing at a certain depth from the crucible surface, the focal point of the optical lens should be scanned in the depth direction from the surface. Specifically, an image of the inner surface of the crucible is photographed using a digital camera, the inner surface of the crucible is divided into certain areas to obtain a reference area S1, and the air bubble occupied area S2 is obtained for each reference area S1. The content rate Ps=(S2/S1)×100(%) is calculated.

In the calculation of the bubble content rate based on the volume ratio, the reference volume V1 is obtained from the depth at which the image was taken and the reference area S1. Further, assuming that the bubble is spherical, the volume V2 of the bubble is calculated from the diameter of the bubble. Then, from V1 and V2, the volume bubble content rate Pv=(V2/V1)×100(%) is calculated. In the present invention, this volumetric bubble content Pv is defined as "bubble content". In addition, the arithmetic mean value obtained from the bubble diameters calculated assuming that the bubbles are spherical is defined as the “average bubble diameter”.

The reference volume is 5 mm × 5 mm × depth (depth) 0.45 mm. Just do it. In addition, the focal length of the optical lens is shifted in the depth direction of the reference volume V1 to capture the bubble contained inside the reference volume and measure the diameter of the bubble.

The bubble layer 12 is the main layer that makes up the crucible wall. The bubble layer 12 is provided to improve heat retention of the silicon melt in the crucible and to disperse the radiant heat from the heater surrounding the crucible to heat the silicon melt in the crucible as uniformly as possible. Therefore, the bubble layer 12 is provided over the entire crucible from the crucible side wall portion 10a to the bottom portion 10b. The thickness of the bubble layer 12 is the thickness of the crucible wall minus the thickness of the transparent layer 11 and the outer semi-molten layer 13, and varies depending on the crucible site. The bubble content of the bubble layer 12 can be determined, for example, by measuring the specific gravity (Archimedes method) of an opaque quartz glass piece cut out from the crucible.

The bubble content of the bubble layer 12 is higher than that of the transparent layer 11, preferably 0.5 to 5 vol%, more preferably 0.5 to 4 vol%. This is because if the bubble content of the bubble layer 12 is 0.5 vol % or less, the function of the bubble layer 12 cannot be exhibited, and the heat retention is insufficient. Moreover, if the bubble content of the bubble layer 12 exceeds 5 vol %, the expansion of the bubbles may greatly deform the crucible, resulting in a decrease in single crystal yield and insufficient heat transfer. In particular, if the bubble content rate of the bubble layer 12 is 0.5 to 4 vol %, deformation of the crucible can be further prevented and heat transfer can be further enhanced.

In this embodiment, the bubble layer 12 of the bottom portion 10b of the crucible has a single layer structure of an inner bubble layer 12a made of silica glass to which aluminum is not added. On the other hand, the bubble layer 12 of the side wall portion 10a of the crucible includes an inner bubble layer 12a made of silica glass to which aluminum is not added, and an Al-doped layer 12a made of silica glass to which aluminum is added and provided outside the inner bubble layer 12a. It has a two-layer structure of the outer bubble layer 12b. When the outer layer of the crucible side wall portion 10a contains aluminum, crystallization of the outer surface 10o of the crucible side wall portion 10a can be promoted to increase the strength of the crucible.

The concentration of aluminum contained in the Al-added outer cell layer 12b is preferably 30 ppm or more and 95 ppm or less, and particularly preferably 50 ppm or more and 90 ppm or less. When the aluminum concentration is lower than 30 ppm, the outer surface of the crucible is crystallized in a patchy manner, and the entire surface cannot be uniformly crystallized. Also, when the aluminum concentration is higher than 95 ppm, the outer surface of the crucible can be crystallized to form a thick crystal layer, but the crystal layer becomes too thick and cracks occur, or before the crystal layer becomes thick, However, the crucible may not be supported by the crystal layer and may be deformed. However, if the aluminum concentration is within the above range, it is possible to crystallize the entire outer surface of the crucible and uniformly form a crystal layer with an appropriate thickness. Strength can be increased. The concentration of aluminum contained in quartz glass can be measured by secondary ion mass spectrometry.

The bubble content of the Al-added outer bubble layer 12b is preferably higher than the bubble content of the inner bubble layer 12a. According to this, it is possible to increase the strength of the crucible as well as the heat insulating property, and it is possible to suppress the increase in temperature of the inner surface of the crucible. The Al-added outer cell layer 12b can be formed using a raw material silica powder to which an aluminum compound is added. Together with this, the bubble content of the Al-added outer bubble layer 12b can be increased.

The lower end portion 12b _e of the Al-added outer bubble layer 12b provided on the side wall portion 10a of the crucible has a tapered shape, and the reduction rate of the thickness of the lower end portion _12b is preferably 0.5 mm/mm or less. Here, the rate of decrease in the thickness of the lower end of the Al-added outer bubble layer is the change in the thickness of the tapered shape of the Al-added outer bubble layer on the line along the outer surface of the crucible connecting the center of the bottom of the crucible and the upper end of the rim. talk about quantity. Thus, if the rate of decrease in the thickness of the lower end portion 12b _e of the Al-added outer bubble layer is gradual, stress concentrates on the boundary between the Al-added outer bubble layer 12b and the inner bubble layer 12a, causing cracks. can be prevented.

The outer semi-molten layer 13 is a layer formed by cooling silica powder, which is the raw material of the crucible, in an incompletely melted state. Since the outer semi-molten layer 13 has a surface condition rich in undulations, light incident from the outer surface side of the crucible is greatly scattered and reflected, and has a certain influence on the infrared transmittance of the unused crucible. .

The outer surface semi-molten layer 13 is provided on the entire outer surface of the crucible from the center of the bottom portion 10b of the crucible to the upper edge of the rim of the side wall portion 10a. A portion of the outer semi-molten layer 13 in contact with the Al-added outer bubble layer 12b is the Al-added semi-molten layer 13a made of the same raw material silica powder as the Al-added outer bubble layer 12b. On the other hand, the outer semi-molten layer 13 below the Al-added outer bubble layer 12b is an Al-free semi-molten layer 13b formed of normal raw material silica powder to which Al is not added (Al-free silica powder). be.

Whether or not the outer surface semi-molten layer 13 is formed on the outer surface of the crucible can be determined by measuring the outer surface of the crucible by X-ray diffraction. It can be determined by whether or not For example, when the object to be measured is a crystal layer, a peak indicating crystallinity is detected, but a halo pattern with a blurred diffraction image is not detected. Conversely, when the object to be measured is a non-crystalline layer (amorphous layer), a halo pattern in which the diffraction image is blurred is detected, and no peak indicating crystallinity is detected. When the outer surface semi-molten layer 13 formed on the outer surface of the crucible is removed, the surface of the glass is exposed and no peak is detected by the X-ray diffraction method. Thus, it can be said that the semi-molten layer is a layer in which a halo pattern in which the diffraction image is blurred and a peak indicating crystallinity are mixed when measured by the X-ray diffraction method. Further, it can be said that the crystalline layer is a layer from which a peak is detected by the X-ray diffraction method, and the non-crystalline layer is a layer from which a halo pattern in which the diffraction image is blurred is detected.

Since the outer semi-molten layer 13 is made of a sintered body of unmelted or semi-molten silica powder, a large number of crystal nuclei are present in the outer semi-molten layer 13 . In addition, since the silica powder is not completely melted, the aluminum contained in the Al-added semi-molten layer 13a is present at a high concentration on the surface of the silica powder, and the closer to the surface of the outer surface semi-molten layer 13, the more aluminum tends to be unevenly distributed. is strong. Therefore, when the Al-added semi-molten layer 13a is formed, even if the aluminum concentration of the Al-added outer bubble layer 12b is somewhat low, the crystallization of the outer surface of the crucible can be promoted and the strength of the crucible can be increased. In particular, crystallization with many crystals in the Al-added semi-molten layer 13a as nuclei progresses rapidly not only in the depth direction from the outer surface of the crucible but also in the direction along the outer surface. Even if it is changed, the entire surface is finally devitrified.

The thickness of the outer semi-molten layer 13 including the Al-added semi-molten layer 13a is preferably 5 to 500 μm. If the thickness of the outer surface semi-molten layer 13 is less than 5 μm, the effect as a crystal nucleus is weak, so initial crystallization is slow and the crucible cannot stand on its own. This leads to foaming and peeling of the crystal layer. On the other hand, when the thickness of the outer semi-molten layer 13 is more than 500 μm, the difference in thermal expansion coefficient between the excessively thick outer semi-molten layer and the glass layer causes the outer surface to peel during the pulling process of the silicon single crystal. There is a possibility that the crystal pulling process cannot be continued due to the deformation of the crystal. The thickness of the outer semi-molten layer 13 can be measured, for example, from the cross section of the crucible sample.

In order to prevent contamination of the silicon melt in the crucible, it is desirable that the quartz glass forming the transparent layer 11 has high purity. Therefore, the quartz glass crucible 1 according to the present embodiment includes a synthetic layer 14a made of synthetic silica powder, a natural layer 14b made of normal natural silica powder to which Al is not added, and a natural layer 14b made of natural silica powder to which Al is added. and an Al-added natural layer 14c formed of silica powder. Synthetic silica powder can be produced by vapor-phase oxidation of silicon tetrachloride (SiCl ₄ ) (dry synthesis method) or hydrolysis of silicon alkoxide (sol-gel method). Natural silica powder is silica powder produced by pulverizing natural minerals containing α-quartz as a main component into granules. Furthermore, the natural silica powder to which Al is added is the natural silica powder to which Al is added.

The aluminum concentration in the surface layer portion of the Al-added semi-molten layer 13a is 100 ppm or more, and the aluminum concentration in the deep layer portion of the Al-added semi-molten layer 13a deeper than the surface layer portion is preferably lower than the aluminum concentration in the surface layer portion. That is, it is preferable that aluminum is unevenly distributed near the surface of the Al-added semi-molten layer 13a. When the concentration of aluminum in the surface layer portion of the Al-added semi-molten layer 13a is higher than that in the deep layer portion, the effect of promoting crystallization by the Al-added semi-molten layer 13a can be enhanced.

FIG. 3 is a schematic diagram for explaining the state of the quartz glass crucible during crystal pulling.

As shown in FIG. 3, the quartz glass crucible 1 is used while being housed in a carbon susceptor 20, and the quartz glass crucible 1 supports a large amount of silicon melt 5. As shown in FIG. Therefore, the inner surface of the crucible receives a large liquid pressure from the silicon melt. Since the quartz glass crucible 1 placed at a high temperature equal to or higher than the melting point of silicon softens, the outer surface of the crucible conforms to and adheres to the inner surface of the carbon susceptor 20 .

On the other hand, in the quartz glass crucible 1 according to the present embodiment, the crystallization of the outer surface 10o of the crucible progresses from the initial stage of crystal pulling, and the crystallization rate is high. can increase the strength of As a result, the strength of the side wall portion 10a of the crucible can be ensured before the side wall portion 10a of the crucible fits into the carbon susceptor 20, and the crucible can stand on its own. In this way, a small gap 20g can be formed between the side wall portion 10a of the self-supporting crucible and the carbon susceptor 20, and the gas in the quartz glass generated with the crystallization of the crucible can escape from this gap 20g. It is possible to prevent foaming and peeling of the crystal layer 19 on the outer surface 10o of the crucible.

In addition, foam peeling of the crystal layer means that when the quartz glass crystallizes, the gas components dissolved in the quartz glass are discharged, and the gas accumulates at the interface between the crystal layer and the glass layer, causing the crystal layer and the glass to separate. This is a phenomenon in which layers are peeled off. When the crystal layer is in close contact with the carbon susceptor 20, the gas cannot diffuse outward through the crystal layer. The gas diffused through the gap 20g can be released through the gap 20g. If the crystal layer is thick, diffusion of the gas through the crystal layer cannot catch up with the generation of gas, leading to foaming and peeling. However, if the crystal layer is thin, it is possible for the gas to escape through the crystal layer.

4 to 6 are schematic diagrams for explaining the method for manufacturing a quartz glass crucible according to this embodiment.

The quartz glass crucible 1 according to this embodiment can be manufactured by a so-called rotary mold method. In the rotary mold method, first, as shown in FIG. 4, Al-added natural silica powder 15 to which aluminum is added, and Al-free silica powder, which is normal natural silica powder to which aluminum is not added, are placed on the inner surface 30i of a rotating mold 30. A natural silica powder 16 and a synthetic silica powder 17 are sequentially added to form a deposited layer 18 of these silica powders. These raw material silica powders are stuck to the inner surface 30i of the mold 30 by centrifugal force and remain in a fixed position, and are maintained in the shape of the crucible.

Next, as shown in FIG. 5, an arc electrode 31 is placed in the mold 30, and the deposited layer 18 of raw material silica powder is arc-melted from the inside of the mold 30. Next, as shown in FIG. Specific conditions such as heating time and heating temperature must be appropriately determined in consideration of conditions such as crucible raw material and size. At this time, the amount of air bubbles in the fused quartz glass is controlled by evacuating the deposited layer 18 of raw material silica powder from a large number of air holes 32 provided on the inner surface 30i of the mold 30 . Specifically, at the start of arc melting, the transparent layer 11 is formed by increasing the suction force from a large number of air holes 32 provided on the inner surface 30i of the mold 30, and after the transparent layer 11 is formed, the suction force is weakened to remove bubbles. A layer 12 is formed.

The arc heat is gradually transmitted from the inside to the outside of the deposited layer 18 of the raw material silica powder and melts the raw material silica powder. The bubble layer 12 can be produced separately. If the reduced-pressure melting is performed by increasing the reduced-pressure force at the timing when the silica powder melts, the gas in the arc atmosphere is not confined in the glass, and silica glass containing no air bubbles is formed. Further, if normal melting (atmospheric pressure melting) is performed by weakening the reduced pressure at the timing of melting silica powder, the arc atmosphere gas is confined in the glass to form quartz glass containing many bubbles.

The inside of the deposited silica powder layer 18 is melted by arc heating at a temperature exceeding the melting temperature of the glass, but the inside of the mold 30 does not exceed the melting temperature of the glass, so unmelted powder remains. Further, in the vicinity of the glass melting temperature boundary, an outer semi-molten layer 13 is formed by sintering the silica powder in an unmelted or semi-molten state. Here, the outer semi-molten layer 13 of the side wall portion 10a of the crucible becomes an Al-added semi-molten layer 13a in which natural silica powder to which aluminum is added (Al-added silica powder) is sintered in a semi-molten state, and the corners of the crucible. The outer semi-molten layers 13 of the portion 10c and the bottom portion 10b are Al-free semi-molten layers 13b in which natural silica powder to which aluminum is not added (Al-free silica powder) is sintered in a semi-molten state. The thickness of the outer semi-molten layer 13 can be adjusted by the temperature gradient during arc melting. , the outer surface semi-molten layer 13 can be made thinner.

After that, the arc heating is terminated and the crucible is cooled. As described above, the quartz glass crucible 1 is completed in which the transparent layer 11, the inner bubble layer 12a, the Al-added outer bubble layer 12b, and the outer semi-molten layer 13 are provided in order from the inner surface side to the outer surface side of the crucible wall.

Next, as shown in FIG. 6, after taking out the quartz glass crucible 1 from the mold 30, the outer surface of the quartz glass crucible 1 is subjected to high-pressure cleaning (honing) so that the thickness of the outer semi-molten layer 13 is reduced to 5 μm or more and 500 μm or less. adjust. This means that the outer surface semi-molten layer 13 is left as much as possible without being removed. Since the Al-added semi-molten layer 13a is formed by rapidly cooling unmelted or semi-molten raw material silica powder to which Al is added, the raw material silica powder closer to the surface of the Al-added semi-molten layer 13a maintains its original shape. and tends to have a high concentration of aluminum on the surface. On the other hand, excess raw silica powder adhering to the surface of the Al-added semi-molten layer 13a is removed by washing with high-pressure water, and the aluminum concentration on the surface of the Al-added semi-molten layer 13a changes depending on the degree of washing at this time.

Conventionally, the Al-added semi-molten layer on the outer surface of the crucible has been sufficiently removed, and the surface layer portion of the Al-added semi-molten layer with a high aluminum concentration has hardly remained. If the silica powder with a high aluminum concentration that adheres to the outer layer of the crucible wraps around the inside of the crucible, it will cause not only dislocation of silicon but also contamination, so it is better to remove Al-added silica powder as much as possible. was thought. On the other hand, in the present invention, the crystallization of the outer surface of the crucible is prioritized, and the Al-added semi-molten layer is left as much as possible within the range where there is no problem of silicon contamination or dislocation, so that the crucible can be formed while preventing foaming and peeling of the crystal layer. The outer surface of the can be crystallized to increase the strength of the crucible.

As described above, the quartz glass crucible according to the present embodiment includes an Al-added outer cell layer made of silica glass to which aluminum is added, and an Al-added silica powder provided outside the Al-added outer cell layer. Al-added semi-molten layer sintered in a semi-molten state, and the average concentration of aluminum contained in the Al-added outer bubble layer and the Al-added semi-molten layer is 30 ppm or more and 95 ppm or less. Not only can it be crystallized to form a thick crystal layer, but deformation of the crucible due to foaming and exfoliation of the crystal layer can be suppressed. Therefore, the strength of the crucible can be increased, and a quartz glass crucible that is less likely to deform during the process of pulling a single crystal can be provided.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Needless to say, it is included within the scope.

For example, in the above embodiment, the Al-added outer bubble layer and the Al-added semi-molten layer are provided only on the side wall portion 10a of the crucible. An Al-added semi-molten layer may be provided. However, if the crucible bottom portion 10b is provided with the Al-added outer bubble layer and the Al-added semi-molten layer, cracks may occur and melt leakage may occur. It is preferable not to provide the Al-added semi-molten layer.

<Study on Al concentration in crucible outer layer>
Silicon single crystals were pulled using various quartz glass crucibles having different Al concentrations in the Al-added outer bubble layer. The Al concentration of the Al-added outer bubble layer was measured by TOF-SIMS (Time-Of-Flight Secondary Mass Spectrometry). The Al concentration and the thickness of the outer semi-molten layer are the values obtained by destructive measurement from another sample manufactured under the same conditions. After that, the self-sustaining state of the crucible, the crystallized state, and the presence or absence of foam exfoliation were evaluated. Table 1 shows the results.

(Example 1)
A silicon single crystal was pulled using a quartz glass crucible having an outer semi-molten layer and an Al-added outer bubble layer with an Al concentration of 30 ppm. After that, when the state of the crucible inside the carbon susceptor was evaluated, it was found that the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a self-supporting state. In addition, the entire outer surface of the crucible was crystallized, and foaming and peeling of the crystal layer did not occur.

(Example 2)
A silicon single crystal was pulled using a silica glass crucible having an outer semi-molten layer and an Al-added outer bubble layer with an Al concentration of 70 ppm. After that, when the state of the crucible inside the carbon susceptor was evaluated, it was found that the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a self-supporting state. In addition, the entire outer surface of the crucible was crystallized, and foaming and peeling of the crystal layer did not occur.

(Example 3)
A silica glass crucible having an outer semi-molten layer and an Al-added outer bubble layer having an Al concentration of 95 ppm was prepared. A silicon single crystal was pulled using this crucible. After that, when the state of the crucible inside the carbon susceptor was evaluated, it was found that the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a self-supporting state. In addition, the entire outer surface of the crucible was crystallized, and foaming and peeling of the crystal layer did not occur.

(Comparative example 1)
A silica glass crucible having an outer semi-molten layer and an Al-added outer bubble layer having an Al concentration of 25 ppm was prepared. A silicon single crystal was pulled using this crucible. After that, when the state of the crucible inside the carbon susceptor was evaluated, the outer surface of the crucible was crystallized in a patchy manner. Also, the side wall of the crucible was in a self-supporting state without being in close contact with the carbon susceptor, but it fell slightly inward.

(Comparative example 2)
A silica glass crucible having an outer semi-molten layer and an Al-added outer bubble layer having an Al concentration of 120 ppm was prepared. A silicon single crystal was pulled using this crucible. After that, when the state of the crucible in the carbon susceptor was evaluated, it was found that the entire outer surface of the crucible was crystallized, but the crystal layer was foamed and peeled, and was separated from the glass layer on the inner surface side. The inner glass layer was deformed.

From the above results, if the Al concentration of the Al-added outer bubble layer is too low, the crystallization of the outer surface of the crucible becomes insufficient, so that the strength of the crucible becomes insufficient and deformation easily occurs. It was found that the crucible was deformed due to foaming and detachment. However, it was found that if the Al concentration of the crucible outer layer is 32 to 94 ppm, the strength of the crucible can be increased and the deformation can be suppressed.

<Study on the thickness of the outer semi-molten layer>
Silicon single crystals were pulled using various quartz glass crucibles having different thicknesses of the outer semi-molten layer. After that, the self-sustaining state of the crucible, the crystallized state, and the presence or absence of foam exfoliation were evaluated. Table 2 shows the results.

(Example 4)
A silicon single crystal was pulled using a silica glass crucible having an Al-added outer bubble layer with an Al concentration of 70 ppm and an outer semi-molten layer with a thickness of 5 μm . After that, when the state of the crucible inside the carbon susceptor was evaluated, it was found that the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a self-supporting state. In addition, the entire outer surface of the crucible was crystallized, and foaming and peeling of the crystal layer did not occur.

(Example 5)
A silicon single crystal was pulled using a silica glass crucible having an Al-added outer bubble layer with an Al concentration of 70 ppm and an outer semi-molten layer with a thickness of 500 μm. After that, when the state of the crucible inside the carbon susceptor was evaluated, it was found that the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a self-supporting state. In addition, the entire outer surface of the crucible was crystallized, and foaming and peeling of the crystal layer did not occur.

(Comparative Example 3)
A silicon single crystal was pulled using a quartz glass crucible having an Al-added outer bubble layer with an Al concentration of 72 ppm and an outer semi-molten layer with a thickness of 3 μm . After that, when the state of the crucible in the carbon susceptor was evaluated, it was found that the side wall of the crucible was in close contact with the carbon susceptor and did not stand on its own. In addition, the outer surface of the crucible was crystallized in a patchy pattern, and foaming and peeling of the crystal layer occurred.

(Comparative Example 4)
A silicon single crystal was pulled using a quartz glass crucible having an Al-added outer bubble layer with an Al concentration of 73 ppm and an outer semi-molten layer with a thickness of 620 μm. After that, when the state of the crucible in the carbon susceptor was evaluated, it was found that most of the outer surface peeled off due to the difference in thermal expansion coefficient between the excessively thick outer semi-molten layer and the glass layer, and the crucible was deformed. .

From the above results, it was found that if the outer surface semi-molten layer is too thin, the crystallization of the outer surface of the crucible does not progress, so that the crucible fits into the carbon susceptor and cannot stand on its own, resulting in foaming and peeling of the crystal layer. It was also found that if the outer semi-melting layer is too thick, the outer surface peeling occurs in most parts due to the difference in thermal expansion coefficient between the outer semi-melting layer and the glass layer, and the crucible deforms.

<Consideration of lower end taper shape of Al-added outer bubble layer>
Silicon single crystals were pulled using various quartz glass crucibles having different rates of change in the taper shape of the lower end portion of the Al-added outer bubble layer formed on the side wall of the crucible. The condition of the crucible was then evaluated. Table 3 shows the results.

(Example 6)
A silicon single crystal was pulled using a quartz glass crucible having a tapered change rate of 0.07 mm/mm at the lower end of the Al-added outer bubble layer. After that, when the state of the crucible was evaluated, no cracks were found.

(Example 7)
A silicon single crystal was pulled using a quartz glass crucible in which the rate of change in the taper shape of the lower end portion of the Al-added outer bubble layer was 0.1 mm/mm. After that, when the state of the crucible was evaluated, no cracks were found.

(Example 8)
A silicon single crystal was pulled using a silica glass crucible in which the change rate of the taper shape at the lower end of the Al-added outer bubble layer was 0.5 mm/mm. After that, when the state of the crucible was evaluated, no cracks were found.

(Comparative Example 5)
A silicon single crystal was pulled using a silica glass crucible having a taper shape change rate of 0.7 mm/mm at the lower end of the Al-added outer bubble layer. After that, when the state of the crucible was evaluated, it was found that a crack had occurred near the lower end of the side wall.

From the above results, it was found that cracks tend to occur due to stress concentration at the boundary between the Al-added layer and the Al-free layer when the rate of change in the tapered shape at the lower end of the Al-added outer bubble layer is large. .

1 quartz glass crucible 5 silicon melt 10a sidewall portion 10b bottom portion 10c corner portion 10i crucible inner surface 10o crucible outer surface 11 transparent layer 12 bubble layer 12a inner bubble layer 12b Al-added outer bubble layer 12b _e lower end portion 13 of Al-added outer bubble layer Semi-molten layer 13a Al-added semi-molten layer 13b Al-free semi-molten layer 14a Synthetic layer 14b Natural layer 14c Al-added natural layer 15 Al-added natural silica powder 16 Al-free natural silica powder 17 Synthetic silica powder 18 Silica powder deposited layer 19 Crystal layer 20 Carbon susceptor 20g Gap 30 Mold 30i Mold inner surface 31 Arc electrode 32 Vent hole

Claims (6)

A quartz glass crucible having a cylindrical side wall, a curved bottom, and a corner positioned between the side wall and the bottom and having a larger curvature than the bottom,
a transparent layer made of silica glass containing no air bubbles;
a bubble layer provided outside the transparent layer and made of silica glass containing a large number of bubbles;
An outer semi-molten layer provided outside the bubble layer and formed by sintering the raw material silica powder in a semi-molten state,
The bubble layer includes an inner bubble layer made of silica glass to which aluminum is not added, and an Al-added outer bubble layer provided outside the inner bubble layer and made of silica glass to which aluminum is added,
at least part of the outer semi-molten layer in contact with the Al-added outer bubble layer is an Al-added semi-molten layer to which aluminum is added;
The average concentration of aluminum contained in the Al-added semi-molten layer is 30 ppm or more and 95 ppm or less,
The Al-added outer bubble layer and the Al-added semi-molten layer are provided at least on the side walls,
The bubble layer in the side wall portion has a two-layer structure of the inner bubble layer and the Al-added outer bubble layer,
The foam layer at the bottom is a single-layer structure of the inner foam layer,
the lower end portion of the Al-added outer bubble layer has a tapered shape,
A silica glass crucible for pulling a silicon single crystal, wherein a rate of decrease in thickness of the lower end portion is 0.5 mm/mm or less. 2. The silica glass crucible according to claim 1, wherein the Al-added semi-molten layer has a thickness of 5 μm or more and 500 μm or less. 3. The quartz glass crucible according to claim 1, wherein the Al-added outer bubble layer in the side wall portion has a higher bubble content than the inner bubble layer. The concentration of aluminum in the surface layer portion of the Al-added semi-molten layer is 100 ppm or more,
The quartz glass crucible according to any one of claims 1 to 3, wherein a deep portion of said Al-added semi-molten layer, which is deeper than said surface layer portion, has a lower aluminum concentration than said surface layer portion. A method for manufacturing a silica glass crucible having a cylindrical side wall, a curved bottom, and a corner positioned between the side wall and the bottom and having a larger curvature than the bottom, comprising:
A step of sequentially filling Al-added silica powder and Al-free silica powder onto the inner surface of a mold that matches the outer shape of the quartz glass crucible to form a deposited layer of silica powder;
A transparent layer made of silica glass that does not contain bubbles by heating and melting the deposited layer of silica powder from the inside of the mold and adjusting the decompression force of the deposited layer from the inner surface side of the mold; Quartz provided outside the transparent layer and comprising a bubble layer made of silica glass containing a large number of bubbles, and an outer surface semi-molten layer provided outside the bubble layer and formed by sintering raw silica powder in a semi-molten state. forming a glass crucible;
adjusting the thickness of the outer semi-molten layer of the quartz glass crucible taken out from the mold to 5 μm or more and 500 μm or less;
The average concentration of aluminum contained in the Al-added silica powder is 30 ppm or more and 95 ppm or less,
In the step of forming the deposited layer of silica powder,
The bubble layer in the side wall portion has a two-layer structure of an inner bubble layer and an Al-added outer bubble layer ,
The cell layer at the bottom has a single-layer structure of the inner cell layer,
the lower end portion of the Al-added outer bubble layer has a tapered shape,
Quartz for pulling a silicon single crystal, wherein the amounts of the Al-added silica powder and the Al-free silica powder are adjusted so that the thickness reduction rate of the lower end portion is 0.5 mm/mm or less. A method for manufacturing a glass crucible. 6. The method for producing a silica glass crucible for pulling a silicon single crystal according to claim 5, wherein the deposited layer of silica powder is formed by depositing Al-added natural silica powder, Al-free natural silica powder and synthetic silica powder in this order. .

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