KR102342049B1 - Quartz glass crucible for pulling silicon single crystal and producing method thereof - Google Patents

Abstract

(Project) During the pulling process of silicon single crystal, not only the entire outer surface of the crucible is reliably crystallized, but also the foaming and peeling of the crystal layer is prevented, thereby increasing the strength of the crucible.
(Solution) The quartz glass crucible 1 includes a transparent layer 11 made of silica glass that does not contain bubbles, and a bubble layer 12 that is provided on the outside of the transparent layer 11 and is made of silica glass containing a plurality of bubbles. ) and, provided on the outside of the bubble layer 12 and includes an outer semi-molten layer 13 in which raw silica powder is sintered in a semi-melted state. The bubble layer 12 is provided on the outside of the inner bubble layer 12a and the inner bubble layer 12a made of silica glass to which aluminum is not added, and is an Al added outer bubble layer 12b made of silica glass to which aluminum is added. ), and at least a part of the outer surface semi-molten layer 13 in contact with the Al-added outer bubble layer 12b is an Al-added semi-melted layer 13a to which aluminum is added. The average concentration of aluminum contained in the Al-added semi-molten layer 13a is 30 ppm or more and 95 ppm or less.

Description

Quartz glass crucible for pulling silicon single crystal and manufacturing method thereof

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 manufacturing the same.

A quartz glass crucible is used for pulling up 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 produce a silicon melt, a seed crystal is immersed in the silicon melt, and a large single crystal is placed at the lower end of the seed crystal by gradually pulling up the seed crystal while rotating the crucible. to grow According to the CZ method, it is possible to grow a large-diameter single crystal, and it is possible to improve the productivity of the silicon single crystal.

Regarding a quartz glass crucible, for example, Patent Document 1 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. In addition, in Patent Document 2, at least the inner layer of the corner part is made of a transparent synthetic layer, the middle layer is a transparent or opaque natural layer or natural synthetic mixed layer, and the outer layer is an opaque natural layer, and the thickness of the inner layer becomes thinner from the bottom of the crucible to the top. A crucible structure is described.

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

Japanese Patent Laid-Open No. 2000-247778 International Publication 2004/106247 Pamphlet Japanese Patent Laid-Open No. 2009-84114 Japanese Patent Laid-Open No. 2010-202515

According to the conventional quartz glass crucible in which an Al addition layer is provided on the outer layer of the crucible, it is possible to improve the strength of the crucible by crystallizing the outer surface of the crucible. However, when the aluminum concentration is high, there is a problem that the crystal layer is foamed and peeled and the strength of the crucible is lowered, and when the aluminum concentration is low, there is a problem that crystallization takes time and sufficient strength cannot be obtained.

Accordingly, it is an object of the present invention to provide a quartz glass crucible capable of increasing the strength of the crucible by early crystallization of the outer surface of the crucible and suppressing foaming and peeling of the crystal layer, and a method for manufacturing the same.

In order to solve the above problems, the quartz glass crucible for pulling up silicon single crystal according to the present invention includes a transparent layer made of silica glass that does not contain bubbles, and a silica glass that is provided on the outside of the transparent layer and contains a plurality of bubbles. A bubble layer and an outer semi-molten layer provided on the outside of the bubble layer, in which raw silica powder is sintered in a semi-melted state, wherein the bubble layer is an inner bubble layer made of silica glass to which aluminum is not added; It is provided on the outside of the inner bubble layer, and includes an Al-added outer bubble layer made of silica glass to which aluminum is added, and at least a portion of the outer semi-molten layer in contact with the Al-added outer bubble layer is Al added with aluminum added. It is a semi-molten layer, 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 reliably crystallizing the entire outer surface of the crucible during the pulling process of the silicon single crystal. In particular, since the initial crystallization of the outer surface of the crucible can be accelerated by the presence of the semi-molten layer on the outer surface to which aluminum is added, the strength of the crucible can be secured and independent before the crucible is softened and fused to the carbon susceptor. As a result, a slight gap can be formed between the crucible and the carbon susceptor, and gas in the quartz glass that is generated along with the crystallization of the crucible can be discharged from this gap. A decrease in the strength of the crucible or generation of particles can be prevented.

In the present invention, the thickness of the Al-added semi-molten layer is preferably 5 μm or more and 500 μm or less. When the thickness of the Al-added semi-molten layer is less than 5 μm, the effect as a crystal nucleus is weak, so the initial crystallization is slow, and the crucible cannot stand on its own. Therefore, it leads to foaming and peeling of a crystal layer. On the other hand, when the thickness of the Al-added semi-melted layer is greater than 500 μm, external peeling due to the difference in thermal expansion coefficient between the excessively thick Al-added semi-melted layer and the glass layer occurs during the pulling process of the silicon single crystal, and the crucible is deformed. As a result, there is a fear that the crystal pulling process cannot be continued. However, when 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 foaming and peeling of the crystallized outer surface of the crucible can be prevented.

The quartz glass crucible according to the present invention has a cylindrical side wall portion, a curved bottom portion, a corner portion positioned between the side wall portion and the bottom portion, and having a greater curvature than the bottom portion, and the Al addition outside It is preferable that the bubble layer and the said Al addition semi-molten layer are provided at least in the said side wall part. In this way, 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 to make it self-supporting, and the inner side of the crucible falls (inward falling-down), etc. It is possible to suppress the deformation of the side wall of the

It is preferable that the foam layer in the side wall portion has a two-layer structure of the inner foam layer and the Al-added outer foam layer, and the foam layer in the bottom portion has a single-layer structure of the inner foam layer. In this case, the lower end of the Al-added outer bubble layer has a tapered shape, and the reduction rate of the thickness of the lower end is preferably 0.5 mm/mm or less, more preferably 0.2 mm/mm. When the reduction rate of the thickness of the lower end of the Al-added outer bubble layer is gentle, stress is concentrated at the boundary between the Al-added layer and the Al-free layer, thereby preventing cracks from occurring.

It is preferable that the bubble content rate of the said Al-added outer cell layer in the said side wall part is higher than the bubble content rate of the said inner side cell layer. According to this, the heat insulation property can be improved together with the intensity|strength of a crucible, and temperature increase of the inner surface of a crucible can be suppressed.

In the present invention, the aluminum concentration of the surface layer portion of the Al-added semi-melted layer is 100 ppm or more, and the aluminum concentration of the deep portion of the Al-added semi-melted layer deeper than the surface layer portion is preferably lower than the aluminum concentration of the surface layer portion. When the concentration of aluminum in the surface portion of the semi-molten Al-added layer is higher than that in the deep portion, the crystallization promoting effect of the Al-addition semi-melted layer can be enhanced. Since the Al-added semi-melted layer is formed by cooling raw silica powder to which Al is added in a semi-molten state, the Al concentration increases as it approaches the surface that maintains the original shape. 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-melted layer changes depending on the degree of washing at this time. Incidentally, the distribution of the aluminum concentration in the Al-added semi-molten layer is microscopically non-uniform, and in particular, ^{it is preferable that the high Al concentration part in the 1 mm 3} area of the Al-added semi-melted layer is unevenly distributed in the form of a mesh. , it is preferable that a high concentration region having an Al concentration higher than 60 ppm and a low concentration region lower than 25 ppm are mixed.

In the conventional quartz glass crucible, the outer surface semi-molten layer was not formed or, if formed, the thickness was very thin, so that the initial crystallization of the outer surface of the crucible was not reached. On the other hand, in the present invention, for example, by weakening the current flowing to the arc electrode in the second half of the arc melting process, the temperature gradient at the time of heating the raw silica powder is smoothed, and the progress rate of vitrification is reduced slow down Then, the arc continues in the low current state. Arc melting time becomes longer than usual. Accordingly, the thickness and shape of the quartz glass hardly change from that in the normal case, but the outer semi-molten layer is formed to be thicker than usual. In particular, in the present invention, by forming the outer 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.

In addition, the method for manufacturing a quartz glass crucible for pulling up a silicon single crystal according to the present invention comprises the steps of filling the inner surface of a rotating mold with Al-added silica powder and Al-free silica powder in order to form a silica powder deposition layer; A transparent layer made of bubble-free silica glass by heating and melting the powdery deposited layer from the inside of the mold and adjusting the pressure reducing force of the deposited layer from the inside of the mold; A step of forming a quartz glass crucible comprising a bubble layer made of silica glass containing a plurality of bubbles, and an outer semi-melted layer provided on the outside of the bubble layer, in which raw silica powder is sintered in a semi-molten state; , adjusting the thickness of the outer semi-molten layer of the quartz glass crucible taken out from the mold to be 5 μm or more and 500 μm or less, wherein the average concentration of aluminum contained in the Al-added silica powder is 30 ppm or more and 95 ppm It is characterized by the following.

According to the present invention, it is possible to manufacture a quartz glass crucible capable of reliably crystallizing the entire outer surface of the crucible during the pulling process of silicon single crystal, as well as preventing foaming and peeling of the crystal layer, thereby increasing the strength of the crucible.

In the present invention, the silica powder deposition layer is preferably one in which the Al-added natural silica powder, the Al-free natural silica powder and the synthetic silica powder are sequentially deposited. Accordingly, a high-purity transparent layer can be formed on the inner surface of the crucible, and contamination of the silicon melt in the crucible can be prevented.

According to the present invention, it is possible to provide a quartz glass crucible capable of increasing the strength of the crucible by crystallizing the outer surface of the crucible while preventing foaming and peeling of the crystal layer, and a method for manufacturing the same.

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

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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

1 and 2, this quartz glass crucible 1 is a container made of silica glass for supporting a silicon melt, and has a cylindrical side wall portion 10a and a gently curved bottom portion 10b. And, it has a corner part 10c which is located between the side wall part 10a and the bottom part 10b, and has a larger curvature than the bottom part 10b.

The diameter (caliber) of the quartz glass crucible 1 is preferably not less than 24 inches (about 600 mm), and preferably not less than 32 inches (about 800 mm). This is because such a large-diameter crucible is used for pulling up a silicon single crystal ingot for semiconductors with a diameter of 200 mm or more, and it is required that it is not deformed well even after using it for a long time.

The thickness of the crucible is slightly different depending on the part. 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 part 10a of a large crucible of 32 inches or more is 10 mm or more, 40 inches (approx. 1000 mm) or more, the thickness of the side wall portion 10a of the large crucible is preferably 13 mm or more. This is because a large-capacity crucible needs a sufficient thickness not to be deformed by the pressure from a large amount of silicon melt.

The quartz glass crucible 1 according to the present embodiment includes a transparent layer 11 (a bubble-free layer) made of silica glass that does not contain bubbles, and is provided on the outside of the transparent layer 11, and contains a plurality of minute bubbles. A bubble layer 12 (opaque layer) made of silica glass and an outer semi-melted layer 13 provided on the outside of the bubble layer 12 and formed by cooling the raw silica powder in an unmelted or semi-melted state. have.

The transparent layer 11 is a layer constituting the inner surface 10i of the crucible in contact with the silicon melt, and is provided to prevent the single crystallization rate from lowering due to air bubbles in the quartz glass. The thickness of the transparent layer 11 is preferably 0.5 to 10 mm, and an appropriate thickness for each part of the crucible is used so that the bubble layer 12 is not exposed due to dissolution loss during the pulling process of single crystals. is set Like 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. Therefore, it is also possible to omit the formation of the transparent layer 11 .

"Bubble-free" means that the transparent layer 11 has a bubble content and a bubble size such that the single crystallization rate does not decrease due to bubbles. If bubbles exist near the inner surface of the crucible, the bubbles near the inner surface of the crucible cannot be trapped in the quartz glass due to dissolution of the inner surface of the crucible. This is because (quartz pieces) may peel off. When the crucible fragments released from the melt are transported to the growth interface of the single crystal through the convection of the melt and are introduced into the single crystal, it causes dielectric dislocation of the single crystal. Also, when the bubbles released from the melt float to the solid-liquid interface due to dissolution loss on the inner surface of the crucible and are introduced into the single crystal, it causes a pin hole. It is preferable that the bubble content of the transparent layer 11 is 0.1 vol% or less, and it is preferable that the average diameter of a bubble is 100 micrometers or less.

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

In order to detect bubbles existing at a certain depth from the surface of the crucible, the focus of the optical lens may be scanned in the depth direction from the surface. In detail, an image of the inner surface of the crucible is taken using a digital camera, the inner surface of the crucible is divided for each predetermined area and referred to as a reference area (S1), and the area occupied by the bubble (S2) is calculated for each reference area (S1). It calculates|requires, and area bubble content rate Ps=(S2/S1)*100 (%) is computed.

In calculation of the bubble content rate by volume ratio, the reference volume V1 is calculated|required from the depth and reference area S1 which image|photographed the image. Further, the bubble is regarded as a spherical shape, and the volume (V2) of the bubble is calculated from the diameter of the bubble. And from V1 and V2, the volume bubble content rate Pv=(V2/V1)*100 (%) is computed. In the present invention, this volumetric bubble content rate (Pv) is defined as "bubble content rate". Moreover, the arithmetic mean value calculated|required from the diameter of the bubble calculated by considering the bubble to be spherical is defined as "average diameter of bubble".

However, the standard volume is 5 mm × 5 mm × depth (depth) 0.45 mm, and the minimum bubble diameter to be measured is 5 μm (ignoring those with a diameter less than 5 μm), You have to have resolution. In addition, by shifting the focal length of the optical lens in the depth direction of the reference volume V1, the bubbles contained in the interior of the reference volume are captured to measure the diameter of the bubbles.

The bubble layer 12 is a major layer constituting the crucible wall. The bubble layer 12 is provided to increase the heat retention of the silicon melt in the crucible, and to distribute 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 in the whole crucible from the side wall part 10a of the crucible to the bottom part 10b. The thickness of the bubble layer 12 is a value obtained by subtracting the thickness of the transparent layer 11 and the outer semi-molten layer 13 from the thickness of the crucible wall, and varies depending on the portion of the crucible. The bubble content rate of the bubble layer 12 can be calculated|required by the specific gravity measurement (Archimedes method) of the opaque quartz glass piece cut out from a crucible, for example.

The bubble content rate of the bubble layer 12 is higher than that of the transparent layer 11, and it is preferable that it is 0.5-5 vol%, and it is more preferable that it is 0.5-4 vol%. It is because the function of the bubble layer 12 cannot be exhibited when the bubble content rate of the bubble layer 12 is 0.5 vol% or less, and heat retention becomes inadequate. In addition, when the bubble content of the bubble layer 12 exceeds 5 vol%, the crucible is greatly deformed due to the expansion of the bubble and there is a risk that the single crystal yield may decrease, and furthermore, heat transfer property (heat transfer property) Because this is insufficient. In particular, when the bubble content of the bubble layer 12 is 0.5 to 4 vol%, the deformation of the crucible can be further prevented, and the heat transfer property can be further improved.

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

The concentration of aluminum contained in the Al-added outer bubble 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 mottled form, and the entire surface cannot be uniformly crystallized. In addition, when the aluminum concentration is higher than 95 ppm, a thick crystal layer can be formed by crystallizing the outer surface of the crucible. Foaming and peeling occurs at the interface, the crucible is not supported by the crystal layer, and there is a risk of deformation. However, when the aluminum concentration is within the above range, the entire outer surface of the crucible can be crystallized to uniformly form a crystalline layer of an appropriate thickness, thereby preventing foaming and peeling or cracking, thereby increasing the strength of the crucible. The concentration of aluminum contained in the quartz glass can be measured by secondary ion mass spectrometry.

It is preferable that the bubble content rate of the Al addition outer bubble layer 12b is higher than the bubble content rate of the inner side bubble layer 12a. According to this, the heat insulation property can be improved together with the intensity|strength of a crucible, and temperature increase of the inner surface of a crucible can be suppressed. The Al-added outer bubble layer 12b can be formed using raw silica powder to which an aluminum compound is added. The bubble content of the layer 12b can be increased.

_{The lower end 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 12b e} is preferably 0.5 mm/mm or less. Here, the reduction rate of the thickness of the lower end of the Al-added outer cell layer refers to the amount of change in the thickness of the taper shape of the Al-added outer cell 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. _{As such, if the reduction rate of the thickness of the lower end portion 12b e} of the Al-added outer bubble layer is gentle, stress is concentrated at the boundary between the Al-added outer cell layer 12b and the inner cell layer 12a to prevent cracks from occurring can be prevented

The outer semi-molten layer 13 is a layer formed by cooling in an incompletely molten state of silica powder, a raw material of the crucible. Since the outer semi-molten layer 13 has a surface state with many undulations, scattering or reflection of light incident from the outer surface side of the crucible is large, and has a certain influence on the infrared transmittance of the crucible in an unused state.

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 end of the rim of the side wall portion 10a. Among them, a part of the outer semi-molten layer 13 in contact with the Al-added outer bubble layer 12b is the Al-added semi-melted layer 13a formed 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-melted layer 13b formed of normal raw silica powder (Al-free silica powder) to which Al is not added.

Whether the outer semi-molten layer 13 is formed on the outer surface of the crucible is determined by measuring the outer surface of the crucible by X-ray diffraction, a halo pattern in which the diffraction image peculiar to amorphous is blurred and a peak indicating crystallinity It can be judged by whether or not they are mixed. For example, when the measurement target is a crystalline layer, a peak indicating crystallinity is detected, but a halo pattern with a blurred diffraction image is not detected. Conversely, when the measurement target is an amorphous layer (amorphous layer), a halo pattern with a blurred diffraction image is detected, and a peak indicating crystallinity is not detected. When the outer semi-molten layer 13 formed on the outer surface of the crucible is removed, the surface of the glass is exposed, so that the peak is not detected by the X-ray diffraction method. As described above, it can be said that the semi-molten layer is a layer in which a halo pattern with a blurred diffraction image and a peak indicating crystallinity are mixed when measured by X-ray diffraction method. In addition, it can be said that the crystalline layer is a layer in which a peak is detected by the X-ray diffraction method, and the amorphous layer is a layer in which a halo pattern with a blurred diffraction image is detected.

Since the outer semi-molten layer 13 is made of a sintered body of unmelted or semi-molten silica powder, a plurality of crystal nuclei exist in the outer semi-molten layer 13 . In addition, since the silica powder is not all melted, aluminum contained in the Al-added semi-molten layer 13a is present in a high concentration on the surface of the silica powder, and the closer to the surface of the outer semi-molten layer 13, the more the tendency of the localization of aluminum. 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, crystallization of the outer surface of the crucible is promoted and the strength of the crucible can be increased. In particular, since crystallization with a plurality of crystals as nuclei in the Al-added semi-molten layer 13a proceeds rapidly not only in the depth direction from the outer surface of the crucible, but also in the direction along the outer surface, it is initially devitrified in a speckled form. Even if it is 透化), 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. When the thickness of the outer semi-molten layer 13 is less than 5 μm, the effect as a crystal nucleus is weak, so the initial crystallization is slow, and the crucible cannot stand on its own. Therefore, it leads to foaming and peeling of a crystal layer. On the other hand, when the thickness of the outer semi-molten layer 13 is greater than 500 μm, the outer surface peeling due to the difference in thermal expansion coefficient between the excessively thick outer semi-molten layer and the glass layer occurs during the pulling process of the silicon single crystal, and the crucible There is a possibility that the crystal pulling process cannot be continued by being deformed. The thickness of the outer semi-molten layer 13 can be measured, for example, from a cross section of a crucible sample.

In order to prevent contamination of the silicon melt in the crucible, the quartz glass constituting the transparent layer 11 is preferably of high purity. Therefore, the quartz glass crucible 1 according to the present embodiment includes a synthetic layer 14a formed of synthetic silica powder, a natural layer 14b formed of ordinary natural silica powder to which Al is not added, and Al It has an Al-added natural layer 14c formed of added natural 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). In addition, natural silica powder is a silica powder produced by pulverizing a natural mineral containing α-quartz as a main component to form a powder. Furthermore, Al-added natural silica powder is Al-added natural silica powder.

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

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 in a state accommodated in the carbon susceptor 20 , and the quartz glass crucible 1 supports a large amount of the silicon melt 5 . Therefore, the inner surface of the crucible receives a large hydraulic pressure from the silicon melt. Since the quartz glass crucible 1 placed under a high temperature equal to or higher than the melting point of silicon is softened, the outer surface of the crucible coincides with the inner surface of the carbon susceptor 20 (fusion) and adheres thereto.

On the other hand, in the quartz glass crucible 1 according to the present embodiment, crystallization of the outer surface 10o of the crucible proceeds from the initial stage of pulling up, and the crystallization rate is fast, so that the entire surface of the outer surface 10o of the crucible is ensured. It can be crystallized to increase the strength of the crucible. Accordingly, it is possible to secure the strength before the side wall portion 10a of the crucible is fused to the carbon susceptor 20 to make it 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 gas in the quartz glass generated accompanying crystallization of the crucible is discharged from the gap 20g. It can be pulled out, and foaming and peeling of the crystal layer 19 of the outer surface 10o of the crucible can be prevented.

However, foaming and peeling of the crystal layer is a phenomenon in which the gas component dissolved in the quartz glass is discharged when the quartz glass is crystallized, and the crystal layer and the glass layer are peeled off by the gas pooling at the interface between the crystal layer and the glass layer. . When the crystal layer is in close contact with the carbon susceptor 20, gas cannot be diffused outward through the crystal layer. Gas can be withdrawn from this gap 20g. When the crystal layer is thick, the diffusion of gas through the crystal layer cannot catch up with the generation of gas, leading to foaming and peeling. However, when the crystal layer is thin, it is possible to exhaust gas through the crystal layer.

4-6 are schematic diagrams for demonstrating the manufacturing method of the quartz glass crucible which concerns on this embodiment.

The quartz glass crucible 1 according to the present embodiment can be manufactured by a so-called rotational molding method. In the rotary mold method, first, as shown in Fig. 4, on the inner surface 30i of the rotating mold 30, Al-added natural silica powder 15 with aluminum added, and aluminum is not added with normal natural silica powder. Al-free natural silica powder 16 and synthetic silica powder 17 are sequentially added to form a deposited layer 18 of these silica powders. These raw silica powders are held in a fixed position while being adhered to the inner surface 30i of the mold 30 by centrifugal force, and are maintained in the shape of a crucible.

Next, as shown in FIG. 5 , the arc electrode 31 is installed in the mold 30 , and the deposited layer 18 of raw silica powder is arc-melted from the inside of the mold 30 . Specific conditions such as heating time and heating temperature need to be appropriately determined in consideration of conditions such as the raw material and size of the crucible. At this time, the amount of bubbles in the molten quartz glass is controlled by evacuating the deposition layer 18 of raw silica powder from the plurality of vent holes 32 provided in the inner surface 30i of the mold 30 . Specifically, the transparent layer 11 is formed by increasing the suction force from the plurality of vent holes 32 provided on the inner surface 30i of the mold 30 at the start of arc melting, and the suction force after the formation of the transparent layer 11 is weakened to form the bubble layer 12 .

Arc heat is gradually transferred from the inside to the outside of the deposition layer 18 of the raw silica powder and melts the raw silica powder, so by changing the pressure reduction conditions at the timing when the raw silica powder starts to melt, 11) and the bubble layer 12 can be made separately. When reduced pressure melting is performed to increase the pressure reduction force at the timing at which the silica powder is melted, the arc atmosphere gas is not trapped in the glass, and a quartz glass containing no air bubbles is formed. In addition, if normal melting (atmospheric pressure melting) is performed in which the pressure-reducing force is weakened at the timing at which the silica powder is melted, the arc atmosphere gas is trapped in the glass, and quartz glass containing many bubbles is formed.

The inside of the deposited layer 18 of silica powder is arc heated at a temperature exceeding the glass melting temperature and melted. Since the inside of the mold 30 does not exceed the glass melting temperature, unmelted powder remains. Further, in the vicinity of the boundary of the glass melting temperature, the outer surface semi-melted layer 13 in which silica powder is sintered in an unmelted or semi-melted state is formed. Here, the outer semi-molten layer 13 of the side wall portion 10a of the crucible is an Al-added semi-melted layer 13a in which aluminum-added natural silica powder (Al-added silica powder) is sintered in a semi-melted state, and The outer semi-molten layer 13 of the corner portion 10c and the bottom portion 10b of the crucible is an Al-free semi-melted layer 13b obtained by sintering in a semi-melted state of aluminum-free natural silica powder (Al-free silica powder). ) becomes The thickness of the outer semi-molten layer 13 can be adjusted by the temperature gradient at the time of arc melting, and when the temperature gradient is made gentle, the outer surface semi-molten layer 13 can be thickened, and the temperature gradient is sharpened. In this case, the outer surface semi-molten layer 13 can be made thin.

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

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 cleaned at high pressure (Honing) to form the outer semi-molten layer 13 of the Adjust the thickness to 5 μm or more and 500 μm or less. This means leaving as much of the outer surface semi-molten layer 13 as possible without removing it. 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 closer the Al-added semi-melted layer 13a is to the surface of the raw silica powder, the more its original shape is maintained. and the concentration of aluminum on the surface tends to increase. 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-melted layer 13a depends on the degree of cleaning at this time. is changed

Conventionally, the Al-added semi-molten layer on the outer surface of the crucible was sufficiently removed, and almost no surface layer of the Al-added semi-melted layer containing a high concentration of aluminum remained. Silica powder with a high concentration of aluminum adhering to the outer layer of the crucible turns inside the crucible and causes contamination as well as dielectric dislocation of silicon. On the other hand, in the present invention, the crystallization of the outer surface of the crucible is given priority, and the Al-added semi-molten layer is left as much as possible in the range where there is no problem of silicon contamination or dielectric dislocation, thereby preventing the foaming and peeling of the crystal layer while protecting the outer surface of the crucible. It is possible to increase the strength of the crucible by crystallization.

As described above, the quartz glass crucible according to the present embodiment is provided on the outside of the Al-added outer bubble layer and the Al-added outer bubble layer made of silica glass to which aluminum is added, and Al-added silica powder is semi-melted. It has an Al-added semi-melted layer sintered in its state, and the average concentration of aluminum contained in the Al-added outer bubble layer and the Al-added semi-melted layer is 30 ppm or more and 95 ppm or less, so the outer surface of the crucible is crystallized early to form a thick crystal layer can be formed, and the deformation of the crucible due to foaming and peeling of the crystal layer can be suppressed. Accordingly, it is possible to increase the strength of the crucible and provide a quartz glass crucible that is not easily deformed during the pulling process of single crystals.

As mentioned above, although preferred embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments, and various changes are possible without departing from the main gist of the present invention, and they are also included within the scope of the present invention. of course it is

For example, in the above embodiment, the Al-added outer bubble layer and the Al-added semi-molten layer were provided only on the side wall portion 10a of the crucible, but the entirety including the bottom portion 10b and the corner portion 10c of the crucible. It is also possible to provide an Al-added outer bubble layer and an Al-added semi-melted layer. However, when an Al-added outer bubble layer and an Al-added semi-molten layer are provided at the bottom 10b of the crucible, cracks occur and there is a risk of molten water leakage. It is preferable not to provide an Al-added semi-molten layer.

(Example)

<Consideration on the Al concentration in the outer layer of the crucible>

The pulling up of a silicon single crystal was performed 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: time-of-flight secondary ion mass spectrometry). Incidentally, the Al concentration and the thickness of the outer semi-molten layer are values obtained by fracture measurement from other samples prepared under the same conditions. Thereafter, the self-supporting state of the crucible, the crystallization state, and the presence or absence of foam peeling were evaluated. The results are shown in Table 1.

(Example 1)

The pulling of the silicon single crystal was performed using a quartz glass crucible having an outer surface semi-melted layer and having an Al concentration of 30 ppm in the Al-added outer bubble layer. Thereafter, when the state of the crucible in the carbon susceptor was evaluated, 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)

Silicon single crystal pulling was performed using a quartz glass crucible having an outer surface semi-melted layer and having an Al concentration of 70 ppm in the Al-added outer bubble layer. Thereafter, when the state of the crucible in the carbon susceptor was evaluated, 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 quartz glass crucible having an outer surface semi-melted layer and an Al concentration of 95 ppm in the Al-added outer bubble layer was prepared. Pulling of a silicon single crystal was performed using this crucible. Thereafter, when the state of the crucible in the carbon susceptor was evaluated, 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 quartz glass crucible having an outer surface semi-melted layer and having an Al concentration of 25 ppm in the Al-added outer bubble layer was prepared. Pulling of a silicon single crystal was performed using this crucible. Then, when the state of the crucible in the carbon susceptor was evaluated, the outer surface of the crucible was crystallized in a stained form. In addition, the side wall portion of the crucible was not in close contact with the carbon susceptor and was in a free-standing state, but it fell slightly inside.

(Comparative Example 2)

A quartz glass crucible having an outer surface semi-melted layer and having an Al concentration of 120 ppm in the Al-added outer bubble layer was prepared. Pulling of a silicon single crystal was performed using this crucible. Then, when the state of the crucible in the carbon susceptor was evaluated, the outer surface of the crucible was completely crystallized, but the crystal layer was foamed and peeled off and separated from the glass layer on the inner surface side. The glass layer on the inner surface side was deformed.

From the above results, when the Al concentration in the Al-added outer cell layer is excessively low, crystallization of the outer surface of the crucible becomes insufficient, so the strength of the crucible is insufficient and deformation easily occurs. It was found that the crucible was deformed by peeling. However, it was found that when the Al concentration of the outer layer of the crucible was 32 to 94 ppm, the strength of the crucible could be increased to suppress deformation.

<Review 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 layers. Thereafter, the self-supporting state of the crucible, the crystallization state, and the presence or absence of foam peeling were evaluated. The results are shown in Table 2.

(Example 4)

Silicon single crystal pulling was performed using a quartz glass crucible in which the Al concentration of the Al-added outer bubble layer was 70 ppm and the outer semi-molten layer had a thickness of 5 μm. Thereafter, when the state of the crucible in the carbon susceptor was evaluated, 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)

The pulling up of a silicon single crystal was performed using a quartz glass crucible in which the Al concentration of the Al-added outer bubble layer was 70 ppm and the outer semi-molten layer had a thickness of 500 μm. Thereafter, when the state of the crucible in the carbon susceptor was evaluated, 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)

Silicon single crystal pulling was performed using a quartz glass crucible in which the Al concentration of the Al-added outer bubble layer was 72 ppm and the outer semi-molten layer had a thickness of 3 μm. After that, when the state of the crucible in the carbon susceptor was evaluated, 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 stained form, and foaming and peeling of the crystal layer occurred.

(Comparative Example 4)

Silicon single crystal pulling was performed using a quartz glass crucible in which the Al concentration of the Al-added outer bubble layer was 73 ppm and the thickness of the outer semi-molten layer was 620 μm. Then, when the state of the crucible in the carbon susceptor was evaluated, the outer surface peeling due to the difference in thermal expansion coefficient between the excessively thick outer semi-molten layer and the glass layer occurred in most parts, and the crucible was deformed.

From the above results, it can be seen that if the outer semi-molten layer is excessively thin, crystallization of the outer surface of the crucible does not proceed, so the crucible is fused to the carbon susceptor and cannot stand on its own, and foaming and peeling of the crystal layer occurs. there was. In addition, when the outer semi-molten layer is excessively thick, it was found that the outer surface peeling due to the difference in thermal expansion coefficient between the outer semi-molten layer and the glass layer occurred in most parts, and the crucible was deformed.

<Consideration of bottom taper shape of Al-added outer bubble layer>

The pulling of the silicon single crystal was performed using various quartz glass crucibles having different rates of change in the taper shape of the lower end of the Al-added outer bubble layer formed on the side wall of the crucible. Thereafter, the state of the crucible was evaluated. The results are shown in Table 3.

(Example 6)

The pulling of the silicon single crystal was performed using a quartz glass crucible having a rate of change of the taper shape at the lower end of the Al-added outer bubble layer of 0.07 mm/mm. Thereafter, when the state of the crucible was evaluated, no cracks occurred.

(Example 7)

The pulling of the silicon single crystal was performed using a quartz glass crucible having a change rate of 0.1 mm/mm in the taper shape of the lower end of the Al-added outer bubble layer. Thereafter, when the state of the crucible was evaluated, no cracks occurred.

(Example 8)

The pulling of the silicon single crystal was performed using a quartz glass crucible having a rate of change of the taper shape of the lower end of the Al-added outer bubble layer of 0.5 mm/mm. Thereafter, when the state of the crucible was evaluated, no cracks occurred.

(Comparative Example 5)

The pulling of the silicon single crystal was performed using a quartz glass crucible having a rate of change of the taper shape at the lower end of the Al-added outer bubble layer of 0.7 mm/mm. After that, when the state of the crucible was evaluated, cracks had been generated in the vicinity of the lower end of the side wall portion.

From the above results, it was found that, when the rate of change of the taper shape at the lower end of the Al-added outer cell layer is large, cracks are more likely to occur due to stress concentration at the boundary between the Al-added layer and the Al-free layer.

1 Quartz Glass Crucible
5 silicone melt
10a side wall
10b bottom
10c corner
10i Crucible inside
10o Crucible exterior
11 transparent layer
12 bubble layer
12a inner bubble layer
12b Al-added outer bubble layer
12b _e The lower part of the Al-added outer bubble layer
13 Outer surface semi-melted layer
13a Al-added semi-molten layer
13b Al-free semi-molten layer
14a composite 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 Sedimentary Layer
19 crystal layer
20 carbon susceptor
20g break
30 mold
30i mold inner
31 arc electrode
32 vents

Claims (9)

A transparent layer made of silica glass that does not contain air bubbles;
A bubble layer provided on the outside of the transparent layer and made of silica glass including a plurality of bubbles;
It is provided on the outside of the bubble layer, and includes an outer semi-melted layer in which raw silica powder is sintered in a semi-melted 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 on the outside of the inner bubble layer and made of silica glass to which aluminum is added,
At least a part of the outer semi-molten layer in contact with the Al-added outer bubble layer is an Al-added semi-melted 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 concentration of aluminum in the surface layer portion of the Al-added semi-molten layer is 100 ppm or more,
A quartz glass crucible for pulling up silicon single crystals, characterized in that the aluminum concentration of the deep part of the Al-added semi-molten layer deeper than the surface layer part is lower than the aluminum concentration of the surface layer part. The method according to claim 1,
The thickness of the Al-added semi-molten layer is 5 μm or more and 500 μm or less, a quartz glass crucible. The method according to claim 1 or 2,
It has a cylindrical side wall portion, a curved bottom portion, and a corner portion positioned between the side wall portion and the bottom portion, the corner portion having a greater curvature than the bottom portion,
The Al-added outer bubble layer and the Al-added semi-molten layer are provided at least on the side wall portion. 4. The method according to claim 3,
The cell layer in the side wall portion has a two-layer structure of the inner cell layer and the Al-added outer cell layer,
The said bubble layer in the said bottom part is a single-layer structure of the said inner side bubble layer, The quartz glass crucible. 5. The method according to claim 4,
The lower end of the Al-added outer bubble layer has a tapered shape,
The reduction rate of the thickness of the lower end is 0.5 mm / mm or less, a quartz glass crucible. 5. The method according to claim 4,
The bubble content rate of the said Al addition outer cell layer in the said side wall part is higher than the bubble content rate of the said inner cell layer, The quartz glass crucible. delete A step of filling the inner surface of the 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 bubble-free silica glass by heating and melting the deposited layer of silica powder from the inside of the mold and adjusting the pressure-reducing force of the deposited layer from the inside of the mold, and on the outside of the transparent layer A step of forming a quartz glass crucible comprising a bubble layer made of silica glass comprising a plurality of bubbles, and an outer semi-melted layer provided outside the bubble layer, in which raw silica powder is sintered in a semi-molten state class,
adjusting the thickness of the outer semi-molten layer of the quartz glass crucible taken out from the mold to be 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,
The concentration of aluminum in the surface layer portion of the outer semi-molten layer is 100 ppm or more,
The aluminum concentration of the deep portion of the outer semi-melted layer deeper than the surface layer portion is lower than the aluminum concentration of the surface layer portion. 9. The method of claim 8,
The deposition layer of the silica powder, the Al-added natural silica powder, the Al-free natural silica powder and the synthetic silica powder is deposited in that order, a method of manufacturing a quartz glass crucible for pulling silicon single crystal.

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