JP7024700B2 - Quartz glass crucible - Google Patents

Description

The present invention relates to a quartz glass crucible, and more particularly to a quartz glass crucible used for pulling a silicon single crystal by the Czochralski method (CZ method).

A quartz glass crucible (silica glass crucible) is used for producing a silicon single crystal by the CZ method. In the CZ method, a polycrystalline silicon raw material is heated in a quartz glass rutsubo to generate a silicon melt, the seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled up while rotating the rutsubo. Grow larger single crystals. According to the CZ method, a single crystal having a large diameter can be grown, and the mass productivity of the silicon single crystal can be improved.

Regarding the quartz glass rutsubo, for example, in Patent Document 1, the maximum layer thickness of the synthetic quartz glass inner surface layer is 20 to 80% of the maximum wall thickness of the corner portion, whereby the inner surface layer of the straight body portion and the bottom portion is the corner portion. A quartz glass rut that is formed thinner than the inner layer and has the thickest synthetic quartz glass inner layer at the corners is described.

Patent Document 2 describes a translucent outer layer made of natural quartz glass containing a large number of bubbles and synthetic quartz glass in order to suppress heat convection in the silicon melt and prevent vibration on the surface of the melt. A quartz glass rutsubo having a three-layer structure is described in which a semi-transparent intermediate layer made of synthetic quartz glass and containing a large number of bubbles is provided between the transparent inner layer which is substantially bubble-free.

In Patent Document 3, the thickness of the opaque layer at the corner portion is 25% or more and 80% or less of the total thickness of the opaque layer and the transparent layer, and the thickness of the opaque layer at the straight portion and the bottom portion is the opaque layer and the opaque layer. A quartz glass crucible is described in which the total thickness of the transparent layer is 10% or more and less than 25%, and the thickness of the opaque layer at the corner portion is larger than that of the straight portion and the bottom portion.

In Patent Document 4, the inner surface side of the crucible wall is made of a transparent layer, the outer surface side of the wall is made of an opaque layer, and the thickness of the transparent layer at the curved portion of the crucible is 0.5 mm as compared with the transparent layer of other portions. Described is a quartz crucible for pulling a silicon single crystal, which is thicker than the above, and on the contrary, the thickness of the opaque layer in the curved portion is 0.5 mm or more thinner than that of the opaque layer in the other portion.

Patent Document 5 describes a quartz glass crucible in which a synthetic bubble-free layer, a natural bubble-free layer, a natural bubble layer, and an unmelted particle layer are formed in this order from the inner surface side of the crucible. Further, in the method for producing a quartz crucible, it is described that the film layer formed on the inner surface of the crucible is removed by sublimation in the first stage of the crucible melting process.

Japanese Patent No. 5252157 Japanese Unexamined Patent Publication No. 2001-348294 Japanese Unexamined Patent Publication No. 2016-193809 Japanese Unexamined Patent Publication No. 8-301693 Japanese Unexamined Patent Publication No. 2010-143818

In recent years, with the increase in diameter of silicon single crystals and the lengthening of the crystal pulling process, quartz glass crucibles need to withstand long-term use. In addition, the heat load of the crucible is high due to the high heat insulation performance of the parts inside the raising furnace.

However, the conventional quartz glass crucible cannot maintain its shape in a thermal environment of 1400 ° C or higher when the silicon single crystal is pulled up, causing deformation of the crucible such as buckling and inward tilting, which causes the liquid level of the silicon melt. Problems such as level fluctuations, crucible damage, and contact with internal parts of the furnace become problems. In addition, cristobalite is deposited on the inner surface of the crucible in contact with the silicon melt, and the outer periphery thereof becomes a brown precipitate (brown ring). When this brown ring is peeled off and incorporated into a growing silicon single crystal, it causes dislocation. In particular, the deformation of the crucible promotes the peeling of the brown ring and dislocations are likely to occur. Therefore, it is required to prevent the deformation of the crucible as much as possible.

Further, since the inner surface of the crucible that comes into contact with the silicon melt is gradually melted during the single crystal pulling step, the silicon single crystal grown by the CZ method contains a large amount of oxygen supplied from the crucible. On the other hand, in order to improve the quality of semiconductor devices, it has recently been required to make the oxygen concentration in a silicon single crystal (particularly the oxygen concentration in the pulling axis direction) uniform, and quartz glass that can meet such a requirement. A crucible is desired. In addition, the melt surface may vibrate due to the reaction between the rutsubo and the silicon melt, and if the molten metal surface vibration occurs, the seed crystal cannot be landed, and even if the liquid can be landed, the crystal diameter is not stable. The probability of dislocations occurring in a single crystal is high.

Therefore, an object of the present invention is to provide a quartz glass crucible that is not easily deformed and can reduce the dislocation generation rate.

In order to solve the above problems, the quartz glass rut for pulling a silicon single crystal according to the present invention is made of synthetic quartz molten glass containing bubbles, and has a seal layer constituting the inner surface of the quartz glass rut and synthetic quartz not containing bubbles. It is composed of a synthetic transparent layer made of molten glass and formed on the outside of the sealing layer, and a natural quartz molten glass containing no bubbles, and contains a natural transparent layer formed on the outside of the synthetic transparent layer and a large number of bubbles. It is made of natural quartz molten glass and has a natural bubble layer formed on the outside of the natural transparent layer, and the bubble content of the seal layer is higher than the bubble content of the synthetic transparent layer. ..

Brown rings are likely to occur on the outermost surface of the crucible that has undergone arc melting, and the growth and melting of the brown rings occur at the same time during crystal pulling, and when the brown rings are peeled off, there is a high probability that dislocations will occur in the single crystal. Become. However, in the quartz glass crucible according to the present invention, the sealing layer is formed on the inner surface of the crucible, and the sealing layer is easily melted due to the presence of air bubbles in the sealing layer. Growth can be suppressed, thereby reducing the rate of dislocation occurrence.

In the present invention, the thickness of the seal layer is preferably 0.1 mm or more and 2.0 mm or less. When the thickness of the seal layer is within the above range, it is possible to suppress the vibration of the molten metal surface and the growth of the brown ring at the initial stage of the crystal pulling step. Further, since the seal layer is melted and disappears before the process of growing the straight body portion of the single crystal is started, it is possible to prevent the single crystal from being dislocated due to the seal layer.

In the present invention, the bubble content of the seal layer is preferably 0.1 vol% or more and 5.0 vol% or less, and more preferably 0.1 vol% or more and 3.0 vol% or less. In this case, it is more preferable that the bubble number density of the seal layer is 15 cells / cm ³ or more and 300 cells / cm ³ or less, and the average bubble diameter of the seal layer is 0.2 μm or more and 100 μm or less. If the bubble content, bubble number density and average bubble diameter of the seal layer are within the above ranges, hot water is prevented from dislocating the single crystal due to the inner surface of the rutsubo crystallizing (precipitation of Cristovalite) and peeling. Surface vibration can be suppressed.

The bubble content of the seal layer is preferably lower than the bubble content of the natural bubble layer. This makes it possible to suppress the occurrence of pinholes. Further, it is possible to prevent the infrared transmittance of the seal layer from being greatly reduced and the temperature of the inner surface of the crucible from being excessively lowered. The pinhole is a minute cavity in the crystal formed by the gas or the like in the silicon melt being taken into the silicon single crystal, and is a cause of device failure.

The quartz glass rutsubo according to the present invention is made of natural quartz molten glass containing a large number of bubbles, further includes a hardened crystal layer formed on the outside of the hardened natural cell layer, and contains an alkali metal and alkaline soil contained in the hardened crystal layer. It is preferable that the concentration of the element of the class metal or the earth metal is higher than that of the natural bubble layer. In this case, the concentration of the alkali metal, alkaline earth metal or earth metal element contained in the crystal hardening layer is preferably 10 ppm or more higher than that of the natural bubble layer, and particularly preferably 20 ppm or more. According to this configuration, crystallization of the outer surface of the crucible can be promoted to improve the strength of the crucible, and dislocation of a single crystal due to deformation of the crucible can be suppressed. In addition, the infrared transmittance can be reduced by crystallization of the outer surface of the crucible to suppress the temperature rise of the inner surface of the crucible, and the supply of oxygen due to the melting damage of the crucible can be suppressed.

The quartz glass rutsubo according to the present invention has a cylindrical side wall portion, a curved bottom portion, and a corner portion located between the side wall portion and the bottom portion and having a curvature larger than that of the bottom portion. The wall thickness of the wall is thicker than the wall thickness of the side wall portion and the bottom portion, and the thickness of the synthetic transparent layer at the corner portion is preferably thicker than the thickness of the synthetic transparent layer at the side wall portion and the bottom portion. .. In particular, the maximum wall thickness of the corner portion is preferably 1.1 times or more, more preferably 1.5 times or more the average wall thickness of the side wall portion. By making the wall thickness of the corner portion 1c sufficiently thicker than that of other portions, the strength of the entire crucible can be improved, and deformation such as buckling and sinking of the crucible can be suppressed. Further, since the temperature of the corner portion of the inner surface of the crucible is the highest and the contact time with the silicon melt is long, the amount of melting loss is larger than that of other portions. However, by increasing the wall thickness of the corners and sufficiently increasing the thickness of the synthetic transparent layer at the corners, it is possible to prevent the natural bubble layer from being exposed, and the single crystal is contaminated with impurities and dislocated. Can be prevented. Furthermore, if the synthetic transparent layer is thick, the distance at which impurities in the natural layer diffuse to the inner surface of the crucible can be sufficiently maintained. Therefore, it is possible to prevent the exfoliation of cristobalite and the contamination of the silicon single crystal due to the diffusion of impurities in the natural layer to the inner surface of the crucible.

According to the present invention, it is possible to provide a quartz glass crucible that is not easily deformed and can reduce the dislocation generation rate of a single crystal.

FIG. 1 is a schematic 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 a part (E portion) of the side wall portion of the quartz glass crucible of FIG. 1 in an enlarged manner. FIG. 3 is a schematic diagram for explaining a method for manufacturing a quartz glass crucible. 4 (a) to 4 (d) are diagrams for explaining the formation process of the quartz glass layer.

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

FIG. 1 is a schematic cross-sectional view showing the structure of a quartz glass crucible according to an embodiment of the present invention. Further, FIG. 2 is a schematic cross-sectional view showing a part (E portion) of the side wall portion of the quartz glass crucible of FIG. 1 in an enlarged manner.

As shown in FIG. 1, the quartz glass crucible 1 is a bottomed cylindrical container for supporting a silicon melt, and has a cylindrical side wall portion 1a, a gently curved bottom portion 1b, and a side wall portion 1a. It has a corner portion 1c located between the bottom portion 1b and having a curvature larger than that of the bottom portion 1b.

The present invention is applicable to crucibles of all calibers including crucibles having a small diameter of 14 inches (about 350 mm), but is preferably 24 inches (600 mm) or more, and preferably 32 inches (about 800 mm) or more. More preferred. This is because such a large-diameter crucible is used for pulling up a large silicon single crystal ingot having a diameter of 300 mm or more, and it is required that it is not easily deformed even if it is used for a long time. In recent years, the thermal environment of crucibles has become harsher due to the increase in size of crucibles due to the increase in size of silicon single crystals and the lengthening of the pulling process, and improving the durability of large crucibles is an important issue.

The wall thickness of the crucible varies slightly depending on the part, but the wall thickness of the side wall of the crucible of 14 inches or more is 6 mm or more, the wall thickness of the side wall 1a of the crucible of 24 inches or more is 7 mm or more, and the wall thickness of the large crucible of 32 inches or more. The wall thickness of the side wall portion 1a is preferably 10 mm or more, and the wall thickness of the side wall portion 1a of a large crucible of 40 inches (about 1000 mm) or more is preferably 13 mm or more. This is because a large-capacity crucible needs to have a sufficient thickness so that it will not be deformed by the pressure from a large amount of silicon melt. The wall thickness of the side wall portion 1a of the crucible is generally constant, but the upper end portion tends to be slightly thinner than the lower end portion.

The thickness of the corner portion 1c of the quartz glass crucible 1 is preferably thicker than that of the side wall portion 1a and the bottom portion 1b. In particular, the maximum wall thickness of the corner portion 1c is preferably 1.1 times, more preferably 1.5 times or more the average wall thickness of the side wall portion 1a.

The quartz glass crucible 1 is heated and softened during crystal pulling, and is easily deformed by the pressure from the silicon melt and the weight of the crucible. In particular, the degree of softening of the portion below the liquid surface of the silicone melt is large, and swelling (swelling) of the inner surface of the corner portion is likely to occur. When the crucible is deformed, the brown ring formed on the inner surface of the crucible is peeled off, which causes dislocation of the silicon single crystal. In addition, the temperature of the corners of the inner surface of the crucible is the highest, and the contact time with the silicon melt is long, so the amount of dissolution is larger than in other parts, which causes an increase in the oxygen concentration in the single crystal. Become.

However, by making the wall thickness of the corner portion 1c thicker than that of other portions, the strength of the entire crucible can be improved, and deformation such as buckling and sinking of the crucible can be suppressed, especially in the corner portion. The inner surface buckling can be suppressed. Further, since the temperature of the inner surface of the crucible is relatively low due to the thick wall thickness of the corner portion 1c of the crucible, it is possible to suppress the melting damage of the crucible.

As shown in FIG. 2, the quartz glass crucible 1 according to the present embodiment has a five-layer structure, and from the inside of the crucible, a seal layer 11, a synthetic transparent layer 12, a natural transparent layer 13, a natural bubble layer 14, and a crystal hardening layer. 15 has a structure provided in order.

The seal layer 11 is a synthetic quartz molten glass layer containing bubbles, and suppresses the growth of brown rings generated on the inner surface of the crucible at the initial stage of the silicon single crystal pulling process (liquid landing process to neck process) and silicon. It plays a role in preventing the molten metal from vibrating the surface of the molten metal. Brown rings are likely to occur on the outermost surface of the crucible that has undergone arc melting, and when the brown rings are peeled off, the probability of dislocations occurring in the single crystal increases. Further, if the molten metal surface vibration occurs in the liquid landing process of the seed crystal, the seed crystal cannot be blended with the melt. Further, if the molten metal surface vibration occurs in the neck process of narrowing the crystal diameter, the crystal diameter is not stable and dislocations may occur in the single crystal. Further, when the molten metal surface vibration occurs, the brown ring generated on the surface of the crucible and the quartz piece on the surface of the crucible are easily peeled off by the vibration. However, when the seal layer 11 is provided on the inner surface of the crucible, it is possible to promote the melting damage of the inner surface of the crucible while suppressing the vibration of the molten metal surface of the silicon melt, and the brown ring on the inner surface of the crucible grows significantly. The brown ring can be extinguished with the seal layer 11 before.

The synthetic quartz molten glass layer refers to a quartz glass layer formed by using a synthetic quartz raw material (synthetic silica raw material). Synthetic quartz is, for example, a silica raw material synthesized by hydrolysis of silicon alkoxide. In general, synthetic quartz has a lower concentration of metal impurities and a higher concentration of OH groups than natural quartz. For example, the content of each metal impurity contained in synthetic quartz is less than 0.05 ppm, and the content of OH groups is 30 ppm or more. Whether or not it is synthetic quartz can be comprehensively judged from the concentrations of OH groups and a plurality of metal impurities. As described above, since synthetic quartz has less impurities than natural quartz, it is possible to prevent the elution of impurities from the crucible into the silicon melt.

The seal layer 11 is designed so that the synthetic transparent layer 12 is exposed by melting before the start of pulling up the straight body portion of the silicon single crystal. This is because if the seal layer 11 does not disappear at the start of pulling up the straight body portion, the brown ring may be incorporated into the single crystal and dislocation may occur. Therefore, the thickness of the seal layer 11 is preferably 0.1 to 2.0 mm. If the seal layer 11 is smaller than 0.1 mm, the seal layer 11 disappears immediately, and the effect of providing the seal layer 11 cannot be obtained. Further, when the seal layer 11 is larger than 2.0 mm, the seal layer 11 may not disappear before the start of pulling up the straight body portion. The seal layer 11 may be at least on the side wall portion 1a, whereby crystallization of the inner surface of the crucible and vibration of the molten metal surface of the silicon melt can be suppressed.

The bubble content of the seal layer 11 is preferably higher than that of the synthetic transparent layer 12 and the natural transparent layer 13 and lower than that of the natural bubble layer 14, and the bubble content of the seal layer 11 is 0.1 to 5.0 vol%. It is preferably present, and more preferably 0.1 to 3.0 vol%. In this case, the bubble number density is preferably 15 to 300 cells / cm ³ . The average bubble diameter is preferably 0.2 to 100 μm, preferably 0.2 to 50 μm. When the bubble content, the bubble number density and the average cell diameter in the seal layer 11 are within the above ranges, the melting rate of the inner surface of the rutsubo can be increased, and cristobalite generated on the surface of the seal layer 11 is generated. Cristobalite can be extinguished together with the seal layer 11 before it grows and peels off to prevent dislocation of the single crystal. It is preferable that the bubble content of the seal layer 11 is higher in the upper part of the side wall portion than in the lower part of the side wall portion.

If the bubble content, bubble number density and average bubble diameter of the seal layer 11 exceed the above ranges, pinholes may occur in the crystal. That is, when the inner surface of the rutsubo is melted, many bubbles enter the silicon melt in the rutsubo, and these bubbles are taken into the solid-liquid interface by the melt convection, so that pinholes are generated in the single crystal. Alternatively, if bubbles adhere to the inner surface of the crucible and then are taken into the single crystal by peeling from the inner surface of the crucible while pulling up the straight body portion, pinholes are generated in the single crystal.

The second synthetic transparent layer 12 is a synthetic quartz molten glass layer containing no bubbles and is located outside the seal layer 11. The synthetic transparent layer 12 is provided to prevent dislocation of the silicon single crystal due to the influence of bubbles and generation of pinholes in the single crystal, and to prevent impurity contamination of the silicon single crystal. Since the synthetic transparent layer 12 constitutes the inner surface of the crucible wall after the seal layer 11 is melted and disappears and is in contact with the silicon melt, it is required to have high purity in order to prevent contamination of the silicon melt. ..

The thickness of the synthetic transparent layer 12 is preferably 0.1 to 10 mm, and particularly preferably 0.5 to 10 mm. The synthetic transparent layer 12 is set to an appropriate thickness for each crucible site so that the natural transparent layer 13 is not completely disappeared during the pulling process of the single crystal and the natural transparent layer 13 is not exposed. For example, the thickness of the synthetic transparent layer of the crucible of 14 inches or more is about 0.5 mm. It is preferable that the synthetic transparent layer 12 is provided on the entire crucible from the side wall portion 1a to the bottom portion 1b of the crucible together with the natural transparent layer 13. However, it is also possible to omit the formation of the transparent layer at the upper end portion (rim portion) of the crucible that does not come into contact with the silicon melt.

The fact that the synthetic transparent layer 12 does not contain air bubbles means that air bubbles have been removed to the extent that it looks transparent at first glance. The synthetic transparent layer 12 may have a bubble content to such an extent that the single crystal yield does not decrease due to the rubble debris when the bubbles burst, the bubble content is less than 0.1 vol%, and the number of bubbles. The density is preferably 15 cells / cm ³ or less, and the average bubble diameter is preferably 50 μm or less.

The third natural transparent layer 13 is a natural quartz molten glass layer containing no bubbles and is located outside the synthetic transparent layer 12. That is, the synthetic transparent layer 12 of the second layer and the natural transparent layer 13 of the third layer are the same transparent layer, but are different from the synthetic transparent layer 12 using a synthetic raw material in that the raw material used is a natural raw material. As a result, the concentration of impurities contained in the natural transparent layer 13 is higher than that of the synthetic transparent layer 12. Since the natural transparent layer 13 has a higher viscosity than the synthetic transparent layer 12, it is possible to suppress the thermal expansion of the natural bubble layer 14 provided on the outer surface side of the crucible from propagating to the inner surface side of the crucible. Further, by providing the boundary between the synthetic quartz molten glass layer and the natural quartz molten glass layer in the transparent layer, it is possible to prevent the synthetic quartz molten glass layer from being peeled off due to a heat load. The fact that the natural transparent layer 13 does not have air bubbles means that the air bubbles have been removed to the extent that it looks transparent at first glance, and the natural transparent layer 13 should have the same transparency as the synthetic transparent layer 12. Just do it.

The natural quartz molten glass layer is a quartz glass layer formed by using a natural quartz raw material. Natural quartz is a natural raw material such as natural quartz and silica stone. In general, natural quartz has a higher concentration of metal impurities and a lower concentration of OH groups than synthetic quartz. For example, the content of Al contained in natural quartz is 1 ppm or more, the content of alkali metals (Na, K and Li) is 0.05 ppm or more, and the content of OH groups is less than 80 ppm. Whether or not it is natural quartz can be comprehensively judged from the concentrations of OH groups and a plurality of metal impurities. Since natural quartz has a higher viscosity at high temperatures than synthetic quartz, the heat resistance of the entire crucible can be increased. In addition, natural quartz is cheaper than synthetic quartz and is advantageous in terms of cost.

In the initial stage of crystal pulling (until the start of growing the shoulder part), the brown ring is still small, and since the seal layer constitutes the inner surface of the crucible, the inner surface of the crucible is easily dissolved, so most of the brown rings are still small in size. It disappears by peeling or dissolving. In this way, the number of brown rings decreases in the middle of the crystal pulling, but a part of the brown rings grows without disappearing, and the brown rings that did not disappear peel off during the growth of the straight body. It is presumed that the single crystal undergoes dislocation. Peeling of the brown ring is likely to occur when the inner surface of the crucible is deformed. However, by interposing the natural transparent layer 13 between the synthetic transparent layer 12 and the natural bubble layer 14, deformation of the inner surface of the synthetic transparent layer 12 can be suppressed, and peeling of the brown ring can be prevented.

The fourth natural bubble layer 14 is a natural quartz molten glass layer containing a large number of bubbles. The natural bubble layer 14 is provided to disperse the radiant heat from the heater arranged on the outside of the crucible and heat the silicon melt in the crucible as uniformly as possible. Since the natural cell layer 14 has a larger heat capacity than the transparent layer, the temperature of the silicon melt can be stably controlled. In addition, the heat insulating property of the crucible can be improved, and the sagging of the inner surface of the crucible due to the temperature of the inner surface of the crucible becoming too high, the generation / growth of brown rings, and the increase in the oxygen concentration of the single crystal due to the melting of the crucible are suppressed. be able to. Furthermore, it suppresses the deterioration of the inner surface of the crucible by mitigating the sudden change in heat received from the heater when raising and lowering the crucible, powering on the heater, and shifting the process from the shoulder part of the single crystal to the straight body part, and the silicon single crystal. It is possible to suppress abrupt changes in the oxygen taken in. The natural bubble layer 14 is preferably provided on the entire crucible from the side wall portion 1a to the bottom portion 1b of the crucible.

The bubble content of the natural bubble layer 14 is larger than the bubble content of the seal layer 11, the synthetic transparent layer 12 and the natural transparent layer 13, preferably 0.2 to 5 vol%, and preferably 1 to 4 vol%. Is even more preferable. This is because if the bubble content of the natural bubble layer 14 is 1 vol% or less, the function of the natural bubble layer 14 cannot be exhibited and the heat retention property becomes insufficient. Further, when the bubble content of the natural bubble layer 14 exceeds 5 vol%, the crucible may be greatly deformed due to the expansion of the bubbles, the single crystal yield may decrease, and the heat transfer property becomes insufficient. In particular, when the bubble content of the natural bubble layer 14 is 1 to 4%, the crucible can be further prevented from being deformed and the heat transfer property can be further enhanced.

The fifth crystal hardening layer 15 is a natural quartz molten glass layer containing a large amount of a crystallization accelerator. The crystallization accelerator is an element of an alkali metal, an alkaline earth metal, or an earth metal, and examples thereof include Li, Na, K, Mg, Ca, Sr, Ba, Al, and Ga. When a large amount of crystallization accelerator is contained, crystallization of the outer surface of the crucible can be promoted to increase the strength of the crucible, or the viscosity of the quartz glass softened at high temperature can be increased to cause the crucible to buckle or collapse. Deformation can be prevented. Further, the crystal hardening layer 15 has an effect of lowering the infrared transmittance of the crucible, and moderates the sudden change in heat received from the heater, whereby the sudden change in the oxygen concentration in the silicon single crystal can be suppressed. The total thickness of the natural bubble layer 14 and the crystal hardening layer 15 is a value obtained by subtracting the total thickness of the seal layer 11, the synthetic transparent layer 12 and the natural transparent layer 13 from the wall thickness of the crucible, and varies depending on the crucible site.

The portion where the total thickness of the synthetic transparent layer 12 and the natural transparent layer 13 is maximized is formed in the corner portion 1c, and the thickness of the synthetic transparent layer 12 in the corner portion 1c is the composite in the side wall portion 1a and the bottom portion 1b. It is preferably thicker than the thickness of the transparent layer 12. The corner portion 1c of the crucible is a portion where the temperature of the inner surface of the crucible is highest, and the contact time with the silicon melt is long, so that the amount of melting damage is larger than that of other portions. However, by increasing the wall thickness of the corner portion 1c and further increasing the thickness of the synthetic transparent layer 12 in the corner portion 1c, it is possible to prevent the natural bubble layer 14 from being exposed, and the single crystal is contaminated with impurities. And it is possible to prevent dislocation.

FIG. 3 is a schematic diagram for explaining a method for manufacturing a quartz glass crucible. Further, FIGS. 4A to 4D are diagrams for explaining the formation process of the quartz glass layer.

As shown in FIG. 3, the quartz glass crucible 1 according to the present embodiment can be manufactured by a so-called rotary molding method. In the rotary molding method, a natural quartz powder 21 to which a crystallization accelerator is added, a normal natural quartz powder 22 and a synthetic quartz powder 23 are deposited in this order on the inner surface 30i of the rotating mold 30 to deposit a layer of raw quartz powder. 20 is formed (see FIG. 4 (a)). The raw material quartz powder stays in a fixed position while sticking to the inner surface 30i of the mold 30 due to centrifugal force, and the shape of the crucible is maintained.

Next, the arc electrode 31 is installed in the mold 30, and the deposited layer 20 of the raw material quartz powder is arc-melted from the inner surface 30i side 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 fused silica glass is controlled by vacuuming the deposited layer 20 of the raw quartz powder from a large number of ventilation holes 32 provided on the inner surface 30i of the mold 30.

Since the arc heat is gradually transmitted from the inside to the outside of the raw material quartz powder deposit layer 20 and melts the raw material quartz powder, the sealing layer 11 is changed by changing the depressurizing condition at the timing when the raw material quartz powder starts to melt. , The synthetic transparent layer 12, the natural transparent layer 13, the natural bubble layer 14, and the crystal hardening layer 15 can be made separately. If vacuum melting is performed by increasing the depressurization at the timing when the quartz powder melts, the arc atmosphere gas is not confined in the glass, and the quartz glass does not contain bubbles. Further, if normal melting (atmospheric pressure melting) in which the reduced pressure is weakened is performed at the timing when the quartz powder melts, the arc atmosphere gas is confined in the glass, and the quartz glass contains many bubbles.

Specifically, the seal layer 11 containing air bubbles is formed by slightly weakening the suction force from the ventilation hole 32 at the start of arc melting (see FIG. 4B), and then the suction force is strengthened. The synthetic transparent layer 12 and the natural transparent layer 13 are formed in this order (see FIG. 4 (c)). After that, the natural bubble layer 14 and the crystal hardening layer 15 are formed in order by weakening the suction force (FIG. 4 (d)).

After that, the arc heating is finished and the crucible is cooled. As described above, the quartz glass crucible 1 in which the sealing layer 11, the synthetic transparent layer 12, the natural transparent layer 13, the natural bubble layer 14, and the crystal hardening layer 15 are provided in this order from the inside to the outside of the crucible wall is completed.

As described above, in the quartz glass rutsubo 1 according to the present embodiment, the seal layer 11, the synthetic transparent layer 12, the natural transparent layer 13, the natural bubble layer 14, and the crystal hardening layer 15 are provided in this order from the inner surface side of the rutsubo. Since it has a structure and the bubble content of the seal layer 11 is higher than that of the synthetic transparent layer 12 and lower than that of the natural bubble layer 14, it promotes melting damage of the inner surface of the rutsubo while suppressing the surface vibration of the silicon melt. Can be Therefore, it is possible to prevent the single crystal from being dislocated due to the inner surface of the crucible crystallizing and peeling off, thereby reducing the dislocation occurrence rate of the single crystal. Further, the thickness of the seal layer 11 is 0.1 mm or more and 2.0 mm or less, and the seal layer is melted and disappears before the straight body portion growing step of the silicon single crystal is started, and the synthetic transparent layer is exposed and the crucible is exposed. Since it constitutes the inner surface, it is possible to prevent dislocation of a single crystal and contamination with impurities.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention, and these are also the present invention. Needless to say, it is included in the range.

For example, in the above embodiment, the five-layer structure of the seal layer 11, the synthetic transparent layer 12, the natural transparent layer 13, the natural bubble layer 14, and the crystal cured layer 15 is used, but the outermost crystal cured layer 15 is omitted. It is also possible to have a four-layer structure of a seal layer 11, a synthetic transparent layer 12, a natural transparent layer 13, and a natural bubble layer 14.

<Discussion 1: Consideration of crucibles with different layer structures>
After pulling up a silicon single crystal by the CZ method using a quartz glass crucible with a diameter of 32 inches, the single crystal yield and the degree of deformation of the crucible after use were evaluated. In this evaluation test, a plurality of crucible samples A1 to A3 having different layer structures were prepared, and a plurality of silicon single crystals were pulled up using these crucibles. The results are shown in Table 1.

As shown in Table 1, in sample A1 having a three-layer structure of a synthetic transparent layer / a natural transparent layer / a natural bubble layer and having no seal layer, it is assumed that the crystal can be pulled up because the molten metal surface vibration is intense. However, the crystal yield was 60% or less due to the dislocation of the single crystal.

In the crucible sample A2 having a three-layer structure of a seal layer, a synthetic transparent layer, and a natural bubble layer, the action of the seal layer could suppress the vibration of the molten metal surface and the increase of the brown ring, but the crystal yield was 70% or less. .. It is considered that such deterioration of crystal yield is due to the absence of the natural transparent layer, which causes deformation due to thermal expansion of the natural bubble layer to propagate to the synthetic transparent layer, causing deformation of the inner surface and exfoliation of the brown ring. ..

Further, in the sample A3 having a four-layer structure of a seal layer / synthetic transparent layer / natural transparent layer / natural bubble layer, the crystal yield was 80% or more. In sample A3, the action of the seal layer can suppress the vibration of the molten metal surface and the increase of the brown ring, and the action of the natural transparent layer suppresses the deformation of the synthetic transparent layer due to the expansion of the natural bubble layer, due to the deformation of the synthetic transparent layer. It is considered that the peeling of the brown ring can be suppressed.

<Discussion 2: Consideration of the thickness of the seal layer of the 4-layer crucible>
A plurality of samples B1 to B5 of 4-layer crucibles having different thicknesses of the seal layer were prepared, and the silicon single crystal was pulled up using these crucibles. The results are shown in Table 2.

As shown in Table 2, in sample B1 having a seal layer thickness of 0.05 mm, as in sample A1 without a seal layer, the surface vibration of the molten metal is so intense that crystal pulling cannot be performed, or even if it is possible, it is simple. The crystal yield was 65% or less due to the dislocation of crystals. Further, even in sample B5 having a seal layer thickness of 2.5 mm, dislocations occurred and the crystal yield was 70% or less. On the other hand, dislocations did not occur in the crucible samples B2 to B4 having a thickness of the seal layer of 0.1 to 2.0 mm. From these results, it was found that when the thickness of the seal layer is within the range of 0.1 to 2.0 mm, the effect of suppressing the dislocation of the single crystal can be obtained by the seal layer. If the seal layer is too thick, it is considered that the crystal yield is lowered because the seal layer remains undissolved during the growth of the straight body portion of the single crystal and the brown ring is easily peeled off.

<Discussion 3: Consideration of bubble content, bubble number density, and average bubble diameter in the seal layer>
A plurality of samples C1 to C3 of four-layer crucibles having different air bubble conditions contained in the seal layer were prepared, and the silicon single crystal was pulled up using these crucibles. The results are shown in Table 3.

As shown in Table 3, in sample C1 having a bubble content of 0.1 to 5.0 vol%, a bubble number density of 15 to 300 cells / cm ³ , and an average bubble diameter of 0.2 to 100 μm, the crystal yield was high. It was over 80%. On the other hand, in sample C2 having a bubble content of less than 0.1 vol%, a bubble number density of less than 15 cells / ^cm3 , and an average cell diameter of less than 0.2 μm, the molten metal surface vibration is similar to that of sample A1 without a seal layer. The crystal yield could be reduced to 70% or less due to the dislocation of the single crystal, even if the crystal could not be pulled up due to the severe dislocation.

Further, in the sample C3 having a bubble content of more than 5.0 vol%, a bubble number density of more than 300 cells / cm ³ and an average bubble diameter of more than 100 μm, dislocation formation was suppressed and the crystal yield was 80% or more. However, when the wafer cut out from the single crystal was inspected, pinholes were found. The pinhole occurrence rate of samples C1 and C2 was 0.1% or less, whereas the pinhole occurrence rate of sample C3 was 3% or more. The pinhole occurrence rate is obtained by calculating the number of defective pinhole wafers / (number of wafers that have passed pinholes + number of defective wafers with pinholes). If there are too many bubbles contained in the seal layer, dislocation of the single crystal can be prevented, but it is considered that pinholes are likely to occur in the single crystal. From the above results, if the bubble content is in the range of 0.1 to 5.0 vol%, the bubble number density is in the range of 15 to 300 cells / cm ³ , and the average bubble diameter is in the range of 0.2 to 100 μm, the seal layer is used. It was found that the effect of suppressing dislocation of crystals can be obtained.

<Discussion 4: Consideration of the presence or absence of a hardened crystal layer>
A plurality of samples D1 of a 4-layer crucible without a hardened crystal layer and a plurality of samples D2 of a 5-layer crucible having a hardened crystal layer were prepared, and a silicon single crystal was pulled up using these crucibles. The results are shown in Table 4.

As shown in Table 4, in sample D1 having a four-layer structure of a seal layer / synthetic transparent layer / natural transparent layer / natural bubble layer and no crystal hardening layer, the crucible is less deformed and the crystal yield is 80% or more. Met. On the other hand, in the sample D2 having a five-layer structure of a seal layer / synthetic transparent layer / natural transparent layer / natural bubble layer / crystal hardened layer, the deformation of the crucible was very small, and the crystal yield was 85% or more. In the sample D2 further provided with the crystal hardening layer, it is considered that the effect of suppressing the peeling of the brown ring is further enhanced by sufficiently suppressing the deformation of the crucible.

<Discussion 5: Consideration of maximum wall thickness (maximum / side wall average) at corners>
Prepare samples E1 to E8 of 4-layer crucibles with different maximum wall thickness ratios (maximum wall thickness of corners / average wall thickness of side walls) of the crucibles, and use these crucibles to pull up the silicon single crystal. went. The results are shown in Table 5.

As shown in Table 5, in sample E1 in which the maximum wall thickness ratio of the corner portion is 0.5 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion is larger than that at the corner portion, the synthetic transparent layer disappears and impurities are diffused. The natural transparent layer was exposed by the peeling of cristobalite, and the brown ring was peeled by the deformation (swelling) of the rutsubo, and the crystal yield was 60% or less. Further, in the sample E2 in which the maximum wall thickness ratio of the corner portion was 0.5 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion was smaller than that at the corner portion, the natural transparent layer was not exposed, but the crucible was deformed (deformation of the crucible). The brown ring was peeled off by swelling), and the crystal yield became 70% or less.

The sample E3 in which the maximum wall thickness ratio of the corner portion was 1 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion was larger than that of the corner portion had the same result as the sample E1. The sample E4 in which the maximum wall thickness ratio of the corner portion was 1 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion was smaller than that of the corner portion gave the same result as the sample E2.

Sample E5, which has a maximum wall thickness ratio of 1.1 at the corners and a thickness of the synthetic transparent layer at the side wall and the bottom larger than that of the corners, gives the same results as the samples E1 and E3, and the crystal yield is 70% or less. It became. On the other hand, in sample E6 in which the maximum wall thickness ratio of the corner portion is 1.1 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion is smaller than that at the corner portion, the natural transparent layer is not exposed and the crucible is not deformed. rice field. As a result, the crystal yield of sample E6 was 80% or more.

Sample E7, which has a maximum thickness ratio of the corner portion of 1.5 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion is larger than that of the corner portion, has the same result as the sample E5, and the crystal yield is 70% or less. rice field. Further, the sample E8 having the maximum wall thickness ratio of the corner portion of 1.5 and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion smaller than that of the corner portion gives the same result as the sample E6, and the crystal yield is 80% or more. It became.

From the above results, in the samples E6 and E8 in which the maximum wall thickness ratio of the corner portion is 1.1 or more and the thickness of the synthetic transparent layer at the side wall portion and the bottom portion is smaller than that of the corner portion, the crystal yield is 80% or more. It was found that dislocation formation due to exposure of the natural transparent layer and deformation (swelling) of the crucible can be suppressed.

1 Quartz glass rut 1a Side wall 1b Bottom 1c Corner 11 Seal layer 12 Synthetic transparent layer 13 Natural transparent layer 14 Natural bubble layer 15 Crystal hardening layer 20 Deposit layer of raw material quartz powder 21 Natural quartz powder with crystallization accelerator added 22 Natural quartz powder (normal natural quartz powder)
23 Synthetic quartz powder 30 Mold 30i Mold inner surface 31 Arc electrode 32 Vent

Claims (5)

Quartz glass crucible for pulling up silicon single crystals
A seal layer made of synthetic quartz molten glass containing bubbles and constituting the inner surface of the quartz glass crucible,
A synthetic transparent layer made of synthetic quartz molten glass containing no bubbles and formed on the outside of the sealing layer, and a synthetic transparent layer.
A natural transparent layer made of natural quartz molten glass containing no bubbles and formed on the outside of the synthetic transparent layer, and a natural transparent layer.
It is made of natural quartz molten glass containing a large number of bubbles, and has a natural bubble layer formed on the outside of the natural transparent layer.
The bubble content of the seal layer is higher than the bubble content of the synthetic transparent layer.
The thickness of the seal layer is 0.1 mm or more and 2.0 mm or less.
The bubble content of the seal layer is 0.1 vol% or more and 5.0 vol% or less.
The bubble number density of the seal layer is 15 cells / cm ³ or more and 300 cells / cm ³ or less.
A quartz glass crucible having an average bubble diameter of 0.2 μm or more and 100 μm or less in the seal layer . The quartz glass crucible according to claim 1 , wherein the bubble content of the seal layer is lower than the bubble content of the natural bubble layer. It is made of natural quartz molten glass containing a large number of bubbles, and further includes a crystal hardening layer formed on the outside of the natural bubble layer.
The quartz glass rutsubo according to claim 1 or 2 , wherein the concentration of the alkali metal, alkaline earth metal or earth metal element contained in the crystal hardened layer is higher than that of the natural bubble layer. It has a cylindrical side wall, a curved bottom, and a corner located between the side wall and the bottom and having a greater curvature than the bottom.
The wall thickness of the corner portion is thicker than that of the side wall portion and the bottom portion.
The quartz glass crucible according to any one of claims 1 to 3 , wherein the thickness of the synthetic transparent layer at the corner portion is thicker than that of the synthetic transparent layer at the side wall portion and the bottom portion. The quartz glass crucible according to claim 4, wherein the sealing layer is provided on the bottom portion, the corner portion, and the side wall portion.

Images