JP7696205B2 - Quartz glass crucible and its manufacturing method - Google Patents

Description

The present invention relates to a quartz glass crucible for pulling silicon single crystals by the Czochralski method (hereinafter referred to as the "CZ method").

Quartz glass crucibles used to pull silicon single crystals are quartz components that contain silicon melt, and the inner surface of the crucible that comes into contact with the melt must be a highly pure transparent layer. On the other hand, the outer surface of the crucible usually has an opaque outer layer that generally contains many metal elements other than Si in order to reduce costs and improve high-temperature mechanical properties.

Incidentally, in order to highly purify quartz members, there is a method disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-233999, in which the members are exposed to a halogen gas such as hydrogen chloride to remove metal impurities.
In the method disclosed in Patent Document 1, a quartz member is etched with an HF solution to a depth of 30 μm or more from the surface, and then treated with halogen gas at 400° C. to 1300° C. to remove contained metal impurities.

WO2009/072513 publication

In the method disclosed in Patent Document 1, the quartz member is heated to a high temperature to enhance reactivity. A high temperature of 1000° C. or higher is usually suitable, but there is a risk of the quartz softening at temperatures around 1500° C., so the upper limit of the treatment temperature is about 1300° C.
When heating to this temperature, the heat source is usually placed near the side wall of the heating furnace. If the quartz member is a quartz glass crucible, the crucible is heated from its outer surface. This creates a temperature gradient in the crucible, with the outside being hotter and the inside being colder. In other words, the opaque outer layer is hotter than the transparent inner layer, which is the layer to be highly purified.

However, when the opaque outer layer becomes hot, the diffusion rate of elements at high temperatures increases, causing a problem that metal impurities contained in the opaque outer layer diffuse into the transparent inner layer.
In addition, since the formation of a high-purity layer using halogen gas also depends on the diffusion rate of the elements, there was a problem that in an environment where metal impurities diffuse from the outer layer of the crucible, which is at a higher temperature, it was not possible to form a high-purity layer of sufficient thickness.

The present invention was made under the above circumstances, and aims to provide a quartz glass crucible and its manufacturing method that has a sufficiently thick high-purity layer on the inner surface, which can reduce impurities that dissolve in the silicon melt during the single crystal pulling process, thereby making it possible to obtain high-purity silicon single crystals.

The quartz glass crucible of the present invention, which has been made to solve the above-mentioned problems, is a quartz glass crucible for pulling a single crystal, and has a transparent inner layer and at least one outer layer arranged outside the transparent inner layer, and is characterized in that the transparent inner layer has a distribution in which the content of Fe, Ni, Cr, and Cu is smallest at the surface and maximum at a depth of 20 to 40 μm from the surface.
In the transparent inner layer, the Fe content is 10 ppb or less and the Ni, Cr and Cu contents are 1 ppb or less in the range from 10 μm to 30 μm from the surface.

With this configuration, in a quartz glass crucible having a transparent inner layer, the metal impurity content is lowest at the surface of the transparent inner layer, and the metal impurity content is maximum at a depth of 20 to 40 μm from the surface of the transparent inner layer. In other words, a high-purity layer of sufficient thickness is formed on the surface of the transparent inner layer. This makes it possible to reduce the impurities that dissolve in the silicon melt during the single crystal pulling process, and to obtain a high-purity silicon single crystal.

The method for manufacturing a quartz glass crucible according to the present invention, which has been made to solve the above problems, is characterized by comprising the steps of: manufacturing a quartz glass crucible before high-purification treatment, which has a transparent inner layer and at least one outer layer arranged outside the transparent inner layer; and performing a high-purification treatment in which the transparent inner layer side of the quartz glass crucible before high-purification treatment is heated to a temperature of 1000°C to 1300°C, and halogen gas is supplied to the transparent inner layer side for a predetermined period of time, and the halogen gas reacts with the surface of the transparent inner layer to remove metal impurities.

According to this method, the quartz glass crucible is obtained by heating the quartz glass crucible before the high-purification treatment from its inner surface side and supplying halogen gas to perform the high-purification treatment. In this high-purification treatment, the inner layer side becomes hotter and the outer layer side becomes colder, so that the diffusion of metal impurities from the opaque outer layer, which contains a lot of metal impurities, can be suppressed and the high-purification treatment can be performed efficiently. In this case, heating from the outside of the quartz glass crucible may be used in combination.

The present invention provides a quartz glass crucible and its manufacturing method that has a sufficiently thick high-purity layer on the inner surface, which can reduce impurities dissolved in the silicon melt during the single crystal pulling process and enable the production of high-purity silicon single crystals.

FIG. 1 is a cross-sectional view of a quartz glass crucible according to the present invention. FIG. 2 is an enlarged cross-sectional view of a portion of the quartz glass crucible of FIG. FIG. 3 is a schematic diagram of an apparatus for manufacturing the quartz glass crucible of FIG. FIG. 4 is a cross-sectional view showing a schematic configuration of a purification treatment apparatus. FIG. 5(a) is a graph showing the relationship between the metal impurity content and the depth from the inner surface of the crucible before the high purification treatment, and FIG. 5(b) is a graph showing the relationship between the metal impurity content and the depth from the inner surface of the crucible after the high purification treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a quartz glass crucible and a method for manufacturing the same according to the present invention will be described with reference to the drawings.
Fig. 1 is a cross-sectional view of a quartz glass crucible 1 according to the present invention. Fig. 2 is an enlarged cross-sectional view of a part of the quartz glass crucible of Fig. 1.
This quartz glass crucible 1 is used, for example, in a single crystal pulling apparatus (not shown), and is used in the apparatus while being held by a carbon susceptor (not shown).
That is, in the single crystal pulling apparatus, raw silicon is melted in a quartz glass crucible 1, and a silicon single crystal is pulled up from the molten liquid.

The quartz glass crucible 1 is formed to a diameter (caliber) of, for example, 32 inches, and has a bottom 9 having a predetermined curvature (first curvature), a bottom corner 8 formed around the bottom 9 and having a predetermined curvature (second curvature), and a side 7 extending upward from the bottom corner 8.
1, an outer layer 2 is formed on the outermost side of the side portion 7 from the crucible upper end 6 to below the side portion 7. The outer layer 2 is formed of an Al-doped quartz glass layer to which, for example, Al is added as a crystallization promoter.

Specifically, before use (before high-temperature heating), the outer layer 2 (crystallization promoter-added layer) is in a state where, for example, the primary additive raw material with an Al concentration of 100 ppm is dispersed in the glass, and the Al concentration in the outer layer 2 is 25 ppm. In other words, the layer is formed in a state where parts that will vitrify and parts that will crystallize are mixed. After use (after high-temperature heating), the outer layer 2 does not become a single layer of crystals, but rather the primary additive raw material crystallizes and glass parts and crystallized parts are mixed.

An opaque intermediate layer 3 made of natural quartz glass is formed on the inside of the outer layer 2 .
Further, inside this intermediate layer 3, there is formed a transparent inner layer 4 made of high purity synthetic raw material quartz glass (or natural raw material quartz glass) which comes into contact with molten silicon when the silicon single crystal is pulled up.

Here, opaque means that there are many air bubbles (pores) inside the quartz glass, making it appear cloudy. A natural quartz layer means a silica glass layer manufactured by melting natural raw materials such as quartz, and a synthetic quartz layer means a silica glass layer manufactured by melting synthetic raw materials synthesized, for example, by hydrolysis of silicon alkoxide.

As described above, the outer layer 2 is not formed on the entire outside of the crucible. That is, the outer layer 2 is not formed on the bottom corners 8 and the bottom 9 of the crucible, but is formed only on the sides 7.
That is, as shown in the figure, the crucible bottom corners 8 and the crucible bottom 9 have a two-layer structure formed of an opaque outer layer 5 made of natural raw quartz glass formed continuously from the opaque intermediate layer 3 of the side 7, and a transparent inner layer 4 made of synthetic raw quartz glass (or natural raw quartz glass).
This is to soften the bottom corners 8 and bottom 9 (opaque outer layer 5 ) at the initial stage of starting the single crystal pulling process, and to bring them into close contact with the carbon susceptor supporting the crucible 1 .

As shown in FIG. 2, the outer layer 2 is formed so that the thickness dimension et1 at the crucible side 7 is, for example, 1 mm or more and 40 mm or less. This is because if the thickness is more than 40 mm, the crystallized layer is too thick and it is difficult to obtain adhesion to the carbon crucible, and if it is less than 1 mm, it is difficult to obtain the contribution of improving durability.

The Al concentration of the Al-doped quartz glass of the outer layer 2 is in the range of 10 to 300 ppm, and the grain size distribution of each crystal grain is such that 90% of all crystal grains fall within the range of 50 to 400 μm.
Since crystal grains are distributed in the glass layer of the outer layer 2 in this manner, the tensile stress generated between the glass layer and the intermediate layer 3 is dispersed into small forces on a crystal grain basis, thereby preventing the occurrence of cracks.

The opaque intermediate layer 3 made of natural raw material silica glass has a thickness mt1 at the crucible side portion 7 of 3 mm or more.
Further, the thickness dimension mt2 of the opaque outer layer 5 at the crucible bottom corner 8, which is formed continuously from the opaque intermediate layer 3, is formed to be 6 mm or more, and the thickness dimension mt3 of the opaque outer layer 5 at the crucible bottom 9 is formed to be 6 mm or more.

This is because if the thickness of the opaque intermediate layer 3 in the three-layer portion is less than 3 mm, the effect of preventing the crystallization promoter compound of the opaque intermediate layer 3 from scattering due to the irregular flow of the arc flame during melting of the quartz glass powder is easily reduced, and the crystallization promoter compound of the outer layer 2 passes through the opaque intermediate layer 3 and mixes with the transparent inner layer 4, which may increase the crystallization promoter concentration in the transparent inner layer 4.
Furthermore, if the thickness dimension mt2 of the opaque outer layer 5 at the crucible bottom corner 8 and the thickness dimension mt3 of the opaque outer layer 5 at the crucible bottom 9 are less than 6 mm, it is difficult to obtain sufficient durability.

The transparent inner layer 4 is a transparent layer that is substantially bubble-free and is formed by melting synthetic raw quartz glass (or natural raw quartz glass) and then subjecting it to a high-purification treatment described below to reduce the content of metal impurities such as Fe, Ni, Cr, and Cu.
Specifically, (as shown in the graph of FIG. 5(b)) the content of Fe, Ni, Cr, and Cu metal impurities is lowest at the surface of the transparent inner layer 4, the content of the metal impurities gradually increases from the surface of the transparent inner layer 4 toward the inside, the content of the metal impurities is maximum at a depth of 20 μm to 40 μm, and the content of the metal impurities gradually decreases with depth. That is, as shown in FIG. 2, a highly purified layer 4a of sufficient thickness is formed in which the content of metal impurities is significantly reduced from the surface of the transparent inner layer 4 to a depth of 10 μm to a depth of 30 μm from the surface.

More specifically, at a depth of 10 μm to 30 μm from the surface of the transparent inner layer 4, the Fe content is set to 10 ppb or less, and the Ni, Cr and Cu contents are set to 1 ppb or less.
In this manner, a highly purified layer 4a in which the content of metal impurities is reduced by a high purification process is formed on the surface of the transparent inner layer 4. This makes it possible to reduce the impurities dissolved in the silicon melt in the single crystal pulling process, and to obtain a high-purity silicon single crystal.
In addition, the transparent inner layer 4 has a thickness dimension it1 at the crucible side 7, a thickness dimension it2 at the crucible bottom corner 8, and a thickness dimension it3 at the crucible bottom 9, all of which are formed to be, for example, 3 mm or more.

Next, a method for manufacturing the quartz glass crucible 1 having the above structure will be described.
First, a quartz glass crucible before high purification treatment is manufactured using a quartz glass crucible manufacturing apparatus 10 as shown in Fig. 3. The crucible forming mold 11 of the quartz glass crucible manufacturing apparatus 10 is composed of an inner member 12 made of a gas permeable material such as a metal mold having a plurality of through holes or a highly purified porous carbon mold, and a holder 14 having a ventilation portion 13 on its outer periphery and holding the inner member 12.

A rotating shaft 15 connected to a rotating means (not shown) is fixed to the lower part of the holder 14, and rotatably supports the crucible molding die 11. The ventilation section 13 is connected to an exhaust passage 17 provided in the center of the rotating shaft 15 via an opening 16 provided in the lower part of the holder 14, and this exhaust passage 17 is connected to a pressure reducing mechanism 18.
At the upper portion facing the inner member 12, an arc electrode 19 for arc discharge, an Al-added raw material supply nozzle 20, a natural quartz powder supply nozzle 22, and a high-purity synthetic quartz powder supply nozzle 23 are provided.

The Al-added quartz powder used in the outer layer 2 can be obtained as follows. For example, an aqueous solution of Al nitrate made by dissolving Al nitrate (Al(NO ₃ ) ₃ ) in water in an amount such that the Al concentration in the quartz powder is, for example, 100 ppm, is added to the quartz powder and stirred. After stirring, the mixture is heated at 800 to 1100°C for the purpose of dehydration and removal of acid. This produces a primary additive raw material with a high Al concentration.
Next, the primary additive raw material is mixed with an equal amount of quartz powder to obtain a secondary additive raw material in which the primary additive raw material is uniformly dispersed and has an Al concentration of, for example, 25 ppm. This is used as the Al-added quartz powder to be supplied to the outer layer 2.

In addition, in the Al-doped quartz powder, 90% or more of the primary additive raw material C1 is included in the range of the overall average particle size ±25%. This makes it possible to prevent the primary additive raw material from segregating due to vibration during transportation or stirring when molding the Al-doped quartz powder into a crucible shape.
In addition, in the above example, the primary additive raw material is mixed with an equal amount of quartz powder to form Al-doped quartz powder, but it is desirable that the content of the primary additive raw material in the Al-doped quartz powder be in the range of 1 to 50%, thereby making it possible to create a state in which non-additive quartz powder is interposed between the primary additive raw materials.

When the Al-doped quartz powder thus obtained is used to manufacture a quartz glass crucible using the quartz glass crucible manufacturing apparatus 10, a rotary drive source (not shown) is operated to rotate the rotating shaft 18 in the direction of the arrow, thereby rotating the crucible molding mold 11 at high speed.
Next, Al-doped quartz powder (Al concentration 25 ppm) is supplied from the Al-doped raw material supply nozzle 20 into the crucible molding die 11. The supplied Al-doped quartz powder is pressed against the inner surface of the inner member 12 by centrifugal force and is formed as the outer layer 2. At this time, the primary additive raw material in the outer layer 2 is in a state of being dispersed in the quartz powder.

Here, the position of the lower end of the outer layer 2 is determined as described with reference to FIG. 2, and the bottom corner and bottom are removed. In other words, the outer layer 2 is removed from the bottom corner to the bottom of the quartz glass crucible 1 to be manufactured.

Next, natural quartz powder is supplied from the natural quartz powder supply nozzle 22 so as to form an opaque intermediate layer 3 having a thickness of 3 mm or more on the inner side of the outer layer 2, and an opaque outer layer 5 having a thickness of 6 mm or more at the bottom corners and bottom. The supplied natural quartz powder is pressed against the inner side of the outer layer 2 and the bottom of the inner member 12 by centrifugal force, and is formed into a molded body of the opaque intermediate layer 3 and the opaque outer layer 5.

Next, high-purity synthetic quartz powder having metal impurity contents of Na, K, and Al of 1 ppm or less is supplied from a high-purity synthetic quartz powder supply nozzle 23 so that a transparent layer having a thickness of 3 mm or more is formed on the inner surface side of the opaque intermediate layer 3 and the opaque outer layer 5.
The supplied high purity synthetic quartz powder is pressed against the inner surfaces of the opaque intermediate layer 3 and the opaque outer layer 5 by centrifugal force, and is molded into a green body of the transparent inner layer 4 .

In this manner, a crucible molded body is obtained, which comprises the outer layer 2 in which the Al-added raw material is dispersed, the opaque intermediate layer 3, the opaque outer layer 5 and the transparent inner layer 4.
Furthermore, the pressure inside the inner member 12 is reduced by operating the pressure reduction mechanism 18, and electricity is passed through the arc electrode 19 to heat the crucible molding from the inside, melting the transparent inner layer 4, the opaque intermediate layer 3, the opaque outer layer 5 and the outer layer 2 of the crucible molding, thereby producing a quartz glass crucible 1A before high purification treatment.

Next, the quartz glass crucible 1A before the purification treatment is subjected to a purification treatment. Fig. 4 is a cross-sectional view showing a schematic diagram of the purification treatment apparatus.
This purification treatment apparatus 30 includes a chamber 31 that houses the silica glass crucible 1A, and a mounting table 32 on which the silica glass crucible 1A is placed within the chamber 31. As shown in the figure, the silica glass crucible 1A is placed upside down so that its opening abuts against the mounting table 32.

The purification treatment device 30 also includes a heater 33 for heating the quartz glass crucible 1A, a thermocouple 34 for measuring the heating temperature, a gas supply section 35 for supplying halogen gas into the chamber, and a gas exhaust section 36 for exhausting the atmosphere in the chamber.
As shown in the figure, a heater 33, a thermocouple 34, a gas supply unit 35, and a gas exhaust unit 36 are arranged inside the crucible 1A, and are configured so that the inner surface of the crucible is exposed to halogen gas at high temperature.

Specifically, for example, a quartz glass crucible 1A having a diameter of 32 inches is placed upside down on a table 32 in a chamber 31 as shown in FIG.
At this time, a heater 33, a thermocouple 34, a gas supply unit 35, and a gas exhaust unit 36 are disposed in the crucible 1A.

Next, the heater 33 is driven to heat the sample until the temperature of the thermocouple 34 reaches, for example, 1200° C. Then, the gas supply unit 35 supplies hydrogen chloride gas as halogen gas at 2 L/min and argon gas at 3 L/min, and this state is maintained for 12 hours.
Thereafter, the heater 33 is stopped and the gas is exhausted from the chamber 31 by the gas exhaust section 36, and the crucible is removed from the chamber 31, thereby obtaining a highly purified quartz glass crucible 1.

In this high purification method, when the inner surface of the crucible (the surface of the transparent inner layer 4) reaches a temperature suitable for high purification treatment (e.g. 1200°C), the temperature of the outer surface of the crucible is lower than when a normal furnace is used, which heats the crucible from the outer surface side. This suppresses the diffusion of metal impurities from the opaque outer layer 2, which contains a large amount of metal impurities, to the transparent inner layer 4, making it possible to efficiently purify the surface of the transparent inner layer 4.

In addition, in the quartz glass crucible 1A before the purification process, depending on the manufacturing method, there is a possibility that impurities are concentrated in large amounts on the surface of the transparent inner layer 4, as shown in the graph of Figure 5 (a) (the vertical axis is the metal impurity content, and the horizontal axis is the depth from the surface of the crucible inner layer). When the purification process is applied to such a quartz glass crucible 1A, the metal impurities near the surface are diffused to the inside and removed, as shown in the graph of Figure 5 (b). Therefore, the metal impurity content at the surface is made the lowest, and the maximum value of the metal impurity content that was on the surface side can be moved from the inner surface to a specified depth.

The depth of the maximum value depends on the impurity distribution and purification conditions of the original quartz glass crucible 1A, but since the impurity amount gradient becomes gentler in deeper parts, the depth at which a clear maximum value can be achieved is 20 to 40 μm.

As described above, according to this embodiment, in the quartz glass crucible 1 having the transparent inner layer 4, the metal impurity content is lowest at the surface of the transparent inner layer 4, and the metal impurity content has a maximum value at a depth of 20 to 40 μm from the surface of the transparent inner layer 4. That is, a high-purity layer 4a of sufficient thickness is formed on the surface of the transparent inner layer 4. As a result, it is possible to reduce impurities dissolved in the silicon melt in the single crystal pulling process, and to obtain a high-purity silicon single crystal.
The quartz glass crucible 1 is obtained by heating the quartz glass crucible 1A before the high purification treatment from its inner surface side and supplying halogen gas to perform the high purification treatment. In this high purification treatment, the inner layer 4 side becomes hotter and the intermediate layer 3 and the outer layer 5 side become colder, so that the diffusion of metal impurities from the opaque intermediate layer 3 and the opaque outer layer 5, which contain a large amount of metal impurities, can be suppressed, and the high purification treatment can be performed efficiently.

In the above embodiment, a crucible with a three-layered structure on the side and its manufacturing method are described as an example, but the present invention is not limited to this and can also be applied to, for example, a two-layered quartz glass crucible having a transparent inner layer and an opaque outer layer.

Next, the quartz glass crucible and the manufacturing method thereof according to the present invention will be further described based on examples.
In this example, a high purification process was carried out on the quartz glass crucible having the configuration shown in the above embodiment, and the effect of the present invention was verified.

Example 1
A 32-inch quartz glass crucible was subjected to a high-purification treatment using the high-purification treatment apparatus shown in Fig. 4. That is, the crucible was placed upside down on a mounting table in a chamber and heated to 1200°C by a carbon heater placed inside the crucible, and then hydrogen chloride was flowed at 2 L/min and argon gas was flowed at 3 L/min, and the state was maintained for 12 hours to perform the high-purification treatment.

After this high purification process, the inner surface of the crucible was etched with hydrofluoric acid in 10 μm increments up to 50 μm and analyzed. As a result, the Fe content at the outermost surface was 8 ppb or less, and the Ni, Cr, and Cu contents were 1 ppb or less. Furthermore, from the surface to a depth of 30 μm, the Fe content increased to approximately 50 ppb, and the Ni, Cr, and Cu contents increased to approximately 10 ppb. Furthermore, at a depth of 50 μm from the surface, the Fe content decreased to approximately 30 ppb, and the Ni, Cr, and Cu contents decreased to approximately 5 ppb.

(Comparative Example 1)
A 32-inch quartz glass crucible was placed in the chamber, and the crucible was heated to 1200° C. from the outside by a carbon heater. Pipes were also installed so that gas could be supplied to the inside of the crucible, and then hydrogen chloride was flowed at 2 L/min and argon gas was flowed at 3 L/min, and this state was maintained for 12 hours to carry out a high purification process.
The inner surface of the crucible after this high purification process was melted in hydrofluoric acid in 10 μm increments up to 50 μm and analyzed. As a result, the Fe content at the outermost surface was about 100 ppb, and the Ni, Cr, and Cu contents were 1 to 20 ppb. The metal impurity content decreased with increasing depth from the surface, and at a depth of 50 μm from the surface, the Fe content was about 30 ppb, and the Ni, Cr, and Cu contents were about 5 ppb.

The results of the examples confirmed that the manufacturing method of the quartz glass crucible of the present invention can reduce the metal impurity content of the inner layer surface to its lowest level within a range of 10 μm to 30 μm from the surface, achieving high purity.

Reference Signs List 1 Quartz glass crucible 2 Outer layer 3 Opaque intermediate layer 4 Transparent inner layer 5 Opaque outer layer 7 Side 8 Bottom corner 9 Bottom 10 Quartz glass crucible manufacturing device 30 High purification processing device

Claims (2)

A method for producing a quartz glass crucible for pulling a single crystal, comprising: a transparent inner layer; and at least one outer layer disposed outside the transparent inner layer, the transparent inner layer having a distribution in which the contents of Fe, Ni, Cr, and Cu are lowest at a surface and are maximum at a depth of 20 to 40 μm from the surface ,
A step of manufacturing a quartz glass crucible before a high purification treatment, the quartz glass crucible having a transparent inner layer and at least one outer layer disposed outside the transparent inner layer;
a step of performing a high purification process in which the transparent inner layer side of the quartz glass crucible before the high purification process is heated to a temperature of 1000°C to 1300°C, and a halogen gas is supplied to the transparent inner layer side for a predetermined time, and the halogen gas reacts with the surface of the transparent inner layer to remove metal impurities;
A method for manufacturing a quartz glass crucible, comprising: The method for manufacturing a quartz glass crucible described in claim 1, wherein the content of Fe, Ni, Cr, and Cu in the transparent inner layer is 10 ppb or less for Fe from the surface to a depth of 10 μm to 30 μm from the surface, and 1 ppb or less for Ni, Cr, and Cu.

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