JP4428529B2 - Quartz crucible - Google Patents

Description

  The present invention relates to a quartz crucible used for pulling up a silicon single crystal, and more particularly to a quartz crucible that suppresses liquid level vibrations on the surface of a silicon melt and allows the silicon single crystal to be pulled up stably and at a high yield.

  In the CZ (Czochralski) method, which is a method for producing a silicon single crystal, polysilicon is put in a crucible made of quartz glass and dissolved, and then a seed crystal is put into a melt to pull up the single crystal.

  In recent years, with the demand for larger diameters and lower defects of silicon single crystals, high-temperature and long-time pulling has been performed using synthetic quartz glass crucibles in which impurities to be released are reduced as much as possible. As the synthetic quartz glass crucible, natural quartz glass lined with synthetic quartz glass is used, and has an opaque layer from the outer peripheral surface and a transparent layer from the inner peripheral surface.

  However, when a synthetic quartz glass crucible is used, severe liquid level vibration may occur on the surface of the silicon melt, and the seed crystal may not be squeezed. In addition, when liquid level vibration occurs during the pulling process of single crystal silicon, the single crystal is disturbed and the operability is remarkably deteriorated, such as when silicon is reattached or remelted. In particular, when the diameter of the silicon single crystal is 8 inches or more, the quartz glass crucible to be used has a large diameter, and the influence of liquid surface vibration increases, so that suppression is important.

  In addition, as the diameter of the quartz glass crucible increases, the amount of polysilicon that is dissolved at a time increases, and the cost required for pulling a single crystal of silicon at a time increases. Improvement is also important.

  Quartz glass crucibles are generally known that when the inner layer is made of natural glass, there is less vibration of the silicon melt liquid level, and when the inner layer is made of synthetic glass, vibration of the silicon melt liquid level is likely to occur. It has been.

  In Patent Document 1, the surface tension of the inner surface portion from the upper end of the quartz glass crucible to a position located below the molten metal surface of silicon melt is determined by grinding with a working grinding means, melting with a melting means, or sublimation with a heating means. It is described that, by adjusting and creating wettability on the inner surface of the quartz glass crucible, the molten metal surface vibration of the silicon melt liquid surface when the silicon single crystal is pulled up is suppressed.

  In Patent Document 2, an inner layer of a specific range of a quartz glass crucible straight body is formed of natural quartz glass or natural synthetic mixed silica glass, and an inner layer of a specific range near the bottom is formed of synthetic quartz glass. It describes that it is possible to pull up a silicon single crystal stably and at a high yield even during long-time operation by reducing the occurrence of vibrations on the liquid surface and eliminating the occurrence of rough skin and cristobalite spots.

  In Patent Document 3, a crucible inner layer from a molten metal surface to a predetermined depth below the molten metal surface is formed of natural quartz glass with respect to a molten silicon starting surface of molten silicon in the quartz glass crucible, and a crucible inner layer below the crucible inner layer. It is described that the surface vibration of melted silicon is suppressed by forming the film with synthetic quartz glass.

In addition, the present inventors have proposed to prevent the bubbles confined in the quartz glass crucible from rupturing even under a high heat load so as not to inhibit the single crystallization rate during pulling (Patent Document 4).
JP 2000-72594 A JP 2004-59410 A JP 2004-250305 A JP 2001-233629 A

  However, in the method of Patent Document 1, secondary processing is performed on the inner surface of the quartz glass crucible by grinding by a work grinding means, melting by a melt means, or sublimation by a heating means, and the inner surface of the quartz glass crucible There is a problem in that it is necessary to adjust the surface tension and create wettability there, which complicates the production of the quartz glass crucible and increases the cost.

  In Patent Document 2, natural quartz glass or natural synthetic mixed silica glass is formed in the inner layer in a specific range of the quartz glass crucible straight body, and its thickness is 0.3 to 3 mm to suppress liquid surface vibration. It is considered preferable. When the diameter is increased and the contact time with the silicon melt is increased, such a quartz glass crucible may not be able to sufficiently cope with the roughness of the inner surface. Further, since the inner layer contains natural quartz glass over the entire thickness direction and the natural quartz glass dissolves while in contact with the silicon melt, the impurities are always supplied and the impurities in the silicon single crystal are continuously supplied. There is a problem that a large amount of is contained, which adversely affects the quality of the silicon single crystal.

  In Patent Document 3, the crucible inner layer is formed of natural quartz glass with respect to the molten silicon starting surface of the molten silicon in the crucible, and the thickness of the layer is desirably at least 1 mm or more. Therefore, even when this quartz glass crucible is used, as in Patent Document 2, natural quartz glass dissolves while the inner layer is in contact with the silicon melt, and impurities are constantly supplied, so that the silicon single crystal contains There is a problem that a large amount of impurities are contained, which adversely affects the quality of the silicon single crystal.

  According to the method of Patent Document 4, although the yield can be improved, there is a problem that it is not effective for suppressing liquid surface vibration.

  As a result of diligent research, the present inventors have formed only the extreme surface layer of the straight body portion of the quartz crucible with at least two kinds of glass and formed the inner surfaces of the R to B portions with high-purity quartz glass. The inventors have found that a silicon single crystal can be obtained at a high yield while suppressing the occurrence of liquid surface vibration.

  This is because, as a result of forming the inner surfaces of the R to B parts with high-purity quartz glass, the roughness is reduced, and as a result of forming only the extreme surface layer of the straight body part with at least two kinds of glasses, Due to the difference in the amount of dissolution, a surface roughness larger than R to B appears in the straight body part during pulling of the silicon single crystal, and the occurrence of liquid surface vibration is suppressed. As a result of using only the extreme surface layer of the body, the dissolution of impurities into the silicon melt is completed at the beginning of the silicon single crystal pulling process, so that the incorporation of impurities into the silicon single crystal takes place from seeding to shoulder formation of the silicon single crystal. This is considered to be due to the fact that the amount of impurities taken up is extremely small in the straight body portion of the silicon ingot that is the base material of the silicon wafer, limited to the stage.

  An object of the present invention is to provide a quartz crucible that suppresses the liquid level vibration on the surface of the silicon melt and enables the silicon single crystal to be pulled up stably and with a high yield.

  In order to achieve the above object, according to the present invention, there is provided a quartz crucible having an opaque layer formed from an outer peripheral surface and a transparent layer formed from an inner peripheral surface. It is composed of a composite material made of glass formed of silica sand of the second component, and the glass formed of silica sand of the second component is scattered on the surface of the glass formed of silica sand of the first component. The inner surface of the R to B part is made of glass formed of synthetic quartz sand.

  Here, the silica sand as the second component preferably occupies 10% or more per unit area on the inner surface of the straight body of the quartz crucible.

  Further, the silica sand as the first component is amorphous synthetic quartz sand, and the silica sand as the second component is crystalline natural quartz sand, or crystalline and amorphous synthetic quartz sand. Is preferred.

  The R to B parts are formed by high-temperature heating, the straight body part is formed by low-temperature heating, and the high-temperature heating and low-temperature heating are performed after the transparent layer is formed. It can be performed by moving up and down. In quartz glass obtained by melting silica sand, if it is melted at a high temperature, the Si-O bond is sufficiently cut and recombined, so that a smooth surface is maintained even after reaction with silicon. When it is melted, it is not in a completely amorphous state, but a state in which a crystal structure remains to some extent, resulting in a surface having a relatively large roughness after reaction with silicon.

  In the present invention, a surface roughness larger than the R to B portions appears in the straight body portion by a chemical reaction with the silicon melt. As a result, the liquid level vibration on the surface of the silicon melt is suppressed.

  The straight body portion of the quartz crucible of the present invention is formed by interspersing and fusing glass formed with silica sand of the second component on the surface of glass formed of silica sand of the first component. Therefore, the surface roughness larger than the R to B portions appears in the straight body portion during pulling of the silicon single crystal due to the difference in the amount of dissolution, and the occurrence of liquid level vibration is suppressed.

  Here, if crystalline natural quartz sand is used as the silica sand of the second component, the effect of reducing the occurrence of liquid level vibration and the effect of suppressing the liquid level vibration due to the appearance of a relatively large surface roughness are synergistically effective. In particular, the liquid level vibration can be suppressed. Further, since the R to B parts are made of high-purity glass, a silicon single crystal can be obtained with a high yield.

  In the present invention, even when natural quartz sand is used as the second component silica sand, this amount is very small and scattered in the extreme surface layer, so that the amount of impurities dissolved in the silicon melt is kept small. be able to. In addition, since the dissolution of impurities into the silicon melt ends at the initial stage of the silicon single crystal pulling process, the incorporation of impurities into the silicon single crystal is limited to the shoulder formation stage of the silicon single crystal from seeding. In the straight body portion of the silicon ingot as a base material, the amount of impurities taken up is extremely small.

  In addition, by forming the R to B parts by high temperature heating and forming the straight body part by low temperature heating, the surface of the R to B parts can be maintained smoothly after reaction with silicon, and the surface of the straight body part. Can be promoted to a surface with a relatively large roughness after reaction with silicon.

  Furthermore, since the transparent layer can be made into a composite material in the melting step when forming the transparent layer, there is no need for secondary processing of the transparent layer, and the manufacturing process can be simplified.

  The present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of a quartz crucible according to the present invention. In the figure, a quartz crucible 1 has an opaque layer 2 formed from the outer peripheral surface and a transparent layer 3 formed from the inner peripheral surface. Of the inner surfaces of the transparent layer 3, the inner surface 4 of the straight body portion is a composite of glass formed of silica sand of at least two components so that a relatively large surface roughness appears by reaction with the silicon melt. The inner surface 5 of the corner portion to the bottom portion (referred to as R to B portion here) formed of a material seems to have a very small surface roughness even if the surface roughness appears due to the reaction with the silicon melt. In addition, it is made of synthetic quartz sand. In addition, a corner part means the area | region part which couple | bonds a straight body part and a bottom part.

  FIG. 2 is a schematic cross-sectional view showing the configuration of the straight body portion of the quartz crucible 1. The straight body portion of the transparent layer 3 is formed of a composite material of a glass portion 21 formed of the first component silica sand and a glass 22 portion formed of the second component silica sand. Here, glass portions 22 formed of silica sand of the second component are scattered and fused on the surface of the glass portions 21 formed of silica sand of the first component, It is scattered only on the pole surface of the transparent layer 3.

  The silica sand as the second component should occupy 10% or more, preferably 30% or more, per unit area of the inner surface of the straight body part. If the amount is less than 10%, the portion of the first component, silica sand, that comes into contact with the silicon melt increases, and the effect of suppressing liquid surface vibration is reduced.

  As the first component silica sand, amorphous synthetic quartz sand is generally used. Further, as the second component silica sand, crystalline natural quartz sand is generally used, but crystalline and amorphous synthetic quartz sand, synthetic cristobalite sand, synthetic tridymite sand, etc., and silica polymorphic sand. It may be.

  Synthetic quartz glass and natural quartz glass have different amounts of dissolution in silicon melt, and natural quartz glass has a higher dissolution rate. According to the Kimura melt dynamics project symposium report material, the etching rate of quartz for silicon melt is 2.7 μm / hr at 1430 ° C. for natural quartz glass and 1 μm / hr at 1452 ° C. for synthetic quartz glass. . For this reason, the straight body portion of the quartz crucible made of silica sand of at least two components exhibits a relatively large surface roughness due to a chemical reaction with the silicon melt and suppresses liquid surface vibration. Further, since the R to B portions are formed of synthetic quartz sand, which is high-purity glass, surface devitrification and surface peeling that hinder improvement in the single crystallization rate are suppressed.

  After the polysilicon is put into the quartz crucible 1 and melted, the seed crystal is put into the melt and the single crystal is pulled up, and at the initial stage of the silicon single crystal pulling process, the silicon melt is applied to the inner surface 4 of the straight body portion. A relatively large surface roughness appears due to the reaction. In this case, the silica sand as the second component exists only on the extreme surface of the transparent layer 3, and the inner surface 5 of the R to B parts is formed of synthetic quartz sand, so that the impurities can be dissolved in the silicon melt. Ends at the beginning of the silicon single crystal pulling step. For this reason, the incorporation of impurities into the silicon single crystal is limited from the seeding to the shoulder formation stage of the silicon single crystal, and the amount of impurity incorporation is extremely small in the straight body portion of the silicon ingot that is the base material of the silicon wafer.

  FIG. 3 is a cross-sectional view of an essential part showing an example of a quartz crucible manufacturing apparatus according to the present invention. In the figure, 31 is a mold, 32 is a rotating shaft, 33 is a heat shielding plate, 34 is a graphite electrode, 35A and 35B are raw material introduction pipes, and 36A and 36B are hoppers.

  In manufacturing the quartz crucible, first, the mold 32 is rotated, and natural quartz sand is introduced into the inner peripheral surface of the mold 31 through the introduction pipe 35A. By introducing natural quartz sand while rotating the mold 31, the natural quartz sand sticks to the inner peripheral surface of the mold 31 and accumulates by centrifugal force. The introduction of natural quartz sand may be performed using an apparatus other than the introduction pipe 35A.

  When a predetermined amount of natural quartz sand is deposited on the inner peripheral surface of the mold 31, a voltage is applied between the graphite electrodes 34 to cause arc discharge. The natural quartz sand stuck to the mold is melted by the heat of the arc discharge, and the opaque layer 2 constituting the outer peripheral surface of the quartz crucible is formed.

  If the opaque layer 2 is formed, the transparent layer 3 is subsequently formed. For this purpose, after the melting of natural quartz sand is started and the inner surface thereof is softened, the first component of silica sand is supplied to the mold 31 through the introduction pipe 35A. The supply amount at this time is, for example, 80 to 160 g / min.

  The atmosphere in the vicinity of the arc of the graphite electrode 34 is 2000 ° C. or higher, and the silica sand as the first component supplied to this atmosphere is softened. The softened first component silica sand moves directly onto the opaque layer 2 or once falls on the bottom of the mold 31 and then rises up by centrifugal force and accumulates on the opaque layer 2.

  Next, the second component silica sand is supplied to the straight body of the first component silica sand through the introduction pipe 35B. The second component silica sand softened by the heat of the arc discharge is scattered and fused to the straight body portion of the first component silica sand, and a glass portion formed by the first component silica sand. The transparent layer 3 made of the composite material of the glass portion 22 formed of the silica sand 21 and the second component is formed.

  FIG. 4 is a view obtained by taking a picture of the surface of the straight barrel part of the quartz crucible manufactured as described above. It can be seen that the glass portion 22 formed by welding natural quartz sand is dotted in a substantially circular fashion on the surface of the glass portion 21 formed from amorphous synthetic quartz sand.

  At the stage where the quartz crucible was manufactured, the surface roughness of the surface of the straight body portion was Ra = 0.07 μm. Further, no circular adhesion was observed in the R to B portions of the quartz crucible.

  FIGS. 5 and 6 are photographs obtained by photographing the surfaces of the straight body portion and the R portion after the quartz crucible manufactured as described above is etched by being immersed in 50% HF for 2 hours and 30 minutes. It is. On the surface of the straight body portion shown in FIG. 5, a recess (concave portion) 41 in which a glass portion 22 formed by welding circular natural quartz sand is appeared. The surface roughness of this surface was Ra = 0.58 μm. The surface of the R portion shown in FIG. 6 maintains smoothness even after etching with HF. The surface roughness of this surface was Ra = 0.07 μm. From the above evaluation results, the quartz crucible manufactured as described above can effectively suppress the vibration of the surface of the silicon melt with a relatively large surface roughness appearing in the straight body portion, and can directly control the silicon ingot. It can be seen that the amount of impurities taken up in the barrel can be extremely reduced.

  After the formation of the transparent layer 3, the graphite electrode 34 may be moved downward as necessary to heat the straight body portion at a low temperature and sufficiently heat the R to B portions at a high temperature. When the graphite electrode 34 is moved downward after the formation of the transparent layer 3, the radiant heat increases as the distance from the heating source to the inner surfaces of the R to B portions approaches. On the other hand, the radiant heat to the straight body part decreases. After maintaining this state for a certain period of time, by gradually moving the heating source upward, the radiant heat is uniformly supplied to the straight body part, and the radiant heat gradually decreases from the B part toward the rim part. The inner surface is heated. That is, on the inner surface of the quartz crucible, the R to B parts are glass melted by high-temperature heating, and the straight body part is glass melted by low-temperature heating.

  In the case of glass melted by low-temperature heating, the breaking and recombination of Si—O bonds are limited to the surface of the silica sand particles, so that the crystal structure is left in a state that is not completely amorphous. In the straight body portion in this state, the appearance of a relatively large surface roughness is promoted by a chemical reaction with the silicon melt during the pulling of the silicon single crystal, and the liquid surface vibration is effectively suppressed by this appearance. On the other hand, the R to B parts are heated at a high temperature, and the Si—O bond is sufficiently cut and recombined to be in an amorphous state, and a smooth surface is maintained even after a chemical reaction with the silicon melt. Thereby, the surface devitrification and surface peeling which inhibit the single crystallization rate improvement are suppressed.

  FIGS. 7 and 8 are diagrams obtained by photographing the surfaces of the straight body portion and the R portion after the quartz crucible manufactured as described above is etched by being immersed in 50% HF for 2 hours and 30 minutes. It is. Relatively large irregularities appear on the surface of the straight body portion shown in FIG. The surface roughness of this surface was Ra = 1.35 μm. The surface of the R portion shown in FIG. 6 maintains smoothness even after etching with HF. The surface roughness of this surface was Ra = 0.07 μm. From the above evaluation results, the quartz crucible manufactured as described above can effectively suppress the vibration of the surface of the silicon melt with a relatively large surface roughness appearing in the straight body portion, and can directly control the silicon ingot. It can be seen that the amount of impurities taken up in the body portion can be extremely reduced.

  Specific examples are given below, but the present invention is not limited to these specific examples.

(Specific example 1)
The transparent layer 3 was formed after forming the opaque layer 2 using the apparatus shown in FIG. Thereafter, synthetic quartz sand was scattered on the straight body portion and fused, and then the graphite electrode 34 was held downward and gradually raised, and the inner surfaces 4 and 5 were formed. The resulting quartz crucible had a diameter of 22 inches. When this quartz crucible was filled and melted with polycrystalline silicon and the single crystal was pulled up by the CZ method, vibration of the silicon melt surface did not occur, and a complete single crystal was obtained.

(Specific example 2)
The transparent layer 3 was formed after forming the opaque layer 2 using the apparatus shown in FIG. Thereafter, natural quartz sand was scattered in the straight body portion and fused, and then the graphite electrode 34 was held downward and gradually raised to form the inner surfaces 4 and 5. The ratio of the natural quartz sand fused to the straight body portion to the inner surface was 30% per unit area, and the diameter of the quartz crucible obtained was 24 inches. When this quartz crucible was filled and melted with polycrystalline silicon and the single crystal was pulled up by the CZ method, vibration of the silicon melt surface did not occur, and a complete single crystal was obtained.

(Comparative Example 1)
The transparent layer 3 was formed after forming the opaque layer 2 using the apparatus shown in FIG. The diameter of the resulting quartz crucible was 24 inches. The quartz crucible was filled with polycrystalline silicon, melted, and the single crystal was pulled up by the CZ method. As a result, intense vibration was generated on the surface of the silicon melt, which required time for seeding and disturbance of the single crystal. No single crystal was obtained.

(Comparative Example 2)
The transparent layer 3 was formed after forming the opaque layer 2 using the apparatus shown in FIG. Thereafter, natural quartz sand was fused to the entire inner surface of the crucible to form inner surfaces 4 and 5. The diameter of the resulting quartz crucible was 24 inches. When this quartz crucible was filled with polycrystalline silicon and melted and the single crystal was pulled up by the CZ method, vibrations on the surface of the silicon melt did not occur, but the single crystal was disturbed and the complete single crystal was It was not obtained.

(Comparative Example 3)
The transparent layer 3 was formed after forming the opaque layer 2 using the apparatus shown in FIG. Thereafter, natural quartz sand was fused to the straight body portion to form the inner surfaces 4 and 5. The ratio of the natural quartz sand fused to the straight body portion to the inner surface was 7% per unit area, and the diameter of the quartz crucible obtained was 24 inches. When this quartz crucible is filled with polycrystalline silicon and melted and the single crystal is pulled up by the CZ method, the surface of the silicon melt is vibrated, the single crystal is disturbed, and a complete single crystal cannot be obtained. It was.

It is a schematic sectional drawing which shows one Embodiment of the quartz crucible which concerns on this invention. It is a schematic sectional drawing which shows the form of the straight body part of the quartz crucible 1 which concerns on this invention. It is principal part sectional drawing which shows an example of the manufacturing apparatus of the quartz crucible which concerns on this invention. It is the figure obtained by photographing the straight body part surface of the quartz crucible which concerns on this invention. It is the figure obtained by photographing the straight body part surface after carrying out HF etching of an example of the quartz crucible which concerns on this invention. It is the figure obtained by photographing the surface of the R section after carrying out HF etching of an example of the quartz crucible concerning the present invention. It is the figure obtained by photographing the straight body part surface after performing the HF etching of the other example of the quartz crucible which concerns on this invention. It is the figure obtained by photographing the surface of the R section after carrying out HF etching of other examples of the quartz crucible concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Quartz crucible, 2 ... Opaque layer, 3 ... Transparent layer, 4, 5 ... Inner surface, 21 ... Glass part by silica sand of 1st component, 22 ... 1st Glass part of silica sand of component 2, 31 ... mold, 32 ... rotating shaft, 33 ... heat shielding plate, 34 ... graphite electrode, 35A, 35B ... raw material introduction tube, 36A, 36B ... Hopper, 41 ... depression

Claims (5)

In a quartz crucible having an opaque layer formed from the outer peripheral surface and a transparent layer formed from the inner peripheral surface,
The inner surface of the straight body portion is made of a composite material made of glass formed of at least the first and second component silica sands, and the second component silica is formed on the surface of the glass formed of the first component silica sand. A quartz crucible characterized in that glass formed of sand is scattered and fused, and the inner surfaces of the R to B portions are made of glass formed of synthetic quartz sand. The quartz crucible according to claim 1, wherein the silica sand as the second component occupies 10% or more per unit area on the inner surface of the straight body portion. The first component silica sand is amorphous synthetic quartz sand, and the second component silica sand is crystalline natural quartz sand, or crystalline and amorphous synthetic quartz sand. The quartz crucible according to claim 1 or 2. The parts R to B are formed by high-temperature heating, and the straight body part is formed by low-temperature heating. The high-temperature heating and low-temperature heating are performed by moving the arc melting electrode up and down after the transparent layer is formed. The quartz crucible according to any one of claims 1 to 3, wherein the quartz crucible is obtained by moving the quartz crucible. The quartz crucible according to any one of claims 1 to 4, wherein a surface roughness larger than R to B appears in the straight body portion by a chemical reaction with the silicon melt.