Vitreous silica crucible and method of manufacturing the same

0001The present invention relates to a silica glass crucible and a method for producing the same.

0002A silicon single crystal is generally produced by melting high-purity polycrystalline silicon in a silica glass crucible to obtain a silicon melt, immersing the end of the seed crystal in the silicon melt, and pulling it up while rotating it. .. Silica glass crucibles are generally not attached to the outer surface of the crucible by depositing silica powder on the inner surface of the rotary mold and injecting high pressure water onto the outer surface of the crucible after an arc melting step to melt the silica powder. Many honing steps to remove molten silica powder, rim cutting steps to cut the crucible opening end to a certain width so that the height of the crucible reaches a predetermined value, cleaning steps, drying steps, inspection steps, HF cleaning steps, etc. It is shipped after a process.

<p num="0003"><patcit num="1"><text>Utility Model Registration No. 2533643 Gazette</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 11-209136</text></patcit></p>

<p num="0004"> Each user has his or her own needs, and as a result, the crucible production line will produce a large number of types of crucibles with different specifications, but in particular, the differences in specifications will make a distinction in appearance. If this is not possible, there is a problem that crucibles with different specifications may be mistaken for each other during the manufacturing process.</p><p num="0005"> As a method of preventing the crucible from being mistaken, there is a method of grinding an identification mark indicating the grade of the crucible on the outer surface of the crucible using a diamond air tool or the like as in Patent Document 1. In Patent Document 1, the grade of the crucible is identified by the number of recesses formed on the outer surface of the crucible. However, even if several types of crucibles can be identified by such a method, the type of crucible to be identified should be identified. Since the number of recesses increases as the number of crucibles increases, it is extremely difficult to adopt the technique of Patent Document 1 for identifying crucibles having various specifications from the viewpoint of manufacturing efficiency.</p><p num="0006"> Further, Patent Document 2 describes a method of marking a quartz glass member using a YAG laser marker. Marking with a laser marker is relatively fast, and barcodes, characters, marks, symbols, and Since it is possible to mark various symbols such as arithmetic numbers, it is suitable for identifying many types of quartz glass members having different specifications. However, in the method of Patent Document 2, carbon or the like is baked onto the quartz glass member by irradiating the quartz glass member with a YAG laser in a state where a floor plate made of carbon or the like is in close contact with a predetermined portion of the quartz glass member. By doing so, marking is performed, but when this method is applied to the crucible, there is a problem that the carbon etc. peeled off when the crucible is used for pulling up the silicon single crystal may be mixed in the silicon melt. Also, in order to irradiate the YAG laser through the quartz glass member, it is necessary to irradiate the YAG laser from the inside to the outside of the crucible, but each time marking is performed, the laser marker is moved inside the crucible. Requires a great deal of effort. Therefore, it is extremely difficult to use the technique of Patent Document 2 for marking crucibles.</p><p num="0007"> In this way, none of the prior art techniques can be used to identify a large number of types of crucibles with different specifications, and prevention of crucible mistakes in the manufacturing process depends on the attention of the operator. The current situation is that it is being done.</p><p num="0008"> The present invention has been made in view of such circumstances, and provides a method for manufacturing a silica glass crucible, which can prevent the crucibles from being mistaken for each other in the manufacturing process.</p>

<p num="0009"> According to the present invention, a silica powder layer forming step of depositing silica powder on the inner surface of a mold that defines the outer shape of a silica glass crucible to form a silica powder layer, and melting the silica powder layer by arc heating in the mold. An arc heating step of forming a silica glass crucible by forming a silica glass layer and ending arc heating so that an unmelted silica powder layer remains between the silica glass layer and the mold, and the mold to the above. A take-out step of taking out the silica glass crucible and a honing step of removing the unmelted silica powder layer on the outer surface of the silica glass crucible are provided, and one or more of them are provided after the take-out step and before the honing step. A marking step of marking an identifier composed of a groove line on the outer surface of the silica glass crucible is further provided, and the groove line has a depth of 0.2 to 0.5 mm after the honing step and is formed at an opening of the groove line. A method for producing a silica glass crucible having a width of 0.8 mm or more is provided.</p><p num="0010"> As a result of diligent studies to prevent the crucibles from being mistaken in the manufacturing process, the present inventors first came up with the idea of marking the identifier after the taking-out process and before the honing process. The silica glass crucible immediately after the removal process is unsuitable for marking because unmelted silica powder adheres to the outer surface of the crucible, and it is common to mark the identifier after removing the unmelted silica powder in the honing process. Contrary to this common wisdom, the present inventors have come up with the idea of marking the identifier with unmelted silica powder adhering to the outer surface of the silica glass crucible before the honing process. .. When marking is performed after the honing step, there are one or more steps between the arc heating step and the marking step, and during this time, the silica glass crucible is moved without being assigned an identifier. However, when marking the crucible after the removal process and before the honing process as in the present invention, the crucible is moved to another place immediately after it is removed from the mold. Since the identifier can be marked in front, it is difficult for the crucible to be mistaken.</p><p num="0011"> In addition, we have come up with the idea of marking an identifier composed of one or more groove lines. The "identifier" is a symbol that can be used to identify the type of crucible, for example, a letter, a number, or a barcode. In the present invention, since an identifier composed of one or a plurality of groove lines is used, it is easy to generate a wide variety of types of identifiers, and it is possible to easily identify a wide variety of types of crucibles.</p><p num="0012"> Further, in the present invention, the identifier line has a depth of 0.2 to 0.5 mm after the honing step and a width of 0.8 mm or more at the opening of the groove line. It is also an important point of the present invention that the depth of the line of the identifier and the thickness of the line are in such a range. In the honing step, the unmelted silica powder layer is removed and water enters the groove line, which makes it difficult to visually recognize the groove line. As a result of the study by the present inventor, it is difficult to visually recognize the line groove when the depth after the honing process is less than 0.2 mm or the width is less than 0.8 mm, and therefore it is difficult to visually recognize the identifier. It turned out to be. It was found that the deeper the line groove is, the easier it is to visually recognize the line groove, but when the line groove is deeper than 0.5 mm, cracking of the crucible is likely to occur.</p><p num="0013"> From the above, according to the present invention, it is possible to prevent the crucible from being mistaken in the manufacturing process.</p>

0014<figref num="1">It is a flowchart which shows the manufacturing process of the silica glass crucible which concerns on one Embodiment of this invention.</figref><figref num="2">It is sectional drawing for demonstrating the silica powder layer forming process which concerns on one Embodiment of this invention.</figref><figref num="3">It is sectional drawing for demonstrating the arc heating process which concerns on one Embodiment of this invention.</figref><figref num="4">It is sectional drawing for demonstrating the taking-out process which concerns on one Embodiment of this invention.</figref><figref num="5">It is a figure which shows the structure of the identifier which concerns on one Embodiment of this invention.</figref><figref num="6">It is sectional drawing which shows the structure of the groove line which concerns on one Embodiment of this invention, FIG. 6 (a) shows the state before a honing process, and FIG. 6 (b) shows the state after a honing process.</figref><figref num="7">It is sectional drawing which shows another structure of the groove line which concerns on one Embodiment of this invention, FIG. 7 (a) shows the state before a honing process, and FIG. 7 (b) shows the state after a honing process.</figref><figref num="8">It is a figure which shows the marking method of the identifier using the laser marker which concerns on one Embodiment of this invention.</figref><figref num="9">It is sectional drawing which shows the method of performing laser scanning in a plurality of width direction positions which concerns on one Embodiment of this invention.</figref>

0015Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9. The method for producing the silica glass crucible of the present embodiment includes a silica powder layer forming step of depositing silica powder on the inner surface of the mold 1 that defines the outer shape of the silica glass crucible 14 to form the silica powder layer 3, and a silica powder layer forming step in the mold 1. The silica powder layer 3 is melted by arc heating to form the silica glass layer 13 to form a silica glass crucible 14, and the silica powder layer 15 is arc-heated so that the unmelted silica powder layer 15 remains between the silica glass layer 13 and the mold 1. The arc heating step, the taking-out step of taking out the silica glass crucible 14 from the mold 1, and the honing step of removing the unmelted silica powder layer 15a on the outer surface of the silica glass crucible 14 are provided, and after the taking-out step. Further, prior to the honing step, a marking step of marking an identifier composed of one or more groove lines 16 on the outer surface of the silica glass crucible 14 is further provided, and the groove line 16 has a depth D2 after the honing step. Is 0.2 to 0.5 mm, and the width W2 at the opening of the groove line 16 is 0.8 mm or more. In addition, after the honing step, a rim cutting step of cutting the open end of the silica glass crucible 14 to a certain width, a washing / drying step of cleaning and drying the silica glass crucible 14, and an inspection of the silica glass crucible 14 are performed. The inspection process to be performed is optionally provided. Further, when a foreign substance is found in the inspection step, a grinding step of removing the foreign substance by grinding and a re-arc heating step of arc-heating the silica glass crucible 14 after the grinding are optionally provided. Hereinafter, each process will be described with reference to the flowchart shown in FIG.

00161. Silica powder layer forming step (step S1) In the silica powder layer forming step (step S1), as shown in FIG. 2, silica powder is deposited on the inner surface of the mold 1 that defines the outer shape of the silica glass crucible to form the silica powder layer 3. The mold 1 is rotatable about the shaft 7, and the silica powder is supplied into the mold 1 while rotating the mold 1. Further, the mold 1 is provided with a large number of ventilation holes 5, and when the silica powder layer 3 is melted by arc heating, the silica powder layer 3 is depressurized through the ventilation holes 5.

0017The outer shape of the silica glass crucible is, for example, a shape having a curved portion having a relatively large curvature, a cylindrical side portion having an edge opened on the upper surface, and a mortar-shaped bottom consisting of a straight line or a curved portion having a relatively small curvature. Is. In the present embodiment, the curved portion is a portion connecting the side portion and the bottom portion, and is a portion from a point where the tangent line of the curved portion of the curved portion overlaps with the side portion of the silica glass crucible to a point having a common tangent line with the bottom portion. Means.

0018The silica powder may be a natural silica powder or a synthetic silica powder. Natural silica powder can be produced by pulverizing a natural mineral containing α-quartz as a main component into a powder. Synthetic silica powder is silicon tetrachloride (SiCl)₄) Gas phase oxidation (dry synthesis method) and silicon alkoxide (Si (OR))₄) Can be produced by a method by chemical synthesis such as hydrolysis (sol-gel method). The silica powder layer 3 can be formed, for example, by first depositing natural silica powder and then depositing synthetic silica powder. Natural silica glass formed from natural silica powder has a relatively high viscosity, and synthetic silica glass formed from synthetic silica powder has a very high purity. Therefore, the outer natural silica powder layer and the inner synthetic silica powder layer By forming the silica powder layer 3 in the above, it becomes possible to manufacture a rutsubo having high inner surface purity and high strength.

0019The average particle size of the silica powder is, for example, 200 to 600 μm. This is because if the average particle size is too small, the silica powder tends to fly when the silica powder layer is formed or when the arc melts, and if the average particle size is too large, the surface of the silica powder layer tends to be uneven.

0020By the way, "particle size" is generally expressed by the opening of the test sieve measured by the sieving method, as described in the definition of terms of JIS Z 8901 "test powder and test particles". Indicates the Stokes equivalent diameter by the sedimentation method, the circle equivalent diameter by the microscope method, the sphere equivalent by the light scattering method, and the sphere equivalent value by the electrical resistance test method (also called particle size). However, in the present specification, the measurement of the particle size distribution uses a laser diffraction / scattering type measurement method using a laser beam as a light source. The principle utilizes the fact that when a particle is irradiated with light, the amount of scattered light and the pattern are different depending on the particle size (Mie scattering). When the particles are irradiated with laser light, when the particle size is large, the scattering intensity is strong in the entire circumferential direction, and the scattered light intensity in front is particularly strong. Further, as the particle size becomes smaller, the scattered light intensity becomes weaker as a whole, and strong forward scattered light is detected weakly. Therefore, in the case of particles having a large particle size, when the forward scattered light among the light scattered by the particles is collected by a convex lens, a diffraction image is generated on the focal plane thereof. The brightness and size of the diffracted light are determined by the size (particle size) of the particles. Therefore, the particle size can be easily obtained by using these scattered light information. On the other hand, when the particle size becomes smaller, the intensity of the forward scattered light decreases, and it is difficult to detect with the detector installed in the front. The particle size can be obtained by measuring. The above measurement results are compared with spherical particles showing a scattering pattern equivalent to the obtained light scattering pattern, and output as a particle size distribution. Therefore, the obtained particle size is determined as, for example, the diameter of the particle to be measured, which shows the same pattern of diffracted / scattered light as a sphere having a diameter of 1 μm, as a diameter of 1 μm regardless of its shape. Therefore, in other measurement methods, by visual inspection or image analysis, a "constant direction diameter" that measures randomly oriented particles for a length in a certain axial direction, or an ideal shape (usually a circle) equal to the projected area of the particles. It is different from the "equivalent diameter" that determines the size of the particles, and the aspect ratio that represents the ratio of the major axis to the minor axis of the particles. The "average particle size" means the particle size at an integrated value of 50% in the obtained particle size distribution.

00212. Arc heating process (step S2) Next, in the arc heating step (step S2), as shown in FIG. 3, the silica powder layer 3 is melted by arc heating (arc melting) in the mold 1 to form the silica glass layer 13, so that the silica glass ruts 14 are formed. The arc heating is terminated so that the unmelted silica powder layer 15 remains between the silica glass layer 13 and the mold 1. Arc melting can be performed by rotating the mold 1 around the shaft 7 and causing an arc discharge 10 between the electrodes (usually carbon electrodes) 8. At the time of arc melting, it is preferable to heat the inner surface of the silica powder layer 3 or the silica glass layer 13 so that the temperature is 2000 to 2600 ° C. This is because if the arc melting temperature is too low, the silica powder layer 3 is difficult to vitrify, and if the temperature is too high, energy is wasted. When the silica powder layer is melted, the silica powder layer 3 is depressurized from the mold 1 side through the ventilation holes 5 at a pressure of -50 or more and less than -95 kPa, so that there are virtually no bubbles (air bubble content is 0.5%). Less than (less than) transparent silica glass layer (hereinafter referred to as "transparent layer") 11 can be produced. Further, after forming the transparent layer, by reducing the pressure of reduced pressure to less than + 10 kPa to less than -20 kPa, a bubble-containing silica glass layer having a bubble content of 0.5% or more and less than 50% (hereinafter, "" A bubble-containing layer) 12 can be formed. In the present specification, the bubble content means the ratio (w2 / w1) of the bubble occupied volume (w2) to the constant volume (w1) of the crucible. The silica powder layer 3 is vitrified in order from the inner surface by arc heating. Therefore, even if the inner surface side of the silica powder layer 3 is melted and vitrified, the portion in contact with the mold 1 remains the unmelted silica powder layer 15. If the entire thickness direction of the silica powder layer 3 is vitrified, it becomes very difficult to remove the crucible from the mold 1, so the arc heating is terminated with the unmelted silica powder layer 15 remaining on the outside. ..

00223. Extraction process (step S3) Next, in the take-out step (step S3), the silica glass crucible 14 is taken out from the mold 1 as shown in FIG. The silica glass crucible 14 can be taken out from the mold 1 by, for example, turning the mold 1 upside down. An unmelted silica powder layer adheres to the surface of the silica glass crucible 14 taken out from the mold 1 to form an unmelted silica powder layer 15a. Since most of the unmelted silica powder layer 15 remaining in the mold 1 after the arc heating step does not adhere to the silica glass crucible 14, the thickness of the unmelted silica powder layer 15a on the outer surface of the silica glass crucible 14 is determined. It is considerably thinner than the thickness of the unmelted silica powder layer 15 remaining in the mold 1 after the arc heating step, and may vary depending on various conditions, but the thickness is about 0.5 μm.

00234. Marking process (step S4) Next, in the marking step (step S4), an identifier composed of one or a plurality of groove lines is marked on the outer surface of the silica glass crucible. The "identifier" is a symbol that can be used to identify the type of crucible, for example, a letter, a number, or a barcode. Examples of identifiers include alphabetic characters such as A and B as shown in FIG. A plurality of characters may form one identifier, or one character may form one identifier. The groove line may be a straight line or a curved line. In the case of "A", the identifier is composed of, for example, three linear groove lines shown in (1) to (3). In the case of "B", the identifier is composed of, for example, a linear groove line shown in (1) and two curved groove lines shown in (2) and (3). When an identifier is composed of one or a plurality of groove lines, it is easy to generate a wide variety of types of identifiers, and a wide variety of types of crucibles can be easily identified.

0024FIG. 6A is a cross-sectional view perpendicular to the length direction of the groove line, and is composed of a silica glass layer 13 and an unmelted silica powder layer 15a in this order from the inner surface side. The silica glass layer 13 is composed of a transparent layer 11 and a bubble-containing layer 12 in this order from the inner surface side. The groove line 16 is formed so as to penetrate the unmelted silica powder layer 15a and reach the silica glass layer 13. In the honing step described later, as shown in FIG. 6B, the unmelted silica powder layer 15a is removed, so that only the groove line 16 formed in the silica glass layer 13 remains. Since the groove line 16 needs to be visible after the unmelted silica powder layer 15a is removed, the depth D2 of the groove line 16 after the honing process is 0.2 to 0.5 mm in the marking process, and the groove line 16 is formed. It is necessary to form so that the width W2 at the opening of is 0.8 mm or more. Therefore, for example, when the thickness of the unmelted silica powder layer 15 is 0.5 μm, the groove line 16 before the honing step is formed so that the depth D1 is 0.7 to 1.0 mm. The width W1 at the opening of the groove line 16 before the honing process varies depending on the shape of the groove line 16, but is, for example, about 1.2 to 4 mm.

0025It is one of the important points of the present invention that the line depth and the line thickness of the identifier are in such a range. In the honing step, the unmelted silica powder layer 15a is removed and water enters the groove line 16, which makes it difficult to visually recognize the groove line 16. As a result of the study by the present inventor, it is difficult to visually recognize the line groove 16 when the depth after the honing step is less than 0.2 mm or the width is less than 0.8 mm. Therefore, the identifier can be visually recognized. It turned out to be difficult. It was found that the deeper the line groove 16 is, the easier it is to visually recognize the line groove 16, but when the line groove 16 is deeper than 0.5 mm, cracking of the crucible is likely to occur. Further, the width W2 at the opening of the wire groove 16 after the honing step is preferably 2 mm. This is because when the width exceeds 2 mm, the line width is too thick and the adjacent groove lines 16 tend to overlap, which may make it difficult to recognize the identifier.

0026The cross-sectional shape of the groove line 16 may be substantially V-shaped as shown in FIGS. 6A and 6B, but according to the experiments by the present inventors, the cross-sectional shape of the groove line 16 is substantially V-shaped. In the case of a V-shape, it was found that there is a problem that the ruts are easily cracked in the re-arc heating step described later. Therefore, as a result of diligent studies to solve this problem, the cross-sectional shape of the groove line 16 is an inverted trapezoid as shown in FIGS. 7 (a) and 7 (b) (hereinafter referred to as "inverted trapezoid"). In the case of (referred to as), it was found that the problem that the crucible was easily cracked in the re-arc heating step was solved. Further, when the groove wire 16 has such a shape, it is possible to prevent the crucible cracking when the silicon single crystal is pulled up. The groove line 16 is preferably formed so that the width B2 at the bottom of the groove line 16 is 30 to 95% of the width W2 at the opening of the groove line 16. Specifically, B2 / W2 is, for example, 30,40,50,60,70,80,90,95%, and may be within the range between any two exemplified here.

0027The position where the identifier is marked is not particularly limited, but it is preferable to provide it at a position as far as possible from the silicon melt so as not to adversely affect the pulling up of the silicon single crystal. For example, the open end of the silica glass crucible 14. It is preferable to provide it at a position within 30 mm from. When the rim cutting step is performed, it is preferable to mark the identifier at a position within 30 mm in the bottom direction of the silica glass crucible 14 from the position where the silica glass crucible 14 becomes the open end portion after the rim cutting.

0028The method of marking the identifier is not limited, but in one example, as shown in FIG. 8, the focus of the laser 19 is focused on the outer surface of the silica glass crucible 14 while the laser 19 emitted from the laser marker 17 is focused. This is performed by performing laser scanning so as to move the groove line 16 in the length direction. The length direction of the groove line 16 is the direction indicated by the arrow in FIG. The type of laser is not limited as long as it has a wavelength absorbed by silica glass, but one example is a carbon dioxide laser. A carbon dioxide laser is a laser generated by stimulated emission from carbon dioxide that is excited and has a population inversion. A carbon dioxide laser generally has a wavelength of 9.3 to 10.6 μm and is easily absorbed by silica glass, so that it is suitably used for marking the surface of a silica glass crucible.

0029In one example, the laser marker 17 is attached to a strut 21 and is controlled by a controller 25 via a cable 23. Since the controller 25 can control the three-dimensional position of the laser 19, even for an irradiation target having a curved surface shape such as the outer surface of the silica glass crucible 14, the spot diameter is kept constant and can be freely along the outer surface. Can be irradiated. Further, the controller 25 can control various conditions such as the output of the laser 19, the scanning position, and the scanning speed. The distance D between the laser marker 17 and the silica glass crucible 14 may be appropriately set according to the work distance of the laser marker 17.

0030The intensity of the laser 19 is strongest at the center of the focal spot and weakens as it moves away from the center. Therefore, when marking is performed by moving the focal point of the laser 19 along the length direction of the groove line 16 without changing the position in the width direction, the substantially V-shaped groove line 16 is shown in FIG. 6 (a). Is formed. As described above, such a substantially V-shaped groove line 16 is not preferable because it may cause cracking of the crucible in the re-arc heating step. Therefore, as a result of diligent studies to form the inverted trapezoidal groove line 16 as shown in FIG. 7 (a), the position of the laser 19 in the width direction of the focal point as shown by the arrow in FIG. 9 (a). It was found that it is possible to form an inverted trapezoidal groove line 16 as shown in FIG. 9 (b) by scanning the laser 19 at a plurality of width direction positions by shifting the positions. The number of positions in the width direction is, for example, 3 to 10, preferably 5 to 7. If this number is too small, it is difficult to form the inverted trapezoidal groove line 16, and if this number is too large, marking takes too much time. The number of laser scans at each width direction position is not particularly limited, but is, for example, 1 to 10, preferably 3 to 7, and even more preferably 4 to 6. If an attempt is made to form the line groove 16 having a desired depth and width with a small number of times, the amount of heat applied to the crucible at one time becomes too large, thermal distortion of the crucible occurs, and it is easy to lead to cracking of the crucible. Further, if the number of laser scans is too large, the amount of heat applied to the crucible at each time is too small, and the line groove 16 is difficult to form.

0031The output of the laser 19 at the time of marking is not particularly limited and may be appropriately adjusted while observing the printing state, but is, for example, 15 to 40 W. This is because if the laser output is too low, the line groove 16 is not formed or it takes too long to form, and if the laser output is too high, the crucible is likely to be cracked due to thermal strain. The laser 19 may have a continuous output or a pulse output, but in the case of the pulse output, the line groove 16 becomes a dotted line and the distortion between the points becomes large, so that the continuous output is preferable. The laser scanning speed is, for example, 5 to 30 mm, but it may be appropriately set in consideration of the balance with the laser output so that appropriate marking can be performed.

00325. Honing process (step S5) Next, in the honing step (step S5), the unmelted silica powder layer 15a on the outer surface of the silica glass crucible 14 is removed. As a result, as shown in FIGS. 6 (b) and 7 (b), only the portion formed in the silica glass layer 13 is left in the line groove 16. In the honing step, for example, the unmelted silica powder layer 15a is removed by injecting water (high pressure water) toward the outer surface of the silica glass crucible 14. In the honing step, the portion of the wire groove 16 formed in the unmelted silica powder layer 15a is removed, and water enters the wire groove 16, so that the visibility of the wire groove 16 deteriorates. Therefore, in the marking step, it is necessary to form the line groove 16 so that the line groove 16 can be visually recognized even after the unmelted silica powder layer 15a is removed in the honing step, and the depth after the honing step is 0.2 to 0.5 mm. The wire groove 16 is formed so that the width of the groove line at the opening is 0.8 mm or more. The pressure of the water to be jetted is not limited as long as the unmelted silica powder layer 15a can be removed, and is, for example, 0.1 to 10 MPa, specifically, for example, 0.1,0.2,0.5,1,2,4. , 5,10 MPa, and may be within any two of the ranges exemplified here.

00336. Rim cutting process (step S6) Next, in the honing step (step S6), the open end of the silica glass crucible 14 is excised with a certain width. As a result, the height of the crucible can be set to a desired value.

00347. Cleaning / drying process (step S7) Next, in the washing / drying step (step S7), the silica glass crucible 14 is washed with water or the like and dried.

00358. Inspection process (step S8) Next, in the inspection step (step S8), it is confirmed whether or not the dimensions of the silica glass crucible 14 meet the specifications, and whether or not foreign matter is present in the silica glass crucible 14 is inspected. Those that pass this inspection are packed in bags and shipped. HF cleaning and subsequent drying may be performed prior to bagging.

00369. Grinding process (step S9) For the silica glass crucible 14 that is rejected due to the presence of foreign matter in the silica glass crucible 14 in the inspection step, a grinding step (step S9) is performed to remove the foreign matter by grinding. Foreign matter is removed by this step, but scratches are generated on the inner surface of the crucible during grinding, and these scratches may adversely affect the pulling up of the silicon single crystal, so they are removed by the re-arc heating step.

003710. Re-arc heating step (step S10) In the re-arc heating step (step S10), the surface of the crucible is melted by performing arc heating for a short time on the crucible after the grinding step, and the scratches generated in the grinding step are eliminated. When the groove line 16 has a substantially V shape as shown in FIG. 6 (b), cracking of the crucible is likely to occur in the re-arc heating step, but the groove line 16 is reversed as shown in FIG. 7 (b). In the case of a trapezoidal shape, an inverted trapezoidal shape is preferable because cracking of the crucible is unlikely to occur in the re-arc heating step.

0038As described above, according to the present embodiment, since the identifier is marked after the taking-out step and before the honing step, it is possible to prevent the crucible from being mistaken in the manufacturing step. Further, a customer who uses a crucible having a plurality of specifications wants that the type of crucible can be easily identified. However, the crucible of the present embodiment has a groove line depth of 0.2 to 0.5 mm. Since it has an identifier whose width at the opening of the groove line is 0.8 mm or more, the visibility of the identifier is good and the type of crucible can be easily identified.

<p num="0039"> Silica powder having a thickness of 15 mm is deposited on the inner surface of a mold having an opening diameter of 610 mm, and the silica powder is melted by arc heating while reducing the pressure from the mold side. A glass crucible was prepared. Next, this silica glass crucible is taken out from the mold, and with unmelted silica powder adhering to the outer surface, using a carbon dioxide laser marker with a maximum output of 30 W, the identifier "ABC" is used under the conditions shown in Table 1. Marking was done. The% value of the laser power is the value relative to the maximum power. Next, a honing step was performed to remove unmelted silica powder by injecting high-pressure water onto the outer surface of the silica glass crucible. Immediately after this step, it was confirmed whether the identifier was visible. Those that can be clearly identified are evaluated as "", those that are slightly poorly visible but can be visually recognized are evaluated as "", and those that are extremely difficult to be visually recognized are evaluated as "x". Next, a re-arc heating step was performed on the crucible after the honing step. At that time, the crucible that has been broken is marked with "x", the one with small cracks around the identifier marking is marked with "", and the one without cracks around the identifier marking is marked with "". Evaluation was performed. The results are shown in Table 1.</p><p num="0040"><tables num="1"><img id="000002" he="88" wi="142" file="JP5773382B2_D0001.tif" img-format="tif" img-content="drawing" /></tables></p><p num="0041"> With reference to Table 1, the groove line depth after the honing process is 0.2 to 0.5 mm and the width is 0.8 mm.<u style="single">that's all</u>Example 1 ~<u style="single">3</u>Was a good result of good visibility and good evaluation of fragility in the re-arc heating step. However, when the depth was 0.2 mm, the visibility was slightly inferior, so it was found that the depth is preferably 0.3 mm or more. In addition, the shape of the groove line is approximately V-shaped.<u style="single">Reference example 1</u>In this case, the result of the fragility evaluation was slightly poor, so it was found that the shape of the groove line is preferably an inverted trapezoidal shape. Further, it was found that even if the shape of the groove line is an inverted trapezoidal shape, the fragility evaluation deteriorates when the depth of the groove line is too deep as in Comparative Example 1. Furthermore, it was found that when the groove line is V-shaped as in Comparative Example 2, the fragility evaluation is further deteriorated. Further, when the depth of the groove line is shallower than 0.2 mm as in Comparative Example 3 or when the width of the groove line is narrower than 0.8 mm as in Comparative Example 4, the visibility of the identifier becomes very poor. It turned out.</p>

00421: Mold, 3: Silica powder layer, 5: Vent, 7: Shaft, 8: Electrode, 10: Arc discharge, 11: Clear silica glass layer, 12: Silica glass layer containing bubbles, 13: Silica glass layer, 14 : Silica glass rutsubo, 15: Unmelted silica powder layer, 15a: Unmelted silica powder layer, 16: Groove line, 17: Laser marker, 19: Laser, 21: Strut, 23: Cable, 25: Controller