JPH11199369A - Quartz glass crucible for pulling up silicon single crystal and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a quartz glass crucible capable of improving the yield of a pulled-up silicon single crystal by forming a specific amount of oxygen-lacking defects in a layer at a specified distance from the inner surface of the crucible. SOLUTION: An oxygen-lacking defect part of 20-150 ppm is formed in a layer within 1 mm from an inner surface of a crucible. A carbon mold 12 is charged with a quartz powder 11 so as to form a crucible shape by rotating a crucible-forming mold 10 by a motor 17. The crucible-forming mold 10 charged with the quartz is transferred to a melting room 5. An inert gas (e.g. nitrogen) is flowed from a flowing-in opening 6 to the melting room 5 to replace the atmosphere so that the oxygen concentration of the atmosphere of the melting room 5 may be <=21% (e.g. <=1%). The quartz powder 11 is serially melted by charging an arc electrode 15 with electricity. A vacuum pump 20 is operated just after the start of the arc discharge, and a reduced pressure state is kept for a prescribed time (e.g. 10 min). A reducing gas (e.g. hydrogen) is flowed into the melting room at a 50-300 L/min from the time just before the start of the arc discharge for 5-15 min. Thereafter, the flowing in of the hydrogen is stopped and the arc discharge is maintained for a prescribed time (e.g. 30 min) to provide the objective crucible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a quartz glass crucible for pulling a silicon single crystal and a method for producing the same.
In particular, the present invention relates to a quartz glass crucible for pulling a silicon single crystal having an improved silicon single crystal pulling yield and a method for producing the same.

[0002]

2. Description of the Related Art A silicon single crystal used for a substrate of a semiconductor device is generally manufactured by a Czochralski method (CZ method). In the CZ method, a polycrystalline silicon raw material is loaded into a quartz glass crucible and loaded. The obtained silicon raw material is heated and melted from the surroundings, and the seed crystal suspended from above is brought into contact with the silicon melt and then pulled up.

[0003] The quartz glass crucible used in the CZ method is:
As the purity of silicon single crystals increases, high-purity quartz glass crucibles are also required.

A quartz glass crucible used in the CZ method is generally a method in which quartz powder refined by grinding is supplied into the mold while rotating a rotatable mold, and the quartz powder is crucible-shaped around the mold by centrifugal force. And fused at the same time from the inside with an arc or the like.

[0005] However, the quartz glass crucible manufactured by this mold manufacturing method has a problem that the quartz glass contains many air bubbles.

On the other hand, when a single crystal is produced from polycrystalline silicon by the CZ method using a quartz glass crucible containing such bubbles, crystallization becomes unstable due to bubbles present in the quartz glass crucible. In addition, dislocation is likely to occur in the pulled silicon single crystal, which causes a reduction in yield.

[0007] The main reason for this is that cristobalite in the form of spots is mixed into the molten silicon.

That is, it is considered that the cristobalite in the form of spots is formed in a quartz glass crucible by the following phenomenon.

First, during the pulling of the silicon single crystal, the inner surface of the silicon crucible is eroded by the silicon melt, and the bubbles are broken, so that the inner surface of the crucible is roughened. And cristobalite in the form of spots are formed.

Next, during pulling of the single crystal, precipitated impurities existing near the inner surface of the crucible promote formation of cristobalite on the inner surface of the crucible to form spotted cristobalite similar to the above.

The cristobalite produced in this manner is separated from the crucible, mixed into the molten polycrystalline silicon, and has a problem of adversely affecting the growth of the pulled silicon single crystal.

In order to solve this problem, see, for example,
A silica base is placed in a rotating mold as described in JP-A-22861, silica powder is supplied to the inner surface of the base to form a substantially bubble-free transparent quartz glass layer, and two layers are formed. There is a disclosure of a method for manufacturing a quartz glass crucible.

However, this method has problems that the process is complicated and it is difficult to appropriately control the thickness of the bubble-free transparent quartz glass layer.

Further, in order to prevent impurities caused by cristobalite from being mixed into the molten silicon, a devitrification promoting agent is adhered to the inner surface of the quartz glass crucible, and when the quartz glass crucible is heated to a high temperature, it is devitrified. Japanese Patent Application Laid-Open No. Hei 9-110579 discloses a method for forming a layer of silica and preventing crystalline silica particles from being mixed into molten silicon.

However, since this method uses, for example, metal oxides and other oxides as devitrification accelerators, these oxides may be melted into molten silicon, which may adversely affect single crystallization and silicon wafer characteristics. There is also a question of reliability.

Further, in order to suppress the expansion of the bubbles in the quartz glass crucible and to prevent the fragments of SiO _{2 from} being mixed into the molten silicon due to the cleavage of the bubbles, the inner surface of the quartz glass crucible is maintained at a predetermined temperature. Japanese Patent Application Laid-Open No. 5-124889 discloses a method for producing a quartz glass crucible by heating for a long time. However, since this method involves heating at a relatively high temperature for a long time, the productivity is poor and the production cost is low. There is a problem that the cost increases.

[0017]

Therefore, there is a need for a quartz glass crucible for pulling a silicon single crystal which has a high silicon single crystal pulling yield and is excellent in productivity and a method for producing the same.

The present invention has been made in view of the above-mentioned circumstances, and has been made in view of the above circumstances. A quartz glass crucible for pulling a silicon single crystal has an oxygen deficiency defect formed on the inner surface of the quartz glass crucible and has an improved silicon single crystal pulling yield. And a method for producing the same.

[0019]

Means for Solving the Problems In order to achieve the above-mentioned object, the invention of claim 1 of the present application is directed to a method in which an inner surface of a crucible is positioned at a distance of 1 mm.
The gist of the present invention is a quartz glass crucible for pulling a silicon single crystal, which has an oxygen deficiency defect of 20 to 150 ppm in a layer within mm.

According to the second aspect of the present invention, the oxygen concentration is 21%
A quartz crucible is filled in the following melting chamber in the form of a crucible, and a crucible-forming mold is prepared.The crucible-forming mold is held for a predetermined time while the pressure is reduced. Starting and flowing a predetermined amount of reducing gas into the melting chamber for a predetermined time immediately after the start of arc discharge,
After that, the depressurization of the crucible mold is stopped, and an arc discharge is further performed for a predetermined time in this stopped state, whereby the layer is melted in a reducing atmosphere, and the layer within 1 mm from the inner surface of the crucible has oxygen deficiency defects of 20 to 150 ppm. It is intended to provide a method for producing a quartz glass crucible for pulling a silicon single crystal characterized by the following.

According to a third aspect of the present invention, the crucible mold is held for a predetermined time while depressurizing, the arc discharge is started while the crucible mold is further depressurized, and 50 to 300 liters / min. Per minute of hydrogen in the melting chamber for 5 to 15 minutes, and then the depressurization of the crucible-forming mold is stopped. By continuing arc discharge for a predetermined time in this stopped state, the crucible is melted in a reducing atmosphere and 1 mm from the crucible inner surface. Oxygen deficiency defects in layers within 20 to 150 pp
The gist of the present invention is a method for manufacturing a quartz glass crucible for pulling a silicon single crystal according to claim 3, wherein

According to a fourth aspect of the present invention, the flow of hydrogen is stopped at the same time as the depressurization of the crucible mold is stopped, and an arc discharge is further performed for a predetermined time in this state, whereby the crucible is melted in a reducing atmosphere and the inner surface of the crucible is melted. A method for producing a quartz glass crucible for pulling a silicon single crystal according to claim 4, characterized in that the layer within 1 mm from the surface has oxygen deficiency defects of 20 to 150 ppm.

The invention according to claim 5 of the present invention is a quartz glass crucible for pulling a silicon single crystal, which is heat-treated in a reducing atmosphere and has 20 to 150 ppm of oxygen deficiency defects in a layer within 1 mm from the inner surface of the crucible. The gist is that there is.

According to the invention of claim 6 of the present application, a quartz glass crucible is prepared in a processing furnace, a predetermined amount of an inert gas is flowed into the quartz glass crucible to reduce the oxygen concentration to 1% or less, and the inside of the processing furnace is heated to a predetermined temperature. The inert gas is replaced with a reducing gas while maintaining this temperature, and is maintained for a predetermined time. After the elapse of this time, the inert gas flows into the processing furnace again to lower the furnace temperature to room temperature. The gist of the present invention is to provide a method for producing a quartz glass crucible for pulling a silicon single crystal, which is heat-treated in a reducing atmosphere and has oxygen deficiency defects in a layer within 1 mm from the inner surface of the crucible having 20 to 150 ppm. I have.

According to a seventh aspect of the present invention, a quartz glass crucible is prepared in a processing furnace, and a predetermined amount of an inert gas is flowed into the quartz glass crucible to reduce the oxygen concentration to 1% or less. C., maintaining the temperature, replacing the inert gas with hydrogen and maintaining the temperature for 0.5 to 10 hours. After the elapse of this time, the inert gas is allowed to flow into the processing furnace again to lower the temperature to room temperature. In summary, it is a method of manufacturing a quartz glass crucible for pulling a silicon single crystal, which is heat-treated in a reducing atmosphere and has 20 to 150 ppm of oxygen deficiency defects in a layer within 1 mm from the inner surface of the crucible. I have.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a quartz glass crucible according to the present invention and a method for manufacturing the same will be described below with reference to the accompanying drawings.

FIG. 1 shows a quartz glass crucible 1 according to the present invention.
The layer 3 within 1 mm from the inner surface 2 of the quartz glass crucible 1 is formed as an oxygen deficiency defect layer having 20 to 150 ppm of oxygen deficiency defects.

A manufacturing apparatus used for manufacturing such a quartz glass crucible 1 will be described with reference to FIG.

In the building, there is formed a melting chamber 5 having a floor of 3 × 3 m and a height of 5 m, for example, which is partitioned by a partition wall 4. The melting chamber 5 is provided with an inlet 6 and an outlet 7 for the atmospheric gas. I have. A crucible manufacturing device 8 is provided in the melting chamber 5, and the crucible manufacturing device 8 has a crucible forming die 10 mounted on a turntable 9.

The crucible molding die 10 is formed of a gas permeable member, for example, carbon, and has a quartz powder 11 in a crucible shape.
And a holding jacket 14 which is heat-resistant, for example, made of SUS and is water-cooled. The holding jacket 14 is provided with a gas ventilation path 13 provided on the outer periphery of the carbon mold 12.

Above the crucible-forming mold 10, for example, an arc electrode 15 is provided as a heat source facing the quartz powder 11 filled in a crucible shape.

The gas passage 13 is provided with the holding jacket 1.
4 through an opening 16 provided in the lower part of the motor 4.
Is connected to a gas introduction path 19 provided at the center of a rotating shaft 18 driven by the motor, and the gas introduction path 19 is connected to a vacuum pump 20.

The holding jacket 14 is provided with a cooling passage 21 for water cooling.
Is connected to a water channel 22 provided at the center of the

The manufacturing apparatus used in the method for manufacturing a quartz glass crucible according to the present invention has the above-described structure. Next, a method for manufacturing a quartz glass crucible according to the present invention will be described.

First, the motor 17 is urged to rotate the crucible-molding mold 10 via the rotating shaft 18 so that the carbon mold 12 and the holding jacket 14 constituting the crucible-molding mold 10 are formed.
Is rotated to fill the carbon mold 12 with the quartz powder 11 in a crucible shape.

Next, the crucible-forming mold 10 filled with quartz is transferred to the melting chamber 5. Then, an inert gas, for example, nitrogen is flown from the inflow port 6 into the melting chamber 5 for replacement, and the atmosphere in the melting chamber 5 is set to an oxygen concentration of 21% or less, for example, 1% or less.

The inert gas includes nitrogen, and may be nitrogen, argon, helium, or a mixture of these and nitrogen.

Thereafter, the arc electrode 15 is energized, and the crucible-filled quartz powder 11 is sequentially melted from the inside by heating by arc discharge. Immediately after the start of the arc, the vacuum pump 20 is operated and kept in a reduced pressure state for a predetermined time, for example, 10 minutes.

Immediately before the start of the arc discharge, a reducing gas, for example, hydrogen is introduced into the melting chamber at 50 to 300 l / min, for example, 150 l / min, and this state is maintained for 5 to 15 minutes, for example, 10 minutes. 3 is a reducing atmosphere,
That is, a hydrogen atmosphere is maintained.

After a lapse of a predetermined time, for example, 10 minutes, the depressurization is stopped and the pressure is returned to the atmospheric pressure, and the inflow of hydrogen is also stopped. In this state, the arc discharge is maintained for a predetermined time, for example, 30 minutes to produce a quartz glass crucible 1. .

In this manufacturing process, since the layers other than the layer 3 of the crucible 1 are melted, it is not always necessary to send hydrogen to the melting chamber 5 to maintain a complete reducing atmosphere. Alternatively, the hydrogen may be continuously supplied.

The reducing gas may be carbon monoxide or a hydrocarbon gas such as methane.

The crucible 1 produced by melting in a reducing atmosphere as described above has a thickness of 12 to 20 mm, and has a transparent layer portion of 3 to 7 mm inside, and the transparent layer portion is visible and transparent. When measured with an ultraviolet spectrophotometer, 245
Strong absorption was observed at nm, with about 120 ppm oxygen deficiency defects.

Next, another embodiment of the method for manufacturing a quartz glass crucible according to the present invention will be described.

FIG. 3 is a schematic view showing an atmosphere processing furnace used in another embodiment of the method for manufacturing a quartz glass crucible according to the present invention. The processing furnace 31 includes a main body 32 and this main body 32.
Furnace base 34 provided inside and fixed to bottom 33 of main body 32
The furnace base 34 is provided with an air supply pipe 37 provided with gate valves 35 and 36 for sending an inert gas, for example, nitrogen, and a reducing gas, for example, hydrogen, and an exhaust pipe 39 for discharging gas in a quartz glass crucible 38. Have been.

A quartz ring 41 is provided on the furnace base 34 at an outer periphery of an upper end portion 40 of a quartz glass crucible 38 placed on a bottom surface thereof. An airtight powder seal 42 is spread.

A through hole 43 provided in the bottom 33 and the furnace base 34 and through which the air supply pipe 37 and the exhaust pipe 39 pass is sealed with a seal member 44 made of a powder seal and quartz wool.

The atmosphere treatment furnace used in another embodiment of the method for manufacturing a quartz glass crucible according to the present invention has the above-described structure. And some of the manufacturing steps of the manufacturing method described above.

That is, for example, a 28-inch crucible-forming mold is filled with quartz powder in a crucible shape, and the crucible-forming mold is rotated and melted by arc discharge to produce a quartz glass crucible having an outer diameter of 28 inches.

The upper end of the quartz glass crucible thus manufactured is cut off by a predetermined width, for example, 100 mm, and the upper end is made parallel.

Thereafter, as shown in FIG. 3, the quartz glass crucible 38 is placed on the furnace base 34 with the bottom surface of the quartz glass crucible 38 facing upward so that the air supply pipe 37 and the exhaust pipe 39 are located inside the quartz glass crucible 38. , And a powder seal 42 is spread between the outside of the upper end portion 40 and the quartz ring 41 to keep the inside and outside of the quartz glass crucible 38 airtight.

Thereafter, a predetermined amount, for example, 0.5 m ³ / cm, is put into the quartz glass crucible 38 through the gate valve 35 and the air supply pipe 37.
Processing furnace 31 while flowing an inert gas such as nitrogen for a long time.
The internal temperature is raised to 800 to 1200 ° C., for example, 1100 ° C., and the gate valve 35 is closed, while the gate valve 36 is opened, and a reducing gas instead of nitrogen, for example, hydrogen is supplied through the air supply pipe 37 to a predetermined amount, for example, 0 °. Supply 5 cubic rice / hour. Hydrogen as a reducing gas is continuously supplied for 0.5 to 10 hours, for example, 3 hours, and this state is maintained.

Thereafter, the gate valve 36 is closed, and the gate valve 35 is closed.
Is opened to switch hydrogen to nitrogen, and the temperature is lowered to room temperature while flowing nitrogen.

The quartz glass crucible 1 manufactured by the heat treatment in the reducing atmosphere as described above has a thickness of 12 to 20 mm.
mm, and has a transparent layer portion of 3 to 7 mm inside. When the transparent layer portion is measured by a visible / ultraviolet spectrophotometer, strong absorption at 245 nm is observed and 100 pp.
m oxygen deficiency defects.

The absorption wavelength of 245 nm is
This indicates oxygen deficiency defects in a state where O is removed from -O-Si, and the concentration is based on Lamber-Beer's law.

## EQU1 ## The value of c (absorbed component concentration) can be calculated by the following equation: A = log I0 / I = kcd.

In the above equation, A is the absorbance, I0 is the intensity of the incident light, I is the intensity of the transmitted light, k is the extinction coefficient, and d is the thickness of the sample.

[0057]

Example 1 A cusp (CUSP) type M using a quartz glass crucible having an oxygen deficiency defect of 120 ppm with an outer diameter of 28 inches.
Using a CZ single crystal pulling apparatus, for example, a silicon single crystal having a diameter of 300 mm was pulled. Even when the raw material polysilicon was used for about 100 hours at a charge of 200 kg, no dislocation was observed at all, and a complete silicon single crystal was obtained.

The inner surface of the quartz glass crucible after being used for pulling a single crystal maintains a glossy state as a whole, and the area where cristobalite is observed is about 20%.
Met.

Example 2 A quartz glass crucible manufactured according to another embodiment of the method for manufacturing a quartz glass crucible according to the present invention was used,
Using a cusp type MCZ single crystal pulling device, for example, with a diameter of 30
A 0 mm silicon single crystal was pulled. Even when used with 200 kg of polysilicon for about 100 hours, generation of dislocations was not observed at all, and a complete silicon single crystal was obtained.

The inner surface of the quartz glass crucible after being used for pulling a single crystal maintained a glossy state as a whole, and the area where cristobalite was observed was 20%.

Comparative Example 1 Quartz powder was charged into a decompressible rotary mold composed of a carbon mold and a water-cooled SUS jacket, and the mold was moved to a melting chamber in the atmosphere to start melting by arc discharge. Hydrogen was introduced at 150 liter / min.

After 10 minutes, the pressure was reduced and the flow of hydrogen was stopped, and the arc was maintained for an additional 20 minutes to melt, thereby producing a quartz crucible having an outer diameter of 28 inches.

This crucible had a thickness of 12 to 20 mm and had a transparent layer of 3 to 7 mm on the inner surface side. The transparent layer was measured with a visible / ultraviolet spectrophotometer.
A weak absorption was observed at 5 nm, and had a 20 ppm oxygen deficiency defect.

Using this crucible, a single crystal was pulled by a cusp type MCZ pulling apparatus.

Approximately 10 with a 200 kg charge of polysilicon
It was used for 0 hours, and a single crystal having a diameter of 300 mm was pulled. Dislocations occurred in the pull tail, and the single crystallization ratio was 80.
%Met. The inner surface of the quartz glass crucible after use for pulling was noticeably rough overall, and the area where cristobalite was observed was about 70%.

Comparative Example 2 Quartz powder was charged into a decompressible rotary mold composed of a carbon mold and a SUS water-cooled jacket, and the mold was moved to a melting chamber where the oxygen concentration was reduced to 1% or less by a nitrogen flow, and the pressure was reduced. Hold for 10 minutes. After that, melting was started by arc discharge. When hydrogen was introduced at a flow rate of 300 liters / minute immediately after the start of the arc, vapor of SiO ₂ was generated violently,
Arc interruption frequently occurred due to adhesion to the electrode. After 10 minutes, the decompression and the inflow of hydrogen were stopped, and the arc was maintained for an additional 20 minutes for melting to produce a quartz crucible having an outer diameter of 28 inches.

On the inner surface of this crucible, many problems were found due to the paper falling from the electrode. The transparent layer had 200 ppm oxygen deficiency defects.

[0068]

As described above, the quartz glass crucible according to the present invention has an oxygen deficiency defect of 20 to 150 ppm in a layer within 1 mm from the inner surface of the crucible. Since the generation is small, the dislocation of the single crystal does not occur, and the yield of the silicon single crystal can be improved. Also, a method for easily manufacturing such a quartz glass crucible is provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a quartz glass crucible according to the present invention.

FIG. 2 is a conceptual diagram of a manufacturing apparatus used in a method for manufacturing a quartz glass crucible according to the present invention.

FIG. 3 is a conceptual diagram of a manufacturing apparatus used in another embodiment of the method for manufacturing a quartz glass crucible according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quartz glass crucible 2 Inner surface 3 layer 4 Partition wall 5 Melting chamber 6 Inflow port 7 Outflow port 8 Crucible manufacturing apparatus 9 Turntable 10 Mold for crucible molding 11 Quartz powder 12 Carbon mold 13 Vent path 14 Holding jacket 15 Arc electrode 16 Opening 17 Motor 18 Rotating shaft 19 Gas introduction path 20 Vacuum pump 21 Cooling path 22 Water path 31 Processing furnace 32 Main body 33 Bottom part 34 Furnace base 35 Gate valve 36 Gate valve 37 Air supply pipe 38 Quartz glass crucible 39 Exhaust pipe 40 Upper end 41 Quartz ring 42 Powder Seal 43 Through hole 44 Seal member

Claims (7)

[Claims] 1. A quartz glass crucible for pulling a silicon single crystal, characterized in that a layer within 1 mm from the inner surface of the crucible has 20 to 150 ppm of oxygen deficiency defects. 2. A crucible-forming mold is prepared in a melting chamber having an oxygen concentration of 21% or less, which is filled with quartz powder in a crucible shape, and the crucible-forming mold is held for a predetermined time while depressurizing the crucible-forming mold. Arc discharge is started while the mold is depressurized, and a predetermined amount of reducing gas is flowed into the melting chamber for a predetermined time immediately after the start of the arc discharge, and then the depressurization of the crucible mold is stopped. By performing the arc discharge for a time, it is melted in a reducing atmosphere, and oxygen-deficient defects are formed in a layer within 1 mm from the inner surface of the crucible.
A method for producing a quartz glass crucible for pulling a silicon single crystal, comprising 150 ppm. 3. Holding the crucible mold for a predetermined time while depressurizing the mold, further starting arc discharge while decompressing the crucible mold, and starting 50 to 50 minutes after the start of the arc discharge.
300 liters / minute of hydrogen was flowed into the melting chamber for 5 to 15 minutes, and then the depressurization of the crucible mold was stopped. By continuing arc discharge for a predetermined time in this stopped state, the crucible was melted in a reducing atmosphere and melted in the crucible. The method for producing a quartz glass crucible for pulling a silicon single crystal according to claim 3, wherein the layer within 1 mm from the surface has oxygen deficiency defects of 20 to 150 ppm. 4. The flow of hydrogen is stopped at the same time as the decompression of the crucible mold is stopped, and an arc discharge is further performed for a predetermined time in this state to melt in a reducing atmosphere and form a layer within 1 mm from the inner surface of the crucible. 20-150 oxygen deficiency defects
The method for producing a quartz glass crucible for pulling a silicon single crystal according to claim 4, wherein the crucible has a content of 1 ppm. 5. A heat treatment in a reducing atmosphere, wherein the layer within 1 mm from the inner surface of the crucible has an oxygen deficiency defect of 20 to 150 mm.
A quartz glass crucible for pulling a silicon single crystal, characterized by having ppm. 6. A quartz glass crucible is prepared in a processing furnace,
A predetermined amount of an inert gas is flowed into the quartz glass crucible to lower the oxygen concentration to 1% or less, and the inside of the processing furnace is heated to a predetermined temperature, and while maintaining this temperature, the inert gas is replaced with a reducing gas. After a predetermined time is maintained, an inert gas is flown into the processing furnace again after the elapse of this time, and the temperature in the furnace is lowered to room temperature, whereby the heat treatment is performed in a reducing atmosphere, and oxygen deficiency occurs in a layer within 1 mm from the inner surface of the crucible. 20-150ppm defect
A method for producing a quartz glass crucible for pulling a silicon single crystal, comprising: 7. A quartz glass crucible is prepared in a processing furnace,
A predetermined amount of an inert gas is flowed into the quartz glass crucible to reduce the oxygen concentration to 1% or less, the temperature in the processing furnace is raised to 800 to 1200 ° C., and the inert gas is replaced with hydrogen while maintaining this temperature to 0%. 0.5 to 10 hours, after this time elapses, an inert gas is again flown into the processing furnace to lower the temperature to room temperature, thereby performing heat treatment in a reducing atmosphere, and oxygen deficiency in a layer within 1 mm from the inner surface of the crucible. 20-150p defect
pm, a method for producing a quartz glass crucible for pulling a silicon single crystal.