JP6795461B2 - Manufacturing method of quartz glass crucible - Google Patents

Description

The present invention relates to a method for producing a silica glass crucible, and more particularly to a method for producing a silica glass crucible which is suitably used for melting a raw material such as polycrystalline silicon in pulling up a semiconductor single crystal such as silicon.

Semiconductor single crystals such as silicon are mainly produced by the Czochralski (CZ) method. In the production of a silicon single crystal by this CZ method, a silicon single crystal seed crystal is landed in a silicon raw material melt obtained by melting polycrystalline silicon, and the seed crystal of the silicon single crystal is gradually pulled up while rotating to form a silicon single crystal ingot (hereinafter referred to as a silicon single crystal ingot). , Silicon ingot) is grown.

In pulling up a silicon single crystal by the CZ method as described above, the container for heating and melting the raw material is generally made of natural quartz glass in which a natural material such as crystal is melted and vitrified in the outer layer, and synthetic silica glass in the inner layer. Quartz glass rutsubo is used.
When this quartz glass glass crucible is filled with polycrystalline silicon and heated to a temperature equal to or higher than the melting point of silicon (about 1400 ° C.), the inner surface of the crucible is usually covered with brown ring-shaped cristobalite, so-called. A brown ring (also called a brown mold) is generated.
This brown ring gradually expands by heating, and the inner surface is roughened or peeled. As a result, the peeled pieces are mixed in the silicon raw material melt, dislocations occur in the silicon single crystal, and the silicon single crystal. It caused a decrease in the yield of.

As a solution to this problem, Patent Document 1 describes that a purified natural silica raw material powder having a Na concentration of 0.2 ppm or less is molded into a crucible shape, and further covers the inner surface of the crucible-shaped molded body. As described above, a synthetic silica raw material powder having a concentration of Na, K, Li, Ca, Al, Ti, Fe, and Cu of 0.1 ppm or less, an average particle size of 150 μm, and a maximum particle size of 210 μm is introduced. Then, a method for producing a silica glass crucible, which is vitrified by vacuum arc melting in a high cleanliness environment, is shown.

Further, Patent Document 2 describes a step of producing a quartz glass crucible having an outer layer made of opaque quartz glass containing bubbles and an inner layer made of transparent quartz glass containing substantially no bubbles, and the prepared quartz glass. The above-mentioned step of roughening the region of the inner surface of the crucible that comes into contact with the silicon melt when holding the silicon melt, and heat treatment of the quartz glass crucible whose inner surface is roughened. A method for producing a silica glass crucible for pulling single crystal silicon, which includes a step of crystallizing the surface of the roughened region, is shown.

JP-A-2010-280567 Japanese Unexamined Patent Publication No. 2016-33093

In the invention described in Patent Document 1, browning is suppressed by forming the inner layer of the crucible-shaped molded body with a synthetic silica raw material powder having a high purity and a specific particle size. Further, in the invention described in Patent Document 2, browning is suppressed by roughening the region of the inner surface of the quartz glass crucible that comes into contact with the silicon melt when the silicon melt is held. ing.

By the way, in recent years, due to an increase in the recharge process (adding a raw material for polycrystalline silicon with one crucible and pulling up the silicon ingot multiple times), the environment in which the crucible is used is becoming hotter and longer. ..
With this lengthening of time, even if the crucible is as shown in Patent Documents 1 and 2, more cristobalite is formed on the inner surface of the crucible, and the silicon ingot is likely to be dislocated by peeling during use. There was a problem. Therefore, as the number of recharges (pulls) increases, dislocations of the silicon ingots are likely to occur, so that the number of silicon ingots to be pulled up is limited.
Therefore, manufacturing quartz glass crucibles that suppress the formation of cristobalite and increase the number of crucibles has great merits for the user in terms of manufacturing cost and manufacturing efficiency.

We focused on the brown mark in the early stages of cristobalite. Since cristobalite (so-called brown ring) is formed around this brown mark, we think that if we can reduce the brown mark in the initial stage of cristobalite, it will lead to the reduction of cristobalite (so-called brown ring). I did a lot of research.
As a result, he discovered a phenomenon peculiar to the brown mark and came up with a method for producing a quartz glass crucible capable of suppressing the phenomenon, and completed the present invention.

An object of the present invention is to provide a method for producing a quartz glass crucible capable of suppressing brown marks.

The method for manufacturing a quartz glass rut according to the present invention, which has been carried out to achieve the above object, is to manufacture a quartz glass rut pot in which a quartz glass raw material powder is melted by arc discharge in a rotating rut molding mold to mold the rut. In the method, natural quartz glass raw material powder is deposited along the inner surface of the rutsubo molding mold to form a natural quartz glass powder layer, and then synthetic silica raw material powder is deposited along the inner surface of the natural quartz glass powder layer. Then, the synthetic silica raw material powder is deposited so as to cover the upper end of the natural quartz glass powder layer, the synthetic silica raw material powder layer is formed, and the raw material powder laminate is formed, and the raw material powder is subjected to arc discharge. It is characterized by including a step of forming a rutsubo-shaped body in which a transparent quartz glass layer is formed inside the laminated body and an opaque quartz glass layer is formed outside the raw material powder laminated body.

In this way, in the step of forming the raw material powder laminate, the synthetic silica raw material powder is deposited so as to cover the upper end of the natural quartz glass powder layer, so that when the rutsubo shape is formed by arc discharge, the natural quartz glass The scattering of the powder is suppressed, and the adhesion of the synthetic silica raw material powder layer to the inner surface is suppressed.

When the natural quartz glass powder adheres to the inner surface of the synthetic silica raw material powder layer, recesses called pits are formed on the inner surface of the crucible shape. This recess causes a brown mark.
Therefore, in the production method of the present invention, since the synthetic silica raw material powder is deposited so as to cover the upper end portion of the natural quartz glass powder layer, the scattering of the natural quartz glass powder is suppressed.
As a result, the generation of recesses caused by the natural quartz glass powder is suppressed, and the generation of brown marks is suppressed.

After forming the crucible shape, it is desirable to include a cutting step of cutting the two layers of the transparent quartz glass layer and the opaque quartz glass layer at the upper end of the crucible shape.
If the transparent quartz glass layer covering the upper end portion of the opaque quartz glass layer remains, there is a risk of deformation due to a decrease in viscosity, which is not preferable.

Here, in the step of forming the raw material powder laminate, it is desirable that the thickness of the synthetic silica raw material powder laminated at the upper end of the natural quartz glass powder layer is at least 80 mm.
When the thickness of the synthetic silica raw material powder at the upper end portion is less than 80 mm, the recess may be formed on the inner surface of the crucible shape, which is not preferable.

Further, an intermediate layer made of a natural quartz glass raw material powder layer or a synthetic silica raw material powder layer is formed between the natural quartz glass powder layer and the synthetic silica raw material powder layer, and the upper end portion of the natural quartz glass powder layer is formed. The synthetic silica raw material powder to be covered may be deposited so as to cover the upper end portion of the intermediate layer.
As described above, the method for producing the quartz glass rubbing according to the present invention is not limited to the two-layer type quartz glass rubbing manufactured from the natural quartz glass powder layer and the synthetic silica raw material powder layer, and the natural quartz glass powder. It can also be applied to three or more fused silica glass pots in which an intermediate layer composed of a quartz glass raw material powder layer or a synthetic silica raw material powder layer is formed between the layer and the synthetic silica raw material powder layer.

According to the present invention, it is possible to obtain a method for producing a quartz glass crucible capable of suppressing brown marks.

FIG. 1 is a schematic configuration diagram showing a manufacturing apparatus for carrying out the present invention. FIG. 2A is an enlarged view of a main part of the raw material powder laminate according to the present invention, and FIG. 2B is an enlarged view of a main part of the conventional raw material powder laminate. FIG. 3 is a cross-sectional view showing a crucible shape according to the present invention. FIG. 4 is a diagram showing an analysis region of elemental analysis on the brown mark and the glass surface in the vicinity of the brown mark. FIG. 5 is a diagram showing the results of elemental analysis performed by the laser ablation method on the glass surface B near the brown mark. FIG. 6 is a diagram showing the results of elemental analysis of the brown mark by the laser ablation method. FIG. 6 is a diagram showing a recess (pit) formed on the inner surface of the quartz glass crucible. FIG. 8 is a diagram showing a brown mark formed on the inner surface of the quartz glass crucible.

The present invention is a method for producing a quartz glass crucible that suppresses the generation of brown marks, which was made by discovering a peculiar phenomenon of brown marks.
First, the peculiar phenomenon of the brown mark discovered by the present inventor will be described with reference to FIGS. 4 to 6.

As shown in FIG. 4, the present inventor performed elemental analysis on the brown mark A and the glass surface B near the brown mark by the laser ablation method. The arrows in the figure indicate the analysis direction.
The results are shown in FIGS. 5 and 6. FIG. 5 shows the results of each elemental analysis on the glass surface B near the brown mark, FIG. 6 shows the analysis of each element on the brown mark BM, FIGS. 5 and 6 (a) are Na, and (b) is Mg. (C) shows the analysis results of Al, (d) shows the analysis results of K, (e) shows the analysis results of Cu, and (f) shows the analysis results of Ti. The vertical axes of FIGS. 5 and 6 (a) to 6 (f) are vaporized quartz whose contained elements are counted by ICP-MS. For example, in the case of Al, the count number of Al is divided by the count number of Si. Is. Further, the horizontal axes of FIGS. 5 and 6 (a) to 6 (f) represent the measurement time.

As shown in FIGS. 5 and 6 (a) and 6 (b), Na and Mg are detected on both the brown mark BM and the glass surface in the vicinity of the brown mark.
On the other hand, as can be seen from FIGS. 5 and 6 (c) and 6 (f), Al and Ti are detected more in the brown mark than in the glass surface in the vicinity of the brown mark, and their tendencies are different. That is, in the brown mark, a peculiar phenomenon that a large amount of Al and Ti elements was found was found.

These Al and Ti are elements that are abundantly contained in the natural quartz glass raw material powder, and are considered to be caused by the natural quartz glass powder raw material in the outer layer.
That is, in order to suppress the generation of brown marks, it is important to suppress the scattering of the natural quartz glass powder and the adhesion of the synthetic silica raw material powder layer to the inner surface, and it is possible to reduce the brown marks. If possible, the amount of Chris barite can be reduced.

As described above, the present invention focuses on suppressing the scattering of the natural quartz glass powder from the peculiar phenomenon that the brown mark contains a large amount of Al and Ti elements, and to the inner surface of the synthetic silica raw material powder layer. The brown mark is reduced by suppressing the adhesion of the powder.

Next, a method for producing a quartz glass crucible according to the present invention will be described with reference to FIGS. 1 to 3.
The method for producing a quartz glass crucible according to the present invention is performed using, for example, the quartz glass crucible manufacturing apparatus 10 as shown in FIG. The crucible forming mold 11 of the quartz glass crucible manufacturing apparatus 10 includes an inner member 12 made of a gas permeable member such as a mold having a plurality of through holes or a highly purified porous carbon mold. , A venting portion 13 is provided on the outer periphery thereof, and the holding body 14 holds the inner member 12.

Further, a rotating shaft 15 connected to a rotating means (not shown) is fixed to the lower portion of the holding body 14 to rotatably support the crucible forming mold 11. The ventilation portion 13 is connected to the exhaust port 16 provided in the center of the rotating shaft 15 via the opening 17 provided in the lower part of the holding body 15, and the ventilation portion 13 is connected to the decompression mechanism 18. Has been done.
An arc electrode 19 for arc discharge, a raw material supply nozzle 21, and a nozzle 22 that injects nitrogen gas or helium gas and blows the gas onto a predetermined portion of the rutsubo are provided on the upper portion facing the inner member 12. ing.

In order to manufacture a crucible using the quartz glass crucible manufacturing apparatus 10, a rotation drive source (not shown) is operated to rotate the rotation shaft 15 in the direction of the arrow to form a crucible molding die 11. Rotate at speed. Then, the quartz glass raw material powder is supplied into the crucible molding mold 11 from the raw material supply nozzle 21 at the upper part of the crucible molding mold 11.
When the quartz glass raw material powder is loaded into the rotated crucible molding mold 11, the raw material supply nozzle 21 is first loaded with, for example, coarse-grained natural quartz glass raw material powder, and then, for example, on the inner surface thereof. It is configured to be loaded with fine synthetic silica raw material powder. It should be noted that two raw material supply nozzles may be provided to supply the raw material powder separately.

The natural quartz glass raw material powder supplied into the crucible molding mold 11 is pressed against the inner member 12 of the crucible molding mold 11 by centrifugal force to form one layer (natural quartz glass raw material powder layer 1b). ..
Then, following the natural quartz glass raw material powder, the synthetic silica raw material powder is supplied into the crucible molding mold 11. This synthetic silica raw material powder is pressed against the natural quartz glass raw material powder layer 1b by centrifugal force to form one layer (synthetic silica raw material powder layer 1a), and a crucible-shaped two-layer raw material powder laminate 1 is formed as a whole. It is formed.

Here, as shown in FIG. 2A, the synthetic silica raw material powder is deposited along the inner surface of the natural quartz glass powder layer 1b and covers the upper end portion 1c of the natural quartz glass powder layer 1b. Accumulate.
That is, the synthetic silica raw material powder layer 1a is formed so as to cover the inner surface and the upper end portion 1c of the natural quartz glass powder layer 1b so that the natural quartz glass raw material powder layer 1b is not exposed.

Incidentally, in the conventional raw material powder laminate 1, as shown in FIG. 2B, the synthetic silica raw material powder is deposited along the inner surface of the natural quartz glass powder layer 1b, but the natural quartz glass powder layer Not deposited up to the top. This is because the synthetic silica raw material powder is expensive and the manufacturing cost is reduced.

Further, the synthetic silica raw material powder is deposited so that the thickness t of the synthetic silica raw material powder at the upper end portion 1c of the natural quartz glass powder layer 1b is at least 80 mm from the upper end portion of the natural quartz glass powder layer. desirable.
If the thickness t of the synthetic silica raw material powder is less than 80 mm, the natural quartz glass powder may scatter and brown marks may be generated on the inner surface of the quartz glass crucible (pits on the inner surface of the quartz glass crucible). ) May be generated), which is not preferable.

After forming the raw material powder laminate 1, decompression is performed by operating the pressure reducing mechanism 18 in an air atmosphere, and after a predetermined time elapses, the carbon electrode 19 is energized and heated from the inside of the raw material powder laminate to heat the raw material powder laminate 1. 1 is sequentially melted from the inside to form the crucible-shaped body 2 shown in FIG.
At this time, nitrogen gas or helium gas is injected into a portion that tends to reach a high temperature, for example, the bottom of the raw material powder laminate 1, the temperature rise of the synthetic silica glass layer at the portion is suppressed, and aluminum and metal elements are concentrated by vaporization. May be suppressed.

Then, after cooling, the two-layer portion C of the synthetic silica glass layer (transparent quartz glass layer) 2a and the natural quartz glass layer (opaque quartz glass layer) 2b at the upper end of the rutsubo shape 2 is cut. Manufactures quartz glass rutsubo.
If the transparent quartz glass layer covering the upper end portion of the opaque quartz glass layer remains, there is a risk of deformation due to a decrease in viscosity, which is not preferable.

As described above, in the present invention, in the step of forming the raw material powder laminate, the synthetic silica raw material powder is deposited so as to cover the upper end 1c of the natural quartz glass powder layer 1b, so that the synthetic silica raw material powder has a rut shape by an arc discharge. When the body 2 is formed, the scattering of the natural quartz glass powder is suppressed, the adhesion of the synthetic silica raw material powder layer 1a to the inner surface is suppressed, and the generation of brown marks is suppressed.
As a result, when used as a quartz glass crucible, Chris barite can be reduced.

Further, in the above embodiment, a two-layer type quartz glass rutsubo of a natural quartz glass layer (opaque quartz glass layer) 2b and the synthetic silica glass layer (transparent quartz glass layer) 2a has been described as an example.
However, between the natural quartz glass layer (opaque quartz glass layer) 2b and the synthetic silica glass layer (transparent quartz glass layer) 2a, a natural quartz glass layer (opaque quartz glass layer) or a synthetic silica glass layer (transparent quartz glass) It can also be applied to three or more types of quartz glass ruts that form an intermediate layer of layers).

Specifically, an intermediate layer composed of a natural quartz glass raw material powder layer or a synthetic silica raw material powder layer is formed between the natural quartz glass powder layer 1b and the synthetic silica raw material powder layer 1a, and the natural quartz glass powder layer 1b is formed. It is desirable that the synthetic silica raw material powder covering the upper end portion 1c of the above is deposited so as to cover not only the outer layer of the natural quartz glass powder layer but also the upper end portion of the intermediate layer.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

(Experiment 1)
When comparing and examining the brown mark, it is necessary to actually raise the silicon ingot, which increases the experimental cost, so we decided to compare and examine by the number of pits.
When the natural quartz glass raw material powder adheres to the inner surface of the synthetic silica raw material powder layer, a recess P called a pit is formed on the inner surface as shown in FIG. 7. This recess P causes the formation of a brown mark. Further, the generation state of the brown mark is shown in FIG. In FIG. 7, reference numeral P is a recess called a pit, and in FIG. 8, reference numeral BM is a brown mark.

The number of pits P and the number of brown mark BMs are much larger in the number of pits, but this is due to the hydrogen fluoride cleaning of the crucible performed after the quartz glass crucible is manufactured (before the silicon ingot is pulled up), and the pollutants in the pits. This is because most of the crucible is removed and some bits become the starting point of the brown mark.
Therefore, at least, by comparing and examining the number of pits, it is possible to compare and examine the brown mark. Therefore, in the following experiment, it was decided to compare and examine by the number of pits.

In Experiment 1, as shown in FIG. 2, the thickness t of the synthetic silica raw material powder layer from the upper end of the inner member 12 to the upper end 1c of the natural quartz glass powder layer was variously changed, and the pit reduction effect was confirmed. That is, when the thickness t is 0, it means that the upper end of the natural quartz glass powder layer of the outer layer is exposed (the state is not covered with the synthetic silica raw material powder layer), and as the thickness t is increased, the thickness t is increased. It means that the upper end portion is thickly covered with the synthetic silica raw material powder layer.
Further, the crucible was formed by a rotary molding method so that a raw material powder laminate having an inner layer thickness of 3 mm and an outer layer thickness of 13 mm, an outer diameter of 815 mm and a height of 550 mm could be obtained. Then, the crucible molded body was subjected to arc melting at about 2400 ° C. for 0.5 hours by an arc melting method to produce a quartz glass crucible.

Then, after washing with hydrofluoric acid, the inner surface of the crucible was observed using a microscope, and the number of pits (pcs) per 1 mm ² was counted. The results are shown in Table 1.

As is clear from Table 1, it was confirmed that when the thickness of the synthetic silica raw material powder layer exceeds 80 mm, there is an effect of reducing pits.

(Experiment 2)
Next, the thickness t of the synthetic silica raw material powder layer from the upper end of the inner member 12 to the upper end of the natural quartz glass powder layer is set to 80 mm, and as a comparative example, 0 mm and 40 mm, which are the same conditions as those in Experiment 1. A 32-inch quartz glass crucible was manufactured.
Then, five quartz glass crucibles (samples 1 to 5) were produced under each condition, and the silicon ingot was pulled up by the CZ method using the quartz glass crucibles. The pulling condition (use condition) was to dissolve 350 kg of the melt and pull up one ingot having a diameter of 320 mm.

Then, the densities of brown marks were compared. The results are shown in Table 2. As a result, it was confirmed that when the thickness t is 80 mm, the density of the brown mark can be reduced to about 1/2 to 1/3 as compared with the cases where the thickness t is 0 mm and 40 mm.

1 Raw material powder laminate 1a Synthetic silica raw material powder layer 1b Natural quartz glass raw material powder layer 1c Upper end of natural quartz glass powder layer 2 Crucible shape 2a Synthetic silica glass layer (transparent quartz glass layer)
2b Natural quartz glass layer (opaque quartz glass layer)
t Thickness of synthetic silica raw material powder layer at the upper end of natural quartz glass powder layer P Recess (pit)
BM brown mark

Claims (4)

In a method for manufacturing a quartz glass crucible, which melts a quartz glass raw material powder by an arc discharge in a rotating crucible molding mold to mold the crucible.
Natural quartz glass raw material powder is deposited along the inner surface of the rutsubo molding mold to form a natural quartz glass powder layer, and then synthetic silica raw material powder is deposited along the inner surface of the natural quartz glass powder layer, and further. A step of depositing synthetic silica raw material powder so as to cover the upper end of the natural quartz glass powder layer, forming a synthetic silica raw material powder layer, and forming a raw material powder laminate.
The process of forming a crucible-shaped body, in which a transparent quartz glass layer is formed inside the raw material powder laminate and an opaque quartz glass layer is formed outside the raw material powder laminate by arc discharge, is included. A characteristic quartz glass crucible manufacturing method. The quartz according to claim 1, further comprising a cutting step of forming the crucible-shaped body and then cutting the two-layer portion of the transparent quartz glass layer and the opaque quartz glass layer at the upper end portion of the crucible-shaped body. Glass crucible manufacturing method. The first or second claim, wherein in the step of forming the raw material powder laminate, the thickness of the synthetic silica raw material powder laminated on the upper end of the natural quartz glass powder layer is at least 80 mm. Silica glass crucible manufacturing method. An intermediate layer composed of a natural quartz glass raw material powder layer or a synthetic silica raw material powder layer is formed between the natural quartz glass powder layer and the synthetic silica raw material powder layer.
The quartz glass crucible according to any one of claims 1 to 3, wherein the synthetic silica raw material powder covering the upper end portion of the natural quartz glass powder layer is deposited so as to cover the upper end portion of the intermediate layer. Production method.